Effect of Outflow Orientation on Heat Transfer and Pressure Drop in a Triangular Duct With an Array of Tangential Jets

2000 ◽  
Vol 122 (4) ◽  
pp. 669-678 ◽  
Author(s):  
J.-J. Hwang ◽  
B.-Y. Chang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Loss Coefficient ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Characteristics

Experiments are conducted to study the heat transfer and pressure drop characteristics in a triangular duct cooled by an array of tangential jets, simulating the leading-edge cooling circuit of a turbine blade. Coolant ejected from a high-pressure plenum through an array of orifices is aimed at the leading-edge apex and exits from the radial outlets. Three different outflow orientations, namely coincident with the entry flow, opposed to the entry flow, and both, are tested for various Reynolds numbers 12600⩽Re⩽42000. A transient liquid crystal technique is used to measure the detailed heat transfer coefficients on two walls forming the leading-edge apex. Flow rate across each jet hole and the crossflow development, which are closely related to the local heat transfer characteristics, are also measured. Results show that increasing Re increases the heat transfer on both walls. The outflow orientation affects significantly the local heat transfer characteristics through influencing the jet flow together with the crossflow in the triangular duct. The triangular duct with two openings is recommended since it has the highest wall-averaged heat transfer and the moderate loss coefficient among the three outflow orientations investigated. Correlations for wall-averaged Nusselt number and loss coefficient in the triangular duct have been developed by considering the Reynolds number for three different outflow orientations. [S0022-1481(00)01204-4]

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

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.

Local and Average Heat Transfer and Pressure Drop for Refrigerants Evaporating in Horizontal Tubes

1960 ◽  
Vol 82 (3) ◽  
pp. 189-196 ◽  
Author(s):  
M. Altman ◽  
R. H. Norris ◽  
F. W. Staub
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

A test facility is described that has been constructed to investigate local heat transfer and pressure drop for evaporating or condensing refrigerants. The empirical method of B. Pierre [1] for correlating the average heat-transfer coefficients of refrigerants evaporating in horizontal tubes is presented in conjunction with the data of several authors [3–6]. Data on local heat-transfer coefficients and pressure drop are presented for Refrigerant-22 evaporating in two 4-ft-long, 0.343-in-ID straight horizontal tubes, and are correlated by a refinement of the curve proposed in [1]. The procedure of Martinelli-Nelson [9] correlated the data for local pressure drop within 15 per cent.

Heat Transfer to an Airfoil in Oscillating Flow

1971 ◽  
Vol 93 (4) ◽  
pp. 461-468 ◽  
Author(s):  
J. A. Miller ◽  
P. F. Pucci
Keyword(s):  
Heat Transfer ◽  
Oscillation Frequency ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Oscillating Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Consequent Increase

Local heat transfer coefficients to an airfoil in an oscillating stream have been measured for a range of frequencies and oscillation amplitudes. Results at moderate angles of attack are in agreement with previously reported findings. However, at large angles of attack, including those associated with stall in steady flow, a strong periodic starting vortex shed from the leading edge leads to a dramatic reattachment of the flow and consequent increase in local Nusselt Numbers of as much as five-fold. These effects are shown to be amplified by increasing oscillation frequency and amplitude.

Influence of High Mainstream Turbulence on Leading Edge Heat Transfer

1991 ◽  
Vol 113 (4) ◽  
pp. 843-850 ◽  
Author(s):  
A. B. Mehendale ◽  
J. C. Han ◽  
S. Ou
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbulence Decay ◽  
High Turbulence

The influence of high mainstream turbulence on leading edge heat transfer was studied. High mainstream turbulence was produced by a bar grid (Tu = 3.3–5.1 percent), passive grid (Tu = 7.6–9.7 percent), and jet grid (Tu = 12.9–15.2 percent). Experiments were performed using a blunt body with a semicylinder leading edge and flat sidewalls. The mainstream Reynolds numbers based on leading edge diameter were 25,000, 40,000, and 100,000. Spanwise and streamwise distributions of local heat transfer coefficients on the leading edge and flat sidewall were obtained. The results indicate that the leading edge heat transfer increases significantly with increasing mainstream turbulence intensity, but the effect diminishes at the end of the flat sidewall because of turbulence decay. Stagnation point heat transfer results for high turbulence intensity flows agree with the Lowery and Vachon correlation, but the overall heat transfer results for the leading edge quarter-cylinder region are higher than their overall correlation for the entire circular cylinder region. High mainstream turbulence tends not to shift the location of the separation-reattachment region. The reattachment heat transfer results are about the same regardless of mainstream turbulence levels and are much higher than the turbulent flat plate correlation.

A Detailed Experimental Investigation of a Perforated Heat Transfer Surface Applied to Gas Turbine Recuperators

2003 ◽  
Author(s):  
Juan C. Adams ◽  
Peter T. Ireland ◽  
Martin Cerza ◽  
James Oswald
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Compact Heat Exchangers ◽  
Heat Transfer Coefficients ◽  
Extended Surfaces

An effort is made to explain and improve the understanding of the mechanisms behind the thermo-hydraulic performance of perforated extended surfaces used in compact heat exchangers in the laminar flow regime (ReD = 400–2500). A transient liquid crystal technique, which uses Helium as operating fluid, together with digital image photographic processing have been used to provide measurements of local heat transfer coefficients for this geometry. This work has found that through the use of perforated surfaces there exists a local heat transfer enhancement benefit. It has also been found that although perforations cause a partial restart of the thermal boundary layer, a significant overall surface heat transfer enhancement may not be achieved over plain surfaces. It was also found that the distance between the fin’s leading edge and the point of last significant enhancement resulting from a perforation, linearly depends on Reynolds number. Local heat transfer coefficient measurements were validated by single blow experimentation of similar geometries. The transient single blow technique used the curve-matching method to compare predicted and experimental temperatures.

Local Condensation Heat Transfer Characteristics of Refrigerant R1234ze(E) Flow Inside a Plate Heat Exchanger

2017 ◽  
Vol 25 (01) ◽  
pp. 1750004 ◽  
Author(s):  
Mohammad Sultan Mahmud ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Cooling Water ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Plate Heat Exchanger ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Plate Heat ◽  
Heat Transfer Coefficients

In the present study, local condensation heat transfer coefficients of the R1234ze(E) inside a vertical plate heat exchanger (PHE) were investigated experimentally. In the experiment, three vertical flow channels are formed in the test section where refrigerant flows downward in the middle channel and cooling water flows upward in other two channels. The test section consists of eight plates: two of them form a channel of chevron type PHE for refrigerant flow channel, other two flat plates are set for heat transfer measurements, and another consist on cooling water flow channel. Down flow of the condensing refrigerant R1234ze(E) in the center channel releases heat to other channels of cooling water. In order to measure local heat transfer characteristics, a total of 60 thermocouples were set at middle of flow direction and also in the right and left sides of plates in test section. Experiments were conducted for mass fluxes ranging from 10[Formula: see text]kg/m2s to 50[Formula: see text]kg/m2s. The measurement results show that local heat transfer coefficients decrease with increase of wetness with different values in horizontal direction. Further, characteristics of local heat flux and wall temperature distribution as a function of distance from inlet to outlet of refrigerant channel were explored in detail.

Experimental Study on Heat Transfer Characteristics to Supercritical Hydrocarbon Fuel in a Horizontal Micro-Tube

2014 ◽  
Author(s):  
Yanchen Fu ◽  
Zhi Tao ◽  
Guoqiang Xu ◽  
Hongwu Deng ◽  
Zhouxia Jia
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Local Heat Transfer ◽  
Hydrocarbon Fuel ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fuel Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Transfer Characteristics

Supercritical hydrocarbon fuel experimental loop was constructed at Beihang University to study the heat transfer characteristics to supercritical hydrocarbon fuel. The test section, a stainless tube (1.86mm I.D., 2.26mm O.D., 1Cr18Ni9Ti) with the length of 300mm, was placed horizontally above the ground and the local heat transfer coefficients of the test section were systematically measured at fixed supercritical pressure of 5MPa. The mass flux varied from 786.5 to 1573 kg/ (m2 ·s), with the uniform heat flux from 180 to 450kW/m2 and the inlet fuel temperature ranged from 373 to 673K. The experimental investigation was confined to supercritical flows with heat addition only. Hence, heat losses were measured to be taken into consideration for every experimental condition. The experimental results were analyzed that heat transfer enhances at the reduced temperature Tb/Tpc rising from 0.95 to 1.04 and deteriorates when Tb/Tpc is larger than 1.04. The criterions of Shitman and Jackson were selected to judge the heat transfer characteristics in a horizontal micro-tube. The results indicated that buoyancy effects are ignored as the K<0.01 for the micro-scale tube and thermal acceleration is the main factor for the heat transfer characteristics. By direct comparison with an assortment of experimental data, a new correlation was proposed to be more accurate than others in predicting heat transfer phenomena for Chinese RP-3 hydrocarbon fuel in a horizontal micro-tube.

Enhanced Microchannel Heat Sinks Using Oblique Fins

2009 ◽  
Author(s):  
Yong-Jiun Lee ◽  
Poh-Seng Lee ◽  
Siaw-Kiang Chou
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Oblique fins created in a microchannel heat sink can serve to modulate the flow, resulting in local and global heat transfer enhancement. Numerical analysis of laminar flow and heat transfer in such modified microchannel heat sink showed that significant enhancement of heat transfer can be achieved with negligible pressure drop penalty. The breakage of continuous fin into oblique sections causes the thermal boundary layers to be re-initialized at the leading edge of each oblique fin and reduces the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of the smaller oblique channels causes a fraction of the flow to branch into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. The combination of the entrance and secondary flow effect results in a much improved heat transfer performance (the average and local heat transfer coefficients are enhanced by as much as 80%). Both the maximum wall temperature and temperature gradient are substantially decreased as a result.

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