Enhancement of Mist Flow Cooling by Using V-Shaped Broken Ribs

Abstract

Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45 degrees, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1-3.1 W/cm(2) and 3.4-9.4 W/cm(2) for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow.