Critical Heat Flux in Cold Plates of Narrow Channels with Structures for Additional Liquid Supply

Abstract

To develop compact and high-performance cooling systems, experiments on the increase of CHF for flow boiling in narrow channels by improved liquid supply were conducted. A large surface of 150mm in heated length and 30mm in width with grooves of an apex angle of 90 deg, 0.5mm depth and 1mm in pitch was employed. A structure of narrow heated channel between parallel plates with unheated auxiliary channel was devised and tested by using water in different gap sizes and in different combinations of flow rates. The auxiliary channel was installed for the purpose of additional liquid supply to the heating surface from the transverse direction perpendicular to the flow in the main channel. In the present paper, the effect of reduction in liquid flow rate applied to the auxiliary channel was investigated, where the ratios of liquid velocity at the inlet of auxiliary channel to that at the inlet of main heated channel were varied as 1, 2/3 and 1/3. Almost no change in both CHF values and in heat transfer coefficients were observed despite of the reduction in the flow rate for the auxiliary channel. In the case of the same total volumetric flow rate, values of CHF for gap size of 5mm were higher by around 1.5 times than those for gap size of 2mm. CHF values larger than 1×106W/m2 was obtained for mass velocity G= 33kg/m2s at s= 5mm and for G= 82kg/m2s at s= 2mm, where the mass velocities were calculated by hypothetical inlet liquid velocities under the assumption that the total flow rate was distributed at the same velocity to both of heated and unheated channels.