Yu Rao

A Numerical Study of the Flow and Heat Transfer in the Pin Fin-Dimple Channels With Various Dimple Depths

A numerical study was conducted to investigate the effects of dimple depth on the flowand heat transfer characteristics in a pin fin-dimple channel, where dimples are locatedspanwisely between the pin fins. The study aimed at promoting the understanding of theunderlying convective heat transfer mechanisms in the pin fin-dimple channels andimproving the cooling design for the gas turbine components. The flow structure, frictionfactor, and heat transfer performance of the pin fin-dimple channels with various dimpledepths have been obtained and compared with each other for the Reynolds number rangeof 8200–80,800. The study showed that, compared to the pin fin channel, the pin fin-dimple channels have further improved convective heat transfer performance, and the pinfin-dimple channel with deeper dimples shows relatively higher Nusselt number values.The study still showed a dimple depth-dependent flow friction performance for the pinfin-dimple channels compared to the pin fin channel, and the pin fin-dimple channel withshallower dimples shows relatively lower friction factors over the studied Reynolds num-ber range. Furthermore, the computations showed the detailed characteristics in the dis-tribution of the velocity and turbulence level in the flow, which revealed the underlyingmechanisms for the heat transfer enhancement and flow friction reduction phenomenonin the pin fin-dimple channels. [DOI: 10.1115/1.4006098]Keywords: pin fin, dimple, numerical computation, friction factor, heat transferenhancement

Comparisons of Flow Friction and Heat Transfer Performance in Rectangular Channels With Pin Fin-Dimple, Pin Fin and Dimple Arrays

An experimental study was conducted to investigate the flow friction and heat transfer performance in rectangular channels with pin fin-dimple and pin fin arrays in the Reynolds number range of 8200–54000. The friction factor, average Nusselt number and the overall thermal performance parameters of the pin fin-dimple and the pin fin channels have been obtained and compared with the experimental data of a smooth rectangular channel and previously published data of a pin fin channel and a dimpled channel. The comparisons show that the pin fin-dimple channel has a better convective heat transfer performance, a lowered friction factor and a higher overall thermal performance than the pin fin channel. The comparisons also show that the pin fin-dimple channel has a significantly higher heat transfer performance and friction factor than the dimpled channel, however the former’s overall thermal performance becomes distinctively lower than the latter at a higher Reynolds number than 37000.Copyright

Local Heat Transfer Characteristics in Channels With Pin Fin and Pin Fin-Dimple Arrays

A comparative study was conducted to investigate the spatially-resolved local heat transfer characteristics of air turbulent flow in rectangular channels with pin fin and pin fin-dimple arrays. The spatially-resolved Nusselt numbers on the endwall surface of the pin fin and pin fin-dimple channels have been obtained and compared with each other. Compared with the pin fin channel, the pin fin-dimple channel shows distinguishing heat transfer characteristics on the wall beneath the main flow and the wake flow region. Due to the presence of the dimples in the pin fin arrays, additional strong vortex flows are generated near the wall beneath the main flow region, which distinctively increase the heat transfer rates there; however the turbulent mixing in the wake of the pin fins is reduced appreciably, which leads to decreased heat transfer rates in the wake.Copyright

An Experimental Study of Transitional Flow Friction and Heat Transfer Performance of a Channel With Staggered Arrays of Mini-Scale Short Pin Fins

An experimental study was conducted to investigate the friction and heat transfer performance of air transitional flow in a rectangular channel with staggered arrays of short pin fins with transverse spacing-to-diameter of 1.5 and streamwise spacing-to-diameter ratio of 2.5. The friction factor, averaged Nusselt number and the overall thermal performance of the transitional flow have been obtained, and compared with Metzger’s pin fin channel with transverse spacing-to-diameter of 2.5 and streamwise spacing-to-diameter ratio of 2.5. The experimental study has showed that in the Reynolds number range of 1678–8500, the pin fin channel with transverse spacing-to-diameter of 1.5 has a higher convective heat transfer performance, but the enhancement capability decreases with the Reynolds number. For Re 6000 the overall thermal performance of the former is lower than the latter. For both of the pin fin channels, the overall thermal performance gets highest when the flow transition occurs.Copyright

A liquid crystal thermography calibration with true color image processing

Liquid crystal thermography is a high-resolution, non-intrusive optical technique for full-field temperature measurement. We present the detailed calibration data for the thermochromic liquid crystal (TLC) with a useful range of 41-60 \circ C. The calibration is done with true color image processing by using an isothermal calibrator. The hue-temperature curve of the TLC is obtained, and the measurement uncertainty is analyzed. Combined with the image noise reduction technique of a 5×5 median filter, the measurement accuracy of the liquid crystal thermography can be significantly improved by approximately 57.1%.