Effect of Protuberances in the Heat Transfer Enhancement in Mini-Channels

2021 ◽  
Author(s):  
Ariel Cruz Diaz ◽  
Gerardo Carbajal
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Heat Removal ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Mini Channels

Abstract This study presents the effects of adding an array of protrusions in a microchannel for heat transfer enhancement. The presence of mini-channels increases the overall heat transfer area and boosts the mixing development near the solid-fluid interaction; therefore, it can remove more heat than conventional mini-channels without protuberances. A numerical study proved that protuberances in a mini-channel increase the heat transfer performance by disturbing the relative fluid motion near the solid wall. The numerical simulation was performed with three different protuberances arrays: aligned, staggered, and angular. Each array consists of a thin flat plate with a hemispherical shape; the working fluid and the solid materials were water and copper. The study also includes the effect of different Reynolds numbers: 1,000, 1,500, and 2,000. Three heat inputs were applied in the numerical simulation; these were 1W, 3W, and 5W. The study was compared with a simple microchannel with non-protuberances to analyze the microchannel performance regarding heat removal and pressure drop. For heat transfer performance, the best array was the staggering array with a maximum heat removal increase of 5.26 percent. In terms of pressure drop performance, the best array was the aligned array, with a maximum increase of 34.73 percent.

scholarly journals Numerical Simulation Based on Heat Transfer Enhancement of Supercritical Fluid in Micro-Fin Tube

2021 ◽  
Vol 257 ◽  
pp. 01043
Author(s):  
Peng-Fei Chen ◽  
Kang Chen ◽  
Xiao Wang ◽  
Long Wen
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Enhancement ◽  
Supercritical Fluid ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Round Tube ◽  
Fin Tube ◽  
Fin Tubes

With the application of supercritical fluid heat transfer equipment in industrial fields such as solar thermal power generation, chemical industry, aerospace, etc., studying the heat transfer characteristics of supercritical fluid in micro-fin tubes has become a key theoretical basis for the development of micro-fin low-resistance heat transfer enhancement technology. In view of micro-fin tubes with different fin shapes, this paper took into account thermophysical properties of nitrogen under supercritical conditions and completed a numerical simulation study on the heat transfer process of nitrogen in 2 mm micro-fin tubes under supercritical pressure. The temperature field distribution of supercritical nitrogen in the micro-fin tube was analyzed, and the turbulent flow mechanism of the micro-fin was studied. It was found that micro-fin could increase the heat exchange area, destroy the boundary layer, and improve the heat transfer coefficient. This paper took comprehensive heat transfer performance evaluation factor PEC to compare the influence of different fin shapes on heat transfer enhancement performance of the heat exchange unit. It was found that the comprehensive heat transfer factor of the square straight micro-fin tube was about 1.22 times that of the smooth round tube, and PEC of the triangular straight micro tube was about 1.08 times that of the smooth tube. The results suggest that square straight micro-fin tube has significantly superior heat transfer performance than smooth round tube and triangular straight micro-fin tube.

scholarly journals An Experimental Study on Heat Transfer and Pressure Drop of CuO-Water Nanofluid

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Bayram Sahin ◽  
Eyuphan Manay ◽  
Eda Feyza Akyurek
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Horizontal Tube ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Particle Volume

Heat transfer and pressure drop characteristics of water based CuO nanofluid inside a horizontal tube were investigated experimentally. The upper limitation of the particle volume fraction with respect to heat transfer performance was also found. CuO-water nanofluids with volume fractions of 0.5%, 1%, 2%, and 4% were prepared by dispersing the CuO nanoparticles with an average diameter of 33 nm into deionised water. Experiments were carried out under the steady-state, constant heat flux, and turbulent flow regime conditions. The variations of the average Nusselt number and the friction factor with the Reynolds number were presented. For all given particle volume concentrations, heat transfer enhancements were calculated. It was concluded that the particle volume concentrations higher than 1% vol. were not appropriate with respect to the heat transfer performance of the CuO-water nanofluid. No heat transfer enhancement was observed at Re = 4.000. The highest heat transfer enhancement was achieved at Re = 16.000 and ф = 0.005.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

Experimental Heat Transfer Enhancement in Single-Phase Liquid Microchannel Cooling With Cross-Flow Synthetic Jet

2010 ◽  
Author(s):  
Ruixian Fang ◽  
Wei Jiang ◽  
Jamil Khan ◽  
Roger Dougal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Synthetic Jet ◽  
Driving Voltage ◽  
Transfer Performance ◽  
Microchannel Flow ◽  
Transfer Enhancement ◽  
Synthetic Jet Actuator ◽  
Phase Liquid

The present study experimentally investigated a new hybrid cooling scheme by combination of a microchannel heat sink with a micro-synthetic jet actuator. The heat sink consisted of a single rectangular microchannel measured 550 μm wide, 500 μm deep and 26 mm long. The synthetic jet actuator with a 100 μm diameter orifice was placed right above the microchannel and 5 mm downstream from the channel inlet. Micro jet is synthesized from the fluid flowing through the microchannel. Periodic disturbance is generated when the synthetic jet interacts with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and propagated downstream the microchannel. The scale and frequency of the disturbance can be controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. The effects of synthetic jet on microchannel heat transfer performance were studied based on the microchannel flow Reynolds number, the jet operating voltage and frequency, respectively. It shows that the synthetic jet has a greater heat transfer enhancement for microchannel flow at lower Reynolds number. It also shows that the thermal effects of the synthetic jet are functions of the jet driving voltage and frequency. We obtained around 42% heat transfer enhancement for some test cases, whereas the pressure drop across the microchannel increases very slightly. The paper concludes that the synthetic jet can effectively enhance single-phase liquid microchannel heat transfer performance and would have more promising enhancements if multi-jets are applied along the microchannel.

Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets

2011 ◽  
Author(s):  
Youmin Yu ◽  
Terrence Simon ◽  
Min Zhang ◽  
Taiho Yeom ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Single Channel ◽  
Synthetic Jets ◽  
Heat Sinks ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Enhancing Heat Transfer

Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.

Experimental Investigations on Heat Transfer Enhancement in a Horizontal Tube Using Converging and Diverging Conical Strip Inserts

2014 ◽  
Vol 592-594 ◽  
pp. 1590-1595 ◽  
Author(s):  
Naga Sarada Somanchi ◽  
Sri Rama R. Devi ◽  
Ravi Gugulothu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Working Fluid ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Enhancement Of Heat Transfer

The present work deals with the results of the experimental investigations carried out on augmentation of turbulent flow heat transfer in a horizontal circular tube by means of tube inserts, with air as working fluid. Experiments were carried out initially for the plain tube (without tube inserts). The Nusselt number and friction factor obtained experimentally were validated against those obtained from theoretical correlations. Secondly experimental investigations using three kinds of tube inserts namely Rectangular bar with diverging conical strips, Rectangular bar with converging conical strips, Rectangular bar with alternate converging diverging conical strips were carried out to estimate the enhancement of heat transfer rate for air in the presence of inserts. The Reynolds number ranged from 8000 to 19000. In the presence of inserts, Nusselt number and pressure drop increased, overall enhancement ratio is calculated to determine the optimum geometry of the tube insert. Based on experimental investigations, it is observed that, the enhancement of heat transfer using Rectangular bar with converging and diverging conical strips is more effective compared to other inserts. Key words: Heat transfer, enhancement, turbulent flow, conical strip inserts, friction factor, pressure drop.

Numerical Investigation on Flow and Heat Transfer in Matrix Cooling Channels for Turbine Blades

2016 ◽  
Author(s):  
Yigang Luan ◽  
Shi Bu ◽  
Haiou Sun ◽  
Tao Sun
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Structural Parameters ◽  
Turbine Blades ◽  
Channel Width ◽  
Transfer Performance ◽  
Cooling Channel ◽  
Cooling Channels

Matrix cooling is one kind of internal cooling structures applied to protect turbine blades. This paper investigated the flow field and heat transfer performance in matrix cooling channels experimentally and numerically. A testing section (rib angle of 45-deg, rib thickness of 30mm, rib height of 30mm and sub-channel width of 30mm) made of Plexiglas was build and connected to a wind tunnel sysytem. And Transient Liquid Crystal (TLC) technique was applied to obtain the detailed heat transfer distribution on the primary surface inside the matrix cooling channel. The experiment was performed under different Reynolds numbers varying from 18428 to 28327, based on the channel inlet hydraulic diameter; also the overall pressure drop across the channel was measured. Experimental results were used to calibrate the numerical solution obtained by computational fluid dynamics (CFD) method. During the numerical simulation process, structured grids and k-w turbulence model was employed. And a good agreement is obtained between experimental and CFD results for both pressure drop and heat transfer performance. Channels of various structural parameters (rib angle, rib thickness and sub-channel width) were then studied by numerical simulation, three rib angles (30-deg, 45-deg and 60-deg), three rib thicknesses (1.8mm, 3mm and 5mm) and three sub-channel widths (3mm, 5mm and 9mm) were considered, with the rib height 3mm for all the cases. Numerical results showed that the sidewall turnings made the greatest contribution to heat transfer enhancement but caused very large pressure drop meanwhile. The overall heat transfer and pressure drop increase with rib angle and rib width but decrease with sub-channel width. The thermal performance factor decreases with rib angle and rib width, while it showed a non-monotonic dependency on sub-channel width. Among the three structural parameters, rib angle has the most significant effect on the performance of matrix cooling channel.

Heat transfer performance of steam/air flow in inverted V-shaped rib-roughened channels

2021 ◽  
pp. 095765092110161
Author(s):  
Chao Ma ◽  
Bing Ge
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Air Flow ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Ribbed Channel

The heat transfer performance of steam and air flow in a rough rectangular channel with different inverted V-shaped ribs was investigated by infrared thermal imaging technology. Under the conditions that the Reynolds number is in the range of 4000–15,000, the effects of the rib angle on the heat transfer enhancement of the two coolants were obtained. The rib pitch ratio of the flow channel is 10, the ratio of the rib height to the channel hydraulic diameter is 0.078, and the inverted V-shaped rib angle varies from 45° to 90°. The results show that in the inverted V-shaped ribbed channel, the Nu number on both sides of the channel is greatly increased, while the Nu number in the middle of the channel is lower. The local Nu distribution on the surface of the ribbed channel is highly related to the shape of the rib. For different medium cooling, the value and unevenness of the heat transfer coefficient are different, but the shape of the high and low heat transfer coefficient distribution is hardly affected. The heat transfer of both coolants increases as the rib angle decreases from 90° to 45°. Compared with air flow, steam flow cooling shows higher convective heat transfer enhancement. For rib angles of 45°, 60°, 75°, and 90°, under the operating condition of the Reynolds number = 12,000, the area-averaged Nusselt numbers of the steam flow is 23.6%, 27.4% and 13.9% higher than that of the air flow, respectively. Based on the experimental heat transfer data, the correlation in terms of the Reynolds number and the rib angle was developed, which is used to estimate the Nu number for steam and air cooling in the inverted V-shaped rib-roughness channels.

Convective Heat Transfer Enhancement Using Carbon Nanofibers (CNFs): Influence of Amorphous Carbon Layer on Heat Transfer Performance

2013 ◽  
Author(s):  
T. J. Taha ◽  
L. Lefferts ◽  
T. H. Van der Meer
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Surface Area ◽  
Carbon Nanofibers ◽  
Amorphous Carbon ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Transfer Enhancement

In this work, an experimental heat transfer investigation was carried out to investigate the combined influence of both amorphous carbon (a-C) layer thickness and carbon nanofibers (CNFs) on the convective heat transfer behavior. Synthesis of these carbon nano structures was achieved using catalytic chemical vapor deposition process (CCVD) on a 50 μm nickel wire at 650°C. Due to their extremely high thermal conductivity, CNFs are used to augment/modify heat transfer surface. However, the inevitable layer of a-C that occurs during the synthesis of the CNFs layer exhibit low thermal conductivity which may result in insulating the surface. In contrast, the amorphous layer helps in supporting and mechanical stabilizing of the CNFs layer attachment to the polycrystalline nickel (Ni270) substrate material. To better understand the influences of these two layer on heat transfer, the growth mechanism of the CNFs layer and the layer of carbon is investigated and growth model is proposed. The combined impact of both a-C and CNFs layer on heat transfer performance is studied on three different samples which were synthesized by varying the deposition period (16 min, 23min and 30 min). The micro wire samples covered with CNF layers were subjected to a uniform flow from a nozzle. Heat transfer measurement was achieved by a controlled heat dissipation through the micro wire to attain a constant temperature during the flow. This measurement technique is adopted from hot wire anemometry calibration method. Maximum heat transfer enhancement of 18% was achieved. This enhancement is mainly attributed to the surface roughness and surface area increase of the samples with moderate CNFs surface area coverage on the sample.

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