Abstract
This study aims to characterize experimentally the heat transfer in micro-milled multi-microchannels copper heat sinks operating with flow boiling, in the attempt to contribute to the development of novel and high heat flux thermal management systems for power electronics. The working fluid was R-134a and the investigation was conducted for a nominal outlet saturation temperature of 30 ∘C. The microchannels were 1 cm long and covered a square footprint area of 1 cm2. Boiling curves starting at low vapor quality and average heat transfer coefficients were obtained for nominal channel mass fluxes from 250 kg/m2s to 1100 kg/m2s. The measurements were conducted by gradually increasing the power dissipation over a serpentine heater soldered at the bottom of the multi-microchannels, until a maximum heater temperature of 150 ∘C was reached. Infrared thermography was used for the heater temperature measurements, while high-speed imaging through a transparent top cover provided visual access over the entire length of the channels. The average heat transfer coefficient increased with the dissipated heat flux until a decrease dependent on hydrodynamic effects occurred, possibly due to incomplete wall wetting. Depending on the channel geometry, a peak value of 200 kW/m2K for the footprint heat transfer coefficient and a maximum dissipation of 620 W/cm2 at the footprint with a limit temperature of 150 ∘C could be obtained, showing the suitability of the investigated geometries in high heat flux cooling of power electronics. The experimental dataset was used to assess the prediction capability of selected literature correlations. The prediction method by Bertsch et al. gave the best agreement with a mean absolute percent error of 24.5%, resulting to be a good design tool for flow boiling in high aspect ratio multi-microchannels as considered in this study.
Highlights
In the last two decades, power electronics have experienced increasing research and industrial interest, promoted by the broad diffusion of technologies that are strategic to the sustainable development of our society [1]
If Geometry A is taken as the reference case and heat dissipation needs to be increased, the presented results suggest that an increase in heat transfer area by reducing wall thickness may be preferred to a reduction in the channel width
The present study investigated the heat transfer characteristics of R-134a during flow boiling in three copper multi-microchannel heat sinks for power electronics cooling
Summary
In the last two decades, power electronics have experienced increasing research and industrial interest, promoted by the broad diffusion of technologies that are strategic to the sustainable development of our society [1]. An example is power drives, which are used to maximize the efficiency of wind turbines or efficiently manage the traction of electric vehicles. Reliability and lifetime are vital aspects of these electronic systems and they are strongly dependent on the operational temperature. Optimum system development requires the design phase to combine the electronic and thermal aspects. The miniaturization of electronic components has demanded more effective thermal management systems. The thermal management of electronics is implemented by spreading the heat dissipated by the circuitry over an extended surface and removing it by a cooling medium
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