Page 149 - Mechanical Engineer's Data Handbook

138 MECHANICAL ENGINEER'S DATA HANDBOOK

2 c

Cold fluid
ab
4
Heat transferred q= UAB,
1
Overall coefficient u =
1
-+- 1 3.15.2 Multi-pass and mixed-flo w heat
ha hll exchangers
Heat-exchanger effectiveness E =- In some cases the values for Om for parallel- and
lta- ltb counter-flow types may be used for these, with reason-
Note: if one of the fluids is a wet vapour or a boiling able accuracy. Otherwise, correction factors must be
liquid, the temperature is constant and ,t = ,t. used.

Counter Jlow

The temperature range possible is greater than for the
parallel-flow type. The same formulae apply.

Multi-pass-type heat exchanger

Cross-Jlo w Mixed-flow-type heat exchanger

Instead of using 8, as above, 0°K is used, where K is a
factor obtained from tables. 3.15.3 Steam condenser
q= UAKO,
The steam condenser is a particular type of heat
If one fluid is a wet vapour (constant temperature), exchanger in which one fluid is usually cooling water
Om is the same as for parallel-flow and counter-flow and the other wet steam which condenses on the tubes
types. carrying the cooling water. It is assumed that the steam
If 0, and 8, are nearly the same, the arithmetic mean temperature is constant throughout (Le. at the satura-
temperature difference is used: tion temperature). Formulae for cooling-water flow