Calculate the heat transfer area

Basic steps for the selection and design calculation of shell-and-tube heat exchangers: 1. Estimate the heat transfer area and initially select the heat exchanger model. (1) Calculate the heat transfer rate based on the heat transfer requirements. ? (2) Determine the temperatures of the fluid at both ends of the heat exchanger, calculate the qualitative temperature, and determine the fluid properties. ? (3) Calculate the heat transfer temperature difference, and determine the number of shell passes based on the principle that the temperature difference correction factor Δt should be ≥ 0.8. ? (4) Select the two-fluid flow channel, and choose the type of heat exchanger based on the temperature difference between the two fluids. ? (5) Initially select the total heat transfer coefficient K value based on the empirical range of the total heat transfer coefficient. ? (6) Calculate the heat transfer area using the overall heat transfer rate equation, and determine the specific model of the heat exchanger based on S (if it is for design purposes, the basic dimensions of the heat exchanger must be determined). 2? Calculate the pressure drops in the tube side and shell side: Based on the selected type of heat exchanger, calculate the pressure drops in each of these sides to determine whether they meet the required standards. If the requirements are not met, adjust the number of tubes or the spacing between baffle plates, or select other types of heat exchangers, and calculate the pressure drop until the requirements are satisfied. 3? Calculate the overall heat transfer coefficient and the heat transfer area: Using the correlations for convective heat transfer coefficients, determine the convective heat transfer coefficients inside and outside the tube, select the fouling thermal resistance, and then compute the value of the overall heat transfer coefficient. Based on this calculation, the actual heat transfer area is verified using the K value; if the heat transfer area provided by the heat exchanger is 10–20% larger than the required area, then the selected heat exchanger is appropriate. Otherwise, a different value for K must be chosen, and the above steps must be repeated until the requirement is met. http://bbs.hcbbs.com/viewthread.php?tid=246367&highlight=%BB%BB%C8%C8%C6%F7%BB%BB%C8%C8%C3%E6%BB%FD Check out this thread

There’s an example for calculating heat exchangers in the Chemical Process Design Manual; it’s similar to what the original poster mentioned. You can take a look at it

The result I calculated was 14 square meters, while the figure given in the book is 4 square meters

7200*1*(45-15)=S *K* temperature difference; 7200 KG/H, 1 KCAL/(C·KG); (45-15) degrees Celsius. C*S is the heat exchange area in square meters (M2). K=859 KCAL/(H·C·M2) (converted to KCAL/H·C·M2). The overall heat transfer coefficient; temperature difference = 55/LN(85/30) (in degrees Celsius). The C*S area is approximately 4 square meters. This post was last edited by Albertlu on 2009-2-19 at 14:04

I can’t understand any of the calculations above at all. There’s no issue with the units here, and no conversion is necessary either. KJ/S is already equivalent to KW; there’s no need to convert it to KCAL. It’s a very simple calculation: Q = KA@Tm. All that needs to be determined is the total heat transfer amount Q and the value of @Tm. As for Q, it can be calculated as Q = m*Cp*(t1-t2) = (7200/3600)*4.2*(45-15) = 252. As for @Tm, it’s calculated as (@t1-@t2)/2 = (130-45+45-15)/2 = 57.5. Finally, K is calculated as 1, A is Q/K*@Tm = 252/57.5 = 4.38 m2