Effect of Surface Orientation on the Rewetting Phenomena during Jet Impingement Cooling

DOI: 10.1615/IHTC15.hte.009839
pages 4411-4419

Chitranjan Agrawal
College of Technology and Engineering, Maharana Pratap University of Agriculture and Technology

Chitranjan Agrawal
Assistant Professor

Akhilesh Gupta
Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, 247667, India

Barun Chatterjee
Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai-400085, India

KEY WORDS: Heat transfer enhancement, Conduction, Jet impingement, Round water jet, Jet Reynolds number, Re wetting temperature, Wetting delay, Maximum surface heat flux.

Abstract

Rewetting phenomenon is generally observed when a hot surface of a very high temperature is quenched by the flow of sub cooled water. Rewetting is considered at the minimum film boiling point on the standard boiling curve. Rewetting temperature, wetting delay and maximum surface heat flux are some of the parameters over which the rewetting phenomenon is investigated. In this paper the effect of change in surface orientation on the rewetting behavior of a hot horizontal stainless steel sheet is presented. The hot surface of SS-316 and 0.25 mm thickness is cooled by the impingement of sub cooled round water jet. Laboratory water of 22°C temperature, impinges normally to the test surface from a tubes type nozzle of 2.5mm diameter and 250 mm length. The nozzle exit to test surface spacing is maintained at z/d = 4 and jet flow rate is varied to maintain the jet Reynolds number in the range of 5000-24000. Initially the test-surface is heated up to the temperature of 800°C by resistance heating. The investigation for rewetting phenomena is made for the stagnation point with horizontal and vertical orientation of the test surface. The transient surface temperature during the quenching is recorded by minerally insulated K-type thermocouple of 0.25 mm sheath diameter. The transient surface temperature is used further to determine the rewetting parameters i.e. rewetting temperature, wetting delay and maximum surface heat flux.