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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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    An efficient model for predicting heat extraction from a multiple-well enhanced geothermal system in the presence of areal flow

    Jia, ShanpoZhang, XiJeffrey, Robert G.Zhao, Gaofeng...
    17页
    查看更多>>摘要：To maximize the heat production from an enhanced geothermal system (EGS), multiple-well layouts have been proposed. In this paper, a semi-analytical model is developed for predicting heat extraction from a multiple-well system including injection and production wells, which are connected by a single planar aquifer with a constant thickness. By utilizing velocity potentials and streamline functions, analytical solutions for the temperature along streamlines in the Laplace space are obtained, followed by their numerical inversion to time-domain results. The model is verified through comparisons with existing results and those obtained by commercial package. Besides, the model is found to be very efficient in terms of seconds per run, compared to pure numerical models, in saving CPU time and providing acceptable results. After that, the thermal performance of eight different well layouts is compared to find the optimal well layout in terms of heat extraction for the EGS at Qiabuqia geothermal area in the Gonghe Basin, China. It is found that the magnitude and direction of the areal flow, and the well layout significantly influence the fluid flow and thermal behaviors. When the areal flow velocity is low (i.e. 10(-5) m/s), the layout with 4 injection wells (IWs) and 5 production wells (PWs) exhibit the overall best output performance in terms of output thermal power (OTP) and total heat extracted (THE). However, if the areal flow velocity is high (i.e. 5 x 10(-5 )m/s), a dipole-well system, can maximize the OTP and THE if the two wells are placed parallel to the areal flow with the downstream IW and upstream PW.
      原文链接:
    • NSTL
    • Elsevier

    Effect of humidifier characteristics on performance of a small-scale humidification-dehumidification desalination system

    Soomro, Saddam HussainSantosh, RavichandranBak, Chul-UYoo, Chan-Ho...
    12页
    查看更多>>摘要：Desalination, the process of obtaining potable water from seawater, has been regarded as an alternative solution to address the global issue of freshwater shortages. Considering the design, cost, and low-grade energy-driven advantages of the humidification-dehumidification (HDH) desalination process, this study aims to experimentally and theoretically investigate a laboratory-scale HDH system using different hydrophobic packing materials (i.e., hackettes, saddles, and snowflakes). We developed a mathematical model that simulates the HDH process by estimating the temperature, productivity, and gain output ratio (GOR) of each packing material and compared the results with the experimental data. The hackettes humidifier packing was found to exhibit the highest mass transfer coefficient (0.00331 kg/m(2) s), resulting in maximum productivity (0.64 kg/h at 80 ?) and GOR (1.45 at 50 ?). This was followed by saddle packing (0.00291 kg/m(2) s, 0.59 kg/h at 80 ?, and 1.15 at 50?, respectively), which contributed to a better HDH process than snowflakes (0.00227 kg/m(2)s, 0.56 kg/h at 80 ?, and 1.13 at ?, respectively) due to improved heat and mass transfer efficiency in saddle packing. In addition, the effects of operating parameters (e.g., feed temperature, feed salinity, air, and water mass flow rates) on the thermal performance of HDH systems with different packings were investigated. It was confirmed that the results of the mathematical model were in good agreement with the experimental data.
      原文链接:
    • NSTL
    • Elsevier

    Defining the cooling and heating solar efficiency of a building component skin: application to a modular living wall

    Azkorra-Larrinaga, Z.Erkoreka-Gonzalez, A.Perez-Iribarren, E.Romero-Anton, N....
    16页
    查看更多>>摘要：The thermal evaluation of building components composed of a base wall with a solar passive skin solution, such as a vertical/roof greenery system, ventilated facade, reflective painting, etc., is usually performed as a whole. In this research, it has been proven that, independently of the base wall thermal inertia and insulation level, the temperature of the outermost surface layer of any building component during sunny hours is mainly dependent on the ambient air temperature and relative humidity, the incident global solar radiation and the building skin behaviour. The latter assumption has been proven on the south wall of a reference building simulated with TRNSYS. The south wall properties have been varied and the building has been subjected to different climates. The assumption's validity has been checked for twelve south wall cases: a combination of 2 thermal transmittance, 2 thermal inertia and 3 climates. Each case has been simulated for a whole year. Based on this finding and the local ambient conditions for sunny hours, the hypothetical achievable maximum and minimum temperatures for the outermost surface layer have been defined. Then, based on the outermost surface temperature experimental measurements, the cooling and heating solar efficiencies valid for any skin solution have been defined. Furthermore, the developed methodology has been applied to a vertical living wall tested for a whole year under the accuracy and quality procedure of the PASLINK method. In this way, the cooling and heating solar efficiencies were experimentally determined for this skin solution for both, the hot cold seasons. The study has shown that the cooling efficiency during the hot season is 90.8%. As expected, even during sunny summer hours, the presence of water positively affects the performance of the facade, as it brings the base wall external surface temperature close to the ambient wet bulb temperature, therefore reducing the cooling load of the building. For the cold season, the cooling efficiency was similar, at 90.3%, which means a heating efficiency of 9.7%. Again, even for sunny winter hours, the values of the external surface temperature tend towards the ambient air wet bulb temperature, resulting in an increase in the heating demand. These experimental efficiency values allow the heating or cooling behaviour of different skin solutions to be comparable with a single number that is independent of the base wall composition. In addition, independently of the base wall composition, once the experimental efficiency value of a given skin solution is known, it allows (during sunny hours) the base wall outermost surface temperature to be calculated with precision. The latter makes it possible to increase the accuracy of the estimation of the heating and cooling demands of such methods as the degree-day method.
      原文链接:
    • NSTL
    • Elsevier

    Simplified effectiveness and number of transfer unit model for a vacuum membrane dehumidifier applied to air conditioning

    Cheon, Seong-YongCho, Hye-JinJeong, Jae-Weon
    15页
    查看更多>>摘要：This paper purposed to develop a simplified model for a vacuum membrane dehumidifier in an air conditioning system. The proposed model is a gray model that uses mathematical equations that are deducted from the effectiveness and number of the transfer unit of the heat exchanger and a regression equation for the ratio of humidity capacities (X factor) analogous to the heat capacities ratio of heat exchangers. The applicability of the simplified effectiveness and number of transfer unit methods to vacuum-based membrane dehumidifiers in air conditioning systems has been validated via numerical simulation and experimental data. The error bound for the validation of the numerical simulation and experimental data for dehumidification performance (i.e., outlet humidity ratio and dehumidification effectiveness) was 20%. In addition, an operation example using the simplified model was performed to control the vacuum pressure of the vacuum-based membrane dehumidifier in the air-conditioning system. The results show that the proposed algorithm using the simplified model exhibits an energy-saving potential of 42.4% compared to the conventional vacuum-based membrane dehumidification operated in a variable air volume system.
      原文链接:
    • NSTL
    • Elsevier

    The performance evaluation for thermal protection of turbine vane with film cooling and thermal barrier coating

    Meng, ZeweiLiu, YongbaoLi, YujieHe, Xing...
    12页
    查看更多>>摘要：When conducting wind tunnel heat transfer test to evaluate the cooling performance of the turbine, it is difficult and costly to simulate the extremely high temperature gas of the real working conditions, and small temperature difference and room temperature test is usually used instead. In order to evaluate the cooling performance under real working conditions from the experimental results at room temperature, the corresponding evaluation method needs to be studied. In this paper, a turbine vane with film cooling and thermal barrier coating (TBC) is used as the study object. By introducing an improved driving temperature and adopting one-dimensional heat transfer analysis, an improved analytical expression of overall cooling effectiveness, which is independent of temperature, is derived and analyzed. Through numerical calculation, the overall cooling effectiveness defined by different reference temperatures are compared. The results show that the heat transfer of the turbine vane with film cooling and TBC is complicated. The influence of the internal cooling should be considered when calculating the external convective heat transfer. The temperature-independent overall cooling effectiveness on the TBC surface and the superalloy surface are obtained, respectively. The improved overall cooling effectiveness is more sensitive to the thermal resistance of the superalloy compared with the thermal resistance of the TBC. The overall cooling effectiveness can be improved by increasing the internal or external convective heat transfer coefficient. In order to obtain an accurate overall cooling effectiveness (dimensionless wall temperatures), it is necessary to satisfy similarities of four dimensionless parameters, including the B-iot numbers (Bi-TBC ,Bi-w), the ratio of external and internal convective heat transfer coefficients (h(e)/h(i)) and the ratio of gained convective heat transfer coefficient and external convective heat transfer coefficient (h(e,i)/h(e)).
      原文链接:
    • NSTL
    • Elsevier

    Experimental study on heat transfer and pressure drop characteristics in a microchannel heat exchanger assembly with S-shaped fins

    Song, YinxiZhou, XiangZhang, FeixiJiao, Ming...
    11页
    查看更多>>摘要：Experimental studies on the water-to-water heat transfer and flow resistance characteristics of a microchannel heat exchanger assembly with S-shaped fins were conducted using the high-temperature and high-pressure water open experimental loop at Shanghai Jiao Tong University. The effects of different Reynold numbers of both the hot and cold sides on the heat transfer and flow resistance characteristics were analyzed. Correlations for the Nu number and friction factor for both the hot and cold sides were gained based on the experimental data. The same Nusselt correlation was used for both the hot and cold sides, and the fitting results showed satisfactory accuracy, where the fitting error was within & PLUSMN;15%. The power-law scheme was used to fit the total friction factor correlations, and the fitting results showed a fitting error of & PLUSMN;15% and & PLUSMN;12% for the hot and the cold sides, respectively. The correlations proposed in this study can be used in the design of this type of heat exchanger.
      原文链接:
    • NSTL
    • Elsevier

    Benefits of metal-organic frameworks sorbents for sorbent wheels used in air conditioning systems

    Shahvari, Saba Zakeri R.Kalkhorani, Vahid Ahmadi D.Wade, CaseyClark, Jordan...
    13页
    查看更多>>摘要：Sorbent wheels are used in air conditioning systems to aid in dehumidification. The sorbents conventionally employed in these devices have linear, Type I or II water sorption isotherms requiring high regeneration temperatures. Metal Organic Frameworks (MOFs), a new class of sorbent materials, can be regenerated at much lower temperatures thanks to their Type IV or V isotherms and steep adsorption step. In this work we investigate the benefits of using MOFs as sorbents in dehumidification wheels in air conditioning systems. We first develop a first-principles model of a typical system in the Modelica language and validate it with experimental data . We then investigate the effect of replacing the most commonly used solid sorbent, silica gel, with each of several systematically selected MOFs. Our results show that the best performing MOFs of the candidates tested (Co2Cl2(BTDD) (Co), Al-fumarate (Al) or CAU-23 (Al)) can regenerated at temperatures as low as 40-60 degrees C depending on ambient conditions, in contrast to 80-140 degrees C for silica gel. Also, energy requirements of a MOF-based sorbent wheel can be from 1/2 to 1/8 of the energy required for silica gel-based systems depending on ambient conditions.
      原文链接:
    • NSTL
    • Elsevier

    Thermofluid characterization of nanofluids in spray cooling

    Marseglia, GuidoSanches, M.Ribeiro, A. P. C.Moreira, A. L. N....
    17页
    查看更多>>摘要：The current study addresses a parametric characterization of nanofluid sprays as a way to improve the thermal performance of spray cooling systems. The nanofluids are prepared using as base solution of distilled water with 0.05% (m/m) cetyltrimethylammonium bromide - CTAB in which nanoparticles of alumina and silver are mixed at different concentrations, namely 0.5%, 1% and 2% (m/m). The effect of the shape of the nanoparticles is also considered. These nanofluids are sprayed using a pressure-swirl atomizer and impact, vertically at two different heights, onto an AISI 304 stainless steel foil. This foil is heated by Joule effect, with two imposed currents, delivering 915 and 2100 W/m(2). Infrared thermography is used to measure the thermal footprint from which the dissipated heat flux is calculated. Results show that, in steady state operation, the lowest surface temperature is obtained with the 0.5% (m/m) alumina nanofluid, while increasing alumina nanoparticles, concentration increases the radial temperature distributions on the surface. Results also show a mild effect of the shape of the nanoparticles. Hence, lowest surface foil temperatures are achieved with the silver nanofluid with spherical particles, when compared with the same nanofluid with triangular particles. Heat transfer coefficients decreased with increasing thermal conductivity and dynamic viscosity of the nanofluids. On the other hand, a positive correlation is found between the specific heat capacity of the nanofluids and the spray cooling capacity. For the range of experimental conditions covered in this work, nanofluids have proven to increase the thermal performance of the spray.
      原文链接:
    • NSTL
    • Elsevier

    Life cycle assessment of desiccant-Dew point evaporative cooling systems with water reclamation for poultry houses in hot and humid climate

    Harrouz, Jean PaulKatramiz, ElvireGhali, KamelOuahrani, Djamel...
    19页
    查看更多>>摘要：Desiccant - dew point evaporative based cooling systems is known to be an effective system for the ventilation and cooling of poultry houses in hot and humid climates. However, they suffer from high water consumption that hinders their application in desert regions. In this work, it is proposed to integrate a water reclamation unit with the cooling system to produce water from the adsorbent's humid regeneration stream. The performance of the hybrid cooling and water reclamation unit is evaluated for two desiccants: conventional (silica gel), which is cheap but has low water capacity, and novel (MIL-101-Cr, a type of metal organic framework), which is expensive but has high water capacity. The system was sized, and its operation was optimized using both adsorbents for a case study of a typical poultry house module located in the predominantly hot and humid climate of Qatar. This is achieved by developing numerical models for the different system's subcomponents, which are then validated with the published data. An artificial neural network was trained using the numerical model of water adsorption to accelerate the computational time of the genetic algorithm used for the performance optimization. A lifecycle cost comparative analysis is conducted to determine the integrated system most costeffective adsorbent.Over the entire cooling season, it was found that the hybrid system using MIL-101-Cr resulted in 17% and 48% reduction in the thermal and electrical energy consumption compared to the one using silica gel. This has offered thus a 27% lower operating cost with a payback period of 11 years using the current market price of MIL-101-Cr.
      原文链接:
    • NSTL
    • Elsevier