Category Archives for Mechanisms of Heat Transfer

Approximate Overall Heat Transfer Coefficient

The calculation of overall heat transfer coefficient U using the equations previously presented can be rather tedious. Heat transfer specialists have computer programs to calculate this value. There are some quick approximation techniques. Table 2-8 comes from the Gas Processors … Continue reading

09. September 2009 by Jack
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Outside Film Coefficient (Shell-and-Tube Exchangers)

For shell-and-tube heat exchangers with shell-side baffles, the shellside fluid flow is perpendicular to the tubes. In this arrangement, the outside film coefficient can be calculated from the following equation:

09. September 2009 by Jack
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Outside Film Coefficient (in a Liquid Bath)

The outside film coefficient for a process coil in a liquid bath heater is the result of natural or free convection. Temperature variations in the fluid cause density variations. These density variations in turn cause the fluid to circulate, which … Continue reading

09. September 2009 by Jack
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Inside Film Coefficient

The inside film coefficient represents the resistance to heat flow caused by the change in flow regime from turbulent flow in the center of the tube to laminar flow at the tube surface. The inside film coefficient can be calculated … Continue reading

09. September 2009 by Jack
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Overall Heat Transfer Coefficient

The overall heat transfer coefficient is a combination of the internal film coefficient, the tube wall thermal conductivity and thickness, the external film coefficient, and fouling factors. That is, in order for the energy to be transferred through the wall … Continue reading

09. September 2009 by Jack
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Overall Temperature Difference

The temperature difference may not remain constant throughout the flow path. Plots of temperature vs. pipe length for a system of two concentric pipes in which the annular fluid is cooled and the pipe fluid heated are shown in Figures … Continue reading

08. September 2009 by Jack
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Multiple Transfer Mechanisms

Most heat transfer processes used in production facilities involve combinations of conduction and convection transfer processes. For example, in heat exchangers the transfer of heat energy from the hot fluid to the cold fluid involves three steps. First, the heat … Continue reading

08. September 2009 by Jack
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Radiation

The transfer of heat from a source to a receiver by radiant energy is radiation. The sun transfers its energy to the earth by radiation. A fire in a fireplace is another example of radiation. The fire in the fireplace … Continue reading

08. September 2009 by Jack
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Convection

The transfer of heat within a fluid as the result of mixing of the warmer and cooler portions of the fluid is convection. For example, air in contact with the hot plates of a radiator in a room rises and … Continue reading

08. September 2009 by Jack
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Conduction

The transfer of heat from one molecule to an adjacent molecule while the particles remain in fixed positions relative to each other is conduction. For example, if a piece of pipe has a hot fluid on the inside and a … Continue reading

08. September 2009 by Jack
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