Experimental Investigation of the Air Flow Behavior and Heat Transfer Characteristics in Microchannels With Different Channel Lengths

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Zhi Tao ◽  
Zhibing Zhu ◽  
Haiwang Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Critical Reynolds Number ◽  
Flow Behavior ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Poiseuille Number ◽  
Channel Lengths

This paper attempts to experimentally investigate the influence of channel length on the flow behavior and heat transfer characteristics in circular microchannels. The diameters of the channels were 0.4 mm and the length of them were 5 mm, 10 mm, 15 mm, and 20 mm, respectively. All experiments were performed with air and completed with Reynolds number in the range of 300–2700. Results of the experiments show that the length of microchannels has remarkable effects on the performance of flow behavior and heat transfer characteristics. Both the friction factor and Poiseuille number drop with the increase of channel length, and the experimental values are higher than the theoretical ones. Moreover, the channel length does not influence the value of critical Reynolds number. Nusselt number decrease as the increase of channel length. Larger Nusselt numbers are obtained in shorter channels. The results also indicate that in all cases, the friction factor decreases and the Poiseuille number increases with the increase of the Reynolds number. It is also observed that the value of critical Reynolds number is between 1500 and 1700 in this paper, which is lower than the value of theoretical critical Reynolds number of 2300.

Experimental Investigation of the Air Flow Behavior and Heat Transfer Characteristics in Microchannels With Different Channel Lengths

2016 ◽  
Author(s):  
Zhibing Zhu ◽  
Zhi Tao ◽  
Yitu Tian ◽  
Haiwang Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Flow Behavior ◽  
Channel Length ◽  
Traditional Theory ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Poiseuille Number ◽  
Channel Lengths

This paper attempts to experimentally investigate the influence of channel lengths to the flow behavior and heat transfer characteristics in circular microchannels. The diameter of circular microchannels are 0.4mm and the lengths of them are 10mm and 20mm, respectively. All tests were performed with air. The experiments were completed with Reynolds number in the range of 300∼2700. Results of experiments show that the length of microchannels has remarkable effects on the performance of flow behavior and heat transfer characteristics. For the flow behavior, both the friction factor and Poiseuille number drop as the channel length increases, and all the experimental value are higher than the theoretical one. Moreover, the channel length doesn’t influent the value of critical Reynolds number. For the heat transfer characteristics, Nusselt number decreases with the increase of the channel length. The channel length also has a huge influence on the thermal performance. A better thermal performance is obtained in a shorter channel. The results also indicated that in both cases, the friction factor decreases with the increase of the Reynolds number. At the same time, the Poiseuille number increases when the Reynolds number keeps rising. This phenomenon is different from traditional theory that Poiseuille number is widely considered as a constant in laminar regime. It is also observed that the value of critical Reynolds number is between 1500 and 1700 in this paper, this value is lower than the value of theoretical critical Reynolds number of 2300. Nusselt number increases as the increase of the Reynolds numbers, however, the traditional theory considered that it is a constant in laminar regime.

scholarly journals Numerical investigation of fluid flow and heat transfer characteristics in sine, triangular, and arc-shaped channels

2007 ◽  
Vol 11 (1) ◽  
pp. 17-26 ◽  
Author(s):  
Zakir Hossain ◽  
Sadrul Islam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Critical Reynolds Number ◽  
Navier Stokes ◽  
Heat Transfer Characteristics ◽  
Single Wave ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Wavy Channels

Time dependent Navier-Stokes and energy equations have been solved to investigate the fluid flow and heat transfer characteristics in wavy channels. Three different types of two dimensional wavy geometries (e.g. sine-shaped, triangular, and arc-shaped) are considered. All of them are of single wave and have same geometric dimensions. Periodic boundary conditions are used to attain fully developed flow. The flow in the channels has been observed to be steady up to a critical Reynolds number, which depends on the geometric configuration. Beyond the critical Reynolds number a self-sustained oscillatory flow has been observed. As a result of this oscillation, there is increased mixing between core and the near-wall fluids, thereby increasing the heat transfer rate. For the same geometric dimensions, flow becomes unsteady at relatively lower Reynolds number in the arc-shaped channel. .

scholarly journals Numerical Investigations on Heat Transfer Characteristics of Single Particle and Hybrid Nanofluids in Uniformly Heated Tube

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 876
Author(s):  
Kunal Sandip Garud ◽  
Moo-Yeon Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Performance Evaluation ◽  
Friction Factor ◽  
Volume Fraction ◽  
Evaluation Criteria ◽  
Hybrid Nanofluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

In the present study, the heat transfer characteristics, namely, heat transfer coefficient, Nusselt number, pressure drop, friction factor and performance evaluation criteria are evaluated for water, Al2O3 and Al2O3/Cu nanofluids. The effects of Reynolds number, volume fraction and composition of nanoparticles in hybrid nanofluid are analyzed for all heat transfer characteristics. The single particle and hybrid nanofluids are flowing through a plain straight tube which is symmetrically heated under uniform heat flux condition. The numerical model is validated for Nusselt number within 7.66% error and friction factor within 8.83% error with corresponding experimental results from the previous literature study. The thermophysical properties of hybrid nanofluid are superior to the single particle nanofluid and water. The heat transfer coefficient, Nusselt number and pressure drop show increasing trend with increase in the Reynolds number and volume fraction. The friction factor shows the parabolic trend, and the performance evaluation criteria shows small variations with change in Reynolds number. However, both friction factor and performance evaluation criteria have increased with increase in the volume fraction. The 2.0% Al2O3/Cu with equal composition of both nanoparticles (50/50%) have presented superior heat transfer characteristics among all working fluids. Further, the heat transfer characteristics of 2.0% Al2O3/Cu hybrid nanofluid are enhanced by changing the nanoparticle compositions. The performance evaluation criteria for 2.0% Al2O3, 2.0% Al2O3/Cu (50/50%), 2.0% Al2O3/Cu (75/25%) and 2.0% Al2O3/Cu (25/75%) are evaluated as 1.08, 1.11, 1.10 and 1.12, respectively.

Effect of Porosity on Flow Behavior and Heat Transfer Characteristics of Sintered Woven Wire Mesh Structures

2015 ◽  
Author(s):  
Liu Yangpeng ◽  
Xu Guoqiang ◽  
Xiang Luo ◽  
Ma Jiandong ◽  
Li Haiwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Test Piece ◽  
Flow Direction ◽  
Flow Behavior ◽  
Wire Mesh ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Test Pieces ◽  
Mesh Structures

The structure of sintered woven wire mesh is one of classical porous medium. The porosity is one of the major parameters for the porous media. This paper presents the experimental results of the effect of porosity on internal flow behavior and heat transfer characteristics of sintered metal wire mesh structures. All the three test pieces made of stainless steel wires with the same wire diameter (d = 0.14mm) were sintered after woven. One of them was sintered using two sintered metal wire mesh structures with different porosities (55% and 26%) so that the porosity changed along the flow direction. The porosities of the other two test pieces are 55% and 26%, respectively. The experiments were completed with the Reynolds number in the range of 10 to 42. The permeability and inertia coefficient of each test piece were obtained as well as the friction factor. Infrared camera was used to measure the wall temperature of the test pieces to get the Nusselt numbers. The results show that for all test pieces permeability increases as porosity increases, while inertia coefficient shows the opposite trend. Pressure drop of all pieces increases with respect to the mass flow rate. Friction factor decreases as the Reynolds number increases. The curves for test piece #3 fall between those for test piece #1 and #2 and are more close to that for test #2. Nusselt number increases when the Reynolds number keeps arising. However, The Nusselt numbers of the test piece with changed porosity are influenced by the flow direction. There are no significant correlations of the flow behavior and heat transfer characteristics between the test piece with changed porosity and the other two test pieces with constant porosities.

Single-phase fluid flow and heat transfer characteristics of nanofluid in a circular microchannel: Development of flow and heat transfer correlations

2020 ◽  
Vol 234 (18) ◽  
pp. 3689-3708 ◽  
Author(s):  
Mangal Singh Lodhi ◽  
Tanuja Sheorey ◽  
Goutam Dutta
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Friction Factor ◽  
Nanoparticle Concentration ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Circular Microchannel

The convective heat transfer in microchannels with the use of nanofluids has proved to be a potential candidate for cooling of micro-electromechanical system devices. The current research article presents the experimental study on fluid flow and heat transfer characteristics of [Formula: see text]/water nanofluid in a microchannel under thermally developing laminar flow at Reynolds number ranging from 300 to 1000. The experimental set-up of a circular microchannel test section with an inner diameter of [Formula: see text] and length of [Formula: see text] is fabricated to conduct the experimental study. The effect of nanoparticle concentration ([Formula: see text]), Reynolds number ([Formula: see text]) on fluid flow and heat transfer characteristics of [Formula: see text]/water nanofluid have been measured and compared with that of distilled water (DW). The results indicate that the maximum enhancement in local heat transfer coefficient is achieved up to [Formula: see text], while friction factor is achieved up to [Formula: see text] for [Formula: see text]/water nanofluid with nanoparticle concentration of [Formula: see text] as compared to DW. The results showed that the performance evaluation criterion of [Formula: see text]/water nanofluid is greater than unity ([Formula: see text]), implying the benefits of nanofluids as compared to DW. Moreover, the predicted data obtained by the present proposed correlations for friction factor and local Nusselt number using [Formula: see text]/water nanofluid show reasonably good agreement with the deviations of [Formula: see text] and [Formula: see text], respectively, with the numerical data as compared to the predicted data obtained by the existing correlations available in the literature.

scholarly journals Effects of Reynolds number, baffle angle, and baffle distance on three-dimensional turbulent flow and heat transfer in a circular pipe

2015 ◽  
Vol 19 (5) ◽  
pp. 1633-1648 ◽  
Author(s):  
Oguz Turgut ◽  
Erkan Kizilirmak
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Three Dimensional ◽  
Circular Pipe ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

In this study, steady-state three-dimensional turbulent forced convection flow and heat transfer characteristics in a circular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number Re of 3000-50,000, Prandtl number Pr of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle a of 30o-150o. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that circular pipe having baffles has a higher Nusselt number and friction factor compared to the smooth circular pipe without baffles. Maximum Nusselt number and friction factor are obtained for the baffle angle of 90o. Nusselt number increases while baffle distance increases in the range of studied; however, friction factor decreases. Periodically fully developed conditions are obtained after a certain module. Thermal performance factor increases with increasing baffle distance in the rage of studied but decreases with increasing Reynolds number; maximum thermal performance factor is obtained for the baffle angle of 150?. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. The accuracy of the results obtained in this study is verified by comparing the results with those available in the literature for smooth circular pipes. All the numerical results are correlated within accuracy of ?10 and ?15% for average Nusselt number and Darcy friction factor, respectively.

Numerical Simulation on Heat Transfer Characteristics of Turbulent Gas Flow in Micro-Tubes

2011 ◽  
Author(s):  
Kyohei Isobe ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Ichiro Ueno
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Wall Temperature ◽  
Gas Flow ◽  
Tube Diameter ◽  
Turbulence Energy ◽  
Stagnation Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Turbulent Gas Flow

Numerical simulations were performed to obtain for heat transfer characteristics of turbulent gas flow in micro-tubes with constant wall temperature. The numerical methodology was based on Arbitrary-Lagrangian-Eulerinan (ALE) method to solve compressible momentum and energy equations. The Lam-Bremhorst Low-Reynolds number turbulence model was employed to evaluate eddy viscosity coefficient and turbulence energy. The tube diameter ranges from 100 μm to 400 μm and the aspect ratio of the tube diameter and the length is fixed at 200. The stagnation temperature is fixed at 300 K and the computations were done for wall temperature, which ranges from 305 K to 350 K. The stagnation pressure was chosen in such a way that the flow is in turbulent flow regime. The obtained Reynolds number ranges widely up to 10081 and the Mach number at the outlet ranges from 0.1 to 0.9. The heat transfer rates obtained by the present study are higher than those of the incompressible flow. This is due to the additional heat transfer near the micro-tube outlet caused by the energy conversion into kinetic energy.

scholarly journals Effect of the size of graded baffles on the performance of channel heat exchangers

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 767-775 ◽  
Author(s):  
Djamel Sahel ◽  
Houari Ameur ◽  
Touhami Baki
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Computer Code ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Enhancement Of Heat Transfer ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Friction Factors

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 ? 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%

scholarly journals Heat transfer and flow region characteristics study in a non-annular channel between rotor and stator

2012 ◽  
Vol 16 (2) ◽  
pp. 593-603 ◽  
Author(s):  
M. Nili-Ahmadabadi ◽  
H. Karrabi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Characteristics ◽  
Annular Channel ◽  
Flow Region ◽  
Air Gap ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Slip Ring

This paper will present the results of the experimental investigation of heat transfer in a non-annular channel between rotor and stator similar to a real generator. Numerous experiments and numerical studies have examined flow and heat transfer characteristics of a fluid in an annulus with a rotating inner cylinder. In the current study, turbulent flow region and heat transfer characteristics have been studied in the air gap between the rotor and stator of a generator. The test rig has been built in a way which shows a very good agreement with the geometry of a real generator. The boundary condition supplies a non-homogenous heat flux through the passing air channel. The experimental devices and data acquisition method are carefully described in the paper. Surface-mounted thermocouples are located on the both stator and rotor surfaces and one slip ring transfers the collected temperature from rotor to the instrument display. The rotational speed of rotor is fixed at three under: 300rpm, 900 rpm and 1500 rpm. Based on these speeds and hydraulic diameter of the air gap, the Reynolds number has been considered in the range: 4000<Rez<30000. Heat transfer and pressure drop coefficients are deduced from the obtained data based on a theoretical investigation and are expressed as a formula containing effective Reynolds number. To confirm the results, a comparison is presented with Gazley?s (1985) data report. The presented method and established correlations can be applied to other electric machines having similar heat flow characteristics.

Numerical Investigation on Heat Transfer of Al2O3/Water Nanofluid in a Shell and Tube Heat Exchanger

2014 ◽  
Vol 591 ◽  
pp. 3-6
Author(s):  
M. Raja ◽  
R. Vijayan ◽  
R. Vivekananthan ◽  
M.A. Vadivelu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Numerical Investigation ◽  
Volume Concentration ◽  
Heat Transfer Characteristics ◽  
Tube Heat Exchanger ◽  
Transfer Characteristics ◽  
Shell And Tube ◽  
Suspended Nanoparticles

In the present work, the effect of nanofluid in a shell and tube heat exchanger was studied numerically. The effects of Reynolds number, volume concentration of suspended nanoparticles on the heat transfer characteristics were investigated using CFD software. Finally, the effect of the nanofluid on Shell and tube heat exchanger performance was studied and compared to that of a conventional fluid (i.e., water).

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