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Applied thermal engineering
Elservier Science Ltd.
Applied thermal engineering

Elservier Science Ltd.

1359-4311

Applied thermal engineering/Journal Applied thermal engineeringISTPSCIEI
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    Self-adaptive cooling of chips with unevenly distributed high heat fluxes

    Li, XiuXuan, Yimin
    10页
    查看更多>>摘要：The heat load scenario of a real chip is unsteady and spatially variable and gives rise to regions of concentrated high power. Conventional liquid cooling techniques are always inadequate to tailor the flow distribution to the changing thermal environment and cool the resulting high-heat-flux regions effectively. In this work, the selfadaptive cooling for unevenly distributed high heat fluxes is proposed. It contains a matrix of microfluidic units with integrated thermal-sensitive hydrogel valves. The units are independently controlled and deliver the coolant to where it is needed. A numerical model is developed to investigate the flow and temperature distribution of the cooling unit. By introducing the self-adaptive mechanism, the near-wall flow is enhanced remarkably. Nonuniform heat fluxes of up to 460 W/cm2 are effectively dissipated by means of the developed self-adaptive cooling method. The maximum surface temperature drop amounts to 22.6 K, meanwhile the total flow rate can be reduced by nearly an order of magnitude. The microfluidic unit array adapts to local heat fluxes by reconfiguring its internal flow-channel structure automatically and thus movable hotspots are elaborately cooled. The self-adaptive cooling scheme offers both effective and smart thermal management for modern electronic devices.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation and multiparameter analysis of variable conductance heat pipes

    Guo, YuandongLiu, ChangPan, HaoranLyu, Wei...
    12页
    查看更多>>摘要：This paper presents an experimental investigation of the influence of multiple parameters on the thermal performance of variable conductance heat pipes (VCHPs) according to theoretical design and analysis. The operating characteristics of four VCHPs, such as the steady-state temperature, thermal resistance, and degree of self-control, were systematically analysed and compared. The design principles were examined considering the structural matching design, thermal-physical properties, and charging mass of the fluids. The examined types included the cold-gas reservoir VCHP (CGR-VCHP) and the hot-gas reservoir VCHP (HGR-VCHP), whose steady-state operating temperatures and thermal resistances were compared. The HGR-VCHP attained a higher degree of self-control than the CGR-VCHP for the same heat pipe (HP) structure size. The effects of the reservoir volume of the CGR-VCHP were experimentally and theoretically assessed. Compared to a small volume of 33.66 mL, a large volume of 43.27 mL increased the self-control, with dT(va)/dQ dropping from 0.272 K/J to 0.042 K/J. Moreover, the temperature difference decreased from 13.6 to 2.09 degrees C under the same heat load increase of 50 W. Both R22 and ammonia were chosen as working fluids due to their similar sensitivity factors. The self-control ability of the ammonia CGR-VCHP was higher than that of the R22 CGR-VCHP based on the obtained experimental and theoretically calculated results. This research provides valuable insights into VCHP multiparameter analysis, which are of great significance for the practical application of VCHPs in self-control thermal.
      原文链接:
    • NSTL
    • Elsevier

    Research on coupling performance of heat transfer and throttling of microchannel J-T effect cryocoolers

    She, HailongCui, XiaoyuWeng, JianhuaChang, Zhihao...
    15页
    查看更多>>摘要：To solve the shortcomings of small cooling capacity of the current Joule-Thomson (J-T) cryocooler, a multi-layer microchannel J-T cryocooler is designed and fabricated by printed circuit board technology. The characteristic of the cryocooler is that there exists heat transfer while throttling. The coupling effect of heat transfer and throttling affects the overall performance of cryocooler. Therefore, the steady-state model was established for each part of the cryocooler. The P-h diagram of N-2 was calculated by the model. Considering the variation of J-T coefficient (mu(jt)) in the process, the coupling performance of heat transfer and throttling in the J-T cryocooler were analyzed. A new parameter, J-T efficiency (eta(jt)), was proposed to evaluate the J-T effect. Additionally, according to the dependence of mu(jt) with temperature and pressure, the refrigeration performance of the cryocooler under different working conditions was simulated. The results show that the heat transfer in the throttle can enhance the throttling effect. When the inlet temperature is 285.0 K and the inlet pressure increases to 18.00 MPa, the N-2 temperature at the cold end reaches 116.3 K, and the gross cooling capacity is 4.55 W. When the inlet pressure is 6.00 MPa and the inlet temperature reduces to 195.0 K, the temperature at the cold end can reach to the saturated temperature of 103.2 K, and the maximum gross cooling capacity is 7.68 W. For the two groups of working conditions, the heat transfer in the throttle can enhance the J-T effect. eta(jt) reaches 95.87% and 94.76%, the proportion of temperature drop caused by J-T effect is 56.10% and 68.03% of the total temperature drops, respectively. Finally, the variation laws of inlet temperature and eta(jt) are analyzed when N-2 reaches saturated temperature under different pressures to guide the selection of inlet parameters.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation of tank stratification in liquid air energy storage (LAES) system

    Heo, Jin YoungPark, Jung HwanLee, Jeong Ik
    17页
    查看更多>>摘要：Liquid air energy storage technology is a technology that stores liquid air in case of excess power supply and evaporates the stored liquid air to start a power generation cycle when there is an electric power demand. When liquid air is stored for a long-time during operation, safety and performance degradation can be caused or mitigated by the tank stratification. To investigate the tank stratification phenomenon and associated issues, an experimental facility is constructed. The heat ingress is controlled with respect to changing vacuum level in the experiment. Furthermore, the conditions under which stratification occurs are defined in terms of temperature and concentration, and based on this, the stratification stability ratio and the stability map are defined and evaluated experimentally. The results show that the time required for destratification is 8-29% shorter for liquid air mixture cases than for liquid nitrogen. Moreover, the time required for destratification is 2.4 times longer for the high tank pressure cases, and it is 39% shorter for the case of high heat ingress. From experimental observations, an operation strategy utilizing stratification inside the liquid air storage tank is newly suggested that can minimize the boil-off gas of liquid air in the tank.
      原文链接:
    • NSTL
    • Elsevier

    Experimental study of water freezing process improvement using ultrasound

    Daghooghi-Mobarakeh, HoomanSubramanian, VarunPhelan, Patrick E.
    11页
    查看更多>>摘要：The phase change process of freezing water is an important application in several fields such as ice making, food freezing technologies, pharmaceuticals, etc. Due to the widespread usage of ice-related products, process improvements in this technology can potentially lead to substantial energy savings. It is well known that supercooling has a negative effect on the overall time and energy consumption of the freezing process. Therefore, ultrasound is proposed as a technique to improve the freezing process by eliminating the supercooling effect and the resulting energy savings is investigated. An experimental study was conducted to analyze the energy expenditures in the freezing process with and without the application of ultrasound. After a set of preliminary experiments, an intermittent application of ultrasound at 3.52 W & 8.25 W power levels was found to be more effective than constant-power application. The supercooling phenomenon was thoroughly studied through iterative experiments. It was also found that the application of ultrasound during the freezing process led to the formation of shard-like ice crystals. From the intermittent ultrasound experiments performed at 3.52 W & 8.25 W power levels, energy savings relative to no-ultrasound processes of 12.4% and 10.8% were observed, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Experimental study on the influence of bionic channel structure and nanofluids on power generation characteristics of waste heat utilisation equipment

    Tu, JianglinQi, CongTang, ZhiboTian, Zhen...
    26页
    查看更多>>摘要：To recover waste heat resources and improve the utilisation rate of waste heat, a cogeneration system based on bionics was designed. To maximise the utilisation rate of waste heat, the effects of different bionic channel structures (angular frequency omega = 20, 25, and 30 rad/s; amplitude A = 1, 2, and 3 mm; and phase shift alpha = 0 degrees, 90 degrees, and 1801 on the power generation characteristics were studied experimentally. The innovation of this study lies in designing bionic structures with different shapes and replacing traditional working fluids with nanofluids. The experimental results showed that, when the working medium was a CuO-H2O nanofluid, the temperature at the hot end of the thermoelectric plate increased by 7.19%. For different bionic structures, the thermoelectric conversion efficiency of waste heat utilisation equipment with omega = 30 rad/s, A = 3 mm, and alpha = 180 degrees was the highest, being 15.29%, 18.79%, and 6.97% higher than those with omega = 20 rad/s, A = 1 mm, and alpha = 0 degrees, respectively. The results of this study can provide guidance for the design and operation of the power generation characteristics of waste heat utilisation equipment.
      原文链接:
    • NSTL
    • Elsevier

    Thermodynamic analysis of a CCHP system integrated with a regenerative organic flash cycle

    Ai, TianchaoChen, HongweiJia, JiandongSong, Yangfan...
    14页
    查看更多>>摘要：Combined cooling, heating and power (CCHP) systems have received wide attention for their potential of high efficiency and energy conservation. In this work, a novel CCHP system is designed coupling the solar thermal input (ST) system and the regenerative organic flash cycle (OFC) system. The OFC subsystem could recycle two kinds of heat sources to achieve cascade utilization of heat energy. The CCHP-ST-OFC system is evaluated by comparing with the conventional CCHP system and the CCHP-ST-ORC system (organic Rankine cycle). The effects of several operating parameters on the thermodynamic performance are discussed. Based on the negative feedback regulation, an operation strategy is proposed and applied to buildings to verify the thermodynamic economy. The results demonstrate that the electricity and heat provisions are 275.0 kW and 211.5 kW, which are 4.7 kW and 19.3 kW higher than the CCHP-ST-ORC system. The electricity of the OFC subsystem is 15.0 kW and 47% higher than the ORC system. Moreover, changing the smoke outlet temperature in the waste heat recovery equipment could effectively adjust the heat provision and power generation. The trend of the day and night power generation with the mass flow rate of the heat source is reversed. The energy provision and performance increased with the increasing partial load ratio of the internal combustion engine. The building case study reveals that the exergy efficiency of the CCHP-ST-OFC system is 38.7% and the primary energy ratio is 53.1%, respectively. Meanwhile, the natural gas consumption of the CCHP-ST-OFC system is 5.14 x 105 m3/year, with a 9% reduction than the CCHP-ST-ORC system.
      原文链接:
    • NSTL
    • Elsevier

    Significant energy saving in industrial natural draught furnace: A model-based investigation

    Karem, S.Al-Obaidi, M. A.Alsadaie, S.John, Y. M....
    21页
    查看更多>>摘要：In all industrial petrochemical plants and refineries, the furnace is the source of heat resulting from fuel combustion with air. The model-based furnace simulation is considered one of the efficient methods help to reduce the energy loss and maintain fixed refinery revenues, conserving energy, and finally reducing external fuel consumption and total fuel cost. In this paper, a model-based simulation is carried out for a natural air draught industrial scale furnace related to Liquified Petroleum Gas (LPG) production plant in Libya to thoroughly investigate the most responsible factors in lowering the furnace butane exit temperature, which is supposed to be two degrees Fahrenheit higher than inlet temperature. Therefore, to resolve this industrial problem, Aspen Hysys V10, coupling with EDR (exchanger design and rating) is used to carry out rigorous model-based simulation. This is specifically used to assess the impact of heat loss from inside the firebox to the surrounding medium and heat loss from the furnace stack and walls, besides the effect of excess air on the furnace efficiency. Furthermore, this research intends to verify whether the operating conditions, such as furnace tubes inlet flow rate, temperature and pumping pressure, are conforming to the upstream process design specifications or need to be adjusted. The results confirm that increasing furnace outlet temperature two degrees Fahrenheit from off specification 190 degrees F instead of 184 degrees F is successfully achieved by decreasing upstream stream flowrate 25% below the operating value and cutback excess air gradually until 20%. Also, the results clarify the necessity of increasing the flue gas temperature by 7% over design condition, to gain a significant reduction of heat loss of 31.6% and reach as low as 35.5 MBtu/hr. This improvement is achieved using optimum operating conditions of an excess air of 20%, and flue gas oxygen content of 3.3% delivered to stack. Accordingly, the furnace efficiency has been increased by 18% to hit 58.9%. Furthermore, the heat loss from the furnace walls can be also reduced by 68% from 5.41 MBtu/hr to 1.7 MBtu/hr by increasing the refractory wall thickness to 6 in., which entails an increase in the furnace efficiency by 3.66% to reach 58.96%. Decreasing the heat loss fraction through the refractory wall, pip doors, expansion windows and refractory hair cracks would also increase the efficiency by 21% to reach a high of 59.7%. Accordingly, a significant reduction in daily fuel consumption is observed, which costs 1.7 M$ per year. The outcomes of this research clearly show the potential of reducing the operation and maintenance costs significantly.
      原文链接:
    • NSTL
    • Elsevier

    Investigations on the impact of phase change on single plume flash boiling radial expansion and drop-sizing characteristics

    Xu, QinglinQiu, ShuyiWang, ShangningHung, David...
    13页
    查看更多>>摘要：Flash boiling atomization has been considered a promising approach to enhance spray atomization. Increasing the fuel temperature or reducing the ambient pressure can promote the phase-change of the spray, and boiling can be achieved during this process, so that spray atomization can be enhanced. However, the strong evaporative feature of flash boiling atomization induced a high vapor concentration in the plume thus changes spray characteristics. To understand the impacts of the vapor phase on spray properties in the aspects of radial expansion and drop sizing, this investigation is carried out based on a customized single-hole fuel injector with practical fuel injection settings. High-speed backlit imaging and Phase Doppler Interferometry are used to quantify the characteristics of flash boiling sprays under various boundary conditions. Macroscopic and microscopic spray morphologies were captured and it was shown that the geometry of the flash boiling spray plume was significantly impacted by the expansion of the compressed vapor phase. The evaporation of the droplets was studied by the single droplet evaporation model and the results were compared against drop sizing measurements. It was found that the evaporation and elimination of liquid droplets might affect the statistical interpretation of the drop sizing results, which is a notable feature for flash boiling sprays.
      原文链接:
    • NSTL
    • Elsevier

    Parametric study of a regenerative heat exchanger for ventilation with a periodic change in the air flow direction

    Aktershev, S. P.Mezentsev, I., VMezentseva, N. N.
    8页
    查看更多>>摘要：A two-dimensional mathematical model of a regenerative heat exchanger for a ventilation system with a periodic change in the air flow direction is developed. This system allows a significant economy of the thermal energy for heating buildings in winter. Such devices are quite compact, has no moving details and do not require significant electrical power for their operation, while they can provide the ventilation needs of both whole buildings and individual rooms in multi-storey buildings. The definition of energy efficiency of a regenerative heat exchanger is formulated in terms of reducing the loss of thermal energy. It is shown, that regenerative heat exchanger can really reduce thermal energy losses by ventilation more than by 90%. Parametric studies are fulfilled using the method of numerical simulation and the influence of operating and design parameters of the heat exchanger on its energy efficiency is revealed. In numerical calculations, a group of parameters that most strongly affect the energy efficiency of the ventilation system is identified, and recommendations for optimizing these parameters are given.
      原文链接:
    • NSTL
    • Elsevier