Heat Transfer to Turbulent Swirling Flow Through a Sudden Axisymmetric Expansion

1987 ◽  
Vol 109 (3) ◽  
pp. 613-620 ◽  
Author(s):  
P. A. Dellenback ◽  
D. E. Metzger ◽  
G. P. Neitzel
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Bulk Fluid ◽  
Maximum Heat ◽  
Flux Boundary Condition ◽  
Nusselt Numbers ◽  
Maximum Heat Transfer

Experimental data are presented for local heat transfer rates in the tube downstream of an abrupt 2:1 expansion. Water, with a nominal inlet Prandtl number of 6, was used as the working fluid. In the upstream tube, the Reynolds number was varied from 30,000 to 100,000 and the swirl number was varied from zero to 1.2. A uniform wall heat flux boundary condition was employed, which resulted in wall-to-bulk fluid temperatures ranging from 14° C to 50°C. Plots of local Nusselt numbers show a sharply peaked behavior at the point of maximum heat transfer, with increasing swirl greatly exaggerating the peaking. As swirl incressed from zero to its maximum value, the location of peak Nusselt numbers was observed to shift from 8.0 to 1.5 step heights downstream of the expansion. This upstream movement of the maximum Nusselt number was accompanied by an increase in its magnitude from 3 to 9.5 times larger than fully developed tube flow values. For all cases, the location of maximum heat transfer occurred upstream of the flow reattachment point.

Heat Transfer in Separated, Reattached, and Redevelopment Regions Behind a Double Step at Entrance to a Flat Duct

1967 ◽  
Vol 89 (2) ◽  
pp. 163-167 ◽  
Author(s):  
E. G. Filetti ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Duct Flow ◽  
Double Step ◽  
Maximum Heat ◽  
Transfer Rates ◽  
Maximum Heat Transfer ◽  
Flow Cross

Experimental data are presented for local heat transfer rates near the entrance to a flat duct in which there is an abrupt symmetrical enlargement in flow cross section. Two enlargement area ratios are considered, and Reynolds numbers, based on duct hydraulic diameter, varied from 70,000 to 205,000. It is found that such a flow is characterized by a long stall on one side and a short stall on the other. Maximum heat transfer occurs in both cases at the point of reattachment, followed by a decay toward the values for fully developed duct flow. Empirical equations are given for the Nusselt number at the reattachment point, correlated as functions of duct Reynolds number and enlargement ratio.

Effect of Periodicity of Non-Uniform Sinusoidal Side Heating on Natural Convection in an Anisotropic Porous-Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 1613-1618 ◽  
Author(s):  
S. Kapoor ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Stream Function ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Porous Enclosure

A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.

Local Heat Transfer Downstream of Abrupt Circular Channel Expansion

1970 ◽  
Vol 92 (1) ◽  
pp. 53-60 ◽  
Author(s):  
P. P. Zemanick ◽  
R. S. Dougall
Keyword(s):  
Heat Transfer ◽  
Experimental Work ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Working Fluid ◽  
Published Data ◽  
Circular Channel ◽  
Nusselt Numbers ◽  
Channel Expansion

Experimental work was performed to determine local Nusselt numbers in the region beyond an abrupt expansion in a circular channel. Three expansion geometries, ratios of upstream-to-downstream diameter of 0.43, 0.54, and 0.82, were tested with air as the working fluid. Data are shown for Reynolds numbers from 4000 to 50,000–90,000 depending on geometry. Selected comparisons with previously published data for air and water are included.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

Heat Transfer in Reciprocating Planar Curved Tube With Piston Cooling Application

2005 ◽  
Vol 128 (1) ◽  
pp. 219-229 ◽  
Author(s):  
Shyy Woei Chang ◽  
Yao Zheng
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Interactive Effects ◽  
Experimental Conditions ◽  
Nusselt Numbers ◽  
Curved Tube ◽  
The Individual ◽  
Cooling Passage ◽  
Piston Cooling

This paper describes an experimental study of heat transfer in a reciprocating planar curved tube that simulates a cooling passage in piston. The coupled inertial, centrifugal, and reciprocating forces in the reciprocating curved tube interact with buoyancy to exhibit a synergistic effect on heat transfer. For the present experimental conditions, the local Nusselt numbers in the reciprocating curved tube are in the range of 0.6–1.15 times of static tube levels. Without buoyancy interaction, the coupled reciprocating and centrifugal force effect causes the heat transfer to be initially reduced from the static level but recovered when the reciprocating force is further increased. Heat transfer improvement and impediment could be superimposed by the location-dependent buoyancy effect. The empirical heat transfer correlation has been developed to permit the evaluation of the individual and interactive effects of inertial, centrifugal, and reciprocating forces with and without buoyancy interaction on local heat transfer in a reciprocating planar curved tube.

Study of Flow and Convective Heat Transfer in a Simulated Scaled Up Low Emission Annular Combustor

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Sunil Patil ◽  
Teddy Sedalor ◽  
Danesh Tafti ◽  
Srinath Ekkad ◽  
Yong Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat ◽  
Swirling Flow ◽  
Numerical Study ◽  
Swirl Number ◽  
Maximum Heat ◽  
Number Range ◽  
Maximum Heat Transfer ◽  
Annular Combustor

Modern dry low emissions (DLE) combustors are characterized by highly swirling and expanding flows that makes the convective heat load on the gas side difficult to predict and estimate. A coupled experimental–numerical study of swirling flow inside a DLE annular combustor model is used to determine the distribution of heat transfer on the liner walls. Three different Reynolds numbers are investigated in the range of 210,000–840,000 with a characteristic swirl number of 0.98. The maximum heat transfer coefficient enhancement ratio decreased from 6 to 3.6 as the flow Reynolds number increased from 210,000 to 840,000. This is attributed to a reduction in the normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.98 for the Reynolds number range investigated. The location of peak heat transfer did not change with the increase in Reynolds number since the flow structures in the combustors did not change with Reynolds number. Results also showed that the heat transfer distributions in the annulus have slightly different characteristics for the concave and convex walls. A modified swirl number accounting for the step expansion ratio is defined to facilitate comparison between the heat transfer characteristics in the annular combustor with previous work in a can combustor. A higher modified swirl number in the annular combustor resulted in higher heat transfer augmentation and a slower decay with Reynolds number.

Optimization of Wettability Gradient for Enhancement of Thermal Performance of Micro Heat Pipes

2018 ◽  
Author(s):  
Manjinder Singh ◽  
Naresh Varma Datla ◽  
Supreet Singh Bahga ◽  
Sasidhar Kondaraju
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Variable Mass ◽  
Working Fluid ◽  
Maximum Heat ◽  
Continuous Increase ◽  
Maximum Heat Transfer ◽  
Integration Density ◽  
Heat Transfer Capacity ◽  
Micro Heat Pipes

Continuous increase in the integration density of microelectronic units necessitates the use of MHPs with enhanced thermal performance. Recently, the use of wettability gradients have been shown to enhance the heat transfer capacity of MHPs. In this paper, we present an optimization of axial wettability gradient to maximize the heat transfer capacity of the MHP. We use an experimentally validated mathematical model and interior point method to optimize the wettability gradient. For our analysis, we consider two cases wherein (i) the mass of working fluid is constrained, (ii) mass of working fluid is a design variable. Compared to MHP with uniform high wettability and filled with a fixed mass of working fluid, optimization of the wettability gradient leads to 65% enhancement in heat transfer capacity. Similar comparisons for MHP filled with variable mass of working fluid shows more than 90% increase in the maximum heat transfer capacity due to optimization of wettability gradient.

Study on the Influence of Neighbour Room Heat Transfer on the Indoor Thermal Environment in a Heating Room

2014 ◽  
Vol 1070-1072 ◽  
pp. 2006-2009
Author(s):  
Ye Wang ◽  
Tong Zou ◽  
Wen Ting Hu
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Thermal Environment ◽  
Internal Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Indoor Thermal Environment ◽  
Average Temperature ◽  
Nusselt Numbers ◽  
Temperature Filed

To obtain the influence of the neighbour room heat transfer on the radiator heat transfer characteristics and indoor thermal environment, a new k-ε model is used to numerically simulate the radiator surface heat transfer ability, indoor velocity field and temperature filed at different neighbour room heat transfer temperature differences. The results indicate that both the radiator surface temperature and the average Nusselt numbers on radiator surface are approximately increasing with the increasing neighbour room heat transfer temperature differences when the indoor average temperature is up to 18°C. At the same neighbour room heat transfer temperature difference, the local heat transfer ability is decreasing gradually from the bottom to the top of the radiator surface. The temperature gradient close to the floor is decreasing with the increasing neighbour room heat transfer temperature difference and the indoor temperature is tending to be more homogeneous. And the velocity gradients close to the ceiling and the internal surface of east wall are higher for the case that the neighbour room heat transfer is considered.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

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