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Ma F.,Shanghai JiaoTong University | Zhang P.,Shanghai JiaoTong University | Zhang P.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Shi X.J.,Shanghai JiaoTong University
International Journal of Heat and Mass Transfer | Year: 2017

Slush hydrogen is a mixture of solid hydrogen and liquid hydrogen. Compared with pure liquid hydrogen, it can be used as the fuel of rocket and space booster due to its densified feature. In the present study, a numerical model is built based on the Eulerian-Eulerian model and the kinetic theory of granular flow to investigate the hydraulic and heat transfer characteristics of slush hydrogen in a circular pipe under both terrestrial and microgravity conditions. The numerical model is first validated by the experimental results reported in the literature. The flow of slush hydrogen with different inlet velocities and solid volume fractions are numerically studied to investigate the solid volume fraction distribution and velocity profile of the outlet cross-section. Considering the transportation of slush hydrogen in practical applications, the hydraulic characteristics of slush hydrogen in an inclined pipe under terrestrial condition and in a horizontal pipe under microgravity are also investigated. The results show significant influence of the gravity on the solid volume fraction distribution and pressure drop of slush hydrogen. The heat transfer of slush hydrogen is also studied, which shows that the temperature of fluid can be locally decreased sufficiently using slush hydrogen such that the vaporization of liquid hydrogen can be suppressed. Solid hydrogen particle with small diameter can improve heat transfer between the solid phase and liquid phase, and the melting of solid hydrogen is accelerated. It is clarified that the increases of both the inlet velocity and solid volume fraction show positive effects on the local heat transfer coefficient. © 2017 Elsevier Ltd


Liu Z.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants
Refrigeration Science and Technology | Year: 2015

The self-pressurization process of cryogenic liquid hydrogen tank considering the phase change, liquid thermal stratum and surface tension is investigated with a computational fluid dynamic (CFD) model. Validated by the experiment data obtained from the flight test, the improved CFD model is selected to research the influences of reduced gravity on tank pressurization process. In order to recognize the tank pressurization and thermal stratification performance clearly, four gravity levels (1g0, 10-1g0, 10-2g0 and 10-3g0) are considered and compared with each other. The results indicate that the gravity level has a great effect on pressure increasing process. Some valuable conclusions are listed as: (1) Comparing with the pressure difference of 1g0, the pressure differences in reduced gravity varying from 10-1g0 to 10-3g0 are increased by 10.7%, 16.7% and 27.6%, respectively. Opposite to the change tendency of pressure differences, evaporation losses are 1.593kg, 0.637kg, 0.332kg and 0.232kg with the gravity level ranging from 1g0 to 10-3g0. In addition, the phase change form at the beginning of the pressurization process is condensation, with the time continuing, evaporation would become the leading phase change form. Heat leakage through tank wall plays a leading role in tank pressure rising, the effects of evaporation quality are not appeared in short time. (2) With the increasing of gravity levels, the temperature distributions in the ullage region become more uniform, and the liquid stratum layers develop faster. Calculated with CFD model and compared with two theoretical models, it turns out that the relative errors of stratum thickness between CFD model and Tellep model are always smaller than that of stratum thickness between CFD model and Reynolds model. However, it is opposite for the comparison of stratum temperature. (3) Different direction stream cycles are forming in the upper part of the ullage. Many large and small vortex or loops are developing between two slosh baffles. The streamline distribution in the liquid stratum like a plume and forms circulate loop between the tank wall and axis. (4) Influenced by surface tension, liquid close to the tank wall moves up along the wall in reduced gravity. The interface in the gravity level of 10-1g0 is still flat as same as that of 1g0, while others are becoming curved with the interface area increasing.


He K.,University of Science and Technology Beijing | Zhu H.,Hanbao Steel Energy Center | Wang L.,University of Science and Technology Beijing | Wang L.,State Key Laboratory of Technologies in Space Cryogenic Propellants
Applied Energy | Year: 2015

Inspired by energy storage systems for peak load shifting (PLS), this study proposes a PLS utilization mode of electricity-generating coal gas resources for the steel industry in China. The proposed mode can help the steel industry save electricity bills (2.4%) through the introduction of a time-of-use tariff. Data of a steel enterprise are used to prove the economic benefit of the coal gas utilization mode. Given that China produces more than half of converter steel of the total production worldwide, their coal gas resources are abundant. The PLS utilization mode will have a great effect on balancing the power grid. A simulated operation model for PLS coal-fired power units is used to calculate the energy conservation and emission reduction effect of coal-fired power plants under different scenarios. The annual coal savings are 1.7-3.1%, and the annual SO2 and NOX emission reductions are 2.9-12.4% and 44.6-14.1% of the total reduction amount of the steel industry in China, respectively. © 2015 Elsevier Ltd.


Liu Z.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Jin Y.,Xi'an Jiaotong University
Applied Thermal Engineering | Year: 2016

One CFD model is established to investigate the pressurization performance and thermal stratification in the final stage cryogenic liquid oxygen (LOX) tank, which is subjected to aerodynamic heat and space radiations during launch. Iterative calculation with variable physical properties in each time step, both aerodynamic heat and space radiation have been considered by compiling one UDF and implanting it into the CFD model. It turns out that aerodynamic heat has caused large influence on tank pressurization performance, while the effect of space radiation on tank pressurization is not obviously reflected. Influenced by the injection gas, tank pressure fluctuates between the minimum and the maximum pressure limit and the ullage mass decreases due to condensation during the active-pressurization. Meanwhile, the basic parallel advance trend of temperature distribution is roughly formed. During the pressurized discharge, tank pressure experiences a sharp decline at first, then decreases linearly, finally reduces with a larger rate. The liquid temperature increases gradually to the direction of advance as liquid height declines. Moreover, the residual liquid temperature increases obviously. With the heat continuous transferring from the ullage to the liquid, the ullage is under condensation during the whole process. © 2016 Elsevier Ltd


Liu Z.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Zhou K.,Xi'an Jiaotong University
Energy Conversion and Management | Year: 2016

Full use and effective management of cold capacity are significant for improving the performance of heat exchanger in the thermodynamic vent system (TVS). To understand the operation principle of TVS easily, the thermodynamic analysis, based on the ideal gas state equation and energy conservation equation, is detailed introduced. Some key operation parameters are optimized and suggested. As the low mass flow rate and low heat fluxes are involved in flow boiling of the annular pipe fluid, the Kandlikar's boiling heat transfer correlation is selected to predict the flow boiling process, after validated with the related experimental results. One quasi-steady state model is established to investigate the heat transfer performance of double-pipe heat exchanger in normal gravity, with the bulk fluid natural convection, annular pipe two-phase boiling and inner pipe forced convection coupled from outside to inside. Determined by the local pressure and temperature, the fluid thermophysical properties are variable with the pipe length and time. With the variable fluid thermophysical properties, both the static analysis and the transient thermal performance of TVS heat exchanger are investigated respectively. Meanwhile, effects of the external natural convection and the pipe sizes on the thermal and flow performance of heat exchanger are detailed researched and analyzed. Some valuable conclusions are obtained and significant to optimize the TVS heat exchanger design. © 2016 Elsevier Ltd


Wang L.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Li C.,Xi'an Jiaotong University | Zhao Z.,Xi'an Jiaotong University
Cryogenics | Year: 2013

Predictions of thermal and pressurization performance in a liquid hydrogen (LH2) tank during liquid discharge is of significance to the design and optimization of a rocket pressurization system. In this paper, a computational fluid dynamic (CFD) model is introduced to simulate the pressurized discharge event of LH2 tank. The wall region together with the fluid region is simultaneously considered as the computational domain, and low-Re k-ε model is applied to account for the fluid-wall heat exchange effect. Liquid-vapor phase change effect is also involved in the model. Comparison of the numerical results with existing experimental data suggests that the CFD model has a good adaptability in pressurization computation. Detailed characteristics, such as pressurant gas requirement, pressure altering history, and temperature distribution inside the tank, can be obtained by the model. The difference of pressurant gas, selecting helium or vapor H 2, may result in the variations in pressure and temperature histories. Pressurization by vapor H2 supplies a higher pressure and also a temperature rise, which is significant to consider the selection of pressurant gas. The influences of phase change effect and injector structure on pressurization behaviors are also analyzed. The computational results show that liquid-vapor phase change has a slight influence on the pressurization behaviors. Significant pressure decay at the beginning stage of process may occur in the case of no-diffuser injector application since the incoming gas is excessively cooled by cold LH2. The results show that the present CFD model has a good adaptability in the prediction of pressurization behaviors and is a useful tool for the design and optimization of a pressurization system. © 2013 Published by Elsevier Ltd. All rights reserved.


Wang L.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Zhao Z.,Xi'an Jiaotong University | Zheng J.,Xi'an Jiaotong University
Asia-Pacific Journal of Chemical Engineering | Year: 2014

The pressurization performance of cryogenic tanks during discharge is investigated by a computational fluid dynamic approach. A series of cases accounting for the effects of various influence factors such as inlet gas temperature, ramp time of inlet gas temperature, wall thickness, outflow rate, injector structure, and liquid supercooling on pressurization behaviors are computed and analyzed successively. Several valuable conclusions have been drawn as follows: (1) Increasing inlet gas temperature, applying a thin wall to construct the tank, and increasing the outflow rate are beneficial to the reduction of gas requirements, (2) Ramp process and use of a straight pipe injector may lead to an excessive pressure drop at the beginning of discharge, (3) Use of straight pipe injector can remarkably reduce the gas requirement but lead to a large loss of liquid propellant as well as a large weight of final ullage gas, and (4) The mode of mass transfer within the tank is close related to the injector structure and liquid supercooling. A trend of mass transfer toward evaporation can be observed by increasing the liquid temperature, especially for the straight pipe injector case. Generally, the results of this paper might be beneficial to the design and optimization of a pressurization system. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.


Wang L.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Zhao Z.,Xi'an Jiaotong University | Liu Z.,Xi'an Jiaotong University
International Journal of Heat and Mass Transfer | Year: 2013

A computational fluid dynamic (CFD) model, which can simultaneously account for the heat exchanges inside the tank and outside aerodynamic heating, is constructed to investigate the transient thermal and pressurization performance of cryogenic tank during discharge. Besides the fluid and tank wall regions, the foam region is also considered as the computational domain. Reference enthalpy method is used to account for the outside aerodynamic heating effect. The predictive ability of the CFD model is evaluated on the basis of the comparisons between its results and experimental data and a good agreement is obtained. Then the model is used to predict a pressurized discharge event, and the thermal and pressurization behaviors are obtained and analyzed. The results show that outside aerodynamic heating cannot penetrate the foam layer to facilitate the pressurization performance. Conversely, a certain proportion of energy might be transferred from heated tank wall to foam layer, which exert a negative effect on the pressurization behaviors. The aerodynamic heating effect may not be accounted for in the CFD simulation of a foam-insulated tank, if the thermal performance at outer surface of the tank is not particularly concerned. Generally, this paper supplies an effective way to predict pressurization performance and expresses valid results of the thermal performance inside and outside the cryogenic tank during discharge. It is also stated that the CFD model has a better accuracy in predicting pressurization characteristics.


Zheng J.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Wang L.,Xi'an Jiaotong University | Tan H.,Xi'an Jiaotong University
Cryogenics | Year: 2014

Contact heat transfer across mechanically pressed solid/solid contacts with or without interstitial bonding material is an important phenomenon in cryogenic engineering. This paper introduces an improved thermal contact resistance (TCR) model. The model, which considers both plastic and elastic deformation, matches well with the experimental data for pressed stainless steel 304 contacts in the range 110-150 K and 1-7 MPa. A method is also suggested to evaluate the microscopic effects of the TCR for alloyed metals in the range between liquid nitrogen temperature and room temperature. Based on the improved TCR model and the analysis of the heat transfer across the bonded joints, the thermal joint resistance (TJR) is modeled as the sum of the TCR and the bonding material resistance. The solid/liquid contact resistance is obtained by assuming the ideal gas law holds for the trapped air in the micro gaps. The TJR model indicates that the TJR depends on the bonding area, the bond line thickness, thermal conductivity of the bonding material, the initially applied pressure, the surface roughness, and thermal resistance of the bare contacts. The TJR model predictions are in good agreement with experimental data for joints incorporating bonding materials or thermal greases. © 2013 Elsevier Ltd. All rights reserved.


Zhao Z.,Xi'an Jiaotong University | Li Y.,Xi'an Jiaotong University | Li Y.,State Key Laboratory of Technologies in Space Cryogenic Propellants | Wang L.,Xi'an Jiaotong University | And 2 more authors.
Cryogenics | Year: 2014

Ambient air condensation on a cryogenic horizontal tube is investigated using a newly built mathematical model, in which the liquid film and the vapor boundary layer are coupled together with a major emphasis on the effect of buoyancy. Based on the model, the heat transfer coefficients and the film thickness as well as the interfacial shear are obtained under different conditions to investigate the effects on the flow and heat transfer characteristics of the superheating between vapor and film, the buoyancy in the boundary layer and the subcooling between wall and film. In addition to the flow and heat transfer characteristics of air, the other four different vapors, i.e. H2O, R134a, methane (CH4), argon (Ar), are also discussed. The results show that the superheating has a more significant contribution to the increase of heat transfer coefficient for air comparing to the other vapors, e.g. in the cases of superheating ΔTA¢. © 2014 Elsevier Ltd. All rights reserved.

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