Problems encountered in the graduation project on heat exchangers
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For the graduation project on heat exchangers, the diameter and heat transfer area of the heat exchanger are known, but the flow rate of the fluid is unknown. I would like to ask how to carry out the calculations related to heat transfer. A senior graduate student said that the design is mainly done independently, and the flow rate can also be determined by oneself. It’s possible to estimate the overall heat transfer coefficient and then use the basic equations of heat transfer to calculate Q, thereby determining the flow rate. I’m not sure if this approach works; I would appreciate any guidance from those who are more experienced in this area.
There are so many types of heat exchangers; which type do you work with? You can find many graduation theses on heat exchangers online.
You need to know what the media on both sides of the heat exchange are, what the inlet and outlet temperatures are, as well as what type of heat exchanger it is as mentioned above; even the material of the heat exchange tubes needs to be known in order to determine the overall heat transfer coefficient； Only by knowing this can you work back to determine the flow rate of the medium.
The media used are flue gas with average composition (for which physical property parameters are available) and cooling water. The inlet temperature on the tube side is 33°C and the outlet temperature is 40°C; the inlet temperature on the shell side is 109°C and the outlet temperature is also 40°C. The operating pressure is 0.68 MPa. Simply consider using only the fixed tube sheet type, with ordinary seamless steel plates. Based on the approximate range of K values in heat exchangers, a value of 50 W/m^2*K was used; this resulted in a cooling water flow rate of less than 0.5 m/s. I’m not sure what the problem is
Do not use empirical values for the overall heat transfer coefficient; since you now have a rough idea of the heat exchanger’s structure, you should calculate this coefficient based on the actual structure of the heat exchanger. This way, you will obtain an accurate value for the flow rate.
Professional books generally provide complete calculation pathways; based on these, an EXE calculation formula can be developed, allowing for simple adjustments to the calculations.
Professional books generally provide complete calculation pathways; based on these, an EXE calculation formula can be developed, allowing for simple adjustments to the calculations.
But when calculating the heat transfer coefficient α, the Reynolds number must be determined based on the flow velocity; what should be done in this case? {:3_65:}
One can assume a value for this first, for example 1 m/s; ultimately, fitting is used to determine the exact value. If you have the capability, you can program the calculation process, which will make things much simpler. Alternatively, you can refer to the calculation table I’ve prepared for shell-and-tube heat exchangers – you can access it by clicking on my signature.