A study of heat transfer from stationary and moving plates cooled by planar jets of water

David Arnold Zumbrunnen, Purdue University

Abstract

The steel and electronics industries are becoming increasingly interested in low turbulence, liquid planar jets to remove heat in order to improve their respective technologies. Planar jet systems are replacing less effective circular jet systems in many modern steel mills for cooling moving strips and plates. The central thrust of research in microelectronics is to increase the density of electronic components. Concomitantly, heat fluxes due to dissipative losses become greater and more effective cooling methods, such as the use of liquid jets, have become necessary. However, uncertainty regarding heat transfer coefficients and mechanisms complicates the designs of systems where planar jets may prove effective. Experimental apparatuses and methods were developed to measure local heat transfer coefficients under transient conditions on moving and stationary impingement surfaces. Problems associated with very rapidly changing temperatures on a moving surface were addressed by a new experimental method. The effects of impingement velocity, nozzle width, nozzle height, and temperature were investigated. Various heat transfer modes pertaining to steel mills were identified. Theoretical models of jet impingement and film boiling were developed to aid in correlating experimental data and to serve as predictive tools. For single phase forced convection, experimental results with the stationary impingement surface indicated that heat transfer coefficients exceed theoretical values for laminar flow by nearly a factor of two. This difference was attributed to the influence of turbulence in the jet on the boundary layer development. Heat transfer coefficients were not appreciably affected by surface motion over the range of plate speeds used in the experiments. However, at higher plate speeds, theoretical heat transfer distributions became more uniform as the plate speed increased, with values at the stagnation point remaining unchanged. The theoretical model of forced convection film boiling indicated that conduction across the vapor layer is substantially increased by surface motion, reducing the importance of radiation. In nucleate boiling, the peak heat transfer coefficient was shifted in the direction opposite to the plate motion where surface temperatures were higher.

Degree

Ph.D.

Advisors

Viskanta, Purdue University.

Subject Area

Mechanical engineering

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