Interview Short Question Answers on Heat Exchangers Q Which of the arrangement of heat exchangers (HEX) is better, (i) parallel flow,(ii) Counter flow. Explain the reasons. Counter flow HEX is better because of the following reasons: (i) Average temperature difference is more. (ii) There is less variation in temperature difference all along the length of the […]
Interview Short Question Answers on Heat Exchangers Q. Explain multi-pass heat exchangers? When are these used? These heat exchangers are of three types. 1. Firstly multi-pass shell heat exchanger In these, fluid passes through more than one shell and the other fluid passes through a single tube pass, it is multi-shell pass heat exchanger. 2. […]
LMTD – Counter Flow Heat Exchanger DERIVATION OF LMTD FOR COUNTER FLOW HEAT EXCHANGER Assumptions used 1. U is constant all along the HEX. 2. Steady flow conditions. 3. Specific heats of hot and cold fluids are constant 4. Flow rates of hot and cold fluids are constant. 5.There is no heat loss to the […]
ANALYSIS OF HEAT EXCHANGER (a) LMTD METHOD (i) when all the four temperatures are known. q.=U A LMTD (ii) When fouling is to be considered q.=Udirty A LMTD where f=1/Udirty –1/Uclean Values of f and Uclean are given in standard tables. (i) ANALYSIS OF MULTIPASS HEAT EXCHANGERS For multipass shell/multipass tube / multipass both in shell and […]
LMTD – Parallel Flow Heat Exchanger DERIVATION FOR LOGARITHMIC MEAN TEMPERATURE DIFFERENCE ‘ LMTD ‘ FOR A PARALLEL FLOW HEAT EX-CHANGER It is an equivalent constant temperature difference in place of variable temperature difference in actual. It will give constant average rate of heat transfer. ASSUMPTIONS USED IN DERIVATION OF LMTD Assumptions used 1. U […]
Heat Exchangers–2 DEFINITION OF OVERALL HEAT TRANSFER COEFFICIENT ‘U’ Overall heat transfer coefficient for conduction and convection taking place simultaneously.Its units are W/m2 K. 1/UA =1/hiAi+fi + ln (r2/r1)/2πkL +1/hoAo + fo Where fi and fo are fouling resistances on the inner and outer surfaces. CALCULATION OF U (i) On the basis of Ai (ii) On the basis of Ao […]
Heat Exchangers Definition of heat exchanger, definition of compact HEX, Types of HEX, Practical applications of HEX, Definition of U, Resistance of a HEX, Fouling in a HEX, How to account for Fouling, Methods of analysis for HEX, LMTD method, NTU method, Design equation for a Simple HEX, Design equation for a multi-pass HEX, Factor […]