Heat Transfer In Channel Research Articles

Rib Spacing effect on Heat Transfer and pressure loss in a Rectangular channel with semicircular ribs

Ribs of various shapes are used for heat transfer enhancement but its performance is significantly depends on geometrical features and flow conditions. This study experimentally find out the influence of rib spacing, semicircular shape ribs with three rib spacing ratio (P/e) = 8, 10 and 12 are studied and located on lower wall of the rectangular channel. Reynolds numbers varied from 10000 to 29,000 and the blockage ratio of the channel (e/Dh) was 0.151.Result show that semicircular rib performed better than plain plate but found more friction. semicircular rib with rib spacing of 50 mm (P/e =10) shows highest thermal performance, enhanced avg. 39 % heat transfer than rib spacing of 40 and 60 mm (P/e=8 & 12). Friction losses observed highest in rib spacing ratio of 8,found average 10 % more friction compared to rib spacing ratio of 10 & 12. Semicircular rib with spacing ratio 8 shows least thermal performances compared to other configurations.

Effect of heat transfer channels on thermal conductivity of silicon carbide composites reinforced with pitch-based carbon fibers

In this study, silicon carbide (SiC) composites reinforced with pitch-based carbon fibers and composed of heat transfer channels were fabricated by combining chemical vapor infiltration and reactive melting infiltration method. It was observed that the internal heat conduction skeleton of pitch-based carbon fibers was sequentially formed. The thermal conductivities from room temperature to 500 °C along through-thickness direction and in-plane direction were investigated. The results showed that Cpf/SiC composites with heat transfer channels possessed excellent thermal conductvity in two directions, and the thermal conductivity increased with increasing volume content of heat transfer channels. The thermal conductivity in through-thickness direction reached 38.89 W/(m·K), and that for in-plane direction reached 112.42 W/(m·K). Theoretical calculations were empolyed to study the temperature dependence of the Cpf/SiC composites. The variations in slope A′ and intercept B′ values of fitted curves were in good agreement with the experimental results. To verify the reliablilty of the theoretical model, the Cpf/SiC composites were heated at 1650 °C for 2 h and the thermal conductivity exhibited further improvement due to the formation of more perfect crystalline structure. Thermal conductivity through thickness direction improved to 43.49 W/(m·K), and that in in-plane direction improved to 142.49 W/(m·K), which could be identified by the theoretical model. Finally, the leading edge model was established by using ABAQUS finite element analysis software to evaluate the potential application of the composites. Owing to the outstanding thermal conductivity, the leading edge obtained by using Cpf/SiC composites in this study exhibited lower temperature gradient and a more uniform temperature distribution. Moreover, less thermal stress and displacement were generated during heating process.

Determination of heat transport mechanism using nanoparticle property and interfacial nanolayer in a nanofluidic system

Elucidation of heat transport mechanism is the key for the preparation and application of nanofluids with high thermal conductivity. However, the effect of microscopic parameters on nanoparticle property, especially thermal conductivity of nanofluids has limited studied. To establish the relationship between nanolayer structure characteristics and thermal conductivity, Al2O3, CuO, and Cu nanoparticles were dispersed in deionized water (W). The thermal conductivity of nanofluids was measured at various temperatures (293–333 K) and volume fractions (0.5–2.0 vol%). The thermal conductivity of nanofluids decreased in the following order: CuO/W > Al2O3/W > Cu/W nanofluids. Nanoparticles with a high thermal conductivity do not always exhibit a high thermal conductivity of nanofluids. Then, number density (N), nanolayer structure, and its thickness (δ) were obtained from a molecular dynamics simulation. The simulation results show that two obvious interfacial nanolayers exist around the central nanoparticle; however, the interfacial potential of the first layer is much higher than that of the second layer. Therefore, the morphology of the first layer mainly determines the thermal conductivity in a nanofluidic system. However, the trend of number density differs from that of thermal conductivity. Moreover, the thickness of interfacial nanolayer is similar for different nanofluids. Thus, only the number density or thickness of nanolayer is not a determined parameter to evaluate the thermal conductivity. A new parameter, N/δ (ratio of number density and thickness), is described to quantitatively evaluate the relationship between nanolayer structure and thermal conductivity. The high value of N/δ indicates that denser and more ordered liquid molecules arrange around the nanoparticles, creating a higher heat transfer channel than other regions and thus exhibiting a higher thermal conductivity of nanofluids.

Heat transfer characteristics of supercritical water in channels: A systematic literature review of 20 years of research

• More experiments are required to validate the existing the turbulence model. • Turbulence model with Algebraic heat flux model (AHFM) may be promising. • Heat transfer peak occurs as the fluid approaches the pseudo-critical temperature. • To achieve the high accuracy, piecewise correlation may be an effective method. • Internally ribbed tube combined with inclined angles may be a research direction. Supercritical water (SCW) is one of the high-profile fluids between scholars, which has great potential in the thermal industry. Therefore, it may serve as a promising fluid utilized in nuclear and boiler systems. This paper presents a comprehensive review in terms of the published literature on supercritical water heat transfer in channels. Three types of heat transfer, involving normal, enhanced and deteriorated heat transfer, are classified in this article. Firstly, the thermo-physical properties of supercritical water are illustrated to explain the reasons for the different heat transfer behavior. Heat transfer enhancement and deterioration appear to have greater potential and draw some researchers’ interest. In short, transformation of geometry or operating conditions, such as, channel structure, mass flux and heat flux, would induce variations of thermo-physical properties. Consequently, heat transfer performance can be significantly affected. The heat transfer characterization and affecting factors were evaluated. Some unusual phenomena were explained. Then, the developed heat transfer coefficients (HTC) were compared with the experimental data available in the open literature. The results indicated that the reliable accuracy could be achieved through these correlations except the pseudo-critical region. Additionally, the mechanism and the onset of heat transfer deterioration were revealed and estimated. Finally, this review also identifies the current challenges regarding this research through analysis and comparison. These challenges deserve to be efficiently solved and optimized to enhance supercritical water heat transfer in the future.

Numerical study of gas dynamics and heat transfer in matrix channels at various rib angles

The results of numerical simulation of the separation flow in matrix channels by the RANS method are presented. The simulation is performed at the Reynolds number Re = 12600, determined by the mass-average velocity and the height of the channel. The distribution of the local Nusselt number is obtained for various Reynolds numbers in the range of 5÷15⋅103 and several rib angles. It is shown that the temperature distribution on the surface is highly nonuniform; in particular, the maximum heat transfer value is observed near the upper edge facets, in the vicinity of which the greatest velocity gradient is observed.

Investigation of the influence of Taylor-Gortler vortexes on heat transfer of annular channel

This article is about the influence of Taylor-Gortler vortices on heat transfer in concentric annular channels with turbulent decaying swirling flows. The study shows that the occurrence and transformation of secondary vortex structures has a significant effect on the distribution of heat flux over the annular channel surface. An explicit is relationship between the radial velocity fluctuations and the heat flux density distribution. The highest intensity of heat transfer on the outer surface is observed in the areas of positive radial velocity values, while on the inner surface it is observed in the areas of negative radial velocity values.

Two-Phase Flow Regimes and Heat Transfer Coefficients With R245fa in Manifolded-Microgap Channels

Manifold microchannels have shown high performance in embedded two-phase cooling of high heat flux electronics, demonstrating several examples of heat dissipation of 1 kW from 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chips, with low pumping power requirements. The heat transfer coefficients (HTCs) in previous studies of chip-scale manifold-microchannel coolers exhibited a peak at relatively low quality (about 0.2–0.4) and steeply declined thereafter with increasing quality. However, manifold microchannels—arrays of manifolded-microgap channels—are a more complex geometry than traditional, straight, and circular channels and therefore generate more complex two-phase flow phenomena, which influences the resulting heat transfer performance. To better characterize the flow and heat transfer in such channels, in this study, the fluid flow and wall heat transfer in a visualization test section was imaged with a high-speed optical camera and thermography. R245fa served as the working fluid due to its low-pressure operation (approximately 1.8 atm at 30 °C) and excellent thermal properties, including high latent heat, high specific heat, and high thermal conductivity. The results are reported in terms of the channel outlet flow regime and HTCs under varying heat fluxes and mass fluxes with two manifold designs. The flow regimes and HTCs are compared with well-regarded predictive relations developed for more traditional channel geometries. The emergence of intermittent, and then persistent, dryout was associated with intermittent rivulet flow at the channel outlet and was observed to cause declining average wall HTCs, even while high HTCs occurred at the consistently wetted inlet region.

Impact of Ceramic Matrix Composite Topology on Friction Factor and Heat Transfer

AbstractCeramic matrix composites (CMCs) are of interest for hot section components of gas turbine engines due to their low weight and favorable thermal properties. To implement this advanced composite in a gas turbine engine, characterizing the influence of CMC’s surface topology on heat transfer and cooling performance is critical. However, very few published studies have reported the flow and heat transfer effects caused by this unique surface topology. This study is an experimental and computational investigation to evaluate the effect of weave orientations, relevant to CMC surfaces, on the resulting pressure loss and convective heat transfer within an internal channel. The weave pattern was additively manufactured as the walls of a scaled-up coupon containing a single channel. For each of the three weave orientations, bulk pressure losses and convective heat transfer coefficients were measured over a range of Reynolds numbers. Scaling the pressure losses in terms of a friction factor and convective heat transfer coefficients in terms of a Nusselt number showed the importance of choosing the appropriate definition of the hydraulic diameter, which was particularly important for the friction factor. A coupon having one wall with the weave surface increased pressure loss and heat transfer compared to a smooth wall with the largest increases occurring when the CMC weave strands were perpendicular to the flow. Friction factor augmentations were much higher than heat transfer augmentations. When adding the weave to a second channel wall, pressure loss and heat transfer were further increased. Orienting the CMC strands perpendicular to the flow consistently showed the largest augmentations in heat transfer over a smooth channel, but at a much higher pressure loss penalty than that seen with the CMC strands parallel to the flow.

Impact of velocities and geometry on flow components and heat transfer in plate heat exchangers

• Influence of velocity on flow is investigated experimentally and numerically. • The flow is mainly determined by substreams velocity and angle β . • Higher velocities promote furrow component and at fixed Re entail lower f and Nu. • Redefined Re , Nu and f shall reflect substreams flow path and velocity. • Numerical results are best validated in terms of heat flux and pressure drop. This study aims at better understanding of the complex flow phenomena in plate heat exchangers. This is identified in the literature to be crucial for improvement of numerical models and generalized heat transfer and pressure drop correlations with respect to their applicability in heat exchanger optimization. 3D numerical simulations of the flow in corrugated channels of plate heat exchangers with different corrugation angles ( β 28° and 65°) were performed in order to investigate in detail complex flow patterns and their influence on the heat transfer and pressure drop at laminar, transient and turbulent flow conditions. The study is supported by the visualization and thermal–hydraulic tests ( Re = 0.1–6037) carried out on the channels with corresponding chevron angles, using fluids of different viscosity to explore effects of different velocities at fixed Re numbers. Consequent alternation of flow patterns is believed to cause recorded differences in heat transfer and pressure drop data. Results from the simulations are analysed in different sections of the channels in light of the flow substreams, velocity distribution, wall shear stress and wall heat flux distribution. They confirm assumptions from the present visualization tests on the longitudinal and furrow substreams interactions and characteristics, as well as on the thermally and hydrodynamically developing flow conditions within a basic cell. A suitability of comparing simulations and experimental data in terms of Fanning friction factor and Nusselt number is discussed relative to the definitions of characteristic length, hydraulic diameter and mean velocity at different flow patterns. The computed heat transfer and pressure drop is in a relatively good agreement with the performed tests and literature data. The presented numerical-experimental analysis outlines importance of the substreams velocity on their interactions and flow components size, which in turn determines PHE channel heat transfer and pressure drop characteristics. The present findings may serve for improvement of CFD modelling, generalized correlations and definition of Re , Nu and f to allow for comparison of heat transfer and pressure drop data at different geometries and flow conditions.

Characteristics analysis of an exhaust thermoelectric generator system with heat transfer fluid circulation

Low heat transfer performance in the exhaust channel limits the thermoelectric conversion efficiency of the internal combustion engine exhaust thermoelectric generator. Enhanced heat transfer of exhaust channel improves the thermoelectric performance of the generator, though with an increase in exhaust back pressure. A new type of thermoelectric generator with heat transfer fluid circulation is proposed. A heat transfer fluid replaces the exhaust after heat exchange with the exhaust into the generator. It is possible to improve the thermoelectric performance of the system, counting on the high heat transfer coefficient of the heat transfer fluid in the generator without changing the exhaust channel. A mathematical model of the novel system is constructed, considering the system structure, resistance power consumption, temperature dependence of the physical properties of the module. The influence of structural parameters and heat transfer fluid parameters on thermoelectric performance are analyzed using this model. It is found that the peak net output power of the new generator can be increased by 77.5 % compared with the traditional generator, while the number of modules can be reduced by 83.2%. Therefore, an optimal exhaust heat exchanger configuration is obtained to maximize the net output of the system. In addition, as the heat transfer fluid flow rate increases, the net output power goes up and then down, an optimal heat transfer fluid flow rate can be obtained. The results also give technical guidance on the design and operation criteria of the thermoelectric generator.

Effects of binary hybrid nanofluid on heat transfer and fluid flow in a triangular-corrugated channel: An experimental and numerical study

The flow and heat transfer over a modulated surface in the form of triangular protrusions using MWCNTs-TiO2 nanohybrids were investigated, and its results are detailed in this paper. The nanomaterials were functionalized and prepared at weight concentrations of 0.025%-wt., 0.05%-wt., 0.075%-wt., and 0.1%-wt., then had its morphology elucidated using the high-resolution transmission electron microscopy (HR-TEM), field emission transmission electron microscopy (FE-SEM), and Energy Dispersive X-Ray Analysis (EDX). The mixture's thermophysical properties at 303 K were determined and utilized in the investigation's numerical aspect. A steady-state 2D analysis of flow over a modulated surface was solved in ANSYS-FLUENT with turbulent flow at 5000 ≤ Re ≤ 15,000. The model was validated using the Dittus-Boelter Eq., and its average error was 9.840%. The heat transfer was enhanced by 13.181%, 18.056%, 22.033% and 26.107% for nanoparticles' weight concentrations of 0.025%-wt., 0.05%-wt., 0.075%-wt., and 0.1%-wt., respectively. The water flow and MWCNTs-TiO2 nanohybrids' turbulent kinetic energy, pressure, velocity, turbulence intensity contours, and velocity vectors were determined, and correlations were formed from the results to predict the average Nusselt number for the DW and MWCNTs-TiO2 as a function of the nanoparticles' weight concentrations.

Experimental study of propane condensation heat transfer and pressure drop in semicircular channel printed circuit heat exchanger

In this study, the propane condensation heat transfer and pressure drop performance of a printed circuit heat exchanger was experimentally investigated. 30 experimental cases with different mass flux, saturation pressures and vapor quality were conducted. By analyzing these data, a heat transfer correlation similar to the Akers et al. correlation was presented [19]. The newly proposed correlation has a mean square percent error of 5.9% over the equivalent Reynolds number range from 690 to 5600. For the condensing pressure drop correlation, the Lockhart and Martinelli correlation showed the best performance [27].

Heat transfer in an impingement cooling channel under isothermal boundaries at high rotation numbers

The jet impingement cooling technology is usually applied in the turbine blade leading edge which suffers the highest heat flux and needs priority protection. Therefore, heat transfer performances in a rotating impingement cooling channel under an isothermal boundary are experimentally studied. Both the jet-to-target surface spacing and the jet-to-jet spacing are 3 times the jet hole diameter. The effects of Coriolis force and buoyancy force on heat transfer are focused. And the maximum rotation number and buoyancy number reaches 1.63 and 8.06, respectively. The Reynolds number varies from 7119 to 21,358. Besides, numerical simulations are conducted to predict the flow field. The results show that the heat transfer in the impingement channel is determined by the radial mass-flowrate distribution of supply channel in both static and rotating states. Moreover, the rotation enhances the heat transfer at both ends but decreases the heat transfer in the middle-radius due to the stagnant zone induced by Coriolis force in the supply channel, resulting in large thermal stress on the target surface. However, the heat transfer is insensitive to the rotational effects when the rotation number exceeds 0.42. There is a critical rotation number for each location, before which the effect of buoyancy force could be neglected. Once the rotation number is greater than this value, the effect of buoyancy force increases with the wall-to-fluid temperature ratio.

Condensation heat transfer performance in multi-fluid compact heat exchangers with wavy and strip fins

The effect of different geometrical parameters of wavy and strip fins in a three-fluid plate-fin compact heat exchanger on the condensation heat transfer in the middle heat exchanger has been experimentally investigated. The three-fluid heat exchanger consisted of three heat exchangers with strip and wavy fins. In the examined system, the hot and cold fluids flowed through the adjacent heat exchangers (strip channels), while the middle heat exchanger (wavy channels) was occupied with a single-component two-phase flow (condensed vapor). The Nusselt number, the friction factor, the heat transfer surface contribution between the middle heat exchanger and each of the adjacent heat exchangers, and the thermal performance factor were calculated using the measured data at the inlets and outlets of the heat exchangers, and by using the thermal balance equations between the fluids passing through the heat exchangers. In the examined heat exchanger, the hot and cold flows had a cross-direction with the two-phase fluid flow. The two-phase Reynolds number, the vapor quality, and the heat transfer surface contribution of the middle heat exchanger with the adjacent heat exchangers were 50–4800, 0.1–0.67, and 0.19–0.7, respectively. The results show that the two-phase flow pattern in the wavy channels of the middle heat exchanger is stratified and wavy. According to the findings, a higher thermal performance factor is observed when the ratio of the wavy channel heat transfer surface to the heat transfer surface of the cold or hot flows is closer to 1. Also, with higher wave amplitude to wavelength ratios, lower pitch to height ratio of the fins, the lower wavelength to the fin length ratios, and lower fin pitch to wave amplitude ratios are obtained a higher thermal performance factor.

Effects of magnetic field gradient on heat transfer and irreversibility in a channel

In this study, the effects of magnetic field (MF) gradient on the ferrofluid (water/Fe3O4) heat transfer and entropy generation in a horizontal channel under constant heat flux were numerically investigated. Two permanent magnets were installed at different angles (0°, 45°, 90°) around the channel to create a magnetic field. By installing the magnets at different directions, the intensity of MF, the amount of Kelvin force, and the effects of magnets on hydrodynamic behavior, heat transfer, and entropy generation were investigated. The remnant magnetic flux density (Br ) of the magnets was set to 0–0.4 T, While, the volume percentage of nanoparticles and the Reynolds number were considered to be 5% and 100, respectively. The results showed that increasing the angle of the magnets increased the MF gradient, and the Kelvin force was greater when the MF gradient was higher. Furthermore, the angle of the magnets affects the hydrodynamics and ferrofluid velocity. Also, the presence of the MF and increasing the angle of the magnets increased the Nusselt number. So that, when Br was 0.4 T, the average Nusselt number in the 90° configuration of the magnets was about 4.5% more than that of 0° and 45°. In addition, entropy generation analysis showed that generally, the presence of an MF reduced the total entropy generation. Also, the effect of the MF gradient caused that the total entropy to decrease in 0° and 45° configurations was approximately 2%, while this reduction was 14% in the 90° configuration.

Optimization of heat transfer and pressure drop of the channel flow with baffle

Abstract In this article, the numerical analysis has been carried out to optimize heat transfer and pressure drop in the horizontal channel in the presence of a rectangular baffle and constant temperature in two-dimension. For this aim, the governing differential equation has been solved by computational fluid dynamics software. The Reynolds numbers are in the range of 2,000 &lt; Re &lt; 10,000 and the working fluid is water. While the periodic boundary condition has been applied at the inlet, outlet, and the channel wall, axisymmetric boundary condition has been used for channel axis. For modeling and optimizing the turbulence, k–ω SST model and genetic algorithm have been applied, respectively. The results illustrate that adding a rectangular baffle to the channel enhances heat transfer and pressure drop. Hence, the heat transfer performance factor along with maximum heat transfer and minimum pressure drop has been investigated and the effective geometrical parameters have been introduced. As can be seen, there is an inverse relationship between baffle step and both heat transfer and pressure drop so that for p/d equal to 0.5, 1, and 1.25, the percentage of increase in Nusselt number is 141, 124, and 120% comparing to a simple channel and the increase in friction factor is 5.5, 5, and 4.25 times, respectively. The results of modeling confirm the increase in heat transfer performance and friction factor in the baffle with more height. For instance, when the Reynolds number and height are 5,000 and 3 mm, the Nusselt number and friction factor have been increased by 35% and 2.5 times, respectively. However, for baffle with 4 mm height, the increase in the Nusselt number and friction factor is 68% and 5.57 times, respectively. It is also demonstrated that by increasing Reynolds number, the maximum heat transfer performance has been decreased which is proportional to the increase in p/d and h/d. Moreover, the maximum heat transfer performance in 2,000 Reynolds number is 1.5 proportional to p/d of 0.61 and h/d of 0.36, while for 10,000 Reynolds number, its value is 1.19 in high p/d of 0.93 and h/d of 0.15. The approaches of the present study can be used for optimizing heat transfer performance where geometrical dimensions are not accessible or the rectangular baffle has been applied for heat transfer enhancement.

Comprehensive thermal properties of molten salt nanocomposite materials base on mixed nitrate salts with SiO2/TiO2 nanoparticles for thermal energy storage

The purpose of this investigation is to find and prepare novel heat storage materials to meet the requirement of Concentrating Solar Power (CSP) system. This paper focuses on the formulation, fabrication and characterization of a novel molten salt nanocomposite for high-temperature heat energy storage. The molten salt nanocomposite is based on eutectic quaternary salt, and two different concentrations of SiO 2 and TiO 2 nanoparticles are added to improve its specific heat capacity and thermal conductivity by microwave method. Concerning the material characterization, a suite of techniques was used, including simultaneous thermal analysis (STA) and laser flash analysis (LFA). The consequences demonstrate that the melting point and latent heat of molten salt nanocomposites can be reduced by adding two different concentrations of nanoparticles at the same time. The specific heat is 28.1% higher than that of the pure quaternary salt, and 6.3% and 9.8% higher than that of adding SiO 2 and TiO 2 nanoparticles separately when adding 0.1 wt% SiO 2 and 0.9 wt% TiO 2 nanoparticles to the quaternary nitrate. Compared with pure quaternary salt, the thermal conductivity of the molten salt nanocomposites increased by 53.7%, which was 16.8% and 6.3% higher than that of adding SiO 2 and TiO 2 nanoparticles separately. Upon inspection with scanning electron microscopy, a high-density nanostructure and heat transfer channel were observed, which appear to be the reason for the enhancement of specific heat and thermal conductivity of the material. Finally, the molten salt nanocomposite has a broad application prospects in high-temperature thermal storage system. • Novel molten salt nanocomposite is prepared by microwave method for heat storage system. • Two different concentrations of nanoparticles are added to the salt simultaneously. • The specific heat and thermal conductivity of quaternary salt are improved. • The concentration of nanoparticles can affect the thermal properties of molten salt. • The honeycomb structure is the reason for the increase of thermal performance.

Numerical investigation on fin configuration improvement of 2 K sub-atmospheric plate-fin heat exchangers for the superfluid helium cryogenic systems

• The corrugated-serrated fin was proposed for the first time as a new type of fin. • A new structural parameter Lw number was defined to better describe the fin. • Numerical model under low temperature conditions was established. • The performance of corrugated, serrated and corrugated-serrated fins was compared. In order to improve the flow and heat transfer performance of 2 K sub-atmospheric pressure plate-fin heat exchanger, a new type of corrugated-serrated fin is proposed by combining corrugated and serrated fin. The Lw number is defined as a new structural parameter to describe the new type of fin. The numerical model of flow and heat transfer in the fin channels takes into account the influence of low temperature conditions with variable physical properties and has been fully verified by experimental data. Numerical investigation is performed to study the thermohydraulic characteristics of serrated fin, corrugated fin and corrugated-serrated fin. Meanwhile, three performance evaluation criteria Colburn factor j , friction factor f and TE-factor are used to qualitative compare their flow, heat transfer and overall thermo-hydraulic performance. The results reveal that the heat transfer performance of new corrugated-serrated fins is the best. Colburn factor j of the new fins increases by 19.97%~38.22% compared with corrugated fin, and increases by 25.09%~33.83% compared with serrated fin. The flow performance of the corrugated-serrated fin is slightly worse, but the overall thermo-hydraulic performance is better, especially at low Reynold number. Besides, the effects of various structural parameters on the thermohydraulic characteristics of the corrugated-serrated is obtained. The conclusions provide theoretical guidance on the design of 2 K sub-atmospheric plate-fin heat exchanger.

A Numerical Study on Heat Transfer in the Channel with Delta Winglet Pair Vortex Generators

In this study, the effect of the vortex generators on the heat transfer and flow characteristics in a rectangular channel is investigated numerically by finite volume method. The governing equations are discretized using QUICK scheme. The numerical results are validated against published experimental data. In this paper, the effects of the winglet aspect ratio and the distance between the vertices of the winglets on the heat transfer and hydrodynamic characteristics of the flow are surveyed. In addition, to achieve the optimum amount of heat transfer, it is important to know the proper arrangement of the triangular winglet pairs as well as their suitable position. Therefore, the appropriate values of the longitudinal and transverse pitch are presented in this paper. The results show that the winglet with the aspect ratio of 1.75 has the best thermal and hydrodynamic performance. Furthermore, the transverse pitch of 1.24 causes 6.5% growth in the average Nusselt number.

Caputo Time Fractional Model Based on Generalized Fourier’s and Fick’s Laws for Jeffrey Nanofluid: Applications in Automobiles

This article aims to examine Jeffery nanofluid with joint effects of mass and heat transfer in a horizontal channel. The classical model is transferred to the Caputo fractional model by using the generalized Fourier’s and Fick’s laws. The nanofluids are formed by dispersing two different nanoparticles, silver and copper, into a based fluid. A novel transformation has been applied to the mass and energy equation and then solved by using the sine Fourier and the Laplace transformation jointly. The exact solution is given in terms of a special function, that is, the Mittag-Leffler function. The Sherwood number and Nusselt number are calculated and displayed in the tabular form. The effect of embedded parameters on the velocity, concentration, and temperature profile is discussed graphically. It is noted that the heat transfer rate of EO is improved by 28.24% when the volume fraction of Ag nanoparticles is raised from 0.00 to 0.04.