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Thermal science and engineering progress
Elsevier Ltd.
Thermal science and engineering progress

Elsevier Ltd.

2451-9049

Thermal science and engineering progress/Journal Thermal science and engineering progressSCI
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    Synergetic promotion of 4Mn10Ce/gamma-Al2O3 catalyst to Pt/xBa/Ce0.5Zr0.5O2 catalysts for NOx removal from diesel exhausts

    Lei, LiliYu, DanWang, PanWu, Gang...
    7页
    查看更多>>摘要：In this investigation, Pt/xBa/Ce0.5Zr0.5O2 catalysts were prepared by deposition and incipient wetness impregnation method and the physio-chemical properties of samples were characterized with XRD and BET. The experiments were carried out to evaluate the effect of 4Mn10Ce/gamma-Al2O3 on the removal of NOx over the Pt/xBa/ Ce0.5Zr0.5O2 catalysts and NO-TPD was employed for determining the NOx adsorption. The results showed that the larger diffraction peak width of Ce-Zr oxides and specific area were found over Pt/15Ba/Ce0.5Zr0.5O2. Based on the NOx storage and storage-reduction experiments, it was found that the decline of NOx storage efficiency was attributed to the decomposition of nitrites and nitrates under high temperatures beyond 350 degrees C, and the inhibition of reactions of NOx with Ba by the NO oxidation. NO2 was stored more easily and faster than NO, which contributed to NOx storage after 4Mn10Ce/gamma-Al2O3 catalyst added. The stability of stored species was undermined at higher temperature due to H-2 consumption by 4Mn10Ce/gamma-Al2O3 catalyst leading to shortage of reductant and more reaction heat. The optimal concentration of O-2 at around 7.5% can provide more O-II for the oxidation process of NO and improve the performance of NOx reduction.
      原文链接:
    • NSTL
    • Elsevier

    Thermal management of Electronics: Numerical investigation of triangular finned heat sink

    Hithaish, DoddamaniSaravanan, VUmesh, C. K.Seetharamu, K. N....
    17页
    查看更多>>摘要：The micro pin fin heat sink is an innovative method to enhance heat dissipation from the electronic system. The various geometrical configuration of the triangular micro pin fin heat sink (TMPFHS) for the fluid and heat transfer characteristics is numerically investigated in the present work. Finally, the best configuration is proposed. Three different configurations of triangular pin fin have been considered (i) uniformly varying the fin height ranging 0.25 mm-0.75 mm. (ii) Orientation of fin both in the clockwise and counter-clockwise direction (30 degrees, 40 degrees, 50o, and 60 degrees) (iii) Change in the direction of fins facing upstream fluid from forward triangular to backward triangular between two successive rows and vice versa. A 3-Dimensional numerical simulation is carried out for a triangular finned heat sink arranged staggered manner subjected to 10 W/cm2. A single-phase laminar flow is considered for Reynolds numbers ranging from 100 to 900 using coolant water. Results reveal that the heat dissipation rate for all the configurations increases substantially with the rise in pressure drop. A Non-dimensional parameter thermal performance index (TPI) is employed to access the superior heat sink in maximum dissipation and minimum pressure drop. The TPI with alternate forward and backward arrangement outperforms all other configurations of the range 1.01-1.44.
      原文链接:
    • NSTL
    • Elsevier

    A novel method for removing noncondensable gas from loop heat pipe

    Anand, A. R.
    14页
    查看更多>>摘要：Noncondensable gas (NCG) is a critical issue in loop heat pipes (LHPs) for space missions and can arise due to plenty of reasons. Compensation chamber (CC) of an LHP, being a nearly stagnant point, accumulates NCG that arises due to any reason. NCG in an LHP intended for space use should be removed before its hermetic sealing itself. In this paper, a novel method is presented for the first time to completely remove NCG from LHPs through a series of attempts using a simple setup consisting of a pressure sensor, a rough vacuum pump and a metering valve connected to the CC. The method is demonstrated on an LHP with flat evaporator with acetone as working fluid and air as NCG. When the LHP operates, a certain amount of NCG is removed from the CC through the vacuum pump by momentarily opening and closing the metering valve in each attempt. Through a series of test runs, based on a decrease in the operating temperature and an increase in the maximum heat transport prior to deprime in each test run with reference to those of the previous test run, it is ascertained that a certain amount of NCG is removed in each attempt. A unique model is also proposed to predict the NCG mass based on the CC pressure and the predicted CC liquid level. Results of the proposed model are validated with those of previous experiments in the LHP containing capacitance gauge for CC liquid level measurement.
      原文链接:
    • NSTL
    • Elsevier

    Simulation and experimental determination of temperature in the joint zone during explosive welding

    Pai, Vladimir V.Lukyanov, Yaroslav L.Lysak, Vladimir, IKuz'min, Sergey, V...
    8页
    查看更多>>摘要：This paper presents methods for the temperature calculation based on experimental data on the interface bond and in the heat-affected zone under conditions of impulse metal deformation during explosive welding. The methods are based on the formation of a thermocouple during the explosive welding of copper and constantan, with a hot junction on the boundary. An inverse computational solution is proposed to determine the temperature-time relationship at the interface from the measured potential distribution on one of the thermocouple reference junctions. The dependence of the joint (copper-constantan interface) temperature on time, defined by the maximum and residual temperatures, is determined. The temperature in the heat-affected zone spaced 0.3 mm apart from the weld is obtained. Major heat emission as well as metal melting occur in a narrow zone, significantly smaller than the zone of severe plastic deformation (wave formation zone). A mathematical model of the explosive welding temperature field is proposed, in good agreement with the experimental results.
      原文链接:
    • NSTL
    • Elsevier

    Experimental study on CHF of one-side heated rectangular heat sink with regard to fusion divertor cooling

    Lim, Ji HwanPark, MinkyuPark, Se Hyeon
    17页
    查看更多>>摘要：When the critical heat flux (CHF) is reached, the heat transfer efficiency rapidly decreases. Therefore, CHF must be considered as a potential hazard for a stable cooling system operation. In particular, securing the thermal margin of plasma-facing-components inside the tokamak loaded with ultra-high heat flux is directly related to system safety. According to this necessity, in this study, CHF of flat rectagular channel under one-side high-heat load condition was experimentally explored. As a result of analyzing the effect of system parameters on CHF, it was observed that mass flow rate and sub-cooling had a proportional relationship with CHF, whereas pressure had an inverse relationship with CHF. This is because a high mass flow rate and high sub-cooling promote forced convection heat transfer and quickly remove vapors from the flow path, but an increase in pressure reduces liquid surface tension and latent heat, causing early boiling. In addition, the predicton performance of the existing sub-cooled flow boiling CHF correlations was evaluated under the one-side high heat load condition. However, the large difference in experimental conditions and the structural difference between circular tube and rectangular channel made them under-predict the experimental values. Accordingly, we developed new optimized CHF correlations using a Python code grafted with machine learning technology. The developed correatlion can be utilized when evaluating the thermal safety margin of the future tokamak, and can be a great help when establishing a cooling system operation strategy.
      原文链接:
    • NSTL
    • Elsevier

    Drying kinetics and properties evolution of apple slices under convective and intermittent-MW drying

    Joardder, Mohammad U. H.Karim, M. A.
    7页
    查看更多>>摘要：Intermittent microwave-convective drying (IMCD) is a relatively advanced drying technology that is used to overcome the shortcomings of microwave, convective, and microwave-convective drying. No research has been done on the evolution of mechanical properties during IMCD of apple. This research aims to shed new light on the effect of heating patterns on the evolution of the mechanical properties of the apple slice. In this research, comparisons of drying and rehydration kinetics of conventional drying IMCD derived samples have also been carried out in light of their mechanical properties changes. The result shows significant differences in drying and rehydration kinetics between IMCD dried and convective dried food materials. To remove the same amount of moisture, convective heating takes about 10 times more time compared with IMCD. Moreover, better rehydration capacity and appearance have been found in IMCD dried samples. Eventually, IMCD offers an energy-efficient quick drying option along with retaining higher quality than conventional drying.
      原文链接:
    • NSTL
    • Elsevier

    Theoretical framework for estimating design reactor pressure for water-based hydrothermal carbonization (HTC) systems

    Alvarez-Murillo, AndresLibra, Judy A.Ro, Kyoung S.
    11页
    查看更多>>摘要：Hydrothermal carbonization (HTC) has been shown to be a valuable system component in sustainable management strategies for wet organic residues from agriculture, industries and municipalities. While the reaction temperatures in HTC are much lower than those in alternative thermochemical processes, the pressures reached in HTC are much higher, rising with temperature as the autogenic pressure of water rises, and as reaction gas is produced from hydrothermal reactions. An important basis for designing cost-effective equipment for the HTC systems is understanding the safety aspects and costs associated with the reactor pressure. This paper presents a theoretical framework to predict the expected HTC reactor pressure for hydrothermal reactions with biomass that produce CO2. A model was developed that uses the thermodynamic properties of CO2-water mixtures at HTC reaction conditions and was validated using well-defined experiments with CO2-H2O. Comparison of the pressures predicted by the theoretical model to actual pressures in HTC reactions with real biomass (bark mulch, sugar beet pulp) showed relative errors ranging from -18.5% to 7.3%. A simple design procedure was suggested to predict HTC reactor pressure and demonstrated on a further case. The results of a sensitivity analysis showed that the pressure estimation is most affected by the parameters related to the amount of CO2 formed during the HTC reaction. The easy-to-follow methodology developed in this study will help researchers, design engineers, and manufacturers to estimate the pressure reached in the HTC reactor based on desired design goals and promote the widespread use of HTC for converting wet wastes into value added hydrochar which can improve soil health and reduce environmental pollution.
      原文链接:
    • NSTL
    • Elsevier

    Operational regimes in a confined pulsatory two-phase thermosyphon

    Bhardwaj, UtsavDas, Shyama Prasad
    16页
    查看更多>>摘要：The major loopholes in existing criteria used for the classification of various flow characteristics/patterns in the confined two-phase closed thermosyphons (TPCTs), and the additional accountable parameters have been recognized. The phenomenology of flow regimes in confined TPCTs, and the influence of confinement on their heat transfer characteristics need to be understood better. Also, the mitigative solutions to enhance the operational limits of a confined TPCT need to be developed. So, a visual and detailed study of the thermohydrodynamics of TPCTs is essential. The current research presents a confined pulsatory two-phase thermosyphon (PTPT), which is a hybrid cooling device derived by combining the ideologies of a pulsating heat pipe (PHP) and a TPCT. The functioning of PTPT involves thermosyphon phenomena in its evaporator coupled with oscillations of a liquid-vapor interface in its condenser. An experimental study of different flow regimes, viz. bubbly, bubbly/slug, geyser, slug, churn and annular flows, and associated heat transfer mechanisms observed in the PTPT at different applied thermal boundary conditions has been performed. The two-phase flow in PTPT has been rigorously mapped and an empirical flow regime map has been developed using the confinement and Jakob numbers for regime characterization. Contrary to the conventional notions, highly confined as well as unconfined flow patterns have been observed within a narrow range of the confinement number, with unconfined ones at the highest confinement number. The film-flow along with the corresponding instabilities, nucleation and growth of vapor bubbles, inter-regime transitional states, and associated pressure fluctuations have been studied in detail.
      原文链接:
    • NSTL
    • Elsevier

    Convective heat transfer and friction factor characteristics of molten salts in spirally fluted tubes

    Zhang, ShengSun, Xiaodong
    16页
    查看更多>>摘要：Spirally fluted tubes have been widely used for heat exchangers due to their superior heat transfer enhancement. However, most of the previous studies focused on the effects of a limited number of geometric parameters, i.e., the flute pitch and flute depth, on convective heat transfer and friction factor characteristics of low-Prandtlnumber fluids, i.e., air and water. The correlations developed in these studies may not be accurate or applicable for medium-Prandtl-number fluids, such as molten salts. A numerical analysis using a Computational Fluid Dynamics (CFD) tool, STAR-CCM+, is therefore carried out in this study to systematically investigate the effects of four geometric parameters, including the flute pitch p, flute depth e, flute start number N-s (or flute helix angle theta), and trough length L-tr on convective heat transfer and friction factor characteristics of a medium-Prandtlnumber fluid, FLiNaK (46.5LiF-11.5NaF-42KF mol %), in spirally fluted tubes. In addition, the convective heat transfer and Darcy friction factor correlations are proposed and validated, with +/- 20% uncertainties, for medium-Prandtl-number fluids under the following conditions: Re = 88-1600, Pr = 2.5-40, p/Dc = 0.44-3.51, e/D-c = 0.10-0.40, theta/90 = 0.20-0.81, and L-tr/D-c = 0.71-2.16. The correlations proposed help improve the design of spirally fluted-tube heat exchangers.
      原文链接:
    • NSTL
    • Elsevier

    Analyzing the combustion oscillation of a gas turbine for syngas based on the characteristic time-scale theory

    Mu, YanfeiLi, ZongyanLuo, KunFan, Jianren...
    9页
    查看更多>>摘要：When the ambient temperature is less than 10 degrees C in winter, the gas turbine for syngas in Huaneng Tianjin integrated gasification combined cycle (IGCC) power station has an evident combustion oscillation phenomenon, which seriously affects the production safety and efficiency. This study used the characteristic time-scale theory to guide the operation, thereby reducing the combustion oscillation of the gas turbine for syngas. The work progressed as follows. First, the boundaries of the combustion oscillation and maximum temperature safe limitations were defined based on the operational data from the extreme ambient temperature in summer and winter in the Huaneng Tianjin IGCC power station. Then, the mathematical model of combustion with critical parameters, such as ignition delay time, the adiabatic temperature of the flame, and flame speed, was constructed using the binary quadratic regression method under various combinations of dry syngas, natural gas, and steam flow rates. Finally, an operation scheme for reducing the combustion oscillation of the gas turbine for syngas in winter was designed, as well as the limitation boundary and computation model. This operation scheme can effectively reduce the combustion oscillation in winter; this was confirmed in actual operation. The results of this study should assist gas turbine designers in improving the safety, reliability, and stability of syngas turbines.
      原文链接:
    • NSTL
    • Elsevier