Heat Transfer Performance Of Microchannels Research Articles

Heat transfer performance of microchannels with different reentrant cavities based on field synergy principle and entropy production analysis

The performance analysis of three types of microchannels with reentrant cavities were investigated in this study. The flow and heat transfer characteristics were analyzed according to the field synergy principle and entropy production. The results indicated that as the Reynolds number ranged from 200 to 1000, the Darcy friction factor of microchannels with reentrant cavities decreased sharply and then slowly. Among microchannels examined, a microchannel with circular reentrant cavities exhibited the smallest Darcy friction factor in the Reynolds number range of 200–1000. The Nusselt number of microchannels with reentrant cavities increased with the Reynolds number range of 200–1000. Among the microchannels, the microchannel with circular reentrant cavities had the largest Nusselt coefficient, from 6.07 to 10.29. According to the principle of field synergy, the heat transfer field of microchannel with circular reentrant cavities had the smallest synergy angle (α), from 85.1°to 83.2°, and the best field synergy. According to an analysis of the entropy production, the entropy production caused by heat transfer in microchannels with reentrant cavities gradually decreased as Reynolds number range from 200 to 1000. The microchannel with circular reentrant cavities had minimal entropy production caused by heat transfer; thus, it had the best heat transfer performance. The flow entropy production of microchannels with reentrant cavities increased with the Reynolds number. Among the microchannels, the microchannel with circular reentrant cavities had the smallest entropy production caused by flow. The present study aims to provide alternative ways to evaluate flow and heat transfer performance of microchannels.

Analysis of enhanced thermal transmission mechanism with microstructures by field synergy theory

This study numerically examines the impact of oblique ribs and staggered herringbone microstructures on the heat transfer performance of microchannels. The results indicate that the Nux values of the oblique rib (Type A) and staggered herringbone (Type B) microchannels exhibit significantly higher performance compared to smooth rectangular (Type C) microchannels. The oblique ribs and staggered herringbone microstructures improve heat transfer efficiency along the flowing direction, leading to an evident increase followed by horizontal fluctuations in Nux . In contrast, the Nux of Type C without microstructures decreases significantly at the inlet and subsequently remains relatively constant. The bottom temperature Tw of Type A and B are lower than the temperature of Type C. The results of field cooperation analysis indicate that the synergistic fields of the oblique ribs microchannels primarily exist along both sidewalls, while they are present at the fluid center for the staggered herringbone microchannels. Type A exhibits a slightly stronger heat transfer effect despite having a smaller synergistic area compared to Type B.

Improvement of flow and heat transfer performance of microchannels with different ribs using topology optimization

Microchannel is an important technology to solve the heat dissipation problems associated with the high integration of electronic devices based on forced liquid-cooling. In this work, a topology optimization method is introduced to generate adaptive rib shape and arrangement in the straight microchannel, wavy microchannel and microchannel with fan-shaped reentrant cavities. Numerical simulations demonstrate that topology optimized ribs can promote heat transfer effectively. Especially in the wavy microchannel, the average temperature of channel base with the topology optimized ribs improves 27.0%, 30.1% and 71.4% in comparison with those with square ribs, circular ribs and no ribs, respectively. Pressure drops of the microchannel with topology optimized ribs are 64%, 45% and 36% lower than those of the microchannel with square ribs, and 51%, 39%, 28% lower than those of the microchannel with circular ribs, when channel shapes are straight, wavy and fan-shaped reentrant cavities, respectively. The above results are attributed to the shape and arrangement of topology optimized ribs, which promotes fluid mixing and reduces low-velocity regions. Microchannels with topology optimized ribs always possess superior flow and heat transfer performance for all channel shapes. The wavy microchannel with topology optimized ribs owns the best overall performance, which is due to the excellent adaptation of topology optimized ribs in the wavy microchannel.

Investigation on the heat transfer performance of microchannel with combined ultrasonic and passive structure

With efficient heat dissipation capacity, the microchannel heat sink (MCHS) can be exploited and applied in the development of new energy technologies. With 2.8 MHz high-frequency ultrasonic, the flow and heat transfer performance in different kinds of microchannel was studied. These microchannels included rectangular straight microchannel, 90° fan-shaped and triangular combined cavity microchannel and 90° fan-shaped and triangular combined cavity circular fin microchannel. Furthermore, the comprehensive performance of the microchannel was analyzed and evaluated in detail from different aspects such as flow characteristics, heat transfer characteristics, field synergy and efficiency analysis. At the low Reynolds number, the acoustic streaming effect induced by ultrasonic could destroy the wall boundary layer and improve the heat transfer between the fluid and the wall. However, with the increase of Reynolds number, the flow velocity gradually dominated the heat transfer process. Meanwhile, the ultrasonic mainly acted on improving the synergy between the flow and temperature fields. Moreover, the combination of cavity structure and ultrasonic was conducive to increasing the action depth of acoustic wave in the fluid, which was much easier to induce the acoustic streaming effect. Thus, the effect of ultrasonic enhancement could be greatly strengthened. More importantly, the efficiency of using ultrasonic to enhance heat transfer was higher than that of pump power. This work can contribute to the mechanism and improve the efficiency of active and passive enhancement of microchannel heat transfer by using high-frequency ultrasonic.

The simulation analysis on the influence of non-closed droplet structure on thermal/ flow performance of pin fin heat sinks

In order to improve the heat transfer performance of microchannels, considering from balance flow resistance and increasing heat transfer area, a non-closed droplet pin fin array microchannel has been designed. The purpose of this paper is to study the inner influence of non-closed droplet structure on convection heat transfer by means of simulation. Through the simulation tool ANSYS Fluent, the working conditions of heat flux density from 5 W/cm2 to 85 W/cm2 are simulated respectively, with the inlet flow as 1.5 kg/h and the inlet fluid temperature as 40 °C unchanged. Along with the increase of heat flux density (5 W/cm2 ⩽ q ⩽ 85 W/cm2), the pressure drop, the bottom temperature as well as the heat transfer coefficient continue to rise, but the rising rates are various. Such variation could be explained by the different heat exchange processes: single phase heat transfer, bubble nucleation, growth and migration and then dry phenomenon, which can be observed from the vapor phase distribution results. The distribution of vapor phase under multiple heat flux explains the variation of pressure and temperature in different stages. It could be concluded that the non-closed droplet pin fin has a strong fractal effect on the fluid. After multiple shunting and confluence, the flow velocity of the fluid on both sides is significantly greater than that between the fins, whose average velocity is 0.135 m/s faster than that between the pins. Besides, the heat transfer effect of the corresponding walls on both sides is also better than that between the pin fins. Because the pin fin has the characteristics of droplet structure, the boundary layer on both sides of the pin fin will be separated and the heat transfer performance will be enhanced. The temperature of the pin fin head is lower, and the temperature of the pin fin tail is higher, with an average difference as about 9.32 °C. The comparison research between non-closed droplet and traditional droplet pin fin has been conducted, as well. It could be concluded that when 5 W/cm2<q < 60 W/cm2, the heat transfer coefficient of the opening droplet microchannel is higher, with pressure drop lower. The main reason is that the improvement of the non-closed structure reduces the kinetic energy loss caused by the collision, and promotes the emergence and growth of the vaporization core.

매니폴드 구조를 포함하는 마이크로채널의 압력 강하 및 냉각 성능 향상에 관한 수치해석적 연구

In this study, the flow characteristics and heat transfer performance of microchannel with layered manifold structure were compared and analyzed theoretically and numerically. For the numerical analysis model, a microchannel with a width of 0.5 mm and a height of 1 mm and a manifold structure were designed at the inlet and outlet, and 25℃water was used as the cooling fluid. The boundary condition of the numerical analysis was performed by applying a flow rate variable of 0.3 ~ 1.1L/min under the heat flux of 31.25W/㎠ to the heat source. As a result of the study, the microchannel with layered manifold showed cooling performance with a temperature difference of 50℃or more under the condition of a pressure drop of less than 0.5 kPa compared to the existing microchannel.

Experimental Study on Microchannel with Addition of Microinserts Aiming Heat Transfer Performance Improvement

Microchannel technology rapidly established itself as a practicable solution to the problem of the removal of extremely concentrated heat generation in present-day cooling fields. By implementing a better design structure, altering the working fluids and flow conditions, using various materials for fabrication, etc., it is possible to increase the heat transfer performance of microchannels. Two parameters that affect how well a microchannel transfers heat were only recently coupled, and the complicated coupling of the parameter that affects how well a microchannel sink transfers heat is still not well understood. The newest industrial developments, such as micro-electro-mechanical systems, high performance computing systems, high heat density generating future devices, such as 5G/6G devices, fuel cell power plants, etc., all present thermal challenges that require the use of microchannel technology. In this paper, single-phase flow in microchannels of various sizes, with or without microinserts, is described in terms of its thermal-fluid flow properties, including fluid flow characteristics and heat transfer characteristics considering the compound effects of variations of channel size and addition of microinserts. The trials were carried out using distilled water that had thermo-physical characteristics that varied with temperature. A microchannel with microinserts was developed for managing the high heat generation density equipment. The fluid flow and heat transfer characteristics are explored and analyzed for Reynolds numbers ranges from 125 to 4992, for 1 mm channel size, and from 250 to 9985, for 2 mm channel size. The cooling performance criteria are pressure drop characteristics, heat transfer characteristics, and overall performance, whereas the testing parameters were chosen for the variations in channel size and the addition of microinserts. The influence of inserting microinserts on microchannels is discussed. Results suggest that by inserting microinserts, the performance of the heat transfer of microchannels is significantly improved and, also, fluid flow resistance is increased. The criteria of the thermal performance factor are employed to assess the overall performance of the microchannel. Significant intensification of heat transfer is observed with indication that the addition of microinserts to microchannels and reduction in channel sizes exhibited improved overall performance.

Heat transfer performance of microchannels with round grooves and ribs based on field synergy principle and entropy production analysis

ABSTRACT Four kinds of microchannels with round grooves and ribs were designed: round grooves (round), round grooves and single–sided ribs (round–single), round grooves and odd-symmetric ribs (round–odd), and round grooves and doubly symmetric ribs (round–double). The effects of rib arrangement on the heat transfer performance of microchannels with round grooves and ribs were numerically investigated and then compared with the microchannel with no grooves or ribs. The heat transfer characteristics were analyzed and compared in accordance with the field synergy principle and entropy production. Results indicate that the heat transfer field of round and round–double microchannels exhibited the smallest synergy angle (α) and the best field synergy. The round–double microchannel produced the lowest entropy caused by heat transfer and had a minimal irreversible loss; thus, it exhibited the best heat transfer performance.

Numerical Investigation of Heat Transfer Performance of Microchannel with Wall-Mounted Obstacles Using Hybrid Nanofluids

In the present study, the thermal performance of a microchannel with rectangular, triangular and circular shaped wall-mounted blocks on the top and bottom walls are studied numerically using hybrid nanofluids (Cu+Al/water, Cu+Al2O3/water, Ag+CuO/water, Ag+Al2O3/water) and ionic Nanofluid (Al2O3/[C4mim] [NTf2]). A constant Reynolds number equal to 10, volume fraction for first and second nanoparticle as 0.1 and 0.05 respectively, wall temperature of 27°C and coolant inlet temperature of 20°C are considered. The microchannel with triangular block showed maximum heat transfer performance. The Nusselt number of the microchannel with triangular blocks and nozzle at the inlet was enhanced by 145.76%. The maximum Nusselt number has been found for (Ag+Al2O3)/water hybrid nanofluid which is 13.8 %, 30 %, 37.12 % and 640 % greater as compared to (Ag+CuO)/water, (Cu+ Al2O3)/water, (Cu+ Al)/water and base fluid respectively. The microchannel with ionic nanofluid enhanced by 208 % as compared to water.

Numerical Analysis for Augmentation of Thermal Performance of Single-Phase Flow in Microchannel Heat Sink of Different Sizes with or without Micro-Inserts

With the development of miniaturized and enormous heat density generating novel technologies, the microchannel heat sink is rapidly establishing itself in modern cooling fields. Enhancement of heat transfer performance of microchannels is done by incorporating improved design structure, changing working fluids and flow conditions, using different materials for fabrication, etc. Coupling of two parameters influencing heat transfer performance of microchannels is in a nascent age, and complex coupling of heat transfer influencing parameters of microchannel sinks has not been clearly understood yet. This study provides the thermal-fluid flow features–fluid flow characteristics and heat transfer characteristics- of single-phase flow in microchannel of different sizes with or without microinserts by the use of computational fluid dynamics. The numerical simulation is performed by employing distilled water with thermophysical properties that depends on temperature for the Reynolds number range of 56–2242. The effect of microinserts on characteristics of fluid flow and heat transfer is analyzed. The results of numerical analysis show that heat transfer performance in microchannel with microinserts is enhanced effectively, however resistance in fluid flow is increased simultaneously. The 0.5 mm microchannel with microinserts shows the best performance of heat transfer characteristics with enhancement of 1–9% in the Reynolds number range of 56–2242 with simultaneous maximum increase in pressure drop by 14.5%. It’s overall performance, evaluated by thermal performance factor, is found to be best among all cases of three different channel sizes with and without microinserts. The maximum enhancement of heat transfer is found to be in case of 0.5 mm channel size with microinserts by a factor of 1.09. The maximum pressure drop is increased is found to be by factor of 2.28 in case of 2 mm channel size with microinserts.

Investigation on the heat transfer and energy-saving performance of microchannel with cavities and extended surface

Microchannel heat sinks (MCHSs) are widely used in microelectronic systems and are one of the most effective heat sinks in the 21st century. In this work, the fluid flow and heat transfer performance of different extended surfaces (cylindrical fins, rectangular fins, water droplets) of triangular combined cavity, 90° fan-shaped and triangular combined cavity were investigated. The comprehensive performance in microchannels were analyzed and evaluated in detail by different aspects, including flow characteristics, heat transfer characteristics, pressure drop characteristics, comprehensive thermal strengthening performance and thermal strengthening performance aimed at energy saving. The result indicated that the microchannel with the triangular combined cavity exhibited the best heat transfer performance at a low Reynolds number. However, as the Reynolds number gradually increasing, the microchannel with 90° fan-shaped and triangular combined cavity presented more obvious advantages. Furthermore, the microchannel is evaluated by the comprehensive thermal enhancement performance and the enhanced performance evaluation aiming at energy-saving. When Re<144.6, the comprehensive heat transfer performance of the microchannel with triangular combined cavity cylinder fins was the best, and the energy-saving effect was excellent. The microchannel of the 90° fan-shaped and triangular combined cavity cylindrical fins at Re>144.6 had better comprehensive heat transfer performance and energy-saving effects. Because of the combined effect of the boundary layer redevelopment and the cold and heat exchange of the fluid in the channel, the microchannel with cavity and the extended surface has better heat transfer and energy-saving performance than that of the traditional rectangular microchannel.

Heat Transfer Performance of a Novel Microchannel Embedded with Connected Grooves

To improve the heat transfer performance of microchannels, a novel microchannel embedded with connected grooves crossing two sidewalls and the bottom surface (type A) was designed. A comparative study of heat transfer was conducted regarding the performances of type A microchannels, microchannels embedded with grooves on their bottom (including types B and C), or on the sidewalls (type D) as well as smooth rectangular microchannels (type E) via a three-dimensional numerical simulation and experimental validation (at Reynolds numbers from 118 to 430). Numerical results suggested that the average Nusselt number of types A, B, C, and D microchannels were 106, 73.4, 50.1, and 12.6% higher than that of type E microchannel, respectively. The smallest synergy angle β and entropy generation number Ns,a were determined for type A microchannels based on field synergy and nondimensional entropy analysis, which indicated that type A exhibited the best heat transfer performance. Numerical flow analysis indicated that connected grooves induced fluid to flow along two different temperature gradients, which contributed to enhanced heat transfer performance.

Numerical investigation of flow boiling characteristics in cobweb-shaped microchannel heat sink

In recent years, researchers have conducted extensive studies on the improvement of heat transfer performance of microchannels, however, exploiting biomimetic microchannels to enhance the flow boiling heat transfer performance is still relatively rare. In this study, inspired by the cobweb structures in nature, cobweb-shaped microchannels with horizontal inlet and outlet (CMHS-H) and cobweb-shaped microchannels with inclined inlet and outlet (CMHS-I) are proposed. Flow boiling simulations are carried out with the inlet temperature of 300 K at the bottom heat flux of 75–125 W/cm2 under different mass fluxes by utilizing volume of fluid (VOF) model. The flow boiling characteristics of the CMHS-I and CMHS-H are studied and compared with those of the rectangular microchannel heat sink (RMHS). The results demonstrate that both the CMHS-H and CMHS-I can enhance the heat transfer coefficient and reduce the wall temperature due to the flow disturbance and increased heat transfer area; whereas the CMHS-H is effective to reduce the pressure drop and suppress the flow instability at high mass flux. At high heat flux, the CMHS-H shows the best heat transfer performance and the most stable flow boiling behavior. This study provides a promising approach of using biomimetic microchannels to dissipate high heat flux associated with advanced electronics.

Thermohydraulic characteristics and entropy analysis of a novel clockwise and anti-clockwise twisted sinusoidal wavy micro-channel under pulsating inlet condition

Heat transfer performance of microchannel are becoming an important area of research with the current fast growing scenario of high speed computing and miniaturized electronic devices. These devices pile up large amount of heat accompanied by smaller surface area to release it. The current work examines unsteady, laminar flow heat transfer inside a novel twisted sinusoidal wavy microchannel. The channel with square cross section is wavy in nature as well as twisted. The first half portion of the channel is twisted clockwise, whereas the twist in the remaining part is having counterclockwise twist. The novel geometry promotes mixing of fluid layers leading to transport augmentation. The inlet pulsation follows sinusoidal pattern in time. The thermal performance parameter of the proposed novel geometry was assessed within a Reynolds number range of 1–100. Both the pulsation amplitude and Strouhal number are varied during the course of this study. To solve the governing equations, a finite volume based method was utilized. The Nusselt number data shows significant enhancement for the sinusoidal inlet velocity as compared to that of the steady case, i.e. without inlet flow pulsation. The performance enhancement criterion combining heat transfer and pressure drop shows significant improvement over steady flow case as well as for one-way twisted tube. Entropy generation, which is the measure of dissipated energy, is also reported in the present work.

Improvement of temperature uniformity in microchannel with pin-fin based on endwall fillet structure

Energy and mass transfer process are involved in many industries, such as energy, transportation, aeronautics and astronautics, electronic, manufacturing, among which, the heat exchanger plays a very key role. With the development of science and technology and the increasing requirements for energy conservation and emission reduction, the efficiency of heat exchange system has to be promoted to meet the demand of higher heat intensity and thermal load. The high-efficient and energy-saving compact heat exchanger such as microchannel heat sink has gained more attractions in academic researches and engineering applications. Microchannel with pin-fin is widely used in engineering applications due to its high efficiency in heat and mass transfer, but the high temperature region formed in the rear of the cylinder and the non-uniformity temperature field increase the temperature gradient and generate extra thermal spreading resistance, which would, to a large extend, influence the regulation of the system and the economy and reliability of the equipments. Therefore, the endwall fillet structure is proposed in this work, based on researches about the performance of CDA (controlled diffusion airfoil) blade with fillet, to improve the temperature uniformity and heat transfer performance of microchannel with pin-fin. The periodical laminar flow and heat transfer performances are comparatively studied. The results show that the flow resistance coefficient f of the microchannel with filleted pin-fin does not increase significantly compared to traditional pin-fined microchannel, which means the introducing of the fillet will enhance the heat transfer while f of the microchannel is almost a constant. The maximum increase of f is only 2.03%. Moreover, two separate symmetrical secondary flows develop in microchannel with smooth cylinder, with one on the top of the other. After adding the proposed structures, at low Reynolds number, the lower span-wise secondary flow is enhanced as the radius increases and these two span-wise secondary flows gradually merge into one which develops along the normal direction. At high Reynolds number, the mainstream low-temperature core region is obvious asymmetry: it moves downwards gradually as Reynolds number increases. Besides, at low Reynolds number (0–120), the fillet improves the heat and mass transfer between the main stream core and areas near the wall, enhances the thermal uniformity of the pin-fin and heated walls, improves the heat transfer performance of the rear of the cylinder and eliminates the high temperature area in the pin-fin. And local high-temperature region on the top half of the microchannel decreases, which contributes to the extension of low-temperature region and the decrease of average temperature. As the radius of the fillet increases, the effects mentioned above are gradually enhanced. The heat transfer coefficient of the channel reaches a maximum augmentation of 16.93%, and the flow resistance coefficient of the microchannel with filleted pin-fin does not increase significantly. Comparing with the synthetical thermal performance coefficient of pin-fined microchannel heat sink, that of the proposed filleted pin-fin microchannel increases 16.22% at most. As the Reynolds number increases, the influence of the fillet structure decreases. The study motivation of combining separation flow researches of rotatory machines with heat transfer enhancement, as well as the resulting design are a beneficial attempt for scientific research and engineering application.

Two-Phase Analysis on the Conjugate Heat Transfer Performance of Microchannel With Cu, Al, SWCNT, and Hybrid Nanofluids

This numerical study has been carried out by developing two-phase mixture model with conjugate heat transfer. Pure and hybrid nanofluids (HyNF) with particle as well as base fluid hybridization are used in analyzing the performance of microchannel under forced convection laminar flow. The flow as well as heat transfer characteristics of pure water, copper (Cu), aluminum (Al), single-walled carbon nanotube (SWCNT), and hybrid (Cu + Al, water + methanol) nanofluids with various nanoparticle volume concentrations at different Reynolds numbers are reported. Sphericity-based effective thermal conductivity evaluation is considered in the case of SWCNT nanofluids by using volume and surface area of nanotubes. A significant enhancement in the average Nusselt number is observed numerically for both pure and hybrid nanofluids. Pure nanofluids such as Al, Cu, and SWCNT with 3 vol % nanoparticle concentration enhanced the average Nusselt number by 21.09%, 32.46%, and 71.25% in comparison with pure water at Re = 600. Whereas, in the case of hybrid nanofluids such as 3 vol % HyNF (0.6% Cu + 2.4% Al) and 3 vol % SWCNT (20% Me + 80% PW), the enhancement in average Nusselt number is observed to be 23.38% and 46.43% in comparison with pure water at Re = 600. The study presents three equivalent combinations of nanofluids (1 vol % Cu and 0.5 vol % SWCNT), (2 vol % Cu, 1 vol % SWCNT and 3 vol % HyNF (0.6% Cu + 2.4% Al)) as well as (2 vol % SWCNT and 3 vol % SWCNT (20% Me + 80% PW)) that provides a better switching option in choosing efficient working fluid with minimum cost based on cooling requirement. The study also shows that by dispersing SWCNT nanoparticles, one can enhance the heat transfer characteristics of base fluid containing methanol as antifreeze. The conduction phenomena of solid region cause the interface temperature between solid as well as fluid regions to increase along the length of the microchannel. The developed numerical model is validated with the numerical and experimental results available in the literature.

Numerical Investigation of MHD Nanofluid Forced Convection in a Microchannel Using Lattice Boltzmann Method

In this paper, flow and heat transfer of water–Al2O3 nanofluid in a two-dimensional microchannel that is under the influence of a uniform magnetic field is investigated. The thermal boundary conditions applied on the channel walls are constant temperature at the lower wall and insulated at the upper one. Lattice Boltzmann method is used to obtain the velocity and temperature fields. The effects of relevant parameters such as the Reynolds number (5–25), the nanoparticles volume fraction (0–4%) and the Hartmann number (0–10) are investigated on heat transfer coefficient and friction factor. The results show that the microchannel heat transfer performance is improved 19% by increasing the Reynolds number from 5 to 25. The magnetic field does not have remarkable effect on the heat transfer coefficient, but increases the friction factor up to 86%. Also, heat transfer coefficient enhances 17% by increasing the nanoparticles volume fraction up to 4%, but the rate of improvement in heat transfer coefficient decreases at higher Reynolds and Hartmann numbers.

Effect of Reverting Channels on Heat Transfer Performance of Microchannels with Different Geometries

This study investigated the effect of reverting microchannels inside a heat sink on increase of cooling rate as well as the effect of their different configurations on maximum temperature and pressure drop. Based on the convection heat transfer mechanism, selection of the embedded microchannels’ configurations including circular, square and triangular ones, was studied for geometric optimization of the discussed heat sinks. The goal was to minimize the thermal resistance through optimizing the geometries. The volume ratio was defined as the ratio of the volume taken up by microchannels to the solid volume (portion of the heat sink not occupied by microchannels) and was considered as 0.05. According to the results, in addition to obtaining a more uniform temperature distribution, reverting channels remarkably reduced the maximum temperature. Moreover, the heat sink with square shape showed less thermal resistance as compared to the other two geometries.

Numerical Investigation on Conjugate Heat Transfer Performance of Microchannel Using Sphericity-Based Gold and Carbon Nanoparticles

ABSTRACTNumerical study has been carried out on the laminar forced convection flow of nanofluids in a wide rectangular microchannel. The flow and heat transfer characteristics of gold and of single-walled carbon (SWCNT) nanofluids are investigated in order to find an efficient and cost-effective heat transfer fluid. The effects of nanoparticle volume concentration and of spherical and cylindrical particulate sizes on the conjugate heat transfer performance of the microchannel are reported. The effective thermal conductivity of a nanofluid is evaluated on the basis of particle sphericity by considering the volume and surface area of the nanoparticles. The average convective heat transfer coefficient increases with increase in Reynolds number and volume concentration. Moreover, sphericity-based thermal conductivity evaluation showed that increasing the length of the SWCNT nanoparticle has significant effect on the heat transfer performance, concluding that axial heat conduction dominates the radial heat conduction within the nanoparticle. The carbon nanofluid is identified as an optimized heat transfer fluid with better heat transfer characteristics in comparison with the gold nanofluid. It also reduces the cost of the working fluid. The variations in the interface temperature between solid and fluid regions are reported for nanofluids with different concentrations at different Reynolds numbers. The diameter and length of the SWCNT nanoparticle show a significant effect on heat transfer characteristics.

Recent Trends, Challenges and Scope in Single-Phase Liquid Flow Heat Transfer in Microchannels-A Review

Miniaturization of electronic gadgets has increased the power density and reduced the sizes of these gadgets drastically. Heat dissipation and stable operation of these electronic devices is challenge for researchers. Microchannel passages providing high surface area to volume ratio gives high heat transfer rates from small areas has emerged as potential heat dissipating and thermal control devices for Micro-Electro Mechanical Systems (MEMS). High performance microchannel heat exchangers are also attractive in applications where space and/or weight constraints dictate the size of a heat exchanger or where performance enhancement is desired. In this review paper a small attempt is made to look into the recent developments and methods to enhance the heat transfer performance of microchannels by using channel geometry, coolant and structural materials. It has been also observed that Nanofluids as coolants in microchannels have excellent potential to enhance the heat transfer performance and are quickly establishing as future coolant to be reckoned with, further challenges faced by researchers and future research scope in the field of single-phase liquid flow heat transfer in microchannels are identified.