The experimental study on the boiling bubble behaviors and heat transfer performance of the deionized water across various pin fins

Abstract

Microchannel heat sink is widely utilized as one of the effective heat dissipation methods with lower heat transfer temperature difference. In this paper, visual experiment study has been conducted to focus on the inner relationship between heat transfer/flow properties in macroscopic aspect with bubble dynamic characteristics in microcosmic aspect. Results show that along with the increases of Re, the value of convective heat transfer coefficient(h) increases as well. Correspondingly, the pressure drops show a tendency as increasing, decreasing lately, then increasing again. The bubbles in the undergo the same four process: film boiling process, transition process from film to nucleate boiling zone, nucleate boiling process and single-phase convection process. And the variation of pressure drop is one-to-one correspondence with the four heat transfer process. Besides, the triangle pin fin holds the higher heat transfer coefficient, which may be explained from the quantities and the sequence of appearance of bubbles in nucleate heat transfer process. The migration diameter as well as coverage rate of bubbles appears the tendency as ascending firstly then down lately with the increase of Re, which fit the conclusion in macroscopic aspect in heat transfer/flow properties. It could be found that the migration size is mainly influenced by the flow rate as well as the density of bubbles. In this way, the position of bubble occurred is the key point effecting bubble growth time and growth radium. Three zones have been divided to summarize the dynamic behaviors of bubbles in different positions: The migration diameter of bubbles in Zone I in the biggest, with that in Zone II moderate and that in Zone II lowest. The tail of pin fin (Zone I) makes the bubbles more easily to merge the surrounding new nucleated small bubbles to a bigger size, with more residence time to leave the bubble growing bigger. The general growth size of bubbles in ellipse pin fin is smallest, around 0.08 mm and with growth cycle short as 0.616 s. Simultaneously, that of the triangle one is biggest, with the size as 0.099 mm and growth time as 2.112 s.