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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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    Modeling the effect of dual-core energy recovery ventilator unit on the energy use of houses in northern Canada

    Li J.Zmeureanu R.Ge H.
    17页
    查看更多>>摘要：The use of single-core energy recovery ventilator (ERV) reduces the heating energy use in northern houses, but has the disadvantage of reducing the required outdoor air supplied to the house during the defrost operation by air recirculation, which might affect the indoor air quality. A dual-core ERV also reduces the heating energy use, but in addition supplies a continuous outdoor air flow rate in compliance with standards. This paper evaluates the advantage of using the dual-core ERV in northern houses. First, this paper presents new correlation-based models of supply air temperature and humidity after the ERV unit, based on laboratory-controlled experimental data. Second, the energy use for ventilation and heating, and ventilation rates are simulated with TRNSYS program for northern houses at three arctic locations. They are compared with Montreal conditions as reference. The single-core ERV unit significantly reduces heating energy use in arctic locations by about 27%, compared with the case without heat recovery, however the outdoor airflow rate during the defrost is smaller than minimum standard requirements by about 13% in Kuujjuaq (below Arctic Circle) and 24% in Resolute (above Arctic Circle). The dual-core ERV unit removes the frost while continuously supplying the minimum required outdoor air to the indoors, however at the cost of minor increase of the heating and fan energy use compared with the single-core ERV unit.
      原文链接:
    • NSTL
    • Elsevier

    Energy balance analysis of a DI diesel engine with multiple pilot injections strategy and optimization of brake thermal efficiency

    Guler M.Ozkan M.
    20页
    查看更多>>摘要：In this study, multiple pilot injections (MPI) strategy having two pilot injections was applied to direct injection (DI) diesel engine running at partial load which is usually within legal emission cycle. Optimization of timing and quantity of the pilot injections is a key factor in achieving performance and emission targets. Due to the advantages of pilot injections in terms of smooth and gradual release of energy from the fuel, the energy distribution in the engine has been put under scope and investigated thoroughly. The effects of varying the timing and quantity of both pilot injections within a reasonable range on brake thermal efficiency, total exhaust energy, in-cylinder heat transfer and friction were investigated and results were presented using a well calibrated and validated thermodynamic model. Relative sensitivity analysis and Spearman correlation coefficients analysis were performed to show the effects of each MPI parameter on the total fuel energy components. The variation of 2nd pilot injection quantity determined the most influential parameter on brake thermal efficiency with a relative sensitivity value of 0.4612, on in-cylinder heat transfer with a relative sensitivity value of 0.4708, on total exhaust energy with a relative sensitivity value of 0.4757 and on friction power with a relative sensitivity value of 0.4677 respectively. Similar to the variation in the 2nd pilot injection quantity, the variation in the 1st pilot injection quantity affected these responses in the same way but with less effect. Timing variations in both pilot injections were found out to be the third and the fourth parameters affecting responses. Especially the variation in 2nd pilot injection timing has the least effect on components of total fuel energy. Retarding both pilot injections increased the brake thermal efficiency and the variation of both pilot injection timing has similar effect on brake thermal efficiency. Retarding the 1st pilot injection timing augmented the total exhaust energy while reducing the in-cylinder heat transfer to coolant and friction power. Non-dominated Sorting Genetic Algorithm-III (NSGA-III) optimization tool was used for finding the optimal timing and quantity of both pilot injections to maximize brake thermal efficiency. A growth of 0.29% at a rate of %1 in the brake thermal efficiency was achieved. Additionally, an increase of 0.74% at a rate of 2.4% in the total exhaust energy has the potential to be used and recovered in the turbine.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation on the heat removal capacity of secondary side passive residual heat removal system for an integrated reactor

    Li J.Liu M.Xiao Y.Xiong Z....
    11页
    查看更多>>摘要：An experimental facility named Intermediate Heat Exchange Loop (IHEL) is built to simulate the secondary side passive residual heat removal system. The IHEL mainly includes a helically coiled Once-Through Steam Generator (OTSG), a condenser, a cooling water tank, and associated piping and valves. The steam is produced by the water-to-water heat exchange method in the SG secondary side. The heat from the SG primary side is carried to the cooling water tank by the IHEL through a two-phase natural circulation method. The natural circulation characteristics of the IHEL under the low pressure (nearly atmospheric pressure) and low water inventory conditions are investigated. The result shows that the heat removal capacity of the IHEL is good at these conditions, and it is determined by the parameters of the SG primary side and IHEL together. In the present test conditions, for the parameters of the SG primary side, the heat removal rate will increase with the increase of mass flow rate or heat source temperature. For the parameters of the IHEL, the heat removal rate is not sensitive to the initial non-condensable gas content. The heat removal rate is not sensitive to the resistance level when the heat source temperature is low, while it will decrease with the increase of resistance level when the heat source temperature is high. A very meaningful conclusion is that the natural circulation has been established successfully in the very lower water inventory condition (L = 14.8% in the present study), and the heat removal rate almost remains constant with the increase of the water inventory, which indicates the IHEL is robust and is beneficial for the system design.
      原文链接:
    • NSTL
    • Elsevier

    Limit cycle analysis and maldistribution mitigation for multi-channel cooling system

    Jin Q.
    11页
    查看更多>>摘要：Flow boiling in microchannel can be applied for large heat load dissipation due to its high heat transfer coefficient, compact structure, and low refrigerant flow. However, instabilities in microchannel cooling systems, like pressure drop oscillation and flow maldistribution, can deteriorate cooling performance, cause component damage, and result in unbalanced temperatures. In this study, we explore the effects of heat load on limit cycles and temperature distributions for microchannel cooling systems with single, two, and multiple channels. The objective is to analyze the pressure drop oscillation characteristics and understand the changing patterns of limit cycles at different operating conditions, based on which control strategies can be developed for flow instability suppression. Numerical results show that the limit cycles are identical for channels with equal heat loads and the same pressure drop characteristics. Thus, mass fluxes and temperatures are evenly distributed. For unequally heated channels, the one with the smallest heat load would have a limit cycle crossing both positive and negative regions of the pressure drop characteristic curve, while the limit cycles of the channels with larger heat loads would oscillate only at the positive slope region (the high vapor quality side). Based on the understanding of limit cycles for multiple channels, we investigated the temperature distributions and pressure drop oscillations under the individual and combined effects of thermal and mass flow connections among channels. Results show that the thermal and mass flow connections would reduce the temperature difference for channels experiencing unequal heat loads, and a strong enough connection would result in the same limit cycles and synchronized temperatures for all channels.
      原文链接:
    • NSTL
    • Elsevier

    Energy, exergy, economy, and environmental (4E) analysis of a multi-generation system composed of solar-assisted Brayton cycle, Kalina cycle, and absorption chiller

    Alrobaian A.A.
    19页
    查看更多>>摘要：Employing multi-generation concept and renewable energy sources are two promising tools to overcome exorbitant consumption of fossil fuels. In this paper, the aforementioned techniques have been used to supply the energy demand of a commercial building. To do so, a novel tri-generation system is proposed and analyzed from energy, exergy, economic, and environmental points of view. This multilateral analysis provides a comprehensive view for the owner and decision makers whether the energy conversion system has a sustainable design from several points of view. Brayton cycle assisted with solar energy, bottoming Kalina cycle, absorption chiller, and waste heat recovery exchanger are used to supply the energy demand. Energy analysis reveals that the plant must be connected to the grid in order to meet the gap between absorption chiller production rate and the user cooling demand. The annual energy export to the grid equals to 4670 MWh while 2294 MWh electricity must be imported. Considering the exergy analysis, round-trip exergy efficiency of the plant is 42.11%. Brayton cycle has the highest share in the exergy destruction and corresponds to 93.00% of the annual exergy destruction. Based on the economic evaluation, the net system costs during its life cycle are 2.02 M$. Finally, sensitivity analysis is conducted to investigate the change in system performance by varying the key design parameters.
      原文链接:
    • NSTL
    • Elsevier

    Effects of the Y-shape stud and outer insulating layer on heat dissipation and wall temperature of the hot cyclone in a circulating fluidized bed boiler

    Yao Y.Huang Z.Zhang M.Yang H....
    12页
    查看更多>>摘要：The hot cyclones in circulating fluidized bed (CFB) boilers often face the problems of high heat dissipation and high wall temperature in the operation, which may decrease the strength of the steel layer and present a danger to workers. To solve these problems, the heat dissipation characteristics through the cyclone wall and the key parameters of this process need to be known. In this study, a numerical simulation was conducted to estimate the wall temperature field of a hot cyclone in a 440 t/h CFB boiler. The effects of the Y-shape stud arrangement and the outer insulating layer on the heat flux and the wall temperature were qualitatively and also quantitatively analyzed. It was found that the Y-shape stud does enhance the heat dissipation of the cyclone wall. A denser Y-shape stud arrangement results in higher temperatures of the steel layer and also the outer surface. Moreover, the heat flux of the inner surface, the maximum temperature of the steel layer, and the outer surface are all well linear with the stud number. However, how the studs arrange on the steel layer has very sight effects on the heat flux and wall temperature at a certain stud number. Adding an insulating layer on the outer wall surface can reduce the heat dissipating capacity of the hot cyclone and also decrease the outer surface temperature. The effects of Y-shape studs on the heat dissipation and wall temperature are also weakened. While the outer insulating layer results in a rapid increase of the steel layer temperature, which may bring extra risk to the cyclone wall. Based on the simulation results, reducing the unnecessary studs and covering an insulating layer thinner than 20 mm are suggested.
      原文链接:
    • NSTL
    • Elsevier

    Thermal pollution level reduction by sweeping jet-based enhanced heat dissipation: A numerical study with calibrated Generalized k-ω (GEKO) model

    Li Z.Liu Y.Zhou W.Wen X....
    30页
    查看更多>>摘要：Thermal pollution is commonly the damage to natural ecosystems caused by industrial water discharge into the environment above ambient temperature. The highly efficiently dissipative sweeping jet actuator is thus considered as the solution to the reduced thermal pollution level. The thermal dissipation capacities of free steady, pulsed, and sweeping jets with a Reynolds number of 49,761 and a Strouhal number of 0.0152 are compared by numerical simulation. The Reynolds stress model (RSM) is used as the turbulence model, with the Generalized k-ω (GEKO) model innovatively used to calibrate jet dissipation rates. The temperature fields are first compared to confirm the overwhelming temperature dilution effect of the sweeping jet in both streamwise and normalwise directions. Then the reasons for the enhanced heat dissipation by sweeping jet are explained by numerous time-averaged and time-resolved contours of the distributions of flow-related physical quantities. The time-averaged flow fields directly show that the sweeping jet has the fastest streamwise velocity decay and the most uniform spanwise momentum distribution due to the continuous transverse oscillation, and hence has the moderate turbulence kinetic energy (TKE) over a wide spanwise range due to the destruction of the potential core commonly seen in a steady jet. The relative turbulence kinetic energy fields, excluding the contribution to turbulence generation from velocity magnitudes, show that the alternating formation and dissipation of shear layer-induced vortices most contribute to the inherent unsteady patterns. In the planes perpendicular to the streamwise direction, the spacings between adjacent velocity contour lines of the sweeping jet increase at the fastest rate with the streamwise distance, indicating the excellent entrainment capacity. The difference among the three primary Reynolds stresses of the sweeping jet is smaller than that of the other two jets, indicating that the sweeping jet converts more streamwise momentum into spanwise and normalwise velocity and turbulence and thus has higher spatial homogeneity. Pathlines of massless particles dispersed in the near-field show that the sweeping jet has the most substantial entrainment capability due to the longest motion distance of the traces originating outside the jet shear layer, although it is difficult for the ambient fluids to penetrate the central jet impact region. Finally, three mixing potential metrics, i.e., jet decay rate, jet spreading rate, and entrainment factor, are used to evaluate the three jets' more general mixing characteristics qualitatively. To extract the sweeping jet's centerline velocity and spreading width, the Lagrangian transformation, which invariably aligns the jet ejection direction with x-axis, is performed on the phase-averaged velocity flow fields. The near-field results show that compared with the steady jet, the sweeping jet boasts a 176% increase in the jet decay rate, a 241% increase in the jet spreading rate, and a 369% increase in the entrainment factor. In the far-field, the entrainment capacity of the sweeping jet is not as good as that of the pulsed jet but is still 68% higher than that of the steady jet. In all, this paper establishes a theoretical basis for the application of fluid oscillators to heat pollution level reduction and more general scenarios involving requirements for enhanced heat and mass transfer by proposing the standard mixing indicators of sweeping jets similar to those of conventional jets, and also serves as a pioneering example for the future possible extension of the GEKO model to a broader range of industrial CFD simulations.
      原文链接:
    • NSTL
    • Elsevier

    Performance Evaluation of hi-k Lung-inspired 3D-printed Polymer Heat Exchangers

    Ahmadi B.Bigham S.
    10页
    查看更多>>摘要：Polymer heat exchangers are attractive thermal management solutions due to their low-cost, lightweight, antifouling, and anti-corrosion characteristics. They, however, demonstrate poor thermal characteristics mainly due to the low thermal conductivities of typical polymers. Additive manufacturing of high thermal conductivity polymer heat exchangers utilizing complex heat transfer topologies could potentially address the issue. In this study, thermal performances of 3D-printed polymer heat exchangers with intricate internal geometries including a lung-inspired design at low-to-high thermal conductivities are experimentally and numerically examined. It was found the effective thermal conductivity of a 3D-printed polymer heat exchanger is close to the through-plane thermal conductivity. It was also identified that through-plane leakage in thin 3D-printed polymer walls is a major challenge associated with 3D-printed polymer heat exchangers. The issue was remedied by in-situ infusion of an epoxy layer during the 3D-printing and a post-curing process. Experiments conducted at various thermo-hydraulic conditions showed that the high thermal conductivity lung-inspired polymer heat exchanger offers high thermal duties at reduced pressure drop penalties and exceptionally high effectiveness of 70–80% that is comparable to that of metal-based heat exchangers. At an air Reynolds number of 1200, the volume-based power density of the high thermal conductivity lung-inspired design is 522 kW/m3, which is a 101% improvement compared with a typical plate-and-frame design. This study concludes that the thermal performance of a polymer heat exchanger strongly depends on both material (i.e., thermal conductivity) and architecture (i.e., an optimum design with a minimal thermal resistance between hot and cold sides). Insights gained from this study could offer new pathways for designing innovative 3D-printed polymer heat exchanger technologies with unprecedented heat transfer rates at reduced pressure drop penalties for lightweight, antifouling, and/or anti-corrosion applications.
      原文链接:
    • NSTL
    • Elsevier

    Comparison of dual-pressure organic Rankine cycle using zeotropic mixtures

    Wang M.Liu H.Zhang J.
    13页
    查看更多>>摘要：The dual-evaporation organic Rankine cycle (DORC) using zeotropic mixtures can effectively reduce the irreversible loss both in the evaporator and condenser, and thus improve the net power output compared to the DORC using pure working fluid. This paper investigated the DORC using zeotropic mixtures for recovering low-grade energy. The effects of different condensation temperatures (fixed dew point and fixed bubble point condensation temperature, optimized condensation temperature), temperature glide of zeotropic mixtures and cooling water temperature rise on the net power output of the DORC were investigated. The results indicate that the DORC using zeotropic mixtures under optimal mass fraction can improve the net power output by 6.4–16.6% compared to the DORC using pure working fluid. In selecting the zeotropic mixtures for the DORC, the maximum value of the temperature glide of the zeotropic mixtures under condensation pressure should be larger than the cooling medium temperature increase. The irreversible loss in the evaporator is the most among the four irreversible losses, followed by that in the condenser. However, the effect of irreversible loss in the condenser on the variation trend of the total irreversible loss is the most significant.
      原文链接:
    • NSTL
    • Elsevier

    Comparison of solidification performance enhancement strategies for a triplex-tube thermal energy storage system

    Huang X.Yao S.Zhou R.Luo J....
    20页
    查看更多>>摘要：To enhance the solidification performance of phase change material in a triplex-tube thermal energy storage system, a two-dimensional model is established in this paper. The solidification performance of the system is studied by numerical simulation, and the method of adding multistage inner tubes and longitudinal fins is proposed to strengthen the solidification. Firstly, the size of eight fins in the initial model is studied to select the most suitable model, and the most difficult solidification area of the system is found through the study of dynamic temperature response at the position points. Then, multiple inner tubes and T-shaped fins are added to the area and a response surface method is used to optimize the design. The solidification performance of the system can be improved by 50.19% when the diameter of the multistage tube is 4 mm in the best position. The results show that enhancement of solidification property of phase change material by multistage inner tube is better than that by fin. The effects of physical parameters such as multistage inner tubes diameter, cold fluid temperature, and fin structure on solidification performance are also discussed. Finally, the effect of natural convection on the solidification process of phase change material is analyzed.
      原文链接:
    • NSTL
    • Elsevier