How to calculate the wall temperature of a shell-and-tube heat exchanger

It is best to use heat exchanger calculation software (thermodynamics) for the calculations; when determining the heat transfer area required for the heat exchanger, the software can also determine the average wall temperature； If no software is available, the average wall temperature of the shell-side cylinder is generally determined by averaging the inlet and outlet temperatures of the medium flowing in the shell side. Determining the average wall temperature of the heat exchange tubes is more complicated; usually, the average of the inlet and outlet temperatures of the medium flowing in the tube side is taken, and this value is then averaged with the average temperature of the shell side, after which further adjustments are made.

This post was last edited by wiseboy on 2012-1-3 17:35, version 1. This issue has been mentioned many times: only by fully and thoroughly calculating all the heat transfer in a heat exchanger can the wall temperature be calculated correctly. Any method for calculating heat transfer that is incomplete, even if it yields a wall temperature, is incorrect ； 2. You can use THEM, HTRI, HTFS to calculate the entire heat exchanger; wall temperature is just one of the many parameters taken into account in these calculations ； 3. If you have to do the calculations by hand, then try using the method of trial and error slowly. Note that when calculating the wall temperature, you cannot use simplified algorithms; otherwise, the resulting wall temperature may contain fundamental errors (an inverted temperature gradient). Key point: In the calculation of heat exchangers involving natural convection heat transfer or steam condensation heat transfer, the wall temperature cannot be determined independently, as the formulas for the film coefficients of natural convection and steam condensation already include the wall temperature. Calculating the membrane coefficient is complicated because the wall temperature is unknown. An effective approach is to establish a system of heat transfer equations for solution. The approach used in \"Principles of Chemical Engineering\" is intended to teach the principles, but it is not a good method, let alone one that should be adopted in modern design. Heat exchanger engineers should focus more effort on optimizing the design rather than painstakingly working through those mathematical problems, wasting time and effort in doing so. These “trial and error” methods should be replaced by software, after all, technology has advanced to this point.

What was said on the 3rd floor is great; why not use functions from high-level languages when trying various approaches repeatedly?

It seems you have a good understanding of these heat exchanger software programs. I would like to ask a few questions regarding the HTFS software: 1. Do the wall temperatures of the shell side and tube side refer to the temperatures of the outer and inner walls of the heat exchange tubes, or rather the temperatures of the shell and the heat exchange tubes? 2. When I swapped the media in the shell side and the tube side, the wall temperature changed significantly. For heat exchange tubes, it’s just a matter of swapping the media inside and outside the tubes – so why is there such a big difference? There are also some issues in HTRI: temperature, Average/Skin ； wall temperature, Min/Max ； Bulk temperature – which positions do these temperatures refer to respectively?

This post was last edited by wiseboy on 2012-5-28 10:31. When two fluids exchange, the change in the shell-side wall temperature is much greater. The wall temperature of the casing is an average value, as the temperature of the casing is uneven and changes over time.

There should be a difference between the wall temperature of the heat exchange tube and the temperature of the fluid. Some people say that strength calculations must be carried out through thermal analysis – what is your opinion on this? How do you usually proceed?

Those large design institutes and engineering companies use software to perform process calculations in order to determine the wall temperatures of the tube side and shell side. However, for some private manufacturing firms, the orders they receive are rarely for entire projects, and the clients seldom provide detailed and standardized heat exchange parameters. As a result, when it comes to equipment design, these parameters have to be estimated arbitrarily; even if asked, the clients are likely to give estimates as well. It’s a frustrating situation – if problems arise during use, then both parties end up arguing over them.

Then, consider the extreme cases: one maximum value and one minimum value. For example, for the shell, it’s 180–120, and for the tube side, it’s 40–60. In that case, use 180 as the wall temperature of the shell and 40 as the wall temperature of the tube side. What’s the point of arguing about this?

Are there any professionals looking for a job? The Shanghai office is seeking a thermal energy engineer with experience in the research, development, design, and testing of fluid heat exchange systems.