Convective Heat Dissipation Research Articles

Design and performance assessment of a triply-periodic-minimal-surface structures-enhanced gallium heat sink for high heat flux dissipation: A numerical study

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.

Facemask vapor trapping, condensation, and thermoregulation

The widespread adoption of facemasks in various contexts has highlighted challenges associated with prolonged mask-wearing. Despite their effectiveness in preventing the spread of pathogens, issues such as discomfort, stuffiness, and fogging of eyeglasses can deter individuals from wearing masks consistently. Understanding the mechanisms of thermal and humidity regulation during facemask use is crucial for addressing these challenges. This study investigates the impact of face mask-wearing on facial thermoregulation and moisture accumulation, comparing conditions with and without masks. An integrated computational model was developed to consider respiratory flows, tissue heat generation, skin convective heat dissipation, the influence of inhaled cool air and exhaled warm air, and their interactions with the mask media. Model validation was conducted using complementary Schlieren imaging and transient temperature measurements. Results reveal significant increases in facial temperature with well-fitted masks and highlight the role of trapped moisture inside the mask. Thermo-humidity variations beneath the mask and condensations in the mask were quantified, providing insights into facemask-wearing thermoregulation. The effects of moist vs. dry air, steady vs. tidal breathing, and with vs. without buoyancy were quantitatively compared. These findings have implications for improving mask design and promoting adherence in diverse environmental settings. Addressing these discomfort-related challenges is crucial for enhancing mask adherence and ensuring adequate protection.

Novel adjustable backflow structure in electric coolant pump for balancing hydraulic performance and reducing temperature rise

An electric coolant pump serves as the source for coolant circulation in the thermal management of electric vehicles. To address the thermal issues for the printed circuit board integrated within the electric coolant pump, a novel backflow structure with an adjustable orifice diameter is designed from the impeller outlet to the printed circuit board to promote convective heat dissipation. Eventually, this flow returns to the impeller inlet, thereby altering the hydraulic performance of pump. The balance between hydraulic performance and temperature rise is achieved by adjusting the orifice diameter. Considering the variations in coolant properties with respect to temperature, numerical simulations of the electric coolant pump are performed using the unsteady compressible Reynolds-Averaged Navier-Stokes Equations. There is good agreement between experimental and numerical simulations results in both cases with and without an orifice. On an average, by increasing the orifice diameter by 1.5 mm which results in a 1.11 % decrease in efficiency, a 0.008 decrease in pressure coefficient, and a reduction of temperature by 2.98 K on printed circuit board. As the orifice diameter increases, leakage losses in the rear side chamber increases with the improvement of heat dissipation. The clash between the backflow jet and the inflow from the suction pipe results in significant entropy generation, forming jet vortices and increasing in pressure fluctuation. However, when the orifice diameter exceeds 3 mm, the cooling advantages no longer justify the trade-off in hydraulic performance. Thus, 3 mm orifice diameter is an optimal compromise between hydraulic performance and temperature control.

Bioinspired Wearable Thermoelectric Device Constructed with Soft‐Rigid Assembly for Personal Thermal Management

AbstractThe development of high‐performance thermoelectric devices (TEDs) with personal thermoregulation is crucial for the advancement of next‐generation wearable technologies. Most efforts focus on optimizing mechanical flexibility in fully encapsulated devices, but parasitic heat loss induced by the layer‐packed polymer matrices with high thermal impedance typically leads to degradation in sensing and bidirectional conversion capabilities. Here, a bioinspired architectural strategy is proposed for this problem that demonstrates the feasibility of single‐sided assembly based on a soft‐rigid “skin‐spine” configuration to improve heat utilization efficiency. With active TE units connected via serpentine electrodes, skin‐spine‐structured wearable thermoelectric devices (SSSW‐TEDs) are successfully fabricated enabling temperature sensing and bidirectional heat‐to‐electricity conversion under mild forced convection. This contributes to significant enhancements in power delivery (by 300%) and cost‐benefit analysis (by 100%) through efficient air convection heat dissipation. Moreover, SSSW‐TED enables personal thermal regulation by harnessing body heat, cooling the skin, and perceiving behaviors such as touching and blowing. This study not only provides novel insights for high‐performance TEDs but also lays the foundation for the widespread implementation of skin thermoregulation.

The thermo-mechanical coupling method of brake disc based on dynamic convective heat transfer

With the increase of train speed, the brake disk receives more heat input, causing its own temperature to reach a higher level. Due to the complex structure of the brake disk, its convective heat transfer coefficient is difficult to calculate, which makes the analysis of the convective heat dissipation between the brake disk and the air complicated. In this article, based on the software FLUENT and ABAQUS, by combining the fluid-solid coupling method and the thermo-mechanical coupling method, the dynamic convective heat transfer and the transient temperature field of brake disk are simulated. The maximum value of dynamic convective heat transfer coefficient is 483 W/m2 ∙ K at the running speed of 350 km/h. As for the transient temperature field, not only the contact relationship between the brake disk and the brake pad is considered, but also the dynamic convective heat transfer between the brake disk and the surrounding air domain is applied. The simulation results are more in line with the actual situation and the engineering application.

Enhancement of Natural Convection Heat Dissipation Using Longitudinal Elliptic Perforations Fins

Enhancement of Natural Convection Heat Dissipation Using Longitudinal Elliptic Perforations Fins

Modeling and numerical studies of high-precision laser powder bed fusion

In order to comprehensively reveal the evolutionary dynamics of the molten pool and the state of motion of the fluid during the high-precision laser powder bed fusion (HP-LPBF) process, this study aims to deeply investigate the specific manifestations of the multiphase flow, solidification phenomena, and heat transfer during the process by means of numerical simulation methods. Numerical simulation models of SS316L single-layer HP-LPBF formation with single and double tracks were constructed using the discrete element method and the computational fluid dynamics method. The effects of various factors such as Marangoni convection, surface tension, vapor recoil, gravity, thermal convection, thermal radiation, and evaporative heat dissipation on the heat and mass transfer in the molten pool have been paid attention to during the model construction process. The results show that the molten pool exhibits a “comet” shape, in which the temperature gradient at the front end of the pool is significantly larger than that at the tail end, with the highest temperature gradient up to 1.69 × 108 K/s. It is also found that the depth of the second track is larger than that of the first one, and the process parameter window has been determined preliminarily. In addition, the application of HP-LPBF technology helps to reduce the surface roughness and minimize the forming size.

Carbon fiber composite core conductor operation risk assessment model based on various types of monitoring data

Abstract As the national economy grows gradually and the scale of urbanization expands, the standard for power transmission is also continuously increasing. Currently, the existing transmission lines can no longer meet the rising power demand, thus urgently requiring the construction of power transmission capacity expansion. Although there are many strategies for increasing capacity, the development of enhanced conductor material is indeed its greatest advantage. However, among the various options for increasing capacity, the development of capacity-enhancing wires is also the most advantageous. Carbon fiber conductors, which are known as “black gold,” are the perfect material for this purpose. Given the inherent economic value, high brittleness, and complexity of the installation process of carbon fiber materials, this study proposes an operational risk assessment model for carbon fiber composite core conductors based on multiple monitoring data. For the first time, the influence between quarterly lightning strike probability and arc droop as well as the temperature drop effect on overhead transmission conductors by convective heat dissipation from natural wind are taken into account. The expected arc sag size of the conductor in the future period can be predicted according to the meteorological forecast, which can effectively prevent the impact of flashovers and wire breakage on the operation of the power grid. In addition, the practicality and functionality of the assessment model have been verified by real accident data.

Mechanism of jet velocity affecting surface quality based on electrode dynamics under temperature field

Electrolyte jet machining (EJM) is a rapid method for preparing metal surface microstructures. The local temperature changes at the anode interface caused by electrochemical heat and jet velocity are to be determined, and the mechanism of the effect of different jet velocities on the surface quality of the anode is not clear. Therefore, an EJM simulation model considering temperature was developed, and the etching profiles were compared with and without the effect of temperature. The simulation results show that considering the temperature field can improve the prediction accuracy of the simulation. In addition, simulation and experimental results show that high electrochemical heat is favourable for increasing the conductivity of the electrolyte and generating a high-quality surface. Enhanced convective heat dissipation at high jet velocities reduces the conductivity of the electrolyte in the machining area, generating low-quality surfaces. It is worth noting that excessively low jet velocity can accumulate anode electrolysis products at the interface, affecting machining accuracy. This paper analyzes the mechanism of the influence of different jet velocities on the surface quality of an anode in combination with the electrode dynamics under the influence of the temperature field. This analysis is crucial for achieving high surface quality in EJM.

A theoretical stability of mixed convection 3D Sutterby nanofluid flow due to bidirectional stretching surface

Host (base) fluids are unable to deliver efficient heating and cooling processes in industrial applications due to their limited heat transfer rates. Nanofluids, owing to their distinctive and adaptable thermo-physical characteristics, find a widespread range of practical applications in various disciplines of nanotechnology and heat transfer equipment. The novel effect of this study is to determine the effects of mixed convection, and activation energy on 3D Sutterby nanofluid across a bi-directional extended surface under the impact of thermophoresis diffusion and convective heat dissipation. The flow equations are simplified in terms of partial differential equations (PDEs) and altered to non-dimensional ODEs by implementing classical scaling invariants. Numerical results have been obtained via the bvp4c approach. The physical insights of crucial and relevant parameters on flow and energy profiles are analysed through plotted visuals. Some factors have multiple solutions due to shrinking sheets. So stability analysis has been adapted to analyses stable solutions. Graphical representations demonstrate the reliability and accuracy of the numerical algorithm across a variety of pertinent parameters and conditions. A comparison between existing results and previously published data shows a high degree of compatibility between the two datasets. The present study extensively explored a multitude of practical applications across a diverse spectrum of fields, including but not limited to gas turbine technology, power generation, glass manufacturing, polymer production, wire coating, chemical production, heat exchangers, geothermal engineering, and food processing.

Experimental study of a vertically mounted bifacial photovoltaic sunshade

BIPV (building-integrated photovoltaic) technology can convert incident solar energy directly into electricity while reducing cooling energy consumption. Using PV modules as a sunshade also prevents glare. Recently, the application of bifacial photovoltaic technology in the building sector has shown promise for achieving building energy-saving and carbon-neutral goals. In this study, we conducted an experiment to evaluate the thermal, light, and electrical performance of a vertically mounted bifacial photovoltaic sunshade (BiPVS). Over three consecutive days, the average daily power generation was 709.4 kJ for the west-oriented PV module and 636.7 kJ for the east-oriented one. The average electrical efficiencies were 15.67 % and 25.62 %. By applying BiPVS, the daily average illuminance levels were reduced by 2.48–4.64 % for the measurement point at 1.0 m distance from the window and 12.32–12.40 % for the point at 2.0 m distance. Additionally, we suggested two improvement solutions, including reserving intervals between the PV module and the window to facilitate natural convective heat dissipation and enlarging the height of the BiPVS. The results of this study demonstrate the energy-saving potential of the innovative BiPVS in low-carbon or zero-carbon building designs, and provide new ideas for the development of solar building integrated technology.

Indoor Climate Monitoring in Office Buildings—Comparative Analysis of Two Office Buildings without Air Conditioning

Against the background of climate protection and the rising costs of a fossil-fuel-based energy supply, the interest in the energy performance and indoor climate of buildings in real operation is rising. This paper, therefore, deals with the indoor climate investigation of two medium-sized office buildings in Germany by taking measurements over a whole year. These relate to one new building and one refurbished building. Sensors of various types were installed and operated in a large number of office rooms, so that in total results are available for over 100 rooms, typically occupied by one or two persons. The analysis focuses on the indoor temperature in summer and the air quality in winter based on the CO2 concentration. The comfort classes according to DIN EN 16798 including the adaptive comfort approach are used as a basis to cluster the results. Both buildings have movable sun protection and openable windows but no facilities for active cooling. They, thus, represent a large number of existing ‘low tech’ office buildings in Germany and central Europe. The results reflect the respective building concepts but also show a wide range between the rooms due to the user preferences and behaviour. The refurbished building shows better results, especially in terms of air quality but also in terms of summer room temperatures. This underlines the benefit of the targeted measures as a result of an analysis of the deficits in the existing building before the refurbishment. The additional measures for decentralised mechanical ventilation and passive cooling are having positive effects. As part of the projects, further measures to improve the indoor climate were investigated in both buildings. In one case, this involved CO2 traffic lights to stimulate personal window ventilation in winter, and in the other, the use of newly developed individual ceiling fans supports convective heat dissipation on the human body during hot spells in summer. The positive effect could be demonstrated for both measures.

An analytical model for wearable thermoelectric generators harvesting body heat: An opportunistic approach

Wearable thermoelectric generators (WTEGs) have the potential to transform body heat into electrical energy, thereby establishing a sustainable power reservoir for wearable electronics and offering a promising alternative to traditional chemical batteries. This paper presents an opportunistic analytical model that investigates the energy conversion performance of a human skin-WTEG system. The model incorporates a one-dimensional bioheat transport equation to account for metabolic heat generation within skin tissue and heat exchange resulting from the blood perfusion, while a comprehensive three-dimensional analysis of the WTEG captures convective heat dissipation occurring between the WTEG and ambient surroundings. Analytical solutions for the temperature profile and power density of WTEGs are obtained, along with an approximate closed-form expression for the matched load resistance. The results demonstrate the significant impact of blood perfusion and convective heat dissipation on the WTEG performance. The optimal fill factor and height of thermoelectric couples for maximum power output are also determined. This model will assist in predicting and optimizing the performance of WTEG devices in practical applications.

Numerical and experimental research on electromagnetic-thermal and leakage defects characteristics of the high voltage cable terminal

Thermal and insulation performance of the High Voltage Cable Terminal (HVCT) could effectively improve the reliability and economy of power energy transmission. In this paper, a numerical model of the electromagnetic heat flow field was proposed to analyze the heat transfer and temperature characteristics of HVCT under oil leakage defects. This model was the first validated using operation data from the actual equipment and the relative error was less than 1.51%. The effects of oil leakage fault on the global and local temperature distribution of the HVCT were then investigated under different load currents. In addition, the local temperature rise effect of different ambient temperatures on the HVCT oil leakage defect was also considered. Finally, combined with reference indicators such as oil level, temperature, and temperature gradient, a qualitative and quantitative evaluation of the oil leakage fault of HVCT was performed. The results showed that the temperature of the core, surface, and their maximum temperature gradient were linearly related to the ambient temperature. However, the temperature of the core at the oil leak exceeded the normal temperature by up to 7.2 °C with 1000A load current, and the temperature gradient change reaches 681.3 °C/m, which indicated that the convection heat dissipation effect of the oil-deficient part was poor, and the heat accumulates near the cable core. Therefore, the numerical model and analytical results presented in this paper provided an important method for online temperature monitoring and fault analysis of HVCTs.

Design of Liquid–Air Hybrid Cooling Garment and Its Effect on Local Thermal Comfort

Personal cooling garments were reported effective in improving thermal comfort in hot environments. In this study, three liquid–air hybrid cooling garments and one control garment were designed and made: aluminum-tube fan cooling (AAL), silicone-tube fan cooling (SAL), silicone-tube fan cooling with inner yarn fabric (YAL), and a control garment (CON) without the cooling sources. Subject trials were performed by eight female subjects in a climate chamber to simulate a summer indoor working environment at 32 °C and 50% relative humidity. The results showed that the liquid–air hybrid cooling garment provided effective convective and conductive heat dissipation compared with the no-cooling (CON) stat, chest, belly, shoulder, back, hand, thigh, and calf. The horizontal e, resulting in a decrease in local body skin temperature. Compared with the CON, the liquid–air cooling garment resulted in a maximum reduction of 1 °C for the mean torso skin temperature and 1.5 °C for the localized shoulder skin temperature. The AAL had a better cooling effect on the torso skin temperature compared with the SAL, and the cooling of the AAL was 0.5 °C lower than that of the SAL for the shoulder skin temperature. The presented liquid–air hybrid cooling garments were effective in cooling the body and improving thermal comfort. They were portable, accessible, and sustainable in hot indoor environments compared with air conditioners. Therefore, they could save energy.

Topology Optimization Design for Heat Dissipation Performance of Semiconductor Ignition Device

Abstract The trend of miniaturization and intgration of the electronic device has put forward higher requirements on efficiency of heat radiating, which can hardly be satisfied by the traditional forced convection heat dissipation method. In this paper, the strategy of topology optimization technique is adopted to greatly improve the heat dissipation efficiency of a semiconductor ignition device. The penalization method is used to implement the topology optimization process. Three kinds of objective functions of thermal compliance, temperature variance and geometric average temperature were separately applied in the topological optimization of two typical uniform heat generation cases, and the resulted topologically optimization results were analyzed and compared. Based on the two benchmark cases, the appropriate objective function was selected to conduct structural optimization of semiconductor bridge ignition devices with the aim of making the highest temperature in the design domain the lowest possible. Additionally, a parametric study on the effect of thermal conductivity on topology optimization results was conducted, which leads to a design suggestion beneficial for heat dissipation and material selection.

Analysis of High-Temperature Superconducting Current Leads: Multiple Solutions, Thermal Runaway, and Protection

The multiple steady states of Ag/Bi2212-composite high-Tc superconducting leads modeling current delivery to a superconducting magnet have been numerically calculated. The model is based on longitudinal conduction combined with convective heat dissipation from a helium gas stream along the conductor. Because of the nonlinearities introduced by the voltage–current relationship and the temperature-dependent material properties, up to three solutions have been identified within the range of parameters considered. Linear stability analysis reveals that two of them are stable, i.e., the superconducting and the normal branches, while the remaining one is unstable. The limit points separating the stable from the unstable steady states form the blow-up threshold, beyond which any further increase in the operating current results in a thermal runway. Interesting findings are that for low filling ratios no bounded solution exists when the length of the lead exceeds the lower limit point, while very high maximum temperatures may be encountered along the normal solution branch. The effect of various parameters such as the conduction–convection parameter, the applied current, and the reduction in coolant flow (LOFA) on the bifurcation structure and their stabilization effect on the blow-up threshold are also evaluated. Apart from the steady and unsteady operating modes, the multiplicity analysis is also used to identify the range of the design and operating variables where safe operation, with a sufficient margin from the onset of instabilities, may be established, thus facilitating the protection of the leads and the device connected to it.

The effects of topological configuration and geometric parameters on heat transfer and fluid flow characteristics of lattice-based heat sinks

Traditional pin-fin heat sinks could provide only thermal exchange. Whereas the topology and geometry of lattice-based heat sinks make them suitable for simultaneous thermal and structural applications. In this work, we numerically demonstrate the convective heat dissipation performance of periodic pyramidal and tetrahedral lattice-based heat sinks. The motivation for the study is to discover the effects of topological and geometrical parameters of the lattice structure on the heat and fluid flow characteristics of lattice-based heat sinks which are not yet presented in the literature. Hence, we consider pyramidal and tetrahedral lattice topologies with two different L/D ratios (8.8 and 5). Three-dimensional numerical simulations based on the finite volume method were carried out at constant pumping power with water as a coolant for applied heat flux in the range of 10–50 W/cm2. The thermo-hydraulic performance is characterized by the efficiency index and area goodness ratio as a function of pumping power in the laminar regime. The convective heat transfer coefficient values range from 2129 to 6510 W/m2 K for the operating conditions considered in this study. Also, in terms of overall combined thermo-hydraulic performance, the tetrahedral heat sink with the L/D ratio of 5 was found to be 50–53%, 18–25%, and 22–30% more efficient than the P8.8, T8.8, and P5 heat sinks, respectively, for the range of pumping powers considered. The thermo-hydraulic characteristics presented in this study enable the design of lattice-based heat sinks for specific applications with collective pressure drop and heat transfer constraints.

Thermal-induced effects on ultrafast laser filamentation in ethanol

Fs laser filamentation in ethanol is studied for bottom-up nanomaterials synthesis at different laser repetition rate. Measurements of energy loss, visible conical images, transmitted beam profile and the optical emission spectra show that laser repetition rate affects ultrafast laser filamentation in ethanol significantly because of the induced thermal processes. Firstly, near the threshold laser energy for self-focusing, high laser repetition rate could interfere with the process, via thermal defocusing that inhibits the onset of filamentation. An enlarged, near flat-top laser beam is produced for the conditions that favor thermal lensing. Secondly, at high laser energy, thermal defocusing effect is saturated as convective heat dissipation occurs. Thus, self-focusing prevailed and led to filamentation at all repetition rates. The strong convection at high laser repetition rate increases the rate of reactions for nanodiamonds synthesis, as the flow of fresh ethanol precursor to the localized filamentation zone is enhanced.

Convective Heat Transfer Coefficient of Insulation Paper–Oil Contact Surface of Transformer Vertical Oil Channel

Insulation paper is the primary inter-turn insulation material for transformer windings. However, insulation paper is a poor conductor of heat and seriously impacts the natural convective heat dissipation in the winding oil channels. In order to study the convective heat transfer performance of the transformer vertical oil channel, the heat transfer characteristics of the two-dimensional boundary layer of the insulation paper–oil contact surface were analysed, and a characteristic number equation with a roughness correction factor was established. Based on the similarity principle and modelling theory, an experimental apparatus was designed to determine the convective heat transfer coefficient of the insulation paper–oil contact surface. Coefficients were obtained for different qualitative temperatures and characteristic lengths. Parametric fitting of the experimental data was carried out to obtain the correction factors. The results show that the natural convective heat transfer coefficient h of the insulation paper–oil contact surface is positively and linearly related to qualitative temperature and inversely related to characteristic length. For temperatures of 312.9 K to 328.1 K and characteristic lengths of 3 cm, h ranges from 116.15 to 144.38 W/(m2 · K). For temperatures of 319.0 K to 337.9 K and lengths of 6 cm, h ranges from 103.79 to 131.14 W/(m2 · K). The correction factor of the characteristic equation coefficient is 1.067. The maximum deviation of h calculated with a coefficient of 0.63 and an exponent of 0.25 is 5.93%. The results are essential for modelling the transformer space thermal circuit and solving the hot-spot temperature problem.