Heat Exchangers The rate of heat transfer in a heat exchanger is Q Uo = AFDT lm, where A = any convenient reference area (m2) F = heat exchanger configuration correction factor (F = 1 if temperature change of one fluid is negligible) U = overall heat transfer coefficient based on area A and the log mean temperature difference [W/(m2·K)] ?T
environment temperature which is assumed fixed The convective heat transfer coefficient, )?=?( ,???? In reality, electrical resistance varies with temperature and is expressed as: = 0[1+ (???? 0)] (11) and t he heat balance from eqn (6 ) becomes: 2 [1+ (???? 0)]=2 [????????(???? 4 4)+ ??( ,???? )(???? )] (12) We note that the heat
insulated tip case by a corrected length defined as Corrected fin length L c is defined such that heat transfer from a fin of length L c with insulated tip is equal to heat transfer from the actual fin of length L with convection at the fin tip t the thickness of the rectangular fins D the diameter of the cylindrical fins
higher heat transfer coefficient The distance between two baffles is baffle spacing Multiple Passes Shell-and-tube heat exchangers can have multiple passes, such as 1-1, 1-2, 1-4, 1-6, and 1-8 exchangers, where the first number denotes the number of the shells and the second number denotes the number of passes
(2) Convection h is the heat transfer coefficient, Btu/[h ft2 oF] dx The overall heat transfer coefficient, U, is an approximate value Use a correction factor, F
drop and heat transfer coefficient were those in which correlations were tubes However, this method is restricted to a fixed baffle cut (25 ) and cannot
Shell-side heat transfer coefficient Where hi is heat transfer coefficient for ideal cross flow past a tube bank Jc : Segmental baffle window correction factor
The overall heat transfer coefficient U is dominated by the smaller convection Correction factor F charts for common shell-and-tube heat exchangers 19
U=the overall heat transfer coefficient, W/m2oC; A= heat-transfer area, m2; Tm= the mean temperature difference,oC; Y = geometric correction factor LOGO
We know that the outside heat transfer coefficient is given by the equation F is the correction factor to account for the 8 tube passes in this heat exchanger
3 5 Calculation of Heat Transfer Coefficient and Pressure Drops 31 3 6 Heat Transfer Figure 3 1 Fixed Tube Sheet Shell and Tube Heat Exchanger 24 5