查看更多>>摘要：Recently emerged composite Fe3O4-CNTs/water nanofluids, serves as a new working medium with high controllability and special flow properties under magnetic field, which can be utilized for the energy saving and cooling of wireless charging equipment. Herein, we studied a cooling system with superhydrophobic (SHP) surface coupled with magnetic nanofluids. Experiments on convective heat transfer are carried out, and the performance of SHP surface is evaluated comprehensively. In addition, the influence of micro-groove, gas-liquid ratio and magnetic field intensity on the heat transfer performance of system is also studied through numerical simulations. Compared with the traditional forced convection cooling method, magnetic fluid on SHP surface destroys the thermal boundary layer under magnetic field, reduces the overall thermal resistance, and improves the heat exchange effect. Compared with water, magnetic fluid can increase the system temperature difference to 21.53%, meanwhile, the heat transfer efficiency of the whole cooling system can improve by 31.39%, under magnetic field. Furthermore, a new idea of flow model on SHP surface is also proposed in this work. Reported results illustrate an advanced cooling method realized via utilization of SHP surface with magnetic nanofluids and magnetic regulation.
查看更多>>摘要：In this work, the adsorption/desorption kinetics of a consolidated bed, for adsorption heat pumps application, coated with a new composite adsorbent material based on SAPO-34 zeolite in a matrix of sulfonated poly(etherether-ketone) was investigated. The heat exchanger was coated by drop casting with a composite zeolite/polymer mixture containing 90 wt% of SAPO-34 powder. The adsorption/desorption kinetic was investigated using the Thermal Large Temperature Jump method and compared with the same heat exchanger filled with loose grains of SAPO-34. The coated heat exchanger exhibits very high specific cooling capacity with a very fast adsorption kinetic. The characteristic times were approximately 39% lower compared to zeolite grains filled adsorber. Analogously, the obtained maximum specific power value was 85% higher than that of the uncoated one.
查看更多>>摘要：A flow boiling heat transfer experiment has been carried out in a square arranged 5 x 5 vertical rod bundle. The inlet pressure of the test section ranges from 3.5 to 7 MPa, mass flux varies from 250 to 500 kg/m(2).s, heat flux changes from 180 to 200 kW/m(2), and the vapor quality is lower than 0.25. The wall superheating degree data at the onset of nucleate boiling (ONB) point and the heat transfer data of both subcooled and saturated flow boiling regions are obtained. Parametric effects on wall superheating degree at ONB point and flow boiling heat transfer coefficient (HTC) are examined. For the present test conditions, an increase in mass flux or system pressure will decrease the wall superheating degree. The HTC in the subcooled and saturated boiling regions is not sensitive to the change of mass flux, while it increases in system pressure. The experimental data also have been compared with the existing empirical correlations. For the wall superheating degree, the existing ONB correlations are all significantly deviated from the experimental data, and a new ONB correlation is proposed to predict the experimental data. For the HTC in the subcooled boiling region, the Shah correlation provides good prediction accuracy for the current experimental data. For the HTC in the saturated boiling region, the selected correlations are all significantly deviated from the experimental data, and a new saturated boiling correlation that has a higher prediction accuracy for present data is established.
查看更多>>摘要：Impingement/effusion cooling systems are widely used in gas turbines owing to their extremely high cooling effectiveness. However, excessive flow resistance has become an obstacle to its wider application. Previous studies have focused more on improving the heat transfer performance, usually without focusing on its pressure loss. In this paper, a novel roughened target plate is proposed to improve heat transfer while reducing pressure loss. Two novel streamlined roughness elements are proposed: similar round protuberances and similar trapezoid ribs. The experiments were performed using the transient liquid crystal (TLC) method, adopting the transverse heat conduction correction technique. The influence of the Reynolds number (Re) and rib height on the heat transfer performance and related pressure loss was experimentally investigated. All data were compared with the flat plate. A numerical simulation was also conducted to provide flow field analysis to explain the enhancement mechanism. The results show that the protuberance can shorten the jet-to-plate distance to enhance heat transfer in the stagnant region. The surface of the arc side of the protuberance and rib can prevent the impinging jets from making sharp turns, resulting in reduced pressure loss. The maximum enhancement for the area-averaged Nusselt number (Nu) was achieved by the highest rib. The pressure loss for all roughened plates was lower than that of the flat plate. The rib with a moderate height provided the highest pressure loss reduction. The highest rib provided the highest heat transfer improvement at equal pumping powers of up to 26.2%. This study confirms the capacity of streamlined roughness elements to enhance impingement heat transfer with reduced pressure loss.
查看更多>>摘要：Due to the high importance of heat transfer, especially convection type, in industrial applications finding some methods to increase the rate of heat transfer and consequently the efficiency of the heat transfer equipment has always been of interest to researchers. Ultrasound is a highly efficient and reliable technique for enhancing convective heat transfer due to its unique phenomena inside the fluid under its irradiation, such as acoustic cavitation and acoustic streaming. In heat exchangers, equipment in which forced convection is the dominant mechanism, ultrasound has shown a positive effect on increasing the efficiency by enhancing forced convective heat transfer itself and reducing fouling. The present paper summarizes some of the research literature regarding the applications of ultrasound interference in free and forced convection heat transfer systems, focusing more on those published in the last decade.
查看更多>>摘要：This paper reports an analysis on leading edge impingement cooling of a turbine blade under real operation conditions of gas turbine. In the experiments, both mainstream and cooling air are heated to real high temperatures, and overall cooling effectiveness on the external blade mid-span surface is measured. Numerical strategy including RNG k-epsilon turbulence model is validated by the experimental data. Impingement cooling models with and without separators (Model A and Model B) are used as specimens, and the effects of high temperature conditions, separators and temperature ratios are discussed. The results indicate that: 1) When jet Reynolds number, mass flow ratio and temperature ratio are matched to the real conditions, the Nusselt numbers predicted by low temperature conditions can be generally matched, exclude the forepart of the internal surface at the blade leading edge. But the error of overall cooling effectiveness on the blade external surface is not neglected. 2) The application of separators can prevent the heat transfer deterioration caused by cross flow with extending the heat exchange area, thus the leading edge with separators can be further cooled over 30 K compared to the traditional design. 3) Under the real operating conditions of gas turbine, two new correlations between the surface averaged Nusselt number with jet Reynolds number and temperature ratio are suggested.
查看更多>>摘要：The solar-driven interfacial water evaporation technique enables to sustainably produce potable water from sewage, wastewater, and seawater. Limited by the advanced functional materials and structures, however, the contradiction between high evaporation rate and low heat loss needs to be further optimized in terms of improving energy efficiency. Herein, a two-dimensional solar absorber in which the vertical substrate pumps water to the top surface for sustainable evaporation and reducing heat conduction channels between the evaporation surface and the bulk water is introduced. In addition, the surplus heat of the solar absorber is directly and quickly conducted to a thermoelectric device for electricity generation. This configuration endows the hybrid device with a power density of 1.2 W m(- 2) at an external resistance of 4 omega together with an evaporation rate of 4.51 kg m(- 2) h(-1) at 4 suns illumination. Importantly, both the fast response of the hybrid device to the optical concentration and the repeatability of the output current are well supported. Such a hybrid device provides an opportunity to construct an on-site and/or off-network water treatment system with low energy consumption and trade investment.
NSTL
Elsevier