Transient boiling critical heat flux on horizontal vertically oriented ribbon heater with treated surface condition in pool of water

Abstract

The deep understanding of transient pool boiling critical heat flux (CHF) phenomena with treated surface and its correlation in water at saturated and subcooled conditions are becoming increasingly important for the database for the further enhancement of the design of liquid cooling technologies. Transient CHF using horizontal cylinders with different surfaces have been reported. However, there is a need to find the effect of surface wettability (contact angle) on transient CHF. This paper aims to study the steady and transient CHF due to exponentially increasing heat inputs, Q = Q0exp(t/τ) , using horizontal vertically oriented platinum ribbon in a pool of water with respect to pressure, subcooling, surface roughness and contact angle. The exponential period, τ, was varied from 5 ms to 10 s. We used three ribbon heaters with different surfaces, namely, commercial surface (CS), treated surface I (TS-I) polished by buff paper together with alumina, and treated surface II (TS-II) finished by emery paper. For the surface condition, surface roughness and contact angle of each ribbon were measured prior to pool boiling experiment. The acquired non-boiling heat transfer, steady and transient CHF were evaluated with existing corresponding equations. The steady-state CHFs measured on the TS-I were tested with the corresponding results of commercial surface. The three groups of transient CHF with different physical mechanisms, the enhancement of transient CHF in light of surface condition and transient CHF degradation depending on pressure and subcooling were reported.

Keywords

• transient critical heat flux
• ribbon
• surface roughness
• contact angle
• treated surface