The Experts below are selected from a list of 117 Experts worldwide ranked by ideXlab platform
Haijun Wang - One of the best experts on this subject based on the ideXlab platform.
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development of a new forced convection heat transfer Correlation for co2 in both heating and cooling modes at supercritical pressures
International Journal of Thermal Sciences, 2011Co-Authors: Alan Michael Kruizenga, Yushan Luo, Mark Anderson, Michael L Corradini, Haijun WangAbstract:Abstract Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures in a prototypic printed circuit heat exchanger under both cooling and heating conditions have been performed in this present study. The experiment test section has nine semi-circular channels with a hydraulic diameter of 1.16 mm and a length of 0.5 m. Primary operational parameters include inlet pressure of 7.5–10 MPa, mass fluxes of 326 kg/m 2 s and 762 kg/m 2 s, inlet temperatures from 10 °C to 90 °C and the average heat flux was 30 kW/m 2 . Beyond reproducing the regular experimental cases, numerical modeling also implemented higher heat fluxes of 60 kW/m 2 and 90 kW/m 2 in order to investigate the effect of heat flux. Good agreement was found between the experiments and FLUENT simulations using an SST k – w model with the near-wall region being completely resolved. The distinctive behavior of convection heat transfer at supercritical pressures between heating and cooling modes was systematically analyzed. A more physically reasonable property-averaging technique, Probability Density Function (PDF)-based time-averaged property, was developed to account for the effect of nonlinear dependency of properties on instantaneous local temperature. Furthermore, experimental and computational data were compared to empirical predictions by the Dittus–Boelter and Jackson Correlations. The results showed that Dittus–Boelter Correlation has better precision for the average value of the predicted heat transfer coefficient but cannot take account of the effect of heat flux. In contrast, the Jackson Correlation, with property ratio correction terms to account for the distribution of the properties in the radial direction, could predict the distinction of heat transfer characteristics under heating and cooling conditions. However, it overestimates the average value of heat transfer coefficient in the whole range of the experiment conditions. Finally, a new Correlation evaluated by PDF-based time-averaged properties for forced convection heat transfer of CO 2 in both heating and cooling mode at supercritical pressures was developed. Comparison of experimental and computational data with the prediction results by the new developed Correlation reveals that it works quite well; i.e., more than 90% data in either heating or cooling mode with various heat fluxes are predicted within an accuracy of ±25%.
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experimental investigation on heat transfer from a heated rod with a helically wrapped wire inside a square vertical channel to water at supercritical pressures
Nuclear Engineering and Design, 2009Co-Authors: Haijun Wang, Yushan Luo, Xiaobao Shi, Tingkuan Chen, Eckart Laurien, Yu ZhuAbstract:Abstract A supercritical water heat transfer test section has been built at Xi’an Jiaotong University to study the heat transfer from a 10 mm rod inside a square vertical channel with a wire-wrapped helically around it as a spacer. The test section is 1.5 m long and the wire pitch 200 mm. Experimental conditions included pressures of 23–25 MPa, mass fluxes of 500–1200 kg/m 2 s, heat fluxes of 200–800 kW/m 2 , and inlet temperatures of 300–400 °C. Wall temperatures were measured with thermocouples at various positions near the rod surface. The experimental Nusselt numbers were compared with those calculated by empirical Correlations for smooth tubes. The Jackson Correlation showed better agreement with the test data compared with the Dittus-Boelter Correlation but overpredicted the Nusselt numbers almost within the whole range of experimental conditions. Both Correlations cannot predict the heat transfer accurately when deterioration occurred at low mass flux and relatively high heat flux in the pseudocritical region. Comparison of experimental data at two different supercritical pressures showed that the heat transfer was more enhanced at the lower supercritical pressure but the deterioration was more likely to occur at the higher pressure, meaning increased safety. Based on a comparison with an identical channel without the helical wrapped wire, it was found that the wire spacer does not enhance the heat transfer significantly under normal heat transfer conditions, but it contributes to the improvement of the heat transfer in the pseudocritical region and to a downstream shift of the onset of the deterioration. The Jackson buoyancy criterion is found to be valid and works well in predicting the onset of heat transfer deterioration occurring in the experiments without wire.
Alan Michael Kruizenga - One of the best experts on this subject based on the ideXlab platform.
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development of a new forced convection heat transfer Correlation for co2 in both heating and cooling modes at supercritical pressures
International Journal of Thermal Sciences, 2011Co-Authors: Alan Michael Kruizenga, Yushan Luo, Mark Anderson, Michael L Corradini, Haijun WangAbstract:Abstract Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures in a prototypic printed circuit heat exchanger under both cooling and heating conditions have been performed in this present study. The experiment test section has nine semi-circular channels with a hydraulic diameter of 1.16 mm and a length of 0.5 m. Primary operational parameters include inlet pressure of 7.5–10 MPa, mass fluxes of 326 kg/m 2 s and 762 kg/m 2 s, inlet temperatures from 10 °C to 90 °C and the average heat flux was 30 kW/m 2 . Beyond reproducing the regular experimental cases, numerical modeling also implemented higher heat fluxes of 60 kW/m 2 and 90 kW/m 2 in order to investigate the effect of heat flux. Good agreement was found between the experiments and FLUENT simulations using an SST k – w model with the near-wall region being completely resolved. The distinctive behavior of convection heat transfer at supercritical pressures between heating and cooling modes was systematically analyzed. A more physically reasonable property-averaging technique, Probability Density Function (PDF)-based time-averaged property, was developed to account for the effect of nonlinear dependency of properties on instantaneous local temperature. Furthermore, experimental and computational data were compared to empirical predictions by the Dittus–Boelter and Jackson Correlations. The results showed that Dittus–Boelter Correlation has better precision for the average value of the predicted heat transfer coefficient but cannot take account of the effect of heat flux. In contrast, the Jackson Correlation, with property ratio correction terms to account for the distribution of the properties in the radial direction, could predict the distinction of heat transfer characteristics under heating and cooling conditions. However, it overestimates the average value of heat transfer coefficient in the whole range of the experiment conditions. Finally, a new Correlation evaluated by PDF-based time-averaged properties for forced convection heat transfer of CO 2 in both heating and cooling mode at supercritical pressures was developed. Comparison of experimental and computational data with the prediction results by the new developed Correlation reveals that it works quite well; i.e., more than 90% data in either heating or cooling mode with various heat fluxes are predicted within an accuracy of ±25%.
Yushan Luo - One of the best experts on this subject based on the ideXlab platform.
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development of a new forced convection heat transfer Correlation for co2 in both heating and cooling modes at supercritical pressures
International Journal of Thermal Sciences, 2011Co-Authors: Alan Michael Kruizenga, Yushan Luo, Mark Anderson, Michael L Corradini, Haijun WangAbstract:Abstract Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures in a prototypic printed circuit heat exchanger under both cooling and heating conditions have been performed in this present study. The experiment test section has nine semi-circular channels with a hydraulic diameter of 1.16 mm and a length of 0.5 m. Primary operational parameters include inlet pressure of 7.5–10 MPa, mass fluxes of 326 kg/m 2 s and 762 kg/m 2 s, inlet temperatures from 10 °C to 90 °C and the average heat flux was 30 kW/m 2 . Beyond reproducing the regular experimental cases, numerical modeling also implemented higher heat fluxes of 60 kW/m 2 and 90 kW/m 2 in order to investigate the effect of heat flux. Good agreement was found between the experiments and FLUENT simulations using an SST k – w model with the near-wall region being completely resolved. The distinctive behavior of convection heat transfer at supercritical pressures between heating and cooling modes was systematically analyzed. A more physically reasonable property-averaging technique, Probability Density Function (PDF)-based time-averaged property, was developed to account for the effect of nonlinear dependency of properties on instantaneous local temperature. Furthermore, experimental and computational data were compared to empirical predictions by the Dittus–Boelter and Jackson Correlations. The results showed that Dittus–Boelter Correlation has better precision for the average value of the predicted heat transfer coefficient but cannot take account of the effect of heat flux. In contrast, the Jackson Correlation, with property ratio correction terms to account for the distribution of the properties in the radial direction, could predict the distinction of heat transfer characteristics under heating and cooling conditions. However, it overestimates the average value of heat transfer coefficient in the whole range of the experiment conditions. Finally, a new Correlation evaluated by PDF-based time-averaged properties for forced convection heat transfer of CO 2 in both heating and cooling mode at supercritical pressures was developed. Comparison of experimental and computational data with the prediction results by the new developed Correlation reveals that it works quite well; i.e., more than 90% data in either heating or cooling mode with various heat fluxes are predicted within an accuracy of ±25%.
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experimental investigation on heat transfer from a heated rod with a helically wrapped wire inside a square vertical channel to water at supercritical pressures
Nuclear Engineering and Design, 2009Co-Authors: Haijun Wang, Yushan Luo, Xiaobao Shi, Tingkuan Chen, Eckart Laurien, Yu ZhuAbstract:Abstract A supercritical water heat transfer test section has been built at Xi’an Jiaotong University to study the heat transfer from a 10 mm rod inside a square vertical channel with a wire-wrapped helically around it as a spacer. The test section is 1.5 m long and the wire pitch 200 mm. Experimental conditions included pressures of 23–25 MPa, mass fluxes of 500–1200 kg/m 2 s, heat fluxes of 200–800 kW/m 2 , and inlet temperatures of 300–400 °C. Wall temperatures were measured with thermocouples at various positions near the rod surface. The experimental Nusselt numbers were compared with those calculated by empirical Correlations for smooth tubes. The Jackson Correlation showed better agreement with the test data compared with the Dittus-Boelter Correlation but overpredicted the Nusselt numbers almost within the whole range of experimental conditions. Both Correlations cannot predict the heat transfer accurately when deterioration occurred at low mass flux and relatively high heat flux in the pseudocritical region. Comparison of experimental data at two different supercritical pressures showed that the heat transfer was more enhanced at the lower supercritical pressure but the deterioration was more likely to occur at the higher pressure, meaning increased safety. Based on a comparison with an identical channel without the helical wrapped wire, it was found that the wire spacer does not enhance the heat transfer significantly under normal heat transfer conditions, but it contributes to the improvement of the heat transfer in the pseudocritical region and to a downstream shift of the onset of the deterioration. The Jackson buoyancy criterion is found to be valid and works well in predicting the onset of heat transfer deterioration occurring in the experiments without wire.
Srinath V Ekkad - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical investigation of heat and fluid flow in a square duct featuring criss cross rib patterns
Applied Thermal Engineering, 2018Co-Authors: Prashant Singh, Srinath V EkkadAbstract:Abstract This paper presents findings from experimental and numerical study of heat and fluid flow in a straight square duct featuring rib turbulators in a criss-cross pattern formed by 45° angled rib turbulators. Two ribbed configurations with criss-cross pattern – Inline and staggered, have been studied where the baseline case was smooth duct with no heat transfer enhancement feature. Detailed heat transfer coefficients were calculated using transient liquid crystal thermography by employing 1-D semi-infinite conduction model. Heat transfer and pressure drop measurements were carried out for Reynolds number ranging from 30,000 to 60,000. For understanding of heat transfer enhancement mechanism, numerical investigations were carried out using SST k-ω turbulence model. Numerical predictions of near-wall fluid dynamics and turbulent transport has been presented in conjunction with experimentally obtained detailed heat transfer coefficients to demonstrate the heat transfer characteristics of ribbed duct. Nusselt numbers normalized with respect to Dittus-Boelter Correlation for developed turbulent flow in circular duct varied between 2.7 and 3.1 for inline and staggered configurations and the thermal hydraulic performance varied between 1.2 and 1.5 for the range of Reynolds number investigated.
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a new cooling design for rib roughened two pass channel having positive effects of rotation on heat transfer enhancement on both pressure and suction side internal walls of a gas turbine blade
International Journal of Heat and Mass Transfer, 2017Co-Authors: Prashant Singh, Weihong Li, Srinath V EkkadAbstract:Abstract This paper presents a new cooling design for a typical two-pass channel of a high pressure stage turbine blade. Gas turbine blades are subjected to elevated heat loads on the pressure and suction walls. In order to enhance heat transfer from the surfaces to the relatively colder internal air (gas), rib turbulators are installed on the opposite walls of two-pass channel. Combination of Coriolis force and centrifugal buoyancy force result in increase in heat transfer on trailing walls (along the pressure surface, and radially outward coolant flow) and leading walls (along the suction surface, radially inward flow) and vice versa. This leads to non-uniform cooling in both the passes and hence a non-optimum usage of cooling potential. The present study is focused on utilizing the Coriolis force favorably in both the passes by rotating the typical arrangement of two-pass channels by 90°. Detailed heat transfer coefficients were measured by transient liquid crystal thermography under rotating conditions. In order to match the direction of Buoyancy force as it exists in actual engines, colder air was passed during the transient experiment. The heat transfer experiments were carried out at a Reynolds number of 20000 and Rotation numbers of 0 and 0.1. The Nusselt numbers have been reported in two forms, (a) normalized with respect to Dittus-Boelter Correlation for developed turbulent flow in circular duct, (b) normalized with corresponding Nusselt number obtained from smooth channel experiments. In order to understand the heat transfer characteristics of both traditional and new design, numerical simulations were also carried out for all configurations and at all experimental conditions to obtain flow and heat transfer predictions. A combined experimental and numerical discussion has been provided to explain the findings of the present study and to support the proposed design. It has been reported that the new design has 11% higher heat transfer enhancement at 8% lower pumping power compared to the traditional two pass rib roughened duct.
Michael L Corradini - One of the best experts on this subject based on the ideXlab platform.
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development of a new forced convection heat transfer Correlation for co2 in both heating and cooling modes at supercritical pressures
International Journal of Thermal Sciences, 2011Co-Authors: Alan Michael Kruizenga, Yushan Luo, Mark Anderson, Michael L Corradini, Haijun WangAbstract:Abstract Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures in a prototypic printed circuit heat exchanger under both cooling and heating conditions have been performed in this present study. The experiment test section has nine semi-circular channels with a hydraulic diameter of 1.16 mm and a length of 0.5 m. Primary operational parameters include inlet pressure of 7.5–10 MPa, mass fluxes of 326 kg/m 2 s and 762 kg/m 2 s, inlet temperatures from 10 °C to 90 °C and the average heat flux was 30 kW/m 2 . Beyond reproducing the regular experimental cases, numerical modeling also implemented higher heat fluxes of 60 kW/m 2 and 90 kW/m 2 in order to investigate the effect of heat flux. Good agreement was found between the experiments and FLUENT simulations using an SST k – w model with the near-wall region being completely resolved. The distinctive behavior of convection heat transfer at supercritical pressures between heating and cooling modes was systematically analyzed. A more physically reasonable property-averaging technique, Probability Density Function (PDF)-based time-averaged property, was developed to account for the effect of nonlinear dependency of properties on instantaneous local temperature. Furthermore, experimental and computational data were compared to empirical predictions by the Dittus–Boelter and Jackson Correlations. The results showed that Dittus–Boelter Correlation has better precision for the average value of the predicted heat transfer coefficient but cannot take account of the effect of heat flux. In contrast, the Jackson Correlation, with property ratio correction terms to account for the distribution of the properties in the radial direction, could predict the distinction of heat transfer characteristics under heating and cooling conditions. However, it overestimates the average value of heat transfer coefficient in the whole range of the experiment conditions. Finally, a new Correlation evaluated by PDF-based time-averaged properties for forced convection heat transfer of CO 2 in both heating and cooling mode at supercritical pressures was developed. Comparison of experimental and computational data with the prediction results by the new developed Correlation reveals that it works quite well; i.e., more than 90% data in either heating or cooling mode with various heat fluxes are predicted within an accuracy of ±25%.