Enhancement of pool boiling on structured surfaces using HFC-4310 and water

This experimental study investigated the effects of geometric parameters of boiling on structured surfaces. The structured surfaces were created by bending fins having triangular cuts of specific size and pitch. The tunnels between the fins were made by electrical discharge machining. The surface geometric parameters include the pore geometry (pore angle = 30 or 60°and pore length = 0.3 or 0.5 mm), pore pitch (0.6 or 1.0 mm), and tunnel height (0.7 or 1.0 mm). Water or HFC-4310 was used as the working fluid, and the tests were performed at a 60 or 70°C saturation temperature. The heat flux varied between 30 and 550 kW/m². For boiling in water, the larger pore pitch (1.0 mm) yields better performance than a 0.6 mm pitch for the same type of pores, and a smaller fin height (0.7 mm) is preferred to the 1.0 mm fin height. However, these parameters have no significant influence for boiling in HFC-4310, whose latent heat and surface tension are much smaller than water. The best structured surface yields about sixfold boiling heat transfer enhancement over the plain surface in water and fivefold in HFC-4310. This enhanced boiling surface yields 0.03 K/W evaporation resistance at 91W heat input for water on a 16 mm diameter circular heating area.