The Effect of Self-Rewetting Fluids and Surface Wettability Modification on the Thermal Performance of a Two-Phase Flat-Shaped Thermosyphon

Two-phase flat-shaped thermosyphons have been studied to optimize their thermal performance and reduce the hot spot temperature. A two-dimensional model was employed to observe the evaporation and condensation process in the thermosyphon. Simulating the phase change process was achieved through an in-house user-defined function (UDF), which obtains mass and energy source terms, added to ansysfluent code. Utilizing 1-Buthanol aqueous solution instead of water as the working fluid induces a Marangoni flow to a hotter region and prevents the dry-out phenomenon in the evaporator section. Also, employing a super hydrophilic evaporator makes the liquid spread on the evaporator more evenly, and hinders drying out. Using a super hydrophobic condenser accelerates the detachment of the condensed liquid from the condenser and reduces the accumulation of liquid on the condenser. Furthermore, it accelerates the return of the liquid to the evaporator section to recharge the liquid and prevent the dry-out phenomenon. It has been observed that by using the 1-Buthaol solution, the condensed liquid is more likely to fall back on the center part of the evaporator, which has the highest temperature. Altering the working fluid to 1-Buthanol aqueous solution yields a temperature drop of 10 K for the maximum temperature for a 100 W heat input. The temperature drop increased to 39 K by utilizing a super hydrophobic condenser and super hydrophilic evaporator instead of a bare copper. It has been observed that increasing the filling ratio in the thermosyphon increases the thermal inertia and reduces the hot spot temperature.