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[ASME ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - San Francisco, California, USA (Monday 27 August 2018)] ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel
摘要： For improving the functionality and signal speed of electronic devices, components have been miniaturized and an increasing number of elements have been packaged in the device. As a result there has been a steady rise in the amount of heat necessitated to be dissipated from the electronic device. Recently microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging, In the present study an experimental study of subcooled flow boiling in a high-aspect-ratio, one-sided heating rectangular microchannel with gap depth of 0.52 mm and width of 5 mm was conducted with deionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 ℃. The boiling curves, flow pattern and onset of nucleate boiling of subcooled flow boiling were investigated through instrumental measurements and a high speed camera. It was found that the slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, and the slope was greater for lower mass fluxes, with lower superheat required for boiling incipience. As for the visualization images, for relatively lower mass fluxes the bubbles generated were larger and not easy to depart from the vertical upward placed narrow microchannel wall, giving elongated bubbly flow and reverse backflow. The thin film evaporation mechanism dominated the entire test section due to the elongated bubbles and transient local dryout as well as rewetting occurred. Meanwhile the initiative superheat and heat flux of onset of nucleate boiling were compared with existing correlations in the literature with good agreement.
关键词： microchannel heat sinks,heat transfer,subcooled flow boiling,electronic cooling,flow pattern visualization
更新于2025-09-09 09:28:46
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Numerical investigation and experimental validation of an infrared measurement approach for surface heat flux distribution using a multi-color-reference
摘要： Accurate measurement of heat flux (HF) is significant in both industrial engineering and scientific research. It is acknowledged that the radiative HF can be easily determined by radiometers. In order to measure the conductive or convective HF distribution flowing across a surface, this paper presents a novel non-contact measuring method based on the infrared (IR) technique and inverse heat transfer method (IHTM). In addition, a specially designed multi-color-reference (MCR) which is composed of four sectors with four different known emissivity will be attached to the focused surface in the practical measurement. Therefore, different radiation signals among the four different sectors of MCR as well as the focused surface will be detected by an IR camera, through which a whole radiation temperature map can be obtained. Based on the differences in the radiation temperatures of the surface and MCR, the IHTM can be adopted to yield useful boundary conditions such as emissivity of the surface, convective heat transfer coefficient, and the critical HF distribution. The measuring method presented in this study combines the advantages of contact and non-contact measurement, which can accurately obtain the HF distribution under the difficult-contacted conditions such as the HF monitoring of a boiling furnace, HF estimating of the aerodynamic heating surface, etc. Numerical simulation and experimental verification were organized to justify the newly-developed measuring method. Relative error in the simulation is estimated to be less than 2%, and that in the experiment is calculated to be around 4.23%. The result displays a relatively high precision of the measuring method, demonstrating that such a method can be applied in practical application.
关键词： Infrared technique,Heat flux measurement,Emissivity,Heat transfer,IHTM
更新于2025-09-09 09:28:46
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Thermal performance of vortex-based solar particle receivers for sensible heating
摘要： We report a first-order assessment of a novel vortex-based solar particle receiver and the sensitivity of its thermal performance to a number of key operational parameters. This assessment is made with a one-dimensional numerical model developed here to adapt the zonal method to calculate heat and mass transport within the enclosure of the solar vortex receiver (SVR) and to incorporate radiative and convective heat transfer between the particle phase, the air phase and the receiver wall together with re-radiative and conductive loss from the receiver. This simplified one-dimensional model allows for the systematic assessment of first order trends of mass and energy balance within the SVR and is used here to advance understanding of the dominant mechanisms controlling its thermal performance. Sensitivity studies of the thermal performance of the SVR reveal that the receiver can be configured to operate as either an air-heater or a particle-heater, depending primarily on the particle mass loading. For the present SVR configuration, the critical value of mass loading, / ≈ 1 was found to define the boundary, above which the device acts as a particle heater, and below which it acts as an air heater. Furthermore, an assessment of the two-phase flow direction found that a counter-flow (relative to the incident concentrated solar radiation) tends to result in a higher efficiency than a co-flow direction. The first order trends of the sensitivity of thermal performance of the SVR to the particle and air mass flow rates, particle size and receiver length were also assessed, finding that the ratio of receiver thermal input to heat capacity of the two-phase flow has a controlling influence on the thermal efficiency of the SVR, particularly with the front entry configuration. Overall receiver thermal efficiencies of up to 88% were predicted for the SVR operating with high mass flow rates of both particles and air, but it is expected that the thermal efficiency of the device for all operating conditions assessed here would increase with an increase in receiver scale from the laboratory-scale device considered here.
关键词： Solar particle receiver,Heat transfer,CST,Solar vortex receiver,Concentrated solar thermal
更新于2025-09-09 09:28:46
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[ASME ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - San Francisco, California, USA (Monday 27 August 2018)] ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - Practical Concerns for Adoption of Microjet Cooling
摘要： As power densities in advanced electronics continue to rise, the need for high performance thermal solutions becomes increasingly important. Liquid jet impingement has been applied to cooling high power-density electronics due to its ability to dissipate large heat fluxes while maintaining an acceptable operating temperature in the device. Recently, microjets have been embedded within the device substrate, forming a compact solution that is highly scalable. Many practical questions remain, however, on whether microjet technology is ready for actual implementation. In this work, we address several important questions that impede adoption of the technology. Numerical analysis and experimental data are provided to demonstrate the tradeoff between thermal performance and driving pressure requirements through pumping analysis. Additional mechanical concerns regarding robustness to clogging and resistance to erosion are addressed through a 1000-hour extended lifetime test.
关键词： electronics cooling,microjet cooling,erosion,heat transfer,thermal management,clogging
更新于2025-09-09 09:28:46
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Tomography-based determination of Nusselt number correlation for the porous volumetric solar receiver with different geometrical parameters
摘要： Pore-scale numerical models of the porous volumetric solar receiver are established in this paper. By using the X-ray computed tomography and the imaging processing techniques, models of porous media with different geometrical parameters are reconstructed. The conjugate heat transfer process in the porous volumetric solar receiver is solved based on the direct pore-scale numerical simulation. The turbulent effect of fluid flow inside porous geometry is considered by the Shear-Stress Transport k-ω model and the absorbed solar energy is simulated by following the Beer’s law. The results present that the inlet velocity and the geometrical parameters influence the thermal performance of the porous volumetric solar receiver. Larger inlet velocity tends to enhance the convective heat transfer between fluid and solid phases meanwhile decreases noticeably the overall temperature. Receiver with larger porosity is preferred because it limits the reflection losses. The Nusselt number increases as the porosity becomes larger. As a result, the general correlation of Nusselt number for the porous volumetric solar receiver is derived as a function of porosity and Reynolds number. This correlation is applicable with the porosity ranging from 0.74 to 0.89 and the pore Reynolds number ranging from 3 to 233.
关键词： Solar energy,Pore-scale numerical simulation,Convective heat transfer,Volumetric solar receiver,Nusselt number correlation,Porous media
更新于2025-09-09 09:28:46
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Modeling and analysis of solar air channels with attachments of different shapes
摘要： Purpose – This paper aims to report the results of numerical analysis of turbulent ?uid ?ow and forced-convection heat transfer in solar air channels with baf?e-type attachments of various shapes. The effect of recon?guring baf?e geometry on the local and average heat transfer coef?cients and pressure drop measurements in the whole domain investigated at constant surface temperature condition along the top and bottom channels’ walls is studied by comparing 15 forms of the baf?e, which are simple (?at rectangular), triangular, trapezoidal, cascaded rectangular-triangular, diamond, arc, corrugated, t, S, V, double V (or W), Z, T, G and epsilon (or e)-shaped, with the Reynolds number changing from 12,000 to 32,000. Design/methodology/approach – The baf?ed channel ?ow model is controlled by the Reynolds-averaged Navier–Stokes equations, besides the k-epsilon (or k-e) turbulence model and the energy equation. The ?nite volume method, by means of commercial computational ?uid dynamics software FLUENT is used in this research work. Findings – Over the range investigated, the Z-shaped baf?e gives a higher thermal enhancement factor than with simple, triangular, trapezoidal, cascaded rectangular-triangular, diamond, arc, corrugated, t, S, V, W, T, G and e-shaped baf?es by about 3.569-20.809; 3.696-20.127; 3.916-20.498; 1.834-12.154; 1.758-12.107; 7.272-23.333; 6.509-22.965; 8.917-26.463; 8.257-23.759; 5.513-18.960; 8.331-27.016; 7.520-26.592; 6.452-24.324; and 0.637-17.139 per cent, respectively. Thus, the baf?e of Z-geometry is considered as the best modern model of obstacles to signi?cantly improve the dynamic and thermal performance of the turbulent air?ow within the solar channel. Originality/value – This analysis reports an interesting strategy to enhance thermal transfer in solar air channels by use of attachments with various shapes
关键词： Air ?ow,Heat transfer,Turbulent regime,Baf?e,Solar air channel,CFD
更新于2025-09-09 09:28:46
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[ASME ASME 2017 Power Conference Joint With ICOPE-17 collocated with the ASME 2017 11th International Conference on Energy Sustainability, the ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2017 Nuclear Forum - Charlotte, North Carolina, USA (Monday 26 June 2017)] Volume 2: I&C, Digital Controls, and Influence of Human Factors; Plant Construction Issues and Supply Chain Management; Plant Operations, Maintenance, Aging Management, Reliability and Performance; Renewable Energy Systems: Solar, Wind, Hydro and Geothermal; Risk Management, Safety and Cyber Security; Steam Turbine-Generators, Electric Generators, Transformers, Switchgear, and Electric BOP and Auxiliaries; Student Competition; Thermal Hydraulics and Computational Fluid Dynamics - Heat Transfer Performance of LiF–NaF–KF Salt in a Corrugated Receiver Tube With Non-Uniform Solar Flux
摘要： The heat flux on the receiver tube is non-uniform because of uneven solar flux and receiver structure, which causes overheating and thermal stress failure of receiver and affected safe operations of the Concentrated Solar Power(CSP) system. In order to reduce the temperature difference in receiver tube wall and improve the efficiency of CSP system, the ternary eutectic salt LiF–NaF–KF (46.5–11.5–42 wt.%, hereafter FLiNaK), which has a better high thermal stability than that of nitrate salts at operating temperature of 900 °C, is selected as HTF, and heat transfer performance of FLiNaK in a corrugated receive tube with non-uniform heat flux is simulated by CFD software in the present work. The numerical results reveal that the non-uniform heat flux has a great influence on the temperature distributions of the receive tube and FLiNaK salt. Compared with the result of bare tube, the corrugated tube can not only significantly reduce the temperature difference in tube wall and salt by improving the uniformity of temperature distribution but also enhance the heat transfer of the salt, where the heat transfer coefficient increases with the Reynolds number and heat flux. Moreover, the enhanced effect of the corrugated tube depends on both the pitch and the height of ridges. It is found that the heat transfer coefficient of the salt gets a maximum when the ratio of the height of ridge to the pitch is 0.2. The research presented here may provide guidelines for design optimization of receiver tube in CSP system.
关键词： heat transfer,FLiNaK,non-uniform heat flux,corrugated tube,Concentrated Solar Power
更新于2025-09-04 15:30:14
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A Performance Evaluation of a Solar Air Heater Using Different Shaped Ribs Mounted on the Absorber Plate—A Review
摘要： In this paper, the effect of various shapes of ribs used in Solar Air Heaters (SAHs) was discussed. The review is concentrated on the geometry of the rib and its location on the SAH panel. Both numerical and experimental works were considered for discussion with dry air and Nano ?uids as a working ?uid. The in?uence of various shapes, such as an L shape, W shape, V shape, Multiple V shape, V shape with a gap, detachable & attachable ribs etc., was analyzed. The common fact observed from this analysis is that the implementation of arti?cial roughness in the absorber plate results in a considerable increase in the rate of heat transfer. Further, it is observed that ‘Multiple V-shaped with open between the ribs’ results in the maximum thermal enhancement when compared to the other shapes.
关键词： shape of rib,solar air heater,friction factor,heat transfer
更新于2025-09-04 15:30:14
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - MicroSol-R: Versatile solar facility for research and industry
摘要： Since February 2016, a new CSP micro-power plant called “MicroSol-R” is in operation at PROMES-CNRS. This platform aims at developing research and innovation in the field of heat transfer fluids, thermal energy storage, solar thermal power conversion at small scale, power plant operation strategy, etc. In addition, it was designed to be a useful tool for training. MicroSol-R is a versatile facility open to collaboration with industry and laboratories. This paper presents the facility and first results after one year of operation. The performances and characteristics of the solar field, the thermocline heat storage and the organic Rankine cycle are presented.
关键词： CSP,thermal energy storage,solar thermal power,heat transfer fluids,organic Rankine cycle,MicroSol-R
更新于2025-09-04 15:30:14
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The Monte Carlo Ray-Trace Method in Radiation Heat Transfer and Applied Optics || Fundamentals of Ray Tracing
摘要： A ray is defined as the collection of straight-line path segments followed by an energy bundle from its point of emission to its point of absorption. The definition includes the possibility of intermediate reflection, scattering, refraction, and even diffraction events. Ray tracing involves the application of basic mathematics to the process of identifying the intersection of ray segments with surfaces. Most engineering and science students acquire the required mathematical tools long before they enter university. The current chapter provides a review of the mathematical principles governing ray tracing and the related issues of meshing and indexing.
关键词： Monte Carlo Method,Radiation Heat Transfer,Applied Optics,Mathematical Principles,Ray Tracing
更新于2025-09-04 15:30:14