Showing papers on "Subcooling published in 2020"
TL;DR: In this paper, a surface oxidation and chemical modification method is employed to modify copper foam surface's wettability, and the surface is covered with a nanosheet to improve thermal performance.
64 citations
TL;DR: In this paper, the authors investigated the effect of liquid subcooling on the heat transfer performance of a graphene oxide (GO) nanocoating surface with distilled water at atmospheric pressure, and they found that the enhanced wettability and high thermal conductivity of the surface were mainly attributed to the increased surface roughness.
45 citations
TL;DR: In this article, the authors developed a wet steam model to investigate the flow structure inside a supersonic separator with the co-existence of non-equilibrium condensation and shock waves.
45 citations
TL;DR: In this paper, a nano phase change material emulsion (NPCME)-based cooling system for prismatic Li-ion batteries under high-rate discharge was presented, and the results indicated that the NPCME can obtain a better cooling effect than water if the inlet temperature is below and near the melting point.
43 citations
TL;DR: In this paper, a honeycomb-like microporous super-hydrophobic surface was studied with non-condensable gases (NCG) concentrations up to 28% for stable coalescence-induced droplet jumping with high heat flux.
41 citations
TL;DR: In this article, the effects of nano-oil on various performance parameters of the vapour compression refrigeration systems such as refrigeration capacity, compressor power, compressor discharge temperature and last but not the least, the coefficient of performance (COP) of the refrigeration system.
Abstract: The current research is focused on the application of nanoparticles in vapour compression refrigeration systems. The major aim of the study is to investigate the effects of nano-oil on various performance parameters of the vapour compression refrigeration systems such as refrigeration capacity, compressor power, compressor discharge temperature and last but not the least, the coefficient of performance (COP) of the refrigeration system. Nano-oil was prepared by dispersing Al2O3 nanoparticles in PAG oil. Al2O3 nanoparticles were chosen because of aluminium oxide's superior thermophysical properties and a low dielectric constant in comparison to other commonly used nanoparticles such as CuO and TiO2. The above-mentioned performance parameters were compared for broadly two different cases, viz., VCRS working on R134a/PAG mixture and VCRS working on R134a/PAG/Al2O3 (R134a/nano-oil) mixture. The system analysis was conducted at several evaporator temperatures ranging from -11 °C to 1 °C and at two different condenser temperatures, viz., 30 °C and 34 °C. The dispersion of nanoparticles into the compressor oil resulted in a higher degree of subcooling at the condenser exit. It was also found that the COP of the system increased by as much as 6.5 % due to the addition of nanoparticles in the system.
41 citations
TL;DR: In this article, the effects of heat flux, subcooling, nozzle-to-surface height, and injection pressures on the surface temperature uniformity in a spray cooling application were studied, and the distribution of droplet diameter and the spray volumetric flux was found to significantly vary under the above experimental conditions.
39 citations
TL;DR: In this article, the significant effects of imposed wall heat flux oscillation on bubble characteristics of subcooled flow boiling with R-134a in horizontal annular ducts are experimentally performed in details.
35 citations
TL;DR: It is reported that the density of template-free electrodeposited copper nanocones can maximally reach 1.5 × 106 /mm2 by the synergistic control of substrate surface roughness, poly(ethylene glycol) molecular weight and PEG concentration.
Abstract: Currently, it is still a great challenge to obtain copper-based high-efficient dropwise condensation heat transfer (CHT) interfaces via template-free electrodepositing technologies. Here, we report that the density of template-free electrodeposited copper nanocones can maximally reach 1.5 × 106/mm2 by the synergistic control of substrate surface roughness, poly(ethylene glycol) (PEG) molecular weight, and PEG concentration. After thiol modification, the densely packed copper nanocone samples can present low-adhesive superhydrophobicity and condensate microdrop self-jumping function at ambient environment. Condensation heat and mass transfer characterizations show that the CHT coefficient of copper surfaces can maximally enhance 98% for 20 °C vapor and 51% for 40 °C vapor by in situ growth of superhydrophobic densely packed copper nanocones. Although the dropwise condensation mode can change from the jumping mode to the mixed jumping and sweeping mode and the shedding-off mode along with the increase of surface subcooling and vapor temperature, the CHT performance of the nanosample is still superior to that of the contrast flat hydrophobic surface during the whole testing range of surface subcooling. As vapor temperature increases to 80 °C, the CHT performance of the nanosample is inferior to that of the contrast sample. The CHT enhancement under low-temperature vapor should be ascribed to the enhancement of small-drop mass transfer ability caused by low-adhesive superhydrophobicity nature of nanosample surfaces. Their performance degradation mainly results from increased drop-drop drag force along with the increase of surface subcooling and vapor temperature. In sharp contrast, the CHT deterioration under high-temperature vapor should be ascribed to larger drop-surface adhesion and drop-drop drag force. The former is caused by vapor penetration, whereas the latter is caused by the dramatically increased nucleation density and growth rate of condensates. These findings would help design and develop copper-based high-efficiency condensation heat transfer interfaces.
35 citations
TL;DR: In this article, interconnected microchannels with reentrant cavities (IMRCs) were developed by using facile and effective microfabrication methods to enhance the pool boiling performance in industrial applications for high heat-flux electronics cooling.
34 citations
TL;DR: In this article, the authors developed reentrant microchannels structures (RMS) by the Selective Laser Melting (SLM) technique for pool boiling enhancement, which were of parallel Ω-shaped Reentrant channels with rough wall surfaces built of bronze powder.
TL;DR: In this article, the optimal working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system were determined and two correlations were proposed to determine the optimal pressure and sub-cooling as function the gas-cooler outlet temperature and the evaporation level.
Abstract: Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level.
TL;DR: In this paper, a theoretical model was developed to investigate the effects of the pinch point in gas cooler and the utilization of internal heat exchanger (IHX) on the optimal discharge pressure and system performance.
Abstract: In transcritical CO2 heat pump water heater, the pinch point in gas cooler and the utilization of internal heat exchanger (IHX) both have a significant impact on the optimal discharge pressure and system performance. A theoretical model was developed to investigate the effects, and the results demonstrated that when the water inlet temperature was low, the pinch point prevented the gas cooler outlet temperature from approaching the water inlet temperature at low discharge pressure, which impaired the coefficient of performance (COP). The application of IHX could reduce the gas cooler outlet temperature by 4.9 °C when the water inlet temperature was 10 °C and the discharge pressure was 8.5 MPa. In this condition, combining with the subcooling effect of IHX, the COP was accordingly improved by 26.3%. Regardless of the working condition, using IHX lowered the optimal discharge pressure and enhanced corresponding optimal COP. In addition, parametric analyses were conducted, and the results indicated that the augment of water outlet temperature and ambient temperature resulted in the rise of optimal discharge pressure. The increase of water inlet temperature mostly enlarged the optimal discharge pressure as well. Overall, the optimal discharge pressure varied within a range of 8.53 MPa to 13.38 MPa. The reduction of optimal discharge pressure caused by using IHX intensified with the increase of water inlet and outlet temperature. Nevertheless, the effect of ambient temperature was various depending on the working condition. The reduction of optimal discharge could be up to 1.18 MPa when the effectiveness of IHX was 0.6.
TL;DR: In this article, a new idea by coupling the pinning act of the micro-pin-fins and the cluster bubble nucleation of nonuniform nanowalls, was proposed to improve the boiling performance on micro-nano composited surface in the low surface tension liquid.
TL;DR: In this paper, a wettability gradient was introduced to gradually change the pattern widths of the hydrophobic and hydrophilic surfaces to enhance condensation heat transfer under low subcooling conditions.
TL;DR: In this article, a two-phase, three-dimensional numerical method for subcooled flow boiling has been developed using a self-defined solver based on OpenFOAM.
TL;DR: In this paper, a high-speed camera was used to closely observe the bubble behaviors on a horizontal aluminum heating surface under high mass flux, and the experimental results indicated that both bubble departure diameter (BDD) and bubble contact diameter (BCD) reduce with increasing system pressure, increasing flow velocity, increasing subcooling, and decreasing wall superheat.
TL;DR: In this article, the authors investigated the influence of surface condition, solid thermal properties and liquid subcooling on transient boiling heat transfer on fuel rodlet surface temperature and heat flux.
TL;DR: In this article, a three-dimensional, laminar, multi-phase, transient numerical model is developed to simulate flow boiling in microchannels and the results show that the vapour blocking in the channel near the outlet is primarily responsible for instabilities and oscillations in the pressure drop, the surface temperature, and the mass flux.
TL;DR: In this paper, the authors investigated the pool boiling heat transfer performance of non-uniform micro-pillar surfaces and found that surface area enhancement ratio and wickability are not the decisive factors that influences CHF for FC-72, and the uniformity of microstructures should be considered when predicting the CHF.
TL;DR: In this paper, a comparison of the thermal performance of two medium temperature sugar alcohol based PCMs of erythritol (C4H10O4) and xylitol (C5H12O5) was presented.
Abstract: Phase change material (PCM) based thermal energy storage systems decrease fossil fuel consumption and can help to reduce environmental impacts. However, extensive application of PCMs are hindered owing to their low thermal conductivity, causing slow charging and discharging processes. In the present work, a comparison of the thermal performance of two medium temperature sugar alcohol based PCMs of erythritol (C4H10O4) and xylitol (C5H12O5) in a vertical double spiral coil unit is presented. Effects of the operating parameters such as volume flow rate and inlet temperature of the heat transfer fluid (HTF) Therminol-55 on the phase change behavior of the PCMs were investigated. Temperature variation of PCMs at different locations of the storage unit, melt fraction and heat storage/discharge rate were obtained. Melting of PCMs was a faster process owing to the impact of natural convection. Furthermore, the double spiral coil storage unit provided suitable thermal performance, achieving high PCM melting rate. Quantitatively, erythritol stored 790 kJ of heat in 60 min for an HTF inlet temperature of 155 °C. For the same flow rate and HTF temperature difference, xylitol stored 450 kJ of heat in 35 min. Therefore, erythritol exhibited superior charging characteristics than xylitol; however, subcooling obstructed the discharging performance of erythritol. On the other hand, no subcooling effect was noticed during the discharging of xylitol.
TL;DR: In this article, comparative energy, exergy and economic analysis of natural refrigerant couples working in a cascade refrigeration system incorporated with a flash tank in its higher temperature cycle and a flash intercooler with indirect sub-cooler in its lower temperature cycle have been done.
TL;DR: In this article, the authors experimentally explored heat transfer through a horizontal metal-foam tube with a constant wall heat flux during the sub-cooled flow boiling of water.
TL;DR: In this paper, the phase change rate of MPCMS in laminar heat transfer from inlet to outlet, considering the influence of wall material of micro-encapsulated phase change material (MPCM) particles on heat transfer process, were established respectively, and the accuracy of the models were verified.
TL;DR: In this article, the phase field method was used to conduct simulation and predict dendrite growth behavior during the crystallization of sea ice, and an experimental setup focusing on the directional crystallisation of binary water-NaCl solutions was established to verify the theoretical model.
TL;DR: In this article, an ORC test rig with switchable evaporators and condensers is established to investigate the operation behavior of these heat exchangers and the influences of their heat transfer area on the performance of the ORC system.
TL;DR: In this paper, a novel solar-assisted resorption-subcooled compression hybrid heat pump system with higher heating capacity under cold climate condition for space heating is proposed, which combines the different strengths of vapor compression heat pump (VCHP) and absorption-resorption heat pump(ARHP).
TL;DR: In this article, a mathematical model of dropwise condensation of moist air over a textured surface has been developed in order to evaluate the efficacy and sustainability of condensation in various operating parameters, such as temperature, relative humidity, subcooling of the substrate, thermophysical properties of the condensing substrate, and physico-chemical properties.
TL;DR: In this paper, the effect of inlet subcooling on the flow boiling characteristics of HFE-7200 in a multi-microchannel heat sink was evaluated at a mass flux of 200 kg/m2 s and system pressure of 1 bar.