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.

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.

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.

Thermal conductivity coefficient of metals at temperature, °C

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.

Characteristics of thermal conductivity of materials

The concept of thermal conductivity of materials is characterized by the ability to transfer thermal energy within a certain object from heated parts to cold ones. The process is carried out by atoms, molecules, electrons and occurs in any body with an uneven temperature distribution.

From the standpoint of kinetic physics, this process occurs as a result of the interaction of particles of molecules in hotter areas within the sample with other elements characterized by a lower temperature. The mechanism and rate of heat transfer depends on the state of aggregation of the substance.

The thermal conductivity category involves determining the heating rate of a material sample and the movement of a temperature wave in a certain direction. The indicator depends on physical parameters:

• density;
• temperature of phase transition to liquid state
• speed of sound propagation (for dielectrics).

Thermal conductivity of brass and bronze

The table shows the thermal conductivity values ​​of brass, bronze, as well as copper-nickel alloys (constantan, copel, manganin, etc.) depending on temperature - in the range from 4 to 1273 K.

The thermal conductivity of brass, bronze and other copper-based alloys increases when heated. According to the table, L96 brass has the highest thermal conductivity of the alloys considered at room temperature. Its thermal conductivity at a temperature of 300 K (27°C) is 244 W/(m deg).

Also copper alloys with high thermal conductivity include: brass LS59-1, tombac L96 and L90, tin tombac LTO90-1, rolled tombac RT-90. In addition, the thermal conductivity of brass is generally higher than that of bronze. It should be noted that bronzes with high thermal conductivity include: phosphorus, chromium and beryllium bronzes, as well as BrA5 bronze.

The copper alloy with the lowest thermal conductivity is manganese bronze - its thermal conductivity coefficient at a temperature of 27°C is 9.6 W/(m deg).

The thermal conductivity of copper alloys is always lower than the thermal conductivity of pure copper, all other things being equal. In addition, the thermal conductivity of copper-nickel alloys is particularly low. The most thermally conductive of them at room temperature is cupronickel MNZhMts 30-0.8-1 with a thermal conductivity of 30 W/(m deg).

Table of thermal conductivity of brass, bronze and copper-nickel alloysAlloyTemperature, KThermal conductivity, W/(m deg)Copper-nickel alloysBrassBronze

Metal characteristics

The melting temperature of brass, depending on its composition, ranges from 880-950°C. Thus, with an increase in zinc impurity in the material under consideration, the melting point will decrease. It is worth noting that brass, due to its properties, can be welded well.

Brass is processed by resistance welding and can be rolled. The uncoated surfaces of the metal in question turn black when in contact with air. Brass has a yellow color and is highly polished. The non-ferrous metal in question can be melted within certain temperature limits, depending on the impurities in the composition of the material.

Metal Specifications

• Melting point – 880-950°C;
• Material density – 8,300-8,700 kg/cubic meter;
• Specific heat capacity - 0.377 kJ kg−1 K−1 at 20°C;
• Electrical resistivity - (0.07-0.08)·10−6 Ohm·m.

It is useful to know that bismuth, as well as lead, have a detrimental effect on brass, since they reduce the ability to deform when hot.

What are the advantages of non-ferrous metal, grade and application?

Brass belongs to the category of non-ferrous metals. It is useful to know about the chemical and physical benefits that brass has.

Advantages

• Corrosion resistance;
• High degree of fluidity;
• Excellent anti-friction properties;
• Slight tendency to segregation;
• Excellent technological properties;
• Excellent mechanical properties.

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The list presented above does not limit the advantages and beneficial properties of this metal. You should not ignore the most popular brands of material, as well as application.

Melting point of brass

The melting point of brass of the considered brands varies in the range from 865 to 1055 °C. The most fusible is manganese brass LMts58-2 with a melting point of 865°C. Low-melting brasses also include: L59, L62, LAN59-3-2, LKS65-1.5-3 and others.

L96 brass has the highest melting point (1055°C). Among the refractory brasses, according to the table, we can also distinguish: brass L90, LA85-0.5, tin tombac LTO90-1.

Melting point of brassBrass, °СBrass, °С

Melting point of bronze

The melting point of bronze ranges from 854 to 1135°C. Bronze AZHN11-6-6 has the highest melting point - it melts at a temperature of 1408 K (1135°C). The melting point of this bronze is even higher than the melting point of copper, which is 1084.6°C.

Bronzes with a low melting point include: BrOTs8-4, BrB2, BrMTsS8-20, BrSN60-2.5 and the like.

Melting temperature of bronze Bronzet, °С Bronzet, °С

Note: The melting and boiling points of other common metals are given in this table.

Thermal conductivity of non-ferrous metals and technical alloys

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.

Non-ferrous metals and alloys: nickel Ni, monel, nichrome; nickel alloys (according to GOST 492-58): cupronickel NM81, NM70, constantan NMMts 58.5-1.54, copel NM 56.5, monel NMZhMts and K-monel, alumel, chromel, manganin NMMts 85-12, invar; magnesium alloys (according to GOST 2856-68), electron, platinum-rhodium; soft solders (according to GOST 1499-70): pure tin, lead, POS-90, POS-40, POS-30, Rose alloy, Wood alloy.

The table shows that magnesium alloys and nickel have high thermal conductivity (at room temperature). Low thermal conductivity is characteristic of nichrome, invar and Wood's alloy.

Thermal conductivity coefficients of alloys

The table shows the thermal conductivity values ​​of alloys in the temperature range from 20 to 200ºС. Alloys: aluminum bronze, bronze, phosphor bronze, invar, constantan, manganin, magnesium alloys, copper alloys, Rose alloy, Wood's alloy, nickel alloys, nickel silver, platinum-iridium, electron alloy, platinum-rhodium.

Thermal conductivity coefficient of other materials

MaterialHumidity mass fraction % W/(m•K)

Thermal conductivity coefficient of asbestos and foam concrete at different temperatures

(ρa=576kg/m3, ρп=400kg/m3,λ, W/(m•K))

Material-18oС0oС50oС100oС150oС

Thermal conductivity coefficient of liquid W/(m•K) at different temperatures

Material0oС50oС100oС

Specific resistance and temperature coefficient of expansion (CTE) of metal wire (at 18ºС)

The table shows the values ​​of electrical resistivity and CTE of metal wire made of various metals and alloys. Wire material: aluminum, tungsten, iron, gold, brass, manganin, copper, nickel, constantan, nichrome, tin, platinum, lead, silver, zinc. As can be seen from the table, nichrome wire has a high electrical resistivity and is successfully used as incandescent heating coils for many household and industrial devices.

Specific heat capacity of multicomponent special alloys

The specific (mass) heat capacity of multicomponent special alloys is given in the table at temperatures from 0 to 1300ºС.

Heat capacity dimension cal/(g deg). Heat capacity of special alloys: alumel, bell metal, Wood's alloy, Invar, Lipowitz alloy, Manganin, Monel, Rose alloy, phosphorus bronze, chromel, Na-K alloy, Pb - Bi alloy, Pb - Bi - Sn, Zn - Sn - Ni - Fe - Mn.

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.

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.

The high thermal conductivity of copper, along with other remarkable properties, has given this metal a significant place in the history of the development of human civilization. Products made from copper and its alloys are used in almost all areas of our lives.

Which conducts heat better: aluminum or copper?

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.

Differences between copper and aluminum

The main concerns regarding winding material selection reflect five characteristic differences between copper and aluminum:

Table: Five characteristic differences between copper and aluminum

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.

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.

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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.

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.

Connectivity

Oxides, chlorides, sulfides or base metals that are more conductive on copper than on aluminum. This fact makes cleaning and protecting aluminum connectors more important. Some consider copper and aluminum compounds to be incompatible. Also questionable is the mating of connections between the aluminum of the transformers and the copper connection wire.

Expansion coefficient

When temperature changes, aluminum expands almost a third more than copper. This expansion, along with the ductile nature of aluminum, causes some problems for improperly installed bolted connections.

To avoid loosening of the connection, it must be spring-loaded. By using either cup washers or pressure washers, the necessary elasticity during articulation can be achieved without compressing the aluminum.

When using proper fittings, aluminum connections can be equal in quality to copper ones.

Thermal conductivity

Some argue that since the thermal conductivity of copper is higher than aluminum, this has the effect of reducing the hot spot temperature of the transformer winding.

This is only true when the copper and aluminum winding conductors are of the same size, geometry and design.

Therefore, for any power transformer of a given size, the thermal conductivity characteristics of aluminum can be very similar to copper.