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Heat is the thermal energy transit from one
system to another. The thermal energy can originate from any kind of energy
according to the first law of thermodynamics. Transfer of heat is due to unique
property of matter, temperature, and is governed by second law of
thermodynamics, which dictates that free flow of heat is possible only from a
body of higher temperature to that at a lower temperature.
All heat transfer processes, therefore, involve the transfer of energy and obey
the first as well as the second law of thermodynamics. The energy in transit
cannot be measured or observed directly, but the effects it produces can be
observed and measured. From our viewpoint, the determination of the rate of heat
transfer needs special consideration.
The transport of heat energy from one region to another occurs by any (or a
combination) of similar methods. In literature such three methods of heat
transmission are recognized by the terms conduction, convection and radiation
respectively.
If the flow of heat is a result of transfer of internal energy from one molecule
to other, the process is called conduction. Through solids, this is the only
possible mode of heat transmission. In liquid and gases, however, the molecules
are no longer confined to a certain point but constantly change their positions
even if the substance is at rest. The heat energy is transported along with the
motion of these molecules from one region to another. This process is called
convection. All solid bodies as well as liquids and gases have a tendency of
radiating thermal energy in the form of electromagnetic waves and of absorbing
similar energy emerging from the neighboring bodies. This type of heat transport
is known as thermal radiation.
In industrial processes, heat transfer may occur due to one or due to a
combination of more than one of these three modes of transport.
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Introduction |
Combined heat transfer process |
Heat transfer in cooling tower |
Variables affecting performance of CT heat transfer |
Heat transfer within
cooling system (heat exchanger) |
Types of heat exchanger |
Basic design
procedure and theory |
Designing a test heat exchanger |
Log Mean Temperature
difference | L.M.T.D. Correction factors |
Overall heat transfer coefficient |
Elaborated method for calculating U values |
Effect of scale formation |
Condensation of steam |
Condenser, where the hot fluid temperature varies |
Significance of pressure |
Significance of flow rate |
Methods of checking steam
condenser performance |
Common conversion factors
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