Vapor Pressure and Temperature Analyses on a Gravity-Assisted Wrapped Screen Wick Annular Heat Pipe

Internal pressure and temperature measurements were made on a wrapped screen mesh wick annular heat pipe using distilled water as the working fluid. High-resolution pressure transducers were connected to two probes and inserted into the evaporator and condenser regions of the heat pipe's vapor flow passage to gather local static and differential pressure information. Optical fiber distributed temperature sensors (OFDTS) and K-type thermocouples were used to collect internal and external surface temperature measurements at various axial locations. With the heat pipe in the vertical orientation (gravity-assisted), simultaneous measurements of the vapor pressure, temperature, and external surface temperature were conducted for heat loads of 25 W, 50 W, and 75 W. The vapor flow frictional coefficient was calculated based on the data at multiple vapor flow Reynolds numbers, which correspond to a given input power. Ad-ditional time-frequency analysis was performed on the pressure drop information to gain insight on the flow behavior, characteristics, and infer regime occurring within the vapor core region of the heat pipe. The results of these pressure drop measurements and frictional coefficients provide a valuable database that supports the advancement of heat pipe modeling and validation for advance reactors applications such as, small modular reactors (SMR), and microreactors.