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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
正式出版
收录年代

    Multi-objective optimization of a concrete thermal energy storage system based on response surface methodology

    Liu, ChunyuYang, Haibin
    13页
    查看更多>>摘要：This paper focusses on the numerical investigation of a concrete thermal energy storage (CTES) system using air as heat transfer fluid (HTF). To reduce the number of simulations and treat complex interactions between parameters, the response surface models for multiple responses are established based on 27 specific design points which are determined by central composite rotation design (CCRD). With the response surface models, the effects of the CTES system's design parameters on its performance are analyzed. The results indicate that the HTF velocity is the most important factor affecting the charging time and charging energy efficiency. The HTF inlet temperature substantially influences the energy storage. The interactions also have a crucial influence on the performance indices. The optimization is carried out to minimize the charging time, and maximize the energy storage and the charging energy efficiency simultaneously. The optimal parameter combination is optimized by the desirability function. The discharging process is further considered, so that the overall performance of the cycle process is optimal. The geometrical parameter of 22 tubes and 4 fins is considered appropriate under the selected operating conditions. The proposed method provides an efficient means to efficient design of CTES unit.
      原文链接:
    • NSTL
    • Elsevier

    Multiobjective geometry optimization of microchannel heat exchanger using real-coded genetic algorithm

    Garcia, John Carlo S.Tanaka, HirokiGiannetti, NiccoloSei, Yuichi...
    13页
    查看更多>>摘要：In this paper, a multiobjective optimization of the structure of a flat-tubed microchannel heat exchanger is performed to reduce its volume and fan power at a specified capacity. Design variables include tube height, tube width, tube length, fin height, and fin pitch. A weight-based, real-coded genetic algorithm is implemented to optimize the design variables within their specified range of dimensions. To further improve the numerical simulations of the microchannel heat exchanger performance, correlations for the air-side Nusselt number, friction factor, and fin efficiency are developed and validated. In the optimization, the Pareto optimal fronts are obtained by varying weights of the two conflicting objectives. A reference microchannel heat exchanger operating at different capacities is optimized. Results show that the volume and fan power of the reference microchannel heat exchanger can be reduced by up to 45% and 51% respectively, depending on the weighting factor selected. The optimization approach of this study provides the optimal solutions at the given domain of geometric parameter dimensions.
      原文链接:
    • NSTL
    • Elsevier

    Experimental study on the cell-jet temperatures of abused prismatic Ni-rich automotive batteries under medium and high states of charge

    Li, WeifengGao, ZhenhaiZhang, BaodiOuyang, Minggao...
    9页
    查看更多>>摘要：The temperature of the battery jet is one of the key basic parameters for the design of battery thermal management system (BTMS) for vehicles, with sufficient results under combustion conditions in the presence of air. However, the original temperature distribution of battery jet in an inert atmosphere and its variation with the state of charge are not very clear for prismatic Ni-rich automotive batteries. This is closer to the real inside environment of the battery pack. In this work, a 50 Ah commercial prismatic cell with a Li(Ni0.6Mn0.2Co0.2)O-2 cathode is triggered to thermal runaway using external heating in a sealed chamber with a nitrogen atmosphere to avoid combustion caused by oxygen from the outside. The results show that the farther away from the safety valve, the lower the temperature of the jet. The jet temperature and its rise rate show an increasing trend with the maximum value of 701 degrees C and 173 degrees C/s detected with increasing states of charge. Therefore, the BTMS design needs to take into account the high thermal load and high thermal shock caused by thermal runaway even in the absence of external air to participate in the combustion.
      原文链接:
    • NSTL
    • Elsevier

    Passive sub-ambient cooling: radiative cooling versus evaporative cooling

    Aili, AblimitYin, XiaoboYang, Ronggui
    10页
    查看更多>>摘要：Day-and-night radiative sky cooling has emerged as a potential alternative to conventional cooling technologies such as refrigeration-based air conditioning and evaporative wet cooling. Both radiative cooling and evaporative cooling can passively achieve sub-ambient cooling without consuming electricity. Although both cooling techniques are subject to impacts from various weather conditions, the extents of the impacts under the same conditions are not well understood. In this work, we experimentally and theoretically study the thermal performances of a passive radiative cooler and a passive evaporative cooler when exposed to a clear night sky. We show that evaporative cooling is better suited for high-temperature and low-humidity weather conditions, with the measured sub-ambient temperatures of the radiative and evaporative coolers being-13.5 degrees C and-15.0 degrees C, respectively, at a low relative humidity of 13% and a high ambient temperature of 26.0 degrees C. On the other hand, radiative cooling is relatively more resilient than evaporative cooling under high-humidity and/or low temperature weather conditions, with the measured sub-ambient temperatures of the coolers being-11.5 degrees C and-10.5 degrees C, respectively, at a slightly higher relative humidity of 32.0% and a slightly lower ambient temperature of 17.0 degrees C. Depending on water availability and weather conditions, both evaporative cooling and radiative cooling can be adopted as mutually supplemental cooling technologies.
      原文链接:
    • NSTL
    • Elsevier

    Off-design modeling of a microturbine combined heat & power system

    Hampel, Christopher A.Braun, Robert J.
    13页
    查看更多>>摘要：There is increasing interest in decision support software tools that evaluate the techno-economic potential of distributed energy system technologies for deployment in combined heat and power (CHP) applications, such as commercial buildings, microgrids, and connected communities. This trend is particularly evident among end-users looking to integrate renewable resources with more traditional CHP technologies for on-site generation and enhanced resiliency. However, many of these software tools do not account for part-load and off-design characteristics of prime mover and heat recovery equipment, resulting in lower accuracy for both the optimal selection and sizing and the economic value proposition of integrated hybrid renewable energy-CHP systems. Microturbine technology is an attractive distributed energy resource whose performance is sensitive to both part-load and off-design (i.e., excursions of ambient conditions away from the design point temperature and pressure) operating conditions but is widely unreported. In the present work, we address this deficiency by developing a detailed, thermodynamic model of a commercial 200 kW microturbine CHP system and paramaterizing results for incorporation into the Renewable Energy Optimization (REopt) tool developed by the National Renewable Energy Laboratory. The details of the microturbine model, including model benchmarking and validation, are presented. Microturbine off-design modeling includes part-load analysis, assessment of ambient sensitivities, and mapping heat recovery heat exchanger response to hot water grade requirements. The model is then exercised in several illustrative examples to depict the numerous factors which alter electric power, electric efficiency, and hot water recovery. Model results show, for example, predictions of a 4 percentage point electric efficiency range occurring between intake air temperatures of -18 to 50 degrees C. Likewise, the model closely predicts the 25 % loss in heat recovery while at -18 degrees C and the 8 % gain in heat recovery while at 35 degrees C. An additional case shows how heat recovery may increase or decrease by 9.5 % of the design value when changing the return water temperature plus-or-minus 22 degrees C. In particular, the impact of ambient conditions on best-possible microturbine performance is conveyed through hourly simulations of the system subjected to the weather of different geographic locations within the United States.
      原文链接:
    • NSTL
    • Elsevier

    A comparative study of pool boiling heat transfer in different porous artery structures

    Zhang, KaiBai, LizhanJin, HaichuanLin, Guiping...
    11页
    查看更多>>摘要：A novel porous artery structure is proposed and experimentally validated to enhance the pool boiling heat transfer performance based on the concept of "phase separation and modulation". In the experiment, multiple rectangular arteries are formed in the bottom of a porous structure, and a thin copper microporous layer is placed between the heating surface and the rectangular arteries. Compared with conventional porous structures, this novel porous artery structure can effectively improve the pool boiling heat transfer performance due to i) increased nucleation site density, ii) improved liquid replenishment by capillarity, and iii) effective liquid/vapor phase separation. Experimental results show that comparing with boiling heat transfer on a plain surface, a 200% higher in CHF, and a 144% higher in heat transfer coefficient (HTC), together with a 59% lower in superheat at the onset of nucleate boiling (ONB) are obtained for this new structure. In addition, the effects of the top and bottom microporous layer thickness and the artery depth on the pool boiling heat transfer performance are investigated, and the inherent physical mechanisms are analyzed.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation on stable/unstable flow behaviors of parallel boiling channels under forced vertical vibrations

    Lee, Wei-ChengChang, Yu-HsienHo, AilingLee, Jin-Der...
    16页
    查看更多>>摘要：Experimental tests were carried out to investigate the dynamic behaviors of parallel boiling channels under stable and unstable flow conditions with/without forced vertical vibrations. The parallel channels with a length of 1.91 m and diameter of 11.9 mm were attached to a vertical vibration platform. The inlet flow was controlled with average velocity of 0.142-0.277 m/s and subcooling of 6.0-12.6 degrees C, and the parallel channels were loaded with heat flux of 12.5-36.9 kW/m2. Overall 35 flow conditions were tested along with three static and vibration subset conditions (f = 0, 1.06 and 1.62 Hz), which covered the stable and unstable flow conditions in the parallel channels, and the dynamic variations of void fraction, pressure difference and temperature were recorded and analyzed. A non-dimensional void difference was proposed to identify the system stability of parallel channels, and fast Fourier transform (FFT) was utilized to extract the dominant frequencies of flow behaviors. While system is stable under vibrations, the dominant frequencies of flow properties were identical to the vibration frequencies; whereas if the system is unstable, the extracted frequencies were dominated by unstable flow oscillations, which are much lower than the vibration frequencies. In addition, the unstable flow oscillation frequencies can increase with increasing inlet velocity and heat flux, and an empirical correlation was proposed for estimating the oscillation frequencies, which can predict the present database with an averaged accuracy of 8.85%.
      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

    Numerical investigation on thermal-hydraulic characteristics of the micro heat sink with gradient distribution pin fin arrays and narrow slots

    Yan, YunfeiXue, ZongguoXu, FuleiLi, Lixian...
    11页
    查看更多>>摘要：Targeting at decreasing the pressure drop in the micro heat sink, a gradient distribution pin fin arrays and narrow slots (GPN) is proposed. In addition, in order to further reduce the pressure drop of the micro heat sink, three improved are proposed, including GPN48, GPN2244, GPN264 by changed the number and position distribution of the pin fin arrays in the narrow slots. The results show that the pressure drop of the three improved gradient distribution pin fin arrays and narrow slots decreases by 28.7%-33.4% at a certain volumetric flow rate (Qv = 120 ml/min, Re = 563) when comparing with the conventional gradient distribution. Furthermore, when Re ranged from 188 to 1125, the maximum wall temperature of the three improved gradient distribution pin fin arrays and narrow slots decreases by 4.4 K-26.6 K when comparing with the gradient distribution (GPN). When the Re = 563, the heat flux limit of GPN is only 82 W/cm(2), while GPN48, GPN2244 and GPN264 reached 109 W/cm(2), 114 W/cm(2) and 120 W/cm(2) respectively. Especially, comparing with GPN, the average heat transfer coefficient of GPN48, GPN2244 and GPN264 increases by 11.9%-23.0% (Re = 118), which greatly improves the application reliability in the micro heat sink.
      原文链接:
    • NSTL
    • Elsevier

    Performance analysis of acceleration effect on paraffin melting in finned copper foam

    Tang, JinchengXie, YongqiChang, ShinanYan, Zhenrong...
    12页
    查看更多>>摘要：Phase change material (PCM) has great potential in thermal control of aircraft electronic components because of their excellent latent heat capacity. In the current work, a finned copper foam phase change energy storage unit (PCESU) was fabricated using n-eicosane, 97.2% porosity copper foam and 0.8 mm fins. The effects of four different heating power i.e. 40 W, 45 W, 50 W, 55 W corresponding to heat flux of 0.4 W/cm(2 ) 0.45 W/cm(2 ) 0.5 W/cm(2), 0.55 W/cm(2) at four different centrifugal acceleration magnitudes, i.e. 0 g, 5 g, 9 g, 13 g with three different acceleration directions on the thermal performance of PCESU were experimentally studied in a systematic manner. Experimental results indicated that: (1) the acceleration direction has a significant effect on the thermal performance of PCESU which can be improved for the cases of vertical and opposite directions, whereas restrained for the case of same direction. Under acceleration condition, the average melting time for the cases of opposite and same direction are 15.19% and 37.10% longer than that for the case of vertical direction, respectively. The temperature difference of PCESU while the melting is completed is 95.12% higher than that for the case of vertical direction on average. (2) the effect of acceleration magnitude on the heat transfer performance can be determined significantly when the acceleration direction is applied. The melting time decreases with the increase of the acceleration magnitude along vertical direction and increases along same direction. The temperature difference decreases with the increase of the acceleration magnitude along vertical direction, whereas increases along opposite or same direction. Moreover, the melting time and temperature difference for acceleration magnitude changing from 0 g to 5 g have an obvious larger change rate than that from 5 g to 9 g and 9 g to13 g. (3) the melting time is negatively correlated to the heating power, whereas the temperature difference is positively correlated to the heating power. The proposed two-dimensional (2D) simplified model can be helpful to reveal the physical mechanism of the thermal performance of PCESU.
      原文链接:
    • NSTL
    • Elsevier