Influence of phase change on self-pressurization in cryogenic tanks under microgravity

Abstract

Future operations of many fluid, thermal and power systems and their ability to store, transfer, and manage a variety of single or multiphase fluids in reduced gravity environment are of great importance. For many of these systems, cryogenic conditions will play an important role. Cryogenic vaporization, caused by heat leakage into the tank from the surrounding environment, is one of the main causes of mass loss and leads to self-pressurization of the storage tanks. Available publications on self-pressurization and stratification of cryogenic tanks mainly focus on the convection and surface evaporation influences. Because large superheats increase the likelihood of evaporation in the liquid, the evaporation and its effect on vapor pressure under microgravity is studied numerically in this paper. The effects of reduced gravity, contact angle of the vapor bubble, and surface tension are investigated. The computations are carried out by using the CFD software package, Ansys Fluent, and an in-house developed code to calculate the source term associated with the phase change. A coupled level set and the volume-of-fluid method (CLSVOF) are used to solve a single set of conservation equations for the whole domain and the interface between the two phases is tracked or captured. A heat and mass transfer model is implemented into the Fluent code for solving problems involving evaporation or condensation. Results show that small tiny vapor regions caused by the evaporation process change the pressure rise. Vortices are observed due to the vapor dynamics. Nomenclaturec p Specific heat at constant pressure J/(kg·K) D Diameter of the tank [m] d bw Departure diameter of a vapor bubble (m) E Energy [J] F Body force [N/m 3 ] f Vapor bubble departure frequency (1/s) g Gravitational acceleration [m/s 2 ] H Height of the tank [m] k Thermal conductivity [W/(m·K)] L Heated length [m] L H Latent heat [J/kg] n Normal direction [m], also number of active nucleation sites P Pressure [Pa] q w Wall heat flux [W/m 2 ] Ra Rayleigh number, 2 4 2 p w Ra g c q L k βρ µ = r Radial coordinate [m] M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 2 S h Source term in energy equation [W/m 3 ] s Width of the rib [m] T Temperature [K] t Time [s] t g Growth time [s] t w Waiting time [s] V r Velocity vector [m/s] x, y, z Coordinates [m]Greek symbols α Volume of fluid fraction [-] α Heat transfer coefficient [W/m 2 K]

Pressurization performance and temperature stratification in cryogenic final stage propellant tank

“…According to the initial liquid height (2962 mm), initial tank pressure (0.435 MPa) and LOX temperature (88.8 K), when the external heat flux q is about 1.0 W/m 2 , the Rayleigh number 17 , which means that the natural convection is in turbulent. Moreover, as the low Re k-e model has been validated with great prediction ability especially for the pressurization discharge process [21,22,27], the low Re k-e model is selected in the present simulation.…”

“…Fu et al [16] numerically studied the self-pressurization of LH 2 tank with transverse ribs. Thereafter, Fu et al [17] also researched the self-pressurization of LH 2 tank with interface evaporation considered under microgravity. Additionally, tank pressurization process and thermal stratification were also investigated by Liu et al [18][19][20].…”

Study on the Self-Pressurization Laws of Cryogenic Liquid Krypton Tank for the Electric Propulsion System

“…) where r in Equations (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) denotes the evaporation and condensation coefficients, the default value of 0.1 was taken for the experiments for faster verification of the conclusions. The energy source term, the mass source term of the gas and liquid phase, and the saturation temperature mentioned above are written by user-defined functions and explained in the simulation software to realize the gasliquid phase change process.…”

“…In recent years, domestic and foreign scholars have carried out a lot of simulation analysis works on the heat and mass transfer process of self-pressurization in chemical cryogenic propellant tanks such as liquid hydrogen, liquid oxygen, and liquid methane based on CFD (Computational Fluid Dynamic) method. To study the phase change process at the gas-liquid interface and compare the pressurization process in the tank under various gravity conditions, Fu et al [8,9] built a two-dimensional axisymmetric model for cylindrical tanks. Sun et al [10,11] discussed Fluent software's phase transition model.…”

Effect of micro- and elevated gravity condition on the evolution of stratification and self-pressurization in a cryogenic propellant tank

“…The effect of insulation thickness, subcooling and wind velocity on the evolution of stratification was investigated by Joseph et al [5], who reported that higher tank pressure leads to higher liquid stratified mass. Fu et al [6] developed a numerical model to predict stratification, which focused on evaporation and its effect on vapour pressure under microgravity conditions. Extensive studies are required to predict the stratification in the micro-and higher gravity condition.…”