Parthasarathi Ghosh

In the last decade, researchers working on direct contact condensation (DCC) have focused their attention on studying the effect of liquid cross-flow, in contrast to the conventional stagnant liquid pool condensers. Currently, the major applications of DCC in liquid cross-flow include the sterilization process of milk and the mixing of oxygen-rich turbine drive gas with liquid oxygen (LOX) at the booster turbopump exit of a typical staged combustion cycle-based rocket engine. In this work, attempt has been made to develop and validate a two-fluid two-phase model for predicting the complex phenomena of steam injection into a cross-flow of subcooled water. A correlation for interaction length scale has been developed for DCC cases. The correlation includes the effect of all the critical operating parameters such as liquid subcooling, steam mass flux, and liquid velocity, which hitherto has not been available in the literature. The unstable nature of steam plumes has been investigated, and critical Weber numbers for predicting stable to unstable transition in a DCC cycle have been computed. The associated pressure and temperature oscillations due to unstable nature of plume have been studied. The critical design parameters for direct contact condenser such as the heat transfer coefficients and dimensionless vapor penetration lengths have been quantified and analyzed.

Generally, the pressure inside the propellant tank has to be maintained within the acceptable limits to avoid cavitation at the pump inlet. Heat and mass transfer processes occurring inside the tank has a considerable effect on the amount of pressurant gas entering to pressurize the tank. Ullage collapse leads to an increase in mass and mass flow rate of pressurant. Experimental data on tank pressurization is limited because of the enormous costs of performing large scale tank experiments using cryogenic fluids under controlled conditions. In this paper, collapse factor or pressurant gas mass has been investigated for certain combinations using Epstein and Anderson’s correlation and dimensional analysis and compared with the available experimental data. In some cases, operating pressure is kept constant while, in other cases, inlet gas temperature is kept constant. Combinations of pressurant and propellant like GH2- LH2, GN2-LOX, GHe -LOX are taken into account.

An approach for experimental investigation of the optimum sensor current of a superconducting level sensor is established and is then used for the investigation of the same of a NbTi and a MgB2/SS level sensors in liquid helium. On comparing the experimental results with that of the computational model established earlier, to simulate the operation of a superconducting level sensor, it was found that both agree closely. This shows the validity of the computational model for the characterization of a superconducting level sensor. Further on, the operation of these level sensors in a two-current method was studied. The results showed a higher heat load and level measurement time. However, it indicated an opportunity of retaining the linearity of the voltage versus liquid level curve even under high boil-off rate inside the cryostat. To scrutinize these findings, the NbTi level sensor operation in liquid helium was studied up to a boil-off rate of 5.77 g/s. It was observed that the sensor operation was not affected; however, the two-current method showed a more accurate level measurement compared to the one current method.

An automated level control in cryogenic systems requires a precise and continuous level measurement. If properly characterized, superconducting level sensors are a viable option for the same. The operation of a superconducting level sensor is based on the difference in the heat transfer from the sensor wire to the liquid and the gaseous phases of the cryogen. The higher heat transfer in the liquid phase results in a superconductive status, whereas the lower heat transfer in the gaseous phase results in a normal conductive status with a voltage drop corresponding to the length of the wire in the gaseous phase. Hence, it demands a judicious selection of the sensor and the operational parameters such as the current input, for an accurate level measurement as well as the reduction of the liquid boil off. In this paper, to simulate the operation of a superconducting level sensor, a model has been developed by taking the steady-state heat balance along the sensor wire. It is then used for the investigation of the sensor current, voltage output at various liquid levels, and temperature profile of the sensor wires of NbTi and MgB₂ /SS level sensors in LHe. Furthermore, design guidelines have been proposed for an MgB₂/SS superconducting level sensor for LH₂ level measurement. The parameters considered for the analysis are the sensor wire diameter and the active length. In addition, the effect of an external resistor on the sensor operation is also studied.

As a part of the developmental effort towards the realization of a staged combustion cycle based liquid rocket engine, a program on simulation of the LOX booster pump for performance characterization has been taken up. Earlier reported work shows that the pump inducer works satisfactorily under cavitating conditions for the throttling range varying from 90% to 113%. However stall occurs below 90% of the designed flow rate which is to be strongly associated with the inlet backflow vortices due to flow separation [1]. It is envisaged that leading edge sweep may help in to controls the incipience and growth of the backflow vortices at the inlet leading edge tip of axial flow inducer leading to a wider operating range. In this paper, steady state 3D CFD analysis of rotating inducer is performed to examine the effect of leading edge sweep on the performance of axial flow LOX pump inducer using ANSYS^® CFX and has been compared with the performance of the inducer reported by Mishra and Ghosh [1].

For low cost, high thrust, space missions with high specific impulse and high reliability, inert weight needs to be minimized and thereby increasing the delivered payload. Turbopump feed system for a liquid propellant rocket engine (LPRE) has the highest power to weight ratio. Turbopumps are primarily equipped with an axial flow inducer to achieve the high angular velocity and low suction pressure in combination with increased system reliability. Performance of the turbopump strongly depends on the performance of the inducer. Thus, for designing a LPRE turbopump, demands optimization of the inducer geometry based on the performance of different off-design operating regimes. In this paper, steady-state CFD analysis of the inducer of a liquid oxygen (LOX) axial pump used as a booster pump for an oxygen rich staged combustion cycle rocket engine has been presented using ANSYS^® CFX. Attempts have been made to obtain the performance characteristic curves for the LOX pump inducer. The formalism has been used to predict the performance of the inducer for the throttling range varying from 80% to 113% of nominal thrust and for the different rotational velocities from 4500 to 7500 rpm. The results have been analysed to determine the region of cavitation inception for different inlet pressure.

Supercritical helium owing to its single-phase characteristics and enhanced heat transfer near the pseudo-critical region is envisaged as a potential coolant for superconducting magnets used in particle accelerators and fusion devices. However, near the transposed critical line, there is a wide fluctuation of thermophysical properties like specific heat at constant pressure, density, thermal conductivity, viscosity, etc. As a consequence of this fluctuation, heat transfer and fluid flow studies become difficult for accurate prediction of heat transfer coefficient and friction factor. In this paper, numerical simulation of supercritical helium flowing under turbulent conditions in a horizontal heated tube is performed using computational fluid dynamics (CFD) software ANSYS FLUENT v12.0.16. It is found that results of pressure drop obtained from simulation closely match experimental data in case of fluctuation free regimes. The friction factor indicating the frictional pressure drop occurring in a horizontal tube can be matched to existing correlations within given accuracies for fluctuation regimes. A correlation for friction factor that yields better results than those in literature is proposed based on the simulation data obtained. The accurate determination of the overall pressure drop in the tubes along with the optimum flow rates gives the estimation of pumping power required for enhanced heat transfer with flow of supercritical helium.