What does \"temperature cross\" mean during HYSYS heat exchanger simulation?
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When performing heat exchanger simulations in HYSYS and selecting the weighted design model, what does the message \"temperature cross\" mean? How to solve it
The temperatures cross; you can try changing it to a counter-current configuration, which allows such temperature crossings.
Temperature cross is a fundamental concept related to the pinch point concept. Put it another way: in a heat exchanger, the cold stream, which absorbs heat from the hot stream, never has an inlet temperature higher than the outlet temperature of the hot stream; if it did, the cold stream would have to obtain some heat from other sources, such as external utilities. For example, if the cold stream has an inlet temperature of 20°C and an outlet temperature of 50°C, while the hot stream has an inlet temperature of 90°C, its outlet temperature will never drop below 20°C. If the outlet temperature of the hot stream is below 20°C, this is referred to as “temperature cross,” meaning that the cold stream is obtaining heat from outside this unit, usually from public utility sources. In general, this concept is very important for designing heat exchanger networks. For more information, refer to the concept of pinch temperature. I hope this helps.
Sorry for missing one point: in HYSYS, for heat exchangers, there are 4 types. (1) The endpoint type – this refers to situations where there is only a single phase, and the temperature change is linear. (2) The weighted type – as you asked, this is used when phase changes occur during the heat transfer process; it’s advisable to choose this type in such cases. HYSYS divides the heat exchanger into zones so that the LMTD can be calculated accurately. (3) The steady-state rating type – this is an extension of the endpoint type. (4) The dynamic rating type – this is a combination of the endpoint type and the weighted type. Thanks
I have changed the flow direction of the first tube pass from co-current to counter-current. Yet the alarm banner still indicates a temperature crossover issue. I’m not sure what’s wrong with it. As you suggested, I used a weighted model for the exchanger design. Could you please give me some advice? Thank you
If a Shell & Tube design is used, a series configuration can be adopted
The problem can be solved using a counterflow process
flymxcaoh, could you show it in more detail? What I’m doing is trying to use a counter, but it seems there’s no difference.