An experimental study was carried out to explore the heat transfer characteristics on the outside of smooth and enhanced tubes, during evaporation and condensation of R134A in the annulus of a tube-in-tube heat exchanger. The three-dimensional enhanced surface tube consisted of primary enhancement patterns and secondary patterns; results were compared to the performance of an equivalent smooth tube. The equivalent external diameter of the inside horizontal copper tubes used in this study was 19.05 mm, while the outer tube varied in size, allowing a comparison of heat transfer for different annulus dimensions. Tests were conducted with a fixed inlet/outlet vapor quality and a constant saturation temperature for varied mass velocities in the range of 30 to 100 kg/(m²∙s). For condensation, the ratio of heat transfer coefficient enhancement (enhanced tube/ smooth tube) was up to 1.78; this can be attributed to the turbulence increase, as well as liquid film re-distribution, produced from the dimples. Furthermore, the condensation heat transfer coefficient increased rapidly with increasing mass flux. For flow boiling in the annulus between the 1EHT tube and outer tube, the heat transfer coefficient during boiling was 11–36% higher when compared to the smooth tube at x_ave = 0.35, while the performance of the 1EHT tube was not as good as the smooth tube at x_ave = 0.5. The heat transfer deterioration can be explained by decreased effective nucleate flow boiling heat transfer area and the flow pattern transition between a slug/wavy-stratified flow to wavy-stratified flow.

The increasing power density of SiC power modules presents significant challenges in achieving uniform high-heat-flux thermal management, which is often limited by conventional packages. To address this, an embedded microfluidic-cooled SiC power module is developed, combining embedded microchannels and nano-silver sintering to enable efficient and uniform cooling. Microchannels were directly fabricated beneath the die footprint in the direct-bonded copper substrate using picosecond laser etching, with a crossover double-layer manifold integrated into the baseplate to facilitate large-area liquid distribution. The thermal performance and temperature uniformity of the proposed design were first validated using SiC thermal test chips (SiC TTCs). Our results demonstrated an ultralow junction-to-fluid thermal resistance of 0.064 K/W and a coefficient of performance greater than 20 000, representing a 52% reduction and more than a 10-fold improvement over conventional heat sinks, respectively. The design allowed reliable heat dissipation up to 655 W at a coolant flow rate of 3 g/s, reducing junction temperature gradients by 86%. Finally, when applied to a practical SiC power module, the improved thermal performance of the new architecture led to an increase in current capacity by 43%. The proposed codesigned integrated microfluidic-cooled packaging architecture offers an efficient and easy-to-extend solution for next-generation high-power-density power electronics.