Fouling Factor. Variable Coefficient of Heat Transfer. Closure

Note that the substantially lower velocity assumed for the cold air does not yield a comparably low Reynolds number. Neglecting the conductive resistance of the tube walls, we have 

The present example shows how to go about determining the size of a heat exchanger. No further attempt will be made here to refine the foregoing calculations. Clearly, like any problem of engineering design, this problem requires a number of trials until the assumed and found values of unknowns coincide. For example, we implicitly assumed atmospheric flow for both fluids. Otherwise the densities should be adjusted accordingly. Also, to determine the size of pumps, we need to know the pressure drop in the hot and cold fluids. The efficiency of our heat exchanger is reasonably low. It can be improved at the expense of increased heat transfer area, which in turn increases the pressure drop and the size of the pumps. 

FOULING FACTOR. VARIABLE COEFFICIENT OF HEAT TRANSFER. 

In Chapter 6 we have learned that heat transfer coefficient varies with the distance from the entrance of a pipe. However, so far in this chapter we have assumed a uniform coefficient throughout the exchanger. This assumption coupled with mean fluid properties usually gives satisfactory answers. Yet in situations involving chain polymers 

In this chapter we studied the most commonly encountered heat exchangers, sometimes called recuperators. Two other types of heat exchangers, the regenerator and cooling tower, are also utilized, although much less frequently. In regenerators, the hot fluid and cold fluid successively occupy the same space, and the exchange of heat is 

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Sec. 7.5 Fouling Factor. Variable Coefficient of Heat Transfer. Closure O 385... 

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