Quantitative Experimental Investigation on the Flow Characteristics of Nanofluids in Turbulent Flow

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Jizu Lv ◽  
Chengzhi Hu ◽  
Zhenxian Zhang ◽  
Minli Bai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Transfer Enhancement ◽  
Basic Fluid ◽  
Field Disturbance ◽  
Perturbation Effect

Abstract In addition to the increase of thermal conductivity, heat transfer enhancement mechanism for nanofluids also includes the changes of the flow characteristics, therefore it is needed to take an in-depth research on nanofluids flow characteristics. In this paper, the flow characteristics of H2O and SiO2-H2O nanofluids in a rectangular convex channel (channel composed of continuous staggered rectangular convex platform) at the Reynolds numbers 2300, 2500, 3000 and 4000 are studied by the quantitative PIV method (Fig. 1a). The rectangular convex channel (Fig. 1b) has periodic perturbation effect on the fluid flow, so that the flow direction is changed for several times, and vortexes are generated, which makes turbulence enhanced. In this way, flow is in the intense turbulent state under a low flow rate. Results show that the flow fields becomes more chaotic by the addition of nanoparticles (Fig. 2 and 3). Both the number and the size of vortices increase observably. The vorticity of nanofluids is also enhanced compared with H2O, and with the increase of Reynolds number, the increased ratio in the vorticity magnitude is getting higher (Fig. 4). At different Reynolds number, the pressure loss of nanofluids increases by 2.27%, 2.23%, 1.5% and 14.7%, respectively. As shown the flow resistance does not increase significantly compared to base fluids, especially at low Reynolds number. It can be concluded that the interaction between nanoparticles and the basic fluid strengthens the flow field disturbance, which is benefit to the heat transfer of nanofluids.

The Spacer Grid Effect on Heat Transfer at Low Flow Rate in a 5×5 Rod Bundles

2016 ◽  
Author(s):  
Da Liu ◽  
Hanyang Gu ◽  
Shengjie Gong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Transfer Enhancement ◽  
Spacer Grid ◽  
Maximum Enhancement ◽  
Low Reynolds Numbers

It is widely acknowledged that the spacer grid has great effect on heat transfer downstream of it. The conventional correlations to predict the augmentation of the spacer were carried out on high Reynolds numbers. However, recent studies have shown that Reynolds number on the heat transfer enhancement is not negligible when the Reynolds number is lower than about 10000. An experiment to investigate the single-phase convective heat transfer downstream of the spacer grid at low flow rate has been performed in a 5×5 rod bundle. The test section was uniformly heated by a DC power and cooled by water. The Reynolds number covered from about 2000 to 10000. The experiment showed that the existing correlations for heat transfer enhancement by a spacer grid underestimated the maximum enhancement at the grid exit of the spacer grid at low Reynolds numbers. As the Reynolds number decreases, the maximum enhancement increases, nevertheless, when Reynolds number decreases to about 4300, the maximum enhancement tend to converge at a certain value. A new correlation has been proposed to account for the Reynolds number effect on heat transfer enhancement downstream of the spacer grid at low Reynolds numbers and which gave good predictions.

A Note on the Comparative Analysis Between Rectangular and Modified Duct Heat Exchanger

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Rajneesh Kumar ◽  
Varun Goel ◽  
Anoop Kumar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Characteristics ◽  
Radius Of Curvature ◽  
Transfer Enhancement ◽  
Rectangular Array ◽  
Flow Passage ◽  
Rounded Corner ◽  
The Cost ◽  
Similar Combination

Abstract The plate fin heat exchangers usually have either rectangular or triangular shaped flow passage. In comparison to triangular flow passage, rectangular flow passage gives comparatively higher heat transfer at the cost of higher pumping power. In the present investigation, flow passage is modified by rounding the corner of triangular passage to investigate the heat and flow characteristics of air flowing through it. Comparison of performance between modified and rectangular flow passage has also been presented and discussed. The radius of curvature of the rounded corner has been kept constant with value of 0.49 times duct height (H). The dimple was also fabricated at the inner side of the flow passage and arranged in rectangular array. Distance between them was defined by two different dimensionless parameters, relative transverse width (x/h), and relative streamwise length (z/h), whereas, dimensionless height of the protrusion is defined by relative dimple height (h/D). Noticeable increment in both heat transfer and friction factor has been observed by modifying the duct corners and 2.98 times increment in Nusselt number resulted due to dimples in modified duct for h/D, x/h, and y/h value of 0.44, 10, and 10, respectively, in comparison to smooth duct at Reynolds number of 19,500. For similar combination of roughness parameters, highest frictional penalty was estimated with value of 4.46 times that of the smooth duct at Reynolds number of 4400. Additionally, the comparative assessment of heat transfer enhancement (Nuenh), frictional penalty (fpenalty), and thermohydraulic performance index (THPi) has also been carried out to understand the suitability of round cornered duct. In comparison to protruded rectangular duct, 28% higher THPi is obtained in modified duct under similar conditions.

scholarly journals Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Carlo Carcasci ◽  
Bruno Facchini ◽  
Marco Pievaroli ◽  
Lorenzo Tarchi ◽  
Alberto Ceccherini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Flow Direction ◽  
Western World ◽  
Open Area ◽  
Transfer Enhancement ◽  
Test Models

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin–fin geometries, a lattice–matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice–matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height, which span from a possible application in the midchord region up to the trailing edge region of a gas turbine airfoil. For each rib height, two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet subchannel hydraulic diameter, from 2000 to 12,000. Heat transfer coefficients (HTCs) were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, five in the main flow direction, and two in the tangential one. Metal temperature was measured with embedded thermocouples, and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.

Air-Side Heat Transfer Enhancement and Pumping Power Penalty in Air-Cooled Heat Exchangers With Dimpled Fins

2017 ◽  
Author(s):  
Tung X. Vu ◽  
Lokanath Mohanta ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Fold Increase ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Power Penalty ◽  
Flat Tubes

In this work, we focus exclusively on heat transfer enhancement techniques for the air-side heat transfer in air-cooled heat exchangers/condensers. An innovative dimpled fin configuration is explored. Experiments, in which both heat transfer and drag are measured, are conducted with flat tubes in three configurations: without fins, with plain fins and with dimpled fins. Reynolds numbers based on the hydraulic diameter of the finned passages are varied between 600 and 7000. Results indicate that fins are more advantageous at lower Reynolds numbers since the increase in drag at higher Reynolds numbers quickly erases any advantage due to an increase in heat transfer rate. As an example, for the plain fins versus a bare tube at a Reynolds number of 600, there is a 7 fold increase in heat transfer with only a 5 fold increase in drag. However, at a Reynolds number of 7000, both heat transfer and drag increase by approximately 6 times, indicating that the increase in drag has caught up with the heat transfer enhancement. Similarly, while dimpled fins do result in higher heat transfer compared with the plain fins, the advantage is also more prominent at lower Reynolds numbers where heat transfer enhancement is higher than the associated increase in pumping power.

Heat Transfer and Pressure Loss Measurements in a Turbulated High Aspect Ratio Channel With Large Reynolds Number Flows

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Shantanu Mhetras ◽  
Je-Chin Han ◽  
Michael Huth
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Aspect Ratio ◽  
Compressible Flow ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Transfer Enhancement ◽  
High Reynolds ◽  
Wide Wall

Experiments to investigate heat transfer and pressure loss are performed in a rectangular channel with an aspect ratio of 6 at very high Reynolds numbers under compressible flow conditions. Reynolds numbers up to 1.3 × 106 are tested. The presence of a turbulated wall and the resultant heat transfer enhancement against a smooth surface is investigated. Three dimpled configurations including spherical and cylindrical dimples are studied on one wide wall of the channel. The presence of discrete ribs on the same wide wall is also investigated. A steady state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located at several streamwise locations in the channel walls are used to record the static pressures on the surface. Experiments are performed for a wide range of Reynolds numbers from the incompressible (Re = 100,000–500,000; Mach = 0.04–0.19) to compressible flow regimes (Re = 900,000–1,300,000, Mach = 0.35–0.5). Results for low Reynolds numbers are compared to existing heat transfer data available in open literature for similar configurations. Heat transfer enhancement is found to decrease at high Re with the discrete rib configurations providing the best enhancement but highest pressure losses. However, the small spherical dimples show the best thermal performance. Results can be used for the combustor liner back side cooling at high Reynolds number flow conditions. Local measurements using the steady state, hue-detection based liquid crystal technique are also performed in the fully developed region for case 1 with large spherical dimples. Good comparison is obtained between averaged local heat transfer coefficient measurements and from thermocouple measurements.

scholarly journals Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils

2014 ◽  
Author(s):  
Carlo Carcasci ◽  
Bruno Facchini ◽  
Marco Pievaroli ◽  
Lorenzo Tarchi ◽  
Alberto Ceccherini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Flow Direction ◽  
Western World ◽  
Open Area ◽  
Transfer Enhancement ◽  
Test Models

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin-fin geometries, a lattice-matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice-matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height which span from a possible application in the mid chord region up to the trailing edge region of a gas turbine airfoil. For each rib height two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet sub-channel hydraulic diameter, from 2000 to 12000. Heat transfer coefficients were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, 5 in the main flow direction and 2 in the tangential one. Metal temperature was measured with embedded thermocouples and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.

scholarly journals Effect of Dimpled Surface with Straight Spoiler Turbulators on Heat Transfer and Fluid Flow Characteristics for Channel

2019 ◽  
Vol 8 (12) ◽  
pp. 298-301 ◽  
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Transfer Rate ◽  
Flow Characteristics ◽  
Transfer Enhancement ◽  
Staggered Arrangement ◽  
Fluid Flow Characteristics ◽  
And Performance

An experimental investigation has been carried out for heat transfer enhancement over dimpled surface using spoiler turbulators. The experimentation is carried out over the aluminum plate of 1000 mm x 10 mm x 5 mm and Reynolds number ranging from 10,000 to 33,000. The δ/d ratio for dimple is 0.3, which is kept constant. The pitch for dimples are varied as 16 mm, 18 mm and 20 mm. Turbulators were used over the dimples surface in inline and staggered arrangement which provides different flow structure and produces turbulence. Turbulators are mounted over dimples at an angle of 12o with respect to flat plate. Experimental results were validated using Dittus-Boelter and Blasius equations. Analysis is made using Nusselt number, friction factor and performance index. It has been found that compared to dimpled plate performance of dimpled surface with spoiler tabulator plate is higher. If we compare inline and staggered arrangement, performance of inline arrangement dimple plate with turbulator is higher compared to staggered arrangement. This is due to in staggered arrangement at some locations chocking of flow may takes place which reduces heat transfer rate.

Numerical Investigation of Heat Transfer Enhancement Due to Flow Agitators Between Fins

2021 ◽  
pp. 1-14
Author(s):  
Aditya Patki ◽  
Shankar Krishnan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Visualization ◽  
Heat Transfer Enhancement ◽  
Time Scales ◽  
Reynolds Numbers ◽  
Critical Parameters ◽  
Transfer Enhancement ◽  
Oscillation Cycle

Abstract The paper investigates the heat transfer characteristics of a channel system consisting of mean axial flow and oscillatory cross flow components. A numerical model has been developed to solve the governing equations associated with the flow. The paper identifies advection, diffusion, and oscillation time scales and intensity of squeezing in the channel as critical parameters controlling system behavior. The total Reynolds number parameter is considered in the paper to understand the combined effect of axial and transverse Reynolds numbers on the Nusselt number. Flow visualization techniques are employed to understand the boundary layer changes that occur over an oscillation cycle. Nusselt number is found to increase with a reduction in advection and oscillation time scales. A linear relationship is observed between the Nusselt number and total Reynolds number when the axial and transverse Reynolds numbers are comparable. Non-dimensional pressure drop is primarily defined by only two parameters: axial Reynolds number and squeezing fraction. The flow visualization results indicate significant heat transfer enhancement in a small fraction of the oscillation cycle characterized by flow conditions similar to Couette flow.

Numerical Simulations of Heat and Fluid Flow in Grooved Channels With Curved Vanes

2003 ◽  
Author(s):  
Matthew McGarry ◽  
Antonio Campo ◽  
Darren L. Hitt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchangers ◽  
System Performance ◽  
Vortex Formation ◽  
Electronics Cooling ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Heat And Fluid Flow

The use of vanes in grooved channels for heat transfer enhancement has received more attention in the recent years due to applications in heat exchangers and electronics cooling. The current work focuses on characterizing the vortex formation around heated elements in grooved channels with curved vanes. A computational model is developed to examine the effect that the vortices have on heat transfer and system performance for a range of Reynolds numbers of 100 to 800. These vortices explain the previously observed characteristics in system performance for geometries with the use of curved vanes. At a Reynolds number of 400 these vortices inhibit heat transfer and increase pressure drop in the channel, resulting in significant decreases in system performance.

Effects of a High Porous Material on Heat Transfer and Flow in a Circular Tube

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Koichi Ichimiya ◽  
Tetsuaki Takeda ◽  
Takuya Uemura ◽  
Tetsuya Norikuni
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Porous Material ◽  
Entropy Generation ◽  
Circular Tube ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Equivalent Diameter

This paper describes the heat transfer and flow characteristics of a heat exchanger tube filled with a high porous material. Fine copper wires (diameter: 0.5 mm) were inserted in a circular tube dominated by thermal conduction and forced convection. The porosity was from 0.98 to 1.0. The working fluid was air. The hydraulic equivalent diameter was cited as the characteristic length in the Nusselt number and the Reynolds number. The Nusselt number and the friction factor were expressed as functions of the Reynolds number and porosity. The thermal performance was evaluated by the ratio of the Nusselt number with and without a high porous material and the entropy generation. It was recognized that the high porous material was effective in low Reynolds numbers and the Reynolds number, which minimized the entropy generation existed.

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