Heat Transfer In Channel Research Articles

Thermohydraulic performance study of the effect of winglet inserts and a corrugated wall in a rectangular channel

This numerical study investigates the enhancement of heat transfer and pressure drop characteristics in rectangular channels with transverse corrugations and longitudinal winglet vortex generators. Numerical simulations cover a range of Reynolds numbers (Re) (5000–20000) using channels with uniform wall heat flux and fixed wavelength. The study evaluates the influence of geometrical parameters (corrugated channel amplitude and winglet length) on flow and temperature characteristics, average Nusselt number (Nu), and pressure drop. Corrugated channels alone create stationary transverse vortices that impede heat transfer. However, integrating winglet vortex generators introduces beneficial longitudinal vortices, disrupting stationary vortices, perturbing the thermal boundary layer, enhancing near-wall turbulence, and improving fluid mixing and heat transfer compared to smooth and corrugated channels. At Reynolds number (Re)20,000, corrugated channels with winglets exhibit 167.7 % and 61.8 % higher Nusselt numbers compared to smooth and corrugated channels, respectively. However, this enhanced heat transfer accompanies increased pressure drop. Both heat transfer and pressure drop rise with higher Reynolds numbers (Re), corrugation amplitude, and winglet length. This study provides insights into heat transfer mechanisms in corrugated channels and the potential for improvement through winglet vortex generators.

Analysis on the flow and heat transfer performance of SCO2 in airfoil channels with different structural parameters

As an important component of the system, the performance of the printed circuit heat exchanger (PCHE) has a significant impact on the efficiency and compactness of the supercritical carbon dioxide (SCO2) Brayton cycle system. Optimization of the structural parameters of airfoil fins can improve the performance of PCHE flow channels, but it has not received enough attention. Therefore, it is of great significance to investigate the effects of structural parameters such as the maximum thickness (Wf), the distance from the position where the maximum thickness is located to the leading-edge (Df), and the radius of the leading-edge (Rf) of the airfoil fins on the flow heat transfer performance of SCO2 in the channel of PCHE. A three-dimensional numerical model is developed and validated for performance analysis of the PCHE, meanwhile the thermal-hydraulic performance of channels with different structural parameters of the airfoil fins is compared. The results show that with the increase of the Wf of the airfoil fins, the heat transfer characteristics of the PCHE channel are gradually enhanced, and the flow characteristics are gradually weakened. When the maximum thickness of the airfoil fins is in the front, the heat transfer and flow characteristics of the PCHE channel are better. As the Rf of the airfoil fins increases, the heat transfer characteristics and flow characteristics of the PCHE channel fluctuate. The change of the turbulent kinetic energy, the boundary layer thickness, the synergistic effect of the velocity field and the temperature gradient field, and the local entropy production in the channel can well explain the mechanism of the flow and heat transfer of the SCO2 in the airfoil fin channel. In addition, among the channels with different structural parameters of the airfoil fins, the Fin-5 airfoil fin channel with Wf of 1.5 mm, the Fin-6 airfoil fin channel with Df of 0.6 mm and the Fin-13 airfoil fin channel with Rf of 1.46 mm are recommended. Their comprehensive performance is 2.0–6.3%, 0.9–5.6% and 0.13–1.81% higher than that of the Fin-3 airfoil fin channel, respectively.

An investigation into a semi-porous channel's forced convection of nano fluid in the presence of a magnetic field as a result of heat radiation

This study investigates the impact of heat radiation on magnetically-induced forced convection of nanofluid in a semi-porous channel. The research employs Akbari-Ganji's and Homotopy perturbation methods to analyze the effects of multiple parameters, including Hartmann number, Reynolds number, Eckert number, radiation parameter, and suction parameter, on the flow and heat transfer characteristics. The results demonstrate that increasing Reynolds number, suction, and radiation parameters increases temperature gradient, providing valuable insights into improving heat transfer in semi-porous channels. The study validates the proposed methods by comparing the results with those obtained from other established methods in the literature. The main focus of this work is to understand the behavior of nanofluids in semi-porous channels under the influence of magnetic fields and heat radiation, which is essential for various industrial and engineering applications. The future direction of this research includes exploring the effects of different nanoparticle shapes and materials on heat transfer performance and investigating the influence of other parameters, such as buoyancy forces and variable properties, on the flow and heat transfer characteristics. The findings of this study are expected to contribute to the development of more efficient thermal management systems in the future.

Numerical investigation of the hydrothermal performance of novel vortex generators in a rectangular channel by employing inclination and rotational angles

Vortex generators are passive methods of heat transfer enhancement in any thermal system. However, more research is needed to compare the effects of vortex generators having unique shapes on the flow distribution for high heat transmission. Also, a research gap exists in analyzing how different angular orientations of the vortex generator (VG) affect thermohydraulic performance. Therefore, this CFD study aims to propose a total of five novel vortex generator shapes applying modification on a rectangular VG shape, analyzing and comparing the heat transfer and pressure drop properties in a rectangular channel for the Reynolds number varying in the range of Re=4000–11,000. VG-1 (vortex generator-1) with three triangles on its top side, VG-2 with concave shape arc, VG-3 combined with a rectangle and a triangle, VG-4 consists of a rectangle and two triangles at two corners, while VG-5 consists of a rectangle with a triangular inside cut. Among the five designs, VG-1 gives the most optimal hydrothermal performance, incrementing Nusselt number and friction factor of about 38.2 % and 80.38 %, respectively. Combining these two dimensionless parameters, we get the maximum thermal performance factor, TPF, for VG-1, whereas VG-2 performs the least in terms of TPF. Moreover, compared with conventional rectangular VG, VG-1 performed the best with a 1.63 % increase in TPF. Considering the effect of different angular orientations, VG-1 was further studied by applying five vertical inclination angles and four horizontal rotation angle configurations to investigate the impact of inclination and rotational angles. Minimizing the pressure drop penalty, the 30˚ inclination design had the best hydrothermal performance overall, with the highest TPF range of 1.19–1.41, whereas 120˚ variants had the lowest TPF, at 1.09–1.31. Also, for the configuration of the horizontal rotations, 30˚ angle gives the best result, having a slight edge over 150˚case with 1.17–1.41 TPF. Finally, the best cases from vertical inclination and horizontal rotation are combined in a new hybrid configuration, which yielded the maximum TPF of 1.22–1.45, indicating that this configuration is the most effective among all the cases.

Review and Analysis of Heat Transfer in Spacer-Filled Channels of Membrane Distillation Systems.

Membrane distillation (MD) is an attractive process for the concentration of seawater brines. Modelling and simulation of membrane distillation processes requires a better knowledge of the heat transfer coefficients in spacer-filled channels which are usually determined by applying empirical correlations for the Nusselt number. In this study, first, a comprehensive literature review on heat transfer correlations was conducted. It was found that the empirical correlations often used for MD simulation result in strongly varying Nusselt numbers that differ by up to an order of magnitude at low Reynolds numbers. Then, heat transfer in spacer-filled channels was investigated experimentally in a membrane distillation system using an aluminum plate instead of a flat-sheet membrane. Numerous tests were carried out with sodium chloride solutions in a wide range of salinities, between 1 g/kg and 95 g/kg, and temperatures, between 30 °C and 80 °C, yielding high heat transfer coefficients in a range of 1500 to 8300 W/(m2K) at relatively low Reynolds numbers, between 100 and 1500, clearly showing the influence of the spacers on heat transfer. A new empirical Nusselt correlation (Nu=0.158Re0.652Pr0.277) was derived which represents the experimental data with a deviation of 10% and is valid for 100<Re<1500 and 2<Pr<7. Computational fluid dynamics simulations were performed to analyze the variations of the fluid properties across the boundary layer due to temperature differences. The simulations showed only minor deviations of the heat transfer coefficients in the hot and cold fluid channels for small driving temperature differences.

Synergistic effect of ribs and particles on flow and heat transfer in channels using the CFD-DEM-IBM method

To investigate the synergistic effect of the surface structure and particles on flow and heat transfer during forced convection, a model for two-phase flow and heat transfer was established using the computational fluid dynamics-discrete element method-immersed boundary method (CFD-DEM-IBM). The effects of rib size and particle physical properties on the flow and heat transfer were studied. The results showed that large-scale vortices rolling forward were formed in the particle-laden flow, and heat transfer in the rib gaps was intermittently enhanced. Convective heat flux was weakened, and conductive heat flux was strengthened when the height of the ribs was too high or the spacing was too small. Particles with high thermal conductivity promoted conductive and convective heat transfer. Small particles easily entered the rib gaps to strengthen the heat transfer, but this inhibited heat conduction at flat surface. Fluid laden with a mixture of particle sizes enhanced the convective heat transfer.

Microstructure and thermal properties of copper matrix composites reinforced by 3D carbon fiber networks

Three-dimensional (3D) carbon fiber (CF) networks were constructed by electrodeposition using Cu foam as template, and then 3D CF/Cu composites were prepared by hot pressing sintering. Experimental investigations revealed the successful formation of a well-connected 3D CF network embedded within the Cu matrix. The constructed 3D CF networks are conducive to establishing effective heat transfer channels in the composites. The thermal conductivity of the 3D CF/Cu composite with 20 vol% CF in the X–Y plane and Z plane are 418 ± 3 Wm−1K−1 and 415 ± 5 Wm−1K−1, respectively. The thermal conductivity of the composites is significantly enhanced, and the thermal conductivity becomes isotropic. Additionally, the construction of the 3D CF network promotes efficient heat transfer in CF/Cu composites, providing a promising strategy for the development of advanced CF/metal thermal management materials.

Synthesis of vertically aligned and interconnected BN fiber skeleton for significantly improving thermal conductivity of PVDF

Seeking efficient thermal management materials for electronic components is urgent and important. BN has high thermal conductivity and good insulating properties, making it an ideal polymer filler for improving thermal conductivity. Currently, because of the weak interaction between BN and its high melting point, it is extremely difficult to construct a BN three-dimensional skeleton by direct sintering to achieve efficient heat transfer channels. In this work, vertically aligned BN three-dimensional skeletons with fiber walls were synthesized in one step by combining the in-situ conversion of precursor fibers and directional freeze-drying technology. The precursor fibers were expelled by the directionally grown ice crystals, forming vertically aligned fiber walls. Importantly, molten B2O3 produced during air calcination made the fibers bond to each other, thus obtaining the vertically aligned and interconnected BN fiber skeleton. Benefiting from the short-path fast heat transfer and low interfacial thermal resistance of the fiber walls, the obtained vertically aligned BN skeleton exhibited obvious structural advantages, resulting in composites with a unidirectional thermal conductivity of 1.372 W/(m·K) with the filling content of 25.7 wt% and high enhancement efficiency per unit volume of 32.6 %. This approach is expected to open a new avenue for developing highly thermally conductive composites with great potential.

Investigation of neutronic and thermal–electric coupling phenomenon in a 100 kWe-level nuclear silent heat pipe-cooled reactor

Heat pipe-cooled reactors are attractive because of their compact structure, high power capacity and reliability, and inherent safety features. These reactors are distinguished by the use of high-temperature heat pipes that directly bridge the reactor core and energy conversion devices, thus creating a tightly knit modular system. However, comprehensive coupled analysis of these reactors remains challenging because of the intricate multiphysics interactions involved. To address this, the neutronic and thermoelectric coupled phenomena of heat pipe-cooled reactors are investigated in this study. Models are introduced for the point reactor kinetics, core heat transfer, channel heat transfer, two-phase two-dimensional heat pipes, thermoelectric coupling, and cold plates. The channel heat transfer is refined in a 100 kWe-level nuclear silent heat pipe-cooled reactor and a model for the three-dimensional heat transfer process in its thermoelectric matrix established, which effectively resolves the calculation distortions of the lumped model. The maximum deviation between the calculation results from the proposed model and the verification data for a full-system coupled computation is less than 10 K. The core temperature difference from the three-dimensional model is five times that of the lumped model with a maximum average fuel temperature difference of 225.7 K. The maximum and average thermoelectric conversion efficiencies are 15.56 % and 14.43 %, respectively. The failures of one, five, and nine heat pipes are analysed. The failure of a single heat pipe has negligible effects with a peak fuel temperature surge of only 121 K. In contrast, a failure involving nine heat pipes leads to a peak fuel temperature spike of 778 K and a 47.1 % increase in the maximum heat transfer power, marking a critical operational threshold. It is therefore imperative to consider the safety margin in the potential failure of multiple central heat pipes during the preliminary design stages.

Experimental investigation of heat transfer in the trapezoidal channel with lateral outflow under rotation conditions

The heat transfer characteristics of wedge-shaped transverse outflow channels with different pin-fins under rotating conditions were measured experimentally. The Reynolds number varies from 10,000 to 70,000, and the rotation number varies from 0 to 0.6. For non-rotating state, the Nussel number decrease along the flow direction on the pin–fin rough surface as inner smooth area, albeit marginally. For rotating state, the enhancement of Nusselt number ratio in the outer pin-fins area is significantly weaker than inner smooth area. The heat transfer of the leading and trailing surfaces shows an increasing trend with the ascend of the rotation number. At the same time, due to the Coriolis force, the heat transfer of the trailing surface is stronger than that of the leading surface. Results show that the total heat transfer of the four experimental models intensify with the increase of the total cross-sectional area of the pin-fins. In particular, the total cross-sectional area of pin fin is increased by 3 times, and the heat transfer of channel can be strengthened by 46–77%. The effective method to increase the total cross-sectional areas of the pin fins is to increase their diameters.

A novel design of heat recovery system from exhaust stacks' silencers in a simple cycle gas turbine

This paper aims to evaluate the potential of heat recovery from the integrated heat exchanger within the exhaust stack silencer baffles in a simple cycle gas turbine. Heat transfer channels were incorporated into the upstream (nose) and downstream (tail) sections of the parallel silencer baffles in the exhaust stack. The gas turbine exhaust gas represents the hot side flow across the baffles' sections. The integrated heat exchanger system offered an advantage of extracting waste heat from the exhaust stream, while reducing pressure drop on the flow and improving acoustic attenuation.In this work, a series of parametric studies were carried out across a range of internal and external heat transfer area configurations within the silencers to maximize the heat transfer. Further enhancement opportunities were introduced and discussed based on the conducted parametric studies and practical aspects borne out of common industry practice. The proposed heat recovery system was implemented to power the gas fuel performance heater which is used to enhance the gas turbine cycle performance through utilization of the extracted waste heat while keeping lower exhaust pressure drop in the stack.The obtained results showed that the proposed integrated heat exchanger within the silencers has a potential of generating a 5.48 MW net gain from the gas turbine exhaust stacks which are normally lost to the atmosphere from the simple cycle exhaust stack. The proposed heat recovery system proved significant fuel savings that lead to economic benefits and reduction in CO2 emissions.

Numerical investigation on boiling heat transfer in a rectangular channel under sub-atmospheric environment

Water evaporators are often used as heat sinks in spacecraft. The aim of this study is to investigate the heat transfer characteristics and the spatial and temporal characteristics of bubble formation in an airborne water evaporator at an absolute pressure of 7 KPa. In order to achieve this, a rectangular single-channel model based on the structure of the water evaporator is established. Since the temperature change of the glycol in the water evaporator is not obvious when it flows through the rectangular single-channel, the inner wall surface is set to be 333.15 K in order to reduce the computational cost in the simulation. In this paper, a VOF method is adopted to numerically investigate the heat transfer characteristics of the boiling in the upper pool of the rectangular channel under a low-pressure(7 kPa) environment. Good agreement was obtained by comparing the numerical results with the experimental data with the error within 6 %. The numerical results show that bubbles rise along the wall, combine with nearby small bubbles, grow and attach to the wall, and slide along the wall until they are discharged from the top of the wall. The perturbations generated by the bubbles cause the heat transfer coefficient and wall temperature to fluctuate, with the maximum fluctuation of the wall temperature being around 5 K. In addition, the effects of different rectangular channel structure sizes (0.5 mm, 1.5 mm, and 2.5 mm) on the boiling heat transfer and bubble characteristics were investigated. A channel size of 0.5 mm leads to severe bubble coalescence, which increases the wall temperature and deteriorates the heat transfer performance. When the channel spacing is increased, bubble coalescence is improved, but a channel spacing of 2.5 mm results in less bubble turbulence and weaker heat transfer performance.

Modified mica-supported phase change materials for efficient solar thermal conversion and thermal energy management

To improve the solar thermal conversion performance of composite phase change materials and further practical applications, the rational design and realization of excellent thermal properties, electrical properties, shape stability, and fast response to solar energy are essential. Three-dimensional layered composite phase change materials loaded with paraffin wax were prepared by vacuum impregnation method using polyethylene glycol grafted nanocellulose modified mica as the carrier. The prepared materials exhibited high bulk resistivity (1.47 × 1013 Ω cm), excellent thermal conductivity (1.3 W/m K), outstanding solar energy conversion efficiency (98.3%), good thermal stability and reusability. It was noteworthy that the thermal conductivity of the composite was improved by 619.05% compared to pure paraffin. The three-dimensional layered structure of directional stacking and the polyethylene glycol-linked heat transfer channels greatly improved the thermal conductivity of the composite phase change material. These findings provide ideas for designing innovative materials that combine energy storage and other functional properties.

A multimodal cooling garment for personal thermal comfort management

Intelligent thermoregulation garments for personal thermal management (PTM) are essential to improve thermal comfort and reduce energy consumption. However, current attempts are unable to simultaneously address the aforementioned demands because of constraints including the environment, energy consumption, and wearing comfort. Here, we report a multi-effect cooling garment (MECG) with synergism regulation mechanism for personal thermal comfort management. By decently integrating radiative cooling fabrics, thermoelectric cooling devices, and heat transfer channels on textiles, MECG exhibits improved wearability and excellent personalized thermoregulation ability, not merely cooling function. Studies have demonstrated that MECG can greatly improve human thermal comfort and lessen the hot and sticky discomfort that comes with high temperatures. It is wirelessly controllable and can raise the air conditioning system's summertime setpoint temperature by about 4 °C. Owing to its exceptional thermal management performance and personalized thermoregulation ability, we expect the MECG concept to provide promising design guidelines for next-generation intelligent thermoregulation garments.

In-situ embedding of carbon dots in boron nitride for enhancing phosphor stability and fluorescent film heat dissipation

The aggregation-induced quenching effect and poor thermal stability issues of carbon dots (CDs) limit their further development in the solid-state lighting and display field. In this work, a red carbon dot/boron nitride nanosheet (rCDs/BNNS) composite was synthesized using boron nitride as a carrier by in-situ embedding of rCDs. Thanks to the uniform dispersion of rCDs and the restraint of BNNS, the prepared rCDs/BNNS composite has excellent fluorescence stability and thermal stability. rCDs/BNNS composites as fluorescent markers can be used to detect potential fingerprints on various surfaces. Furthermore, rCDs/BNNS were dispersed into polyvinyl alcohol (PVA) polymers to prepare rCDs/BNNS/PVA flexible luminescent films. In addition to the excellent stability inherited from rCDs/BNNS, the thin film also exhibits high heat dissipation by reason of the establishment of a heat transfer channel in the PVA by rCDs/BNNS. Moreover, thin films can still maintain original fluorescence after undergoing hundreds or thousands of bends, while possessing sufficient tensile strength. This study provides a facile pathway for the preparation of highly stable CDs luminescent materials, and has a promising application in the forensic identification and flexible luminescent devices' thermal management fields.

Numerical investigation of rocket engine cooling channel heat transfer for different LNG under trans-critical conditions

Hydrocarbon impurities in Liquified Natural Gas LNG may produce undesired phenomena such as pseudo boiling and two-phase flow. This can be an issue for rocket engine cooling channels. This study investigates the impacts of hydrocarbon impurities on LNG thermophysical and transport properties. It estimates the required relative roughness to improve the cooling capabilities with appropriate pressure drops for different LNG mixtures flowing in the rocket engine cooling channel. The Reynolds-averaged-Navier–Stokes equations are numerically solved for a straight cooling channel with a circular cross-section and uniform heat flux. LNG’s thermophysical and transport properties are calculated using the GERG equation of state and extended corresponding states, respectively. The turbulent models are validated numerically for supercritical LNG, vapor methane, and supercritical hydrogen. The results show that hydrocarbon compositions play a significant role in cricondenbar pressure. When the hydrocarbon impurities increase, the phase envelope develops, and cricondenbar pressure increases. The impacts of various relative wall roughness configurations on the cooling capabilities and pressure drops are sensitive under transcritical processes and hydrocarbon compositions. This study provides a systematic understanding of the relationships between cooling channel surface roughness, Nusselt Number, and LNG composition, offering designers the ability to optimize heat transfer in rocket engine cooling systems.

Deep-learning accelerating topology optimization of three-dimensional coolant channels for flow and heat transfer in a proton exchange membrane fuel cell

To quickly optimize the cooling performance of three-dimensional coolant channels in a proton exchange membrane fuel (PEMFC) cell, a generative adversarial network (GAN) model that adopts small-scale sample data to predict the coolant channel topology structure is constructed. The coordinate information of the topological pseudo-density field is directionally input into the neural network to improve prediction accuracy. The results show that more microtopologies in the coolant channels can be predicted with the GAN model than with traditional thermal–fluid–structural topology optimization. The topological configuration with a maximum temperature of 0.15 K, lower than the training dataset, is achieved. The well-trained GAN model can generate topological structures for the optimization objective, that is, thermal performance superior to the training set. The proposed model can also generate topological structures with better fluid and structural performance, which is 20.44% and 9.25% superior to that of the training dataset, respectively. The computation time required by the GAN model is <1 s, while the computation time for the same case is 30.2 h using the traditional thermal–fluid–structural topology optimization. These findings can aid in designing coolant channels in PEMFCs.

Heat transfer enhancement by electrohydrodynamics in wavy channels

The present study numerically investigated the heat transfer process occurred in a wavy channel enhanced by electrohydrodynamics (EHD). The mechanisms of the EHD-enhanced heat transfer in wavy channels differ from those in a straight channel. An advantageous position for single electrode is proposed to be above the peak of wave in a continuous wavy channel. Strategies for aligning multielectrodes in the EHD-enhanced continuous or discontinuous wavy channels are proposed based on interpretation on the simulation outcomes for single electrode. The ratio of horizontal section length to wave length (l/λ) significantly affects the heat transfer enhancement, unlike the case in continuous wavy channel (l/λ = 0). The optimal electrode arrangement for continuous wavy channels is inappropriate for discontinuous wavy channels, the electrodes should be placed above the junction of wave and horizontal section. The design criteria are proposed for enhanced heat transfer performance in discontinuous wavy channels with multiple electrodes: the electrode spacing should be as large as possible to minimize the barrier effect when the ratio l/λ < 0.15; however it is beneficial to reduce the electrode spacing when the ratio l/λ > 0.15.

Analysis of transient laminar forced convective heat transfer in parallel-plate channels with time-varying thermal boundary conditions of the inlet and wall

The problem of transient laminar forced convective heat transfer in parallel-plate channels with time-varying thermal boundary conditions of the inlet and wall is thoroughly investigated in this study. By employing the methodologies of generalized integral transform technique (GITT) and Duhamel's theorem, we successfully derive an analytical solution for this problem. To validate the accuracy of our analytical findings, a comparison is made with the corresponding numerical solution, demonstrating a remarkable level of agreement between the two approaches. In order to obtain the general patterns of heat transfer, we employ a decoupling technique to separate the thermal response in the case of harmonic temperature boundary conditions of the inlet and wall. This approach enables us to uncover the intricate relationship between the weight coefficient of heat input and the two-dimensional spatial location of the channel, as well as the dimensionless angular frequency of heat input. Furthermore, we present the corresponding dimensionless cut-off angular frequency of heat input at various locations within the channel. To gain further insights, we conduct an in-depth analysis of the effects of integration time or distance on the dimensionless optimum angular frequency corresponding to the dimensionless maximum average heat flux.

Experimental Study of Thermal Hydraulic Performance Improvement in Solar Air Heater Channel With V-Shaped Porous Baffles

Abstract Experiments have been conducted to determine how several geometrical parameters of V-shaped porous baffles influence flow characteristics and heat transfer in a rectangular channel. Experiments were conducted on geometric parameters, namely, a relative baffle height (e/H) of 0.4–1, a relative baffle pitch (P/e) of 3–6, open area ratio values of 21–34%, and a single attack angle (α) of 60 deg. Using Reynolds numbers ranging from 2500 to 12,000, V-shaped porous baffles have been examined. Based on a relative baffle pitch of 5, a relative baffle height of 1, and an open area ratio of 21%, the maximum increases in the Nusselt number (Nu) and friction factor (f) were 2.84 and 7 times, respectively. A maximum value of 1.69 is found at e/H = 0.40, P/e = 6, and b = 34% for the thermo-hydraulic performance parameter. Correlations for (Nu) and (f) are developed as functions of P/e, e/H, and Re.