Visualization of thermo-fluid behavior of loop heat pipe with two evaporators and one condenser under various orientations with uneven heat loads

This research conducted experimental investigations into the operating characteristics of a Multi-evaporator loop heat pipe (MLHP) with two evaporators and one condenser under uneven heat load conditions. Notably, it pioneered the visualization of the detailed internal flow phenomena in the evaporator cores, and compensation chambers (CCs). Two categories of experiments were conducted. The first category focused on heat load sharing conditions by heating a single evaporator in three different attitudes: gravity-assisted (with the condenser positioned above the evaporators), horizontal (with the condenser positioned at the same height as the evaporators), and anti-gravity (with the condenser positioned below the evaporators). These tests were the pioneering effort to investigate the effects of gravitational head on the heat load sharing phenomena. The second category of experiments simulated normal operating conditions, involving heating both evaporators with different heat loads in the horizontal attitude. These tests were the pioneering attempt to examine the hysteresis effect on internal flow phenomena in each evaporator core and CC under various heat load conditions. To further investigate the hysteresis effect in MLHP, a comparison of the internal flow phenomena in the evaporator and CC was made at the identical heat loads in different heat loads cycle tests. The findings indicated that internal flow phenomena in each evaporator core and CC depended not only on the current heat loads but also on the previous heat load conditions. Temperature measurements were conducted to establish the relationship between visualization results and temperature variations. The visualization results and the corresponding temperature data were used to summarize pressure and temperature profiles for each component of the MLHP. This included the two novel pressure and temperature profiles unveiled in the normal operating tests with different heat loads and the two novel pressure and temperature profiles unveiled in the heat load sharing tests.