Enhanced Heat Transfer Performance Research Articles

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.

EXPERIMENTAL STUDIES ON THE EFFECT OF AL2O3+WATER NANOFLUID CONCENTRATIONS ON HEAT TRANSFER COEFFICIENT IN A CLEANROOM AIR HANDLING UNIT

Nanofluid, Fluid-based heat transfer is essential in various industrial cooling and heating applications within production and space industries. Unlike solid materials such as metals and metal oxides, traditional heat transfer fluids like water, ethylene glycol, and oil exhibit relatively lower thermal conductivity. However, nanofluids, which involve suspending solid nanoparticles in a base fluid, offer a notable enhancement in heat transfer performance compared to conventional fluids. the Al2O3+Water nanofluid and pure water. 10% pressure rise at 4% volume with higher power & 11.61% higher thermal conductivity at 50°C. These enhancements are observed across different nanoparticle concentrations and Peclet numbers, indicating the efficacy of nanoparticle manipulation in augmenting heat transfer efficiency. Importantly, the research's novelty lies in its exploration of the impact of varying nanofluid concentrations on heat transfer parameters within a cleanroom air handling unit, offering valuable insights for optimizing heat transfer efficiency in controlled and critical environments and addressing a significant research gap in the field.

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.

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.

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.

Numerical investigation of the flows and heat transfer characteristics of internal cooling channels with separated ribs in gas turbine blades

Gas turbine engines play a crucial role in numerous industrial domains, including power generation, aviation, and marine propulsion. One of the major challenges in designing gas turbine engines is managing the high temperature generated by the combustion process. Internal cooling is a commonly used technique to maintain the temperature of critical components, such as turbine blades, within a safe operating range. Rib turbulators are widely used in internal cooling systems to enhance heat transfer performance by promoting turbulence in the fluid flow. Nevertheless, the existence of a continuous rib within the cooling channel can result in elevated temperatures near the rib section, potentially diminishing the overall system efficiency. In response to this challenge, a new rib turbulator design, denoted as the “separated rib,” has been introduced to mitigate the high-temperature zone. Through the utilization of the passing-gap design in the separated rib configuration, the coolant flow passes through the gap, effectively eliminating the region of extreme heat and augmenting the secondary flow. Consequently, it results in a notable enhancement of heat transfer performance within the ribbed channel. The numerical simulations are performed by solving three-dimensional (3D) Reynolds-averaged Navier–Stokes equations using the commercial software ANSYS CFX. The working fluid is steam, and the heat transfer performance is evaluated in terms of the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The results show that the separated rib configuration has approximately 17.3% higher Nusselt number than the original ribbed configuration when the Reynolds number (Re) changes from 5000 to 60 000. The separated rib configuration consistently shows higher TPF values between about 1.6 and 1.9 than the original rib configuration, where TPF is smaller than 1.35. Furthermore, the heat transfer correlation related to the Reynolds number was developed to predict heat transfer performance. The heat transfer correlations align closely with the numerical simulation results, showing about 17.4% and 34.3% improvements in Nu and TPF, respectively, for our newly designed system compared to the old version.

Interfacial heat transfer and melt-front evolution at a Fractal Cantor structured interface under various PCM melting conditions

With the aim to investigate heat transfer characteristics of PCM on micro-textured hot surface, this study numerically investigates the heat transfer process of PCM at fractal Cantor structured surfaces using the total enthalpy-based lattice Boltzmann method, which is partly validated by experimental testing. The thermal slip length and liquid velocity distribution are assessed as evaluation criteria. Results show that Fractal Cantor structure can significantly stimulate localized thermal convection, thereby reducing the average thermal slip length from 0.3 mm to approximately 0.14 mm. When the Fourier number exceeds 0.1, both thermal conduction and convection should be considered within the melted layer. With the fractal level increasing, a more uniform melt-front evolution can be observed, consequently, minimizing the total melting time by 500 s with the fractal level of 3. Elevating Ste and gravity can significantly increase the flow rate of liquid PCM by augmenting superheat degree and buoyancy effect, thereby enhancing convective heat transfer strength and reducing thermal slip length. According to the orthogonal design, though the fractal level demonstrates minimal range values for both maximum velocity and Rayleigh number, it elevates the sensitivity to the variation of boundary conditions. Ste yields the most significant enhancement in heat transfer performance.

CFD analysis of novel two-pass, sinusoidal corrugated, trapezoidal channel for solar air heater

Solar is regarded as a clean and reliable source of energy. Solar air heaters (SAHs) are one of the most prevalent applications of solar energy. SAHs have normally low thermal efficiency. In order to increase thermal efficiency, a sinusoidal wave corrugation is employed on the base wall of the twin-pass channel of an absorbent plate with a sharp bend. A parametric study was conducted to study the effect of flow and geometric parameters i.e. wave height, pitch, and propagation angle of the wave with respect to flow inlet on performance parameters. Computational Fluid Dynamics (CFD) tool was implemented to examine the performance parameters i.e. heat transfer enhancement, pressure drop, and thermal performance factor. In comparison to the orthogonal ones, inclined corrugation is more efficient in terms of heat transfer. With the increase in roughness height, pitch, and corrugation angle, an increasing trend was observed in Thermal Performance Factor, followed by a diminishing trend. The corrugated channel having a roughness height ratio of 19, two waves in a single block with a 45° wave propagation angle seemed to be an optimal configuration with 35% enhancement in thermal performance factor as compared to the smooth channel, hence representing promising augmentation.

Research on enhanced heat transfer performance at the solid-liquid interface of diamond coatings through diamond submicron cones composite microstructures

Diamonds with excellent thermal conductivity have proven to be effective in addressing heat dissipation challenges. However, with the increasing power of electronic devices, the demand for surface heat dissipation capability is growing higher. Continuously improving the thermal performance of diamond devices is conducive to promoting the development of high-power electronic components. In this study, a novel diamond coating with microgroove-submicron cone composite structures was prepared by inductively coupled plasma etching technology, microwave plasma chemical vapor deposition and bias plasma etching technology. Droplet evaporation experiments demonstrated that the evaporation time of droplets on diamond coatings with microstructures and diamond submicron cones was 42 % shorter compared to ordinary diamond coatings. This finding indicates that surface micro-submicron structures play a crucial role in enhancing the solid-liquid heat transfer performance of diamond heat dissipation devices. The micro-submicron structures create a significantly larger contact area, which leads to enhanced heat transfer, active bubble generation, and droplet vibration phenomena, thereby facilitating bubble escape. Furthermore, the surface generated by ion etching exhibits graphite phase and terminal oxidation, which enhances the hydrophilicity of the surface phase and further improves the heat transfer efficiency of solid-liquid.

Experimental study on enhanced heat transfer performances and optimized strategies of cascade sensible-latent heat storage radiator

Improving the thermal efficiency of radiator and minimizing the energy loss in distribution networks are crucial for space heating. However, existing studies primarily focused on optimizing the thermal performance or indoor environment of individual units, yet rarely revealed the enhanced heat transfer performance from initial power supply to final heat utilization. To address this gap, this study developed a cascade sensible-latent heat storage radiator, and improved the thermal performance in the following ways. Firstly, by adsorbing paraffin wax with expanded graphite, the thermal conductivity rose from 0.2 to 3.5 W/(m‧K). Secondly, through cascading sensible and latent heat storage bricks, the heat charging/discharging efficiency increased by 11.9 %/14.6 %. Finally, by enhancing the airflow from 0.05 to 0.28 m/s, the heat discharging efficiency and entransy dissipation amount increased by 15.8 % and 225.8 kJ‧K, respectively. The total energy utilization efficiency was improved by 7.4 %, and the dissatisfaction caused by draft and noise both met the personnel requirement. The total annual cost of developed radiator was merely 30 % and 60 % of the direct electric heating radiator and sensible heat storage radiator, respectively. Therefore, the sensible-latent heat storage radiator offered advantages in improving the energy utilization efficiency, indoor thermal environment and cost effectiveness performance.

Numerical Analysis of Fluid Flow and Heat Transfer Characteristics of Novel Microchannel Heat Sink

Microchannel heat sinks have gained prominence in the field of thermal management, offering compact and efficient solutions for dissipating heat flux from high performance electronic devices. Escalating heat flux in modern electronic devices, such as those found in telecommunication equipment, industrial automation equipment, solar devices, and data centre servers has driven the continuous development of microchannel heat sink to achieve efficient thermal management. The critical challenge in thermal management for these devices is to develop a microchannel that enhances heat transfer performance and minimises pressure drop. Heat transfer and pressure drop are two competing factors that determine the practicability of the design for real world application. Improvement in heat transfer performance usually results in an increase in pressure drop and pumping power. This study addresses the challenges of designing microchannel through comprehensive numerical analysis of fluid flow and heat transfer characteristics of a novel design that combines ribs, secondary channels, and tertiary channels. The numerical results showed that the novel microchannel design achieves a favourable balance between heat transfer and pressure drop, demonstrating its potential to be used in application where high heat transfer and efficiency are paramount. To assess the performance of the microchannels, thermal resistance, a measure of system’s resistance to heat transfer is used. At the same pumping power, thermal resistance in the new design is consistently lower compared to other designs.

Understanding heat transfer and flow characteristics of additively manufactured pin fin arrays through laser-induced fluorescence and particle image velocimetry

This article investigates the thermal and hydrodynamic performance of three distinct additively manufactured fin array configurations in a cooling channel: cylindrical, optimized, and perforated fin. The optimized fin design was achieved through the application of a genetic algorithm (GA) to enhance heat transfer efficiency. Experimental assessments were conducted to quantify the heat transfer characteristics and pressure drop across these fin configurations where water is the working fluid and the Reynolds number ranges from 1100 to 5100, along with visualization using Laser-Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) techniques. Results reveal that the optimized fin array, generated through genetic algorithm optimization, demonstrates a notable enhancement in heat transfer coefficient, exhibiting an improvement of up to 44 % when compared to the traditional cylindrical fin configuration. Furthermore, the perforated fined array showcases a 63 % enhancement in heat transfer performance compared to the cylindrical fin array without apparent increase of pressure drop. The utilization of LIF and PIV techniques offers insights into the heat transfer and fluid velocity distributions within the cooling channel. These visualization methods provide a profound understanding of the flow patterns, flow mixing phenomena, and heat exchange associated with the pin fin designs, facilitating a deeper comprehension of the underlying heat transfer mechanisms.

Research on the enhanced heat transfer performance of SCO2 caused by vortex generators with different geometric dimensions in novel airfoil channels

The performance of printed circuit heat exchangers (PCHEs) has a significant impact on the heat transfer efficiency and compactness of the supercritical carbon dioxide (SCO2) Brayton cycle system suitable for the fourth-generation nuclear energy system. Compared to PCHEs with other types of channels, the airfoil fin PCHEs have superior flow heat transfer performance. The installation of vortex generators (VGs) in the heat transfer channels can enhance heat transfer efficiently, but the application of them to PCHEs is very limited. In order to improve the performance of PCHE with airfoil fin channels, a novel channel structure combining airfoil fin channels with rectangular VGs is proposed, and the effect of geometric parameters of VGs on the thermal-hydraulic performance of the channels is also investigated. The results show that the VG improves the synergistic effect of velocity field and temperature gradient field, leading to the increase of turbulent kinetic energy and decrease of heat transfer entropy production in the channel, which finally promotes the enhancement of heat transfer. The comprehensive performance of the airfoil fin channel with VGs is 5.95%–19.47% higher than that of the conventional airfoil fin channel. The increase in the height and length of the VGs improves the heat transfer performance of the channel, and the increase in the width of the VGs weakens the heat transfer performance of the channel, and both increase the flow resistance of the channel. By comparing the comprehensive performance, it is found that the VGs have the best height of 0.2 mm, the best length of 0.8 mm and the best width of 0.04 mm. In addition, according to the noise performance statistics (NPS), the height of the VG contributes more to the Nu and Fanning friction coefficients of the airfoil fin channels.

Performance study on turbulent heat transfer using rectangular air duct integrated with continuous and intermittent ribs turbulators

To continue the scientific path specialized in enhancing the thermal performance of thermal systems, several tests are carried out to improve the overall performance of a rectangular duct as air flows through it. This study reports experimentally and numerically the heat transfer enhancement and overall performance of a rectangular air duct with various arrangement of continuous and intermittent ribs turbulators. The ribs are inserting in several array arrangements at a 90o relative to the direction of flow. Three ribs lengths s= 30, 60 and 150 mm employed with the several arrangements that?s tested in the current study, with the pitch ratios (p/e)= 5.0 and height ratios (e/H) = 0.330. These cases include: continuous ribs case (CR), intermittent-continuous-intermittent ribs case (ICIR) and intermittent-ribs (IR). Reynolds number (Re) is ranging from 10,000 to 35,000. The experimental work was performed by designed and fabricated test rig while the numerical work was performed in commercially ANSYS Fluent 17.2. the outcomes show that (IR) case offers the best overall performance for all tested velocities, its 1.54 for experimental study and 1.57 for numerical study at Re=10000. Also, the highest friction factor values are found in (IR) case, it is found to be 0.082 in Re=10000.

The adoption of novel cooling liquids for enhancing heat transfer performance of three-dimensional integrated circuits with embedded micro-channel

The nanofluids (including MWCNT based nanofluid and SWCNT based nanofluid) and liquid metal Ga68In20Sn12 are proposed to replace the conventional water as cooling liquid of micro-channel for enhancing heat transfer performance of three-dimensional integrated circuits (3-D ICs) in this paper. An equivalent thermal model of 3-D ICs with integrated micro-channel is established to investigate the heat transfer performances for using different cooling liquids. The results show that the steady-state temperature for MWCNT based nanofluid, SWCNT based nanofluid and Ga68In20Sn12 as cooling liquids can be reduced over 25.698%, 28.771% and 35.735% than the conventional water scheme in a four-layers stacked chip, respectively. Besides, it is found that the steady-state temperature of all die layer in 3-D ICs can be further reduced by increasing the micro-channel size and flow velocity of cooling liquid. Therefore, the proposed novel materials (i.e., nanofluids and Ga68In20Sn12) as cooling liquids have excellent application prospect in solving thermal problems of 3-D ICs.

Heat transfer performance enhancement and mechanism analysis of thermal energy storage unit designed by using a modified transient topology optimization model

The spatial layout of the highly conductive fin and phase change materials (PCM) and the thermophysical properties of PCM are important factors restricting the heat transfer rate of the latent heat thermal energy storage (LHTES). The current fin design concentrates on the limited design space, and rarely adopts the optimizing form of unconstrained structure evolution in the process. So this study proposes a modified transient topology optimization (TO) model to seek the optimal distribution of the fins embedded into PCM subject to the constraints of fin area and specified time. This topology optimization problem is formulated using the density-based material design variable in governing equations, physical constraints, etc. The design freedom and procedural iterative solving of TO model allow for the free evolution of innovative fin structures and elucidate the interaction mechanism between the fin design and physical occurring processes. The double interpolation function, variable regularization, adjoint-based sensitivity analysis and GCMMA algorithm are established to further improve TO model to obtain high-precision solutions. Using above methods, the regular evolution mechanism of fins and physical performance parameters and the trade-off between performance and structure are analyzed. Then, the effects and reasons of pure paraffin (PW) and the adding carbon nanotubes (nPW) on changes in topology structure and performance parameters are also comparatively studied. Finally, by comparing TO-fins with conventional rectangular fins, the superiority of the established method is verified, and the performance improvement mechanism and extent of TO-fins are revealed. Results show that TO-fin LHTES with nPW can achieve better performance than TO-fin LHTES with PW under fewer branches and shorter branch length. The uniform distribution and multi-branch characteristics of TO-fins greatly shorten the heat conduction path, and its local segmentation of whole PCM enhances the local convection effect.

Effect of symmetrical and asymmetrical structures of transverse tube on heat transfer performance of nanofluids in a solar collector system

AbstractIn an effort to enhance the heat transfer performance of solar collectors, this paper proposed to replace the smooth tube with symmetrical and asymmetrical transversely corrugated tubes, and to couple with SiO2‐H2O nanofluids for heat transfer of solar collectors. Effects of nanofluids mass fraction (w = .0%, .1%, .3%, and .5%), Reynolds number (3000, 4000, 5000, 6000, and 7000), and groove radius (1.5, 2, and 2.5 mm) on the flow and heat transfer properties of nanofluids in solar collectors were studied. The comprehensive evaluation index was used to consider the heat transfer property and flow resistance of fluid flow at the same time. Results showed that with the augment of nanofluids mass fraction, Reynolds number, and groove radius, the heat transfer enhancement performance of the collector becomes better. Among them, when the Reynolds number is 4000, the asymmetric transversely corrugated tube with a nanofluids mass fraction of .5% and a groove depth of 2.5 mm has the best comprehensive flow and heat transfer performance, and the comprehensive evaluation index can reach 1.62. The study results in this paper are beneficial to the coupling of nanofluids and transversely corrugated tubes and their application in the domain of enhanced heat transfer of solar collectors.