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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM

Category:	Heat Transfer Technology
Question:	What's the best way to operate/control a double pipe heat exchanger to avoid the vaporization of the cooling medium for high temperature duties?
Keywords:	v1i1,double,pipe,heat,exchanger,water,hammer,parallel,countercurrent,flow,control
Answer:	BACKGROUNDWhile cooling a very hot viscous product, the water flow rate is being controlled by the process side outlet temperature. The water flow rate is being reduced to a rate at which it forms an annulus, vaporizes, and cause hammer in the equipment. ANSWERThis is a common scenario when a double-pipe exchanger is operated in counter-current flow. It become difficult to control and the utility side can vaporize causing problems as noted.By putting the fluids in parallel configuration, you create a situation where you can throttle the water outlet in accordance with the desired process fluid outlet temperature in an accurate and controlled manner. You can do this manually or automatically with a temperature transmitter-temp controller-water control valve. Depending on the process outlet temperature, you may have to maintain a pressure in the annulus that corresponds to the water outlet temperature. If your water has dissolved solids, this may not work due to solids precipitation and eventual plugging in the annulus. In that case, use another cooling fluid in a closed loop with indirect cooling.Source: CERP Message Board
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