首页期刊导航|Applied thermal engineering
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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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    A design methodology for thermal storages in heat pump systems to reduce partial-load losses

    Paolo ContiAlessandro FrancoCarlo BartoliDaniele Testi...
    16页
    查看更多>>摘要：The paper deals with the sizing and the arrangement of thermal energy storages in heat pump systems for building service. Partial-load losses are an increasingly important phenomenon in high-efficiency buildings, even for inverter heat pumps, due to the low average thermal demand compared to the installed capacity. The paper discusses partial-load losses through the data collected during a "hardware-in-the-loop" experimental campaign. Then, it presents a straightforward methodology that can be practically used by HVAC designers to easily determine the volume and the best arrangement of thermal energy storages in heat pump systems. Shortly, thermal storage in a series configuration is an effective solution to make the compressor work at its maximum performance, provided that the thermal efficiency of the storage is higher than the partial-load penalization coefficient of the heat pump. The proposed design methodology is applied to a test case, consisting of a high-efficiency dwelling: depending on the heat pump control characteristics, the electricity consumption can be reduced up to 45% using a thermal storage. For standard values of the degradation coefficient (0.75-0.9), the seasonal energy saving is in the range 10-20% with a tank loss coefficient lower than 5 W/K.
      原文链接:
    • NSTL
    • Elsevier

    Thermal energy storage enhancement of a forced circulation solar water heater's vertical tank unit using phase change material

    Saif ed-Din FertahiA. SamaoualiT. BouhalA. Arid...
    21页
    查看更多>>摘要：This work aims to investigate the thermodynamic effect of phase change material integration within vertical storage tanks that are connected to forced circulation solar water heaters, on their thermal energy storage capability. The phase change material is encapsulated in cylindrical and elliptical capsules, which are integrated at the bottom, middle and top sections of the tank. Hence, three parametric studies were carried out depending on the geometry of the encapsulation, besides to their integration position inside the tank, through computational fluid dynamic calculations. The numerical model was established under "OpenFOAM" and the enthalpy-porosity method for the phase change phenomena modeling was validated against the experimental data of the literature. For this purpose, the following thermal performance indicators were used: temperature, liquid fraction contours and the tank's energy storage efficiency. It was found that the time required for a complete melting of the phase change material inside the cylindrical capsules is higher than that of the elliptical ones (beyond 17.50 s), for a fixed integrating location. Otherwise, 21, 23 and 17.50 s were necessary for the melting of the phase change material filling the vertical ellipse (top configuration), horizontal ellipse (bottom configuration) and cylindrical cavity (middle configuration) respectively. In addition, results showed that the shapes of phase change materials affect the thermal storage efficiency. For example, 25, 28 and more than 40 s were sufficient to reach 100% of the vertical tank's storage efficiency for the following top configurations: vertical ellipse, horizontal ellipse and cylindrical cavity, respectively. Finally yet importantly, integrating the phase change materials at the middle section of the tank can be considered as the optimal configuration, because it allows a gain of 2℃ compared to the bottom and top zones.
      原文链接:
    • NSTL
    • Elsevier

    Performance characteristics of direct contact refrigeration system based on phase change materials and different refrigerants

    Gansong LuMing LiYali LiuYing Zhang...
    15页
    查看更多>>摘要：In conventional ice storage refrigeration systems, the evaporator copper tube is immersed in a cold storage tank. Therefore, the thickness of the ice layer increases, the thermal conductivity of the evaporator decreases, resulting in a decrease in the system efficiency. To improve the efficiency of the refrigeration system, a new type of direct contact refrigeration system is designed and developed in this study. The direct contact between the refrigerant and water causes ice blockage in the nozzles and pipes. This is a common problem in direct contact refrigeration systems, and therefore, it is necessary to solve this problem. Four types of working media (R22, R134a, R410A, and HR223) are used to solve the problem of ice blockage in nozzles, and the impact on the system performance is discussed. The results showed that the working medium possesses a large latent heat of phase change, resulting in high system efficiency, however, and ice blockage still exists in the nozzles; the maximum efficiency of the system is 1.68. Water is replaced by phase change material (PCM), and the material is used for heat exchange with the refrigerant. The PCM is tetrabutylammonium bromide hydrate (TBAB), and the performance of TBAB with five mass fraction (25 wt%, 30 wt%, 35 wt%, 40 wt%, and 45 wt%) in the system is analysed. The results indicated that the refrigeration system with TBAB can solve the problem of ice blockage in nozzles. In addition, based on the experimental results, the coefficient of performance (COP) of the refrigeration system with TBAB concentration of 25 wt%, 30 wt%, 35 wt%, 40 wt%, and 45 wt% is 3.11, 4.55, 6.23, 4.83, and 4.46, respectively. A series of experiments demonstrate that TBAB of 35 wt% exhibited the best performance in the direct contact refrigeration system. This paper presents a novel and innovative approach to solve the problems of ice blockage in direct contact refrigeration systems to improve system efficiency.
      原文链接:
    • NSTL
    • Elsevier

    Thermal storage integrated into air-source heat pumps to leverage building electrification: A systematic literature review

    Conrado ErmelMarcus V. A. BianchiAna Paula CardosoPaulo S. Schneider...
    17页
    查看更多>>摘要：Air-source heat pumps (ASHPs) can support a decarbonized economy by replacing combustion appliances in homes and electrifying heating systems in buildings. However, ASHPs have not seen significant adoption primarily due to deteriorated performance under cold conditions-at very low temperatures they require auxiliary resistance heating to meet the heating demand and defrost the evaporator. The additional heat lowers the system efficiency. Thermal energy storage (TES) is a candidate technology to help overcome some of these issues. This paper presents a systematic literature review to map the existing research on the integration of TES into ASHPs. Our review of 59 publications indicates that thermal storage increases the ASHP coefficient of performance by 27% on average, albeit with higher initial cost compared to conventional fossil-fueled heating systems. Phase change materials may be ideal to be integrated with ASHPs due to their high energy density and compact design, but only a few publications address TES sizing and design. First and Second Laws of Thermodynamics are widely used to create metrics to assess ASHP-TES integration, and only recently have cost and environmental impact been explored. This literature review suggests that more comprehensive metrics are needed to evaluate the potential benefits of ASHP-TES systems.
      原文链接:
    • NSTL
    • Elsevier

    A Thermal-hydraulic assessment of condensing tube bank heat exchangers for heat and water recovery from flue gas

    Negar MohammadalihaMohammad AmaniMajid Bahrami
    10页
    查看更多>>摘要：Condensing heat exchangers are capable of recovering a significant amount of latent heat at temperatures below 100℃ from the flue gas of combustion-based heating systems due to the presence of water vapor in their exhaust streams. However, the condensation of acids along with water vapor creates a highly-corrosive environment in these heat exchangers. As such, a large majority of these heat exchangers are made from corrosion-resistant alloys, such as stainless steel. Polymer-based materials are cost-effective and have great corrosion-resistant properties. Since the performance parameters of a heat and water recovery unit depend on the size and compactness of their heat exchangers, it is challenging to compare the overall performance of stainless-steel condensing heat exchangers with polymeric ones based on the data available in the literature. The main goal of the present study is to develop and assess the thermal-hydraulic performance of a proof-of-concept condensing heat exchanger made of fluorinated ethylene propylene compared to the same condensing heat exchanger made of stainless steel for heat and water recovery from flue gas. For this purpose, an in-depth parametric study is conducted experimentally to evaluate the water recovery efficiency, total heat recovery rate, and pressure drop in the flow paths. The results revealed that the water recovery efficiency of the unit with a specific size, declines when the mass flow rate of the gas increases, although it enhances the total heat recovery of the unit. Moreover, increasing the volumetric flow rate of the heat transfer fluid flow slightly increases the total heat recovery of the stainless-steel condensing heat exchanger, but has a negligible impact on the total heat recovery rate of the polymer-based heat exchanger. Increasing the humidity ratio of the flue gas or the inlet temperature of heat transfer fluid does not have any significant effect on the flue gas pressure drop. These findings are significantly important and novel as they unlock the potential of using polymer-based materials with thermally conductive additives for latent heat recovery from flue gas.
      原文链接:
    • NSTL
    • Elsevier

    Critical factors and parameters for hybrid Photovoltaic-Thermoelectric systems; review

    D. T. CotfasP. A. CotfasS. MahmoudinezhadM. Louzazni...
    23页
    查看更多>>摘要：Creativity and innovation play an important role in the renewable energy development domain. Alongside research, these lead to the identification of the optimum solutions to use photovoltaic cells and thermoelectric modules (PV/TE) together in a hybrid system. This review paper outlines and discusses critical factors and important design parameters for components and for the hybrid system. In this paper, active material properties of PV and TE devices are introduced. Geometrical structural parameters leading to maximum power generation and conversion efficiency are discussed, and also the new trend in the design of the photovoltaic modules is considered for their integration in the urban landscape. Moreover, performance of the hybrid system is conjugated to effective boundary conditions caused by the solar irradiation, temperature and applied cooling technologies. Furthermore, this review paper, considers the thermal effect of the TE module on the PV cells and electric connections. The thermal interface materials, thermo-mechanical stability, maximum power point tracking techniques including the inverse analysis, the feasibility of the hybrid system, comparison, and uncertainty analysis are also discussed.
      原文链接:
    • NSTL
    • Elsevier

    Frosting mechanism and behaviors on surfaces with simple geometries: A state-of-the-art literature review

    Zhang LongSong MengjieDeng ShimingShen Jun...
    25页
    查看更多>>摘要：Frosting causes negative impacts in many technical and engineering fields, such as refrigeration, air source heat pump, aircraft, wind power generation, and power grids. To alleviate the negative impacts of frosting, studies on frosting characteristics, avoiding and delaying frosting, and defrosting mechanisms and methods have been carried out for decades. Among these studies, frosting characteristics, which are the fundamental basis for defrosting, avoiding, and delaying frosting are consistently the hot research spots. Considering that complex structures can be usually regarded as the combination of simple geometries, in this paper, a comprehensive review of the literature related to the frosting mechanism and behaviors on surfaces with simple geometries is presented. The former covers frost formation process and morphology, frost layer structure model, and frosting characteristic parameters, such as frost thickness and effective frost thermal conductivity. The latter is further divided into six parts based on the configurations of cold surfaces, including flat plates with a fixed surface temperature, flat plates with a fixed base temperature, cylinders, parallel plates, set of fins and semipermeable membranes. Based on the review, the research gaps in the related study fields are identified, and recommendations for further research are offered. The literature review presented in this paper can provide a comprehensive and systematic reference for the people who are working in the study fields where frosting is commonly encountered.
      原文链接:
    • NSTL
    • Elsevier

    Thermal-hydraulic performance of zigzag channels with Bending number below unity for printed circuit heat exchanger

    Shenghui LiuMinyun LiuRuilong LiuRui Guo...
    14页
    查看更多>>摘要：Zigzag-channel printed circuit heat exchanger is one of the leading candidates for the pre-cooler of supercritical carbon dioxide Brayton cycle. A dimensionless number, Bending number, is newly proposed to characterize the bending amplitude of zigzag channels in printed circuit heat exchanger. The existing studies are examined with the help of Bending number and it is found that the thermal-hydraulic performance of zigzag channels with Bending number below unity has not been investigated. To remedy this situation, the thermal-hydraulic performance of zigzag channels with Bending number 0.49 is tested. Experimental result shows an enhancement in convective heat transfer of supercritical carbon dioxide at its pseudo-critical zone. It is also found that there is no obvious transition from laminar flow to turbulent flow within Reynolds number 1560-45700. Flow and heat transfer correlations for the tested zigzag channels are proposed. The new developed Fanning friction factor correlation predicts almost 100% of the experimental data within ±20% error band, and the new developed heat transfer correlation predicts 78.6% of the experimental data within ±25% error band. Comparison with Ngo's correlations, Kim's correlations, and Saeed's correlations demonstrates that both Fanning friction factor and Nusselt number are higher with larger Bending number. Analysis of the thermal-hydraulic performance, (Nu/Nu_0)/(f/f_0)~(1/3), of the tested zigzag channels shows that its combined performance is improved obviously compared with straight channels when both Re and Pr are large.
      原文链接:
    • NSTL
    • Elsevier

    Prospects of heat transfer approaches to dissipate high heat fluxes: Opportunities and challenges

    Ali KosarKhellil Sefiane
    10页
    查看更多>>摘要：The present paper presents a brief discussion of selected promising approaches adopted to achieve high heat fluxes dissipation. The selected techniques include flow boiling in microchannels, spray cooling, use of nanofluids and surface modification. Whilst the two first approaches are established two-phase heat transfer techniques, the use of nanofluids and surface modification are comparatively new approaches used to enhance heat transfer. Achievements, challenges and new research directions in the selected techniques are covered to provide an overview and guideline for researchers and engineers working in this field.
      原文链接:
    • NSTL
    • Elsevier

    Impact of an internal heat exchanger on a transcritical CO_2 heat pump under optimal pressure conditions Optimal-pressure performance of CO_2 heat pump with IHX

    Ramon A. Oton-MartinezFernando Illan-GomezJose R. Garcia-CascalesF. J. S. Velasco...
    12页
    查看更多>>摘要：Transcritical R744 (CO_2) heat pumps are a low-GWP high-efficiency alternative for domestic hot water generation and space heating. For high set-point temperatures, however, the COP drops and the optimum operating pressure increases. For this reason, the effect on system performance achieved by the inclusion of an Intermediate Heat Exchanger (IHX) is analyzed in depth. This is carried out by means of a numerical-experimental approach in which the effectiveness of the IHX and other characteristic parameters of the heat pump cycle are studied as a function of the IHX heat transfer area. The numerical modeling of the heat pump components is implemented for transient simulations of system heating-up process. Experimental tests with and without IHX are carried out with a water-to-water heat pump that feeds an accumulator tank, to assess its influence on the system's COP and the electrical consumption. Simulations reveal that improving the efficiency of the IHX, by increasing the exchange area, improves the system's performance. For the cases with higher IHX exchange area, the optimum pressure in the system is lower. For the heating experiments, the resulting thermodynamic COP is 7.55% higher in the case with IHX, while the effective COP increases by 4.26%. In consequence, the use of the IHX is recommended for the conditions analyzed.
      原文链接:
    • NSTL
    • Elsevier