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An oscillating heat pipe (OHP) is an effective heat transfer device for the thermal management of electronic devices. However, the heat transfer mechanism of the OHP was not fully understood due to its complicated operation characteristics. In this paper, the thermal performance of an OHP was experimentally studied. The condensation and evaporation temperature variations were monitored under different heat inputs and were then used to evaluate the OHP system operating characteristics. Thermal resistance was used as a key parameter to evaluate the thermal performance of the OHP system. The results indicated that as the heat input increased from 25 to 100 W, the average thermal resistance decreased while the stable evaporating and condensing temperatures increased. The equivalent heat transfer coefficient was derived theoretically. It showed that the reciprocal of the radial heat transfer coefficient increased with increasing liquid film thickness. Based on this result, an empirical correlation was proposed to evaluate the thermal resistance of an OHP system. This correlation was validated using both the experimental data provided in this study and the data collected from the open literature. The comparison results indicated that the proposed empirical correlation could reasonably predict the thermal resistance under different filling ratios and heat inputs. [ABSTRACT FROM AUTHOR]

In response to the problems of high mass and high thermal resistance in traditional cold plate collectors, the author proposes a shaped and efficient micro-channel collector structure design for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density. The author conducted numerical and experimental studies on the laminar heat transfer in a highly efficient micro-channel shaped collector for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density, the results show that: The relative deviation between the simulated and experimental values of the pressure drop of the micro-channel collector using perfluorotriethylamine as the working fluid is within -20%, and the relative deviation between the simulated and experimental values of the surface temperature is within +3 ° C, the predicted trend of the pressure drop and temperature field of the collector is in good agreement with the experimental values, indicating the feasibility of using numerical simulation methods for performance analysis and design optimization of 3-D printed micro-channel collectors. As the flow rate increases, the pressure drop of the collector increases approximately linearly, while the value increase of the total heat transfer coefficient gradually decreases, and increasing inlet temperature or heating power will reduce pressure drop of collector and increase total heat transfer coefficient. The influence of gravity on the pressure drop and total heat transfer coefficient of micro-channel collectors is less than 1. The straight through micro-channel collector has lower pressure drop and stronger heat transfer ability compared to the folded type collector. [ABSTRACT FROM AUTHOR]

Heat pipe is a two-phase heat transfer device with high effective thermal conductivity and transfer huge amount of heat with minimum temperature gradient in between evaporator and condenser section. This paper objective is to predict the thermal performance in terms of thermal resistance, R, and heat transfer coefficient, h, of screen mesh wick heat pipe with deionized water-TiO2 as working fluid. The input process parameters of heat pipe such as heat load, Q, tilt angle, θ, and concentration of nanofluid, ϕ, were modeled and optimized by utilizing response surface methodology with MINITAB-17 software to attain minimum thermal resistance and maximum heat transfer coefficient. The minimum thermal resistance of 0.1764 °C per W and maximum heat transfer coefficient of 1411.52 W/m² °C was obtained under the optimized conditions of 200 W heat load, 57.2° tilt angle, and 0.159 vol.% concentration of nanofluid. [ABSTRACT FROM AUTHOR]

This paper discusses the experimental studies performed on a single closed loop pulsating heat pipe (CLPHP) to evaluate its thermal performance. The pulsating heat pipe is brass which has a single closed loop. Aluminium oxide (Al2O3) and deionized (DI) water nanofluid were utilized as working fluids, with different volume concentrations of aluminium oxide nanoparticles of 0.05 %, 0.5 % and 1%. The aluminium oxide particles are mixed with water in the two-step method to produce a stable suspension. Experiments are carried out in the horizontal mode with watt loads of heat inputs ranging from 10 w to 100 w. The temperature differences between the evaporator and condenser portions, thermal resistance, heat transfer coefficient and thermal conductivity are the parameters used to determine thermal performance. The thermal resistance of aluminium oxide and DI water nanofluid was the lowest, having 48 % less than that of water. The effective thermal conductivity of the heat pipe improves as the concentration of nanoparticles increases. The comparison between experimental results and computational fluid dynamics (CFD) simulation results CLPHP was carried out under the same condition. [ABSTRACT FROM AUTHOR]

Double-layer heat tubes have been designed to effectively reduce the occurrence of heat pipe rupture accidents. However, inter-tube thermal contact resistance can decrease heat transfer efficiency, thus hampering the heat dissipation in the primary loop system of lead-bismuth reactors. Therefore, optimizing the design of double-layer heat tubes is necessary. This work focuses on the double-layer heat exchanger of a lead-bismuth reactor and utilizes gallium-based graphene nanofluids as a thermal interface material to fill the gap between the heat tubes. Furthermore, the impact of the length, wall thickness, outer diameter, and spacing of heat tubes on the heat transfer performance of the double-layer heat exchanger with and without the nanofluids has been analyzed. The study aims to optimize the JF factor and cost-effectiveness ratio (CER). Genetic algorithms are employed to optimize and evaluate the heat transfer performance of the main heat exchanger based on the four aforementioned parameters. Consequently, a new design scheme is obtained for the double-layer heat exchanger, which increases the optimized overall heat transfer coefficient of the main heat exchanger by 5.79%, pressure drop in the primary loop by 2.32%, JF factor by 5%, and CER by 24.62%. These results demonstrate that the gallium-based graphene nanofluids can effectively enhance the heat transfer performance of the double-layer heat exchanger while reducing the likelihood of steam generator tube rupture accidents. [ABSTRACT FROM AUTHOR]

Thermal control systems have been introduced as an important part of electronic devices, enabling thermal management of their electronic components. Loop heat pipe (LHP) is a passive two-phase heat transfer device with significant potential for numerous applications, such as aerospace applications, high-power LEDs, and solar central receivers. Its advantages are high heat transfer capability, low thermal resistance, long-distance heat transfer, and compact structure. The essential role of wick structures on the performance of LHPs has already been highlighted, but no comprehensive review is available that deals with different parameters such as LHP design and wick size, which are largely decisive and effective in achieving a practical level of thermal transmission governed by wick structures. To rely on this necessity, this article summarizes, analyzes, and classifies advancements in the design and fabrication of wick structures. The main conclusion to be drawn after careful monitoring and weighing of the related literature is that LHPs with composites and additively manufactured wicks show a higher heat transfer coefficient than other conventional structures. Indeed, future works should be focused on the design of more structurally efficient wicks, which may allow us to optimize materials and geometrical parameters of wick structure for higher heat transfer through LHPs. [ABSTRACT FROM AUTHOR]