What is the thermal conductivity of aluminum

Thermal conductivity of metals

All products used by humans are capable of transmitting and maintaining the temperature of the object or environment they touch. The ability of one body to transfer heat to another depends on the type of material through which the process takes place.

The properties of metals allow heat to be transferred from one object to another, with certain changes depending on the structure and size of the metal structure.

The thermal conductivity of metals is one of the parameters that determines their operational capabilities.

What is thermal conductivity and why is it needed?

The process of transferring the energy of atoms and molecules from hot objects to products with a cold temperature is carried out during the chaotic movement of moving particles. Such heat exchange depends on the state of aggregation of the metal through which the transmission passes.

Depending on the chemical composition of the material, thermal conductivity will have different characteristics.

This process is called thermal conductivity, it consists in the transfer of kinetic energy by atoms and molecules, which determines the heating of a metal product during the interaction of these particles, or is transferred from a warmer part to one that is less heated.

The ability to transfer or store thermal energy makes it possible to use the properties of metals to achieve the necessary technical goals in the operation of various components and assemblies of equipment used in the national economy.

An example of such an application would be a soldering iron that heats up in the middle part and transfers heat to the edge of the working rod, which is used to solder the necessary elements.

Knowing the properties of thermal conductivity, metals are used in all industries, using the required parameter for its intended purpose.

The concept of thermal resistance and thermal conductivity coefficient

If thermal conductivity characterizes the ability of metals to transfer the temperature of bodies from one surface to another, then thermal resistance shows an inverse relationship, i.e. the ability of metals to prevent such transfer, in other words, to resist. Air has high thermal resistance. It is he who, most of all, prevents the transfer of heat between bodies.

The quantitative characteristic of the change in temperature of a unit area per unit of time by one degree (K) is called the thermal conductivity coefficient. The international system of units usually measures this parameter in W/m*deg. This characteristic is very important when choosing metal products that must transfer heat from one body to another.

Table 1

Metal	Thermal conductivity coefficient of metals at temperature, °C
— 100		100	300	700
Aluminum	2,45	2,38	2,30	2,26	0,9
Beryllium	4,1	2,3	1,7	1,25	0,9
Vanadium	—	—	0,31	0,34	—
Bismuth	0,11	0,08	0,07	0,11	0,15
Tungsten	2,05	1,90	1,65	1,45	1,2
Hafnium	—	—	0,22	0,21	—
Iron	0,94	0,76	0,69	0,55	0,34
Gold	3,3	3,1	3,1	—	—
Indium	—	0,25	—	—	—
Iridium	1,51	1,48	1,43	—	—
Cadmium	0,96	0,92	0,90	0,95	0,44 (400°)
Potassium	—	0,99	—	0,42	0,34
Calcium	—	0,98	—	—	—
Cobalt	—	0,69	—	—	—
Lithium	—	0,71	0,73	—	—
Magnesium	1,6	1,5	1,5	1,45	—
Copper	4,05	3,85	3,82	3,76	3,50
Molybdenum	1,4	1,43	—	—	1,04 (1000°)
Sodium	1,35	1,35	0,85	0,76	0,60
Nickel	0,97	0,91	0,83	0,64	0,66
Niobium	0,49	0,49	0,51	0,56	—
Tin	0,74	0,64	0,60	0,33	—
Palladium	0,69	0,67	0,74	—	—
Platinum	0,68	0,69	0,72	0,76	0,84
Rhenium	—	0,71	—	—	—
Rhodium	1,54	1,52	1,47	—	—
Mercury	0,33	0,09	0.1	0,115	—
Lead	0,37	0,35	0,335	0,315	0,19
Silver	4,22	4,18	4,17	3,62	—
Antimony	0,23	0,18	0,17	0,17	0,21
Thallium	0,41	0,43	0,49	0,25 (400 0)
Tantalum	0,54	0,54	—	—	—
Titanium	—	—	0,16	0,15	—
Thorium	—	0,41	0,39	0,40	0,45
Uranus	—	0,24	0,26	0,31	0,40
Chromium	—	0,86	0,85	0,80	0,63
Zinc	1,14	1,13	1,09	1,00	0,56
Zirconium	—	0,21	0,20	0,19	—

What does thermal conductivity depend on?

Studying the ability of heat transfer by metal products, it was revealed that thermal conductivity depends on:

• type of metal;
• chemical composition;
• porosity;
• sizes.

Metals have different crystal lattice structures, and this can change the thermal conductivity of the material. For example, in steel and aluminum, the structural features of microparticles affect differently the rate of transfer of thermal energy through them.

The thermal conductivity coefficient can have different values ​​for the same metal when the exposure temperature changes. This is due to the fact that different metals have different melting degrees, which means that under other environmental parameters, the properties of the materials will also differ, and this will affect thermal conductivity.

Measurement methods

To measure the thermal conductivity of metals, two methods are used: stationary and non-stationary. The first is characterized by the achievement of a constant value of the changed temperature on the controlled surface, and the second - by a partial change in it.

Stationary measurement is carried out experimentally, requires a lot of time, as well as the use of the metal under study in the form of blanks of the correct shape, with flat surfaces. The sample is placed between the heated and cooled surface, and after touching the planes, the time during which the workpiece can increase the temperature of the cool support by one degree Kelvin is measured. When calculating thermal conductivity, the dimensions of the sample being studied must be taken into account.

Non-stationary research methods are used in rare cases due to the fact that the result is often biased. Nowadays, no one except scientists is involved in measuring the coefficient; everyone uses long-established experimental values ​​for various materials. This is due to the constancy of this parameter while maintaining the chemical composition of the product.

Thermal conductivity of steel, copper, aluminum, nickel and their alloys

Ordinary iron and non-ferrous metals have different structures of molecules and atoms. This allows them to differ from each other not only in mechanical properties, but also in thermal conductivity properties, which, in turn, affects the use of certain metals in various sectors of the economy.

table 2

Steel has a thermal conductivity coefficient at an ambient temperature of 0 degrees. (C) equal to 63, and when the degree increases to 600, it decreases to 21 W/m*degree. Aluminum, under the same conditions, on the contrary, will increase the value from 202 to 422 W/m*deg. Aluminum alloys will also increase thermal conductivity as the temperature increases. Only the value of the coefficient will be an order of magnitude lower, depending on the amount of impurities, and range from 100 to 180 units.

Copper, with a temperature change within the same limits, will reduce thermal conductivity from 393 to 354 W/m*deg. At the same time, copper-containing brass alloys will have the same properties as aluminum ones, and the thermal conductivity value will vary from 100 to 200 units, depending on the amount of zinc and other impurities in the brass alloy.

The thermal conductivity coefficient of pure nickel is considered low; it will change its value from 67 to 57 W/m*deg. Alloys containing nickel will also have a coefficient with a reduced value, which, due to the content of iron and zinc, ranges from 20 to 50 W/m*deg. And the presence of chromium will reduce the thermal conductivity in metals to 12 units, with a slight increase in this value when heated.

Application

The state of aggregation of materials has a distinctive structure of molecules and atoms. This is what has a great influence on metal products and their properties, depending on their purpose.

The different chemical composition of components and parts made of iron allows them to have different thermal conductivities. This is due to the structure of metals such as cast iron, steel, copper and aluminum. The porosity of cast iron products promotes slow heating, and the density of the copper structure, on the contrary, accelerates the heat transfer process. These properties are used for rapid heat removal or gradual heating of inert products. An example of using the properties of metal products is:

• kitchen utensils with various properties;
• pipe soldering equipment;
• irons;
• rolling and sliding bearings;
• plumbing equipment for heating water;
• heating devices.

Copper tubes are widely used in radiators of automobile cooling systems and air conditioners used in everyday life. Cast iron radiators retain heat in the apartment, even with an inconsistent supply of coolant at the required temperature. And radiators made of aluminum contribute to the rapid transfer of heat to the heated room.

When high temperatures occur as a result of friction of metal surfaces, it is also important to take into account the thermal conductivity of the product. In any gearbox or other mechanical equipment, the ability to remove heat will allow the mechanism parts to maintain strength and not be subject to destruction during operation. Knowledge of the heat transfer properties of various materials will allow you to competently use certain alloys of non-ferrous or ferrous metals.

Source: https://prompriem.ru/metally/teploprovodnost.html

Properties of aluminum: specific gravity and thermal conductivity, production, application, alloys and melting point

Aluminum is an element from the periodic table known to everyone from school chemistry courses. In most compounds it exhibits trivalency, but at high temperatures it achieves some degree of oxidation. One of its most important compounds is aluminum oxide .

Main characteristics of aluminum

Aluminum is a silvery metal with a specific gravity of 2.7 * 103 kg/m3 and a density of 2.7 g/cm3. Lightweight and plastic, it is good as a conductor of electricity, due to the fact that the thermal conductivity of aluminum is quite high - 180 kcal/m*hour*deg (the thermal conductivity coefficient is indicated). The thermal conductivity of aluminum exceeds that of cast iron by five times and that of iron by three times.

Due to its composition, this metal can be easily rolled into a thin sheet or drawn into wire. When it comes into contact with air, an oxide film (aluminum oxide) is formed on its surface, which protects against oxidation and ensures its high anti-corrosion properties . Thin aluminum, such as foil or powder of this metal, burns instantly when heated to high temperatures and becomes aluminum oxide.

The metal is not particularly resistant to aggressive acids. For example, it can be dissolved in sulfuric or hydrochloric acids even if they are dilute, especially if they are heated. However, it does not dissolve in either dilute or concentrated and cold nitric acid, due to the oxide film. Aqueous solutions of alkalis have a certain effect on the metal - the oxide layer dissolves and salts are formed containing this metal as part of the anion - aluminates.

It is known that aluminum is the most common metal in nature, but , the Danish physicist H. Oersted was able to obtain it This metal is the third most abundant element in nature and is the leader among metals. The earth's crust contains 8.8% aluminum. It was found in the composition of micas, feldspars, clays and minerals.

Aluminum production and use

The production process is very energy-intensive and therefore the first large plant in our country was built and launched in the 20th century. The main raw material for the production of this metal is aluminum oxide. To obtain it, it is necessary to remove impurities from minerals containing aluminum or bauxite.

Next, natural or artificially produced cryolite is melted using an electrolytic method at a temperature just below 1000 ºС. Then they begin to gradually add aluminum oxide and related substances necessary to improve the quality of the metal. In the process, the oxide begins to decompose and aluminum is released.

The purity of the resulting metal is 99.7% or higher.

This element has found its application in food production as foil and cutlery; in construction, its alloys with other metals are used, in aviation, electrical engineering as a copper substitute for cables, as an alloying additive in metallurgy, aluminothermy and other industries.

What is the melting temperature of metals?

The melting temperature of metals is the value of the heating temperature of the metal at which the process of transition from the initial state to another begins, that is, the process opposite to crystallization (solidification), but inextricably linked with it.

So, to melt, the metal is heated from the outside to the melting temperature and continues to be heated to overcome the phase transition boundary. The bottom line is that the melting temperature indicator means the temperature at which the metal is in phase equilibrium, that is, between a liquid and a solid. In other words, it exists simultaneously in both states. And to melt it, you need to heat it above the boundary temperature so that the process goes in the right direction.

It is worth saying that only for pure compositions the melting temperature is constant. If the metal contains impurities, this will shift the phase transition boundary, and, accordingly, the melting temperature will be different. This is explained by the fact that the composition with impurities has a different crystal structure, in which the atoms interact with each other differently. Based on this principle, metals can be divided into:

• easy melting, such as mercury and gallium, for example (melting temperature up to 600°C)
• medium-melting ones are aluminum and copper (600-1600°C)
• refractory - molybdenum, tungsten (more than 1600°C).

Knowledge of the melting temperature indicator is necessary both in the production of alloys for the correct calculation of their parameters, and in the operation of products made from them, since this indicator determines the limitations of their use. A long time ago, for convenience, physicists compiled this data into one table. There are tables of melting temperatures for both metals and their alloys.

Melting point of aluminum

Melting is the process of processing metals, usually in special furnaces, to obtain an alloy of the desired quality in a liquid state. As mentioned above, aluminum is a medium-melting metal and melts when heated to 660ºC. In the manufacture of metal products, the melting temperature influences the choice of melting furnace or unit and, accordingly, used for casting refractory forms.

The indicated temperatures refer to the melting process of pure aluminum. Since in its pure form it is used less often, and the introduction of impurities into its composition changes the melting point. Aluminum alloys are made in order to change any of its properties, increase strength, for example, or heat resistance . The following are used as additives:

• zinc
• copper
• magnesium
• silicon
• manganese.

The addition of impurities entails a decrease in electrical conductivity, a deterioration or improvement in corrosion properties, and an increase in relative density.

Typically, adding other elements to a metal causes the melting point of the alloy to decrease, but not always. For example, adding copper in a volume of 5.7% leads to a decrease in the melting point to 548ºC. The resulting alloy is called duralumin; it is subjected to further thermal hardening. And aluminum-magnesium compositions melt at a temperature of 700 - 750ºС.

During the melting process strict control of the melt temperature is necessary , as well as the presence of gases in the composition, which are detected through technological tests or by vacuum extraction. At the final stage of production of aluminum alloys, they are modified.

Source: https://stanok.guru/cvetnye-metally-i-splavy/alyuminiy/udelnyy-ves-teploprovodnost-i-temperatura-plavleniya-alyuminiya.html

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

Properties of aluminum

The properties of aluminum, one of the metals belonging to group 13 according to the periodic table of chemical elements, are quite extensive. Main groups of properties: physical and chemical. This lightweight metal combines many physical characteristics regarding density, thermal conductivity, corrosion resistance and ductility.

The physical properties of aluminum depend, like many metals, on the degree of purity of the metal. Only the special purity of the material, closest to unity (99.996%), guarantees the highest performance in terms of physical properties. It is thanks to its high performance that the metal lends itself well to forging, stamping and other types of processing.

What’s noteworthy is that aluminum lends itself to almost any type of welding, be it contact, gas or another type. The silvery-white light metal is characterized by high thermal conductivity but has low density. Electrical conductivity is also quite high, so the material is constantly used in the cable industry. The list of physical properties of light metal is completed by remarkable anti-corrosion resistance and high ductility.

Material Density

The density of aluminum is the expression of the mass of the material in terms of content per unit volume. Density is also called the limit of the mass of a substance in relation to the volume occupied by this substance. It is by this formula that the density of a light metal of high purity is calculated.

Its indicator is 2.7 * 10 cubed kg/m3. Density is a property on which another characteristic of the material depends, namely strength. Since the density of light metal is quite low, its strength is correspondingly low.

Therefore, aluminum is not used as a design material.

To increase the strength of the metal, other elements with a higher density are added to it. Under the influence of denser additives, the strength of aluminum increases dramatically. Also, strength indicators can be increased by using mechanical or heat treatment.

As a result of a successful combination in alloys, aluminum acquires valuable structural qualities, expressed in good mechanical strength with a low material density.

Aluminum-based alloys in some industries successfully replace metals (alloys) such as copper or tin, zinc or lead.

Thermal conductivity

The thermal conductivity of aluminum is one of its physical properties. It, like many, depends on the purity of the structure of the material. That is, the closer to unity the purity of aluminum, the higher its thermal conductivity properties. Technical aluminum, the percentage of which is approximately 99.49, has a thermal conductivity (at 200 degrees Celsius) of 209 W/(m*K). If technical aluminum has a percentage of 99.70, then the value of its thermal conductivity reaches 222 W/(m*K).

At a time when the material is electrolytically refined and its purity is 99.9%, the thermal conductivity value already at 190 degrees Celsius rises to 343 W/(m*K). Unlike strength, which increases when aluminum is alloyed with other metals, thermal conductivity properties in this case decrease.

An example is the addition of Mn. Just two percent of such an additive can reduce the thermal conductivity of aluminum from a value of 209 W/(m*K) to a value equal to 126 W/(m*K).

It is also worth noting that the thermal conductivity properties of aluminum are so high that only copper and silver have an advantage over them.

The melting point of aluminum is a fairly significant indicator that is taken into account by any industry that works with this material.

The melting point is an unstable indicator; it largely depends on what materials are used for admixture with aluminum. The speed of processing of the material, that is, one might say, production capabilities, depends on the melting temperature.

Aluminum is most often processed in Russia, Australia, Canada and the USA. In these countries, a large share of the industry is involved in aluminum smelting.

Each country has its own smelting technologies, which over time, thanks to experiments with the addition of various materials, have made it possible to reduce the melting point of aluminum to the minimum possible.

The most accurate, standard indicator of the melting point of aluminum is 660.32 degrees Celsius. Due to such a large indicator, melting of the material can only be organized in special conditions and specially equipped rooms.

To carry out this process at home, the first thing you need is equipment. Typically a crucible muffle furnace is used for this.

Heat capacity

The heat capacity of aluminum, if we take the indicator of constant pressure and temperature 291, will be 581 cal/degree, mol. But the heat capacity of the material can change significantly if the temperature is low.

The high heat capacity index dictates the conditions regarding the use of sufficiently powerful heat sources. Sometimes he even uses the heating method. The height of the coefficient of linear expansion, as well as a small modulus of elasticity, can create significant welding deformations.

This circumstance dictates the conditions for using clamping devices with an increased level of reliability.

The resulting deformations in structures, which should be approached responsibly, are eliminated after welding.

It is worth noting that high values ​​of properties such as heat capacity and thermal conductivity, relative to aluminum itself, as well as its alloys, significantly influence which welding method should be chosen. Specific heat capacity of aluminum, measured in J/(kg*deg.

Celsius), is equal to the value of 920. If we take the specific heat capacity indicators, it should be noted that they change depending on the state of aggregation of the material.

Resistivity

The resistivity of aluminum is higher compared to the same value of copper. But the resistivity of copper can be significantly affected by a processing method such as annealing. This method has virtually no effect on aluminum. At the same time, the temperature coefficients of copper and aluminum are identical. Oxide insulation is often used in the cable industry.

The heat resistance of oxidized aluminum wire is 400 degrees Celsius. In general, the resistivity of the material in question exceeds that of copper by 1.65 times.

Aluminum wires are often subjected to oxide insulation. In order to apply this method to copper wire, it must be coated with at least a thin layer of aluminum.

Oxidized aluminum is used to make coils that can operate at high temperatures.

Chemical properties

The chemical properties of aluminum express its valency and the properties of interaction with surrounding spheres. The first thing worth noting is that aluminum has fairly high chemical activity. If we consider the range of metal stresses, this material will occupy a place between magnesium and zinc. Aluminum is characterized by rapid oxidation by oxygen taken from the air, resulting in a strong protective oxide film.

It is this film that is an obstacle to further oxidation of the material. Also, the oxide film protects aluminum products from interaction with other substances, contact with which can lead to destruction of the structure of the material. It is the protective film that plays the role of a factor that increases the anti-corrosion resistance of aluminum. If this oxide protection is violated, the material easily interacts with moisture even at normal temperatures.

Source: https://promplace.ru/vidy-metallov-i-klassifikaciya-staty/svoistva-aluminiya-1507.htm

Electrical and thermal conductivity of aluminum

• 1 Thermal conductivity of copper and aluminum table
• 2 Properties of aluminum: density, thermal conductivity, heat capacity Al
  • 2.1 Specific heat capacity of aluminum
  • 2.2 Thermophysical properties of aluminum alloys AMts, AMg, D16, AK, etc.
  • 2.3 Thermal conductivity of aluminum alloys
  • 2.4 Properties of aluminum alloys with silicon, copper, magnesium and zinc
  • 2.5 Thermal conductivity of aluminum alloys depending on temperature
  • 2.6 Thermal conductivity of aluminum alloy with lithium
  • 2.7 Density, thermal conductivity, heat capacity of aluminum alloys Amts, Amg1, Amg2, D1, D16
  • 2.8 Thermal conductivity, heat capacity and resistivity of alloy 1151T
  • 2.9 Temperature coefficients of linear expansion (CTE) of alloy 1151T
  • 2.10 Thermophysical properties of aluminum alloys of the Al-Cu-Mn system
  • 2.11 Thermophysical properties of aluminum alloys of the Al-Mg-Si system
  • 2.12 Specific heat capacity of high-strength aluminum alloys V93, alloy 1933, V95, alloy 1973, V96, etc.
  • 2.13 Thermal conductivity of high-strength aluminum alloys V93, alloy 1933, V95, alloy 1973, V96, etc.
• 3 Features of the composition, properties and characteristics of aluminum
• 4 Properties of aluminum

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: https://varimtutru.com/elektro-i-teploprovodnost-alyuminiya/

What is aluminum: history of discovery, physical properties and applications, thermal conductivity and density - Machine

Aluminum is a silvery-white, lightweight paramagnetic metal. First obtained by the Danish physicist Hans Oersted in 1825. In the periodic table of D.I. Mendeleev it has the number 13 and the symbol Al, the atomic mass is 26.98.

Aluminum production

To produce aluminum, bauxite is used - a rock that contains aluminum oxide hydrates. The world's reserves of bauxite are almost unlimited and are incommensurate with the dynamics of demand.

Bauxite is crushed, ground and dried. The resulting mass is first heated with steam and then treated with alkali - most of the aluminum oxide passes into the alkaline solution. After this, the solution is stirred for a long time.

At the electrolysis stage, alumina is exposed to an electric current of up to 400 kA. This allows the bond between the oxygen and aluminum atoms to be broken, leaving only liquid metal.

The aluminum is then cast into ingots or various elements are added to it to create aluminum alloys.

Aluminum alloys

The most common elements in aluminum alloys are copper, manganese, magnesium, zinc and silicon. Less common are alloys with titanium, beryllium, zirconium and lithium.

Aluminum alloys are conventionally divided into two groups: cast and wrought.

To make casting alloys, molten aluminum is poured into a mold that matches the configuration of the resulting product. These alloys often contain significant silicon impurities to improve castability.

Wrought alloys are first cast into ingots and then shaped into the desired shape.

This happens in several ways depending on the type of product:

1. By rolling, if necessary, to obtain sheets and foil.
2. By pressing, if you need to obtain profiles, pipes and rods.
3. Molding to obtain complex shapes of semi-finished products.
4. Forging, if you need to obtain complex shapes with increased mechanical properties.

Aluminum alloy grades

To mark aluminum alloys in accordance with GOST 4784-97, an alphanumeric system is used, in which:

• A - technical aluminum;
• D - duralumin;
• AK - aluminum alloy, malleable;
• AB - avial;
• B - high-strength aluminum alloy;
• AL - cast aluminum alloy;
• AMg - aluminum-magnesium alloy;
• AMts - aluminum-manganese alloy;
• SAP - sintered aluminum powders;
• SAS - sintered aluminum alloys.

After the first set of characters, the alloy grade number is indicated, and after the number is a letter that indicates its condition:

• M - alloy after annealing (soft);
• T - after hardening and natural aging;
• A - clad (a pure layer of aluminum is applied);
• N - hard-worked;
• P - semi-hardened.

Aluminum-magnesium alloys

These ductile alloys have good weldability, corrosion resistance and a high level of fatigue strength.

Aluminum-magnesium alloys contain up to 6% magnesium. The higher its content, the stronger the alloy. Each percent increase in magnesium concentration increases the tensile strength by approximately 30 MPa and the yield strength by approximately 20 MPa.

Under such conditions, the relative elongation decreases, but only slightly, remaining within 30–35%.

However, when the magnesium content exceeds 6%, the mechanical structure of the alloy in the cold-worked state becomes unstable, and corrosion resistance deteriorates.

To improve strength, chromium, manganese, titanium, silicon or vanadium are added to the alloys. Impurities of copper and iron, on the contrary, negatively affect alloys of this type - they reduce weldability and corrosion resistance.

Aluminum-manganese alloys

These are strong and ductile alloys that have a high level of corrosion resistance and good weldability.

To obtain a fine-grained structure, alloys of this type are alloyed with titanium, and manganese is added to maintain stability in the cold-worked state. The main impurities in Al-Mn alloys are iron and silicon.

Aluminum-copper-silicon alloys

Alloys of this type are also called alcusines. Due to their high technical properties, they are used in sleeve bearings, as well as in the manufacture of cylinder blocks. They have high surface hardness, so they are difficult to break in.

Aluminum-copper alloys

The mechanical properties of alloys of this type in a heat-strengthened state sometimes even exceed the mechanical properties of some low-carbon steels. Their main drawback is their low corrosion resistance, which is why these alloys are treated with surface protective coatings.

Aluminum-copper alloys are alloyed with manganese, silicon, iron and magnesium. The latter has the greatest influence on the properties of the alloy: alloying with magnesium significantly increases the yield strength and strength. Adding iron and nickel to the alloy increases its heat resistance, and silicon increases its ability to undergo artificial aging.

Aluminum-silicon alloys

Alloys of this type are otherwise called silumins. Some of them are modified with additions of sodium or lithium: the presence of literally 0.05% lithium or 0.1% sodium increases the silicon content in the eutectic alloy from 12% to 14%. The alloys are used for decorative casting, the manufacture of mechanism cases and elements of household appliances, since they have good casting properties.

Aluminum-zinc-magnesium alloys

Durable and well processed. A typical example of a high-strength alloy of this type is B95. This strength is explained by the high solubility of zinc and magnesium at a melting point of up to 70% and up to 17.4%, respectively. When cooled, the solubility of elements decreases noticeably.

The main disadvantage of these alloys - low corrosion resistance during mechanical stress - is corrected by alloying with copper.

Avial

Avial is a group of alloys of the aluminum-magnesium-silicon system with minor additions of other elements (Mn, Cr, Cu). The name is derived from the abbreviation of the phrase “aviation aluminum”.

Avial began to be used after the discovery by D. Hanson and M. Geiler of the effect of artificial aging and thermal hardening of this group of alloys due to the release of Mg2Si.

These alloys are characterized by high ductility and satisfactory corrosion resistance. Forged and stamped parts of complex shapes are made from aircraft. For example, spars of helicopter rotor blades. To improve corrosion resistance, the copper content is sometimes reduced to 0.1%.

The alloy is also actively used to replace stainless steel in mobile phone cases.

Physical properties

• Density - 2712 kg/m3.
• Melting point - from 658°C to 660°C.
• Specific heat of fusion - 390 kJ/kg.
• Boiling point - 2500 °C.
• The specific heat of evaporation is 10.53 MJ/kg.
• Specific heat capacity - 897 J/kg·K.
• Electrical conductivity - 37·106 S/m.
• Thermal conductivity - 203.5 W/(m K).

Chemical composition of aluminum alloys

Aluminum alloys
Brand	Mass fraction of elements, %	Density, kg/dm³
GOST	ISO209-1-89	Silicon (Si)	Iron (Fe)	Copper (Cu)	Manganese (Mn)	Magnesium (Mg)	Chromium (Cr)	Zinc (Zn)	Titanium (Ti)	Other	Aluminum no less
Every	Sum
AD000	A199.8 1080A	0,15	0,15	0,03	0,02	0,02	0,06	0,02	0,02	99,8	2,7
AD00 1010	A199.7 1070A	0,2	0,25	0,03	0,03	0,03	0,07	0,03	0,03	99,7	2,7
AD00E 1010E	EA199.7 1370	0,1	0,25	0,02	0,01	0,02	0,01	0,04	Boron:0.02 Vanadium+titanium:0.02	0,1	99,7	2,7

In the distant past, due to the high cost of aluminum, it was used to make jewelry. Thus, scales with aluminum and gold bowls were presented to D. I. Mendeleev in 1889.

When the cost of aluminum decreased, the fashion for jewelry made from this metal passed away. But even today it is used to make jewelry. In Japan, for example, aluminum is used to replace silver in the production of national jewelry.

Cutlery

Aluminum cutlery and cookware continue to be popular. In particular, aluminum flasks, pots and spoons are widely used in the army.

Glass making

Aluminum is widely used in glass making. High reflectivity and low cost of vacuum deposition are the main reasons for using aluminum in the manufacture of mirrors.

Food industry

Aluminum is registered as a food additive E173. It is used as a food coloring and also to preserve food from mold. E173 colors confectionery products in a silver color.

Military industry

Due to its light weight and low cost, aluminum is widely used in the manufacture of small arms - machine guns and pistols.

Rocketry

Aluminum and its compounds are used as rocket fuel in two-component rocket propellants and as a combustible component in solid rocket propellants.

Aluminum energy

In the aluminum energy industry, aluminum is used to produce hydrogen and thermal energy, as well as to generate electricity in air-aluminum electrochemical generators.

Source: https://regionvtormet.ru/svarka/chto-takoe-alyuminij-istoriya-otkrytiya-fizicheskie-svojstva-i-primenenie-teploprovodnost-i-plotnost.html

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

Thermal conductivity of aluminum alloys

01.10.2019

Thermal conductivity is the property of transferring energy from a heated area of ​​a material to a colder area. The indicator is taken into account in calculations in the manufacture of various alloys.

Information about the thermal conductivity index

The process of heat transfer in the body of any substance occurs between the atomic and molecular bonds of the material, in which the temperature regime is uneven. Any substance heats up gradually, transferring heat energy from area to area. This heat transfer depends on the state of the substance. Heat conductivity depends on: 1. The state of aggregation of the substance, 2. The heating rate. 3. Density indicator. 4.

Melting temperatures. The heat conductivity coefficient is the amount of heat passing through a unit area of ​​a material in a certain period of time when temperatures change. What does heat conductivity depend on? Aluminum has a crystal structure - a cube. At a temperature of 200C, specific gravity = 2.7 g/cm3. The melting temperature is from +657 to +660.2 0C.

If aluminum is of high purity, then the metal begins to melt at +1800 to 2060 0C. The specific heat capacity during the heating period increases, and the coefficients of expansion and thermal conductivity also increase. The thermal conductivity of aluminum, compared to other metals, is considered high. Aluminum reacts with oxygen to form an oxide film on the surface. The latter protects the metal from further oxidation.

Aluminum alloys have unique properties: 1. When aluminum melts, the hydrogen present in it dissolves, which leads to the formation of pores in the metal. If the composition contains impurities of calcium, potassium or sodium, it also leads to porosity. 2. The structure of the material becomes homogeneous upon cooling if the alloy contains additives of iron, vanadium, nickel or zirconium. 3.

Aluminum alloys remain inert to some chemical elements. The presence of substances such as sulfur and its derivatives precipitate, forming slag, and do not affect the change in structure and properties of the alloys. 4. Under the influence of nitrogen, phosphorus or carbon, the properties of the material do not change.

The strength of aluminum in its pure form is low, so casting technology is used extremely rarely for the production of finished products. As a rule, these are cast ingots, manufactured for further rolling and forging.

Products made from aluminum alloys are divided by type of technological cycle: 1. Foundry. Produce cast products. 2. Deformable. The shape is given under pressure (pressing, forging, stamping). Aluminum products used in construction are made from a high-strength alloy. List of standard indicators, taking into account which alloys are characterized: 1. Thermal conductivity. 2.

Transition from one state of aggregation to another. 3. The presence of alloying additives that affect product quality and durability (strength). Information on thermal conductivity is indicated in reference literature, but the main evaluation criteria will be: 1. Density. 2. Thermal conductivity. 3. Linear expansion (coefficient). 4. Temperature at which strength changes. 5.

Corrosion resistance. 6. Electrical resistivity. After the analysis, it is easy to establish the coefficient of dependence of thermal conductivity on the temperature of the metal.

Which aluminum alloys have greater thermal conductivity?

If aluminum products contain copper, zinc, magnesium or silicon, then the percentage of thermal conductivity in them increases noticeably compared to aluminum in its pure form.

Thermal conductivity table:

Heat conductivity increases with increasing temperature. Alloy AD1 has greater thermal conductivity. Used for the production of profiles, stampings, ingots and other similar products.

The highest thermal conductivity of aluminum alloys under normal conditions is observed in aluminum alloy AD1 - thermal conductivity at 20 0C is equal to 210 W/(m•deg).

The lowest thermal conductivity of aluminum alloys was recorded for casting alloys AK4, AL1, AL8.

Source: https://metromet.ru/novosti/tep-alyuminiy/

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.

Thermal conductivity of aluminum and brass

Thermal conductivity: Aluminum 180-200 W/m*K

Plain copper 300-320 W/m*K

Density: Ral=2700 kg/m3

Рmed=8940 kg/m3, where P is the density

Specific Heat Capacity: Aluminum - 880 J / kg*K

Copper - 385 J / kg*K

we see that: · the density of copper is approximately 3.31 times higher than that of aluminum · the thermal conductivity of copper is approximately 1.66-1.75 times higher than that of aluminum

· the heat capacity of a copper radiator is approximately 2.28 times less than that of an aluminum radiator, with equal mass.

Thus, if radiators are the same in size and shape, then one made of copper will be 3.31 times heavier, its heat capacity will be approximately 1.44 times greater than that of aluminum. Therefore, under the same load, the copper radiator will heat up 1.44 times less. With a larger temperature difference between the processor core and the radiator, heat transfer is more efficient, therefore, a copper radiator is better. But in practice, I replaced the copper radiator with an aluminum one and won.

Why? In this case, I replaced the small but heavy radiator from Thermaltake Volcano 10, with frequent thin fins, with a twice as large radiator from Titan D5TB/Cu35 with rather sparse and thick fins. The mass of the radiators is approximately equal, so the heat capacity of an aluminum radiator will be greater. Therefore, it will take longer to heat up. In addition, there is less resistance to air flow due to the larger width of the channels.

Consequently, more air passes through the aluminum radiator, and it (the air) picks up more heat. The heat balance is established at the lowest temperature level, since, firstly, per unit time more heat is released into the atmosphere due to the larger amount of passing air, and the heat exchange area of ​​​​both radiators is approximately equal.

And secondly, the radiator itself heats up more slowly due to its greater heat capacity, so it takes longer for an aluminum radiator to reach the same temperature as a copper radiator, which aggravates the first situation. In addition, it is possible that unventilated zones formed in the Thermaltake Volcano 10 radiator, in which warm air stagnated.

The main advantage of copper, high thermal conductivity, does not have a significant effect in this case, due to the weak air flow, as a result of which both aluminum and copper radiators manage to evenly distribute heat over the surface of their fins and, therefore, a unit area of ​​\u200b\u200bthe fins of both radiators gives off approximately the same amount of heat to the air.

Everything written here reflects my personal point of view and nothing more. I did not try to adhere to classical terminology and may have used incorrect definitions, for which I ask you not to judge me harshly.

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Constructive criticism is accepted here.

from here

Impurities contained in copper (and, naturally, interacting with it) are divided into three groups.

Forming solid solutions with copper

Such impurities include aluminum, antimony, nickel, iron, tin, zinc, etc. These additives significantly reduce electrical and thermal conductivity . The grades that are primarily used for the production of conductive elements include M0 and M1. If the copper alloy contains antimony, its hot pressure treatment becomes significantly more difficult.

Impurities that do not dissolve in copper

These include lead, bismuth, etc. Although they do not affect the electrical conductivity of the base metal, such impurities make it difficult to process by pressure.

Impurities that form brittle chemical compounds with copper

This group includes sulfur and oxygen, which reduces the electrical conductivity and strength of the base metal . The presence of sulfur in the copper alloy greatly facilitates its machinability by cutting.

INTRODUCTION

Spring alloys belong to a special group of mainly metallic materials, which, in addition to the high mechanical properties required for them, obtained either by cold plastic deformation or by precipitation hardening methods [1], also have a resistance to small plastic deformations, or an elastic limit. Continue reading →

Thermal diffusivity of metals

The table shows the values ​​of the thermal diffusivity coefficient of pure metals depending on temperature. The thermal diffusivity of metals is indicated in the temperature range from -250 to 1600°C in the dimension m 2 /s.

The following metals are considered: aluminum, cadmium, sodium, silver, potassium, nickel, lead, cobalt, beryllium, lithium, antimony, bismuth, magnesium, zinc, tungsten, tin, antimony, iron, platinum, gold, copper, rhodium, molybdenum, tantalum, iridium.

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Based on the thermal diffusivity values ​​in the table, we can distinguish metals with the highest and lowest values ​​of this property. A metal such as bismuth has the lowest thermal diffusivity The thermal diffusivity of pure silver is 158.3 m 2 /s at 100°C. This metal has the highest value of this characteristic.

It should be noted that as the temperature of a metal increases, its thermal diffusivity decreases, with the exception of platinum and cobalt.

Source: https://morflot.su/teploprovodnost-aljuminija-i-latuni/