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Gravity effects on boiling from flat horizontal surface determined in heat flux range defined as discrete bubble region for various subcoolings, fluid properties, and heat transfer rates
Boiling heat transfer to liquid hydrogen and nitrogen was investigated experimentally. Results are presented from a study of bulk boiling inside a cylindrical tube under vertically upward forced-flow conditions. A 0.555-inch-inside-diameter and 16 (1/8)-inch-long electrically heated stainless-steel tube was used. The range of variables studied for hydrogen were mass velocity of 2850 to 17,000 pounds per hour per square foot, local heat flux of 3600 to 40,000 Btu per hour per square foot, inlet pressure of 30 to 74 pounds per square inch absolute, and inlet subcooling of 0° to 9° R. Nitrogen test conditions were mass velocity of 15,000 to 56,000 pounds per hour per square foot, local heat flux of 2300 to 40,000 Btu per hour per square foot, inlet pressure of 47 to 56 pounds per square inch absolute, and inlet sub cooling of 1° to 6° R. The axial distribution of the tube-wall temperatures is presented. A transition in the type of boiling heat transfer was obtained. The critical heat flux corresponding to this transition was determined over a range of flow and heating rates and local qualities. At specific combinations of flow and transition location, a range of critical-heat-flux values was obtained and maximum values were determined. The maximum critical heat flux increased with increasing fluid-flow rate and decreased with increasing length of tube before transition. Similar variations of the maximum critical heat flux have been reported for water. The tube-inner-wall temperatures upstream of transition were essentially uniform and were only slightly greater than the fluid saturation temperature. The Wall-temperature profiles downstream of transition generally resembled those obtained in film-boiling studies and appeared to be strongly dependent upon local quality at the point of transition. Maximum wall temperatures of 9000 and 18000 R were obtained with hydrogen and nitrogen, respectively. Fluctuations of pressure, flow rate, and temperature occurred during some of the boiling tests. Under some conditions, maximum critical-heat-flux values were attained during steady-state operation with fluctuations. In other cases the fluctuations became uncontrolled, and critical-flux values less than the maximum values were obtained upon restabilization of the test conditions. No measurable pressure drop across the test section was obtained at any condition.
Force analysis of saturated and subcooled bubbles during nucleate boiling, determining removal force of gravity
Vapor replacement in propellant feed duct with subcooled liquid to meet engine starting requirement of space vehicle parked in orbit
Zero gravity effects on boiling from flat horizontal surface for various subcoolings, fluid properties and heat transfer rates
Pressurized tank and subcooled fuel approaches to tankage systems for methane fueled supersonic transport
Results of an experimental and theoretical study of factors affecting self-sustaining hydrodynamic oscillations in boiling-water loops are reported. Data on flow variables, and the effects of geometry, subcooling and pressure on the development of oscillatory behavior in a natural-circulation two-phase-flow boiling loop are included.
Subcooled liquid and slush hydrogen fuels in propulsion stages of Saturn S-4C manned Mars flyby vehicle for improved payload ratios
Forced-convection boiling at low heat flux and flow velocities in zero gravity for slightly subcooled distilled water
Surface roughness and contamination, drop volume and liquid subcooling effects on Leidenfrost temperature
Two phase critical flow of saturated and subcooled high pressure liquid nitrogen through convergent- divergent nozzle, comparing with water
Buoyancy effects on the critical heat flux and general data trends for a liquid nitrogen internal flow system were determined by comparison of upflow and downflow data under identical test conditions. The test section had a 1.28 cm diameter flow passage and a 30.5 cm heated length which was subjected to uniform heat fluxes through resistance heating. Test conditions covered a range of pressures from 3.4 to 10.2 atm, inlet velocities from 0.23 to 3.51 m/sec, with the liquid nitrogen temperature at saturated inlet conditions. Data comparisons showed that the critical heat flux for downflow could be up to 36 percent lower than for upflow. A nonmonotonic relationship between the critical heat flux and velocity was determined for upflow but not for downflow. A limiting inlet velocity of 4.12 m/sec was determined to be the minimum velocity required to completely suppress the influence of buoyancy on the critical heat flux for this saturated inlet flow system. A correlation of this limiting fluid velocity is presented that was developed from previously published subcooled liquid nitrogen data and the saturated data of this investigation.
Chondrule-like spherules were formed from individual freely falling subcooled droplets of alumina, enstatite, forsterite, enstatite-albite and forsterite-albite mixtures that had been melted with a focused continuous CO2 laser beam. Their textures (rimmed, excentro-radial, barred, glassy) are strikingly similar to those of many meteoritic chondrules. It is suggested that the phenomena associated with rapid crystallization from the supercooled melt are responsible for the various textures observed in the artificial spherules as well as in similar meteoritic chondrules. It is suggested that the textures observed would also result from rapid crystallization of relatively slowly cooling molten droplets that may have been produced in larger scale events, including condensation from a nebula of solar composition and solidification in an ambient medium of high temperature.
The inception of bubbles during forced convection was studied experimentally by using trichlorotrifluoroethane (R-113 or Freon-113). The experiments were performed in a rectangular channel, 12.7 x 9.5 mm in cross section. Heating was from a 3.2 mm wide strip embedded in the longer side of the channel. The pressures studied ranged from 3.6 to 20.7 bar, mass velocities from 700 to 600 kg/sq m/sec, and inlet subcoolings from 26 to 97 C. Photographs of the flow were used to determine when bubbles first appeared on the heated surface. These data were compared with wall temperature measurements and inception theories. A reasonable method for calculating the complete boiling curve was found to agree with these results.
The high-capacity, pressure-primed, tunnel-artery wick concept was used in a gas-controlled variable conductance heat pipe. A variety of techniques were employed to control the size of gas/vapor bubbles trapped within the artery. Successful operation was attained with a nominal 6-foot long, 1-inch diameter cold reservoir VCHP using ammonia working fluid and nitrogen control gas. The pipe contained a heat exchanger to subcool the liquid in the artery. Maximum transport capacity with a 46-inch effective length was 1200 watts level (more than 50,000 watt-inches) and 800 watts at 0.5-inch adverse tilt.
Data and high speed movies were acquired on pressurized subcooled liquid nitrogen flowing radially inward through a 0.0076 cm gap. The stagnation pressure ranged from 0.7 to 4 MN/sq m. Steady radial inward choked flow appears equivalent to steady choked flow through axisymmetric nozzles. Transient choked flows through the radial gap are not uniform and the discharge pattern appears as nonuniform impinging jets. The critical mass flow rate data for the transient case appear different from those for the steady case. On the mass flow rate vs pressure map, the slope and separation of the isotherms appear to be less for transient than for steady radial choked flow.
The development of an acquisition system for supplying subcooled liquid hydrogen and liquid oxygen under in-orbit conditions is discussed. The system will be applied to the integrated cryogenic feed requirements for space systems such as a space shuttle cryogenic auxiliary propulsion system (APS) and main propulsion for an advanced spacecraft propulsion module (ASPM). Concepts that use the favorable surface tension characteristics of fine mesh screens are emphasized. The specific objectives of the program are: (1) to evolve conceptual designs for candidate acquisition systems, (2) to formulate the analytical models needed to analyze the systems, and (3) to generate parametric data on overall candidate system performance, characteristics, and operational features in sufficient depth to establish critical design problems and criteria to support a sound system design and evaluation.
A study was performed to determine the desirability of replacing the hydrogen peroxide settling system on the Centaur D-1S with a capillary acquisition system. A comprehensive screening was performed to select the most promising capillary device fluid acquisition, thermal conditioning, and fabrication techniques. Refillable start baskets and bypass feed start tanks were selected for detailed design. Critical analysis areas were settling and refilling, start sequence development with an initially dry boost pump, and cooling the fluid delivered to the boost pump in order to provide necessary net position suction head (NPSH). Design drawings were prepared for the start basket and start tank concepts for both LO2 and LH2 tanks. System comparisons indicated that the start baskets using wicking for thermal conditioning, and thermal subcooling for boost pump NPSH, are the most desirable systems for future development.