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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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    Stratum temperature recovery considering groundwater advection in periodic operations of deep borehole heat exchangers

    Jiao K.Bai B.Yang R.Yu B....
    13页
    查看更多>>摘要：During periodic operations of the deep borehole heat exchanger (DBHE), stratum temperature recovery is significantly affected by groundwater advection, but it has not been fully addressed. In this study, the stratum temperature recovery of long-term and periodic operations of DBHE is quantitatively analyzed via an improved analytical model developed in our previous work. To characterize its dependence on Darcy velocity, recovery rate, quasi-equilibrium time, and thermal impact scope are accordingly defined. Sensitivity analyses of thermal conductivity and thermal dispersion are also conducted. The results show that the recovery rate increases with Darcy velocity but varies slightly with heat extraction power inside the borehole. There is a critical Darcy velocity in periodic operations. When the groundwater advection velocity reaches the critical value, stratum temperature at the borehole wall gets close to its initial state after every recovery period, and multiple low-temperature valleys downstream of the groundwater advection occur. The greater thermal conductivity of medium and thermal dispersivity can result in the higher critical Darcy velocity. The thermal impact scope of the DBHE decreases overall when Darcy velocity increases, while the downstream thermal impact radius has a sharp increase for low Darcy velocities before the decline.
      原文链接:
    • NSTL
    • Elsevier

    A novel active volumetric rotating disks solar receiver for concentrated solar power generation

    Zaversky F.Astrain D.Randez X.
    13页
    查看更多>>摘要：A new active, first of its kind, volumetric receiver prototype is used in this study to obtain the conclusions about its thermal performance. The rotating disks cooling, was studied first, numerically, using a CFD software and second, experimentally, using a laboratory-scale prototype. This study evaluates the convective heat transfer from rotating disks to a transverse air crossflow. The thermal energy exchange on the disk surfaces allows us to calculate the heat transfer coefficient from disk surface temperature and the thermal performance of the receiver prototype and local Nusselt number through the receiver depth are also a key point in the research. The influence of rotational speed and air mass flow on the heat transfer coefficient is also studied. Differences between numerical and experimental results show high concordance, with a relative error below 15% in the worst point. The thermal performance shown by the lab-scale receiver is promising for the further development of the active Open Volumetric Air Receivers (OVAR) technology. The obtained thermal efficiency results show an improvement of around 10% at 900 °C when compared to the current state of the art of volumetric receivers.
      原文链接:
    • NSTL
    • Elsevier

    Thermodynamic and exergoeconomic assessment of a new combined power, natural gas, and hydrogen system based on two geothermal wells

    Mehdikhani V.Khalilian M.Abdolalipouradl M.Mirzaee I....
    16页
    查看更多>>摘要：In the present study, the use of two geothermal wells with different temperatures and pressure characteristics was considered. The application of a combined system is a promising way to improve the system thermodynamically. The possibility of using the combined systems with two geothermal wells has not yet been done. As an attempt to fulfill the gap in the field, a new combined power, natural gas, and hydrogen system was proposed considering two geothermal wells. The system consists of a novel flash configuration, Organic Rankine Cycle (ORC), Liquefied Natural Gas (LNG), and Proton Exchange Membrane (PEM) systems. The proposed system is investigated from energy, exergy, and exergoeconomic aspects. In addition, it aimed to perform a comprehensive parametric study and optimize the system. Engineering Equation Solver (EES) is used to perform the simulation and optimization. The optimization results for the system at High Temperature Well (HTW) of 230 °C and Low Temperature Well (LTW) of 190 °C led to 3.575 kg/hr, 13490 kW, 21651 kW, 17.14%, 44.16%, and 19.86 $/GJ values for the hydrogen production, net output power, total exergy destruction, thermal efficiency, exergy efficiency, and power specific cost, respectively. Additionally, the parametric study showed that the net output power, as well as the thermal and exergy efficiencies, increase by increasing the temperature of HTW and have maximum values with the pressure of separators while the hydrogen production has a constant value. Also, according to the result, the thermal efficiency has been improved by 3.18% compared to similar studies.
      原文链接:
    • NSTL
    • Elsevier

    Thermal, thermodynamic and exergoeconomic investigation of a parabolic trough collector utilizing nanofluids

    Vahedi B.Golab E.Nasiri Sadr A.Vafai K....
    21页
    查看更多>>摘要：The exploitation of solar energy facilitates the renewable energy paradigm. In this regard, parabolic trough collectors (PTC) are considered as a useful set-up to absorb solar energy. Simultaneous study of thermal, thermodynamic, and exergoeconomic performance of PTC systems paves the way for designers and manufacturers to not only have a better insight into understanding the underlying concepts about the operation of PTC systems but also to find the most effective and cost-effective circumstances. This study aims at analyzing a practical PTC system by considering an evacuated absorber tube with glass cover, non-uniform heat flux, and taking into account the convective and radiative heat losses. Obtained results demonstrate that employing the glass cover, especially in the low Reynolds numbers regime could remarkably reduce the heat losses up to 22%. The present analysis indicated that considering oil temperature-dependent properties reduced the friction factor around 94 % in the low Reynolds numbers regime compared to that of the cases based on constant properties. In this work a CFD code in the OpenFOAM software was developed to simulate both laminar and turbulent regimes with Lien cubic k-? model (non-linear eddy viscosity model) by adding three types of nanoparticles (Al2O3,Cu,andSWCNT) individually into the synthetic oil. Moreover, the Buongiorno's model (BGM) which considers Brownian, thermophoresis, and turbulence diffusion phenomena was implemented to model the nanoparticles and base fluid interactions. It was found that adding nanoparticles and increasing the Reynolds number have no substantial impact on thermal efficiency of the system, whereas an optimum Reynolds number was found for exergy efficiency and net profit per unit transferred heat load (ηp) of the system. Although injecting SWCNT into pure oil led to augmentation of average convective heat transfer coefficient, PEC, and exergy efficiency, it was found not to be cost-effective. It was established that the obtained results by homogenous model (single-phase model) and BGM were roughly the same, with relative difference of less than 3.1 and 2.4% for the average Nusselt number and friction factor, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Self-powered solar desalination using solar still enhanced by external solar collector and phase change material

    Al-Harahsheh M.Abu-Arabi M.Ahmad M.Mousa H....
    14页
    查看更多>>摘要：The performance of a self-powered double-glass cover solar still with phase change material (PCM) connected to solar collector was studied. Black painted stainless-steel tubes filled with the required amount of PCM were placed at the bottom of the basin covering its surface area. Three modes of experiments were carried out al with cooling the glass cover: first, the solar still alone (SS), second: the solar still being connected to an external solar collector (SSC) and third: the solar still contains PCM and being connected to an external collector (SSCP). The effect of PCM type (sodium thiosulfate pentahydrate (STP), sodium acetate trihydrate (SAT) and paraffin wax (PWAX)) and its amount on the unit performance were investigated. The effect of hot water flow rate from the solar collector, solar radiation, ambient temperature and wind speed on the unit's performance were also investigated. The novelty of the work lies in combining the above techniques and parameters to improve the still productivity under set of controllable operating conditions. The experimental work was conducted in the months of May, June and July of 2019 in northern Jordan. During May, the daily productivity of the SS and the SSC modes were found to be 2.1 and 9.7 L/m2. During July, the productivity was lower by 20% than that of May. The addition of PCM increased the productivity of the SSC system by about 50%. The type of PCM tested has no significant effect on the unit productivity. The addition of the external solar collector to the SS system unit increased the productivity by about 340%. The overall enhancement in productivity of SSCP reached almost 400% compared to that of SS unit.
      原文链接:
    • NSTL
    • Elsevier

    A weather forecast-based control for the improvement of PCM enhanced radiant floors

    Cesari S.Emmi G.Bottarelli M.
    12页
    查看更多>>摘要：Significant energy savings and thermal comfort improvement related to radiant floor systems may not be achieved when underfloor heating/cooling is adopted in lightweight building envelopes. Phase change materials (PCMs) are suitable candidates for providing the necessary thermal inertia with a minimum effect on the construction technology. Impacting variables like internal heat gains, weather conditions and dynamic energy price require the adoption of advanced control strategies to ensure and maximise the energy benefits of PCMs. Despite the potential of model predictive control using weather prediction data has been widely examined by the literature, there is a lack of studies experimentally analysing their implementation in PCM enhanced radiant floor systems. Within the H2020 European project IDEAS the integration of PCMs in a radiant floor system was examined by the University of Ferrara through numerical and experimental investigation. A first prototype was then installed in a small experimental building characterised by a low thermal capacity. Analysis of the monitoring data for the heating period showed that solar radiation strongly impacts on the lightweight building envelope in a short time. Without suitable control, the contribution of PCM that slowly reduced its heat flux during its transition, together with solar heat gains, resulted in an excessive increase in indoor air temperature, wasting the PCM energy saving potential. The aim of the study is the evaluation of a control strategy to improve the management of PCM enhanced radiant floor systems in relation to forthcoming weather conditions in lightweight buildings. The control routine was implemented in the corresponding dynamic energy model in TRNSYS. Results estimated achievable energy saving equal to about 4% and 8% on the heating and the cooling energy demand respectively.
      原文链接:
    • NSTL
    • Elsevier

    Studies on the effect of flow configuration on the temperature distribution and performance in a high current density region of solid oxide fuel cell

    Lee H.L.Han N.G.Kim M.S.Kim D.K....
    13页
    查看更多>>摘要：The effect of temperature distribution on the performance of solid oxide fuel cells (SOFCs) is analyzed for various channel designs in a high current density region. By considering heat accumulation due to local electrochemical reactions and cooling due to flow patterns, the heat distributions in three flow configurations (co-flow, counter-flow, and cross-flow) are analyzed, with the most appropriate channel in the high power region selected. The average operating temperature of the cell is the highest for the counter-flow configuration and the lowest for co-flow. The temperature of the counter-flow configuration is approximately 10 K higher than that of co-flow. The temperature distribution of counter-flow configuration, however, is the most uniform among different flow patterns. The maximum temperature difference in the counter-flow channel is approximately 8 K, but that in co-flow is approximately 22 K. Furthermore, the performance of the cell using the counter-flow configuration is the best in that it shows 5% higher power density and 3.35% higher system efficiency than the other flow configurations. Therefore, the counter-flow configuration is superior at high power because it has the lowest temperature gradient and the best cell performance. This paper contributes to the commercialization of the fuel cell by presenting appropriate parameters for temperature regulation and suitable flow configuration for operation at high power.
      原文链接:
    • NSTL
    • Elsevier

    Operation scheduling optimization of gas–steam–power conversion systems in iron and steel enterprises

    Hu Z.He D.
    10页
    查看更多>>摘要：Iron and steel enterprises exhibit the characteristics of a large amount of energy conversion equipment, many different energy media, and frequent changes in energy supply and demand. Nonetheless, the actual production process involves multiple working conditions that affect the efficiency of energy conversion equipment and can cause unnecessary start–stop behavior. This significantly impacts the energy consumption and operating cost. Therefore, in this study, an optimal operation scheduling model for gas–steam–power conversion systems was established in integrated iron and steel enterprises, considering the minimum energy operating cost and the energy conversion equipment start-up and shut-down cost as the objective functions. The results of single objective optimization, focusing only on energy operation cost, show that the gasholder can play a storage role and the total operating cost of the system can be reduced by 4.70% compared with an unoptimized system. In a multi-objective optimization considering both the energy operating cost and the start–stop cost of energy conversion equipment, only seven input devices are needed to meet the energy demand (with 1# 35 t boiler shut down). Boiler heat efficiency compares favorably with that of the single objective optimization, and the total cost can be reduced by 5.20% compared with the unoptimized system. These results provide guidance for steel and iron enterprises to improve their equipment efficiency and reduce energy costs.
      原文链接:
    • NSTL
    • Elsevier

    Compression effect of metal foam on melting phase change in a shell-and-tube unit

    Guo J.Du Z.Liu G.Yang X....
    18页
    查看更多>>摘要：Metal foams have high thermal conductivity and can be used to markedly improve the low effective conductivity in phase change materials (PCMs) during the process of melting and solidification. Furthermore, natural convection as a main way to heat transfer should be achieved attention in thermal enhancement. To further accelerate the energy storage rate, porous metal foam was compressed and saturated with PCMs. The latent heat thermal energy storage tubes packed with compressed metal foams under various compression ratios were designed and analyzed compared with uncompressed tubes. Good agreement between experimental results and numerical simulations assessed the applicability of the established numerical model. The observations on the melting process including melting fraction, temperature response distribution and uniformity, velocity field, heat flux and energy storage were further discussed. Results showed that the compressed metal foam had a better performance on improving phase change, achieving a reduction of 13.9% for complete melting time. The enhancement of thermal conductivity and the strengthening of natural convection were synergized. However, over compressing metal foam will not help reduce the melting time, leading a prolonged melting time by 129.4% and serious non-uniformity in the melting process of different regions, as well.
      原文链接:
    • NSTL
    • Elsevier

    A 2-D reduced dynamic model for a shell-and-tube based metal hydride reactor for geometry and operation condition optimal design

    Pan C.Braun J.E.Ziviani D.
    12页
    查看更多>>摘要：An MH reactor is a complex multi-physics system and its optimal design is critical to reduce the operation and investment cost. Geometry and operation condition optimal design reported in the literature is often based on parametric study of high fidelity simulations, which is computationally expensive. In this paper, a framework to develop a fast reduced model for a two-dimensional shell-and-tube based MH reactor is proposed. This framework is generally applicable to parabolic PDEs. A lumped capacity model is used as a reduced model basis. Tuning factors that aim to correct the transportation phenomena in a lumped capacity model are introduced. The tuning factors are correlated to key dimensionless group parameters of the system and are constructed by using data from a high fidelity model (HFM). Comparing to pure data-driven models, the proposed modeling framework has good extrapolation ability and hence requires less high fidelity data. The tuning factors establish parametric dependence of the system for efficient optimal design.
      原文链接:
    • NSTL
    • Elsevier