Evaluation and Optimization of a Cross-Rib Micro-Channel Heat Sink

This article presents a novel cross-rib micro-channel (MC-CR) heat sink to make fluid self-rotate. For a thermal test chip (TTC) with 100 w/cm2, the cross-ribs micro-channel were compared with the rectangular (MC-R) and horizontal rib micro-channel (MC-HR) heat sinks. The results show that, with the cross-rib micro-channel, the junction temperature of the thermal test chip was 336.49 K, and the pressure drop was 22 kPa. Compared with the rectangular and horizontal ribs heat sink, the cross-rib micro-channel had improvements of 28.6% and 14.3% in cooling capability, but the pressure drop increased by 10.7-fold and 5.5-fold, respectively. Then, the effects of the aspect ratio (λ) of micro-channel in different flow rates were studied. It was found that the aspect ratio and cooling performance were non-linear. To reduce the pressure drop, the inclination (α) and spacing (S) of the cross-ribs were optimized. When α = 30°, S = 0.1 mm, and λ = 4, the pressure drop was reduced from 22 kPa to 4.5 kPa. In addition, the heat dissipation performance of the rectangular, staggered fin (MC-SF), staggered rib (MC-SR) and cross-rib micro-channels were analyzed in the condition of the same pressure drop, MC-CR still has superior heat dissipation performance.

Effect of quartz aperture covers on the fluid dynamics and thermal efficiency of falling particle receivers

Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz half-shells are investigated for use as full or partial aperture covers to reduce receiver thermal losses. A receiver subdomain and surrounding air are modeled using ANSYS® Fluent®. The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2), aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting the aperture. Contrary to expected outcomes, results show that quartz aperture covers can increase radiative losses and result in modest to nonexistent reductions in advective losses. The increased radiative losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection. Quartz half-shell total transmissivity was measured experimentally using a radiometer and the National Solar Thermal Test Facility heliostat field. Average measured total transmissivities are 0.97±0.01 and 0.94±0.02 for concave and convex side toward the heliostat field, respectively. Quartz half-shell aperture covers did not yield expected efficiency gains in numerical results due to increased radiative losses, but efficiency improvement in some numerical results and the performance of quartz half-shells subject to concentrated solar radiation suggest quartz half-shell aperture covers should be investigated further.

Reactivity of the Blood Microcirculation System in Primary School Children to the Temperature Factor

The purpose of the study was to investigate the adaptive capacity of the blood microcirculation system in children of primary school age for a functional test with heating. The article deals with the study of the blood microcirculation system in primary school children by laser Doppler flowmetry and the study of the reserve capacity of tissue blood flow in children on a test with increasing temperature factor. Materials and methods. The research was conducted on the basis of the laboratory of physiological research of the Department of Anatomy and Physiology of People and Animals of Bohdan Khmelnytsky Melitopol State Pedagogical University. The surveyed contingent consisted of 80 practically healthy children aged 6 to 9 years old, secondary school students in Melitopol. Based on a comprehensive morphofunctional study, we obtained data on individual-typological features of blood microcirculation in primary school children and the reserve capacity of tissue blood flow using functional tests. It is established that the adaptive features of the blood microcirculation system in boys and girls of early school age are due to different levels of local and central mechanisms of microvessel regulation. Results and discussion. The results obtained during the thermal test indicate different levels of reactivity of the body to increasing the temperature factor and the neurogenic vasoconstrictor effects of the sympathetic nervous system on the vessels of the arteriolar part of the microcirculatory tract. The reaction to the thermal test directly depends on the individual-typological features of blood microcirculation. Conclusion. At a ratio of reaction to thermal influence in children with various types of microcirculation, the maximum increase in tissue perfusion was observed in children with type III of laser Doppler flowgram. This level of microvascular reactivity, as well as the relatively rapid recovery of blood flow after thermal hyperemia is explained by the fact that children with hyperemic type of microcirculation have increased microvascular tone due to neurogenic effects of the sympathetic chain of tissue blood flow regulation. Children with the hypoemic type of microcirculation, on the other hand, have a somewhat reduced sympathetic tone relative to the normoemic type, as a result of which the reserve of capillary blood flow is reduced and the time of blood flow recovery after thermal exposure is prolonged

Application Methods for Refractory Insulation in Hot Particle Storage Bins

The National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories is conducting research on a Generation 3 Particle Pilot Plant (G3P3) that uses falling sandlike particles as the heat transfer medium. G3P3 proposes a system with 6 MWh of thermal energy storage in cylindrical bins made of steel that will be insulated internally using multiple layers of refractory materials[1]. The refractory materials can be applied by stacking pre-cast panels in a cylindrical arrangement or by spraying refractory slurry to the walls (shotcrete). A study on the two methods determined that shotcrete would be the preferred method in order to minimize geometric tolerance issues in the pre-cast panels, improve repairability, and to more closely resemble commercial-scale construction methods. Testing and analysis was conducted which showed shotcrete refractories could be applied with minimal damage and acceptable heat loss.