Thermal and Hydraulic Performance of Counterflow Microchannel Heat Exchangers With and Without Nanofluids

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Hamid Reza Seyf ◽  
Shahabeddin Keshavarz Mohammadian
Keyword(s):  
Reynolds Number ◽  
Brownian Motion ◽  
Performance Index ◽  
Volume Fraction ◽  
Reynolds Numbers ◽  
Hydraulic Performance ◽  
Working Fluid ◽  
Pumping Power ◽  
Mean Diameter ◽  
And Performance

Abstract This paper analyzes the thermal and hydraulic performance of a counterflow microchannel heat exchanger (CFMCHE) with and without nanofluid as working fluid. A 3D conjugate heat transfer simulation is carried out using a finite volume approach to evaluate the effects of inlet Reynolds number, Brownian motion, and volume fraction of nanoparticles on the pumping power, effectiveness, and performance index of CFMCHE. The accuracy of the code has been verified by comparing the results with those available in the literature. A single phase approach is used for the nanofluid modeling. The base fluid used in the analyses as a basis for comparison was pure water. Two types of nanofluids, namely, water-Al2O3 with a mean diameter of 47 nm and water-CuO with a mean diameter of 29 nm, each one with three different volume fractions, are utilized. In addition, two temperature dependent models for the thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion are used. Calculated results demonstrate that the effectiveness and performance index of CFMCHE decrease with increasing Reynolds number. Moreover, it is observed that the relative enhancements in the pumping power become more prominent for higher values of Reynolds numbers. It was also found that the performance index and pumping power are not sensitive to volume fraction at higher and lower Reynolds numbers, respectively.

scholarly journals Computational Modeling on Heat Transfer Enhancement and Fluid Flow Behavior of Al2O3-Water Nanofluid through a Circular Duct

2020 ◽  
Vol 9 (5) ◽  
pp. 1819-1824
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Volume Fraction ◽  
Flow Behavior ◽  
Computational Simulation ◽  
Working Fluid ◽  
Pumping Power ◽  
Circular Duct ◽  
Reynolds Number Flow ◽  
Increase With Increase

In this work, heat transfer behaviour from a isothermal-walled micro channel has been investigated by using Al2O3 -water nanofluid as working fluid. A computational simulation has been carried out for high Reynolds number flow, having different volume fraction of nanoparticles added to it such as; 0%, 1%, 4% and 6%. It has been observed that the properties such as; density, thermal conductivity and viscosity increase with increase in nanoparticles. On the other hand, with increase in the volume fraction of nanoparticles, the specific heat decreases. It also has been observed that the heat transfer from the hot wall increases with Reynolds number and addition of nanoparticles to the nanofluid as well. The friction factor for the flow system decreases with increase the Reynolds number, but for different nanofluids its value is very much closer to each other. With increase in volume fraction of nanoparticles, the pumping power increases. Moreover, with increase in Reynolds number, pumping power increases.

Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers

2001 ◽  
Author(s):  
Miles Greiner ◽  
Paul F. Fischer ◽  
Henry Tufo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Frequency ◽  
Flow Rate ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Spectral Element ◽  
Pumping Power ◽  
Number Systems ◽  
Low Reynolds

Abstract The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.

scholarly journals Entropy generation of a hybrid nanofluid on MHD mixed convection is a lid-driven cavity with partial heating having two rounded corners

2021 ◽  
Vol 321 ◽  
pp. 02004
Author(s):  
Zakaria Korei ◽  
Smail Benissaad
Keyword(s):  
Thermal Conductivity ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Object Oriented ◽  
Reynolds Numbers ◽  
Hybrid Nanofluid ◽  
Driven Cavity ◽  
Partial Heating

This research aims to investigate thermal and flow behaviors and entropy generation of magnetohydrodynamic Al2O3-Cu/water hybrid nanofluid in a lid-driven cavity having two rounded corners. A solver based on C ++ object-oriented language was developed where the finite volume was used. Parameter’s analysis is provided by varying Reynolds numbers (Re), Hartmann numbers (Ha), the volume fraction of hybrid nanofluid (ϕ), radii of the rounded corners. The findings show that reducing the radii of the rounded corners minimizes the irreversibility. Furthermore, the thermal conductivity and dynamic viscosity of hybrid nanofluid contribute to increasing the irreversibility. Finally, the entropy generation is decreased by increasing the Hartman number and increases by rising the Reynolds number.

Low Reynolds-Number Experiments in an Axial-Flow Turbomachine

1964 ◽  
Vol 86 (3) ◽  
pp. 257-295 ◽  
Author(s):  
J. Neustein
Keyword(s):  
Reynolds Number ◽  
Guide Vane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Working Fluid ◽  
Low Reynolds Numbers ◽  
Blade Row ◽  
Overall Performance ◽  
Low Reynolds

The performance of a single-stage, axial-flow turbomachine was studied experimentally at low Reynolds numbers. The study was made with a turbomachine modeled from a large jet-engine type of axial-flow compressor. Low Reynolds numbers were obtained by using a mixture of glycerine and water as the working fluid. The overall performance was determined over a range of Reynolds numbers RT (based on rotor-tip speed and rotor chord) from 2000 to 150,000. The flow rate at each Reynolds number was varied from near shutoff to the maximum permitted by the turbomachine-tunnel systems. Blade-row characteristics were studied by means of quantitative flow surveys before and after each blade row, and by means of extensive flow-visualization experiments within each blade row. The investigation established that sudden or critical changes in performance do not occur in the type of machine tested, between RT of 150,000 and 20,000. Below 20,000 the performance deteriorated more rapidly. A relatively sharp change in performance occurred between RT of 20,000 and 10,000. The results clarified many of the viscous flow details in each blade row which are associated with the deterioration of performance. These effects were very pronounced at RT of 4000 and below. Consequently, a considerable part of the paper is concerned with results obtained at these lower Reynolds numbers. From the point of view of a designer, information is presented in regard to overall performance, guide-vane turning, and guide-vane and stator total-pressure losses, all as functions of Reynolds number. These results are expected to be indicative of performance in turbomachines similar to the one tested here. Other details are concerned with problems such as wall boundary layers, flow reversal at low flow coefficients, lip-clearance flow, flow patterns near shutoff, and flow comparisons in stators with rotating and stationary hubs.

scholarly journals CONVECTIVE HEAT TRANSFER AND POWER SAVING APPLICATION OF SI BASED NANOPARTICLES IN A CIRCULAR PIPE

2020 ◽  
Vol 50 (4) ◽  
pp. 321-327
Author(s):  
Md Insiat Islam Rabby ◽  
Farzad Hossain ◽  
S.A.M. Shafwat Amin ◽  
Tazeen Afrin Mumu ◽  
MD Ashraf Hossain Bhuiyan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Base Fluid ◽  
Volume Fraction ◽  
Numerical Study ◽  
Convective Heat Transfer Coefficient ◽  
Circular Pipe ◽  
Working Fluid ◽  
Pumping Power

A numerical study of laminar forced convection heat transfer for the fully developed region inside a circular pipe filled with Si based nanoparticle is presented for investigating the parameters of heat transfer. Four Si based nanoparticles Si, SiC, SiO2, Si3N4 with 1-5% volume fraction have been mixed with water to prepare nanofluids which is used for working fluid to flow over a circular pipe with 5mm diameter and 700mm length. Heat transfer characteristics and pumping power have been calculated at fully developed region with constant heat flux condition on pipe wall to identify the heat transfer enhancement ratio and pumping power reduction ratio among base fluid water and each nanofluids. It is worth mentioning that utilizing SiC nanoparticle shows not only the highest increment of Nusselt number and convective heat transfer coefficient but also the highest decrement of pumping power requirement and FOM in comparison to the base fluid.

scholarly journals Experimental Investigation of The Influence of Mechanical Forced Vibrations and Heat Flux on Coefficient of Heat Transfer

2018 ◽  
Vol 6 (3) ◽  
pp. 124-129
Author(s):  
Adil Bash ◽  
Aadel Alkumait ◽  
Hamza Yaseen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Forced Vibration ◽  
Vibration Amplitude ◽  
Internal Flow ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
New Correlation

The aim of this paper to verify the influence of vertical forced vibration on the coefficient of heat transfer of the laminar internal flow in a spiral fluted tube. With adopted the water as a working fluid, and flowing Reynolds numbers at the entrance between 228 and 1923, the tube heated under constant heat flux levels ranging from 618-3775 W/m2. The frequencies of vibration ranging from 13 to 30 Hz, and the amplitudes of vibration from 0.001 to 0.002 mm. The results appeared that the coefficient of heat transfer significantly affected by mechanical forced vibration in a flowing of the heated tube. When the vibration amplitude increases, the Nusselt number Significantly increases, with the maximum increases of 8.4% at the amplitude of vibration 0.0022 mm and the frequency 13 Hz. Generally, the coefficient of heat transfer increases with increasing Reynolds number and heat flux. At last, by using the parameters of vibration amplitude, frequency, heat flux and Reynolds number, a new correlation has been derived depends on experimental data.

Wavy-Channel for Microscale Heat Transfer in Macro Geometries

2017 ◽  
Author(s):  
Kai Xian Cheng ◽  
Zi Hao Foo ◽  
Kim Tiow Ooi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Index ◽  
Heat Transfer Performance ◽  
Cnc Machining ◽  
Hydrodynamic Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Number Range ◽  
Reynolds Number Range

Microscale heat and fluid flow in macro geometries have been made practical in terms of cost and fabrication, by superimposing two macro geometries which are fabricated using readily-available CNC machining methods. Wavy-profile has been proposed to enhance heat transfer performance in the microchannel owing to the simplicity of geometry and feasibility to be fabricated using simple turning process. Experimental studies were conducted on single-phase, forced convective heat transfer using water as the working fluid for the Reynolds number range of 1300 to 4600, for a constant heat flux of 53.0 W/cm2. Three sinusoidal waves with different wavelength and same amplitude are studied to examine the effect of the total number of waves on the heat transfer and hydrodynamic performance within constant microchannel length. The maximum performance index, which evaluates heat transfer performance per unit pumping power, is 1.39, achieved by wavy profile with the shortest wavelength at Reynolds number of 2800. The performance index for all the enhanced microchannels peaks at the Reynolds number range of 2500 to 2800. Beyond that, the performance index is not a strong function of the wavelength. At lower Reynolds numbers, profile with the shortest wavelength achieves substantially higher performance indices, as the increment in pressure drop is accompanied by a comparable increment in heat transfer. Future work includes the introduction of correlations for the implementation of such geometries in industrial heat exchangers.

Numerical Investigation of Nanoparticles Shape Impacts on Thermal Energy Transfer and Flow Features of Nanofluid Impingement Jets

2021 ◽  
Vol 143 (11) ◽  
Author(s):  
Behrang Asghari Shirvani ◽  
Javad Sodagar ◽  
Farshid Eynijengheshlaghi ◽  
Ahmad Arabkoohsar
Keyword(s):  
Reynolds Number ◽  
Energy Transfer ◽  
Pressure Drop ◽  
Thermal Energy ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Working Fluid ◽  
Energy Transfer Rate ◽  
Spherical Nanoparticles ◽  
Impingement Jet

Abstract Today, energy transfer enhancement techniques have received much attention for design and manufacturing more efficient systems in various industries such as automotive, computers, electronics, and so forth. One way to achieve high-efficiency cooling systems is to use impingement jet cooling. In the present study, a numerical study has been conducted on nanofluid impingement jet in the vertical position to investigate the fluid flow characteristics and thermal energy transfer features. The working fluid in this study is a nanofluid with water–ethylene glycol mixture as base fluid and nanoparticles of boehmite alumina. The flow is considered to be laminar, steady-state, two-dimensional, symmetrically axial, for which the finite volume method is used to solve the equations. The effect of the Reynolds number variations, the volume fraction of nanoparticle, and different nanoparticle shapes (including spherical, plate, blade, cylindrical, and brick shapes) on thermophysical features of the flow are studied. The results reveal that the increasing Reynolds number and the increasing volume fraction of nanoparticles improves the thermal energy transfer rate. The highest Nusselt number leads to a maximum of energy transfer related to nanofluids with platelet and cylindrical nanoparticles, while the lowest thermal energy transfer rate is related to nanofluids containing spherical nanoparticles. Moreover, it is illustrated that nanofluids with platelets nanoparticles, because of their higher effective viscosity compares to other nanofluids, experience the highest pressure drop and those of with spherical nanoparticles show the lowest pressure drop.

Moderate Reynolds number flows through periodic and random arrays of aligned cylinders

1997 ◽  
Vol 349 ◽  
pp. 31-66 ◽  
Author(s):  
DONALD L. KOCH ◽  
ANTHONY J. C. LADD
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Volume Fraction ◽  
Unit Length ◽  
Reynolds Numbers ◽  
Moderate Reynolds Number ◽  
Random Arrays ◽  
Flow Through ◽  
The Mean ◽  
Square Array

The effects of fluid inertia on the pressure drop required to drive fluid flow through periodic and random arrays of aligned cylinders is investigated. Numerical simulations using a lattice-Boltzmann formulation are performed for Reynolds numbers up to about 180.The magnitude of the drag per unit length on cylinders in a square array at moderate Reynolds number is strongly dependent on the orientation of the drag (or pressure gradient) with respect to the axes of the array; this contrasts with Stokes flow through a square array, which is characterized by an isotropic permeability. Transitions to time-oscillatory and chaotically varying flows are observed at critical Reynolds numbers that depend on the orientation of the pressure gradient and the volume fraction.In the limit Re[Lt ]1, the mean drag per unit length, F, in both periodic and random arrays, is given by F/(μU) =k1+k2Re2, where μ is the fluid viscosity, U is the mean velocity in the bed, and k1 and k2 are functions of the solid volume fraction ϕ. Theoretical analyses based on point-particle and lubrication approximations are used to determine these coefficients in the limits of small and large concentration, respectively.In random arrays, the drag makes a transition from a quadratic to a linear Re-dependence at Reynolds numbers of between 2 and 5. Thus, the empirical Ergun formula, F/(μU) =c1+c2Re, is applicable for Re>5. We determine the constants c1 and c2 over a wide range of ϕ. The relative importance of inertia becomes smaller as the volume fraction approaches close packing, because the largest contribution to the dissipation in this limit comes from the viscous lubrication flow in the small gaps between the cylinders.

A Theoretical and Experimental Study of a Liquid-Lubricated Hydrostatic Journal Bearing

1968 ◽  
Vol 183 (1) ◽  
pp. 647-662 ◽  
Author(s):  
C. Betts ◽  
W. H. Roberts
Keyword(s):  
Journal Bearing ◽  
Reynolds Numbers ◽  
Liquid Sodium ◽  
Working Fluid ◽  
Design Problems ◽  
Static Performance ◽  
Flow Through ◽  
Temperature Liquid ◽  
And Performance ◽  
Semi Empirical

The use of mechanical pumps for circulating high-temperature liquid-sodium coolant in nuclear-powered fast reactors emphasizes the problem of designing suitable bearings. This paper presents a semi-empirical theory which describes the (static) performance of a hydrostatic jet journal bearing for such applications where the flow through the bearing is predominantly turbulent. The theory covers both viscous and turbulent regimes of flow. In the presentation non-dimensional groups are plotted to facilitate direct application of the theory to specific design problems. Experiments using paraffin and water as the working fluid are described; Reynolds numbers of approximately 1700 and 7000 respectively were achieved—compared with Re in excess of 20 000 likely to be encountered in practice. The design and performance of an 8 in diameter bearing for a 6000 gal/min mechanical sodium pump prototype are briefly described.

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