Applied Thermal Engineering最新文献

Most newly constructed buildings are now built to energy-passive standards, which set requirements for specific heating demand, non-renewable primary energy use, building envelope airtightness, and the frequency of exceeding permissible indoor air temperatures in summer. These temperature exceedances relate to the room’s thermal stability, determined by the potential for heat accumulation in surrounding structures over the daily cycle. For buildings with lightweight construction, implementing a Thermal Energy Storage (TES) solution can significantly enhance their energy accumulation ability. This article addresses the design and evaluation of a progressive cooling ceiling system combined with active ventilation system components, including the incorporation of TES based on PCM materials. The proposed solution aims to improve the thermal stability of occupied spaces, thereby significantly reduce the need for mechanical cooling. The research developed a new methodology for measuring the energy performance parameters of modular cooling ceiling systems, with its implementation thoroughly discussed. The evaluation of this solution was conducted within the context of the entire energy system for a reference building, considering various construction types (lightweight, medium, heavy). The overall potential energy savings range from 13% to 32%, depending on the building’s construction, while still meeting the required thermal comfort criteria.

To address the issue of temperature increase in battery modules using liquid cooling plates, a convex pack structure within the flow channel is proposed to enhance flow efficiency. High temperatures can lead to battery performance deterioration, increased safety risks, and reduced service life. The optimal parameters for the convex structure (radius, transverse spacing, and longitudinal spacing) were determined through simulation analysis and orthogonal experiments. The effects of discharge rate, ambient temperature, coolant inlet temperature, and inlet speed on the heat dissipation of the battery module were also studied. The results show that the convex pack structure enhances heat transfer by increasing the contact area and fluid velocity while inducing eddy currents to achieve lateral mixing. The optimal parameters were found to be: radius (r) = 0.75 mm, horizontal spacing (x) = 3.50 mm, and vertical spacing (y) = 4.50 mm. At low discharge rates, the battery performs well, but high discharge rates negatively affect temperature uniformity. An increase in ambient temperature raises the temperature difference and maximum battery temperature. Lower coolant inlet temperatures reduce the maximum temperature but may result in uneven temperature distribution. Achieving a balanced coolant flow rate is essential to minimize temperature variations and control pressure buildup. This research introduces an innovative heat transfer structure, the convex pack, which significantly improves cooling efficiency. Further research on enhanced heat transfer structures is necessary to continue advancing cooling technologies for battery modules.

In this study, experiments were conducted on helium flow within a compact helical tube heat exchanger. High-temperature helium and deionized cooling water, flowing in opposite directions, were allocated to the shell side and tube side, respectively. The Reynolds number of helium ranged from 3 × 10³ to 1.6 × 10⁴ under an operational pressure of 2.1 MPa. Measurements were taken for helium temperature, tube outer-surface temperature distribution, pressure, and mass flow rate to illustrate the flow and heat transfer characteristics. Sensitivity analysis of thermal–hydraulic parameters, including heat transfer power and efficiency under various operational conditions, was performed. The convective heat transfer coefficient and pressure drop were calculated. The transition point (Re = 9000) between laminar and turbulent flow of helium on the shell side was identified, and empirical correlations for the Nusselt number and friction coefficient were proposed. The experimental results indicate that the heat transfer performance of helium in the compact helical tube heat exchanger exceeds that of water in large-scale helical tube heat exchanger by approximately 20.75 % under fully developed turbulence, while the flow resistance characteristics remain essentially consistent.

Traditional proton exchange membrane fuel cell (PEMFC) systems face the challenges of strong thermal–electrical coupling and insufficient heating capacity. This study proposes a PEMFC–heat pump combined system considering dual heat source, which effectively utilizes fuel cell waste heat and environmental heat to achieve significant improvements in thermal–electrical decoupling and heating capacity. Energy, economic, and environmental analysis models were established, and the effects of key parameters on the combined system were systematically analyzed, followed by multi-objective optimization. Results show that the PEMFC current density has the largest effect on the heating capacity, while the heat flow ratio exerts the strongest influence on economic performance. The minimum pollutant emissions are achieved when wind power is adopted for hydrogen production. Under an ambient temperature of 248.15 K, the combined system increases the heating capacity by 12.8 % and reduces the levelized cost of energy and greenhouse gas emissions by 7.85 % and 15.9 %, respectively. The optimal solution presents a strong nonlinear relationship with the PEMFC current density and condenser undercooling, the heat flow ratio is close to the upper limit (0.99), and the operating temperature is close to the lower limit (333.4 K). These findings provide innovative thermoelectric decoupling and efficient energy supply solutions for PEMFC systems and have important implications for accelerating the low-carbon transition of regional energy systems.

During the process of regeneration, freeze concentration exhibits high energy efficiency. The performance of regeneration is directly affected by the separation effect and salinity level of ice under different regeneration conditions. In order to evaluate the energy efficiency of deicing under different conditions, a freeze concentration solution regenerator unit was constructed and equipped with a heat pump system. Based on experimental data, the theoretical model of average distribution coefficient and deicing energy consumption is established to study the influence of ice separation efficiency and solute residue on the deicing energy consumption. Results show the ice salinity reduces the effect of ice amount on regeneration concentration. The increase of icing difficulty and ice salinity are the two main reasons that affect the decrease of deicing operation efficiency of high concentration solution. As the amount of ice separating decreases, the deicing energy efficiency is more sensitivity to the solute residue. The reduction rate of energy consumption is equal to the proportion of influence of solute residue in deicing energy efficiency. From 6%, 8%, 10% and 13% concentration, solute residue increases the deicing energy efficiency by an average of 2.4%, 3.4%, 4.6%, and 6.6%, respectively. The influence of solute residue on deicing operation efficiency can be reduced by increasing separation efficiency. The deicing energy consumption diagram of anti-frost solution freeze concentration system is proposed. The investigations will be helpful to improving the energy efficiency and steadiness of the heat pump with freeze concentration.

In advanced aero-engine thermal management systems, aviation kerosene serving as a coolant unavoidably works in a vibration environment. In this article, the laminar heat transfer performance of Chinese aviation kerosene RP-3 flowing through a horizontal micro-tube under various vibration conditions at supercritical pressures was investigated experimentally. The effects of several impact factors such as system pressure, heat flux, mass flux, inlet temperature, vibration acceleration, and vibration frequency on the heat transfer enhancement were explored in a systematic manner. Experimental results indicate that: (i) the vibration could lead to intense thermal and momentum mixing among different boundary layers of tubular laminar flow and significantly strengthens the heat transfer, and the higher Re can lead to a stronger enhancement effect. The maximum observed HTER across all experimental data is 2.8, occurring at x/d = 224.1 with the inlet temperature of 373 K; (ii) HTER hardly changes with system pressures, exhibiting a maximum relative deviation of 3.9 % at different pressures. Heat transfer enhancement has a strong dependency on heat flux, as the heat flux increases from 36 kW/m² to 108 kW/m², the average HTC increased by up to 36.4 %; (iii) the HTC and HTER monotonically rise with increasing vibration acceleration. Peak values in HTC and HTER are observed at vibration frequencies of 625 Hz, 191 Hz, and 242 Hz; (iv) vibration has little impact on the thermal acceleration but noticeably weakens the buoyancy close to the outlet area at high heat flux. Two well-predicted correlations for the Nu in tubular laminar flow, one with vibration and one without, are proposed.

This study numerically investigates a phase-change material heat sink using gallium and Primitive Triply Periodic Minimal Surface (TPMS) cells structure as in-fill for applications requiring high heat-flux dissipation, e.g., electronics. Initially, we used only gallium without thermal conductivity enhancers, relying solely on buoyancy-driven circulations of melted gallium for the convective cooling of a hot sink base. However, this study aims to surpass gallium’s innate heat-dissipation capability. Therefore, the sink is enhanced with a high conductivity Primitive TPMS cells structure. Hybridization of conduction and convection heat dissipation enhancements is accomplished by using only one layer of the TPMS cells installed at the hot sink base. Comparison with the full TPMS structure filling option is made. In the full TPMS structure filling option, the sink relies mainly on conduction through the TPMS structure’s body and less on natural convection. However, equipping the sink with TPMS structures reduces the overall latent heat storage capacity. Therefore, additional gallium is added to the sink to match the overall gallium content in the baseline case without TPMS structures. Furthermore, the effect of the boundary conditions applied at the wall is explored. The results show considerable improvements in heat dissipation and peak temperatures with the TPMS cells, where by the time 100 s (about 20 s post complete melting) peak temperatures are about 13 percent lower than in the case without TPMS structures. Furthermore, the full structure filling option demonstrates superior performance over the partially filled ones, highlighting the importance of conduction through TPMS cells over convection in the free gallium space. Unlike the partial filling option, conduction in the full filling option has a continuous favorable impact on heat dissipation from the onset of the heating process.

Wavy mini-channel heat sinks (MCHS) can disrupt the development of the thermal boundary layer, resulting in superior performance compared to straight MCHS. For complete utilization of the coolant, this study proposed and optimized a non-uniform sinusoidal MCHS with varying wavelength or varying amplitude along the flow direction. The optimization for five design variables was accomplished through a multi-objective genetic algorithm, where the thermal resistance θ or the pressure drop Δp were defined as two objectives. The computational fluid dynamics (CFD) software was employed to solve all direct problems encountered during the evolutionary process. Compared to the straight MCHS with different channel widths, the optimal designs achieved reductions of 27.74 % in θ or 59.51 % in Δp. Simultaneously, all the optimal values of the wavelength ratio and amplitude ratio indicate that enhancing the heat transfer performance downstream is more efficient. It was observed that among the five design variables, the number of wave cycles is the most relevant parameter with a Spearman’s correlation up to 0.983. Subsequently, a multiple-criteria decision-making approach was employed to ascertain the best compromise solution to balance the two objectives. Although the θ of the best compromise solution could be higher by 38.57 % than that of the lowest θ solution, the Δp presents a more substantial reduction of 92.45 % after the trade-off. Compared to the straight MCHS with the same Δp, the best compromise solution with varying wavelength reduces the θ and the standard temperature deviation by 26.20 % and 76.98 % respectively, while lowering the average base temperature by 3.07 K. Therefore, the optimal non-uniform wavy MCHS, along with the optimization approach presented, is meaningful for practical applications.

Oxygen diffusion controlled combustion occurs when local oxygen transport is slower than the chemistry, commonly found in porous combustible material or combustible material embedded within an inert porous medium. This mode of combustion, such as smouldering, can pose dangerous fire risks and also be harnessed in environmentally beneficial applications. However, the oxygen diffusion limitation is poorly understood in all contexts and persists as a key knowledge gap. Quantitative analysis of oxygen diffusion effects is therefore crucial for understanding the combustion behavior of combustible porous media and developing precise smouldering simulation models. In this paper, a reactive transport model incorporating both oxygen diffusion and chemical consumption was developed. Using coal as the model fuel, the impacts of key parameters on global mass loss during the one-dimensional diffusion combustion of coal samples were simulated and compared with TGA experiments conducted within a range of oxygen concentrations between 3–21%. Using this method, key kinetic and oxygen diffusion parameters were obtained within reasonable ranges by using a genetic algorithm optimization method. With these optimized parameters, the local oxygen distribution profiles in the samples at different inlet oxygen concentrations were simulated. The results indicate that oxygen diffusion can lead to large oxygen concentration differences within the coal samples, exceeding 63% of the inlet oxygen concentration. These oxygen differences can impact the local chemistry throughout the sample, and lead to fundamental errors in analyzing global kinetic analyses, if the transport effects are not considered. Altogether, this study delivers new insights into a potentially rate-limiting phenomenon that is relevant in progressing knowledge on many fire problems and engineering applications.

Range has emerged as a significant barrier to the advancement of electric vehicles, necessitating the development of high-energy–density battery packs. However, the conventional battery integration method, CTM (Cell to Module), has a relatively low space utilization rate, which presents a challenge to the enhancement of vehicle range. Consequently, a novel battery pack integration method, CTP (Cell to Pack), has emerged as a potential solution. In order to enhance the integration degree and effective energy density of the battery pack, a CTP and a symmetric serpentine runner liquid cooling plate are proposed in this paper. A thermal model of a single cell was constructed, and the cooling performance of the battery pack under different discharge conditions was analyzed. The optimal inlet water temperature and coolant mass flow rate were then determined. The findings indicate that the battery pack devised in this study exhibits commendable cooling capabilities and is capable of satisfying the cooling requirements associated with a 2C discharge scenario. Furthermore, when the battery pack is operated under Chinese Light Vehicle Driving Conditions (CLTC), the inlet flow rate of 2 L/min has been observed to reduce the maximum temperature differential by 1.31 °C in comparison to a scenario without internal coolant circulation.