The term specific heat refers to the total amount of heat energy that is needed by one unit of any substance to increase its temperature by 1°C. On the other hand, thermal conductivity is the ability of a given material to transfer or conduct heat energy through it.
Specific Heat vs Thermal Conductivity
The main difference between specific heat and thermal conductivity is that specific heat refers to the amount of heat energy a substance (1 g or 1 kg typically) requires in order to raise its temperature by 1°C, whereas thermal conductivity is a measure of the rate at which heat energy passes through a given material.
Specific heat is generally measured in calories or joules per gram per degree Celsius. Occasionally, the ratio of specific heat capacities of a substance at a particular temperature to those of a reference substance at a reference temperature is also termed specific heat. The formula to calculate specific heat is:
c = ΔQmΔT
where
c refers to specific heat of a substance
ΔQ refers to the heat gained or lost by the substance,
m refers to the mass of the substance, and
ΔT refers to the change in temperature of the substance.
Thermal conductivity is one of the three processes of heat transfer—convection, conduction, and radiation. Its unit is Watts per meter Kelvin. Thermal conductivity depends on some factors such as temperature, moisture content, and density of a material.
K = (QL)/(AΔT)
where
K refers to the thermal conductivity (W/m.K),
Q refers to the heat amount transferred across a material (Joules/second or Watts),
L refers to the distance between two isothermal planes,
A refers to the surface area (square meters), and
ΔT refers to the temperature difference (Kelvin).
Comparison Table Between Specific Heat and Thermal Conductivity
| Parameters of Comparison | Specific Heat | Thermal Conductivity |
| Definition | Specific heat refers to the total amount of heat energy that is needed by one unit of any substance to increase its temperature by 1°C. | Thermal conductivity refers to the given material’s ability to transfer heat energy across it. |
| Symbol | Specific heat is usually denoted as cp or s. | Thermal conductivity is denoted by K. |
| Units | Specific heat is measured usually in calories or joules per gram per degree Celsius or Kelvin (J/(kg K) or J/(kg °C)). | The unit for thermal conductivity is watts per metre-kelvin (W/(m⋅K)). |
| Formula | c = ΔQmΔT | K = (QL)/(AΔT) |
| Influencing factors | Specific heat depends on the type and the phase of a substance. | Thermal conductivity primarily depends on the temperature and the heat transfer direction. |
| Experimental values for some compounds | The specific heat of water is 4,186 joules per kilogram per degree Celsius whereas that of wood is 1,700 joules per kilogram per degree Celsius. | The thermal conductivity of water at 0°C is 0.5610 W/(m K) whereas that of wood is 0.12–0.04 W/(m k). |
| Applications | Substances that have low specific heat capacities are used in cookware like kettles and frying pans. | High thermal conductivity materials are usually used in heat sink applications, whereas low thermal conductivity materials are used as thermal insulators. |
What is Specific Heat?
Specific heat is also known as the massic heat capacity. Itmay also refer to the ratio of specific heat capacities of a substance at any given temperature to those of a reference substance at a reference temperature. It has been demonstrated that specific heats of substances allow calculation of the atomic weights of compounds. Specific heat values are always dependent on the phase and properties of a substance and they are measured empirically and available for reference.
Substances that have a low specific heat capacity are used in cookware like kettles, pots, frying pans, and so on; this is due to the fact that when a small amount of heat is applied, these substances will get heated quickly. Specific heat is used in the construction of handles (cooker and kettle handles), insulators, and oven covers also; because only a small temperature change is observed even after exposure to a high amount of heat.
What is Thermal Conductivity?
Thermal conductivity occurs by molecular agitation within a given substance. That is, heat energy is transported due to random molecular motion. Materials such as aluminum, copper, and silver have high thermal conductivities and are therefore good thermal conductors. Materials such as wood, alumina, polyurethane, and polystyrene have low thermal conductivities. Such materials are thermal insulators.
The thermal conductivity of a substance varies when the substance changes from one phase to another. For example, the thermal conductivity of ice changes when it melts into water.
Main Differences Between Specific Heat and Thermal Conductivity
- Specific heat refers to the heat retained in a system, whereas thermal conductivity refers to the heat transferred within a system or between different systems.
- Thermal conductivity is generally expressed by the symbol ‘k’ but it can also be denoted by ‘λ’ and ‘κ’. Specific heat is denoted as c or s.
- Specific heat depends on the type and phase of a material under study whereas thermal conductivity depends on the temperature, moisture content, and density of a material.
- Specific heat is measured using the mass, the change in temperature, and the heat gained or lost by a substance. Thermal conductivity is measured using the difference in temperature, amount of heat transferred through the material, the distance between the planes, and surface area.
- Specific heat is the ability of a unit of a compound to hold a particular amount of heat energy. Thermal conductivity is the potential of a substance to transfer heat energy.
Conclusion
The specific heat concept is used in the manufacturing of utensils used for cooking. Substances having low specific heats are used for this purpose. Thermal conductivity is used to find out insulator materials and materials used for heat sink applications. Metals that have high thermal conductivity, for example, copper, show high electrical conductivity too. Transfer of heat occurs at a higher rate across high thermal conductivity materials compared to materials of low thermal conductivity.
References
- https://journals.aps.org/prb/abstract/10.1103/PhysRevB.4.2029
- https://aip.scitation.org/doi/abs/10.1063/1.3253100