Heat Transfer in a Rib Turbulated Pin Fin Array for Trailing Edge Cooling

Ribs were added into a pin fin array for a uniquely new cooling concept enabled through additive manufacturing. Both heat transfer mechanisms are highly non-linear; thus, cannot be superimposed. Heat transfer measurements are obtained using the thermochromic liquid crystal technique in a trapezoidal duct with pin fins and rib turbulators. Three pin blockage ratios and four rib heights at Reynolds numbers between 40,000 and 106,000 were tested. The Nusselt number augmentation is generally higher at the longer base of the trapezoidal duct. The same high heat transfer trend is seen at the columns closer to the longer base of the trapezoidal duct than on the shorter base. Through the length of the duct, the flow shifts from the nose region to the larger opening on the opposite wall. Also, it is observed that increasing the blockage ratio as well as increasing the rib height, has a positive impact on heat transfer as ribs act as additional extended surfaces and alter the near-wall flow field. The heat transfer augmentation of pins and ribs is found to not be equal to the sum of both. The observed heat transfer augmentation of the combined cases exceeded over the rib and pin only cases by up to 100%, but the weighted friction factor also doubled. The combination of ribs and pins is an excellent concept to achieve more uniform cooling over an array at higher levels when pressure drop is not of concern.

Single Phase Liquid Cooling of High Heat Flux Devices with Local Hotspot in a Micro-Gap with Non-Uniform Fin Array

Single-phase liquid cooling in micro-channels and micro-gaps has been successfully demonstrated for heat fluxes of ~1 kW/cm2 for silicon chips with maximum temperature below 100 °C. However, effectively managing localized hotspots in heterogeneous integration, which refers to the integration of various components that achieve multiple functionalities, entails further thermal challenges. To address these, we use a non-uniform pin-fin array. Single-phase liquid-cooling performance of four silicon test chips, thermal design vehicles (TDVs), each with a non-uniform pin-fin array, are experimentally examined. We evaluate multiple combinations of hotspot and background heat fluxes using four background heaters aligned upstream to downstream, and one additional hotspot heater located in the center. We examine the thermal performance of cylindrical fin-enhanced TDVs and hydrofoil fin-enhanced TDVs, both with two designs: one with increased fin density around the hotspot only, and another with increased fin density spanning the entire width of the channel. The resulting heat flux ratio of the localized hotspot to background heaters varies from 1 to 5. TDVs with spanwise increased hydrofoil fin density (spanwise hydrofoil) exhibit the best thermal performance with 6%-14% lower hotspot temperature than others. TDVs with spanwise increased cylindrical fin (cylindrical spanwise) maintain a balance between hotspot cooling performance and pressure drops. In general, as the temperature of the hotspot remains around 70? with a heat flux of 625 W/cm2, the non-uniform fin-enhanced micro-gaps appears to be a promising hotspot thermal management approach.

Cooling effectiveness of matrix, pin fin array and hybrid structure: A comparative study

In modern gas turbines, the trailing edge of turbine blades must be cooled by compact heat transfer structures. The basic problems in the design of cooling ducts include enhancing heat transfer, reducing pressure loss and obtaining uniform temperature distribution. The purpose is to improve energy efficiency and guarantee the engine lifespan. In this work, both experiment and numerical simulation are employed to study pressure drop and heat transfer of various kinds of cooling configurations. Pin fin array, matrix and hybrid structures are investigated in a comparative study. Thermochromic liquid crystal technique is applied to obtain heat transfer distribution on the channel surface. The results show that matrix creates much stronger heat transfer than pin fin array with increased pressure loss penalty. Performances of matrix structures are quite different due to the configurations (dense or sparse). Hybrid structures are always worse than the baseline matrix in terms of average thermal performance, due to the higher pressure loss, however, heat transfer can be improved. The performance of hybrid structure depends on the arrangement and diameter of the pin fins. Pin fins in central area provide not only larger pressure loss but also stronger heat transfer than pin fins near the bend region. Cases with larger diameter result in the thermal performance degradation. Compared with sparse matrix, the hybrid structures can compensate for the lower heat transfer enhancement. As for the dense hybrid structures, the average heat transfer capacity can be improved with reasonable pin fin arrangement.