Influence of Different Rib Height on Heat Transfer Augmentation in Rectangular Convergent / Divergent Channels With Continuous Ribs on Bottom Surface

2013 ◽  
Author(s):  
K. Sivakumar ◽  
E. Natarajan ◽  
N. Kulasekharan
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Performance ◽  
Rectangular Channel ◽  
Bottom Surface ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Smooth Channel ◽  
Mean Diameter

The work reported in this paper is a systematic experimental study of friction and heat transfer characteristics of divergent /convergent rectangular ducts with an inclination angle of 1° in the y-direction. Measurements were taken for a convergent / divergent rectangular channel of aspect ratio, AR = 1.25 to 1.35 with three uniform rib heights, e = 3, 6 and 9 mm the ratio between rib height (e) to hydraulic mean diameter (Dm) are 0.0348, 0.0697 and 0.1046, a constant rib pitch distance, P = 60 mm. The flow rate in terms of average Reynolds numbers based on the hydraulic mean diameter (Dm) of the channel was in a range of 20000 to 50,000 is 0.085 m. A ceramic strip of 10 mm thickness is used as a heating coil has been attached on top and bottom surfaces for the test sections. The heat transfer characteristics degraded with increase in the rib height in 90° attached ribs over smooth channel. The heat transfer performance of the divergent/convergent ducts for 3, 6 and 9 mm ribs was conducted under identical mass flow rate based on the Reynolds number. In convergent duct having three test sections each having three different size ribs 3, 6, and 9mm. Similarly, divergent section is also three different rib heights duct. So, in our experiments has totally 6 different ducts were used. In addition, the acceleration / deceleration caused by the cross section area, the divergent duct generally shows enhanced heat transfer behavior for three different rib sizes, while the convergent duct has an appreciable reduction in heat transfer performance.

Effect of droplet characteristics and rotation speed on the flow and heat transfer characteristics of mist/air cooling in a rotating ribbed two-pass rectangular channel

2016 ◽  
Vol 231 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Xinjun Wang ◽  
Feng Zhang ◽  
Daren Zheng ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Performance ◽  
Rotation Speed ◽  
Rectangular Channel ◽  
Air Cooling ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The flow and heat transfer characteristics of mist/air cooling in the rotating ribbed two-pass rectangular channel are numerically investigated using the CFD software ANSYS-CFX. In this article, a comparison in heat transfer performance between the mist/air cooling and the air-only cooling is performed. Additionally, the effect of the initial mist diameter, temperature, velocity and the channel rotation speed on the mist/air cooling performance is analysed. The results show that the droplet flow distance and Nusselt number of the mist/air cooling increase as the initial mist temperature decreases. In addition, as the initial mist diameter decreases, the diameter of mist on the whole channel decreases, resulting in the higher heat transfer, whilst the mist concentration also decreases, leading to the lower heat transfer. Therefore, there is an optimal initial mist diameter which makes the heat transfer performance best. Nevertheless, the droplet movement and heat transfer performance of mist/air cooling are nearly insensitive to the initial mist velocity. It is also noted that the Coriolis force increases with the channel rotation speed, causing the flow deflection becomes more obvious. Consequently, as the channel rotation speed increases, in the first passage the averaged Nusselt number on the trailing wall increases, and that on the leading wall decreases, while the trend in the second passage is reversed.

Numerical Investigation of Impingement Heat Transfer on Concave- and Convex-Dimpled Plate With Different Dimple Arrangements

2016 ◽  
Author(s):  
Feng Zhang ◽  
Xinjun Wang ◽  
Jun Li ◽  
Rui Tan ◽  
Dongliang Wei
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Impingement Cooling ◽  
Transfer Characteristics

The present numerical study is conducted to investigate the flow and heat transfer characteristics for impingement cooling on concave or convex dimpled plate with four different dimple arrangements. The investigation of the impingement cooling on the flat plate is also conducted to serve as a contrast and these results are compared with experimental measurements to verify the computational method. Dimples studied here are placed, relative to impingement holes, in either spanwise shifted, in staggered, in in-line, or in streamwise shifted arrangements. The flow structure, pressure loss and heat transfer characteristics of the concave and convex dimpled plate of four different dimple arrangements have been obtained and compared with flat plate for the Reynolds number range of 15000 to 35000. The results show that compared with flat plate, the added concave or convex dimples only causes a negligible increase in the pressure loss, and the pressure loss is insensitive to concave or convex dimple arrangement patterns. In addition, compared with flat plate, both spanwise shifted and staggered concave dimple arrangements show better heat transfer performance, while in-line concave dimple arrangement show worse results. Besides that, the heat transfer performance for streamwise shifted concave dimple arrangement is the worst. Furthermore, compared with flat plate, all convex dimple arrangements studied here show better heat transfer performance.

Influence of Pin Shape on Heat Transfer Characteristics of Laminated Cooling Configuration

2019 ◽  
Author(s):  
Lei Li ◽  
Honglin Li ◽  
Wenjing Gao ◽  
Fujuan Tong ◽  
Zhonghao Tang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Heat Transfer Performance ◽  
Internal Flow ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Cooling Effectiveness ◽  
Pin Fin ◽  
Blowing Ratio ◽  
Transfer Characteristics

Abstract The laminated cooling configuration can effectively enhance heat transfer and improve cooling effectiveness through combining the advantage of impingement cooling, film cooling and pin fin cooling. In this study, four laminated configurations with different pin shape including circular pin shape, curved rib pin shape, droplet pin shape and reverse droplet pin shape are numerically investigated. Extensive analysis are conducted within the blowing ratio range of 0.2–1.8 to reveal the influence of pin shape on heat transfer characteristics and cooling performance. Compared with circular pin shape, other three pin shapes can enable more complex internal flow field, which greatly affect the heat transfer performance. Among these shapes, the droplet pin shape presents the best capacity on improving heat transfer performance and distribution due to its stramlined shape and little upstream surface, especially at relatively high blowing ratio and the augmentation can be up to 7.91% under the blowing ratio of 1.7. Besides, results show that the cooling effectiveness can be enhanced by adopting curved rib pin shape and the enhancement monotonously increases as the blowing ratio increases. When blowing ratio is 1.7, the improvement can be 2.7%. The reason is that the large lateral blockage decreases the exhausted velocity and hence forms relative firm film coverage.

Convective Heat Transfer Performance of Water and FC-72 in an One Side Heated Rectangular Channel Having Pin-Fins

2008 ◽  
Author(s):  
Liang-Han Chien ◽  
S.-Y. Pei ◽  
T.-Y. Wu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Rate ◽  
Heat Transfer Performance ◽  
Rectangular Channel ◽  
Transfer Performance ◽  
Flow Rates ◽  
Finned Surface

This study investigates the convective heat transfer performance of two fluids (water and FC-72) in a one side heated rectangular channel of 20mm in width and 2mm in height. The heated side has either a smooth surface or a pin-finned surface. The inlet fluid temperature was maintained at 30°C. The total length of the test channel was 113 mm, with a heated length of 25mm. The flow rate varied between 80 and 960 ml/min, and the heat flux was between 18 and 98 W/cm2. Single phase convection was the dominant heat transfer mechanism in the present water tests, and the performance was mainly controlled by flow rate. Contrarily, the heat flux was the major factor for the heat transfer performance in FC-72 as a result of the dominant boiling effect. At a fixed flow rate, the pin-finned surface yielded up to 30% higher heat transfer coefficient and greater critical heat flux than those of a smooth surface. The convective heat transfer coefficient of FC-72 was greater than water at low flow rates (80∼160 ml/min) and heat fluxes between 18 and 35 W/cm2. However, the heat transfer performance of water was superior to FC-72 at high flow rates.

scholarly journals Numerical study on the flow and heat transfer of water-based Al2O3 forced pulsating nanofluids based on self-excited oscillation chamber structure

2021 ◽  
pp. 167-167
Author(s):  
Hong Yuan ◽  
Zhao Wang ◽  
Quan Gao ◽  
Ting Fu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Performance Index ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Excited Oscillation

In this study, the flow and heat transfer characteristics of the forced pulsating Al2O3/water nanofluid were numerically studied. The pulsating excitation of the nanofluid is provided by the Helmhertz self-excited oscillating cavity. The large eddy simulation method is used to solve the equation, and the local Nusselt number and heat transfer performance index are used to analyze the heat transfer characteristics of the nanofluid in the self-excited oscillation heat exchange tube. In addition, the effect of different downstream tube diameters on heat transfer enhancement is discussed. The research results show that the existence of the countercurrent vortex can increase the disturbance of the near-wall fluid, thereby improving the mixing degree of the near-wall fluid and the central mainstream. As the countercurrent vortex migrates downstream, pulse enhanced heat transfer is realized. Furthermore, it was also found that when the downstream tube diameter d2=1.8d1, the periodic effect of the local Nusselt number of the wall is the best and the heat transfer performance index has the most stable pulsation effect within a pulsation cycle. But when d2=2.0d1, the change curve of heat transfer performance index in a pulsating period is the highest, the maximum value is 3.95.

Investigation of the Effect of Cross Section on the Convective Heat Transfer Performance of Nanoemulsion in Microchannel Heat Exchanger

2021 ◽  
Author(s):  
Takele Gameda ◽  
M. Mehdi Kabir ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Cross Section ◽  
Cross Sections ◽  
Heat Transfer Performance ◽  
Operating Conditions ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Microchannel Heat Exchanger ◽  
Transfer Characteristics

Abstract The present study aims to numerically investigate the effect of cross section on the heat transfer performance of single-phase flow of Ethanol/Polyalphaolefin nanoemulsion fluid with ethanol concentrations of 8 wt.% in a microchannel heat exchanger. While the exterior geometry of the microchannels’ solid structure remains the same, four different cross sections of channels including: circular, upward semi-circular, rectangular, and trapezoidal, are designed with keeping the channels’ wetted perimeters, mass flow rate, and Reynolds number constant for comparison purposes. In the present study, the hydrodynamic and heat transfer characteristics, including local Nusselt number, heat transfer coefficient, and velocity profile, were investigated under a uniform wall heat flux boundary conditions within the laminar flow regime. The channel models of different cross sections were developed by the COMSOL-Multiphysics for numerical analysis. The heat transfer characteristics were then compared for different cross sections under the same operating conditions, and the effect of aspect ratio for rectangular and trapezoidal cross sections were also studied.

Heat Transfer Characteristics of Blade Internal Tip Surface by Arrays of Delta-Winglet Vortex Generator Pairs

2020 ◽  
Author(s):  
Zhiqi Zhao ◽  
Lei Luo ◽  
Dandan Qiu ◽  
Xun Zhou ◽  
Zhongqi Wang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Heat Transfer Performance ◽  
Internal Surface ◽  
Main Flow ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Bend Channel ◽  
Delta Winglet

Abstract This paper numerically investigated the effect of the arrays of the delta-winglet vortex generators (DWVGs) pairs on the flow field and heat transfer characteristics of gas turbine blade tip internal surface. Six different arrangements including three inclinations (30°, 45°, 60°) and two aspect ratios of DWVGs are calculated at Reynolds numbers ranging from 6000 to 14,000. The internal cooling passage of gas turbines are simplified as two-pass U bend channel and the U bend channel without any tabulators are considered as Baseline. The detailed flow structure, the evolution of vortices and heat transfer performance over the tip internal surface are presented. The results show that the arrays of DWVGs placed on the tip internal surface have great influence on the tip flow and heat transfer. Small-scale vortices are induced by the DWVGs, which have negligible impact on the main flow. Due to the nature of 180-deg turn, the impingement-like flow contributes the highest heat transfer performance. But too many DWVGs placed on the attachment region will weaken the energy of main flow and therefore reduce the local heat transfer. Besides, the blocked DWVGs (BVG) will enhance the heat transfer at the center line, and the guided DWVGs (GVG) will extend the low-energy flow cluster and thus weakening the heat transfer intensity. The results of this study are useful for understanding the mechanism of heat transfer characteristics in a realistic gas turbine blade by using the arrays of DWVGs.

Heat Transfer Characteristics of Oscillating Heat Pipe With Water and Ethanol as Working Fluids

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Haizhen Xian ◽  
Yongping Yang ◽  
Dengying Liu ◽  
Xiaoze Du
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Inclination Angle ◽  
Heat Transfer Performance ◽  
Filling Ratio ◽  
Working Fluid ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Oscillating Heat Pipe ◽  
Transfer Characteristics

In this paper, experiments were conducted to achieve a better understanding of the oscillating heat pipe (OHP) operating behavior with water and ethanol as working fluid. The experimental results showed that there existed a necessary temperature difference between the evaporator and the condenser section to keep the heat pipe working. The maximum effective conductivity of the water OHP reached up to 259 kW/m K, while that of the ethanol OHP is of 111 kW/m K. Not all the OHPs are operated in the horizontal operation mode. The heat transfer performance of the ethanol OHP was obviously affected by the filling ratio and the inclination angle but the influence law is irregular. The effect of the filling ratio and the inclination angle of the water OHP were smaller than that of the ethanol one. The heat transfer performance of the OHP was improved with increase of operating temperature. The startup characteristics of the OHP depended on the establishment of the integral oscillating process, which was determined by the operating factors. The startup temperature of the ethanol OHP varied from 40°C to 50°C and that of the water, OHP varied from 40°C to 60°C without considering the horizontal operating mode. The water OHP showed a better performance and more stable heat transfer characteristics than the ethanol OHP, which had no obvious advantages of the startup capability as well.

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