Development of an Experimental Facility for Investigating Critical Heat Flux of Saturated Flow Boiling of Refrigerant-123 in Microchannels

An experimental facility is developed to investigate critical heat flux (CHF) of saturated flow boiling of Refrigerant-123 (R-123) in microchannels. Six parallel Microchannels with cross sectional area of 0.2 mm × 0.2 mm are fabricated on a copper block, and a Polyvinyl Chloride (PVC) cover is then placed on top of the copper block to serve as a transparent cover through which flow patterns and boiling phenomena could be observed. A resistive cartridge heater is used to provide a uniform heat flux to the microchannels. The experimental test facility is designed to accommodate test sections with different microchannel geometries. The mass flow rate, inlet pressure, inlet temperature of Refrigerant-123, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative information near the CHF condition in microchannels. A high-speed camera is used to observe and interpret flow characteristics of CHF condition in microchannels. INTRODUCTION Heat sinks are commonly attached to a chip surface as a means of enhancing heat transfer from high-performance logic chips. In order to increase the surface area available for convection heat transfer, a common approach is to use a heat sink consisting of an array of fins. As computer chips become smaller in size and more powerful at the same time, the size of conventional fin-type heat sinks has to increase in order to dissipate the increase in heat generation. Hence, given a computer case, the performance of a computer is often limited by the available space in the case to accommodate the larger heat sinks. One way to enhance heat transfer from high-performance logic chips is the use of a heat sink with many microchannels and liquid water passing through it. As a result, more powerful chips can be incorporated into a given computer case without the issue of over-heated or burned-out chips. The present paper involves cooling of electronic devices using two-phase flow in microchannel heat sink. Two-phase heat transfer has significant advantages over single-phase heat transfer because it can accommodate very high heat fluxes better, flow rates are smaller through the use of the latent heat of vaporization, pressure drop and pumping power are less and (particularly for cooling situations) approximately uniform fluid and solid temperatures are obtained. However, a crucially important factor that must be taken into account in the design of microchannel boiling heat transfer is the CHF condition, which sets the upper thermal limit on the microchannel operation. The present work focuses on the development of an experimental facility to investigate CHF condition in a microchannel heat sink. NOMENCLATURE G Mass flux, kg/ms