Droplet Heat Transfer on Micropost Arrays With Hydrophobic and Hydrophilic Characteristics

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Abdullah Al-Sharafi ◽  
Bekir S. Yilbas ◽  
Haider Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Water Droplet ◽  
Adhesion Force ◽  
Spreading Rate ◽  
Heat Transfer Analysis ◽  
Wenzel State ◽  
Image Velocimetry ◽  
Number Variation ◽  
Temperature And Flow Fields

Heat transfer analysis for a water droplet on micropost arrays is carried out while mimicking the environmental conditions. Since the micropost arrays spacing size alters the state of the hydrophilicity of the surface, the size of the micropost arrays spacing is varied and the resulting heat transfer characteristics are analyzed. Spreading rate of water droplet on the micropost arrays is considered and the adhesion force for the pinning of the water droplet on the micropost arrays is presented. Temperature and flow fields are predicted and the predictions of flow velocity inside the water droplet are validated through the particle image velocimetry (PIV). The Nusselt number variation for various sizes of the micropost arrays is obtained for two droplet volumes. It is found that reducing the solid fraction of micropost array beyond ϕs = 0.25, the Cassie and Baxter state of the surface changes to the Wenzel state; in which case, hydrophobic characteristics changes to hydrophilic characteristics for the water droplet. Heat transfer from the droplet bottom gives rise to development of the buoyancy and the Marangoni currents, which in turn generate two counter rotating circulation cells. The center of circulation cells moves further in the droplet upper part for the hydrophobic droplet case. The Nusselt number attains high values for the hydrophobic droplet at micropost array spacing size b = 10 μm and hydrophobic droplet at spacing size b = 50 μm due to fin effects of the micropost arrays.

Heat Transfer Analysis of Jet Impingement Cooling on a Simulated Ceramic Matrix Composite Surface

2017 ◽  
Author(s):  
Karthik Krishna ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Matrix Composite ◽  
Ceramic Matrix Composite ◽  
Jet Impingement ◽  
Ceramic Matrix ◽  
Heat Transfer Analysis ◽  
Test Surface ◽  
Composite Surface ◽  
The Impact

Ceramic Matrix Composite is a woven material characterized by a significant level of surface waviness of 35–60μm and surface roughness of 5–6μm. To be implemented in a future gas turbine engine they will be cooled traditionally to increase power and efficiency. To analyze the CMC surface effects on heat transfer rate, an impinging circular jet on a simulated CMC surface is studied experimentally and the CMC surface is represented by a high resolution CNC machined surface. The test parameters are jet to plate distance of 7 jet diameters, oblique impingement angles of 45° and 90° and Reynolds numbers of 11,000 to 35,000. The test surface is broken down into constant temperature segments, and individual segment Nusselt number is determined and plotted for the various impingement cases studied. Area-Averaged results show negligible changes in average Nusselt number as compared to the hydrodynamically smooth surface. The impact of the CMC surface feature is negligible compared to the uncertainty in heat transfer coefficient, and therefore traditional design tools can be utilized.

Slip Gas Flow and Heat Transfer in Confined Porous Media With Different Shape Cylinders

2021 ◽  
Author(s):  
Ammar Tariq ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Flow ◽  
Velocity Slip ◽  
Heat Transfer Analysis ◽  
Variable Boundary ◽  
Flow And Heat Transfer ◽  
Multiple Relaxation Time ◽  
Permeability Increase ◽  
Boltzmann Method

Abstract With the recent advances in micro devices, an accurate gas flow and heat transfer analysis become more relevant considering the slip effect. A micro-scale, multiple-relaxation-time (MRT) lattice Boltzmann method with double distribution function approach is used to simulate flow and heat transfer through circular- and diamond-shaped cylinders at the porescale level. The velocity slip and temperature jump are captured at the boundaries using a non-equilibrium extrapolation scheme with the counter-extrapolation method. A pore-scale domain of micro-cylinders comprised of circle and diamond shape are studied. It is found that the permeability increases linearly with an increase in Knudsen number for both circular- and diamond-shaped cylinders. However, the permeability increase for circular obstacle is larger than that of the diamond one. A larger surface area for diamond cylinder will offer more resistance to flow, hence resulting in lower values. For heat transfer, the Nusselt number shows an increase with increasing Reynolds number, however, it decreases with the increase in porosity. Nusselt number values are found to be higher for a circular obstacle. A variable boundary gradient for circular obstacle could be a possible explanation for this difference.

Effect of Porous Medium in Stagnation Point Flow of Ferrofluid Due to a Variable Convected Thicked Sheet

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Maria Imtiaz ◽  
Hira Nazar ◽  
Tasawar Hayat ◽  
Ahmed Alsaedi
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Nusselt Number ◽  
Differential Equations ◽  
Stagnation Point ◽  
Skin Friction Coefficient ◽  
Stagnation Point Flow ◽  
Heat Transfer Analysis ◽  
Series Solutions ◽  
The Impact

Abstract The focus of this paper is to study the effects of stagnation point flow and porous medium on ferrofluid flow over a variable thicked sheet. Heat transfer analysis is discussed by including thermal radiation. Suitable transformations are applied to convert partial differential equations to ordinary differential equations. Convergent results for series solutions are calculated. The impact of numerous parameters on velocity and temperature is displayed for series solutions. Graphical behavior for skin friction coefficient and Nusselt number is also analyzed. Numerical values of Nusselt number are tabulated depending upon various parameters

scholarly journals Turbulent fluid flow and heat transfer analysis of heated rectangular blocks encountered in electronics enclosures

2020 ◽  
Vol 184 ◽  
pp. 01027
Author(s):  
B Ch Nookaraju
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Kinetic Energy ◽  
Vertical Channel ◽  
Reynolds Numbers ◽  
Heat Transfer Analysis ◽  
Computational Investigation ◽  
Turbulent Fluid Flow ◽  
Flow And Heat Transfer ◽  
Pressure Fall

Computational investigation of steady, two-dimensional heat transfer attributes for forced convective chaotic discharge in a vertical channel of cluster of heated rectangular sections is performed. The discharge is deemed to be periodic fully developed so that the issue is determined for two extending zone and explanation is developed to more number of sections. This structure reproduces the driven convective cooling of a cluster of engraved circuit panels confronted in computerize belongings. Two mathematical statements for k- ℇ model is used for modeling for the turbulence and the finite volume methodology is used. Computations are performed for Reynolds numbers ranging from 6000-12000, Prandtl number of 0.7 and various geometric parameters characterizing the problem. As Reynolds number steps up the Nusselt Number increases. Re-circulations undermine the local Nusselt number when matched with comparing variation from a identical plate. The velocity contours, temperature distributions, variation of turbulent kinetic energy and kinetic energy dissipation rates in a vertical channel is found. With the blocks in the cluster, pressure fall is higher in resemblance to plane duct.

Natural Convective Flow in a Three Enclosure System Involving Two High Aspect Ratio Side Enclosures Joined to a Large Square Enclosure With Interfacial Heat Generation

2003 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Heat Generation ◽  
High Aspect Ratio ◽  
Convective Flow ◽  
Square Enclosure ◽  
Number Variation ◽  
Resistance To Heat

A numerical study of free convective flow in a vertical joined three enclosure arrangement has been undertaken. In this arrangement, a vertical heated wall kept at a uniform high temperature is contained in a high aspect ratio rectangular side enclosure. This enclosure is joined to a second high aspect ratio rectangular side enclosure which has the same height as the first side enclosure, the two enclosures being separated by a vertical impermeable dividing wall which offers no resistance to heat transfer. The second side enclosure is joined to a larger square enclosure, the vertical dividing wall between these two enclosures also being impermeable and offering no resistance to heat transfer. The vertical wall of the square main flow enclosure opposite to the dividing wall is maintained at a uniform lower temperature. There is a uniform rate of heat generation in the dividing wall between the inner side enclosure and the main enclosure. The situation considered is an approximate model of a double-paned window exposed to a hot outside environment and covered by a plane blind which in turn is exposed to cooled room. In some such cases there can be significant heat generation in the blind due to the absorbtion of solar energy, this being modeled by the heat generation in the one dividing wall. The flow has been assumed to be laminar and two-dimensional and results have been obtained for a Prandtl number of 0.7. The effects of Rayleigh number, dimensionless width of the side enclosures and dimensionless heat generation rate in the blind on the Nusselt number have been investigated. The results show that for a fixed Rayleigh number and for a given dimensionless first (i.e., outer) side enclosure width, there is a minimum in the Nusselt number variation with the dimensionless width of the second side enclosure. An approximate solution for the Nusselt number variation with the dimensionless width of the second side enclosure for small values of this dimensionless width has also been derived.

Effect of Upstream Viscous Dissipation on Laminar Heat Transfer in Microtubes

2008 ◽  
Author(s):  
I. Ghai ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Distribution ◽  
Viscous Dissipation ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Number Variation ◽  
Uniform Wall ◽  
Uniform Wall Heat Flux

The effect of viscous dissipation on heat transfer in microtubes is analyzed. In particular, the effect of upstream viscous dissipation on the entrance temperature distribution and thereby on the downstream temperature field and Nusselt number is analyzed. Heat transfer characteristics of a steady laminar flow of hydrodynamically developed and thermally developing Newtonian fluid are presented. The case of adiabatic upstream preparation of the fluid and uniform wall heat flux condition in the downstream region is considered. The temperature distribution and Nusselt number variation in the thermally developing region of the tube is shown. The heat transfer characteristics are also contrasted with the solution available in literature, which assumes a uniform temperature distribution in the entrance cross section. A case study quantifying the viscous dissipation effect on water flowing through a microtube is presented.

Conjugate Heat Transfer CFD Predictions of the Surface Averaged Impingement Heat Transfer Coefficients for Impingement Cooling With Backside Cross-Flow

2013 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Reyad A. A. Abdul Hussain ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Cross Flow ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Square Array ◽  
Velocity Turbulence

A 10 row impingement heat transfer configuration with a single sided exit at the end of the impingement gap was modelled using conjugate heat transfer CFD. The predictions were compared with experimental results for an electrically heated, 6.35mm thick, metal wall of nimonic-75, which was impingement cooled. The geometry investigated was a square array of inline impingement 10 × 10 holes with X/D of 4.66 and Z/D of 3.06, where D = 3.27mm. The use of metal walls enabled the local surface averaged heat transfer coefficient h, to be estimated from an imbedded thermocouple that logged the rate of cooling when the heating was removed. Conjugate heat transfer analysis provided local h values, which were surface averaged for comparison with the measured h. The CFD results also provided velocity, turbulence and Nusselt number distributions on the target and impingement jet surfaces. The aerodynamics data enabled the pressure loss of the system to be predicted, which compared well with experimental measurements. The predicted surface distributions of Nusselt number were similar to the surface turbulence kinetic energy distributions, which demonstrated the importance of turbulence in convective heat transfer. Surface averaged heat transfer coefficients were predicted and are in good agreement with the measurements for five coolant mass flow rates. The predicted and measured results for surface averaged h were similar to measurements of other investigators for similar impingement geometries.

scholarly journals Conjugate Heat Transfer Analysis of Flat Plate Subjected to Impingement and Film Cooling

2021 ◽  
Vol 9 (9) ◽  
pp. 1667-1678
Author(s):  
Devaraj K
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flat Plate ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Jet Impingement ◽  
Heat Transfer Analysis ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Abstract: The present computational study involves a flat plate subjected to combined effect of jet impingement and film cooling. A conjugate heat transfer model in conjunction with k-ω SST turbulence model is employed to study the turbulence effects. The effect of Reynolds number varying from 389 to 2140 on static temperature, Nusselt number and film cooling effectiveness has be discussed for the blowing ratios of 0.6, 0.8, 1.0. The variation in the size of vortices formed on the impinging surface with Reynolds number is studied. It has been observed that the local Nusselt number shows a rising trend with the increase in Reynolds number, while the static temperatures follow the downfall in its values. As a result, an enhancement in the effectiveness is observed, which is credited to the capabilities of combined impingement and film cooling. At Reynolds number of 972, the coolant jet is found to be attached to the surface, for this condition the heat transfer phenomena for blowing ratios of 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 2.4, 2.6 are studied to understand the flow distribution on the plate surface. Keywords: Jet impingement, film cooling, effectiveness, conjugate heat transfer

scholarly journals Impact of heat transfer analysis on Carreau fluid-flow past a static/moving wedge

2018 ◽  
Vol 22 (2) ◽  
pp. 809-820 ◽  
Author(s):  
Hashim Ali ◽  
Masood Khan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Skin Friction ◽  
Wedge Angle ◽  
Weissenberg Number ◽  
Heat Transfer Analysis ◽  
Carreau Fluid ◽  
Opposite Behavior ◽  
Moving Wedge

The foremost aspiration of the present endeavor is to investigate the boundary-layer flow of a generalized Newtonian Carreau fluid model past a static/moving wedge. In addition, the effects of heat transfer on the flow field are also taken into account. The governing equations of the problem based on the boundary-layer approximation are changed into a non-dimensional structure by introducing the local similarity transformations. The subsequent system of ODE has been numerically integrated with fifth-order Runge-Kutta method. Influence of the velocity ratio parameter, the wedge angle parameter, the Weissenberg number, the power law index, and the Prandtl number on the skin friction and Nusselt number are analyzed. The variation of the skin friction as well as other flow characteristics has been presented graphically to capture the influence of these parameters. The results indicate that the increasing value of the wedge angle substantially accelerates the fluid velocity while an opposite behavior is noticed in the temperature field. Moreover, the skin friction coefficient for the growing Weissenberg number significantly enhances for the shear thickening fluid and show the opposite behavior of shear thinning fluid. However, the local Nusselt number has greater values in the case of moving wedge. An excellent comparison with previously published works in various special cases has been made.

Shell Side Single-Phase Experimental Heat Transfer Analysis of a Vertically Oriented Single Segmental Baffle Bundle With Dimpled Tubes

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Ahmad Abbas ◽  
Tauseef Ismail ◽  
Zahid Ayub ◽  
Adnan Ayub ◽  
Taqi Ahmad Cheema ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Single Phase ◽  
Tube Bundle ◽  
Method Comparison ◽  
Heat Transfer Analysis ◽  
Shell Side ◽  
Commercial Software ◽  
Experimental Heat ◽  
Shell And Tube

Abstract This paper presents single-phase shell side heat transfer performance of a vertically oriented shell and tube bundle. Steady-state single-phase experiments were conducted to determine the shell side Nusselt number with water and water/glycol solution as working fluids for both counter and parallel flow configurations. Experiments were carried out for Reynolds number varying from 3000 to 15,000 with Prandtl number ranging from 10 to 20. Counter flow configuration showed slightly better performance. Nusselt number correlations are presented for both configurations using a modified Wilson plot method. Comparison of results with previous studies and commercial software are presented. Thermal performance for all flow rate conditions showed close comparison to the results from a reputable commercial software. The correlation was further validated by comparing results for 30 different cases to calculations from 2 widely used commercial softwares. Comparison showed that the correlation can be used for the design of single-phase single segmental shell and tube heat exchangers.

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