International Communications in Heat and Mass Transfer最新文献

As modern science and technology advance, bionics increasingly plays a crucial role in the progress of thermal science. Bionics can provide superior design ideas for battery thermal management. It can boost battery thermal management technologies to a new level. Currently, bionics has relatively few applications in battery thermal management and is still in its infancy. How to design a reasonable bionic heat dissipation structure to enhance system cooling efficiency and temperature homogeneity, and to reduce system energy consumption and weight? This is an urgent problem for researchers today. This paper analyzes and summarizes the contribution of bionics in battery thermal management enhancement from three aspects: temperature homogeneity of the battery module, system energy consumption, and lightweighting. From the perspectives of unique topology structures and surface morphologies of the living organism, we comb through the key scientific problems and the latest research progress, and propose other new technologies that can be used in the future. In the future, we anticipate significant growth in battery thermal management technologies and industrial applications based on bionics driven by the continuous advancement of modern machining technology and the emergence of new theories in bionics.

This study presents exact solutions for the phenomenon of conjugate heat transfer occurring within a solar receiver tube. The investigation focuses on three distinct configurations: (a) tubes with negligible wall thickness, (b) thin-walled tubes, and (c) thick-walled tubes. The primary objective is to offer precise mathematical representations for the distribution of temperature, as well as numerical values of local and average Nusselt numbers. Furthermore, the study delves into the examination of limiting cases to enhance the understanding of the problem at hand and validating the outcomes. The derived solutions are also utilized to conduct a comprehensive analysis of the specific practical scenario involving the flow of molten salt in both Alloy 625 and stainless steel solar receiver tubes. Inspection of the configurations presented in this study demonstrates that the circumferential conduction heat transfer in the tube wall helps to distribute the heat more evenly along the circumference and mitigate the occurrence of localized hot spots.

Alkali metal heat pipes are the vital components within the core of heat pipe-cooled reactors. The mechanism characteristics of alkali metal heat pipes need to be further analyzed. CFD simulation with the traditional Volume of Fluid method provide an essential means to analyze the flow and heat transfer mechanism in alkali metal heat pipes. For Lee heat and mass transfer equation within the VOF method, the evaporation and condensation coefficients have significant effects on the simulation results, and their values are typically determined empirically, which results in inaccurate or even unreasonable simulation results. To establish a reasonable numerical relationship for the evaporation and condensation coefficients of the working fluid, this paper employs a multi-zone modeling approach for heat pipes and proposes an improved VOF method. During the iterative process, the temperature and pressure values in the corresponding regions are updated based on the iteration results. The mass changes caused by evaporation and condensation processes in each wick and vapor chamber region are calculated and compared with the theoretical value. To validate the proposed method, a high-temperature experimental test platform was constructed, and an 820 mm sodium heat pipe was fabricated. Furthermore, experimental research was carried out at different heat pipe inclination angles and under various heat transfer powers, with the experimental results being compared to those obtained from the model simulations. The simulated temperature values at different points of the model agree well with the experimental values at different heat transfer levels. This research provides insights into the multiphase distribution and pressure change within the heat pipe, offering important references for the optimization design of alkali metal heat pipes.

The transition to renewable energy is heavily reliant on batteries and energy storage devices, making them a crucial technology of the modern era. The sensitivity of batteries to temperature has been a constant challenge in the development of this technology. Thermal management, creating uniform temperature and proper heat transfer by cooling is very critical in these systems. The popularity of nePCMs is increasing in energy storage and cooling systems due to their remarkable latent heat during phase change. This is because nano-encapsulated phase change materials are being widely used. They are considered to be one of the most promising particles in this application. This research is a case study free convection of nano-encapsulated Phase Change Materials (nePCM) slurry with a volume fraction of 5% and a polyurethane shell and n-nonadecane core in a rectangular chamber was homogeneously simulated and investigated. The temperature of the left wall remains consistent and there are three fins present to enhance the transfer of heat. The governing equations are transformed into dimensionless form and solved numerically using OpenFOAM software. Various parameters such as fin geometry, chamber angle, Rayleigh number, and melting point temperature are altered to assess their impact on velocity profile components, temperature distribution, Cr contours, Nusselt number, and fin efficiency. Based on the results, Y-shape and T-shape fin geometries can increase the efficiency of water-nePCM fluid by about 10% for Ra = 100 and about 26 % for Ra = 10⁴ compared to I-shape fin. Also, increasing the Rayleigh number from Ra = 100 to Ra = 10⁴ improves the average Nusselt number for water-nePCM nanofluids by about 100 % in each of the fin geometries.

This study aims to examine the evaporation characteristics of single and multiple droplets on a heated substrate. By utilizing a multi-syringe pump, deionized water droplets were precisely deposited on a copper substrate, ensuring uniformity and accuracy in the experimental setup. The shadowgraph technique was instrumental in determining the droplet contact angle and volume with exceptional clarity and precision. This work numerically predicted the vapor distribution and local evaporation flux across the liquid-air interface. A critical assessment of the role of natural convection at varying substrate temperatures was performed by contrasting diffusion-only cases with those incorporating both diffusion and convection. The findings reveal that the droplet pinning motion remains unchanged across different distances between droplets and various substrate temperatures, indicating that neither vapor accumulation nor substrate temperature significantly influences the behavior of the contact line. Notably, the study identifies a reduction in the evaporation rate of closely positioned paired droplets, related to a shielding effect. However, with increasing substrate temperature, the role of natural convection was found to become more pronounced, effectively reducing the overall evaporation time for both single and paired droplets, thus facilitating a quicker evaporation process.

In light of the substantial importance of accurate void fraction predictions for the engineering design and safety evaluation of two-phase systems utilized in space-related applications, this study is dedicated to the investigation of the drift-flux correlation specifically for microgravity conditions. The present study has collected 458 experimental void fraction data taken in microgravity bubbly to annular flows. The analysis of the collected experimental data evident that (1) the distribution parameters vary with the flow conditions, and (2) the drift velocities under microgravity conditions are exceedingly small. However, the distribution parameter models of the reviewed existing drift-flux correlations fail to accurately capture the variation of distribution parameters with flow conditions under microgravity conditions. Moreover, there is a lack of a simple yet effective way to model the drift velocity of microgravity two-phase flow. To overcome the above weaknesses, a new drift-flux correlation has been proposed by (1) taking the flow condition effect on the variation of asymptotic distribution parameters into consideration, and (2) employing the concept of effective body acceleration and considering the decay of drift velocity in annular flow. The newly proposed drift-flux correlation has been evaluated by checking against the collected data and shows good predictive ability.

A wide range of industrial applications rely heavily on heat transfer during vapor condensation from a mixture of water vapor and noncondensable gases (NCG). For a vertically-mounted condenser plate, the vapor-diffusion boundary-layer thickness is influenced by the interplay of the thermogravitational and forced flow fields, eliciting classical mixed convection scenario. This thickness in turn dictates the condensation heat and mass transfer rates. While condensation in presence of NCG under free and forced convection scenarios are well-characterized in the literature, its counterpart in the mixed convection regime is relatively uncharted. Herein, condensation from an upward stream of humid air over a vertically mounted mild steel condenser surface is characterized under different flow velocities. The free-stream flow is thus directed opposite to the thermogravitational flow induced next to the plate. We observe that with increasing the magnitude of the upward flow velocity of the free stream, the condensation heat transfer coefficient (CHTC) initially decreases until it reaches a minimum at 0.4 m/s, beyond which the CHTC rises again with the flow velocity. Using the Nusselt analogy for mixed convection for the relevant flow regimes we substantiate our experimental findings and extend the observation for predicting condensation behavior under different experimental ambient conditions.

To enhance the fin-side heat transfer capability of circle tube-fin heat exchangers, a novel fin with ellipsoidal dimple-protrusion is introduced in this paper. The effect of the ellipsoidal dimple-protrusion with five different attack angles, 0°, 10°, 20°, 30° and 40°, on the flow characteristic and heat transfer performance are numerically investigated and compared with the traditional heat transfer promoting technology by vortex generators. Both the intensity of secondary flow and heat transfer capability are significantly increased by the ellipsoidal dimple-protrusion. In comparison to the smooth channel and the channel mounted with vortex generators, the secondary flow intensity increases by up to 78.62% and 41.57%, and Nu increases by a maximum of 29.01% and 19.03%, respectively, in the range of Re for 1500–5000. The values of thermal performance factor TPF can reach a maximum of 1.161, which is an improvement of 16.1% compared with the smooth channel, and of 4.89% compared with the heat transfer channel with curved vortex generators. Formulas for Nu, f and TPF with deviations less than ±2%, ±9% and ±2% are fitted. The ellipsoidal dimple-protrusion has a superior application potentiality for heat transfer enhancement in fin-side of circle tube-fin heat exchangers.

Determining the latent heat of multi-component cast aluminum alloys is complex. These alloys solidify within the mushy zone, with their latent heat release influenced by factors like composition, cooling rate, and microstructure. Techniques such as DSC and DTA, along with software tools like JMatPro, FactSage, and ThermoCalc, can determine this value, understand solidification parameters, and calculate latent heat. This paper introduces a novel approach using Newtonian, Fourier, and Energy Balance methods simultaneously, for the first time, to calculate the latent heat of pure aluminum and its AlSi7Cu1 alloy. These methods offer advantages in foundry conditions and require no specialized operator for data interpretation. Commercial software typically provides parameters for standard alloys only, necessitating alternative sources for accurate data. Thermal analysis techniques offer a reliable method to acquire missing parameters and calculate latent heat with high precision. Comparing the accuracy of these methods for pure aluminum and its AlSi7Cu1 alloy, using DSC measurement data and commercial software values, indicates successful application on the foundry floor to determine thermophysical properties accurately.

The precision of boring machine tool is significantly compromised by the thermal deviation inherent in the high-speed spindle-bearing assembly. Conventionally, the internal heat of this system is mitigated by using heat pipes. However, the heat dissipation capacity of these pipes does not suffice in reducing the thermal deviation to acceptable levels. The sintered-core heat pipe shows promise. In this research, a sintered-core heat pipe tailored to minimize thermal inaccuracies under rotational condition is pioneered. A gas-liquid phase transition model is devised for the sintered-core heat pipe under rotating working condition, providing a validation of heat dissipation efficacy and elucidating the phase change phenomena within the evaporation segment. Furthermore, the intricate relationship between convective coefficient and the design and operational parameters is determined through the response surface analysis and the variables with the most pronounced impact on the thermal performance of the sintered-core heat pipe are ascertained. Integrating the sintered-core rotating heat pipe into the shaft core of the spindle-bearing system has demonstrated remarkable proficiency in reduction of thermal distortion. Crucially, the thermal deformation of the shaft core with designed sintered-core heat pipe is reduced by over 95% compared to that of a core with an axial rotating heat pipe.