Heat Transfer and Fluid Flow Characteristics in a Sessile Droplet on Oil-Impregnated Surface Under Thermal Disturbance

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Abdullah Al-Sharafi ◽  
Bekir S. Yilbas ◽  
Haider Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Field ◽  
Flow Characteristics ◽  
Surface Tension Force ◽  
Interface Temperature ◽  
Dimensionless Number ◽  
Textured Surfaces ◽  
Sessile Droplet ◽  
Experimental Conditions

The present study examines the flow field and heat transfer inside a sessile droplet on oil-impregnated surface when subjected to a small temperature difference at the droplet–oil interface. Temperature and flow fields inside the droplet are predicted and the flow velocities predicted are validated through the data obtained from a particle image velocimetry (PIV). Several images of droplets in varying sizes are analyzed and the droplet geometric features and experimental conditions are incorporated in the simulations. A polycarbonate wafer is used to texture the surface via incorporating a solvent-induced crystallization method. Silicon oil is used for impregnation of the textured surfaces. It is found that two counter-rotating circulation cells are formed in the droplet because of the combined effect of the Marangoni and buoyant currents on the flow field. A new dimensionless number (Merve number (MN)) is introduced to assess the behavior of the Nusselt and the Bond numbers with the droplet size. The Merve number represents the ratio of the gravitational force over the surface tension force associated with the sessile droplet and it differs from the Weber number. The Nusselt number demonstrates three distinct behaviors with the Merve number; in which case, the Nusselt number increases sharply for the range 0.8 ≤ MN ≤ 1. The Bond number increases with increasing the Merve number, provided that its values remain less than unity, which indicates the Marangoni current is dominant in the flow field.

Research on the Periodicity of Flow Field in a Compressor Sector Cascade

2020 ◽  
Author(s):  
Wenfeng Xu ◽  
Peng Sun ◽  
Guogang Yang
Keyword(s):  
Flow Field ◽  
Design Method ◽  
Flow Characteristics ◽  
Suction Side ◽  
Low Energy ◽  
Experimental Conditions ◽  
Flow Passage ◽  
Aerodynamic Parameters ◽  
Real Flow ◽  
Annular Cascade

Abstract Sector cascade experiments can not only be convenient to measure various aerodynamic parameters but also reveal the real flow characteristics in turbomachinery. However, the sector cascade is only a part of the whole annular cascade. The circumferential angle, the structure of the side guide plate (SGP) and the suction mode on the SGP have a great effect on the periodicity of the flow field. Therefore, the effect of structure on periodicity must be taken into consideration in order to obtain accurate data of the sector cascade experiment. In this paper, a compressor sector cascade composed of a row of adjustable guide vanes (AGVs) and a row of stators is designed. The effect of the circumferential angle, SGP structure and suction position on the periodicity is studied by numerical simulation. An optimal cascade scheme is selected for experimental research. The results show that a larger circumferential angle can weaken the effect of low-energy fluid near the SGP on the middle passages. However, given the limited experimental conditions, the circumferential angle is set at 110° which consists of 15 AGVs and 14 stators. What’s more, the SGP with the same bowed angle of AGV on both sides of the cascade can reduce the influence of the SGP on the adjacent passages and obtain a regular periodicity. The low-energy fluids still accumulate near the SGP. The suction near the stator suction side of the SGP can alleviate the blockage in the flow passage and further improve the periodicity of the cascade. Serious analysis of the experiment results have further identified that the suction near the stator suction side of SGP can make the aerodynamic parameters of the flow field uniform and lead to a good periodicity. At the same time, the feasibility of this design method is verified.

Uncoupling the Conjugate Heat Transfer Problem in a Horizontal Plate Under the Influence of a Laminar Flow

2003 ◽  
Author(s):  
Ricardo S. Va´squez ◽  
Antonio J. Bula
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Energy Equation ◽  
Transfer Problem ◽  
Heat Transfer Problem ◽  
Interface Temperature ◽  
Horizontal Plate ◽  
Steady State Condition ◽  
Heated Body

The conjugate heat transfer process of cooling a horizontal plate in steady state condition is studied. The model considers both solid and fluid regions in Cartesian coordinates. The problem was solved analytically, considering the fluid flowing in a laminar condition and hydrodynamically developed before any interaction with the heated body. The height of the fluid considered was enough to allow the generation of a thermal boundary layer without any restriction. The conservation of mass, momentum and energy equations were considered to turn the problem into a non dimensional form. The heated body presented a constant heat flux at the bottom side, and convective heat transfer at the top side in contact with the fluid. The other two boundary conditions are adiabatic. The energy equation was considered in the solid to turn it into a non dimensional form. The interface temperature was obtained from a regression using the Chebyshev polynomial approximation. As the problem deals with the cooling of a electronics components, the solution presents the mathematical solution of the energy equation for the solid, including the isothermal lines. The non dimensional form allows a thorough analysis of the problem, considering the influence of the different parameters in the conjugate heat transfer problem. The solution is compared with numerical solution of different problems, and the parameters considered are Reynolds number, plate thickness, Prandtl number, and solid thermal conductivity. The results obtained present isothermal lines, local Nusselt number, and average Nusselt number.

Numerical Study on Heat Transfer and Flow Characteristics in Double Turning Areas Ribbed Serpentine Channel With Lateral Outflow

2019 ◽  
Author(s):  
Bo-lun Zhang ◽  
Hui-ren Zhu ◽  
Tao Guo ◽  
Chun-yi Yao ◽  
Zhong-yi Fu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Study ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Suction Side ◽  
Pressure Side ◽  
Maximum Increase ◽  
Serpentine Channel ◽  
Ratio Condition

Abstract The double turning areas ribbed serpentine channel with lateral outflow is an important structure for designing the internal systems of turbine blade. The current work similarly simplifies the internal channel of the real blade. The Nusselt number and pressure coefficient distribution of the double turning areas ribbed serpentine channel with different outflow ratios are numerically researched under static and rotating conditions. The Realizable k-ε turbulence model with enhanced wall treatment is used in the numerical simulation. The inlet Reynolds number is 11000. The rotation numbers vary from 0 to 0.09. Three outflow ratios are 27%/0%/73%, 27%/49%/24% and 27%/73%/0%, respectively. The rotation radius (R) is 46.4d. The result shows that the Nusselt number distribution of the passage 3 under 27%/49%/24% outflow ratio condition is similar to that under 27%/73%/0% outflow ratio condition. There is a large low Nusselt number area in the passage 3 under Dr = 27%/0%/73% condition. The averaged area Nusselt number ratios on the suction side of the passage 1, passage 2 and passage 3 are higher than that on the pressure side under nonrotating condition. Rotation enhances heat transfer on the suction side of the passage 2, and has a positive effect on pressure side heat transfer of passage 1 and passage 3. The averaged area Nusselt number ratio of passage 3 under 27%/73%/0% outflow ratio condition is higher than that under other outflow ratio conditions. With the rotation number increasing, the pressure coefficient of the complete ribbed serpentine channel gradually increases, and the maximum increase is in the first turning area.

Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

scholarly journals Computation of heat transfer of a plane turbulent jet impinging a moving plate

2014 ◽  
Vol 18 (4) ◽  
pp. 1259-1271 ◽  
Author(s):  
Dahbia Benmouhoub ◽  
Amina Mataoui
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Field ◽  
Velocity Ratio ◽  
Local Heat Transfer ◽  
Slight Modification ◽  
Surface Velocity ◽  
Moving Plate ◽  
Jet Velocity

This study examines the performance of one point closure turbulence models in predicting of heat and momentum transfer of impinging flows. The scope of this paper is limited to impinging jet on a moving wall and heat transfer. The impinging distance is fixed to 8 thickness of the nozzle (8e) for this study. Two parameters are considered: the jet exit Reynolds number (10000?Re?25000) and the jet-surface velocity ratio (0?Rsj?4). the flow field structure at a given surface-to-jet velocity ratio is independent of the jet Reynolds number, a slight modification of the flow field is observed for low surface-to-jet velocity ratio (Rsj<0.25) whereas at higher ratios Rsj>0.25, the flow field is significantly modified. Good agreement with experimental results is obtained for surface-to-jet velocity ratio 0?Rsj?2. the purpose of this paper is to consider the case of higher of surface-to-jet velocity Rsj>2. A further study of heat transfer is achieved and shows that the stagnation points the local heat transfer coefficient have a maximum value. The local Nusselt number at the impinging region tends to decrease significantly when Rsj?1.5. The evolution of average Nusselt number is correlated according to the surface-to-jet velocity ratios for each Reynolds number.

scholarly journals Analysis of Heat and Flow Characteristics on Spray Cooling Heat Transfer with an Optimized Hexagonal Finned Heat Sink

2017 ◽  
Author(s):  
Faruk Yesildal ◽  
Kenan Yakut
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Sink ◽  
Cooling Water ◽  
Flow Characteristics ◽  
Optimization Method ◽  
Spray Cooling ◽  
Spray Angle ◽  
Operating Pressure ◽  
Taguchi Optimization

An experimental study was carried out with a hexagonal finned heat sink to obtain valuable information about the thermal and flow characteristics on spray cooling. Water was used as the refrigerant fluid and was atomized by an air-assisted atomizer and some of the variables that affect spray cooling process, such as breakup length and Sauter Mean Diameter (SMD) were obtained using appropriate correlations. The parameters most influential on the Nusselt number were determined and analyzed. Experiments were conducted for optimized conditions. The jet diameter and spray angle were determined via image processing using macroscopic aspects. Nusselt were demonstrated of hexagonal finned heat sink which optimized according to the Taguchi optimization method. The results of the spray analysis showed that SMD decreases with an increase in either air-liquid mass ratio (ALR) or operating pressure resulting in a more uniform spray. As the liquid flow rate increases in all ALR values, the heat transfer rate also increases markedly. As a results of the experiments, Nusselt number, jet width and spray angle correlations were developed. The relationship of ALR-Nu was demonstrated according to fin height and spraying time.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4772

An Approximate Theory for Developing Turbulent Free Shear Layers

1967 ◽  
Vol 89 (3) ◽  
pp. 633-640 ◽  
Author(s):  
J. P. Lamb
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Power Law ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Transverse Motion ◽  
Approximate Theory ◽  
Mean Flow ◽  
Integral Forms ◽  
Position Parameter

The development of a two-dimensional, free turbulent shear layer from an arbitrary initial velocity profile is analyzed theoretically. Included in the analysis are effects of both compressibility and heat transfer with unit turbulent Prandtl number. The mean flow is described by approximate velocity profiles containing an unknown position parameter which is dependent upon the development distance. Integral forms of the continuity and momentum equations are utilized to specify the flow characteristics along the streamline which separates the primary and secondary flow regions. By integrating a simplified form of the transverse motion equation for this dividing streamline, one is able to calculate the position parameter and thus complete the description of the developing flow field. For initial profiles of a power law type, the theory shows that the development distance required for any flow field variable to achieve a specified percentage of its asymptotic value is proportional to the free-stream Crocco number, to the power law exponent, and to the ratio of the ambient to jet stagnation temperatures. The theory is also utilized to estimate the effects of heat transfer and compressibility on the variation of growth rates for fully developed mixing zones.

Effects of Extended Jet Holes to Heat Transfer and Flow Characteristics of the Jet Impingement Cooling

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ahmet Ümit Tepe ◽  
Kamil Arslan ◽  
Yaşar Yetişken ◽  
Ünal Uysal
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Flat Surface ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Impingement Cooling ◽  
Compressor Power

In this study, effects of extended jet holes to heat transfer and flow characteristics of jet impingement cooling were numerically investigated. Cross-flow in the impinging jet cooling adversely affects the heat transfer on the target surface. The main purpose of this study is to reduce the negative effect of cross-flow on heat transfer by extending jet holes toward the target surface with nozzles. This study has been conducted under turbulent flow condition (15,000 ≤ Re  ≤  45,000). The surface of the turbine blade, which is the target surface, has been modeled as a flat plate. The effect of the ribs, placed on the target surface, on the heat transfer has been also investigated, and the results were compared with the flat surface. The parameters such as average and local Nusselt numbers on the target surface, flow characteristics, and compressor power have been examined in detail. It was obtained from the numerical results that the average Nusselt number increases with decreasing the gap between the target surface and the nozzle. In addition, the higher average Nusselt number was obtained on the flat surface than the ribbed surface. The lowest compressor power was achieved in the 5Dj nozzle gap for the flat surface and in the 4Dj nozzle gap for the ribbed surface.

Heat Transfer Enhancement due to V-Shaped Perforated Blocks in a Solar Air Heater Duct

2014 ◽  
Vol 619 ◽  
pp. 125-129 ◽  
Author(s):  
Tabish Alam ◽  
R.P. Saini ◽  
J.S. Saini
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Heated Surface ◽  
Solar Air Heater ◽  
Transfer Enhancement ◽  
Experimental Conditions ◽  
Enhancement Of Heat Transfer ◽  
Relative Pitch ◽  
Pitch Ratio

An experimental study of enhancement of heat transfer due to V-shaped perforated blockages attached to the heated surface has been presented in this paper. The duct equipped with perforated V-blocks had an aspect ratio (W/H) of 12, relative blockage height ratio (e/H) of 0.8, angle of attack (α) of 60° and open area ratio (β) of 20%, while relative pitch ratio (P/e) was varied from 4 to 12. The values of Nusselt number and friction factor of the duct with blockages were compared with values of Nusselt number and friction factor of the smooth duct operating under similar experimental conditions. It was found that there was a significant effect on the Nusselt number ratio and friction factor ratio when the pitch ratio was changed and there was exist an optimum value of pitch ratio. Thermal hydraulic performance was found to be maximum corresponding to relative pitch value of 8.

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.

Sign in / Sign up

Export Citation Format

Share Document