Effect of Non-Condensable gas on condensing performance of HFE7100 With/Without hydrophobic coating

Abstract

• Condensing performance of dielectric fluid HFE7100 on heat sink with NCG is studied. • Presence of NCG significantly reduces the condensation heat transfer coefficient. • Hydrophobic coating enhanced the heat transfer coefficient by 15.6 to 31.8% • Heat transfer coefficient is reduced by 60–70% with NCG in the absence of coating. • The coating increased droplet count and detaching rate in the presence of NCG. Dielectric fluids are employed to avoid electric hazards in the immersion cooling. However, non-condensable gases (NCG) may prevail in the system and impair the condenser performance appreciably. The current study focuses on the experimental investigation of condensation with NCG for immersion cooling. This is the first experimental study in the immersion cooling application to examine the condenser performance in the presence and absence of NCG using dielectric fluid. A test rig was designed with vertical fins in a sealed insulated chamber using HFE 7100 dielectric fluid. Experiments were performed in the presence and absence of NCG (0%, 1.2%); with and without hydrophobic coating for variation input heating load (110–400 W) and operating pressures (0.7 atm, 1 atm). It was found that in the absence of coating, the average heat transfer coefficient (AHTC) is reduced by about 60 to 70% after adding NCG and the AHTC increased by about 15.6 to 31.8% after applying the coating. The inherent resistance of the coating layer showed a slight reduction in the AHTC in the absence of NCG. The coating used in this study has improved the condensation efficiency by increasing the droplet count and droplet rate in the presence of NCG. The flow visualization indicates that the droplet detaching from the heat sink is smaller with a higher falling frequency when the coating is imposed.