I usually use those two methods and compare which value is satisfied (I use the highest one). There are two approach to calculate pressure drop in shell and tube heat exchanger: Kern Method and Bell Method. Check if calculated pressure drop meets requirement. Calculate pressure drop at shell side and tube side.If you feel satisfied with the results, for example the difference between U guess and U calculated is less than 10%, then follow next step. Be careful to check several data that is provided from nomographs ( we will use many nomographs in design of shell and tube heat exchanger). If that happens, revise U guess and follow the whole step over. In the beginning of design, I think we will get big difference between U guess and U calculated. Check if U guess in step 3 is the same as U calculated in step 8.If this data is not available, we need to estimate. Sometimes fouling coefficients are defined by user/contractor. In addition of shell side and tube side heat transfer coefficient, you will also need fouling coefficient at shell side and tube side and also thermal conductivity of tube material to calculate overall heat transfer coefficient. Calculate overall heat transfer coefficient.As for tube side, heat transfer coefficient is a function of L/di, Reynold number, and Prandtl number. For shell side, heat transfer coefficient is a function of baffle cut, tube arrangement, Reynold number, and Prandtl number. Calculate individual heat transfer coefficient (shell side and tube side).I will explain this step in separate section Although this step only contains three words, the actual step is so many. By using equation A = Q/(U x corrected delta T m), you will get estimated heat transfer area. We will get correction factor (F t) from nomograph. We have to calculate corrected delta T m which is a function of temperature ratios (R, S) and configuration of shell and tube heat exchanger (number of tube pass, number of shell pass). Calculate mean temperature difference (delta T m). Actually delta T m itself is not sufficient.The graph is a function of process fluid heat transfer coefficient and service fluid heat transfer coefficient. There is particular graph to estimate overall heat transfer coefficient.
#HEAT EXCHANGER CALCULATION WORD TRIAL#
Select trial value of overall heat transfer coefficient (U guess).So the calculated duty shall be multiplied by 110%. Sometimes, in sizing we have to add contingency, for example 10%. If you have heat capacity properties in inlet side and outlet side, I recommend to use average value. I usually calculate for both shell side and tube side just to ensure that the duty is similar. Define the duty (Q) from mass flow rate, inlet temperature, outlet temperature, and heat capacity.This figure shows you general step-by-step method of design of shell and tube heat exchanger.