Chilldown performance of cryogenic systems is highly influenced by parameters like feed line orientation, thermal mass of the feed system and its distribution, mass flux of the cryogen and heat in-leak. In this work, the impact of feed line orientation and mass flux of cryogen on chilldown is evaluated through a parameter defined as Chilldown Performance Index. A set of experimental data generated with Liquid Nitrogen employing a test section insulated with poly-isocynurate foam is used for this study. Chilldown Performance Index is found to be lower with downward inclination upto 60 degrees downward orientation of test section as compared to that of horizontal orientation. Beyond this, at 90 degrees downward orientation, it is seen to be better as compared to 60 degrees orientation. Chilldown performance improves significantly with upward inclination of test section. Chilldown time is found to be highly sensitive to mass flux, whereas effect on Chilldown Performance Index is not so significant. Experiments also show that chilldown performance is significantly influenced by the distribution of feed line thermal mass. Chilldown is faster in experiments with higher thermal mass distributed near to the inlet to the test section as compared to the case wherein they are distributed near to the exit of the test section. Flow visualisation studies are also conducted employing a vacuum jacketed view glass made of borosilicate material to capture the flow structure prevailing in experiments with different upward and downward orientation and to assess its influence on chilldown. Flow structure is observed to be significantly different in experiments with upward inclination, compared to those with horizontal and downward orientation. Observations made with upward inclination, show the existence of plug or slug flow in the test section, leading to faster chilldown. Flow pattern observed in experiments with 30 degrees and 45 degrees downward orientation is also different compared to other orientations, as liquid flow is mostly confined to the core of the test section, due to gravity effects.

Experimental and numerical computations have been carried out to investigate the evolution of pressure and temperature in the liquid nitrogen (LN2) tank pressurized with gaseous nitrogen (GN2). A parametric study has been carried out to study the effect of ullage volume and pressurant gas (GN2) flow rate (0.25–2 g/s) and temperature (250–350 K) on the pressure evolution and thermal stratification in the tank during active pressurization from 1 bar to 3 bar. Experiments are conducted in a small range of mass flow rates at a given pressurant gas temperature (302 K). The numerical simulations are validated with the experiments and a parametric study has been performed. It has been observed that pressurization time varies linearly with the liquid depth. Thermally stratified mass in LN2 increases with the decrease in pressurant mass flow rate for a given pressure rise. Numerical simulations revealed that mass condensed during the pressurization is a weak function of ullage depth and temperature but a strong function of the mass flow rate. The pressurant gas requirement follows the correlation of Ludwig and Dreyer (2014) for relatively higher mass flow rates. The pressurant gas temperature has a strong influence on the flow pattern in the ullage. The pressurant gas flows along the wall and reaches the interface without disturbing the bulk vapor. Heat transfer at the interface is dominated by the heat carried by the pressurant than by transfer from the bulk vapor

Carbon-carbon composite manufactured by deposition of pyrocarbon (PyC) through chemical vapor infiltration (CVI) has the key issue of being process parametric sensitive which necessitates the detailed study of the effect of process parameters on the rate of PyC deposition. Conventional method of studying the parametric effect by changing one variable at a time keeping the other variables constant has a limitation of more number of experiments and missing the interaction effect among the variables. Here, the effect of process parameters including temperature, pressure, methane gas flow rate, and nitrogen gas flow rate on the mass gain and PyC deposition was studied by Taguchi method, a statistical optimization method, which has the advantage of very few experiments performed at specific pairs of process parameters only. The experiments were performed at three levels of the process parameters. Carbon-Carbon composite material is processed through the CVI process where PyC was deposited on porous carbon fiber preforms at various process conditions as per the Taguchi method. The impact of gas residence time, Reynolds number, Prandtl number, and Peclet number were also investigated. It was observed that the CVI process parameters significantly affect the rate of PyC deposition. Optimized CVI process parameters are essential for achieving a high rate of PyC deposition to reduce the processing time. The findings have revealed that a higher PyC deposition rate arises under high temperatures, pressure, methane gas flow rate, and optimal nitrogen gas flow rate. The effect of the critical interaction of the CVI process parameters on the rate of PyC deposition was also obtained. Based on the experimental studies, process guidelines are proposed for the densification of carbon fibers preform to realize C/C composite products.

We report experiments of steam condensation in water pool for various steam mass flux (53-133 kg/ m2s) and water subcoolings (15-65degree celsius). The process is visualized using high-speed imager, and the images are processed for bubble parameters and interfacial heat transfer. The bubble is observed to undergo a cyclic motion of growth, necking, and separation for the conditions studied. The flow transits towards chugging at higher subcoolings and low vapor mass flux. The heat transfer coefficient increases with vapor mass flux and liquid subcooling. The heat transfer coefficient is estimated to be 0.049-0.89 MW/m(2)K for oscillating regime, while relatively higher values (0.94-1.4 MW/m(2)K) are determined during chugging.

Numerical analysis of the hot oxygen rich exhaust gas flow field during the ground test of engine subsystem is carried out in the present paper. The effect of water injection on the hot gas plume and its impingement velocity on the test bay is studied. The effect of the wind conditions such as velocity and directions on the oxygen concentration in the test facility is also studied. It is found that a single water jet injected at 500kg/s with 55m/s velocity is able to reduce the impingement velocity of the hot gas from 250m/s to 75m/s. Analysis shows that the wind up to 12m/s does not have significant effect on the oxygen concentration in the test facility. The wind blowing opposite to the hot gas flow results in oxygen accumulation at ground level of the test facility.

Numerical simulation is carried out to understand the effect of impeller exit width on centrifugal pump rise, rotating stall progression and oscillation frequency with variation in flow coefficient. Steady and transient flow simulations of centrifugal pump were carried out for different flow rates. A comparative analysis of simulation results shows different degree of rotating stall happening in the pump impeller, which is quantified in terms of number of impeller blade passage affected by stall. Pressure fluctuations at different locations were compared with the test data and oscillation amplitude determined for different mass flow rates. Effect of rotational speed on pressure oscillation is also determined by varying rotor speed. Analysis shows that oscillation frequency is increasing with increased rotational speed and also depends on the rate at which stall bubbles travels through the clearance of impeller and diffuser. Transient analysis shows that these stall regions are rotating at frequency ranging from 11% to 12% of rotor speed.

Chilldown of cryogenic feed lines is the most indispensable part of any process that handles cryogenic fluids. Prediction of chilldown time 'apriori', requires a complete understanding of the influencing factors and the phenomenon involved. In the present study, the effect of feed line orientation and mass flux on chilldown performance is experimentally evaluated using liquid nitrogen. Experiments are carried out with a foam insu-lated stainless steel test section. Tests are performed for two different mass flux conditions with test section held in horizontal position as well as varying upward and downward inclinations. In tests with upward orientation, a significant jump in heat flux at top region is seen when the wall superheat reduces below a critical value and this is attributed to onset of liquid wetting at top region. In tests with downward inclination, a minor increase in the heat flux at top region is seen beyond 30 degrees downward orientation attributable to the flow structure prevailing in the test section. It is noted that heat flux pattern at bottom region is not influenced much by test section orientation. Leidenfrost temperature, minimum wall heat flux, and critical heat flux values obtained from the present study are compared with the predictions made using correlations available in published literature. The findings of the present study would help to understand better the influence of feed line orientation and mass flux on wall heat flux pattern and thereby improve the prediction capability.

Computational Fluid Dynamics (CFD) study of liquid oxygen draining in a spinning tank with and without baffles is carried out for hybrid propulsion rocket.The effect of tank spinning and the presence of baffles on the vortex formation and unusable propellant mass is brought out in this work.The interface of the draining propellant is captured using the Volume of Fluid (VOF) framework while the motion of baffles is simulated through mesh motion technique.Initially, analysis of liquid oxygen draining is carried out in a stationary tank without baffles.It is found that that a vortex is formed in the tank and gas entry in the feed line happens at 21s resulting in unusable propellant of 1.9kg.Subsequent analysis of liquid draining in a spinning tank without baffles shows that gas enters into the feed line earlier as compared to the stationary tank.Finally, the analysis is carried out for propellant draining in spinning tank with baffles.It is found that the momentum imparted by the baffles to the draining fluid increases the unusable propellant mass further compared to tank without baffle.

Isothermal chemical vapor infiltration (I-CVI) process used for the manufacture of carbon fiber-reinforced carbon matrix (C/C) composite products is process parametric sensitive. In this work, the characteristics of the pyro-carbon (PyC) matrix deposited through the I-CVI process are investigated. The chemical kinetics of this process was simulated to study the change in microstructure of PyC with the variation of process parameter. The nature of the carbon deposited at various temperatures, pressure, residence time of gas, and the effect of the molar ratio of methane to nitrogen gas on the microstructure of the deposited (PyC) is examined. The effect of carbon fiber preform porous structure on the I-CVI process and its densification characteristics was further studied. It was observed that during the I-CVI process, pores are playing a major role in the densification characteristics. The results have revealed that the properties of I-CVI processed C/C products can be improved by proper selection and controlling of process parameters. Based on this study, process guidelines are proposed for densification of continuous carbon fiber perform to optimally develop C/C composite products.

This paper describes the experimental and numerical works conducted to decipher the phenomenon of direct contact condensation (DCC). DCC, being a homogeneous condensation process, is characterised by extremely high heat transfer coefficient and very high turbulence across the interface. The study was initiated with experiments of steam condensation in stagnant and flowing water and is being augmented to GN2 condensation in stagnant and flowing LN2. Studies on steam condensation in stagnant water were conducted by injecting steam at different Reynolds numbers, Re (3000 < Re < 20,000) into a stagnant pool of water, stored in a transparent cuboidal test rig (0.48 m × 0.48 m × 0.5 m). Study was carried out for three different pool subcooling, ∆Tsub (50–70) with three different injector orifice diameters, D (2, 4 and 6 mm). Flowing water experiments were implemented with Reynolds number of steam varied from 12,400 to 24,900 and injected perpendicularly into flowing water with Re varied from 14,000 to 74,400. Preliminary experiments were also conducted with GN2 and stagnant LN2, and more comprehensive works are planned for future. Numerical studies of DCC were performed using two-fluid Eulerian framework. A pressure-based coupled solver of ANSYS Fluent was used to solve the governing equations. The condensation of steam in a pool of water was modelled, and the pressure oscillations during the different events of condensation were studied. DCC in cryogenic media was also analysed by injecting gaseous oxygen into flowing liquid oxygen through discrete holes. Salient results of gaseous oxygen condensation in flowing liquid oxygen are reported.