scholarly journals Non-stationary convective heat transfer in an air synthetic impinging jet. Experiment and numerical simulation

2021 ◽  
Vol 2119 (1) ◽  
pp. 012024
Author(s):  
V.V. Lemanov ◽  
M.A. Pakhomov ◽  
V.I. Terekhov ◽  
Z. Travnicek
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Reynolds Stress Model ◽  
Heat Flux Sensor ◽  
Flux Sensor

Abstract An unsteady local heat transfer in an air synthetic non-steady-state jet impingement onto a flat plate with a variation of the Reynolds number, nozzle-to-plate distance and pulses frequency is experimentally and numerically studied. Measurements of the averaged and pulsating heat transfer at the stagnation point are conducted using a heat flux sensor. The axisymmetric URANS method and the Reynolds stress model are used for numerical simulations. For local values of heat transfer, zones with the maximum instantaneous value of heat flux and heat transfer coefficient are identified. The heat transfer increases at relatively low nozzle-to-plate distances (H/d ≤ 4). The heat transfer decreases at high distance from the orifice and target surface. An increase in the Reynolds number causes reduction of heat transfer.

Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces

2015 ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Coupling Effect ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Separation Distance ◽  
Plate Spacing

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.

Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

1972 ◽  
Vol 94 (1) ◽  
pp. 7-14 ◽  
Author(s):  
L. B. Newman ◽  
E. M. Sparrow ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensor ◽  
Forward Region ◽  
Number Range ◽  
Free Stream Turbulence

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

Heat Transfer of Confined Circular Jet Impingement

2001 ◽  
Vol 17 (1) ◽  
pp. 29-38
Author(s):  
Shou-Shing Hsieh ◽  
Jung-Tai Huang ◽  
Huang-Hsiu Tsai
Keyword(s):  
Heat Transfer ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Plate Spacing ◽  
Single Jet

ABSTRACTExperiments for heat transfer characteristics of confined circular single jet impingement were conducted. The effect of jet Reynolds number, jet hole-to-plate spacing and heat flux levels on heat transfer characteristics of the heated target surface was examined and presented. The local heat transfer coefficient along the surface is measured and correlations of the stagnation point, local and average Nusselt number are developed and discussed. Finally, comparisons of the present data with existing results were also made.

scholarly journals Heat Transfer and Flow Characteristics of Circular Jets Impinging on a Horizontal Flat Wall

1997 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Jung-Tai Huang
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Plate Spacing ◽  
Fundamental Understanding ◽  
Circular Jets ◽  
Single Jet

An experimental study was performed in a confined circular single jet impingement. The effect of jet Reynolds number, nozzle-to-plate spacing and heat flux levels on heat transfer characteristics of the heated target surface was examined and presented. Flow visualization was made to broaden our fundamental understanding of the physical process of the type of flow. Transition and turbulent regimes are identified. The local heat transfer coefficient along the surface is measured and correlation of the stagnation point Nusselt number are presented and discussed.

Rod Bundle Heat Transfer: Steady-State Steam Cooling Experiments

2006 ◽  
Author(s):  
J. P. Spring ◽  
D. M. McLaughlin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Steam Cooling

Through the joint efforts of the Pennsylvania State University and the United States Nuclear Regulatory Commission, an experimental rod bundle heat transfer (RBHT) facility was designed and built. The rod bundle consists of a 7×7 square pitch array with spacer grids and geometry similar to that found in a modern pressurized water reactor. From this facility, a series of steady-state steam cooling experiments were performed. The bundle inlet Reynolds number was varied from 1 400 to 30 000 over a pressure range from 1.36 to 4 bars (20 to 60 psia). The bundle inlet steam temperature was controlled to be at saturation for the specified pressure and the fluid exit temperature exceeded 550 °C in the highest power tests. One important quantity of interest is the local convective heat transfer coefficient defined in terms of the local bulk mean temperature of the flow, local wall temperature, and heat flux. Steam temperatures were measured at the center of selected subchannels along the length of the bundle by traversing miniaturized thermocouples. Using an analogy between momentum and energy transport, a method was developed for relating the local subchannel centerline temperature measurement to the local bulk mean temperature. Wall temperatures were measured using internal thermocouples strategically placed along the length of each rod and the local wall heat flux was obtained from an inverse conduction program. The local heat transfer coefficient was calculated from the data at each rod thermocouple location. The local heat transfer coefficients calculated for locations where the flow was fully developed were compared against several published correlations. The Weisman and El-Genk correlations were found to agree best with the RBHT steam cooling data, especially over the range of turbulent Reynolds numbers. The effect of spacer grids on the heat transfer enhancement was also determined from instrumentation placed downstream of the spacer grid locations. The local heat transfer was found to be greatest at locations immediately downstream of the grid, and as the flow moved further downstream from the grid it became more developed, thus causing the heat transfer to diminish. The amount of heat transfer enhancement was found to depend not only on the spacer grid design, but also on the local Reynolds number. It was seen that decreasing Reynolds number leads to greater heat transfer enhancement.

Thermal Transport From a Rotating Disk During Partially Confined Liquid Jet Impingement

2007 ◽  
Author(s):  
Jorge Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Interface Temperature

This paper presents a numerical study that characterizes the conjugate heat transfer results of a semi–confined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the confined insulated wall that ultimately gets exposed to a free surface boundary condition. The solution is made under steady state and laminar conditions. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The study considered various standard materials, namely aluminum, copper, silver, Constantan and silicon; covering a range of flow Reynolds number (220–900), under a broad rotational rate range from 0 to 750 rpm, or Ekman number (7.08×10−5 – ∞), nozzle to target spacing (β = 0.25 – 1.0), disk thicknesses to nozzle diameter ratio (b/dn = 0.25 – 1.67), Prandtl number (1.29 – 124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77) and oil (MIL-7808) as working fluids and solid to fluid thermal conductivity ratio (36.91 – 2222). High thermal conductivity plate materials maintained more uniform and lower interface temperature distributions. Higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire wall. Rotational rate increases local heat transfer coefficient under most conditions. These findings are important for the design improvement and control of semi-confined liquid jet impingement under a secondary rotation induced motion.

Local Heat Transfer in a Rotating Square Channel With Jet Impingement

1999 ◽  
Vol 121 (4) ◽  
pp. 811-818 ◽  
Author(s):  
S.-S. Hsieh ◽  
J.-T. Huang ◽  
C.-F. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient

The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Rej and ReΩ. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25 percent in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.

Confined and Submerged Liquid Jet Impingement Heat Transfer

1995 ◽  
Vol 117 (4) ◽  
pp. 871-877 ◽  
Author(s):  
S. V. Garimella ◽  
R. A. Rice
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Source ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Liquid Jet ◽  
Local Surface Temperature ◽  
Radial Outflow

The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d ≈ 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances. Correlations are proposed for the stagnation and average Nusselt numbers as functions of these parameters.

Modeling of Convective Cooling of a Rotating Disk by Partially Confined Liquid Jet Impingement

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Jorge C. Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Liquid Jet

This paper presents the results of the numerical simulation of conjugate heat transfer during a semiconfined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. This study considered various disk materials, namely, aluminum, copper, silver, Constantan, and silicon; covering a range of Reynolds number (220–900), Ekman number (7.08×10−5–∞), nozzle-to-target spacing (β=0.25–1.0), disk thicknesses to nozzle diameter ratio (b∕dn=0.25–1.67), and Prandtl number (1.29–124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77), and oil (MIL-7808) as working fluids. The solid to fluid thermal conductivity ratio was 36.91–2222. A higher thermal conductivity plate material maintained a more uniform interface temperature distribution. A higher Reynolds number increased the local heat transfer coefficient. The rotational rate also increased the local heat transfer coefficient under most conditions.

Heat Transfer Characteristics of an Impinging Jet in Crossflow

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Lei Wang ◽  
Bengt Sundén ◽  
Andreas Borg ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Velocity Ratio ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Jet In Crossflow

The heat transfer characteristics of an impinging jet into a crossflow have been investigated by the liquid crystal thermography technique. The jet nozzle is circular and is inclined at 10 deg with respect to the target wall. In a turbulent flow regime, the effects of the jet Reynolds number, the velocity ratio, and the crossflow Reynolds number on the heat transfer are examined. The results show that the heat transfer patterns are strongly affected by the jet Reynolds number and the velocity ratio. For a given jet Reynolds number, it is found that the crossflow diminishes the peak Nusselt number in the jet impingement region. However, in the wall jet region, the results suggest that the local heat transfer is nearly independent of the crossflow Reynolds number.

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