Difference Between Heat Transfer And Thermodynamics

1. introduction :

Heat transfer:

Heat transfer is the science that attempt to estimate the energy transfer that may take place between material bodies as a result of a temperature difference. Thermodynamics explains that this energy transfer is defined as heat.

The science of heat transfer attempt to not only to explain how heat energy may be transferred, but also to estimate the rate at which the exchange will take place under certain specified conditions.

The fact that a heat-transfer rate is the preferred objective of an analysis points out the difference between heat transfers and thermodynamics.

Thermodynamics deals with systems in equilibrium; it may be used to estimate the amount of energy required to change a system from one equilibrium

In some cases, theories are available for the prediction of thermal conductivities in liquids and solids, but in general, many open questions and concepts still need clarification where liquids and solids are concerned.

The mechanism of thermal conduction in a gas is a simple one.We identify the kinetic energy of a molecule with its temperature; thus, in a high-temperature region, the molecules have higher velocities than in some lower-temperature region. The molecules are in continuous random motion, colliding with one another and exchanging energy and momentum.

The molecules have this random motion whether or not a temperature gradient exists in the gas. If a molecule moves from a high-temperature region to a region of lower temperature, it transports kinetic energy to the lower-temperature part of the system and gives up this energy through collisions with lower-energy molecules.

Table 1-1 lists typical values of the thermal conductivities for several materials to indicate the relative orders of magnitude to be expected in practice. More complete tabular information is given in Appendix A. In general, the thermal conductivity is strongly