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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
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    Biphilic surface to improve and stabilize pool boiling in vacuum

    Serdyukov, VladimirPatrin, GeorgyMalakhov, IvanSurtaev, Anton...
    11页
    查看更多>>摘要：To date the usage of biphilic surfaces is one of the most promising ways to simultaneously enhance heat transfer and increase critical heat fluxes during boiling. However, the vast majority of studies devoted today to the in-fluence of surfaces with mixed wettability on boiling performance refer to atmospheric pressure conditions. At the same time, the problems of heat transfer rate increasing and stabilizing the boiling process at subatmospheric pressures are particularly acute, which is associated with some features of boiling in a vacuum and its high practical relevance. The paper presents the results of experimental study on the local boiling characteristics, including the bubble departure diameters and emission frequencies, and the heat transfer rate during water boiling on a biphilic surface in the pressure range of 10-102 kPa. As a result of experiments, it was shown that the hydrophobic areas of the fabricated biphilic surface are the sites of continuous vapor bubbles generation in the entire range of the studied pressures. At the same time, the slight increase in the size of detached bubbles and their emission fre-quency from the hydrophobic spots was observed with pressure reduction. It was also demonstrated that in the range of low pressures (less than 40 kPa), the biphilic surface is characterized by noticeably smaller bubble departure diameters and much higher emission frequencies compared to bare surface. The analysis of boiling curves obtained using IR thermography revealed that the developed biphilic surface provides a significant heat transfer enhancement -up to 3.7 times during boiling at subatmospheric pressures compared to bare surface. Moreover, a significant decrease in the surface superheating and in the amplitude of integral temperature oscillations is observed, which represents the boiling stabilization at low subatmospheric pressures (less than 20 kPa) for the fabricated surface.
      原文链接:
    • NSTL
    • Elsevier

    A novel method of measuring microtube wall temperatures by thermocouples to investigate sCO(2) flows

    Oztabak, EfeGokkaya, OguzhanAhn, Hojin
    14页
    查看更多>>摘要：Experimental study on convective heat transfer through microtubes encounters many challenges such as measuring the wall temperature of the tube with a reasonable uncertainty, relatively high heat loss from the outer surface of the tube, and difficulty in measuring the fluid bulk temperature at the tube outlet. These issues become exacerbated with flow at low Reynolds numbers. The present study presents a new method to measure the tube wall temperature with a small solder cast where a thermocouple is embedded. The net heat flux to flows, determined with the heat loss on the outer surface and the axial heat conduction, is integrated to obtain the local mean enthalpy of fluid and then the fluid mean temperature along the tube. Thus, convection heat transfer coefficients are calculated without measuring the mean temperature at the outlet. The new method is successfully validated with laminar water flows through a horizontally configured microtube, 0.501 mm in inner diameter. All Nusselt numbers are found to lie between 4.36 and 4.36 + 10%. Finally, the method developed in this study is applied to supercritical CO2 flowing upward at 8.0 MPa through a microtube, 0.509 mm in inner diameter. For both high and low mass flow rates, a local maximum of the convection heat transfer coefficient is observed at a location where the film temperature is close to the pseudo-critical temperature. On the other hand, the second local maximum of the convection heat transfer coefficient appears only at low mass flow rates.
      原文链接:
    • NSTL
    • Elsevier

    New correlations for the prediction of incipient nucleate boiling in a one-side heated swirl tube

    Lim, Ji HwanPark, MinkyuShin, Seong MinChung, Seong Seock...
    17页
    查看更多>>摘要：Future tokamak cooling systems should always be maintained in a single phase during operation to avoid po-tential hazards caused by vapor. To this end, a correlation to accurately predict sub-cooled flow boiling onset of nucleate boiling (ONB) under the one-side high heat load condition, which is the heat flux condition inside the tokamak, is required. According to this necessity, the ONB of a one-side heated swirl tube was experimentally explored in this study. The inserted swirl tape induces a secondary swirling flow, which causes ONB to occur at a higher heat flux condition than the smooth tube. As the twist ratio of the tape decreased, the ONB heat flux enhancement rate increased. Sub-cooling and mass flow rate have a proportional relationship with ONB heat flux, whereas pressure has an inverse relationship. The prediction accuracy of the existing ONB correlations was evaluated. However, most correlations tended to under-predict the experimental values. Because they were not developed for the purpose of predicting the ONB of the swirl tube under sub-cooled flow conditions, all system parameters and the effect of the swirl tape were not reflected. Therefore, we developed new correlations using Python combined with machine learning.
      原文链接:
    • NSTL
    • Elsevier

    Flow boiling heat transfer, pressure drop and flow patterns of the environmentally friendly refrigerant R1234yf for cooling avionics

    Xu, YuYan, ZihaoLi, Ling
    19页
    查看更多>>摘要：Flow boiling technology is an effective way to solve the heat dissipation problem of avionics. However, studies on the flow boiling characteristics of environmentally friendly refrigerants are still insufficient. To expand the related global database containing both experimental conditions and results, new experimental data are needed. Here, horizontal flow boiling experiments were conducted using R1234yf, and the heat transfer coefficients (HTCs), frictional pressure drops (FPDs) and flow patterns in a 1.88 mm circular minichannel were obtained under mass fluxes, saturation pressures and heat fluxes of 400-870 kg m(-2) s(-1), 0.6-0.8 MPa and 40-65 kW m(-2), respectively. For comparison, experiments using R134a were carried out under the same conditions. The results show that for both R1234yf and R134a, the HTC increased with increasing mass flux, heat flux and saturation pressure, while the FPD decreased with increasing saturation pressure and increased with increasing mass flux but remained almost constant with heat flux. The heat transfer was dominated by nucleate boiling at lower vapor quality and transformed into convective boiling at higher vapor quality, with a threshold vapor quality of around 0.4. Typical flow patterns, including slug flow, throat-annular flow, wavy-annular flow, annular flow, and annular-mist flow, were identified through visualization. Through comparison, it was found that the HTC and FPD of R1234yf are smaller than those of R134a under the same conditions. In addition, based on the experimental HTC and FPD, several correlations yielding smaller predicted deviations are suggested, and new correlations having mean absolute deviations of 9.3 % and 6.3 % for flow boiling HTC and FPD of R1234yf are proposed.
      原文链接:
    • NSTL
    • Elsevier

    Experimental analysis of airflow uniformity and energy consumption in data centers

    Fulpagare, YogeshHsu, Po-HaoWang, Chi-Chuan
    15页
    查看更多>>摘要：Temperature and airflow uniformity are experimentally investigated in this research study along with energy consumption analysis on the laboratory container size small data center. A raised floor plenum (RFP) data center system of size 6 (L) x 3.1 (W) x 2.3 (H) m with one Computer Room Air Handler (CRAH), two rows and each row contains five racks, five 8U simulator cabinets in each rack was constructed to test partial and closed cold aisle containment (CAC). Seven different cases were investigated with variables of perforated tiles (32%, 50 % & 70%), CRAH fan speed (60 Hz, 42 Hz), chiller return water temperature (CRWT) (15 ? & 17 ?) and heating load (full 50 kW, 75% load 37.5 kW). These cases were further analyzed using Rack Cooling Index (RCI) and Supply Heat Index (SHI) along with power consumption scenarios in terms of Coefficient of Performance (COP) and Power Usage Effectiveness (PUE). The uniqueness of this study is experimental investigations of system COP and PUE analysis for a wide range of important variables for partial and closed CAC. It was found that 50% porous tile provided the best airflow and temperature uniformity for the case of partial containment with full and 25% reduced heat load along with full and 30% reduced CRAH speed respectively. Slight recirculation was observed during the reduced CRAH fan speed case at the corner edge of data racks. However, due to additional supply airflow usage, these recirculation's were within the acceptable SHI. Reduction of CRWT reduces the total Heating Ventilation and Air Conditioning (HVAC) power consumption and improves the overall system COP.
      原文链接:
    • NSTL
    • Elsevier

    Flow and heat transfer analysis of a domestic refrigerator with complex wall conditions

    Cui, PeipeiHe, LiangMo, Xiaoabo
    16页
    查看更多>>摘要：The heat transfer and temperature distributions inside the compartments and walls for a domestic refrigerator are vital to food storage and energy consumption. The refrigerator walls consist of many complex structural parts such as anti-condensation tube, vacuum-insulation panels (VIPs) and suction line heat exchanger (SLHX), which are closely related to the heat transfer. To investigate the influence of the complex walls on the heat transfer, this study presents a comprehensive numerical model for the domestic refrigerator with considering the complex wall conditions and an experiment is conducted to validate the accuracy of the model. The flow and temperature distributions inside the compartments are analyzed. The impacts of the anti-condensation tube, VIPs and SLHX on the wall temperature are investigated with and without complex wall conditions. The heat leakage through the walls of the refrigerator into the compartments from the environment is reported. The results show that the complex walls have a large impact on the heat transfer of the refrigerator. The difference in heat transfer between the two conditions with and without complex wall reaches 6.2%. The generic numerical model shows that the complex wall conditions should be considered when the manufacturers calculate the heat load and optimize the wall thickness to design a refrigerator.
      原文链接:
    • NSTL
    • Elsevier

    Novel strategy and multi-scale modelling of integrated multifunctional composite for thermal protection under extreme environment

    Li, WeijieZhang, ZhongweiZhu, MengdieZhang, Jun...
    11页
    查看更多>>摘要：In order to overcome the shortcomings of the heritage thermal protection materials with only a single function as well as the macroscopic evaluation method lacking the consideration of manufacture parameters, in this study, a novel strategy of integrated multifunctional composite with an overall 3-Dimensional reinforcement weave fabric and multifunctional zones was prepared, and a new multi-scale computational modelling for evaluating its thermal protection performance was established. The properties of constitute materials were characterized, as well as the thermal and ablative behavior of the integrated multifunctional composite were tested by oxyacet-ylene test. The new modelling took the detail weaving parameters as well as the physical and chemical mech-anisms of the composite into consideration. The model was solved by our FORTRAN codes. The experimental and simulation results showed that this new integrated composite had high structural efficiency, thermal insulation and recession resistance. The multi-scale computational modelling can be applied on the evaluation of the performance of the integrated woven composite in a bottom-up manner, which gives a refined design method for thermal protection materials.
      原文链接:
    • NSTL
    • Elsevier

    Dehydrogenation performance of metal hydride container utilising MgH2-based composite

    Nyamsi, NyallangWu, ZhenZhang, ZaoxiaoKolesnikov, Andrei...
    16页
    查看更多>>摘要：Mg-based hydrides have gained formidable interest for hydrogen storage applications due to their high intrinsic hydrogen capacity up to 7.6 wt%. However, their ability to absorb/desorb hydrogen is limited by their slow inherent kinetics and the heat and mass transfer within the storage container. The dehydrogenation of the metal hydride material in the container becomes important when coupling with a fuel cell, since the fuel cell requires a constant H-2 flow rate to provide constant power output. In this study, we investigate numerically the dehydrogenation performance of a cylindrical container filled with 300 g of ball milled Mg90Ti10 + 5 wt% C with the objective to identify the operating conditions at which the H-2 flow rate is higher or equal to the threshold for a proper functioning of a fuel cell. The heat exchange in the container is improved by a combination of internal basin-like and external annular fins. The heat transfer characteristics used in the numerical model are determined from the experimental work conducted in our laboratory. The results show that during the dehydrogenation process, at low convective heat transfer coefficient of 5-35 W/m(2) K, the hydride container can supply H-2 to a fuel cell with different power rating from 100 to 250 W for a long period of time with nearly constant flow rate.
      原文链接:
    • NSTL
    • Elsevier

    Sustaining dropwise condensation on nickel-plated copper surfaces with As-grown graphene coatings

    Luo, KaiWang, PengtaoLi, ChenChang, Wei...
    10页
    查看更多>>摘要：Dropwise condensation (DWC) has been extensively investigated owing to its substantially higher efficiency compared with filmwise condensation (FWC). However, performing the highly efficient DWC has been hindered by the durability of existing hydrophobic surface coatings. Graphene grown on Nickel (Ni-Gr composite) has been demonstrated in our previous study to sustain the DWC in an aggressive condition for more than 36 months. Compared with traditional heat exchangers made of copper (Cu) and stainless steel, the high purity requirement of Ni substrate for graphene growth and high material cost greatly limit its practical applications. In this study, the cost-effective nickel-plating technique has been explored to apply the robust Ni-Gr coating on prevail metals such as Cu in industry. DWC can be sustained for more than 180 days without noticeable degradation in a steam/ air mixture environment. After 180 days, the Ni-Gr coating electroplated on the copper surface (Cu-Ni-Gr) can still facilitate DWC with approximately 2.9 times higher condensation heat transfer rate than that of conventional metal surfaces. The consistently superior anticorrosion properties of Cu-Ni-Gr surfaces is further revealed by Tafel tests. An additional 46% lower corrosion rate than the Ni-Gr surface has been characterized. This study manifests a feasibility to implement the sustainable and highly efficient DWC on other popular heat exchanging metals using super-durable Ni-Gr coatings.
      原文链接:
    • NSTL
    • Elsevier

    Performance optimization of pinnate horizontal well in geothermal energy utilization with orthogonal test

    Xie, JingxuanWang, Jiansheng
    15页
    查看更多>>摘要：Aiming at efficiently utilizing the hot dry rock resources, a potential enhanced geothermal system (EGS) with pinnate horizontal well (PHW) is investigated in present work. The multifactor and multilevel orthogonal tests are performed to probe the combined effect of human-made parameters on the reservoir properties, and to find the optimum operation strategy of PHW EGS. To evaluate the heat extraction performance of PHW EGS, geostress balance method is taken into account in the thermo-hydro-mechanical (THM) coupling model. The main factors of different human-made parameters that affect the heat extraction performance have been ranked based on their effect level, which are injection temperature, injection mass rate, production pressure, well spacing and length. In addition, Enthalpy-exergy is employed to evaluate the maximum available work of the extracted thermal energy. The present results demonstrate that the heat extraction performance of doublet EGS can be significantly improved by 12.57 MW ~ 13.60 MW when the branch wells are introduced. The fractured region is mainly affected by the tensile stress, and the compressive stress predominates in reservoir margin. The production temperature is significantly affected by the well spacing, while the water loss rate has a strong correlation with production pressure. Under the recommended operation scheme, the maximum available work of PHW EGS ranges from 20.18 MW to 17.31 MW can be obtained, which accounts for from 23.76 % to 26.12 % of the extraction of thermal energy.
      原文链接:
    • NSTL
    • Elsevier