Effect of Uneven Wall Heating Conditions Under Different Buoyancy Numbers for a One Side Rib-Roughened Rotating Channel

2017 ◽  
Author(s):  
Zhi Wang ◽  
Roque Corral
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Field Investigation ◽  
Numerical Results ◽  
Wall Heating ◽  
Uneven Heating ◽  
A Minor ◽  
Rotating Channel ◽  
Transfer Mechanisms ◽  
Heated Case

This paper investigates the impacts of uneven wall heating conditions under different Buoyancy numbers on flow field and heat transfer performance of a rotating channel with one side smooth and one side roughened by 45 degree inclined ribs. Parametric RANS simulations were conducted under two different wall heating conditions: only ribbed wall heated, as in experiment setup, and all walls heated, under three different Buoyancy numbers. Results are compared, when available, with experimental results. Numerical results show that uneven wall heating has only a minor impact on non-rotating cases and very low buoyancy rotating cases. However, it has a significant influence, on both, the heat transfer behaviour and the flow field, when the Buoyancy number is large. In the ribbed trailing rotating tests, the all walls heated cases show significantly higher heat transfer rate than only the ribbed wall heated cases. The discrepancy is enlarged as Buoyancy number increases. The heat transfer in the all walls heated case increases monotonically with the Buoyancy number whereas in the ribbed wall heated case is slight reduced. In the ribbed leading rotating tests, the heat transfer sensitivity to the heating conditions is not conspicuous, and for both cases, the heat transfer level slightly reduced as Buoyancy number increases. The flow field investigation shows that, there is a significant displacement of main flow in the all walls heated cases than only the ribbed wall heated cases under high Buoyancy numbers. This displacement is due to the buoyancy effect and responsible for the heat transfer differences in uneven heating problems. According to the results obtained in the paper, we conclude that when buoyancy effects are relevant, the heating settings can play a significant role in the heat transfer mechanisms and therefore in the experimental and numerical results.

Effect of Uneven Wall Heating Conditions Under Different Buoyancy Numbers for a One Side Rib-Roughened Rotating Channel

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Zhi Wang ◽  
Roque Corral
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Field Investigation ◽  
Numerical Results ◽  
Navier Stokes ◽  
Wall Heating ◽  
Uneven Heating ◽  
A Minor ◽  
Rotating Channel ◽  
Heated Case

This paper investigates the impacts of uneven wall heating conditions under different buoyancy numbers on flow field and heat transfer performance of a rotating channel with one side smooth and one side roughened by 45 deg inclined ribs. Parametric Reynolds-averaged Navier–Stokes (RANS) simulations were conducted under two different wall heating conditions: only ribbed wall heated, as in experiment setup, and all walls heated, under three different buoyancy numbers. Results are compared, when available, with experimental results. Numerical results show that uneven wall heating has only a minor impact on nonrotating cases and very low buoyancy rotating cases. However, it has a significant influence, on both, the heat transfer behavior and the flow field, when the buoyancy number is large. In the ribbed trailing rotating tests, the all walls heated cases show significantly higher heat transfer rate than only the ribbed wall heated cases. The discrepancy is enlarged as buoyancy number increases. The heat transfer in the all walls heated case increases monotonically with the buoyancy number, whereas in the ribbed wall, heated case is slight reduced. In the ribbed leading rotating tests, the heat transfer sensitivity to the heating conditions is not conspicuous, and for both cases, the heat transfer level slightly reduced as the buoyancy number increased. The flow field investigation shows that there is a significant displacement of main flow in the all walls heated cases than only the ribbed wall heated cases under high buoyancy numbers. This displacement is due to the buoyancy effect and responsible for the heat transfer differences in uneven heating problems. According to the results obtained in the paper, we conclude that when buoyancy effects are relevant, the heating settings can play a significant role in the heat transfer mechanisms and therefore in the experimental and numerical results.

Saturated Pool Boiling Mechanisms During Single Bubble Heat Transfer: Comparison at Two Wall Superheats

2000 ◽  
Author(s):  
Jungho Kim ◽  
Fatih Demiray ◽  
Nagaraja Yaddanapudi
Keyword(s):  
Heat Transfer ◽  
Constant Temperature ◽  
Pool Boiling ◽  
Minor Role ◽  
Dominant Mechanism ◽  
Different Temperatures ◽  
Transient Conduction ◽  
Microlayer Evaporation ◽  
A Minor ◽  
Transfer Mechanisms

Abstract A study of single bubbles growing on a microscale heater array kept at nominally constant temperature was performed. The behavior of bubbles nucleating at a single site at two different temperatures (22.5 K and 27.5 K superheat) is compared for saturated pool boiling of FC-72 at 1 atm. It is concluded that energy is transferred from the surface through similar heat transfer mechanisms at both superheats. Microlayer evaporation was observed to play a minor role in the overall heat transfer, with microconvection/transient conduction being the dominant mechanism. Evaluation of various heat transfer models are made.

Natural Convection of Nanofluid in a Triangle Cavity with Different Angular Positions

2020 ◽  
Vol 12 (3) ◽  
pp. 325-329
Author(s):  
Mohsen Rostami ◽  
Mohammad Saleh Abadi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Natural Convection ◽  
Flow Field ◽  
Boundary Conditions ◽  
Angular Position ◽  
Numerical Results ◽  
Heat Transfer Characteristics ◽  
Current Structure ◽  
Flow And Heat Transfer

The effects of the angular position on the flow and heat transfer of the nanofluid in a triangular cavity is investigated numerically. A triangular cavity is chosen with the same boundary conditions as the published results are available. The comparison between the current numerical results with the available data is made to show the accuracy of the numerical simulation. The current structure of triangular cavity is rotated to investigate the effects of various angular positions on the flow and heat transfer characteristics of nanofluid. For this purpose, the equations of continuity, momentum and energy are solved numerically. The results show that the hot fluid is more freely penetrated into the domain by increasing of the angular position. The velocity of fluid in the flow field becomes maximum for the angle of 120 . Also, the creation of vortices in the flow field depends on the value of angular position.

Vortical Structures in Pin Fin Arrays for Turbine Cooling Applications

2019 ◽  
Author(s):  
Marcel Otto ◽  
Justin Hodges ◽  
Gaurav Gupta ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Shear Layer ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Numerical Results ◽  
Model Parameters ◽  
Flow Physics ◽  
Pin Fin ◽  
Pin Fin Arrays

Abstract Pin fin arrays are common features in the trailing edge region of turbine blades, and provide both structural integrity and increases in heat removal rates. Aforementioned pins act as fins by increasing the flow-wetted area, while also introducing complex flow structures such as von Kármán vortex shedding and horseshoe vortex systems; both directly affecting the global and local heat transfer characteristics over the endwall. The present study utilizes a wind tunnel to investigate the row to row interactions throughout a pin fin array comprised of four staggered rows, with spanwise and streamwise pitches of 2.5 pin diameters with a focus on the flow field downstream of the first row. The channel height to pin diameter ratio of 2. The Reynolds numbers tested based on pin diameter and local maximum velocity are 10,000 and 30,000. PIV is used as the experimental method of choice for acquiring quantitative flow data to study the flow field and derive high fidelity turbulence data and vortex structures with respect to the effects of the upstream rows on the pin fins downstream; this describes the underlying flow physics that drive the local Nusselt Number distribution on the cooled surface. Also, it was found that the wake structure varies over the two Reynolds Numbers significantly due to increased flow instabilities which promote shear layer separation and vortex formation. Flow acceleration due to neighboring pins confines the vortex formation in spanwise direction. The distribution of turbulent kinetic energy and the contribution of all Reynolds Stress Tensor components is reported. The turbulent scheme in the wake region is particularly anisotropic. The test section pressure drop is in agreement with literature for 30,000 Reynolds Number, but larger for smaller Reynolds Numbers. A thorough RANS simulation of the baseline case was conducted by carefully adjusting the turbulence model parameters to accurately reflect this particular experimental setup. The numerical results are in good agreement with heat transfer results and thus are utilized to further understand the underlying flow physics. However, the shear layer breakdown is underpredicted in numerical results resulting in shielded regions in the wake of the pin with artificially low heat transfer. The findings of the study contribute to better understanding of the underlying flow physics in a pin fin cooled airfoil and assist design engineers in making better internal cooling geometries.

Numerical study of uneven wall-heating effect for a one side rib-roughened cooling channel subject to rotation

2018 ◽  
Vol 122 (1257) ◽  
pp. 1697-1710
Author(s):  
Z. Wang ◽  
R. Corral
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Negative Impact ◽  
Numerical Study ◽  
Secondary Flows ◽  
Transfer Performance ◽  
Wall Heating ◽  
Significant Negative Impact ◽  
Uneven Heating ◽  
The Impact

ABSTRACTThis paper investigates the impact of the wall-heating conditions on the heat transfer performance of a rotating channel with one side smooth and one side roughened by 45° inclined ribs. Previous experimental and numerical studies for single-ribbed wall-heated channels showed that rotation has a significant negative impact on heat transfer performance. In order to investigate this uncommon behaviour, RANS simulations were conducted under three different wall-heating conditions in the present study: ribbed wall heated, all walls heated and adiabatic conditions. Numerical results show that the presence of uneven wall-heating conditions has a negligible impact on the stationary case, but it has a large influence on rotational cases, in both, the heat transfer and the flow field. The underlying reason is that in rotating cases, uneven heating results in different buoyancy effects on the trailing and leading walls of the channel that alter the main flow velocity profile. As a consequence, also secondary flows and heat transfer performance are affected.

Two-Phase Fin-Induced Turbulent Cooling for Electronic Devices Using Heat Pump Associated Micro-Gap Heat Sink

2018 ◽  
Vol 7 (3.13) ◽  
pp. 113
Author(s):  
Shugata Ahmed ◽  
Erwin Sulaeman ◽  
Ahmad Faris Ismail ◽  
Muhammad Hasibul Hasan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Field ◽  
Heat Transfer Rate ◽  
Heat Pump ◽  
Transfer Rate ◽  
Electronic Devices ◽  
Numerical Results ◽  
Two Phase ◽  
Heater Temperature

High energy requirement for electronic cooling is a major problem to operate high performance computers and data centres. Developing low cost thermal management systems for micro-electronic devices and micro-electro-mechanical systems (MEMS) is a cutting edge research area. A heat pump system associating micro-gap evaporator with internal micro-fins is a potential candidate for two-phase cooling of these advanced devices. Micro-fins induce pseudo-turbulence in the flow field, which escalates heat transfer rate. In this paper, the system performance of a heat pump using micro-gap evaporator has been investigated numerically and experimentally. As heat transfer rate in the micro-gap evaporator is influenced by turbulence generation, flow field in the inlet and outlet manifolds have been visualized in the numerical simulation to observe fin-induced pseudo-turbulence at the entrance and outlet of the micro-gap evaporator. The simulation has been performed using FLUENT 14.5 release. Experimental work has been carried out to validate numerical results. For experimentation purpose, a test rig has been developed, which contains a test section accommodating the micro-gap evaporator. A heater is provided at the bottom of the evaporator to supply uniform heat flux ranging 1 ~ 8 kW/m2. A pre-heater is installed at the compressor outlet to vary refrigerant temperature at the condenser inlet. The range of pre-heater temperature is 93 ~ 159°C. A variable speed compressor is used. The input frequency to the compressor is varied within the range of  20 ~ 50 Hz to run the compressor at different speeds. Experimental data show good agreement with numerical results. It is observed that in transient state, temperatures and pressures at different locations of the test apparatus fluctuate due to quasi-periodic dry out and surface rewetting nature of the flow. When pre-heater temperature is set at 159⁰C and compressor frequency is increased from 20 Hz to 30 Hz, evaporator wall heat flux escalates 118.2% and heat transfer rate of the condenser increases 65.2%. However, heat transfer rate declines with the further increment of compressor frequency. Coefficient of performance (COP) of the heat pump also increases with the frequency increment from 20 Hz to 30 Hz and declines after surpassing 40 Hz frequency. 

Detailed Investigation on Rib Turbulated Flow Inside a Rectangular Duct

2012 ◽  
Author(s):  
Md. Shaukat Ali ◽  
A. Tariq ◽  
B. K. Gandhi
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Enhancement ◽  
Field Investigation ◽  
Wall Turbulence ◽  
Internal Cooling ◽  
Rectangular Duct ◽  
Transfer Enhancement ◽  
Cross Sectional ◽  
Rib Turbulators

Rib turbulators are the most intensively studied passive technique, which promotes near wall turbulence in the internal cooling passages of heat transfer devices. However, there exists the tradeoff between the pressure penalty and heat transfer enhancement. For suggesting a correct rib configuration for particular application, it is necessary to understand the flow mechanism behind rib tabulators. For this purpose an experimental setup has been designed to investigate the detailed flow field and corresponding effect on heat transfer characteristics using Particle Image Velocimetry and Liquid Crystal Thermography respectively. In the literature the detailed flow field investigation as well as the thermal characterizations behind the rib other than rectangular/square cross sectional shape is found to be limited. The present work is an experimental investigation inside a rectangular duct for flow behind the trapezoidal type of rib with changing angle at different Reynolds numbers. The emphasis is towards assessing the potential impact of varying chamfering angle over the flow structures and its subsequent effect on heat transfer enhancement as well as in obviating the hot spots in the vicinity behind the chamfered rib turbulators.

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