Predictions of Heat Transfer Coefficients and Pressure Drops to Supercritical Pressure HCFC22 Flowing in a Small Tube

2014 ◽  
Author(s):  
Chen-Ru Zhao ◽  
Pei-Xue Jiang ◽  
Han-Liang Bo
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Thermophysical Properties ◽  
Supercritical Pressure ◽  
Buoyancy Effect ◽  
Transfer Coefficients ◽  
Flow Acceleration ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Small Tube

In this paper, experimental flow and heat transfer data of supercritical pressure HCFC22 flowing in a uniformly heated smooth tube with inner diameter of 1.004 mm at p/pc=1.1 obtained by the authors are analyzed accounting for the influence of the thermophysical properties variation, the buoyancy effect, as well as the flow acceleration effect due to thermal expansion. These analyses indicate that both of the sharp thermophysical properties variation in the fluid adjacent to the wall with low density, low specific heat and low thermal conductivity and the flow acceleration effect due to thermal expansion have significant negative effects on the heat transfer under the present study conditions for HCFC22, while for the friction factor, the thermophysical properties variation is the predominant factor. The buoyancy effect on the flow and heat transfer is negligible. A new semi-empirical local heat transfer correlation accounting for the thermophysical properties variation and the flow acceleration effect due to thermal expansion for supercritical pressure fluids flowing through a vertical small tube during heating is proposed. The predicted values agree with 95% of the measured data within ±25%. In addition, a flow correlation with thermophysical properties variation correction terms to predict the friction factors for supercritical pressure fluids is proposed which predicts the measured friction factors within ±25%.

Study of the Effect of Buoyancy on Flow and Heat Transfer of Supercritical Pressure Water in Horizontal Pipes

2011 ◽  
Author(s):  
Shuiqing Yu ◽  
Huixiong Li ◽  
Xianliang Lei ◽  
Yifan Zhang ◽  
Tingkuan Chen
Keyword(s):  
Heat Transfer ◽  
Specific Heat ◽  
Local Heat Transfer ◽  
Supercritical Pressure ◽  
Buoyancy Effect ◽  
Transfer Coefficients ◽  
Horizontal Pipes ◽  
Flow And Heat Transfer ◽  
Pressure Water ◽  
Supercritical Pressure Water

The present paper is devoted to clarify the effect of buoyancy on the flow and heat transfer of supercritical pressure water flowing in horizontal pipes at supercritical pressures. A series of experiments have been designed and carried out in Xi’an Jiaotong University, Xi’an, China to obtain data in relation to flow and heat transfer of supercritical pressure water in pipes with different arrangements. The experimental parameters are as follows: pressures ranging from 23 to 28MPa, heat flux being up to 600 kW/m2, and the fluid mass fluxes being in the range from 100 to 1000kg/(m2s). In this study, distributions of the local wall temperatures and the local heat transfer coefficients around the circumference of the tube are measured at different cross-sections along the flowing direction. On the basis of the experimental data obtained in the study, some criteria available in open literatures, including Gr/Re2.7, Gr/Re2, and Grq/Grth, are employed to estimate the magnitude of buoyancy and the effect of buoyancy on the flow and heat transfer behavior of the supercritical fluid. It is showed that buoyancy is of particular importance for horizontal flows, but play significantly different role in different regions having different characteristics of the specific heat capacity. Strong buoyancy effect exists in the large specific heat region, but in the enthalpy region which is far away from the LSHR, the discrepancy between the temperature of the top wall and that of the bottom wall is small, indicating that the buoyancy effect can be negligible. Based on the present study, it was found that the criteria Grq/Grth is better than others in terms of the capability of evaluating the effect of the buoyancy on the flow and heat transfer of supercritical water.

Direct numerical simulation of convective heat transfer of supercritical pressure in a vertical tube with buoyancy and thermal acceleration effects

2021 ◽  
Vol 927 ◽  
Author(s):  
Y.L. Cao ◽  
R.N. Xu ◽  
J.J. Yan ◽  
S. He ◽  
P.X. Jiang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flow ◽  
Vertical Tube ◽  
Supercritical Pressure ◽  
Dominant Factor ◽  
Turbulent Structures ◽  
Flow Acceleration ◽  
Flow And Heat Transfer

Supercritical pressure fluids are widely used in heat transfer and energy systems. The benefit of high heat transfer performance and the successful avoidance of phase change from the use of supercritical pressure fluids are well-known, but the complex behaviours of such fluids owing to dramatic thermal property variations pose strong challenges to the design of heat transfer applications. In this paper, the turbulent flow and heat transfer of supercritical pressure $\textrm {CO}_2$ in a small vertical tube influenced by coupled effects of buoyancy and thermal acceleration are numerically investigated using direct numerical simulation. Both upward and downward flows with an inlet Reynolds number of 3540 and pressure of 7.75 MPa have been simulated and the results are compared with corresponding experimental data. The flow and heat transfer results reveal that under buoyancy and thermal acceleration, the turbulent flow and heat transfer exhibit four developing periods in which buoyancy and thermal acceleration alternately dominate. The results suggest a way to distinguish the dominant factor of heat transfer in different periods and a criterion for heat transfer degradation under the complex coupling of buoyancy and thermal acceleration. An analysis of the orthogonal decomposition and the generative mechanism of turbulent structures indicates that the flow acceleration induces a stretch-to-disrupt mechanism of coherent turbulent structures. The significant flow acceleration can destroy the three-dimensional flow structure and stretch the vortices resulting in dissipation.

scholarly journals Investigations of Flow and Heat Transfer Characteristics in a Channel Impingement Cooling Configuration with a Single Row of Water Jets

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4327
Author(s):  
Min-Seob Shin ◽  
Santhosh Senguttuvan ◽  
Sung-Min Kim
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Channel Height ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Average Heat ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The present study experimentally and numerically investigates the effect of channel height on the flow and heat transfer characteristics of a channel impingement cooling configuration for various jet Reynolds numbers in the range of 2000–8600. A single array consisting of eleven jets with 0.8 mm diameter injects water into the channel with 2 mm width at four different channel heights (3, 4, 5, and 6 mm). The average heat transfer coefficients at the target surface are measured by maintaining a temperature difference between the jet exit and the target surface in the range of 15–17 °C for each channel height. The experimental results show the average heat transfer coefficient at the target surface increases with the jet Reynolds number and decreases with the channel height. An average Nusselt number correlation is developed based on 85 experimentally measured data points with a mean absolute error of less than 4.31%. The numerical simulation accurately predicts the overall heat transfer rate within 10% error. The numerical results are analyzed to investigate the flow structure and its effect on the local heat transfer characteristics. The present study advances the primary understanding of the flow and heat transfer characteristics of the channel impingement cooling configuration with liquid jets.

scholarly journals Measurement of Unsteady Flow and Heat Transfer in a Linear Turbine Cascade

1992 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Unsteady Flow ◽  
Boundary Layers ◽  
Suction Side ◽  
Turbine Cascade ◽  
Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Background Turbulence ◽  
Hot Film

A detailed experimental study has been conducted on the wake-induced unsteady flow and heat transfer in a linear turbine cascade. The unsteady wakes with passing frequencies in the range zero to 240 Hz were generated by moving cylinders on a squirrel cage device. The velocity fields in the blade-to-blade flow and in the boundary layers were measured with hot-wire anemometers, the surface pressures with a pressure transducer and the heat transfer coefficients with a glue-on hot film. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar on the pressure side in all cases and in the case without wakes also on the suction side. On the latter, the wakes generated by the moving cylinders caused transition, and the beginning of transition moves forward as the cylinder-passing frequency increases. Unlike in the flat-plate study of Liu and Rodi (1991a) the instantaneous boundary layer state does not respond to the passing wakes and therefore does not vary with time. The heat transfer increases under increasing cylinder-passing frequency even in the regions with laminar boundary layers due to the increased background turbulence.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Enhanced Heat Transfer in a Flat Rectangular Duct With Streamwise-Periodic Disturbances at One Principal Wall

1983 ◽  
Vol 105 (4) ◽  
pp. 851-861 ◽  
Author(s):  
E. M. Sparrow ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Local Maxima ◽  
Periodic Disturbances ◽  
Pressure Distributions ◽  
Friction Factors

Experiments were performed in a flat rectangular duct to determine the heat transfer and pressure drop response to periodic, rod-type disturbance elements situated adjacent to one principal wall and oriented transverse to the flow direction. In a portion of the experiments, heat transfer occurred only at the rodded wall, while in the remainder, heat was transferred at both principal walls of the duct. Highly detailed axial distributions of the local heat transfer coefficient were obtained. These distributions revealed the rapid establishment of a periodic (i.e., cyclic) fully developed regime as well as recurring local maxima and minima. Cycle-average, fully developed heat transfer coefficients were evaluated and were found to be much larger than those for a smooth-walled duct. Linear pressure distributions were measured between periodically positioned stations in the fully developed region, and the corresponding friction factors were several times greater than the smooth-duct values. The heat transfer and friction data were very well correlated using parameters that take account of the effective surface roughness associated with the disturbance rods.

Characterization of the Effect of Corrugation Angles on Hydrodynamic and Heat Transfer Performance of Four-Start Spiral Tubes

2001 ◽  
Vol 123 (6) ◽  
pp. 1149-1158 ◽  
Author(s):  
X. D. Chen ◽  
X. Y. Xu ◽  
S. K. Nguang ◽  
Arthur E. Bergles
Keyword(s):  
Heat Transfer ◽  
Evaluation Criteria ◽  
Geometry Optimization ◽  
Longitudinal Direction ◽  
Experimental Results ◽  
Neural Network Modeling ◽  
Transfer Coefficients ◽  
Correlation Models ◽  
Friction Factors ◽  
Double Pipe

A series of four-start spirally corrugated tubes has been subjected to heat transfer and hydrodynamic testing in a double-pipe heat exchanger. The study has been focused on the non-symmetric nature of the corrugation angles along the longitudinal direction. Both friction factors and heat transfer coefficients inside the tubes have been correlated against various process parameters. It can be shown that by altering the internal non-symmetric wavy shapes of the tubes, one is able to manipulate heat transfer and friction characteristics. The experimental results have been compared with some popular correlation models developed previously for both friction and heat transfer for corrugated tubes. Considerable differences between the experimental results and the predictions made using the existing correlations have been found and the probable causes have been discussed. Performance evaluation criteria are presented using the standard constant power criterion. A neural network modeling approach has been taken so that, based on the limited data, one can generate the contour showing the effect of corrugation angle on heat transfer coefficient for geometry optimization purposes.

scholarly journals Effect of the size of graded baffles on the performance of channel heat exchangers

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 767-775 ◽  
Author(s):  
Djamel Sahel ◽  
Houari Ameur ◽  
Touhami Baki
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Computer Code ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Enhancement Of Heat Transfer ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Friction Factors

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 ? 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%

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