Efficiency of a Heat Exchanger

Surely, as long as you state your definition and any assumptions it's fine?

(That is assuming the people marking the asignment actually read it rather than just skimming for the 'right' answer)

A chap I work with is doing a correspondence course in electronics...I've helped him out a bit...you wouldn't believe the stupidity of some questions, the missprints, and the poor marking of perfectly correct answers. (He sent one module back for re-marking and it went from a D to an A!)

www.tranter.com send an email to engineering and ask for help. they have all the software.

As far as I remember (and could find with 10 minutes searching on the web) you should take the temperature difference of the process fluid and divide by the difference in the coolant in temp and the process fliud out temp.

Efficiency = (Tpin-Tpout)/(Tpout-Tcin)

Tpin = process fluid temp in

Tpout = process fluid temp out

Tcin = coolant temp in

Here's one online resource:

http://www.engineeringtoolbox.com/heat-recovery-efficiency-d_201.html

The thin-thout/thin-tcin gives u the effectiveness of the HE or u can call it efficiency probably. But the actual def. of effectiveness is as follows

it is the ratio of heat transfer in actual HE to the heat transfer in a infinite length HE.

due consideration if given to the abv def. it will b understood that at length = infinite, the exit temp of both the fluids will b same in case of parallel flo HE. and there fore max heat transfer. and the same is tru with the counter flo as well.

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!!!!!! B a permutation of good and combination of bad !!!!!

I dont think that effectiveness and efficiency are the same. By definition efficiency is the ratio of the useful energy delivered by a dynamic system to the energy supplied to it (looked it up in merriam webster).

so efficiency concerns with production cost (as in energy, time and money) and effectiveness is how close a HE is capable of reaching the maximum heat transfer (i.e. heat transfer in an infinite length HE).

effectiveness is given by the equation:

E= Qactual/Qmax = mhCph(Thin-Tho)/(mCp)_min(Thi-Tci)

so it doesn't always equal to thin-thout/thin-tcin. depends on the type of fluid and the mass transfer rate. (mCp)_min is the smaller of cold and hot fluid.

From what i know, the quality of a HE is characterized by its effectiveness, and the term efficiency is never used in HE (at least it's not suppose to). Efficiency is used in pumps, boilers, turbines and compressors because there is energy supplied to run such devices whereas in HE there is no energy supplied.

I hope it helps...

That is basically the principle. But don't forget the flow rates and the specific heats of the two fluids. If it is for a refrigerator or a condenser, you will need to include latent heat as well.

If you want to be safe, you should also include the limited conduction between the fluids in the heat exchanger (due to the pipes and the fluids themselves). Depending on the level of the diploma, you can probably get away with some pretty basic assumptions here.

Fyz