Enhanced Heat Transfer Performance Research Articles

Effect of structure parameters on thermal performance of novel punched V-shape VGs for hear exchangers: An experimental approach

The use of perforated technology on the surface of the vortex generator (VG) has been proven to further enhance heat transfer performance by reducing its pressure loss. Based on this technology, a new type of turbulence insert is proposed in this work, which is composed of a V-shaped fixed ring with perforated rectangular VGs. The influence of its number (N = 2, 4, 6), VG area (S = 10, 20, 30 mm2), and pitch (P = 25, 50, 75 mm) on heat transfer and pressure drop under turbulent conditions was investigated through experiments. The results show that the influence of N and S on heat transfer intensity and pressure drop is consistent, but the value of P is inversely proportional to pressure drop and heat transfer intensity. Regardless of the influence of parameters on heat transfer intensity, it is explained by the field synergy number. Within the parameter range studied in this article, the optimal TEF value of 1.42 is attained when S=10mm2, N = 6, and Re=7454.

Enhancing heat transfer performance of aluminum-based vapor chamber with a novel bionic wick structure fabricated using additive manufacturing

Given the lightweight nature and excellent thermal conductivity of aluminum, it offers significant potential for light-weighting of phase-change cooling components. To further enhance the thermal performance of aluminum-based vapor chambers, this study utilized selective laser melting (SLM) to design and integrally manufacture the slightly oleophilic wick for the condenser of the aluminum-based vapor chamber, along with three different superoleophilic wick structures for the evaporator: the gyroid bionic composite porous wick vapor chamber (GBCPVC), the groove composite porous wick vapor chamber (GCPVC), and the uniform porous wick vapor chamber (UPVC). A water-cooling experimental setup was established, and the effects of wick structure, cooling water flow rate, and cooling water temperature on the maximum heat load, temperature uniformity, and thermal resistance of vapor chambers were systematically investigated. The results indicated that the gyroid bionic porous wick structure significantly enhanced the thermal performance of the vapor chamber. Under the same conditions, GBCPVC exhibited lower thermal resistance and superior temperature uniformity, achieving a higher heat load than GCPVC and UPVC. When the cooling water temperature was decreased, its maximum heat load significantly increased. Specifically, at 15 °C, the maximum heat load for GBCPVC reached 300 W, an increase of 33.33 % and 53.33 % compared to 25 °C and 35 °C, respectively. Conversely, a rise in cooling water temperature enhanced the temperature uniformity and reduced thermal resistance of CBCPVC. At 35 °C and a heat load of 120 W, GBCPVC achieved a minimum thermal resistance of 0.034 K/W and a maximum temperature difference of 1.46 °C. Additionally, an increased flow rate enhanced the maximum heat load of GBCPVC, and under high heat loads, it could also reduce the thermal resistance and improve temperature uniformity. This study provides new insights and solutions for the thermal management of phase-change cooling components in aerospace electronic devices.

Numerical Study on the Local Aggregation of Helium Bubbles in Liquid Lithium and Its Thermal Analysis

Abstract Liquid lithium is widely regarded as an optimal cooling medium for space nuclear reactors due to its exceptional heat transfer properties and low density. However, the helium bubbles generated by liquid lithium under space irradiation pose significant hazards to the safe and stable operation of nuclear reactions. This study employs the COMSOL finite element software to construct the level-set two-phase flow models and bubble stream model separately to investigate the local accumulation of helium bubbles and the overall flow of low-concentration gas–liquid mixtures. The main focus is on examining the different distributions of multiple helium bubbles randomly generated in local liquid lithium and the influence of boundary conditions on their accumulation morphology, as well as the impact of low-concentration bubble stream on their overall heat transfer performance. Agglomerated bubbles with radii between 5 μm and 150 μm are classified into three categories based on local concentrations: circular (≤20.37%), irregular elongated (up to 30.44%), and banded (up to 36.31%).The interconnected banded bubbles can be up to 8 times larger than irregularly elongated ones, and they have a positive effect on the distribution of physical quantities and wall temperature perturbations in the pipeline. The increase in inlet velocity triggers bubble impacts and fragmentation, further reducing thermal resistance and enhancing heat transfer performance. When the bubble diameter is less than 15 μm and the bubble concentration is within 1%, the influence of the mixed flow on overall heat transfer is not significant. This study provides insights for manipulating bubble structure and guiding localized and comprehensive thermal analyses.

Investigation and evaluation of heat transfer enhancement for PEMFC under high current density based on a multiphase and non-isothermal electrochemical model

Heat management plays a vital role in the efficient and stable operation of proton exchange membrane fuel cells (PEMFCs), especially at high current densities, which is directly related to the cooling flow field (CFF). In this paper, a non-isothermal electrochemical model coupled with CFF of PEMFC is developed, and the effects of CFF structures on the water and heat transfer performance enhancement of PEMFC at high current densities are studied. In addition, an Evaluation Criteria is expected to be applied to evaluate the heat transfer capacity of CFFs. The results indicate that high temperatures effectively alleviate PEMFC concentration polarization. Due to the twists and turns design within the channel, the heat transfer capability of the Wave CFF performs well, Nusselt number and field synergy angle values respectively 35.7 % higher and 3.34 % lower than those of Parallel CFF. Additionally, the heat transfer performance factor is used to evaluate the heat transfer capability of different cooling flow field structures. The performance factor of the Wave CFF reaches 1.44 at a coolant temperature difference of 1 K.

Thermal enhancement of a heat exchanger of engine via U-cut and V-cut zigzag strip turbulator combined with bubble injection method

This experimental study proposes a new approach to enhance heat transfer performance inside heat exchangers of engine by tandem utilization of bubble injection and a punched zigzag strip turbulator. The side edges of the zigzag turbulator underwent two distinct geometry modifications, involving V and U shape cuts. These cuts were made at varying zigzag angles, ranging from 60° to 150° and four diffirent surface area. The potential improvement in thermal efficiency of the heat exchanger was evaluated at different inlet Reynolds number ranging from 5390 to 10,860. Based on survey results, it has been demonstrated that at a Reynolds number of 5390, the Nusselt number and friction factor increase by 48% and 154% for U-Cut with a bending angle of 150°, and by 61% and 170% for V-Cut, respectively. Hence, V-cut boasts a TEF of 1.15, representing a 6.5% improvement over U-cut. Additionally, to assess further enhancement, air bubbles with flow rate ranging 2–6 LPM were introduced to the central tube while maintaining the superior geometry. The data suggests that incorporating air bubbles can enhance heat transfer up to 142%, achieving a TEF of 1.17 at an air flow rate of 6 LPM.

Experimental investigation of metal foam embedded surface thermal characteristics using air-jet impingement with different orifice geometry

Experimental investigation of metal foam embedded surface thermal characteristics using air-jet impingement with different orifice geometry

Numerical Analysis on Performance Improvement of a Vertical Plate Indirect Evaporative Cooler with Baffles

The performance of the Plate Indirect Evaporative Cooler (PIEC) can be effectively improved by incorporating baffles in the dry channel. However, in the dimensional influence of the baffles on PIEC performance there remains a research gap. In order to investigate the impact of baffle dimensions on the wet bulb efficiency, namely the average heat transfer coefficient and the cooling capacity of the PIEC, this paper proposed and verified a three-dimensional numerical model and method based on the species transport model and the Euler wall film model. At the same time, in order to obtain the equilibrium point between the enhanced heat transfer performance and the additional resistance induced by baffles, a comprehensive performance evaluation index is introduced. The results indicate that, under the same conditions, (1) the baffle effect on PIEC performance is significant at a lower inlet air velocity, and the wet bulb efficiency of the PIEC with baffles can be improved by 22.8%; (2) the baffle effect on PIEC performance is negative if its relative length exceeds 60% or the primary air inlet velocity surpasses 4 m/s under the conditions specified in this paper; and (3) the baffle effect on PIEC performance is significant when its channel height is lower and its channel width is larger, and the wet bulb efficiency of the PIEC with baffles can be improved by 29.3%.

Sensitivity analysis of velocity field influence on condensers’ performance and parallel circuit design based on actual air velocity distribution

Currently, most integral simulations of condensers are based on the assumption of uniform intake air, which differs from real scenarios and leads to imprecise circuit designs. To obtain the actual air velocity distribution and reflect its impacts in the model, a comprehensive methodological system is established in this study. The implementation involves employing the porous media model to simulate air velocity distribution and utilizing the results as the air inlet condition of the distributed parameter model to achieve an integral simulation of condensers. The results indicate that the air velocity distribution is significantly non-uniform. The distribution of air velocity has a limited impact on the performance of single-row tube condenser, but has a significant effect on double-row tube condenser. Minimizing the discrepancy in the positioning of each sub-flow circuit and arranging tubes with large temperature differences in the high air velocity area can enhance heat transfer performance, the “z"-shaped double-tube parallel circuit designed by these theories can continue to improve the heat transfer performance by 2.8 % compared to the single-tube serial circuit with countercurrent arrangement within the accuracy limits of the simulations, and marking a 43.5 % improvement compared to the conventional zigzag-shaped single-tube serial circuit.

The utilization of novel jet extension designs in multi-jet impingement for crossflow mitigation and thermal efficiency enhancement

The aim of this study is to mitigate the distorting effect of crossflow on jet flow and to enhance heat transfer performance in multi-jet impingement heat transfer. To accomplish this objective, novel jet extension designs are proposed: a design with uniform jet extension, a design with linear jet extension in the streamwise direction, a design featuring an initial increase followed by a decrease, a design featuring an initial decrease followed by an increase, and a design where the last five jets exhibit a uniform extension inside the region mostly influenced by crossflow. The effects of various novel jet extension designs on flow and heat transfer are analyzed numerically in this study, focusing on the following: velocity contours, streamlines and velocity vectors, Local Nusselt number variations, variations of the average Nusselt number, friction coefficient, and thermal enhancement factor with Reynolds number. The study findings indicate that the investigated nozzle extension designs yield a notable enhancement of 13.26% in heat transfer. However, it is important to note that these designs may also lead to a substantial rise of 39% in the friction coefficient. In relation to thermohydraulic performance, it is found that all extension designs exhibit better results when compared to the reference state. Notably, the uniform extension design with dimensionless nozzle length of 2 demonstrates a higher degree of thermohydraulic performance.

The integration of double-layer triangular micro-channel in three-dimensional integrated circuits for enhancing heat transfer performance

This paper proposed a new heat dissipation structure called double-layer triangular micro-channel (DLTMC) to solve the increasingly serious thermal problem of three-dimensional integrated circuits (3D-ICs). The matrix equation of heat transmission is established to derive steady-state temperature of 3D-ICs with embedded DLTMC, which is based on equivalent thermal resistance network. According to proposed computation thermal model, the heat transfer performances of 3D-ICs with embedded DLTMC concerning different cooling liquids are investigated, where the impacts of different bottom angle of DLTMC, volume concentration of nanofluid and flow velocity of cooling liquid are considered. The results show that the proposed DLTMC structure can significantly reduce steady-state temperature compared with conventional structure of single layer rectangular micro-channel (SLRMC), the corresponding steady-state temperature for them can be reduced over 32.098 %. Besides, it is demonstrated that the steady-state temperature for MWCNT-water and SWCNT-water nanofluids as cooling liquids can be reduced by 22.490 % and 19.801 % than conventional water case, respectively. Moreover, it is manifested that the increase of bottom angle of DLTMC, volume concentration of nanofluid and flow velocity of cooling liquid can evidently improve heat transfer performance of 3D-ICs. Therefore, the presented results in this paper are beneficial for solving complex thermal problems of 3D-ICs.

Thermal performance analysis of corrugated plate solar air heater integrated with vortex generator

This research investigates the impact of vortex generators integrated with a corrugated absorber plate of solar air heater on the enhancement of heat transfer and thermal-hydraulic performance utilizing a 3D numerical model for Reynolds numbers varying from 7,000 to 25,000. Three different types of vortex generators (rectangular, trapezoidal, and delta) are investigated separately. Vortex generators in two pairs with various angles of attack of 15º, 30º, 45º, and 60º are mounted on the entrance section's upper wall of the domain of computation. The current numerical models are validated by comparisons with experimentally published data. The velocity vectors, turbulent kinetic energy, friction factor, Nusselt number, and thermal-hydraulic performance parameters are examined for the considered current cases considered. The numerical results demonstrate a significant impact of vortex generators on friction loss and transmission of heat. The values of thermal-hydraulic performance for utilizing a corrugated absorber plate integrated with vortex generators are found to be considerably higher than those for using a corrugated absorber plate alone. The highest value of the thermal-hydraulic performance parameter is 0.91 in the case of rectangular vortex generators at Re of 7000 and an angle of attack of 30º.

Pool boiling heat transfer characteristics of low-GWP refrigerants in a horizontal tube bundle configuration

Heat transfer enhancement techniques have been adapted on the shell side to improve the overall performance of the flooded evaporators, such as finned tubes. In recent years, it has been demonstrated that the metal foam structure can offer enhanced heat transfer performance under pool boiling conditions. However, there are not much research in the open literature that examine the feasibility of metal foam embedded tubes in horizontal tube bundle configurations. Therefore, this paper proposed a novel metal foam embedded tube (i.e., foam embedded outside the tube) to improve the heat transfer behavior of flooded evaporators. The experiments were performed on a horizontal tube bundle with a staggered arrangement. Moreover, the performance of low global warming potential (GWP) refrigerants (R-1234yf and R-1234ze(E)) is compared against R-134a for both plain tubes and metal foam tubes with porosities of 81%, 75%, and 62%. The results showed that a metal foam tube with a porosity of 62% showed a maximum heat transfer coefficient (HTC) enhancement of 291% compared to the plain tube. As compared with R-134a, the HTCs of R-1234yf and R-1234ze(E) are nearly 10% higher and 5% lower, respectively.

Bubble Interaction and Heat Transfer Characteristics of Microchannel Flow Boiling With Single and Multiple Cavities

Abstract Flow boiling in microchannels can effectively address the challenges of high power density heat dissipation in electronic devices. However, the intricate bubble dynamics during the two-phase flow in microchannel necessitates understanding the characteristics of complex bubble hydrodynamics. In this study, we perform 2D numerical simulations of flow boiling using the Cahn-Hilliard phase-field method for a 200-µm width microchannel with single and multiple cavities in COMSOL Multiphysics (V5.3). The numerical model successfully captures bubble dynamics, encompassing vapor embryo generation, bubble growth, departure, coalescence, sliding, and stable vapor plug formation. The heat transfer mechanism inside the microchannel is dominated by bubble nucleation and thin-film evaporation. Elevated wall superheats in a single nucleation cavity, and increased mass flux facilitates higher bubble departure frequency and heat transfer performance. Temporal pressure fluctuations are observed inside microchannels in multiple cavities due to bubble coalescence, departure, and subsequent nucleation. Increasing the nucleating cavities from 2 to 5 within the microchannel while maintaining consistent cavity spacing of 100 µm has resulted in nearly 32% enhancement in heat transfer performance. This study offers valuable findings that can help improve the thermal management of electronic devices.

Investigation on the heat transfer and charge/discharge performance of phase change material capsule emulsion based on nanoparticles enhanced thermal conductivity

Both internal encapsulation and external added nanoparticles have been employed in this study to enhance thermal conductivity and explore the corresponding heat transfer characteristics. Specifically, the correlation between thermal conductivity and capsule, nanoparticle content, as well as the enhanced heat transfer/thermal energy storage performance facilitated by internal encapsulation are demonstrated through numerical and experimental study. Furthermore, it compares key parameters like heat transfer and pressure drop, providing quantifiable evidence that the addition of nanoparticles, whether internally or externally, leads to an increase of thermal conductivity by 6.63 %/2.75 % (5 wt%) and 5.92 %/4.26 % (10 wt%), respectively. Internal encapsulation was observed to yield a more substantial enhancement in heat transfer. Moreover, higher capsule concentrations tend to induce an inverted concentration profile near the heat exchange wall, particularly at higher flow rates. Furthermore, encapsulating nanoparticles within these capsules enhances heat transfer performance, with the level of enhancement scaling with the nanoparticle quantity. Increasing the flow rate of emulsion from 0.4 m·s−1 to 0.6 m·s−1 in a horizontal tube resulted in a 26.67 % increase in heat transfer and a 41.55 % increase in pressure drop. As a result of the disturbed heating, thermal fluctuations of external addition showed more pronounced thermal fluctuations due to disrupted heating, while a internal encapsulation exhibited a more stable temperature distribution and superior heat storage performance.

Multi-Parameter Inversion Optimization for Transverse Rib Profile Enhanced Convective Heat Transfer

The convective heat transfer performance of the rib-element approach in the channel is influenced by the transverse rib profile. In present work, a nonlinear multi-parameter optimization method based on inversion optimization is proposed and further used to obtain the optimal rib profile in a rectangular channel. Firstly, four conventional profiles as the original ribbed channel were selected to obtain the convective heat transfer performance of the channel by experiment and numerical solution; secondly, several control points were selected along the profile, and the polar radius was updated, and curve fitting was carried out. The results show that the inversion optimization can optimize the rib profile to improve the convective heat transfer performance. As the number of control points increases, the optimized profile changes hardly. The inversion optimization yields a similar optimized profile regardless of the original rib profile. With the increase of original rib height, the enhanced heat transfer performance of optimized profile is better. For the ribbed channel with original height 0.4 × channel height, as the Reynolds number increases from 6000 to 33,000, the performance evaluation criteria of the optimized profile increase by 14.94% to 21.2% compared with the original triangular profile.

Machine-assisted quantification of droplet boiling upon multiple solid materials

The intricate nature of droplet wetting and boiling on heated nano-/micro-structured surfaces has significant implications for practical applications. However, the multitude of factors influencing these liquid-vapor-solid interactions complicates the understanding of boiling behaviors across a wide range of operating conditions. In this study, we examined droplet impingement boiling over a large range of Weber numbers (We) on various surfaces, from smooth to nano-micro hierarchical ones, and from stationary to vibrated ones. The results indicate that the nano-micro hierarchical surface possesses the greatest heat transfer ability due to its superior superhydrophilicity, enhanced by nano-structures, and the vapor buffer effect caused by micro-structures. Additionally, vibration significantly improves boiling performance by 55.4%. However, contrary to previous findings, a higher We does not always enhance heat transfer performance due to a pronounced water hammer effect. We discovered that when the net pressure reaches a threshold value (∼ 90 kPa), a new phenomenon - jet flow - occurs, leading to a deterioration in heat transfer. Utilizing our database, we trained a machine learning framework to generate accurate droplet boiling data, providing a droplet boiling law that can extensively predict heat transfer performance. This paper proposes a fusion of physics and artificial intelligence to enhance our understanding and application of droplet boiling phenomena. Our findings are expected to contribute to the development of more efficient droplet-based boiling heat transfer devices and configurations across a wider range of industrial settings.

Accurate and robust predictions of pool boiling heat transfer with micro-structured surfaces using probabilistic machine learning models

The accurate and reliable prediction of enhanced heat transfer performance of micro-structured surfaces is crucial to optimally design and operate pool boiling systems. However, the existing empirical models predict the enhanced pool boiling heat transfer with very large errors up to ±81 % even using the experimental data from the same study, mainly due to the complex nature of the pool boiling processes. More importantly, the existing models predict only limited coolant types, surface geometries, and operating conditions. To overcome these challenges, this study examines three deterministic and two probabilistic machine learning (ML) models for accurate and reliable enhanced pool boiling prediction, while using carefully selected key six dimensionless numbers. The models were trained and tested using 1,241 data from 20 experimental studies with 80/20 % of train/test ratio, and the pre-trained models were tested for additional 519 data from 6 studies to evaluate the models reliability. The predicted mean absolute percentage error (MAPE) shows that Bayesian, deep, and 1-D convolutional neural network (1D-CNN) models outperform the random forest and natural gradient (NG) boost models due to their extended hidden layers. The machine learning models improve the MAPE by up to 30 % compared to the existing correlations. Furthermore, a parameter sensitivity analysis is performed using explainable artificial intelligence showing that the boiling Reynolds number is the most critical parameter followed by the kinetic Reynolds and Bond numbers. The probabilistic ML models can also provide the uncertainties to improve prediction reliability compared to the deterministic ones.

Experimental and numerical studies of the effect of perforation configuration on heat transfer enhancement of pin fins heat sink

AbstractIn this study, experimental and computational studies of the impact of forced convective flow on the heat transfer characteristics of staggered pin fins with perforations are investigated in a rectangular channel at constant heat flux with Reynolds numbers (Re) of 2 × 103–12 × 103. In particular, cylindrical pin fins with circular longitudinal (L) perforation, longitudinal/transverse (LT) perforation, and longitudinal/transverse/vertical (LTV) perforation perforations are compared to solid pin fins to find out how adding different perforation arrays affects overall heat transfer performance and also to find the best perforation configuration for maximum performance. ANSYS‐FLUENT is employed for numerical simulation, validated by experimental data. Experimental validation is conducted by attaching the heat sink to a Peltier module, inducing heat generation through current on one face in the Armfield Free and Forced Convection Heat Transfer Service Units HT 19 and HT10XC. Results highlight significant increases in Nusselt number (Nu) for perforated pins compared to solid pins, with L perforations at 8%, LT perforations at 33%, and 67% for LTV perforated pins due to transverse perforations that act as slots, which stir up the primary flow and induce secondary flow generated by vertical perforations. Regarding pressure drops, L perforations reduce by 9%, LT by 19%, and LTV by 27% compared to solid pins. The overall enhancement ratio peaks at the minimum Reynold number, notably achieving a 38% increase in the LTV perforation pin fin array. This innovative study holds promise for diverse electronic applications, offering enhanced heat transfer performance in electronic cooling systems.

Enhancing energy efficiency and heat transfer performance of engine oil flow through hybrid nanoparticles in convergent/divergent channel

Engine oil (EO) is employed as a lubricant in various machinery engines. Efficient heat transfers are a fundamental requirement for all processes. To improve heat transfer rates and reduce the energy loss caused by high temperatures, this study focuses on incorporating Iron Oxide (Fe3O4) and Cupper Oxide (CuO) into the engine oil as suspended particles. However, the focus of this research paper is to analyze entropy generation in a convergent/divergent channel that contains a hybrid nanofluid. Mathematical modeling is utilized to present the continuity, momentum, and energy equations. Using the resemblance transformation variables, the governing dimensional partial differential equations (PDEs) are transformed into a system of non-dimensional ordinary differential equations (ODEs), which are then resolved in ascending order through the BVP4c scheme. The graphical results illustrate the effects of various parameters on fluid velocity, temperature, entropy generation, and Bejan number. The study explores changes in velocity profiles under different Hartmann numbers, revealing opposing variations in divergent and convergent channels. Velocity profiles exhibit similar patterns when varying the porosity parameter. In the convergent passage, a higher porosity parameter results in a higher temperature field. Entropy rises against Eckert and Hartmann numbers in both Convergent and Divergent cases. These insights aid in designing and optimizing machinery engines.

Experimental study on heat transfer performance enhancement of pulsating heat pipes induced by surfactants

Pulsating heat pipe (PHP) is considered as a promising technique to address the thermal dissipation issues in micro-electronic devices, but its heat transfer performance needs to be further enhanced urgently. In this study, the PHP comprehensive performance experimental system was established. Then, the influence of surfactant sodium dodecyl sulfate (SDS) aqueous solution on the heat transfer performance of PHP was experimentally investigated and the visualization of PHP with surfactant was also accomplished. Additionally, based on Marangoni effect and surface tension, a comprehensive analysis was conducted on the impact mechanism of surfactants on PHP. The experimental results indicated that the oscillatory disturbance of the liquid slug inside the PHP is enhanced by the addition of SDS, and the resulting pressure imbalance and temperature difference enhance the directional flow of the working fluid. Meanwhile, under the operating conditions of 30 W working thermal power and the solution concentration of 0.001 wt%, the thermal resistance of PHP was reduced by 30.7 % compared with that of deionized water (DI water). This indicated that the working fluid with low concentration SDS could increase the area of liquid film and reduce the thermal resistance, which is induced by the surface tension and Marangoni effect due to the uneven distribution of surfactants. However, the thermal resistance of PHP with the SDS concentration of 0.2 wt% is higher than that of DI. This means that high concentration of SDS would deteriorate the startup characteristics and the heat transfer performance of PHP. Therefore, high concentrations of surfactants should be avoided from practical application of PHP.