The jet impingement boiling heat transfer with ad hoc wall thermal boundary conditions

Abstract

In a two-phase heat exchanger, the thermal boundary condition at the boiling wall plays an import role. To investigate the characteristics of its flow and heat transfer, it is required to solve a three-domain conjugation heat transfer problem which takes into account of boiling, conduction, and air convection. In the current design, the saturated water flows into a cylindrical chamber with a tube array, whereas the hot air travels outside of chamber and boils the water inside. The effects of the water inlet velocity and hot air inlet mass flow rate are measured in the experiments. A simulation tool with Graphical User Interface code is developed for predicting the three-domain conjugation heat transfer. The boiling heat transfer in the complex case is showed to be well explained in the approach of combining the Rensselaer Polytechnic Institute (RPI) boiling model. The experiments indicate that the wall temperature on the solid-air interface and the transferred energy are independent of water inlet velocity but significantly depend on the air inlet mass flow rate. The wall temperatures in the centre core area (tube array region) are relatively uniform, whereas a huge temperature gradient is measured in the peripheral area. The maximum temperature difference in the core region is only around 17.7% or 24.6% of the core-to-peripheral temperature difference in the cases with the high or low air inlet velocity. The experimental observations have been reproduced in the simulation. The heat transfers on the hot air side and the water boiling side significantly influence each other. Prominent variations of wall temperature and heat flux result in a co-existence of single-phase water convection and the water boiling flow. It demonstrates that the conjugation has to be considered with applying an ad hoc thermal boundary conditions in the cases.