For the very basic, please keep in your mind that the RATE PROCESS will always in proportional to TOTAL DRIVING FORCE divided by TOTAL RESISTANCE. In case of heat transfer, the driving force is differential temperature (dT). The resistances may caused by film fluid at tube (R tube) or at shell (R shell), the material of the tube(Rmetal), and fouling (Rf).
Additional required surface area due to fouling will proportional with Uc x Rf. So please keep in your mind that this factor will have significant impact in case of high Uc. Be careful with the unit of Rf.
The area of heat exchanger shall sufficient to deliver certain duty. You know, the parameter to achieve required area is very easy; A =Q/ (U x delta T). But, what we need to know is how to design it not only with sufficiently area but also in effective cost, also without problem in operation.
An Effective design means that the exchanger has maximum driving force ( max delt T) and minimum resistance (=maximum Uc), has sufficient area and operates well
Maximum driving force can be achieved by maximizing the temperature difference (Delta T = F. LMTD). F value is factor for non idealities of flow arrangement. You should design the heat exchanger with arrangement has F > 0.8 .
Minimum resistance could be achieved by maximizing the heat transfer coefficient. Unfortunately, the heat transfer will depend on many variables. The equation of heat transfer coefficient involves many complex parameters. But, in easy word, to maximize the heat transfer, we need to maximize the cross flows though the tubes bundle. The principle of Bell Delaware Method is give correction factor of heat transfer value for non-idealities of cross flow due to some ‘leakage’ stream.
The coefficient heat transfer will decrease due to some leakage stream (Baffle – to Shell, Tube – to Baffle, By pass stream). The best flow stream is B stream. That is why, in designing STHE we should minimize the leakage stream and maximize B stream.
Hmm,,I think that all I can share to you by today.. Btw, how are you today my friend? Are you Ok there? I hope you have a great day wherever you are , and today will give us the best of everything for our future,
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