查看更多>>摘要：The investigation of advanced large-scale energy storage systems is needed due to the installation and grid-connected generation of instability renewable energy. As the compression heat tends to low temperature, in this paper, a liquid carbon dioxide energy storage system with heat source and its modification are proposed, in which an ice storage carbon dioxide liquefaction scheme and a modified recuperator layout are specially designed. Firstly, thermodynamic and exergoeconomic models are developed to evaluate the proposed systems; Then, a comprehensive understanding of the proposed system is obtained by parametric analysis and multiobjective optimization; Finally, a comparative analysis shows the attractiveness of the proposed system. The results show that the modified recuperator configuration improves the system performance by recovering more turbine exhaust energy, and the relative cost difference is reduced by 6.86%. The efficiency and economy of the system are greatly influenced by the compressor and turbine performance. Multi-objective optimization obtained compromise results of total exergy efficiency and unit output cost of 68.79% and 34.04 $/GJ. The comparative analysis reflects that the proposed system has certain superiorities.
查看更多>>摘要：Intelligent thermal protection systems with self-perception and decision-making functions are preferable for future spacecraft. Online thermal response prediction is a key step to intelligent thermal protection systems. In this paper, the concept of Dynamic Data-Driven Application System between simulations and experiments is employed to achieve online thermal response prediction. In this framework, measured temperature data are injected into an online heat transfer model, and the real-time temperature at the bottom of the thermal protection system is calculated. A demonstration test system is built and experiments were carried out to validate the method. The effects of dynamic data and the number of sensors on the temperature prediction accuracy are analyzed. Dynamic data-driven temperature predictions under transient heat load are also carried out. The dynamic data-driven model can reduce the temperature prediction error from 25.9% to less than 10% based on the experimental results, and increasing the number of sensors can also improve the prediction accuracy. The model also has good adaptability under accidental overload and cyclic load. The Dynamic Data-Driven Application System framework presented in this work can be used for online safety assessment of thermal protection systems and active flight control.
查看更多>>摘要：In an adsorption cooling system (ACS), it is essential to design the most efficient AdHEx in terms of compactness, heaviness, and ACS performance parameters. For this purpose, the coupled effects of structural type, body material, and fin geometrical specifications of its adsorber heat exchanger (AdHEx) need to be investigated. Therefore, a three-dimensional distributed-parameter model is developed and validated to conduct a comprehensive parametric study on finned flat-tube and annular finned-tube AdHExs. In this regard, two different design criteria of AdHEx heat transfer area to adsorbent mass ratio (S/m_(ads)) and inter-particle mass transfer resistance are adopted as common bases of the comparisons. The results indicate that for any given bed geometrical configurations, there exists a certain threshold value for the thermal conductivity of AdHEx body material. For values greater than it, the specific cooling power (SCP) and volumetric cooling power (VCP) are approximately invariant. In contrast, the coefficient of performance (COP) is mainly influenced by the volumetric heat capacity (VHC) of the AdHEx body material such that it steadily decreases by increasing VHC. Independent of body material, utilizing the smallest fin dimensions for an AdHEx leads to the highest SCPs at the cost of lowering COP, dramatically. However, maximizing VCP is more complicated because the variations of VCP with fin height show entirely distinct behaviors for different body materials and AdHEx type. It is found that estimating the superiority of an AdHEx over another is beyond the ability of common rules of thumb because of complicated transport phenomena within the adsorber beds. In light of this, the approach and results of this study properly bridge the gap between the scientific and practical aspects of designing an AdHEx based on application constraints.
查看更多>>摘要：This paper analyses heat and flow transfer in a double-pipe heat exchanger (DPHE). In the DPHE, the turbulators are added to the inner tube to raise its thermal performance. Although this approach increases the heat transfer, the pressure drop raises, leading to greater energy consumption. Therefore, the design of the turbulator should be optimized. This study optimizes the heat transfer and pressure drop of a DPHE with symmetrical 4-digit NACA airfoils with zero angle of attack as a turbulator. These airfoils have been exploited in a DPHE for the first time to reduce pressure drop according to their negligible production vortices. The thermal performance of four types of airfoil-shaped turbulators with different sets of the thickness (t), pitch ratio (PR), and Reynolds number (Re) have been assessed through experimental and computational fluid dynamics. In this context, the correlation of the Nusselt number (Nu) and friction factor (f) has been computed experimentally. Then, an objective function including the friction factor minimization and Nusselt number maximization has been optimized through Genetic algorithm to find the Pareto front. The results highlighted that η enhances under small sets of Re. Further, an increase of t and PR drop result in a greater f and Nu, raising η in overall. Finally, the maximum η = 1.91 has been reached under Re = 6000, t = 0.3, and PR = 1.11.
Yulia Yu. PlaksinaAlexey V. PushtaevAlexander V. UvarovNikolay A. Vinnichenko...
12页
查看更多>>摘要：New hybrid simulation technique is proposed for natural convection flows, which combines experimental measurements of the instantaneous temperature fields with numerical integration of the fluid dynamics equations. Experimental temperature distributions are used to determine the buoyancy term, which enables one to obtain the velocity and pressure fields without extra measurements. Solution of the energy equation is replaced with experimental data, hence the technique can be used even if the energy equation contains unknown source terms or if the boundary conditions for temperature are unknown. The approach is demonstrated for Background Oriented Schlieren (BOS) measurements of three natural convection flows: natural convection near a heated vertical plate, convective plume from a heated horizontal wire and horizontal convection driven by nonuniform radiative heating of liquid surface. The velocity fields, obtained by reconstruction in steady and unsteady flows, exhibit good agreement with numerical simulations if the input temperature data are accurate. Moreover, the hybrid simulation takes into account the flow asymmetries in a particular experimental run. However, spatially limited measurement region or underestimation of the peak temperature, typical for BOS measurements of the thin thermal layers in liquids, lead to underprediction of the velocity and pressure disturbances in hybrid simulation.
Francisco Fernandez HernandezAntonio Atienza-MarquezJose Miguel Pena SuarezJuan Antonio Bandera Cantalejo...
15页
查看更多>>摘要：This paper presents an analysis of a thermal zoning system integrated in a Heating, Ventilation and Air-Conditioning (HVAC) system based on an air-to-water heat pump with a ducted fan coil. Zoned systems are based on independently controlling the temperature of each of the zones of a building. When a zone is not occupied or not in demand, the control board sends a control signal to the zone's motorised damper which interrupts the airflow supply to that room. Although this control system is gaining popularity in the residential sector, the results obtained in terms of thermal comfort and energy consumptions are not evident and should be documented. Besides, the control strategy is based on an algorithm that allows acting on the heat pump, setting the set-point temperature, and on the fan-coil, setting the fan speed. Based on this, it is possible to design an algorithm to optimize the performance of the installation ensuring thermal comfort and achieving energy savings. The thermal zoning and the HVAC control system are modelled and simulated in Trnsys17 for the case of study of a residential dwelling, compared with two different configurations: a non-zoned ducted fan coil and individual fan coils. Important benefits are obtained in the evaluation of thermal comfort, with higher values of PPD in all zones. From the point of view of energy consumption, the influence of the thermal zoning on the performance of the heat pump reports important energy savings. Finally, an economic analysis results in payback periods lower than 4.9 years.
查看更多>>摘要：The widespread application of lithium-ion batteries as the practice facility of energy storage has come alongside much unforeseen fire safety and thermal runaway issues that leads to increasing research interests. A comprehensive understanding of the thermal features of battery packs and the heat exchange process of energy storage systems is imperative. In this paper, a three-dimensional thermo-electrochemical model has been developed to simulate the detailed temperature distribution of battery packs. The numerical analysis of the cooling effect with both natural and forced air ventilation configurations are compared as well. Moreover, the artificial neural network (ANN) model was coupled with the computational fluid dynamics (CFD) simulation results to perform an optimization of a specific configuration battery system considering configuration dimensions and operating conditions simultaneously. The ANN model builds a relationship between battery spacing and ambient cooling properties. It was found that the changing of ambient pressure creates a larger temperature drop under the forced air cooling than that under natural ventilation. The optimum design for the battery pack can decrease the maximum temperature and the temperature difference by 1.94% and 17%, respectively. Overall, the present modelling framework presents an innovative approach to utilising high-fidelity CFD numerical results as inputs for establishing ANN training dataset, potentially enhancing the state-of-art thermal management of lithium-ion battery systems reducing the risks of thermal runaway and fire outbreak.
查看更多>>摘要：To meet the ever-increasing demand for electricity, Hydro-Quebec is investigating the viability of running its existing hydroelectric generators at higher power levels than their current operating limits. To assist in this investigation, numerical models capable of simulating the conjugate turbulent air flow and heat transfer phenomena in these generators were formulated and then validated, by using them to predict these phenomena within a scale model of a hydroelectric generator available at Hydro-Quebec's Research Institute and comparing the results to complementary experimental data. Reynolds-averaged governing equations were used, with turbulent stresses and heat fluxes approximated using eddy-viscosity and eddy-diffusivity approaches, in conjunction with the standard k - ε and a k - ω shear-stress-transport models, constant turbulent Prandtl number, and specialized treatments of the near-wall regions. Variable- and constant-fluid-property formulations (with coupled and decoupled solutions of the fluid flow and heat transfer) were assessed. The discretization of the complex geometry and the governing equations, and solutions of the discretized equations, were done using commercial codes. These numerical models gave favorable and comparable results, with predictions of global flow quantities (such as windage losses and overall mass flow rates) lying within 4%, and average and maximum temperatures of the pole surface within 5℃ and 3℃, respectively, of the corresponding experimental data when using the constant-property, coupled, standard k - ε model with specialized wall functions. However, the equivalent decoupled model, which was the least computationally intensive, was also adequate for the task at hand. Numerical assessments of two alternate ventilation configurations in the scale model were also undertaken. They showed that increasing the surface area of the spider arms reduced the maximum temperature of the pole by 2.6℃; and restricting the rotor inlet area reduced the windage losses and the maximum temperature of the pole by 4.7% and 1.5℃, respectively.
查看更多>>摘要：A procedure is presented that uses estimations of soot volume fraction and temperature fields to (i) calculate the spatially-resolved radiative intensity emitted from soot, and (ii) model the incident radiative power released from the flame by soot particles on a surface. The procedure is validated using both experimental and simulated data obtained from a canonical laminar diffusion flame about 5 cm high. First, estimations of soot volume fraction and temperature derived from non-intrusive experimental measurements are used to calculate the reference soot radiative intensity and to simulate the signals captured by radiometers located at different positions relative to the flame. Then, simulated radiometer signals are processed using different viewfactor methodologies to retrieve the values of integrated soot flame radiation, which are then compared to the reference intensity obtained from soot volume fraction and temperature by solving the radiative transfer equation. Results show that point-source methods accurately estimate the reference intensity (within 2% of error) when using simulated signals from radiometers positioned 7 and 10 cm from the flame axis and up to three times the flame height. Moreover, the double cylinder model accurately estimates flame radiation from measurements performed above three times the flame height.
查看更多>>摘要：An experimental and numerical study of the solid-liquid phase change process of three paraffin waxes, having different characteristic melting temperatures (42, 55, and 64℃) embedded in two different cellular periodic aluminium structures fabricated by additive manufacturing, thought of as passive heat sinks, is reported. The aluminium solid media are composed of repeating elementary cells derived from the body-centred cubic (BCC) model and have a porosity of 87%. The samples were tested in an upright position and laterally heated by applying three different heat fluxes (10, 15, and 20 kW m~(-2)). The experimental results showed the effects of the heat flux, melting temperature, and size of the metal cells on the temperature of the heated surface. Numerical simulations were performed to validate a simplified model for the thermal analysis of the test modules using reduced domains. Owing to the characteristics of the experimental melting front, which is almost parallel to the heated side, suggesting a negligible effect of natural convection, the numerical simulations performed with ANSYS Fluent could be conducted on computational domains that represent only small repetitive portions of the test modules, thus allowing substantial savings in the computational time. This simplified method has been proven to yield results that are in good agreement with the experimental data. Based on the numerical results, when the metal structure is finer, the evolution is faster, and the time required to completely melt the phase change material (PCM) is shorter. This numerical model may be confidently used by thermal engineers to design PCM-based heat sinks for electronics cooling. Finally, an empirical model previously developed for paraffin embedded in metal foams was applied to the present paraffin-BCC composite structures.
NSTL
Elsevier