scholarly journals The role of large-scale vortical structures in transient convective heat transfer augmentation

2013 ◽  
Vol 718 ◽  
pp. 89-115 ◽  
Author(s):  
David O. Hubble ◽  
Pavlos P. Vlachos ◽  
Tom E. Diller
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Vortical Structure ◽  
Time Resolved ◽  
Vortical Structures ◽  
Heat Transfer Augmentation

AbstractThe physical mechanism by which large-scale vortical structures augment convective heat transfer is a fundamental problem of turbulent flows. To investigate this phenomenon, two separate experiments were performed using simultaneous heat transfer and flow field measurements to study the vortex–wall interaction. Individual vortices were identified and studied both as part of a turbulent stagnation flow and as isolated vortex rings impacting on a surface. By examining the temporal evolution of both the flow field and the resulting heat transfer, it was observed that the surface thermal transport was governed by the transient interaction of the vortical structure with the wall. The magnitude of the heat transfer augmentation was dependent on the instantaneous strength, size and position of the vortex relative to the boundary layer. Based on these observations, an analytical model was developed from first principles that predicts the time-resolved surface convection using the transient properties of the vortical structure during its interaction with the wall. The analytical model was then applied, first to the simplified vortex ring model and then to the more complex stagnation region experiments. In both cases, the model was able to accurately predict the time-resolved convection resulting from the vortex interactions with the wall. These results reveal the central role of large-scale turbulent structures in the augmentation of thermal transport and establish a simple model for quantitative predictions of transient heat transfer.

Convective Heat Transfer in Turbulent Flow Near a Gap

2006 ◽  
Vol 128 (7) ◽  
pp. 701-708 ◽  
Author(s):  
D. Chang ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Vortical Structures

Convective heat transfer in a rectangular duct containing a heated rod forming a narrow gap with a plane wall has been simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with a Reynolds stress model. Of particular interest is the role of quasi-periodic coherent structures in transporting fluid and heat across the gap region. It is shown that the local instantaneous velocity and temperature vary widely because of large-scale transport by coherent vortical structures forming in pairs on either side of the rod.

Role of blood as heat source or sink in human limbs during local cooling and heating

1994 ◽  
Vol 76 (5) ◽  
pp. 2084-2094 ◽  
Author(s):  
M. B. Ducharme ◽  
P. Tikuisis
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Steady State ◽  
Heat Source ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Total Heat Loss ◽  
Partial Immersion ◽  
Thermal Steady State

The objective of the present study was to investigate the relative contribution of the convective heat transfer in the forearm and hand to 1) the total heat loss during partial immersion in cold water [water temperature (Tw) = 20 degrees C] and 2) the heat gained during partial immersion in warm water (Tw = 38 degrees C). The heat fluxes from the skin of the forearm and finger were continuously monitored during the 3.5-h immersion of the upper limb (forearm and hand) with 23 recalibrated heat flux transducers. The last 30 min of the partial immersion were conducted with an arterial occlusion of the forearm. The heat flux values decreased during the occlusion period at Tw = 20 degrees C and increased at Tw = 38 degrees C for all sites, plateauing only for the finger to the value of the tissue metabolic rate (124.8 +/- 29.0 W/m3 at Tw = 20 degrees C and 287.7 +/- 41.8 W/m3 at Tw = 38 degrees C). The present study shows that, at thermal steady state during partial immersion in water at 20 degrees C, the convective heat transfer between the blood and the forearm tissue is the major heat source of the tissue and accounts for 85% of the total heat loss to the environment. For the finger, however, the heat produced by the tissue metabolism and that liberated by the convective heat transfer are equivalent. At thermal steady state during partial immersion in water at 38 degrees C, the blood has the role of a heat sink, carrying away from the limb the heat gained from the environment and, to a lesser extent (25%), the metabolic and conductive heats. These results suggest that during local cold stress the convective heat transfer by the blood has a greater role than that suggested by previous studies for the forearm but a lesser role for the hand.

Enclosure Phenomenon in Varying Forced Flow Convection

2019 ◽  
Author(s):  
Ribhu Bhatia ◽  
Sambit Supriya Dash ◽  
Vinayak Malhotra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Relative Effectiveness ◽  
Convection Heat Transfer ◽  
Forced Flow ◽  
Forced Convective Heat Transfer

Abstract Systematic experimentation was carried out on forced convection heat transfer apparatus under varying non-linear flow conditions to understand the energy transfer as heat, with the purpose of enhancing performance of numerous engineering applications. Plate orientations, types of enclosures (solid, meshed, perforated), flow velocity variations etc. are taken as governing parameters to effect convective heat transfer phenomenon which is perceived as deviations in value of heat transfer coefficient. RV zonal system is utilized to simplify the fundamental understanding of heat transfer coefficient variation with surface orientation under varying flow field. The objectives of this work are as follows: 1) To establish relative effectiveness of forced convective heat transfer under varying flow field. 2) To investigate the implications of varying shapes and sizes of perforations on confined forced convective heat transfer. To understand the controlling mechanism and role of key controlling parameters.

Multiple-arrayed pressure measurement for investigation of the unsteady flow structure of a reattaching shear layer

2002 ◽  
Vol 463 ◽  
pp. 377-402 ◽  
Author(s):  
INWON LEE ◽  
HYUNG JIN SUNG
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Vortical Structure ◽  
Single Point ◽  
Pressure Fluctuations ◽  
Vortical Flow ◽  
Recirculation Region ◽  
Stream Velocity ◽  
Vortical Structures ◽  
Wall Pressure Fluctuations

Spatio-temporal characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated through an extensive pressure-velocity joint measurement with an array of microphones. The experiment was performed in a wind tunnel with a Reynolds number of 33 000 based on the step height and the free-stream velocity. Synchronized wavelet maps showed the evolutionary behaviour of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. To see the relationship between the flow field and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering, termed ‘spatial box filtering’ (SBF), was introduced and examined. The vortical flow field was reconstructed using every single-point velocity measurement by means of the conditional average based on the SBF second mode of pressure fluctuations. The flow field showed a well-organized spanwise vortical structure convected with a speed of 0.6U0 and a characteristic ‘sawtooth’ pattern of the unsteady trace of reattachment length. In addition to the coherent vortical structures, the periodic enlargement/shrinkage process of the recirculation region owing to apping motion was analysed. The recirculation region was found to undergo an enlargement/shrinkage cycle in accordance with the lowpass-filtered component of pressure fluctuations. In addition, such modulatory behaviour of the vortical structure as the global oscillation phase was discussed in connection with the conditionally averaged flow field.

Experimental investigation of convective heat transfer augmentation for car radiator using ZnO–water nanofluids

Energy ◽  
2015 ◽  
Vol 84 ◽  
pp. 317-324 ◽  
Author(s):  
Hafiz Muhammad Ali ◽  
Hassan Ali ◽  
Hassan Liaquat ◽  
Hafiz Talha Bin Maqsood ◽  
Malik Ahmed Nadir
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Transfer Augmentation

Experimental and Numerical Investigation of Convective Heat Transfer in a Gas Turbine Can Combustor

2009 ◽  
Author(s):  
Sunil Patil ◽  
Santosh Abraham ◽  
Danesh Tafti ◽  
Srinath Ekkad ◽  
Yong Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Swirl Number ◽  
Number Range ◽  
Heat Transfer Augmentation ◽  
Peak Location

Experiments and numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under cold flow conditions in a Reynolds number range between 50,000 and 500,000 with a characteristic swirl number of 0.7. It is observed that the flow field in the combustor is characterized by an expanding swirling flow which impinges on the liner wall close to the inlet of the combustor. The impinging shear layer is responsible for the peak location of heat transfer augmentation. It is observed that as Reynolds number increases from 50,000 to 500,000, the peak heat transfer augmentation ratio (compared to fully-developed pipe flow) reduces from 10.5 to 2.75. This is attributed to the reduction in normalized turbulent kinetic energy in the impinging shear layer which is strongly dependent on the swirl number that remains constant at 0.7 with Reynolds number. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change.

Convective Heat Transfer and Aerodynamics in Axial Flow Turbines

2001 ◽  
Vol 123 (4) ◽  
pp. 637-686 ◽  
Author(s):  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Pressure Distribution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Surface Pressure ◽  
Three Dimensional ◽  
Axial Flow ◽  
Time Resolved ◽  
Surface Pressure Distribution ◽  
Definition Of

The primary focus of this paper is convective heat transfer in axial flow turbines. Research activity involving heat transfer generally separates into two related areas: predictions and measurements. The problems associated with predicting heat transfer are coupled with turbine aerodynamics because proper prediction of vane and blade surface-pressure distribution is essential for predicting the corresponding heat transfer distribution. The experimental community has advanced to the point where time-averaged and time-resolved three-dimensional heat transfer data for the vanes and blades are obtained routinely by those operating full-stage rotating turbines. However, there are relatively few CFD codes capable of generating three-dimensional predictions of the heat transfer distribution, and where these codes have been applied the results suggest that additional work is required. This paper outlines the progression of work done by the heat transfer community over the last several decades as both the measurements and the predictions have improved to current levels. To frame the problem properly, the paper reviews the influence of turbine aerodynamics on heat transfer predictions. This includes a discussion of time-resolved surface-pressure measurements with predictions and the data involved in forcing function measurements. The ability of existing two-dimensional and three-dimensional Navier–Stokes codes to predict the proper trends of the time-averaged and unsteady pressure field for full-stage rotating turbines is demonstrated. Most of the codes do a reasonably good job of predicting the surface-pressure data at vane and blade midspan, but not as well near the hub or the tip region for the blade. In addition, the ability of the codes to predict surface-pressure distribution is significantly better than the corresponding heat transfer distributions. Heat transfer codes are validated against measurements of one type or another. Sometimes the measurements are performed using full rotating rigs, and other times a much simpler geometry is used. In either case, it is important to review the measurement techniques currently used. Heat transfer predictions for engine turbines are very difficult because the boundary conditions are not well known. The conditions at the exit of the combustor are generally not well known and a section of this paper discusses that problem. The majority of the discussion is devoted to external heat transfer with and without cooling, turbulence effects, and internal cooling. As the design community increases the thrust-to-weight ratio and the turbine inlet temperature, there remain many turbine-related heat transfer issues. Included are film cooling modeling, definition of combustor exit conditions, understanding of blade tip distress, definition of hot streak migration, component fatigue, loss mechanisms in the low turbine, and many others. Several suggestions are given herein for research and development areas for which there is potentially high payoff to the industry with relatively small risk.

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