The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Hua Wang - One of the best experts on this subject based on the ideXlab platform.
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low grade heat utilization by supercritical carbon dioxide rankine cycle analysis on the performance of gas heater subjected to heat flux and convective boundary conditions
Energy Conversion and Management, 2018Co-Authors: Yiqiang Zhang, Yecheng Yao, Guoli Tang, Hua WangAbstract:Abstract The design and optimization of gas heater in supercritical carbon dioxide Rankine cycles faces some challenges, among which an urgent one is the Effect of thermal boundary condition on the performance of gas heater. This work focused on performance comparison and Effects of major operating parameters under two most common thermal boundary conditions regarding to low-grade heat sources, by employing a modified Shear-Stress Transport model where a variable turbulent Prandtl formulation was incorporated. Results show that in the pseudo-critical region thermal boundary condition obviously affected the performance of supercritical carbon dioxide gas heater. Compared with the uniform heat flux condition, at convective boundary condition impairment occurred in both the local enhancement at high mass flux and local deterioration at low mass flux, due to the self-regulation in local heat input. A nearly uniform thermal field under convective boundary condition was achieved by increasing the mass flux of heat source fluid, while increasing the inlet temperature of source fluid was inEffective to that end. Opposite to constant-property fluid heater, flow arrangement dramatically affected axial profiles of local heat transfer coefficient while had a much weaker Effect on local heat flux in supercritical gas heater. Temperature distribution of supercritical carbon dioxide along the heater was insensitive to the flow arrangement. Further studies reveal that thermal boundary Effect was closely related to the Buoyancy Effect. Thermal boundary condition has a minimal Effect on heat transfer of supercritical carbon dioxide when Buoyancy Effect is negligible. Under heavy influence of Buoyancy, thermal boundary Effect was obvious in the form of much weaker local deterioration under convective boundary. Finally, the Jackson Nusselt correlation was found applicable to the prediction of overall heat transfer rate under convective boundary condition, with relative deviations within ±15%.
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numerical analysis of Buoyancy Effect and heat transfer enhancement in flow of supercritical water through internally ribbed tubes
Applied Thermal Engineering, 2016Co-Authors: Guoli Tang, Hua WangAbstract:Abstract Heat transfer to supercritical water in vertical Internally Ribbed Tubes (IRT) with various geometries was numerically investigated in a range of p = 25 MPa, Tb = 590 ~ 700 K, G = 100 ~ 1000 kg⋅m−2⋅s−1, q = 200 ~ 800 kW/m2 and q/G = 0.33 ~ 3 kJ/kg. The Shear-Stress Transport k–ω (SST) model was employed to solve the turbulent flow and conjugate heat transfer. In IRT with different rib geometries, Buoyancy-induced deterioration of heat transfer did not occur and Buoyancy forces continuously enhanced heat transfer at Bo
Chaobin Dang - One of the best experts on this subject based on the ideXlab platform.
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the Effect of geometry parameters on the heat transfer performance of supercritical co2 in horizontal helically coiled tube under the cooling condition
International Journal of Refrigeration-revue Internationale Du Froid, 2019Co-Authors: Xiaoxiao Xu, Jiacheng He, Chaobin DangAbstract:Abstract Experimentally and numerically studied the heat transfer performance of supercritical CO2 (S-CO2) cooled in small (d ≤ 4 mm) horizontal helically coiled tube (HCT). Five HCTs with fixed coil pitch b = 34 mm, coil diameters D ranging from 36–140 mm and tube diameters d ranging from 2 to 4 mm were used. The results showed that the heat transfer coefficient (HTC) has tripled as the tube diameter decreases from 4 to 2 mm. HTC increases up to 30% with the coil diameter decreasing from 140 to 36 mm. Based on the modified theory derived from the straight tube (ST) with upward flow, the onset value of Buoyancy Effect in horizontal HCT was obtained, which confirmed that the Buoyancy in the present experimental study can be neglected. Totally, 33 test runs and 426 points were performed, and from which a new correlation was proposed to evaluate the HTC of S-CO2 in the horizontal HCT under cooling condition.
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the heat transfer of supercritical co2 in helically coiled tube trade off between curvature and Buoyancy Effect
Energy, 2019Co-Authors: Shijie Zhang, Chao Liu, Xinxin Liu, Yadong Zhang, Chaobin DangAbstract:Supercritical CO2 Rankine cycle has great development potential as a power cycle for converting low-grade thermal energy into electricity. Better understanding of supercritical CO2 heat transfer in helically coiled tubes (HCTs) is required for design and operation of supercritical CO2 Rankine cycle power systems. In this work, the SST k∼ω model is employed. A new dimensionless Buoyancy parameter Ψ is proposed which denotes the ratio of gravitational Buoyancy force to overall curvature Effect. Furthermore, a flow regimes map is proposed based on the inclination angle of the dividing streamline between the two vortexes and Buoyancy parameter Ψ. The mixed convection region in HCT is decomposed into a gravitational Buoyancy force dominated heat transfer region (B Region α>45°) and a curvature Effect dominated heat transfer region (C Region α<45°). Subsequently, the Effects of HCT geometry on heat transfer mechanisms are respectively investigated in B and C Region, which help us better understanding the relationship of the Buoyancy criterion and flow characteristics. The results indicate that the Effects of coiled pitch and coiled diameter on heat transfer can be neglected in B Region. In C Region, the heat transfer is suppressed as coiled pitch increases and it will appear oscillation when torsion Effect is strong enough. In addition, the heat transfer is enhanced with curvature increases but except for near the pseudo-critical region.
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numerical investigation on heat transfer of supercritical co2 in heated helically coiled tubes
Journal of Supercritical Fluids, 2015Co-Authors: Kaizheng Wang, Chao Liu, Chaobin DangAbstract:Abstract Numerical simulation on heat transfer of supercritical CO 2 in heated helically coiled tubes is performed to evaluate the performance of turbulence models in predicting heat transfer of supercritical CO 2 in the helically coiled tube, and to help better understanding the heat transfer mechanism. All turbulence models yield similar tendencies in heat transfer coefficient in the helically coiled tube. The SST (shear-stress transport) model gives the best prediction to the experimental data due to accurate predictions of flow separation under adverse pressure gradients. The parameter of Gr / Re 2.7 is incapable of predicting the Buoyancy Effect onset of supercritical CO 2 in the helically coiled tube. The turbulent Prandtl number has little influence on the calculated heat transfer coefficient.
Bonifacio T Doma - One of the best experts on this subject based on the ideXlab platform.
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carbon dioxide solubility in 1 ethyl 3 methylimidazolium trifluoromethanesulfonate
The Journal of Chemical Thermodynamics, 2009Co-Authors: Allan N Soriano, Bonifacio T DomaAbstract:Abstract In this work, we present new solubility results for carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate for temperatures ranging from (303.2 to 343.2) K and pressures up to 5.9 MPa using a thermogravimetric microbalance. Carbon dioxide solubilities were determined from absorption saturation (equilibrium) results at each fixed temperature and pressure. The Buoyancy Effect was accounted for in the evaluation of the carbon dioxide solubility. A highly accurate equation of state and a group contribution predictive method for carbon dioxide and for ionic liquids, respectively, were employed to determine the Effect of Buoyancy on carbon dioxide solubility. The solubility measurements are presented as a function of temperature and pressure. An extended Henry’s law equation was used to correlate the present experimental solubility values and the result was satisfactory.
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solubility of carbon dioxide in 1 ethyl 3 methylimidazolium tetrafluoroborate
Journal of Chemical & Engineering Data, 2008Co-Authors: Allan N Soriano, Bonifacio T DomaAbstract:The solubility of carbon dioxide in the room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and 1-ethyl-3-methylimidazolium tetrafluoroborate for temperatures ranging from (303.2 to 343.2) K and pressures below 5 MPa were measured using a thermogravimetric microbalance. The gas solubilities were determined from absorption saturation (equilibrium) data at each temperature and pressure. The Buoyancy Effect was accounted for in the evaluation of the gas solubilities. An accurate equation of state and density equation for carbon dioxide and ionic liquids, respectively, were employed to determine the Effect of Buoyancy on the gas solubilities. The carbon dioxide solubilities in ionic liquids are presented as a function of temperature and pressure. The experimental solubility pressure data of carbon dioxide in the ionic liquids was successfully represented using an extended Henry’s law correlation.
Peixue Jiang - One of the best experts on this subject based on the ideXlab platform.
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a modified Buoyancy Effect correction method on turbulent convection heat transfer of supercritical pressure fluid based on rans model
International Journal of Heat and Mass Transfer, 2018Co-Authors: Peixue Jiang, Zhenchuan Wang, Ruina XuAbstract:Abstract The performance of the turbulent flow model for predicting the Buoyancy Effect on convective heat transfer of supercritical fluid is severely affected by strongly varying thermal physical properties near the pseudo-critical point. Over-prediction is attributed, at least partly, to the misuse of the constantly turbulent Prandtl number for the turbulent heat flux in the turbulence model. A method that considers the anisotropic turbulent heat flux has been proposed to improve the prediction accuracy of numerical simulation. A Buoyancy Effect model that accounts for the production of turbulent kinetic energy and a turbulent Prandtl number model accounting for turbulent thermal diffusion, which are both based on the anisotropic turbulent heat flux model, was adopted in the original AKN k-e model. Experimental results and direct numerical simulations (DNS) data were used to validate the performance of the “Modified model.” The “Modified model” produced accurate predictions for all heat transfer deterioration cases examined in the present paper. The Buoyancy Effect model reflects the basic mechanism of heat transfer deterioration and recovery due to accurate predictions of turbulent kinetic energy. The value of Prt in the buffer layer obtained with the turbulent Prandtl number model is essential for accurate reproductions of experimental data.
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Buoyancy Effects on turbulent heat transfer of supercritical co2 in a vertical mini tube based on continuous wall temperature measurements
International Journal of Heat and Mass Transfer, 2017Co-Authors: Feng Luo, Peixue JiangAbstract:Abstract Convection heat transfer of supercritical pressure fluid is important in industrial applications such as supercritical power stations, the supercritical CO 2 Brayton cycle, Carbon Capture Utilization and Storage, and the thermal protection for rocket thrusters. Previous research has confirmed that there are three heat transfer regions for convection heat transfer of supercritical pressure fluid flowing inside vertical tubes: normal heat transfer, heat transfer deterioration, and heat transfer enhancement. However, existing research still carries inconsistent results, especially regarding the onsets of heat transfer deterioration of supercritical pressure fluid flow in vertical tubes. Here we propose a new view, by estimating the location where local fluid temperature, T f ( r ) equals to the pseudocritical temperature, T pc , in the transversal section inside the tube, then analyzing the relationship between the location where T f ( r ) = T pc and the turbulent boundary layers in the near wall region, to identify Buoyancy Effects on turbulent heat transfer. By taking advantage of infrared thermometry measurement to achieve continuous wall temperature, theoretical analysis was validated by experiments of supercritical pressure CO 2 in a vertical mini-tube with inner diameter of 0.953 mm. The experiments were performed for a pressure of 7.6–9.5 MPa, inlet mass flux from 255 kg/m 2 s to 685 kg/m 2 s, and heat flux from 12 kW/m 2 to 63 kW/m 2 . It is found that in contrast with the previous results, when the value of y + at the location of T f ( r ) = T pc , y + | T f ( r ) = T pc , less than 5, heat transfer enhances for upward and decreases for downward flow due to the Buoyancy Effect. With the heat flux increasing or mass flux decreasing, the Buoyancy Effect on the turbulent convection heat transfer characteristics of supercritical pressure fluid in a vertical heated tube is be featured as the following regimes: for the upward flow, from no-Effect to slight enhancement, significant reduction, recovery and then enhancement; for the downward flow, from no-Effect to slight weaken, and then enhancement. Moreover, the experimental results showed that y + | T f ( r ) = T pc = 5 is where there is an onset of heat transfer deterioration for the upward flow in a vertical heated tube induced by Buoyancy Effects. The results presented provide a better understanding of the special features of the turbulent convection heat transfer of supercritical pressure fluids in mini channels.
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experimental investigation of convection heat transfer of n decane at supercritical pressures in small vertical tubes
International Journal of Heat and Mass Transfer, 2015Co-Authors: Bo Zhang, Peixue JiangAbstract:Abstract This paper presents experimental investigations of the convection heat transfer of n-decane at supercritical pressures in vertical tubes with inner diameters of 0.95 and 2.00 mm for various inlet pressures, heat fluxes and flow directions. The Effects of the heat fluxes, property variations, Buoyancy and flow acceleration on the convection heat transfer were studied. The results show that for high inlet Reynolds numbers neither Buoyancy nor flow acceleration affects heat transfer significantly, while for low inlet Reynolds numbers Buoyancy strongly reduces heat transfer coefficient in upward flow cases. The threshold for Bo∗ was found to be about 2.0 × 10−7. Two local Nusselt number correlations for the convection heat transfer of supercritical pressures n-decane with and without Buoyancy Effect were developed based on the experimental data.
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convection heat transfer of supercritical pressure carbon dioxide in a vertical micro tube from transition to turbulent flow regime
International Journal of Heat and Mass Transfer, 2013Co-Authors: Peixue Jiang, Chenru ZhaoAbstract:Abstract This paper presents experimental investigations of the convection heat transfer of carbon dioxide at supercritical pressures in a vertical tube with inner diameter of 99.2 μm for various Reynolds numbers, heat fluxes and flow directions. The Effects of Buoyancy and flow acceleration due to heating and pressure drop are evaluated and analysed. The results show that the Effects of flow acceleration are significant and the local wall temperature varies non-linearly for both upward and downward flows at the pressures in the vicinity of critical point and low inlet Reynolds numbers when the heat fluxes are relatively high. The Buoyancy Effect on the heat transfer is negligible in micron scale tubes at inlet Reynolds (from 2600 to 6700) and various heat fluxes (from 85 kW/m2 to 748 kW/m2). The flow acceleration due to heating and pressure drop can strongly influence the turbulence and reduce the heat transfer for high heat fluxes and low inlet Reynolds. Comparison of numerical predictions with the experimental data showed that the AKN low Reynolds number turbulence model gave better agreement than the k–e realizable turbulence model with the enhanced wall treatment.
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a computational study of convection heat transfer to co2 at supercritical pressures in a vertical mini tube
International Journal of Thermal Sciences, 2005Co-Authors: S. He, Peixue Jiang, Yijun Xu, J D JacksonAbstract:Abstract Computational simulations of experiments on turbulent convection heat transfer of carbon dioxide at supercritical pressures in a vertical tube of diameter 0.948 mm have been carried out using low-Reynolds number eddy viscosity turbulence models. The simulations were able to reproduce the general features exhibited in the experiments, although, in some cases, the details between the simulations and the experiments were very different. A better understanding of the problem has been developed based on the information generated by the simulations on the detailed flow and turbulence fields. It has been shown that for mini tubes such as the one used in the current study, the Buoyancy Effect is generally insignificant. However, heat transfer can still be significantly impaired as a result of flow acceleration when the heating is strong, which causes a reduction in turbulence production. Such an Effect can be described in terms of the heating acceleration parameter Ω 1 . This parameter correlates reasonably well the data from all the cases considered in the current study.
Zhu Huang - One of the best experts on this subject based on the ideXlab platform.
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steady mixed convective flow and heat transfer from tandem square cylinders in a horizontal channel
Numerical Heat Transfer Part A-applications, 2017Co-Authors: Renan Yuan, Zhu HuangAbstract:ABSTRACTThe two-dimensional laminar steady mixed convective flow and heat transfer around two identical tandem square cylinders confined in a horizontal channel are simulated by the high-accuracy multidomain pseudo-spectral method. The blockage ratio of the channel is chosen as 0.1, whereas the spacing between the cylinders is fixed with four widths of the cylinder. The Prandtl number is fixed at 0.7, the Reynolds number (Re) is studied in the range 5 ≤ Re ≤ 60, and the Richardson number (Ri) demonstrating the influence of thermal Buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal Buoyancy Effect, the mixed convective flow remains steady. The variations of the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal Buoyancy on fluid flow and heat transfer is discussed and analyzed.
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mixed convection heat transfer from confined tandem square cylinders in a horizontal channel
International Journal of Heat and Mass Transfer, 2013Co-Authors: Zhu Huang, Wei Zhang, Suping WenAbstract:Abstract This paper presents a numerical study on the two-dimensional laminar mixed convective flow and heat transfer around two identical isothermal square cylinders arranged in tandem and confined in a channel. The spacing between the cylinders is fixed with four widths of the cylinder and the blockage ratio and the Prandtl number are fixed at 0.1 and 0.7 respectively. The mixed convective flow and heat transfer is simulated by high accuracy multidomain pseudospectral method. The Reynolds number (Re) is studied in the range 80 ⩽ Re ⩽ 150, the Richardson number (Ri) demonstrating the influence of thermal Buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal Buoyancy Effect, the mixed convective flow sheds vortex behind the cylinders and keeps periodic oscillating. The variations of characteristic quantities related to flow and heat transfer processes, such as the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal Buoyancy on the fluid flow and heat transfer are discussed and analysed.
