When calculating in accordance with GB/T 151 "Heat Exchangers" and the relevant requirements of JB/T 4736, the heat transfer performance of a heat pipe heat exchanger must be based on the medium temperature, corrosiveness, and fin-side operating conditions. In actual verification, design and selection personnel mostly focus on two issues: operating temperature limits and material-working fluid compatibility.
Q: Why must both upper and lower limits be set for the heat pipe operating temperature?
A: A heat pipe relies on the phase change of the working fluid to transfer heat. The operating temperature must be lower than the critical temperature of the working fluid; otherwise, the vapor-liquid interface disappears and heat transfer capability drops significantly. At the same time, it must be higher than the freezing point of the working fluid to avoid startup difficulties caused by freezing. When selecting the RQC-38, the medium temperature and its fluctuation range must be provided so that the tube wall temperature can be checked accordingly, confirming that the actual operating point of the heat pipe falls within the allowable range of the working fluid, rather than being estimated only from the average medium temperature.
Q: How should the tube shell material be matched with the working fluid?
A: Commonly used tube shell materials are copper, aluminum, and stainless steel, and the working fluid can be water, ethanol, ammonia, etc. The core of the match is compatibility: the working fluid must not cause obvious corrosion of the tube shell and fins or generate non-condensable gases; otherwise, heat transfer performance will degrade with operating time. When the medium side is corrosive, the material selection for the tube shell and fins should be checked against the medium composition, and isolation measures should be taken in the structure when necessary.
Q: Why should the fin-side operating conditions be checked separately?
A: The temperature, air volume, and dust content on the fin side directly affect the heat transfer margin and fouling tendency, so only the medium-side parameters should not be used in the calculation. It is recommended to list the operating conditions of both sides in the selection table so that the heat transfer performance can be reviewed according to standard requirements.
