Convective Heat Transfer From a Sphere Due to Acoustic Streaming

1993 ◽  
Vol 115 (2) ◽  
pp. 332-341 ◽  
Author(s):  
A. Gopinath ◽  
A. F. Mills
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Acoustic Streaming ◽  
Reynolds Numbers ◽  
Materials Processing ◽  
Acoustic Levitation ◽  
Simple Experiment ◽  
Wide Range ◽  
Prandtl Numbers

Convective heat transfer from a sphere due to acoustic streaming is examined for large streaming Reynolds numbers. Analytical and numerical solution techniques are used to obtain Nusselt number correlations for a wide range of Prandtl numbers with particular emphasis on the case of Pr~1. A simple experiment performed to confirm some of the predictions is described. The results obtained can be used for the thermal analysis of containerless materials processing in space using acoustic levitation.

scholarly journals Experimental Study of Forced Convective Heat Transfer in a Coiled Flow Inverter Using TiO2–Water Nanofluids

2020 ◽  
Vol 10 (15) ◽  
pp. 5225
Author(s):  
Barbara Arevalo-Torres ◽  
Jose L. Lopez-Salinas ◽  
Alejandro J. García-Cuéllar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Thermal ◽  
Convective Heat Transfer Coefficients

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed.

Development and validation of an incompressible Navier-Stokes solver including convective heat transfer

2015 ◽  
Vol 25 (4) ◽  
pp. 861-886 ◽  
Author(s):  
Konstantinos Stokos ◽  
Socrates Vrahliotis ◽  
Theodora Pappou ◽  
Sokrates Tsangaris
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Laminar Flows ◽  
Navier Stokes ◽  
Content Type ◽  
Strongly Coupled ◽  
Loosely Coupled ◽  
Wide Range ◽  
Coupled Solution

Purpose – The purpose of this paper is to present a numerical method for the simulation of steady and unsteady incompressible laminar flows, including convective heat transfer. Design/methodology/approach – A node centered, finite volume discretization technique is applied on hybrid meshes. The developed solver, is based on the artificial compressibility approach. Findings – A sufficient number of representative test cases have been examined for the validation of this numerical solver. A wide range of the various dimensionless parameters were applied for different working fluids, in order to estimate the general applicability of our solver. The obtained results agree well with those published by other researchers. The strongly coupled solution of the governing equations showed superiority compared to the loosely coupled solution as inviscid effects increase. Practical implications – Convective heat transfer is dominant in a wide variety of practical engineering problems, such as cooling of electronic chips, design of heat exchangers and fire simulation and suspension in tunnels. Originality/value – A comparison between the strongly coupled solution and the loosely coupled solution of the Navier-Stokes and energy equations is presented. A robust upwind scheme based on Roe’s approximate Riemann solver is proposed.

Numerical and Experimental Study of Flow and Convective Heat Transfer on a Rotor of a Discoidal Machine with Eccentric Impinging Jet

2019 ◽  
pp. 1-29
Author(s):  
Chadia Haidar ◽  
Rachid Boutarfa ◽  
Mohamed Sennoune ◽  
Souad Harmand
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Steady State ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Air Flow ◽  
Impinging Jet ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Air Jet

This work focuses on the numerical and experimental study of convective heat transfer in a rotor of a discoidal the machine with an eccentric impinging jet. Convective heat transfers are determined experimentally in steady state on the surface of a single rotating disk. The experimental technique is based on the use of infrared thermography to access surface temperature measurement, and on the numerical resolution of the energy equation in steady-state, to evaluate local convective coefficients. The results from the numerical simulation are compared with heat transfer experiments for rotational Reynolds numbers between 2.38×105 and 5.44×105 and for the jet's Reynolds numbers ranging from 16.5×103 to 49.6 ×103. A good agreement between the two approaches was obtained in the case of a single rotating disk, which confirms us in the choice of our numerical model. On the other hand, a numerical study of the flow and convective heat transfer in the case of an unconfined rotor-stator system with an eccentric air jet impinging and for a dimensionless spacing G=0.02, was carried out. The results obtained revealed the presence of different heat transfer zones dominated either by rotation only, by the air flow only or by the dynamics of the rotation flow superimposed on that of the air flow. Critical radii on the rotor surface have been identified

Combustor Heat Shield Impingement Cooling and its Effect on Liner Convective Heat Transfer for a Model Annular Combustor With Radial Swirlers

2015 ◽  
Author(s):  
David Gomez-Ramirez ◽  
Deepu Dilip ◽  
Bharath Viswanath Ravi ◽  
Samruddhi Deshpande ◽  
Jaideep Pandit ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Heat Shield ◽  
Impingement Cooling ◽  
Annular Combustor

Increasing pressure to reduce pollutant emissions such as NOx and CO, while simultaneously increasing the efficiency of gas turbines, has led to the development of modern gas turbine combustors operating at lean equivalence ratios and high compression ratios. These modern combustors use a large portion of the compressor air in the combustion process and hence efficient use of cooling air is critical. Backside impingement cooling is one alternative for advanced cooling in gas turbine combustors. The dome of the combustor is a primary example where backside impingement cooling is extensively used. The dome directly interacts with the flame and hence represents a limiting factor for combustor durability. The present paper studies two aspects of dome cooling: the impingement heat transfer on the dome heat shield of an annular combustor and the effect of the outflow from the spent air on the liner heat transfer. A transient measurement technique using Thermochromic Liquid Crystals (TLCs) was used to characterize the convective heat transfer coefficient on the backside of an industrial heat shield design provided by Solar Turbines, Inc. for Reynolds numbers (with respect to the hole diameter) of ∼ 1500 and ∼ 2500. Reynolds-Averaged Navier Stokes (RANS) calculations using the k-ω SST turbulence model were found to be in good agreement with the experiment. A standard heat transfer correlation for impingement hole arrays overestimated the mean heat transfer coefficient compared to the experiment and computations, however this could be explained by low biases in the results. Steady state IR measurements were performed to study the effects that the spent air from the heat shield impingement cooling had on the liner convective heat transfer. Measurements were taken for three Reynolds numbers (with respect to the hydraulic diameter of the combustor annulus) including 50000, 90000, and 130000. A downstream shift in the flow features was observed due to the secondary flow introduced by the outflow, as well as a significant increase in the convective heat transfer close to the dome wall.

Two-Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Ahmed El-Habib ◽  
Benjamin Parres
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotation Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Flux Boundary Condition

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with eight ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10%. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state liquid crystal thermography (LCT) was employed to quantify a detailed 2D distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the sixth and eighth rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15,000, 20,000, 30,000, and 40,000. The maximum rotation number values were ranging between 0.12 (Re = 40,000) and 0.30 (Re = 15,000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case, the secondary flows are responsible for high heat transfer gradients on the investigated area.

Free Convection Effects on Laminar Forced Convective Heat Transfer in a Horizontal Isothermal Tube

1982 ◽  
Vol 104 (1) ◽  
pp. 145-152 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Free Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Reynolds Numbers ◽  
Transfer Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers

The influence of free convection due to buoyancy on forced laminar flow of air in the entrance region of a horizontal isothermal tube was investigated. The Graetz numbers ranged form 2.5 to 110.0, the Reynolds numbers ranged from 120 to 1200, the Grashof numbers ranged from 0.8 × 104 to 8.7 × 104, and the ratio L/D was varied from 6 up to 46. The average Nusselt numbers based on the log-mean temperature difference, ranged from 2.0 to 25.9. The heat transfer data were correlated according to the influence of free convection which was found to have a significant effect at points close to the entrance to the tube.

scholarly journals Experimental Investigation into the Forced Convective Heat Transfer of Aqueous Fe3O4 Nanofluids under Transition Region

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Jie Ma ◽  
Yinchen Xu ◽  
Wenlie Li ◽  
Jiantao Zhao ◽  
Shuping Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Transition Region ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Forced Convective Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Initial Expectation

The forced convective heat transfer (FCHT) properties of nanofluids, made of Fe3O4 nanomaterials and deionized water, are firstly measured by a self-made forced convective heat transfer apparatus. The nanofluid flows through a horizontal copper tube in the transition region with Reynolds numbers in the range of 2500–5000. Some parameters including Reynolds number, axial distance, and mass concentration are also investigated. The preliminary results are firstly presented that the heat transfer coefficients of Fe3O4 nanofluids systematically decrease with increasing concentration of nanoparticles under transition region which contradicts the initial expectation.

Optimization of Heat Transfer Rate in the Rectangular Microchannel of Different Aspect Ratios With Constant Cross Sectional Area

2008 ◽  
Author(s):  
F. Kowsary ◽  
N. Noroozi ◽  
M. Rezaei Barmi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Cross Sectional Area ◽  
Heat Sinks ◽  
Sectional Area ◽  
Cross Sectional ◽  
Aspect Ratios

The increased power dissipation and reduced dimensions of microelectronics devices have emphasized the need for highly efficient compact cooling technologies. Microchannel heat sinks are of particular interest due to the very high rates of heat transfer they enable in conjunction with greatly reduced heat sink length scales and coolant mass flow rate. Therefore, in the present work, optimization of laminar convective heat transfer in the microchannel heat sinks is investigated for uniform heat flux and different cross sectional areas of different aspect ratios. Three-dimensional numerical simulations of general form of energy equation were performed to predict Nusselt number in the laminar flow regime. Using these results, an optimum forced convective heat transfer coefficient was computed for several cross sectional areas and Reynolds numbers, utilizing the univariable search method. Different aspect ratios have different influences on Nusselt number in thermally developing and fully developed regions for different cross sectional areas and Reynolds numbers. There exists an optimum Nusselt number for each Reynolds number and cross sectional area by varying aspect ratio. Thus, optimized state is computed and related graphs are presented.

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