Search Results (6)

A three-dimensional structural model of a cylindrical lithium-ion battery pack incorporating composite phase change material (PCM) is developed in this study, and numerical simulations are conducted using CFD software to investigate the heat dissipation characteristics of the battery pack. The results show that the composite PCM effectively suppresses the temperature rise within the battery pack, maintaining both the temperature and the temperature difference in the battery pack within acceptable ranges. Parameter analysis reveals that increasing the radial thermal conductivity of the battery reduces the heating rate and improves the temperature uniformity of the overall system. Within the investigated parameter range, increasing the thermal conductivity of the composite PCM beyond approximately 1 W/(m·K) results in a region of diminishing improvement in thermal performance. Beyond this range, further increases in thermal conductivity result in only marginal reductions in the maximum temperature, indicating that excessive enhancement of thermal conductivity provides limited thermal benefits and should be balanced with latent heat capacity. An increase in the latent heat of the composite PCM lowers both the maximum temperature and the maximum temperature difference at the end of discharge, thereby enhancing system temperature uniformity. Conversely, enlarging the external air convection heat transfer coefficient yields a limited cooling effect while deteriorating the temperature uniformity within the system. Therefore, on the principle of fully utilizing latent heat and minimizing energy consumption, the external convection heat transfer coefficient should be set as low as possible. This study provides theoretical guidance for the parametric design of PCM-based thermal management systems. Full article

Supercritical carbon dioxide (CO₂) is a promising working fluid for advanced power cycles. However, under high heat flux and low mass flux, its heat transfer performance can deteriorate severely, posing significant risks to system safety and efficiency. Inserting obstacles into flow channels is an effective way to suppress such heat transfer deterioration (HTD). In this study, the body-centered cubic (BCC) lattice structure is taken as an example to investigate the effects of the number and arrangement of BCC units on the flow and heat transfer of supercritical CO₂ using numerical simulation, deep learning, and genetic algorithms. The results show that placing a BCC lattice structure upstream of the HTD temperature peak effectively improves local heat transfer, and the deterioration zone is shifted downstream. For a fixed number of BCC units, different spatial arrangements have little impact on pressure drop and only a limited effect on heat transfer enhancement. However, their influence on the suppression of HTD is very significant. Based on the analysis of the optimal arrangement, an approximate optimal method is obtained, in which BCC structures are inserted sequentially at locations 0.5 to 2 tube diameters (D) upstream of each wall temperature peak. A simplified yet effective design strategy is also proposed: the first BCC structure is placed 0.5 to 2 D upstream of the smooth tube’s temperature peak, and the remaining BCC units are then distributed uniformly along the subsequent flow length. In this way, effective suppression of heat transfer deterioration is achieved. Full article

During liquid drainage from intermediate vessels in various industrial processes such as continuous steel casting, aircraft fuel supply, and chemical separation, free-surface vortices commonly occur. The formation and evolution of these vortices not only entrain surface slag and gas, but also lead to deterioration of downstream product quality and abnormal equipment operation. The vortex evolution process exhibits notable three-dimensional unsteadiness, multi-scale turbulence, and dynamic gas–liquid interfacial changes, accompanied by strong coupling effects between temperature gradients and flow field structures. Traditional macroscopic numerical models show clear limitations in accurately capturing these complex physical mechanisms. To address these challenges, this study developed a mesoscopic numerical model for gas-liquid two-phase vortex flow based on the lattice Boltzmann method. The model systematically reveals the dynamic behavior during vortex evolution and the multi-field coupling mechanism with the temperature field while providing an in-depth analysis of how initial perturbation velocity regulates vortex intensity and stability. The results indicate that vortex evolution begins near the bottom drain outlet, with the tangential velocity distribution conforming to the theoretical Rankine vortex model. The vortex core velocity during the critical penetration stage is significantly higher than that during the initial depression stage. An increase in the initial perturbation velocity not only enhances vortex intensity and induces low-frequency oscillations of the vortex core but also markedly promotes the global convective heat transfer process. With regard to the temperature field, an increase in fluid temperature reduces the viscosity coefficient, thereby weakening viscous dissipation effects, which accelerates vortex development and prolongs drainage time. Meanwhile, the vortex structure—through the induction of Taylor vortices and a spiral pumping effect—drives shear mixing and radial thermal diffusion between fluid regions at different temperatures, leading to dynamic reconstruction and homogenization of the temperature field. The outcomes of this study not only provide a solid theoretical foundation for understanding the generation, evolution, and heat transfer mechanisms of vortices under industrial thermal conditions, but also offer clear engineering guidance for practical production-enabling optimized operational parameters to suppress vortices and enhance drainage efficiency. Full article

Swirling hot air is a promising heat transfer enhancement technology for anti-icing applications in aircrafts, where the swirling flow is accompanied by pretty high turbulence and a quite thin boundary layer. It is of interest to investigate the compound heat transfer characteristics of the swirling air configuration combined with surface structures on the internal wall. This paper carries out a series of numerical computations to obtain the Nusselt number and pressure loss data in such a swirling air heat transfer system with four kinds of surface structures (trenches, ribs, dimples and bulges) on the wall and with different tangential inlet jets placed along the tube. At a tube Reynolds number from 10,000 to 50,000, the results show that the surface dimples and bulges are conducive to improving the Nusselt number, but the surface trenches and ribs show a Nusselt number deterioration relative to the smooth swirl tube. Among the four investigated surface structures, the surface bulges perform best, which can enhance the Nusselt number by up to 15.0%, increase the total heat transfer quantity by up to 17.3% and reduce the hot air pressure loss by up to 15.6%. Furthermore, the circumferential velocity distribution and swirl number are introduced to describe the flow fields. The surface trenches and ribs lead to less of a reduction in the circumferential velocity and swirl intensity, while the surface dimples and bulges could significantly suppress the in-tube swirl intensity. Full article

Because of their compact structure, ease of processing and higher heat transfer coefficient, curved-tube heat exchangers are widely applied in various industry applications, such as nuclear power systems, solar-powered engineering, aircraft engine cooling systems and refrigeration and cryogenic systems. Accurate knowledge about the heat transfer characteristics of the supercritical fluids in the tube is critical to the design and optimization of a curved-tube heat exchanger. The available literature indicates that the flow of supercritical fluids flowing in curved tubes affected by the dual effects of the buoyancy force and centrifugal force is more complex compared to straight tubes. Therefore, to obtain insight into their unique characteristics and further research progress, this paper presents a comprehensive review of available experimental and numerical research works on fluids at supercritical pressure flowing in curved tubes. Overall, the secondary flow caused by the curvature enhances the heat transfer and delays the heat transfer deterioration, but it also causes a non-uniform heat transfer distribution along the circumferential direction, and the strengthening performance of the curved tube is damaged. Compared with the more mature theories regarding straight tubes, the flow structure, the coupling mechanism of buoyancy and centrifugal force, and the general heat transfer correlation of supercritical fluids in a curved tube still urgently need to be further studied. Most importantly, studies on the suppression of heat transfer oscillations and heat transfer inhomogeneities specific to curved tubes are scarce. Considering the current status and shortcomings of existing studies, some study topics for supercritical fluids in a curved tube are proposed. Full article

The forced convection of non-Newtonian nanofluid for a backward-facing flow system was analyzed under the combined use of magnetic field and double rotating cylinders by using finite element method. The power law nanofluid type was used with different solid volume fractions of alumina at 20 nm in diameter. The effects of the Re number ($100\le \mathrm{Re}\le 300$), rotational Re number ($-2500\le \mathrm{Rew}\le 3000$), Ha number ($0\le \mathrm{Ha}\le 50$), and magnetic field inclination ($0\le \gamma \le 90$) on the convective heat transfer and flow features were numerically assessed. The non-Newtonian fluid power law index was taken between 0.8 and 1.2 while particle volume fractions up to 4% were considered. The presence of the rotating double cylinders made the flow field complicated where multiple recirculation regions were established near the step region. The impacts of the first (closer to the step) and second cylinders on the heat transfer behavior were different depending upon the direction of rotation. As the first cylinder rotated in the clockwise direction, the enhancement in the average heat transfer of 20% was achieved while it deteriorated by approximately 2% for counter-clockwise directional rotation. However, for the second cylinder, both the rotational direction resulted in heat transfer augmentation while the amounts were 14% and 18% at the highest speeds. Large vortices on the upper and lower channel walls behind the step were suppressed with magnetic field effects. The average Nu number generally increased with the higher strengths of the magnetic field and inclination. Up to 30% increment with strength was obtained while this amount was 44% with vertical orientation. Significant impacts of power law fluid index on the local and average Nu number were seen for an index of n = 1.2 as compared to the fluid with n = 0.8 and n = 1 while an average Nu number of 2.75 times was obtained for the flow system for fluid with n = 1.2 as compared to case for fluid with the n value of 0.8. Further improvements in the local and average heat transfer were achieved with using nanoparticles while at the highest particle amount, the enhancements of the average Nu number were 34%, 36% and 36.6% for the fluid with n values of 0.8, 1 and 1.2, respectively. Full article