K. R. Sridhar

Film Thickness and Wave Velocity Measurements in a Vertical Duct

We describe the experimental investigation of an upward annular air-water flow in a duct with a 6.35 mm by 63.5 mm rectangular cross section. The test section was instrumented to measure the film thickness and the interfacial wave velocity. Flush-wire electrical conductivity probes were used to obtain local film thickness measurement with a spatial resolution of 200 μm or better and a temporal resolution greater than 2 kHz. Measurements of the base films range from 50 μm to ∼325 μm (2% to 10% of half-channel thickness). Statistical analysis shows that the standard deviation of the film thickness is a good measure of the film roughness. The relative roughness and the nondimensional film thickness are correlated as functions of the phasic Reynolds number ratio, R=Re 0.15 l /Re 0.3 g

Lunar base thermal control systems using heat pumps

Abstract There is considerable interest at the present time to design a thermal control system (TCS) for a lunar base. Conventional techniques cannot be used for the purpose due to the lack of a readily available temperature sink during most of the lunar day. The lunar surface near the equatorial regions reaches a maximum of about 390 K during the 336-h lunar day. The projected range of temperatures for operation of sensors and conditioned habitat spaces is 270–293 K. A heat pump augmented TCS can be used to increase the operating temperature of the radiator, thereby enabling heat rejection. Rankine, absorption, and reverse Brayton cycle heat pumps with various working fluids are examined to identify the optimal cycle and working fluid combination. A base-line cooling load of 100 kW to be rejected at 270 K is used in the analysis. A Rankine cycle heat pump operating with R11 as the working fluid and R717 as a rejection loop coolant provides an optimal total TCS mass of 5940 kg at a radiator temperature of 362 K.

Thermal control system for lunar base cooling

The design of a thermal control system (TCS) for cooling a lunar base is considered. Conventional techniques cannot be used for this purpose because of the lack of a readily available heat sink during most of the lunar day. The temperature of the lunar surface near the equator reaches a maximum of about 390 K during the lunar day. The projected range of temperatures for operation of sensors and thermally conditioned habitat spaces is 270-293 K. A heat-pump-augmented TCS can be used to increase the operating temperature of the radiator, thereby enabling heat rejection. The masses of TCSs utilizing Rankine cycle and closed Brayton cycle heat pumps are examined in detail. The TCSs are optimized for minimum total mass. Quantitative comparisons show that the Rankine cycle systems are less massive than the Brayton cycle systems. The optimal total TCS mass for a Rankine cycle heat pump with Rll as the heat pump working fluid and R717 in the rejection loop is 5940 kg at a rejection temperature of 362 K. Sensitivity analyses are performed for radiator-specific mass and power penalties.

Moderate temperature control technology for a lunar base

A parametric analysis is performed to compare different heat pump based thermal control systems for a Lunar Base. Rankine cycle and absorption cycle heat pumps are compared and optimized for a 100 kW cooling load. Variables include the use or lack of an interface heat exchanger, and different operating fluids. Optimization of system mass to radiator rejection temperature is performed. The results indicate a relatively small sensitivity of Rankine cycle system mass to these variables, with optimized system masses of about 6000 kg for the 100 kW thermal load. It is quantitaively demonstrated that absorption based systems are not mass competitive with Rankine systems.

Two-Phase Flow in Packed Columns and Generation of Bubbly Suspensions for Chemical Processing in Space

ABSTRACT For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow packed column operated in two ground-based low gravity facilities (two-second drop tower and KC-135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity. For bubbly suspensions, the experimental hardware for generation of uniformly sized bubbles in Couette flow in microgravity conditions is described. Experimental work was performed on a number of bubbler designs, and the capillary bubble tube was found to produce the most consistent size bubbles. Low air flow rates and low Couette flow produce consistent 2-3 mm bubbles, the size of interest for the “Behavior of Rapidly Sheared Bubbly Suspension” flight experiment. Finally the mass transfer implications of these two-phase flows is qualitatively discussed.