scholarly journals Local heat transfer in a mixing vessel using heat flux sensors

1992 ◽  
Vol 31 (5) ◽  
pp. 1384-1391 ◽  
Author(s):  
Seungjoo Haam ◽  
Robert S. Brodkey ◽  
Julian B. Fasano
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensors

Investigation of Buoyancy Effects in Asymmetrically Heated Near-Critical Flows of Carbon Dioxide in Horizontal Microchannels Using Infrared Thermography

2021 ◽  
Author(s):  
Lindsey V. Randle ◽  
Brian M. Fronk
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Flux ◽  
Infrared Thermography ◽  
Test Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Parallel Microchannels

Abstract In this study, we use infrared thermography to calculate local heat transfer coefficients of top and bottom heated flows of near-critical carbon dioxide in an array of parallel microchannels. These data are used to evaluate the relative importance of buoyancy for different flow arrangements. A Joule heated thin wall made of Inconel 718 applies a uniform heat flux either above or below the horizontal flow. A Torlon PAI test section consists of three parallel microchannels with a hydraulic diameter of 923 μm. The reduced inlet temperature (TR = 1.006) and reduced pressure (PR = 1.03) are held constant. For each heater orientation, the mass flux (520 kgm−2s−2 ≤ G ≤ 800 kgm−2s−2) and heat flux (4.7 Wcm−2 ≤ q″ ≤ 11.1 Wcm−2) are varied. A 2D resistance network analysis method calculates the bulk temperatures and heat transfer coefficients. In this analysis, we divide the test section into approximately 250 segments along the stream-wise direction. We then calculate the bulk temperatures using the enthalpy from the upstream segment, the heat flux in a segment, and the pressure. To isolate the effect of buoyancy, we screen the data to omit conditions where flow acceleration may be important or where relaminarization may occur. In the developed region of the channel, there was a 10 to 15 percent reduction of the local heat transfer coefficients for the upward heating mode compared to downward heating with the same mass and heat fluxes. Thus buoyancy effects should be considered when developing correlations for these types of flow.

Heat-Flux Measurements for a Realistic Cooling Hole Pattern With Multiple Flow Conditions

2013 ◽  
Author(s):  
Jeremy B. Nickol ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat Transfer ◽  
Axial Direction ◽  
Local Heat ◽  
Data Sets ◽  
Adiabatic Wall ◽  
Adiabatic Cooling ◽  
Cooling Hole ◽  
Flux Measurements

Predicting cooling flow migration and its impact on surface heat flux for a turbine operating at design-corrected conditions is a challenging task. While recent data sets have provided a baseline for comparison, they have also raised many questions about comparison methods and the proper implementation of boundary conditions. Simplified experiments are helpful for bridging the gap between the experimental and computational worlds to develop the best procedures for generating predictions and correctly comparing them to experiments. To this end, a flat-plate configuration has been developed that replicates the cooling hole pattern of the pressure side of a high-pressure turbine blade. The heat transfer for this configuration is investigated for a range of flow properties of current interest to the industry using a medium-duration blowdown facility. Heat-flux measurements are obtained using double-sided Kapton heat-flux gauges arrayed in two rows in the axial direction along the centerline of the hole pattern. Gauges are located upstream of the holes, in between rows of holes, and extending far downstream of the last row of holes. New parameters are proposed for analyzing the data including a corrected Stanton number and the length-corrected heat flux reduction parameter. These parameters are used for exploring the influence of Reynolds number and blowing ratio on local heat transfer. In addition, the temperatures of the main flow and the test section walls were varied to determine the effect of cooling on the local adiabatic wall temperature and to enable comparisons using the adiabatic cooling effectiveness.

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-Flux Measurements for a Realistic Cooling Hole Pattern With Multiple Flow Conditions

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Jeremy B. Nickol ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat Transfer ◽  
Axial Direction ◽  
Local Heat ◽  
Data Sets ◽  
Adiabatic Wall ◽  
Adiabatic Cooling ◽  
Cooling Hole ◽  
Flux Measurements

Predicting cooling flow migration and its impact on surface heat flux for a turbine operating at design-corrected conditions is a challenging task. While recent data sets have provided a baseline for comparison, they have also raised many questions about comparison methods and the proper implementation of boundary conditions. Simplified experiments are helpful for bridging the gap between the experimental and computational worlds to develop the best procedures for generating predictions and correctly comparing them to experiments. To this end, a flat-plate configuration has been developed that replicates the cooling hole pattern of the pressure side of a high-pressure turbine blade. The heat transfer for this configuration is investigated for a range of flow properties of current interest to the industry using a medium-duration blowdown facility. Heat-flux measurements are obtained using double-sided Kapton heat-flux gauges arrayed in two rows in the axial direction along the centerline of the hole pattern. Gauges are located upstream of the holes, in between rows of holes, and extending far downstream of the last row of holes. New parameters are proposed for analyzing the data including a corrected Stanton number and the length-corrected heat flux reduction parameter. These parameters are used for exploring the influence of Reynolds number and blowing ratio on local heat transfer. In addition, the temperatures of the main flow and the test section walls were varied to determine the effect of cooling on the local adiabatic wall temperature and to enable comparisons using the adiabatic cooling effectiveness.

Natural Convection Local Heat Transfer on Constant-Heat-Flux Inclined Surfaces

1969 ◽  
Vol 91 (4) ◽  
pp. 511-516 ◽  
Author(s):  
G. C. Vliet
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Plate Theory ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Transfer Data ◽  
Inclined Surfaces

Experimental local heat transfer data are presented for natural convection on constant-heat-flux inclined surfaces using water and air. The data extend to Grz* Pr = 1016, cover angles from the vertical to 30 deg with the horizontal, and include the laminar, transition, and turbulent regimes. In the laminar regime the data correlate well with vertical plate theory when the gravitational component parallel to the surface is used. Transition is strongly affected by inclination, the transition Grz* Pr decreasing from near 1013 for vertical surfaces to approximately 108 for a surface at 30 deg to the horizontal. The turbulent local heat transfer data correlate using the actual gravity rather than the parallel component, and indicates a change in the Grz* Pr exponent from near 0 22 for a vertical surface to approximately 1/4 as the inclination decreases. The turbulent data can be correlated quite well by Nuz = 0.30(Grz* Pr)0.24.

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.

Evaporation Heat Transfer and Pressure Drop in Horizontal Tubes With Strip-Type Inserts Using Refrigerant 600a

1999 ◽  
Vol 122 (2) ◽  
pp. 387-391 ◽  
Author(s):  
S.-S. Hsieh ◽  
K.-J. Jang ◽  
Y.-C. Tsai
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pressure Drops ◽  
Horizontal Tubes ◽  
Evaporation Heat

Results of a study on saturated boiling heat transfer of refrigerant R-600a in horizontal tubes (ID=10.6 mm) with strip-type inserts (longitudinal strip LS with/without perforated holes and cross-strip CS inserts) are reported. Local heat transfer coefficients are measured for a range of heat flux (9.1∼31.2 kW/m2), mass velocity (8.23∼603.3 kg/m2s), and equilibrium mass quality (⩽0.8) and the influences were studied. The data were compared with the performance of the corresponding smooth tubes. Enhancement factors are presented and discussed. Pressure drop measurement was also conducted and it is found that both single-phase and two-phase pressure drops increase with increasing heat flux levels and mass velocities. [S0022-1481(00)00302-9]

Experimental Study on Heat Transfer Characteristics of Water and Ethanol Flow Boiling in Micro-Channel

2013 ◽  
Vol 330 ◽  
pp. 788-791
Author(s):  
Xia Weng ◽  
Dong Yao Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Bond Number ◽  
Micro Channel ◽  
Vapor Quality ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

The Heat transfer characteristics of water and ethanol flow boiling in micro-channel are studied. Flow boiling of different mass and heat flux is carried out in 61 parallel microchannel with hydro diameter of 0.293mm, and the local heat transfer coefficient (HTC) of is calculated. The results indicate that the HTC decreases with the increasing of vapor quality, and depends on heat flux. Two latest correlations are used to predict the experiment, and the results indicate that the Bond number plays an important role in the correlation.

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