Numerical investigation of heat transfer in microchannel using inclined longitudinal vortex generator (original) (raw)
Related papers
2015
The liquid flow and conjugated heat transfer performance of single phase laminar flow in rectangular microchannels equipped with longitudinal vortex generators (LVGs) are numerically investigated. Deionized-water with temperature-dependent thermo-physical properties is employed to conduct the simulations. Three dimensional simulations are performed using an open-source flow solver based on finite volume approach and SIMPLEC algorithm. Five different configurations of the microchannel with different angles of attack of the LVGs are considered. Simulation results are compared with available experimental data and a deviation below 10% is achieved. The results show that there is a 2-25% increase in the Nusselt number for microchannels with LVGs, while the friction factor increased by 4-30%, for Reynolds number ranged from 100 to 1100. The overall performance of some specific configurations of the microchannels with LVGs is higher than that of the conventional smooth microchannels.
Heat transfer enhancement in a micro-channel cooling system using cylindrical vortex generators
International Communications in Heat and Mass Transfer, 2016
Three-dimensional conjugate heat transfer under laminar flow conditions within a microchannel is analysed numerically to explore the impact of a new design of vortex generator positioned at intervals along the base of the channel. The vortex generators are cylindrical with quarter-circle and half-circle cross sections, with variants spanning the whole width of the channel or parts of the channel. Micro-channels with Reynolds number ranging from 100 to 2300 are subjected to a uniform heat flux relevant to microelectronics cooling. To ensure the accuracy of the results, validations against previous microchannel studies were conducted and found to be in good agreement, before the new vortex generators with radii up to 400 µm were analysed. Using a thermal-hydraulic performance parameter expressed in a new way, the VGs described here are shown to offer significant potential in combatting the challenges of heat transfer in the technological drive toward lower weight/smaller volume electrical and electronic devices.
A review of liquid flow and heat transfer in microchannels with emphasis to electronic cooling
Sādhanā
Since the realization of microchannel devices more than three and half decades ago with water as the cooling fluid providing heat transfer enhancement, significant progress has been made to improve the cooling performance. Thermal management for electronic devices with their ever-widening user profile remains the major driving force for performance improvement in terms of miniaturisation, long-term reliability, and ease of maintenance. The ever-increasing requirement of meeting higher heat flux density in more compact and powerful electronic systems calls for further innovative solutions. Some recent studies indicate the promise offered by processes with phase change and the use of active devices. But their adoption for electronic cooling still weighs unfavourably against long-term fluid stability and simplicity of device profile with moderate to high heat transfer capability. Applications and reviews of these promising research trends have been briefly visited in this work. The main focus of this review is the flow and heat transfer regime related to electronic cooling in evolving channel forms, whose fabrication are being enabled by the significant advancement in micro-technologies. Use of disruptive wall structures like ribs, cavities, dimples, protrusions, secondary channels and other interrupts along with smooth-walled channels with curved flow passages remain the two chief geometrical innovations envisaged for these applications. These innovations target higher thermal enhancement factor since this implies more heat transfer capability for the same pumping power in comparison with the corresponding straight-axis, smooth-wall channel configuration. The sophistication necessary to deal with the experimental uncertainties associated with the micron-level characteristic length scale of any microchannel device delayed the availability of results that exhibited acceptable matching with numerical investigations. It is indeed encouraging that the experimental results pertaining to simple smooth channels to grooved, ribbed and curved microchannels without unreasonable increase in pumping power have shown good agreement with conventional numerical analyses based on laminar-flow conjugate heat-transfer model with no-slip boundary condition. The flow mechanism with the different disruptive structures like dimple, cavity and rib, fin and interruption, vortex generator, convergingdiverging side walls or curved axis are reviewed to augment the heat transfer. While the disruptions cause heat transfer enhancement by interrupting the boundary layer growth and promoting mixing by the shed vortices or secondary channel flow, the flow curvature brings in enhancement by the formation of secondary rolls culminating into chaotic advection at higher Reynolds number. Besides these revelations, the numerical studies helped in identifying the parameter ranges, promoting a particular enhancement mechanism. Also, the use of modern tools like Poincare section and the analysis of flow bifurcation leading to chaotic advection is discussed. Among the different disruptive structures, sidewall cavity with rib on the bottom wall within the cavity plays a significant role in augmenting the thermal performance. Among the different converging-diverging side walls or curved axis, the sinusoidal channel provides the highest mixing by the introduction of secondary vortices or dean vortices to augment the heat transfer with less pressure drop. The optimum geometry in terms of high heat transfer with low pressure plays a major role in the design of heat sink. Directions of some future research are provided at the end.
HEAT TRANSFER ENHANCEMENT IN MICROCHANNELS USING AN ELASTIC VORTEX GENERATOR
In this paper a novel heat transfer enhancement mechanism in the microchannel cooling passages with water as coolant is proposed and studied numerically. In this mechanism, an elastic vortex generator placed in the microchannel induces an oscillatory transverse vortex which is responsible for heat transfer enhancement along the channel. A two-dimensional incompressible viscous flow at moderate Reynolds numbers (100–500) in the laminar regime is considered. Due to the presence of the elastic vortex generator, the analysis becomes too complicated since the instantaneous nature of the fluid domain and the deformable elastic boundary requires solving a fluid structure interaction problem. To keep the problem from becoming too complicated, the numerical treatment in this study is two-dimensional. An arbitrary Lagrangian-Eulerian approach along with a structured grid is used to simulate the fluid–structure interaction problem. It may be noted that the fluid–structure interaction phenomenon often occurs as a destructive phenomenon in the engineering systems. However, in the present work it is regarded as a desired outcome. The results are compared with those of the simple channel (i.e., a channel without a vortex generator). For the Reynolds numbers within the tested range, 15–35% increase in the average Nusselt number as well as a 10–70% increase in the friction factor is observed. In addition, it is found that for all the Reynolds numbers tested, the elastic vortex generator gives a higher Colburn/friction factor ratio as compared with the rigid vortex generator.
Thermal and hydrodynamic analysis of microchannel heat sinks: A review
Renewable and Sustainable Energy Reviews, 2013
An impressive amount of investigation has been devoted to enhancing overall thermal and hydrodynamic performance of microchannel heat sinks. The small size of microchannel heat sinks and their ability to dissipate heat generated by modern electronics makes them the first choice for the electronic cooling systems in most devices. In this paper, a comprehensive review of available studies regarding non-circular microchannel heat sinks, with emphasis on rectangular microchannels, was presented and analyzed. This review looked into the methodologies used to analyze and optimize the overall performance of microchannel systems along with channel geometries, flow conditions, the coolants used, structural materials, optimization tools and finally, the form in which the final outcome of each study was presented. The review showed that earlier studies (from 1981 to 1999) were largely conducted using experimental or analytical approaches while more recent studies (from 2000 to the end of 2012) showed a dependency on numerical simulations and evolutionary algorithms. In addition, they also showed that laminar was the prevailing flow condition as out of the 69 articles reviewed, 54 employed laminar flows. Furthermore, the use of liquid coolants was preferable over gaseous coolants. Recent developments in nanofluids are providing alternative coolants that are quickly establishing as coolants to be reckoned with.
Processes
In this study, the numerical conjugate heat transfer and hydraulic performance of nanofluids flow in a rectangular microchannel heat sink (RMCHS) with longitudinal vortex generators (LVGs) was investigated at different Reynolds numbers (200–1200). Three-dimensional simulations are performed on a microchannel heated by a constant temperature with five different configurations with different angles of attack for the LVGs under laminar flow conditions. The study uses five different nanofluid combinations of Al2O3 or CuO, containing low volume fractions in the range of 0.5% to 3.0% with various nanoparticle sizes that are dispersed in pure water, PAO (Polyalphaolefin) or ethylene glycol. The results show that for Reynolds number ranging from 100 to 1100, Al2O3–water has the best performance compared with CuO nanofluid with Nusselt number values between 7.67 and 14.7, with an associated increase in Fanning friction factor by values of 0.0219–0.095. For the case of different base fluids, ...
Heat transfer enhancement in micro-channels caused by vortex promoters
International Journal of Heat and Mass Transfer, 2010
Vortex promoter Micro-channel flow Heat transfer This paper presents a systematic numerical study of the effects of heat transfer and pressure drop produced by vortex promoters of various shapes in a 2D, laminar flow in a micro-channel. The liquid is assumed to be water, with temperature dependent viscosity and thermal conductivity. It is intended to obtain useful design criteria of micro-cooling systems, taking into account that practical solutions should be both thermally efficient and not expensive in terms of the pumping power. Three reference cross sections, namely circular/elliptical, rectangular, and triangular, at various aspect ratios are considered. The effect of the blockage ratio, the Reynolds number, and the relative position and orientation of the obstacle are also studied. Some design guidelines based on two figures of merit (related to thermal efficiency and pressure drop, respectively), which could be used in an engineering environment are provided.
Numerical Simulation of Heat Transfer Enhancement in Periodic Converging-diverging Microchannel
Procedia Engineering, 2015
In this work, the effect of different vortex generators on fin-plate heat exchanger performance with a triangular channel cross-section is examined. The analysis is done using finite volume method. The effects of vortex generators in a channel are investigated by consideration of channel temperature and heat transfer coefficient. Six different vortex generators including a simple rectangular vortex generator (SRW), rectangular trapezius vortex generator (RTW), angular rectangular vortex generator (ARW), Wishbone vortex generators (WW), intended vortex generator (IVG) and wavy vortex generator (WVG) have been investigated. The observations suggest that simple rectangular vortex generator increases the heat transfer of finplate heat exchanger more than other models. This vortex generator increases heat transfer in the heat exchanger by 7%. However, vortex generators increase the pressure drop in heat exchanger. In addition, by increasing the height of the vortex generators the heat transfer rate is increased and the best angle of attack for the installation of vortex generator is 45 o .
The design and fabricate of microchannel and fluidic devices required to understand the basic fundamental terms of heat transfer and fluid mechanic processes. Several authors have been work on microchannel heat sink by applying a traditional method which has been used in macroscale application mainly in laminar flow. In this paper a previous experimental results has been studied in depth and identify the descrepancies. The following data set to be for various researchers shows to describe the geometry used in the microchannel heat sink for laminar flow and turbulent flow. Also compare the different flow configuration used in different shapes of microchannel heat sink. This previous literature also predicts the better flow configuration in microchannel heat sink.
Influence of Transverse Magnetic Field on Microchannel Heat Sink Performance
Journal of Applied Fluid Mechanics
The aim of the present numerical investigation is to analyze the effects of transverse magnetic field on heat transfer and fluid flow characteristics in a rectangular microchannel heat sink (MCHS). The effects of Hartmann number, channel aspect ratio, total channel height and total channel width on heat transfer and fluid flow characteristics are widely investigated. The governing equations for three-dimensional steady, laminar flow and conjugate heat transfer of a microchannel are solved using the finite volume method. The obtained results are discussed with various combinations of pertinent parameters involved in the study. The results reveal that magnetic field can enhance the thermal performance of the MCHS but it is accompanied with a slight increase in pressure drop.