Which metal conducts heat better?

Heat transfer coefficients of steels and other materials: factors affecting the thermal conductivity of alloys

Thermal conductivity is a physical quantity that determines the ability of materials to conduct heat. In other words, thermal conductivity is the ability of substances to transfer the kinetic energy of atoms and molecules to other substances that are in direct contact with them. In SI, this quantity is measured in W/(K*m) (Watt per Kelvin meter), which is equivalent to J/(s*m*K) (Joule per second-Kelvin meter).

The concept of thermal conductivity

It is an intensive physical quantity, that is, a quantity that describes a property of matter that does not depend on the amount of the latter. Intensive quantities are also temperature, pressure, electrical conductivity, that is, these characteristics are the same at any point of the same substance. Another group of physical quantities are extensive, which are determined by the amount of matter, for example, mass, volume, energy and others.

The opposite value for thermal conductivity is thermal resistance, which reflects the ability of a material to prevent the transfer of heat passing through it.

For an isotropic material, that is, a material whose properties are the same in all spatial directions, thermal conductivity is a scalar quantity and is defined as the ratio of the heat flux through a unit area per unit time to the temperature gradient.

Thus, a thermal conductivity of one watt per meter Kelvin means that one Joule of thermal energy is transferred through the material:

• in one second;
• across an area of ​​one meter square;
• at a distance of one meter;
• when the temperature difference on surfaces located one meter apart in a material is equal to one Kelvin.

It is clear that the higher the thermal conductivity value, the better the material conducts heat, and vice versa. For example, the value of this value for copper is 380 W/(m*K), and this metal transfers heat 10,000 times better than polyurethane, whose thermal conductivity is 0.035 W/(m*K).

Heat transfer at the molecular level

When matter heats up, the average kinetic energy of its constituent particles increases, that is, the level of disorder increases, atoms and molecules begin to oscillate more intensely and with greater amplitude around their equilibrium positions in the material. Heat transfer, which at the macroscopic level can be described by Fourier's law, at the molecular level is the exchange of kinetic energy between particles (atoms and molecules) of a substance, without transfer of the latter.

This explanation of the mechanism of thermal conduction at the molecular level distinguishes it from the mechanism of thermal convection, in which heat transfer occurs due to the transfer of matter.

All solids have the ability to conduct heat, while thermal convection is possible only in liquids and gases.

Indeed, solids transfer heat mainly due to thermal conductivity, and liquids and gases, if there are temperature gradients in them, transfer heat mainly due to convection processes.

Thermal conductivity of materials

Metals have a pronounced ability to conduct heat. Polymers are characterized by low thermal conductivity, and some of them practically do not conduct heat, for example, fiberglass; such materials are called heat insulators. In order for this or that heat flow through space to exist, there must be some substance present in this space, therefore in open space (empty space) thermal conductivity is zero.

Each homogeneous (homogeneous) material is characterized by a thermal conductivity coefficient (denoted by the Greek letter lambda), that is, a value that determines how much heat needs to be transferred through an area of ​​1 m² so that in one second, passing through a thickness of one meter of material, the temperature at its ends changes per 1 K. This property is inherent in each material and varies depending on its temperature, so this coefficient is measured, as a rule, at room temperature (300 K) to compare the characteristics of different substances.

If the material is heterogeneous, for example, reinforced concrete, then the concept of a useful thermal conductivity coefficient is introduced, which is measured according to the coefficients of the homogeneous substances that make up this material.

The table below shows the thermal conductivity coefficients of some metals and alloys in W/(m*K) for a temperature of 300 K (27 °C):

• steel 47-58;
• aluminum 237;
• copper 372.1—385.2;
• bronze 116-186;
• zinc 106-140;
• titanium 21.9;
• tin 64.0;
• lead 35.0;
• iron 80.2;
• brass 81-116;
• gold 308.2;
• silver 406.1–418.7.

The following table provides data for non-metallic solids:

• fiberglass 0.03-0.07;
• glass 0.6-1.0;
• asbestos 0.04;
• tree 0.13;
• paraffin 0.21;
• brick 0.80;
• diamond 2300.

From the data under consideration it is clear that the thermal conductivity of metals is much higher than that of non-metals. The exception is diamond, which has a heat transfer coefficient five times greater than copper.

This property of diamond is due to the strong covalent bonds between the carbon atoms that form its crystal lattice. It is thanks to this property that a person feels cold when touching a diamond with his lips.

The property of diamond to transfer thermal energy well is used in microelectronics to remove heat from microcircuits. This property is also used in special devices that allow one to distinguish a real diamond from a fake.

Some industrial processes try to increase the ability to transfer heat, which is achieved either through good conductors or by increasing the contact area between the components of the structure. Examples of such structures are heat exchangers and heat dissipators. In other cases, on the contrary, they try to reduce thermal conductivity, which is achieved through the use of heat insulators, voids in structures and reducing the contact area of ​​elements.

Heat transfer coefficients of steels

The heat transfer ability of steels depends on two main factors: composition and temperature.

Simple carbon steels, with increasing carbon content, reduce their specific gravity, according to which their ability to transfer heat also decreases from 54 to 36 W/(m*K) when the percentage of carbon in the steel changes from 0.5 to 1.5%.

Stainless steels contain chromium (10% or more), which together with carbon forms complex carbides that prevent oxidation of the material, and also increases the electrode potential of the metal. The thermal conductivity of stainless steel is low compared to other steels and ranges from 15 to 30 W/(m*K) depending on its composition. Heat-resistant chromium-nickel steels have even lower values ​​of this coefficient (11-19 W/(m*K).

Another class is galvanized steel with a specific gravity of 7,850 kg/m3, which is obtained by applying coatings to the steel consisting of iron and zinc. Since zinc conducts heat more easily than iron, the thermal conductivity of galvanized steel will be relatively high compared to other classes of steel. It ranges from 47 to 58 W/(m*K).

The thermal conductivity of steel at different temperatures, as a rule, does not change much. For example, the thermal conductivity coefficient of steel 20 with an increase in temperature from room temperature to 1200 °C decreases from 86 to 30 W/(m*K), and for steel grade 08Х13, an increase in temperature from 100 to 900 °C does not change its thermal conductivity coefficient (27-28 W/(m*K).

Factors influencing physical quantity

The ability to conduct heat depends on a number of factors, including the temperature, structure and electrical properties of the substance.

Material temperature

The effect of temperature on the ability to conduct heat differs for metals and nonmetals. In metals, conductivity is mainly due to free electrons.

According to the Wiedemann-Franz law, the thermal conductivity of a metal is proportional to the product of the absolute temperature, expressed in Kelvin, and its electrical conductivity. In pure metals, electrical conductivity decreases with increasing temperature, so thermal conductivity remains approximately constant.

In the case of alloys, electrical conductivity changes little with increasing temperature, so the thermal conductivity of alloys increases in proportion to temperature.

On the other hand, heat transfer in nonmetals is mainly associated with lattice vibrations and the exchange of lattice phonons.

With the exception of high-quality crystals and low temperatures, the path of phonons in the lattice does not decrease significantly at high temperatures, and therefore the thermal conductivity remains constant over the entire temperature range, that is, it is insignificant. At temperatures below the Debye temperature, the ability of nonmetals to conduct heat, along with their heat capacity, decreases significantly.

Phase transitions and structure

When a material undergoes a first-order phase transition, for example from a solid to a liquid or from a liquid to a gas, its thermal conductivity may change. A striking example of such a change is the difference between this physical quantity for ice (2.18 W/(m*K) and water (0.90 W/(m*K).

Changes in the crystal structure of materials also affect thermal conductivity, which is explained by the anisotropic properties of various allotropic modifications of a substance of the same composition. Anisotropy affects different scattering intensities of lattice phonons, the main heat carriers in nonmetals, and in different directions in the crystal. A striking example here is sapphire, whose conductivity varies from 32 to 35 W/(m*K) depending on the direction.

Electrical conductivity

Thermal conductivity in metals changes along with electrical conductivity according to the Wiedemann-Franz law.

This is due to the fact that valence electrons, moving freely throughout the crystal lattice of the metal, transfer not only electrical, but also thermal energy.

For other materials, the correlation between these types of conductivity is not pronounced, due to the insignificant contribution of the electronic component to thermal conductivity (in nonmetals, lattice phonons play the main role in the mechanism of heat transfer).

Convection process

Air and other gases are, as a rule, good heat insulators in the absence of convection. This principle is the basis for the operation of many heat-insulating materials containing a large number of small voids and pores.

This structure does not allow convection to spread over long distances. Examples of such man-made materials are polystyrene and silicide airgel.

In nature, heat insulators such as animal skin and bird plumage work on the same principle.

Light gases such as hydrogen and gel have high thermal conductivities, while heavy gases such as argon, xenon and radon are poor conductors of heat.

For example, argon, an inert gas that is heavier than air, is often used as an insulating gas filler in double-glazed windows and light bulbs.

An exception is sulfur hexafluoride (SF6 gas), which is a heavy gas and has a relatively high thermal conductivity due to its high heat capacity.

Source: https://obrabotkametalla.info/stal/koefficient-teploprovodnosti-i-teploperedachi-stali

Thermal conductivity of steel and other alloys: copper, brass and aluminum, heat transfer

Before working with various metals and alloys, you should study all the information regarding their basic characteristics. Steel is the most common metal and is used in various industries. An important indicator is thermal conductivity, which varies over a wide range and depends on the chemical composition of the material and many other indicators.

This term means the ability of various materials to exchange energy , which in this case is represented by heat. In this case, energy transfer passes from the hotter part to the colder part and occurs due to:

1. Molecules
2. Atoms.
3. Electrons and other particles of the metal structure.

The thermal conductivity of stainless steel will differ significantly from that of another metal - for example, the thermal conductivity of copper will be different than that of steel.

To indicate this indicator, a special value is used, called the thermal conductivity coefficient. It is characterized by the amount of heat that can pass through a material in a certain unit of time.

Indicators for steel

Thermal conductivity can vary significantly depending on the chemical composition of the metal. The coefficient of this value will be different for steel and copper. In addition, with an increase or decrease in carbon concentration, the indicator under consideration also changes.

There are other features of thermal conductivity:

1. For steel that does not have impurities, the value is 70 W/(m* K).
2. Carbon and high-alloy steels have much lower conductivity. Due to an increase in the concentration of impurities, it is significantly reduced.
3. The thermal effect itself can also affect the structure of the metal. As a rule, after heating, the structure changes its conductivity value, which is associated with a change in the crystal lattice.

The thermal conductivity coefficient of aluminum is much higher, which is due to the lower density of this material. The thermal conductivity of brass also differs from that of steel.

Effect of carbon concentration

The carbon concentration in steel affects the amount of heat transfer:

1. Low carbon steels have a high conductivity index. That is why they are used in the manufacture of pipes, which are then used to create the heating system pipeline. The coefficient value varies from 54 to 47 W/(m* K).
2. The average coefficient for common carbon steels is a value from 50 to 90 W/(m* K). That is why such material is used in the manufacture of parts for various mechanisms.
3. For metals that do not contain various impurities, the coefficient is 64 W/(m* K). This value does not change significantly under thermal influence.

Thus, the considered indicator for alloyed alloys may vary depending on the operating temperature.

Why is it important to consider thermal conductivity? A similar value is indicated in various tables for each metal and is taken into account in the following cases:

1. In the manufacture of various heat exchangers. Heat is one of the important carriers of energy. It is used to provide comfortable living conditions in residential and other premises. When creating heating radiators and boilers, it is important to ensure rapid and complete heat transfer from the coolant to the end consumer.
2. In the manufacture of outlet elements. You can often encounter a situation where you need to remove heat rather than supply it. An example is the case of heat removal from the cutting edge of a tool or gear teeth. To ensure that the metal does not lose its basic performance qualities, rapid removal of thermal energy is ensured.
3. When creating insulating layers. In some cases, the material should not conduct thermal energy transfer. For such operating conditions, a metal is selected that has a low heat conductivity coefficient.

The indicator under consideration is determined when testing under various conditions. As previously noted, the thermal conductivity coefficient may depend on the operating temperature. Therefore, the tables indicate several of its values.

Source: https://tokar.guru/metally/stal/teploprovodnost-stali-alyuminiya-latuni-medi.html

Which conducts heat better, aluminum or iron?

Today, radiators are made from a variety of materials, the most common being steel, stainless steel and aluminum.

Always have doubts about which radiator to choose for installation in your home? Obviously, this depends on personal taste, as well as on the requirements that you have set for yourself regarding the quality of the heating of the room.

Aluminum is by far the most environmentally friendly material and has a huge number of advantages.

How to choose a heating radiator: expert advice

In this article we will not consider cast iron radiators, because... they are losing popularity among buyers.

Let's focus on the most popular models.

The material will tell you in detail about the advantages of aluminum and steel batteries.

Aluminum radiators are lightweight

Aluminum radiators are lighter than traditional steel or cast iron radiators, this fact makes it possible to place such a radiator on any wall in the room.

Aluminum batteries can be hung on the wall, even in situations where the thickness does not allow for deep fastening.

This significantly saves the cost of paying for construction work, since they can be hung very quickly and reliably.

We recommend that you familiarize yourself with the range of heating radiators presented in online stores; on the manufacturers' websites you can buy aluminum radiators from leading European manufacturers (ESPERADO, FERROLI, GLOBAL, FARAL, FONDITAL) with a 10-year guarantee!

Aluminum is a corrosion resistant material

Aluminum is not subject to corrosion, which makes it an ideal material for the production of radiators that are intended to be installed in areas such as bathrooms and kitchens where there is high humidity.

  Is it possible to melt aluminum on a gas stove?

Aluminum conducts heat well

Aluminum heats up quickly, making it an excellent heat conductor.

 Aluminum radiators have a low water content, which means that once turned on, such devices give an intense burst of heat and heat up rooms quite quickly.

By installing aluminum radiators, you can quickly achieve the required temperature in the rooms, as they have the shortest response time.

The main advantage is a significant saving in energy costs during the heating season and, as a wonderful bonus, saving money, since aluminum radiators can be turned off while you are away from the house, and when you return home, turn them on and quickly get a warm home without spending a long time waiting.

Aluminum radiators come in a wide range of designs and colors

There is a common belief that efficient heat cannot be beautiful and original. Fortunately, the days when design must give way to superior performance are over.

Aluminum radiators have a diverse range of designs and offer even the most demanding buyer a decent choice.

You can choose your own finishing color that will perfectly match the style of your home, the shape of the radiator will be one hundred percent in harmony with your home or office atmosphere.

Style sacrifice? Absolutely not when you choose aluminum radiators for your home!

Stainless steel

The use of steel for the production of heat exchangers allows us to obtain durable products, which are mainly used for individual heating systems in houses and cottages.

Due to the ability to control the quality of the coolant and the pressure in the system, steel appliances will be an excellent choice for autonomous heating systems.

Provided that high-quality coolant is supplied and the working fluid pressure is moderate, such devices will last more than 30 years.

Steel radiators have low thermal inertia, which means there will be no problems with rapid changes in room temperature. In addition to low thermal inertia, steel radiators have other advantages:

Efficiency

Stainless steel easily conducts heat, which makes a radiator made of steel quite efficient.

Source: https://varimtutru.com/chto-luchshe-provodit-teplo-alyuminiy-ili-zhelezo/

Thermal conductivity coefficient of materials

In recent years, when building a house or renovating it, much attention has been paid to energy efficiency. Given existing fuel prices, this is very important. Moreover, it seems that savings will continue to become increasingly important.

In order to correctly select the composition and thickness of materials in the pie of enclosing structures (walls, floors, ceilings, roofs), it is necessary to know the thermal conductivity of building materials. This characteristic is indicated on the packaging of the materials, and it is necessary at the design stage.

After all, you need to decide what material to build the walls from, how to insulate them, and how thick each layer should be.  

What is thermal conductivity and thermal resistance

When choosing building materials for construction, you need to pay attention to the characteristics of the materials. One of the key positions is thermal conductivity. It is represented by the thermal conductivity coefficient. This is the amount of heat that a particular material can conduct per unit time. That is, the lower this coefficient, the worse the material conducts heat. And vice versa, the higher the number, the better the heat is removed.

Diagram that illustrates the difference in thermal conductivity of materials

Materials with low thermal conductivity are used for insulation, and materials with high thermal conductivity are used to transfer or remove heat. For example, radiators are made of aluminum, copper or steel, as they transfer heat well, that is, they have a high thermal conductivity coefficient.

For insulation, materials with a low thermal conductivity coefficient are used - they retain heat better. If an object consists of several layers of material, its thermal conductivity is determined as the sum of the coefficients of all materials.

During calculations, the thermal conductivity of each of the components of the “pie” is calculated, and the found values ​​are summed up. In general, we obtain the thermal insulation capacity of the enclosing structure (walls, floor, ceiling).

The thermal conductivity of building materials shows the amount of heat that it transmits per unit time

There is also such a thing as thermal resistance. It reflects the ability of a material to prevent heat from passing through it. That is, it is the reciprocal of thermal conductivity. And, if you see a material with high thermal resistance, it can be used for thermal insulation.

An example of thermal insulation materials is the popular mineral or basalt wool, polystyrene foam, etc. Materials with low thermal resistance are needed to remove or transfer heat. For example, aluminum or steel radiators are used for heating, as they give off heat well.

Table of thermal conductivity of thermal insulation materials

To make it easier to keep your house warm in winter and cool in summer, the thermal conductivity of walls, floors and roofs must be at least a certain figure, which is calculated for each region. The composition of the “pie” of walls, floor and ceiling, the thickness of the materials are taken into account so that the total figure is no less (or better yet, at least a little more) recommended for your region.

Heat transfer coefficient of modern building materials for enclosing structures

When choosing materials, it is necessary to take into account that some of them (not all) conduct heat much better in conditions of high humidity. If such a situation may occur for a long period of time during operation, the thermal conductivity for this condition is used in the calculations. The thermal conductivity coefficients of the main materials used for insulation are given in the table.

Name of materialThermal conductivity coefficient W/(m °C)

Dry	At normal humidity	At high humidity
Woolen felt	0,036-0,041	0,038-0,044	0,044-0,050
Stone mineral wool 25-50 kg/m3	0,036	0,042	0,,045
Stone mineral wool 40-60 kg/m3	0,035	0,041	0,044
Stone mineral wool 80-125 kg/m3	0,036	0,042	0,045
Stone mineral wool 140-175 kg/m3	0,037	0,043	0,0456
Stone mineral wool 180 kg/m3	0,038	0,045	0,048
Glass wool 15 kg/m3	0,046	0,049	0,055
Glass wool 17 kg/m3	0,044	0,047	0,053
Glass wool 20 kg/m3	0,04	0,043	0,048
Glass wool 30 kg/m3	0,04	0,042	0,046
Glass wool 35 kg/m3	0,039	0,041	0,046
Glass wool 45 kg/m3	0,039	0,041	0,045
Glass wool 60 kg/m3	0,038	0,040	0,045
Glass wool 75 kg/m3	0,04	0,042	0,047
Glass wool 85 kg/m3	0,044	0,046	0,050
Expanded polystyrene (foam plastic, EPS)	0,036-0,041	0,038-0,044	0,044-0,050

Source: https://stroychik.ru/strojmaterialy-i-tehnologii/teploprovodnost-stroitelnyh-materialov

Thermal conductivity of copper and aluminum table

So what is thermal conductivity? From the point of view of physics, thermal conductivity is the molecular transfer of heat between directly contacting bodies or particles of the same body with different temperatures, at which the energy of movement of structural particles (molecules, atoms, free electrons) is exchanged.

To put it simply, thermal conductivity is the ability of a material to conduct heat. If there is a temperature difference inside the body, then thermal energy moves from the hotter part of the body to the colder part. Heat transfer occurs due to the transfer of energy when molecules of a substance collide. This happens until the temperature inside the body becomes the same. This process can occur in solid, liquid and gaseous substances.

In practice, for example in construction for the thermal insulation of buildings, another aspect of thermal conductivity is considered, associated with the transfer of thermal energy. Let's take an “abstract house” as an example.

In the “abstract house” there is a heater that maintains a constant temperature inside the house, say, 25 ° C. The temperature outside is also constant, for example, 0 °C.

It is quite clear that if you turn off the heater, then after a while the house will also be 0 °C. All the heat (thermal energy) will go through the walls to the street.

To maintain the temperature in the house at 25 ° C, the heater must be constantly running. The heater constantly creates heat, which constantly escapes through the walls to the street.

Coefficient of thermal conductivity

The amount of heat that passes through the walls (and according to science, the intensity of heat transfer due to thermal conductivity) depends on the temperature difference (in the house and outside), on the area of ​​the walls and the thermal conductivity of the material from which these walls are made.

To quantify thermal conductivity, there is a coefficient of thermal conductivity of materials . This coefficient reflects the property of a substance to conduct thermal energy. The higher the thermal conductivity coefficient of a material, the better it conducts heat.

If we are going to insulate a house, then we need to choose materials with a small value of this coefficient. The smaller it is, the better. Nowadays, the most widely used materials for insulating buildings are mineral wool insulation and various foam plastics.

A new material with improved thermal insulation properties – Neopor – is gaining popularity.

The thermal conductivity coefficient of materials is designated by the letter ? (Greek small letter lambda) and is expressed in W/(m2*K). This means that if you take a brick wall with a thermal conductivity coefficient of 0.67 W/(m2*K), a thickness of 1 meter and an area of ​​1 m2.

, then with a temperature difference of 1 degree, 0.67 watts of thermal energy will pass through the wall. If the temperature difference is 10 degrees, then 6.7 watts will pass. And if, with such a temperature difference, the wall is made 10 cm, then the heat loss will already be 67 watts.

More details about the methodology for calculating heat loss in buildings can be found here.

It should be noted that the values ​​of the thermal conductivity coefficient of materials are indicated for a material thickness of 1 meter. To determine the thermal conductivity of a material for any other thickness, the thermal conductivity coefficient must be divided by the desired thickness, expressed in meters.

In building codes and calculations the concept of “thermal resistance of a material” is often used. This is the reciprocal of thermal conductivity. If, for example, the thermal conductivity of foam plastic 10 cm thick is 0.37 W/(m2*K), then its thermal resistance will be equal to 1 / 0.37 W/(m2*K) = 2.7 (m2*K)/ Tue

Thermal conductivity coefficient of materials

The table below shows the values ​​of the thermal conductivity coefficient for some materials used in construction.

Material	Coeff. warm W/(m2*K)
Alabaster slabs	0,470
Aluminum	230,0
Asbestos (slate)	0,350
Fibrous asbestos	0,150
Asbestos cement	1,760
Asbestos cement slabs	0,350
Asphalt	0,720
Asphalt in floors	0,800
Bakelite	0,230
Concrete on crushed stone	1,300
Concrete on sand	0,700
Porous concrete	1,400
Solid concrete	1,750
Thermal insulating concrete	0,180
Bitumen	0,470
Paper	0,140
Light mineral wool	0,045
Heavy mineral wool	0,055
Cotton wool	0,055
Vermiculite sheets	0,100
Woolen felt	0,045
Construction gypsum	0,350
Alumina	2,330
Gravel (filler)	0,930
Granite, basalt	3,500
Soil 10% water	1,750
Soil 20% water	2,100
Sandy soil	1,160
The soil is dry	0,400
Compacted soil	1,050
Tar	0,300
Wood - boards	0,150
Wood – plywood	0,150
Hardwood	0,200
Chipboard	0,200
Duralumin	160,0
Reinforced concrete	1,700
Wood ash	0,150
Limestone	1,700
Lime-sand mortar	0,870
Iporka (foamed resin)	0,038
Stone	1,400
Multilayer construction cardboard	0,130
Foamed rubber	0,030
Natural rubber	0,042
Fluorinated rubber	0,055
Expanded clay concrete	0,200
Silica brick	0,150
Hollow brick	0,440
Silicate brick	0,810
Solid brick	0,670
Slag brick	0,580
Siliceous slabs	0,070
Brass	110,0
Ice 0°C	2,210
Ice -20°С	2,440
Linden, birch, maple, oak (15% humidity)	0,150
Copper	380,0
Mipora	0,085
Sawdust - backfill	0,095
Dry sawdust	0,065
PVC	0,190
Foam concrete	0,300
Polystyrene foam PS-1	0,037
Polyfoam PS-4	0,040
Polystyrene foam PVC-1	0,050
Foam resopen FRP	0,045
Expanded polystyrene PS-B	0,040
Expanded polystyrene PS-BS	0,040
Polyurethane foam sheets	0,035
Polyurethane foam panels	0,025
Lightweight foam glass	0,060
Heavy foam glass	0,080
Glassine	0,170
Perlite	0,050
Perlite-cement slabs	0,080
Sand 0% moisture	0,330
Sand 10% moisture	0,970
Sand 20% humidity	1,330
Burnt sandstone	1,500
Facing tiles	1,050
Thermal insulation tile PMTB-2	0,036
Polystyrene	0,082
Foam rubber	0,040
Portland cement mortar	0,470
Cork board	0,043
Cork sheets are lightweight	0,035
Cork sheets are heavy	0,050
Rubber	0,150
Ruberoid	0,170
Slate	2,100
Snow	1,500
Scots pine, spruce, fir (450550 kg/cub.m, 15% humidity)	0,150
Resinous pine (600750 kg/cub.m, 15% humidity)	0,230
Steel	52,0
Glass	1,150
Glass wool	0,050
Fiberglass	0,036
Fiberglass	0,300
Wood shavings - stuffing	0,120
Teflon	0,250
Paper roofing felt	0,230
Cement boards	1,920
Cement-sand mortar	1,200
Cast iron	56,0
Granulated slag	0,150
Boiler slag	0,290
Cinder concrete	0,600
Dry plaster	0,210
Cement plaster	0,900
Ebonite	0,160

Source: http://ooo-asteko.ru/teploprovodnost-medi-i-alyuminiya-tablitsa/

Which metal conducts heat better?

• List of sections
• Physics
• Study of thermal conductivity of various substances

The author of the work was awarded a third degree winner diploma

The project was developed in accordance with the standard of secondary general education in physics. When writing this project, we considered the study of thermal phenomena and their application in everyday life and technology.

In addition to theoretical material, much attention is paid to research work - these are experiments that answer the questions “In what ways can the internal energy of a body be changed”, “Is the thermal conductivity of different substances the same”, “Why do jets of warm air or liquid rise upward”, “Why do bodies with dark the surface heats up more"; search and processing of information, photographs. Time to work on the project: 1 – 1.5 months. Project goals: * practical implementation of schoolchildren’s knowledge about thermal phenomena; * formation of independent research skills; * development of cognitive interests; * development of logical and technical thinking ;* development of abilities to independently acquire new knowledge in physics in accordance with life needs and interests;

2. Main part.

2.1. Theoretical part

https://www.youtube.com/watch?v=IkABQkk0SSU

In life, we actually encounter thermal phenomena every day. However, we do not always think that these phenomena can be explained if we know physics well. In physics lessons, we learned about ways to change internal energy: heat transfer and work done on a body or the body itself.

When two bodies with different temperatures come into contact, energy is transferred from the body with a higher temperature to the body with a lower temperature. This process will continue until the temperatures of the bodies are equal (thermal equilibrium occurs). In this case, no mechanical work is performed.

The process of changing internal energy without doing work on the body or the body itself is called heat exchange or heat transfer. During heat transfer, energy is always transferred from a more heated body to a less heated one. The reverse process never occurs spontaneously (by itself), i.e., heat transfer is irreversible.

Heat exchange determines or accompanies many processes in nature: the evolution of stars and planets, meteorological processes on the Earth's surface, etc. Types of heat transfer: thermal conductivity, convection, radiation.

Thermal conductivity is the phenomenon of energy transfer from more heated parts of the body to less heated ones as a result of thermal movement and interaction of the particles that make up the body.

Metals have the greatest thermal conductivity - it is hundreds of times greater than that of water. The exceptions are mercury and lead, but even here the thermal conductivity is tens of times greater than that of water.

When a metal knitting needle was lowered into a glass of hot water, very soon the end of the knitting needle also became hot. Consequently, internal energy, like any type of energy, can be transferred from one body to another. Internal energy can be transferred from one part of the body to another. So, for example, if one end of a nail is heated in a flame, then its other end, located in the hand, will gradually heat up and burn the hand.

2.2. Practical part.

Let's study this phenomenon by performing a series of experiments with solids, liquids and gases.

Experience No. 1

They took various objects: one aluminum spoon, another wooden, a third plastic, a fourth stainless alloy, and a fifth silver. We attached paper clips to each spoon with drops of honey. We placed the spoons in a glass of hot water so that the handles with paper clips stuck out of it in different directions. The spoons will heat up and as they heat up the honey will melt and the paper clips will fall off.

Of course, the spoons must be the same in shape and size. Where heating occurs faster, that metal conducts heat better, is more thermally conductive. For this experiment, I took a glass of boiling water and four types of spoons: aluminum, silver, plastic and stainless. I dropped them one at a time into a glass and noted the time: how many minutes would it take for it to heat up. Here's what I got:

Among the large number of parameters characterizing metals, there is such a concept as thermal conductivity. Its importance is difficult to overestimate. This parameter is used when calculating parts and assemblies. For example, gear transmissions. In general, a whole branch of science called thermodynamics deals with thermal conductivity.

The most heat-conducting metal - Metalist's Handbook

The high thermal conductivity of copper and its other useful characteristics were one of the reasons for the early development of this metal by humans. To this day, copper and copper alloys are used in almost all areas of our lives.

Copper plates

A little about thermal conductivity

In physics, thermal conductivity is understood as the movement of energy in an object from more heated small particles to less heated ones. Thanks to this process, the temperature of the object in question as a whole is equalized. The magnitude of the ability to conduct heat is characterized by the thermal conductivity coefficient. This parameter is equal to the amount of heat that a material 1 meter thick passes through a surface area of ​​1 m2 for one second at a unit temperature difference.

MaterialThermal conductivity coefficient, W/(m*K)

Silver	428
Copper	394
Aluminum	220
Iron	74
Steel	45
Lead	35
Brick	0,77

Copper has a thermal conductivity coefficient of 394 W/(m*K) at temperatures from 20 to 100 °C. Only silver can compete with it. And for steel and iron this figure is 9 and 6 times lower, respectively (see table). It is worth noting that the thermal conductivity of products made from copper largely depends on impurities (however, this also applies to other metals). For example, the rate of heat conduction decreases if substances such as:

• iron;
• arsenic;
• oxygen;
• selenium;
• aluminum;
• antimony;
• phosphorus;
• sulfur.

Copper wire

If you add zinc to copper, you get brass, which has a much lower thermal conductivity coefficient. At the same time, adding other substances to copper can significantly reduce the cost of finished products and give them characteristics such as strength and wear resistance. For example, brass is characterized by higher technological, mechanical and anti-friction properties.

Since high thermal conductivity is characterized by rapid distribution of heating energy throughout the entire object, copper is widely used in heat exchange systems. At the moment, radiators and tubes for refrigerators, vacuum units and cars are made from it for rapid heat removal. Copper elements are also used in heating installations, but for heating.

Copper heating radiator

In order to maintain the thermal conductivity of the metal at a high level (and therefore make the operation of copper devices as efficient as possible), forced airflow by fans is used in all heat exchange systems. This decision is due to the fact that as the temperature of the environment increases, the thermal conductivity of any material decreases significantly, because heat transfer slows down.

Aluminum and copper - which is better?

Aluminum has one disadvantage compared to copper: its thermal conductivity is 1.5 times less, namely 201–235 W/(m*K). However, compared to other metals, these are quite high values. Aluminum, like copper, has high anti-corrosion properties. In addition, it has advantages such as:

• low density (specific gravity 3 times less than that of copper);
• low cost (3.5 times less than copper).

Aluminum heating radiator

Thanks to simple calculations, it turns out that an aluminum part can be almost 10 times cheaper than a copper part, because it weighs much less and is made of cheaper material. This fact, along with high thermal conductivity, allows the use of aluminum as a material for cookware and food foil for ovens. The main disadvantage of aluminum is that it is softer, so it can only be used in alloys (for example, duralumin).

For effective heat transfer, the rate of heat transfer to the environment plays an important role, and this is actively facilitated by the cooling of radiators. As a result, the lower thermal conductivity of aluminum (relative to copper) is leveled out, and the weight and cost of the equipment are reduced. These important advantages allow aluminum to gradually replace copper from use in air conditioning systems.

Use of copper in electronics

In some industries, for example, in the radio industry and electronics, copper is essential.

The fact is that this metal is very ductile in nature: it can be drawn into extremely thin wires (0.005 mm), and also can be used to create other specific conductive elements for electronic devices.

And high thermal conductivity allows copper to extremely effectively remove the heat that inevitably arises during the operation of electrical appliances, which is very important for modern high-precision, but at the same time compact equipment.

The use of copper is relevant in cases where it is necessary to deposit a certain shape on a steel part. In this case, a copper template is used, which is not connected to the element being welded. Using aluminum for these purposes is impossible, as it will melt or burn through. It is also worth mentioning that copper can act as a cathode when welding with a carbon arc.

1 - gear, 2 - template fastenings, 3 - welded gear tooth, 4 - copper templates

Disadvantages of the high thermal conductivity of copper and its alloys

Copper has a much higher cost than brass or aluminum. At the same time, this metal has its disadvantages, which are directly related to its advantages. High thermal conductivity leads to the need to create special conditions during cutting, welding and soldering of copper elements. Since copper elements need to be heated much more concentrated compared to steel. Also, preliminary and concomitant heating of the part is often required.

Don’t forget that copper pipes require careful insulation if they make up the main line or distribution of the heating system. Which leads to an increase in the cost of network installation compared to options when other materials are used.

Example of thermal insulation of copper pipes

Difficulties also arise with gas welding of copper: this process will require more powerful torches. When welding metal 8–10 mm thick, two or three torches will be required. While one torch is used for welding, the other is heating the part. In general, welding work with copper requires increased costs for consumables.

It should also be said about the need to use special tools. So, to cut brass and bronze up to 15 cm thick, you will need a cutter capable of working with high-chromium steel 30 cm thick. Moreover, the same tool is enough to work with pure copper only 5 cm thick.

Plasma cutting of copper

Is it possible to increase the thermal conductivity of copper?

Copper is widely used in the creation of microcircuits for electronic devices and is designed to remove heat from parts heated by electric current.

When trying to increase the speed of modern computers, developers were faced with the problem of cooling processors and other parts. One of the solutions was to split the processor into several cores.

However, this method of combating overheating has exhausted itself, and now it is necessary to look for new conductors with higher thermal and electrical conductivity.

One solution to this problem is the recently discovered element graphene. Thanks to graphene deposition, the thermal conductivity of the copper element increases by 25%. However, the invention is still at the development level.

Source: https://ssk2121.com/samyy-teploprovodnyy-metall/

Thermal conductivity of stainless steel

Copper pipes are used in the installation of hot water supply, hot water supply, air conditioning, heating and gas supply systems. They are expensive, but durable, ductile and have excellent corrosion resistance.

But in order for engineering communications from them to last for decades, the connection of copper pipes must be done correctly. There are several technologies for installation, and each of them has its own design features.

The nuances of working with copper pipes

To install internal pipelines in the house, you can choose a pipe made of plastic, metal-plastic or stainless steel. But only a copper analog can last for more than half a century without problems or major repairs.

Properly installed copper pipeline systems in practice work properly throughout the entire service life of a cottage or apartment building.

According to accident statistics, the fittings and solder joints used during installation are more reliable than the copper pipes themselves - if a breakthrough in the system occurs, it is only on the wall of the pipe product

Copper pipes are not afraid of long-term heat loads, chlorine and ultraviolet radiation. When they freeze, they do not crack, and when the temperature of the internal environment (water, wastewater, gas) changes, they do not change their geometry. Unlike plastic analogues, copper pipelines do not sag.

This plastic is subject to expansion at high temperatures; this does not happen with copper by definition.

Copper pipe products have two disadvantages - high price and softness of the metal. However, the high cost of the material pays off with a long service life. And to prevent the walls of the pipes from being damaged from the inside by erosion, filters must be installed in the system.

If there are no contaminants in the water in the form of solid particles, then there will be no problems with the destruction of pipelines.

Requirements for pipe processing and welding

When working with copper pipes, the following rules must be observed:

1. When installing hot water supply or hot water supply by soldering, you should avoid using lead solder - lead is too toxic.
2. The water flow speed should be no higher than 2 m/s, otherwise the smallest particles of sand or other solid substance will gradually begin to destroy the walls of the pipe.
3. When using fluxes, after completion of installation, the pipeline system must be flushed - flux is an aggressive substance and will contribute to corrosion of copper pipe walls.
4. When soldering, do not allow the joint to overheat - this can lead not only to the formation of a leaky joint, but also to a loss of strength of the copper product.
5. Transitions of pipes from copper to other metals (steel and aluminum) are recommended to be made using brass or bronze adapter fittings - otherwise steel and aluminum pipes will quickly begin to corrode.
6. Burrs (metal deposits) and burrs at cutting sites must be removed - their presence leads to the formation of turbulent turbulence in the water flow, which contributes to erosion and reduces the service life of the copper pipeline.
7. When preparing copper pipes for connection, it is strictly forbidden to use abrasives - particles remaining inside after installation will lead to damage to the metal and the formation of a fistula.

If in the plumbing or heating system in a house, in addition to copper, there are also pipes or elements made of other metals, then the water flow should go from them to copper, and not vice versa. The flow of water from copper to steel, zinc or aluminum will lead to rapid electrochemical corrosion of the latter sections of the pipeline.

Copper pipes can be cut and bent without problems; even a novice master can handle connecting them into a single pipeline system. You just need to select the appropriate tools and follow the instructions

Due to the ductility and strength of the metal, copper pipes can be cut and bent without problems. Rotation of the pipeline can be done either by using a pipe bender or using fittings. And for the installation of branches and connections with various devices, there are many parts made of heat-resistant plastics, brass, stainless steel and bronze.

On the interaction of copper with other metals

In most private homes, domestic water pipes are assembled from steel and aluminum pipes. Heating systems also contain radiators made of steel or aluminum. Incorrect insertion into such copper pipe routing is fraught with considerable problems.

According to building codes, in order to exclude corrosion processes in a pipeline from pipes of different metals, the water flow must be directed towards the copper

The most optimal installation option is to use pipes and devices exclusively made of copper and its alloys. Nowadays you can easily find bimetallic aluminum-copper radiators, as well as corresponding fittings and shut-off valves. It is worth combining different metals only in extreme cases.

If combination is inevitable, then copper should be the final element in the chain of pipeline elements. It is impossible to rid it of its ability to conduct electric current. And in the presence of even a weak current, this metal creates galvanic pairs with steel, aluminum and zinc, which inevitably leads to their premature corrosion. When installing a water supply system, bronze adapters must be inserted between them.

Another potential problem is oxygen in the water. The higher its content, the faster the pipes corrode. This applies to pipelines both made of the same metal and those made of different ones.

Often, cottage owners make a serious mistake by frequently changing the coolant in the heating system. This only leads to the addition of completely unnecessary portions of oxygen. It is best not to completely change the water, but to add it when the need arises.

Mounting choice: detachable vs permanent

To connect copper pipes into a single pipeline system, you can use several methods of joining them. Various plumbers use crimp and press fittings, welding or soldering. But before you start work yourself, you need to decide whether the pipeline should be permanent or detachable.

There are three installation technologies for connecting copper pipes:

• electric welding;
• soldering using a torch or electric soldering iron;
• pressing.

All these technologies can be used in the formation of both detachable and one-piece systems. Here it is more a matter of using a variety of fittings and adapters or refusing them.

If a structure cannot be disassembled without destroying its individual parts, then it is considered one-piece - it turns out cheaper, but it is more difficult to repair.

If the pipeline system needs to be detachable, and also easier to repair and add new elements, then the connections must be made detachable. Fittings are used for this:

• compression;
• threaded;
• self-fixing.

It is easier to make detachable connections yourself; you can even do without soldering. They do not require excessively high qualifications from the master. However, such units require constant inspection and tightening of the nuts to prevent leaks. Changes in pressure and temperature in the system lead to weakening of the fasteners. And from time to time it is recommended to tighten them.

If access to copper pipes is planned to be tightly closed with finishing or concrete screed, then it is best to connect them into an integral structure by soldering or welding. This system is more reliable, durable and resistant to abrasions.

Carvings are prohibited on copper products. This metal is too soft in its structure. When installing a detachable pipeline, all threaded connections must be made using fittings. The latter can be connected to a copper pipe by pressing or soldering.

  Electrochemical etching of stainless steel

Three main connection methods

Before connecting sections of copper pipes, they must be cut in accordance with the wiring diagram and prepared. You will need a pipe cutter or hacksaw, a pipe bender and a file. And for cleaning the ends, fine-grained sandpaper will not hurt.

There is no way to start installation without a clear plan and drawing of the pipeline - this is not only a matter of financial expenses, but also an understanding of the scope of work

Only having a diagram of the future pipeline system in hand can you calculate the required amount of consumables. It is necessary to decide in advance where and what diameter the pipes will be installed. It is also necessary to clearly understand how many connecting elements are required for this.

Option #1: Welding

To perform automated or manual welding of copper pipes, electrodes and gas are required to create a protective environment (nitrogen, argon or helium). You will also need a DC welding machine and, in some cases, a torch. The electrode can be graphite, tungsten, copper or carbon.

The main disadvantage of this installation technology is the significant differences in the characteristics of the resulting seam and the pipe metal. They differ in chemical composition, internal structure, electrical and thermal conductivity. If welding is performed incorrectly, the joint may even separate later.

Due to the alloying of copper as a result of the action of the deoxidizer present in the electrode, the weld seam is in many respects very different from the base metal being welded

Only a qualified craftsman can properly weld copper pipes. This requires certain knowledge and skills. This installation option has a lot of technological nuances. If you plan to do everything yourself, but have no experience working with a welding machine, then it is better to use a different connection method.

Option #2: Capillary soldering

In domestic conditions, copper pipes are rarely connected by welding plumbing fixtures. It is too complex, requires specialized skills and is time consuming. It is easier to use the capillary soldering method using a gas torch or blowtorch.

The technology of soldering copper pipes with solder is based on the capillary rise (seepage) of the latter after melting along the gap between two pressed metal planes

Soldering of copper pipes happens:

• low temperature - soft solders and a blowtorch are used;
• high temperature - refractory alloys and a propane or acetylene torch are used.

These soldering methods do not make much difference in the final result. The connection in both cases is reliable and tear-resistant. The seam with the high-temperature method is somewhat stronger. However, due to the high temperature of the gas stream from the burner, the risk of burning through the metal of the pipe wall increases.

Solders are used based on tin or lead with the addition of bismuth, selenium, copper and silver. However, if pipes are soldered for a drinking water supply system, then it is better to avoid the lead option due to its toxicity.

There are two methods for soldering copper pipelines:

• bell-shaped;
• using fittings.

The first option involves expanding the end of one of the connected pipes with a special expander. Then this socket is put on the second pipe, and the joint is soldered using solder. The end is expanded so that there is a gap of 0.1–0.2 mm between the outer and inner walls of the connected products. No more is needed. Solder on it, due to the capillary effect, will still fill the entire available gap.

In this technology, it is important not to damage the pipe during expansion. If it is made of solid copper (R 290), it will have to be pre-fired. In this case, the metal at the joint acquires the properties of a soft analogue. It is important not to forget about these changes when calculating operating pressure parameters in the pipeline.

Source: https://respect-kovka.com/teploprovodnost-nerzhaveyuschey-stali/

Thermal conductivity of metals

From the data presented above, it is clear that the bimetallic heating device has the highest heat transfer rate. Structurally, such a device is presented by RIFAR in a ribbed aluminum housing. in which metal tubes are located, the entire structure is secured by a welded frame. This type of battery is installed in high-rise buildings, as well as in cottages and private houses. The disadvantage of this type of heating device is its high cost.

Important! When this type of battery is installed in houses with a large number of floors, it is recommended to have its own boiler station, which has a water treatment unit. This condition for the preliminary preparation of the coolant is associated with the properties of aluminum batteries

they can be subject to galvanic corrosion when it is supplied in poor quality through the central heating network. For this reason, it is recommended to install aluminum heating devices in separate heating systems.

Cast iron batteries are significantly inferior in this comparative system of parameters; they have low heat transfer and a large weight of the heating device. But, despite these indicators, MS-140 radiators are in demand among the population, the reason for which is the following factors:

Duration of trouble-free operation, which is important in heating systems. Resistance to the negative effects (corrosion) of the thermal fluid.

Thermal inertia of cast iron.

This type of heating device has been operating for more than 50 years; for it there is no difference in the quality of the preparation of the thermal fluid. They cannot be installed in houses where the operating pressure of the heating network may be high; cast iron is not a durable material.

Comparison by other characteristics

One feature of battery operation – inertia – has already been mentioned above. But in order for the comparison of heating radiators to be correct, it must be made not only by heat transfer, but also by other important parameters:

• working and maximum pressure;
• the amount of water held;
• mass.

The limitation on the operating pressure determines whether the heating device can be installed in multi-storey buildings, where the height of the water column can reach hundreds of meters. By the way, this restriction does not apply to private houses, where the pressure in the network is not high by definition. Comparing the capacity of radiators can give an idea of ​​the total amount of water in the system that will have to be heated. Well, the mass of the product is important when determining the place and method of its fastening.

As an example, below is a comparison table of the characteristics of various heating radiators of the same size:

Note. In the table, a heating device consisting of 5 sections is taken as 1 unit, except for the steel one, which is a single panel.

Thermal conductivity and density of aluminum

The table shows the thermophysical properties of aluminum Al depending on temperature. The properties of aluminum are given over a wide temperature range - from minus 223 to 1527 ° C (from 50 to 1800 K).

As can be seen from the table, the thermal conductivity of aluminum at room temperature is about 236 W/(m deg), which allows this material to be used for the manufacture of radiators and various heat sinks.

In addition to aluminum, copper also has high thermal conductivity. Which metal has the greater thermal conductivity? It is known that the thermal conductivity of aluminum at medium and high temperatures is still less than that of copper, however, when cooled to 50K, the thermal conductivity of aluminum increases significantly and reaches a value of 1350 W/(m deg). For copper, at such a low temperature, the thermal conductivity value becomes lower than for aluminum and amounts to 1250 W/(m deg).

Aluminum begins to melt at a temperature of 933.61 K (about 660 ° C), while some of its properties undergo significant changes. The values ​​of properties such as thermal diffusivity, aluminum density and thermal conductivity are significantly reduced.

The density of aluminum is mainly determined by its temperature and depends on the state of aggregation of this metal. For example, at a temperature of 27°C, the density of aluminum is 2697 kg/m3, and when this metal is heated to its melting point (660°C), its density becomes equal to 2368 kg/m3. The decrease in aluminum density with increasing temperature is due to its expansion when heated.

from here

The table shows the thermal conductivity values ​​of metals (non-ferrous), as well as the chemical composition of metals and technical alloys in the temperature range from 0 to 600°C.

Source: https://mr-build.ru/newteplo/teplootdaca-medi-i-aluminia.html

On the thermal conductivity of copper and its alloys

The high thermal conductivity of copper and its other useful characteristics were one of the reasons for the early development of this metal by humans. To this day, copper and copper alloys are used in almost all areas of our lives.