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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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    Multiple simultaneous faults' impacts on air-conditioner behavior and performance of a charge diagnostic method

    Yifeng HuDavid P. Yuill
    14页
    查看更多>>摘要：Although there have been several studies that have focused on the effects of faults on the performance and on the characteristic features that could be used to detect faults, almost none of the research has studied the effects of multiple simultaneous faults. Existing fault detection and diagnosis approaches that have been developed based on single faults may struggle with simultaneous faults. This paper is part of a series that present a methodology and comprehensive measurement data from a battery of laboratory tests on an air-conditioner with combinations of common faults (refrigerant charge, evaporator airflow, non-condensable gas, and liquid line restrictions) imposed, to show how the indicator variables and overall performance are impacted. The system has a microtube condenser and a fixed-orifice (FXO) expansion device, which are found to affect the features' fault sensitivity. This experiment is the first to test these combined faults in an FXO-equipped system, so comparisons are made to a previously studied thermostatic expansion valve-equipped system. Finally, a promising charge diagnostic technology is assessed, to see how it is impacted by other faults. The faults reduced capacity by up to 42%, and efficiency by up to 39%. The charge diagnostic performed well, even with multiple faults present.
      原文链接:
    • NSTL
    • Elsevier

    Performance assessment of a rock aggregate heat exchanger exposed to daily temperature variation

    D. J. CerantolaP. GareauA. HutchisonC. D. Lane...
    13页
    查看更多>>摘要：Opportunities exist to utilize rock aggregate to condition ventilation air at mine sites in humid continental climates. Vale's Creighton mine in Canada proved that a natural heat exchanger offered significant energy savings; however, the system was not suitable to establish design guidelines. A novel prototype-scale outdoor 30 m~3 rock pile heat exchanger experiment was constructed to characterize the thermal response to measurable aggregate parameters with insight shared regarding their sensitivity. This paper validates an unsteady 3D CFD numerical methodology involving the thermal non-equilibrium porous zone model with lab-scale-derived correlations against weather-influenced temperature data and proposes guidelines for improving performance: Increasing pile flatness was beneficial for damping whereas increasing hemispericality was beneficial for phase shifting. A CFD case study requiring 47 m~3/s (100,000 cfm) ventilation flow found that a rock pile constructed using traditional methods could achieve 100% damping with 6,000 m~3 of granitic rock aggregate at a pressure penalty of 2,500 Pa.
      原文链接:
    • NSTL
    • Elsevier

    Flow resistance analysis of non-isothermal supercritical CO_2

    Meng ZhuLei ChenSheng SuSong Hu...
    14页
    查看更多>>摘要：Supercritical carbon dioxide power cycle is considered as one of the promising systems of next generation power cycle. Nevertheless, the hydraulic characteristics of typical heat source components under operating conditions (gas-like region) are not clear, and the present conclusions for flow characteristics of non-isothermal fluids are also not consistent. In this work, the turbulent flow of supercritical CO_2 in a vertical upward tube was studied experimentally and numerically. The range of experiment parameters was set as 750-2800 kg/(m~2s) of mass flux, 10-28 MPa of pressure, 200-410 kW/m~2 of heat flux and 65-500℃ of bulk flow temperature. Furthermore, the feasibility of SST k-omega model was verified by experiment results. The effects of mass flux and pressure on friction pressure drop under non-isothermal conditions are basically consistent with those under isothermal conditions. However, the increase of heat flux leads to the decrease of friction pressure drop and friction factor. Under high heat flux condition, both the viscous shear stress and Reynolds shear stress decrease. The viscous shear stress contributes slightly to the mechanical energy dissipation, hence the Reynolds shear stress is the crux to the change of friction pressure drop. Further studies show that the decrease of density in near-wall region and the decrease of turbulence fluctuation in core region are critical to the decrease of mechanical energy dissipation. According to the theoretical and dimensional analysis, the dimensionless number Xi that can be qualitatively analyzed for the ratio of thermally-induced force to inertial force was obtained. Finally, a high-precision correlation of friction factor was proposed. The proportion of calculated value within 10% and 30% error ranges is 76.65% and 100%, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Theoretical Understanding of thermoelectric energy conversion efficiency in Lead-Free halide double perovskites showing intrinsic defect tolerance

    Lifu YanLingling ZhaoChangying ZhaoShangchao Lin...
    11页
    查看更多>>摘要：Thermoelectric devices based on the Seebeck effect can directly convert waste heat to electricity, but the demand for better thermoelectric materials remains unfulfilled. The lead-free halide double perovskites have recently shown promises for their stability and environment-friendly nature, but impacts from intrinsic defects (vacancies and anti-sites) on their thermoelectric performance remains elusive. Combing first-principle calculations, the Boltzmann transport theory, and the defect formation theory, we investigate the thermoelectric properties of lead-free double perovskite Cs_2NaInCl_6, taking the intrinsic defects into consideration. Our results demonstrate that the pristine Cs_2NaInCl_6 presents thermodynamic, mechanical, and dynamic stability. The band edges are mainly comprised of the electrons from In and Cl atoms. Furthermore, the double perovskite has an ultra-low lattice thermal conductivity and a high Seebeck coefficient, while showing a small charge carrier relaxation time and electric conductivity. Promisingly, the maximum ZT values can reach as high as ～ 1.36 and ～ 1.44 at 800 K temperature, respectively, with optimal extrinsic carrier concentrations of ～ 1.9 × 10~(19) and 5.8 × 10~(20) cm~(-3) for N- and P-type carriers (holes and electrons), and the maximum power generation efficiency can reach ～ 14% (for P-type) when the hot-side temperature is 800 K. Among various intrinsic defect types, we determine the preferable defect types in Cs_2NaInCl_6 based on the minimal defect formation energy criteria. The free carriers can be switched from N- to P-type under these two preferable defects, respectively, with Cl and Na vacancies. Even under a very high defect concentration of 2.1 × 10~(19)/cm~3 considered here, the extra carrier concentrations induced by the defects are only ～ 10~(17) cm~(-3) at 800 K, showing strong defect tolerance in carrier concentration. This work suggests that lead-free halide double perovskites are promising thermoelectric materials, and they show strong intrinsic defect tolerance that prevents a negative impact on the extrinsic doping-controlled carrier concentrations.
      原文链接:
    • NSTL
    • Elsevier

    Numerical study of a dual-PCM thermal energy storage unit with an optimized low-volume fin structure

    M. MozafariKamel HoomanAnn LeeShaokoon Cheng...
    17页
    查看更多>>摘要：Phase Change Materials (PCMs) are widely used as storage mediums in latent thermal energy storage systems and are useful to tackle the inconsistencies in energy supply and demand associated with renewable energy resources. However, weak thermal conductivity is the major disadvantage of PCMs, as they cause slow charging and discharging of thermal energy storage systems. The performance enhancement of a unique thermal energy storage unit design that consists of two PCMs and with optimized fins is demonstrated in the current study. Different arrangements of dual-PCMs are first examined by comparing the overall charging-discharging time. The proposed dual-PCM layout for a horizontal double-pipe energy storage unit, not demonstrated in existing work, reduces the total charging-discharging time by 13.6% compared with the conventional single-PCM case. Results from this study further show that applying nanoparticles is less effective than adding fins for the proposed dual-PCM design configuration. Adding nanoparticles to the dual-PCM design results in 2.2 times shorter charging-discharging time, while the proposed design with fins incorporated results in a remarkable 7.6-fold improvement in charging-discharging time. To further enhance the performance of the energy storage unit, response surface methodology (RSM) is used to predict the optimum fin angles, and results show that fins tilted at 51.1° and 42.6°, measured clockwise from the upper middle section and counter-clockwise from the lower middle section, respectively, reduced the total charging-discharging time by 7.5%. This article exemplifies a systematic approach to designing a high-performance LTES system that leverages the combined benefits of multiple PCMs and optimized fin design.
      原文链接:
    • NSTL
    • Elsevier

    Energy pile groups for thermal energy storage in unsaturated soils

    Fatemah BehbehaniJohn S. McCartney
    15页
    查看更多>>摘要：A coupled heat transfer and water flow model implemented in COMSOL and validated against measurements from a tank scale test was applied to investigate the application of energy pile groups for thermal energy storage in unsaturated soil layers. The novel focus of the investigation was understanding the long-term thermo-hydraulic response of the unsaturated soil within the energy pile group during heat injection at high temperature up to 90℃ and associated impacts on the heat storage performance. Unsaturated soil layers are advantageous for thermal energy storage due to enhanced convective heat transfer during injection associated with vapor diffusion and favorable insulation properties during storage associated with lower thermal conductivity of soils surrounding a heat storage system. Evolutions in temperature and degree of saturation in soil layers having different hydraulic properties and water table depths were simulated during five years of operating a group of five energy piles with inlet fluid temperatures of 90℃ during heat injection and 30℃ during heat extraction. Transient fluctuations in the degree of saturation were observed in all soil layers simulated, but a permanent decrease was only observed for a soil layer having a greater air entry suction after several cycles of heating and cooling. While the heat storage in energy pile groups in unsaturated soil layers was always between that of dry and saturated soils with no groundwater flow, the soil hydraulic properties and water table depth were found to control both the rate of heat transfer and the total heat stored. When comparing the performance of energy pile groups with a group of borehole heat exchangers commonly used in heat storage applications, the energy piles were approximately 1.2 times more effective in extracting heat with a faster response confirming their suitability for heat storage.
      原文链接:
    • NSTL
    • Elsevier

    Effect of microstructure of nanoparticles and surrounding alcohol groups on energy transfer efficiency

    Liang ZhangYuyan JingPingping QuWenjie Wang...
    17页
    查看更多>>摘要：The low solar thermal conversion efficiency is an obstacle to the development of a new generation of high-efficiency energy-saving technologies. An important measure to improve the conversion efficiency is to improve the thermal conductivity of the working fluid. Nanofluids have a higher thermal conductivity than conventional fluids, which provides a strategy idea toward solving this problem. In this paper, three kinds of traditional fluids, ethanol, ethylene glycol (EG) and 1,2-propylene glycol (PG), were used as base solutions, and Cu nanoparticles with different volume fractions were added to form their corresponding nanofluids. The thermal conductivity of the different alcohol solutions and their nanofluid systems were simulated using molecular dynamics and the thermal conductivity enhancement mechanisms of these nanofluids on a micro-level were simulated and analyzed. It was found that the thermal conductivity of the ethanol/EG/PG-water solution was positively correlated with the water content of the system. The addition of Cu nanoparticles improved the thermal conductivity of the three kinds of alcohol nanofluids. The existence of base solution molecular adsorption layer on the surface of nanoparticles was an important factor contributing to the improvement of the thermal conductivity of nanofluids. Through the radial distribution function of the nanofluid system, and the visualization of the molecules in the adsorption layer, it was found that the arrangement of base solution molecules in the adsorption layer was similar to the orderly arrangement of solids. This type of solid-like microstructure rendered better heat transfer performance of the nanofluid than the base solution. Within the scope of this study, the maximum increase in the rate of the thermal conductivity of the ethanol/EG/PG-water solutions was 14.2, 30.6 and 22.6%, respectively. In the alcohol nanofluid system, the thickness of the adsorption layer on the surface of Cu nanoparticles was ～0.45 nm, which increased or decreased slightly based on the type of base solution. The above findings provide an important reference for improving solar thermal conversion efficiency.
      原文链接:
    • NSTL
    • Elsevier

    The impact of employing carbon nanotube and Fe_3O_4 nanoparticles along with intermediate boiling fluid to improve the discharge rate of phase change material

    Hossein HosseininavehIman Rahgozar AbadiOmid MohammadiAlireza Khademi...
    14页
    查看更多>>摘要：Despite the fact that solid-liquid phase change materials (PCMs) have various applications in thermal energy storage systems, the low solidification rate of PCMs, which is due to the low thermal conductivity has limited the range of applications of PCMs. One of the methods of increasing the solidification rate of PCMs is using a boiling fluid as an intermediary between the solid-liquid PCM and the condenser to prevent the direct contact between the phase change material and the condenser tubes, this method is also known as the intermediate boiling fluid (IBF) method. The IBF method has been shown to significantly increase the solidification rate (2 orders of magnitude). In this study, the effect of nanoparticles addition on the solidification rate of PCM in the IBF method is investigated. Paraffin and acetone are used as the solid-liquid PCM and the IBF, respectively. Hence, Carbon nanotubes (CNT) and Fe_3O_4 as carbon-based and metallic nanoparticles, respectively, are dispersed in the acetone at three different concentrations of 1 wt%, 2 wt%, and 4 wt%. The results revealed that, compared to the case without using nanoparticles, the addition of Fe_3O_4 nanoparticles at concentrations of 1 wt%, 2 wt%, and 4 wt% decreases the total solidification time by 4%, 16%, and 20%, respectively. Likewise, the addition of CNT nanoparticles at the same concentrations decreased the total solidification time by 16%, 28%, and 36%, respectively. Furthermore, the addition of Fe_3O_4 and CNT at 4 wt% reduces the solidification start time by 20% and 30%, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Two-stage thermal-hydraulic optimization for Pillow Plate Heat Exchanger with recirculation zone parameterization

    Zheming TongQi YangShuiguang TongXin Chen...
    15页
    查看更多>>摘要：Pillow plate heat exchanger (PPHE) has become a promising alternative to conventional heat exchangers due to their satisfactory heat transfer performance and geometric flexibility. Nevertheless, the presence of recirculation zone (RZ) greatly restricts its thermal-hydraulic efficiency. In this study, a two-stage thermal-hydraulic optimization method with RZ parameterization was proposed. At the first stage, a genetic particle swarm optimization algorithm was developed, which combines a genetic algorithm with particle swarm optimization to maximize the thermal-hydraulic performance of PPHE. While at the second stage, the optimization objective was refined to further enhance the heat transfer characteristics based on geometrical parameters of RZ. The developed CFD model of PPHE was evaluated against existing experimental data and found to be in satisfactory agreement in terms of hydraulic diameter, Nusselt coefficient and pressure drop. Compared to the baseline design, the average PEC of the two-stage optimized PPHE was improved by 29.3% over a Reynolds number ranging from roughly 4,000 to 8,000, while the heat transfer area of RZ was reduced by 25.3% in average. The results revealed that a decreased welding spot pitch ratio contributes to the flow mixing between mainstream and the stagnant fluid downstream of the RZ, while smaller welding spot can significantly improve the turbulent energy dissipation of the mainstream, and therefore enhance the overall heat transfer.
      原文链接:
    • NSTL
    • Elsevier

    Analysis of the exhaust hydrogen characteristics of high-compression ratio, ultra-lean, hydrogen spark-ignition engine using advanced regression algorithms

    Seungmook OhChangup KimYonggyu LeeHyunwook Park...
    16页
    查看更多>>摘要：Hydrogen is a leading alternative fuel for eliminating the carbon emissions of internal combustion engines. Moreover, the use of hydrogen improves the combustion owing to its high flame speed. The hydrogen selective catalytic reduction is a promising solution for the reduction of nitric oxides (NO_x), which is the sole regulated gas species in hydrogen-fueled internal combustion engines. In the present study, hydrogen and NO_x emissions, the crucial species for the catalyst performance, were investigated using a heavy-duty, hydrogen spark-ignition engine. The ratio of H_2 to NO_x was above 100 at the excess air ratio (lambda) of 2.5 or higher. Three-dimensional, numerical simulation showed that the in-cylinder hydrogen distribution was dependent on the engine load and the lambda value. A regression analysis showed that the exhaust hydrogen quantity had a strong correlation with the seven parameters, namely engine speed, the gross indicated effective pressure (IMEPg), lambda, spark timing, total combustion duration, peak in-cylinder temperature, and peak pressure rise rate. Among these parameters, the IMEPg and the lambda value exhibited the highest weights in a neighborhood component analysis. The regression model with the seven features exhibited the highest R~2 value of 0.94 with the squared exponential Gaussian process regression. The proposed prediction model can contribute to not only reducing NO_x emission with aftertreatment, but also maximizing the thermal efficiency of hydrogen-fueled internal combustion engines.
      原文链接:
    • NSTL
    • Elsevier