The Properties of Pure Liquids

By a semiempirical approach, a method is found to calculate the specific heat of a normal pure liquid at constant pressure form the specific heat of the gaseous state at the same temperature. It is also found that the coefficient of thermal expansion, the compressibility, and the velocity of sound of the liquid can be calculated accurately if the density, the molecular weight, and the normal boiling temperature of the liquid at atmospheric pressure are known. Finally, a method of computing the thermal conductivity of all liquids, except liquid metals, from compressibility and density is developed. For normal liquids, the thermal conductivity can again be determined if only the normal boiling temperature, the density, and the molecular weight are known

Flow boiling in straight heated tubes under microgravity conditions

Boiling two-phase flow can transfer large heat fluxes with small driving temperature differences, which is of great interest for the design of high-performance thermal management systems applied to space platforms and on-board electronics cooling in particular. However, such systems are designed using ground-based empirical correlations, which may not be reliable under microgravity conditions. Therefore, several two-phase flow (gas-liquid flow and boiling flow) experiments have been conducted in the past forty years and enabled to gather data about flow patterns, pressure drops, and heat transfers including critical heat fluxes and void fractions in thermohydraulic systems. Previous state of the art data can be found in the papers of Colin et al. (1996), Ohta (2003), and Celata and Zummo (2009). However, there is still a lack of reliable data on heat transfer in flow boiling in microgravity. Therefore, the purpose of our study is to clarify gravity effects on heat transfer characteristics and provide a fundamental description of boiling heat transfer for space applications. Hence, a two-phase flow loop for the study of flow boiling has been built at the IMFT in order to perform experiments in vertical flow in normal gravity and under microgravity conditions during parabolic flights in the aircraft. The test section is a 1mm thick sapphire tube of 6mm internal diameter with an ITO coating on its outer surface. The coating is heated by Joule effect and its temperature is measured in four locations by Pt100 sensors. High-speed movies of the flow are taken with a PCO 1200HS camera. The pressure drop is measured along the test section with two differential pressure transducers Valydine P305D. The mean void fraction upstream and downstream the test section is measured by capacitance probes developed and carefully calibrated at the IMFT. The refrigerant HFE-7000, which was chosen for safety reasons in the aircraft and because of its low saturation temperature at atmospheric pressure (34°C), circulates with mass fluxes G up to 1000 kg/s/m². A wide range of flow boiling regimes are studied, from subcooled flow boiling to saturated flow boiling with vapour mass qualities up to 0.7. The wall heat flux density ranges from 0 to 45 000 W/m². In subcooled boiling, bubbly flow is mainly observed. For saturated conditions the flow patterns are slug and annular flows depending on the quality value (Figure 1). Preliminary data were collected during a first flight campaign and on ground. The wall local heat transfer coefficients are deduced from the wall heat flux density and the local wall temperature measurements. Heat losses are characterized. Joint measurements of pressure drop and mean void fraction along the test section allow to access to the wall shear stress. Preliminary results suggest that gravity has no noticeable effect on heat transfers for mass fluxes G superior to 400 kg/s/m², which implies that lower mass fluxes should be investigated. Results obtained under normal and microgravity conditions are compared to existing models in order to obtain reliable and precise closure laws for boiling heat transfer in microgravity

Nucleation, solvation and boiling of helium excimer clusters

Helium excimers generated by a corona discharge were investigated in the gas and normal liquid phases of helium as a function of temperature and pressure between 3.8 and 5.0 K and 0.2 and 5.6 bar. Intense fluorescence in the visible region showed the rotationally resolved $d^3\Sigma_u^+ \rightarrow b^3\Pi_g$ transition of He$_2^*$. With increasing pressure, the rotational lines merged into single features. The observed pressure dependence of linewidths, shapes and lineshifts established phases of coexistence and separation of excimer-helium mixtures, providing detailed insight into nucleation, solvation and boiling of He$_2^*$-He$_n$ clusters.Comment: 5 pages, 5 figure

Conceptual design for spacelab pool boiling experiment

A pool boiling heat transfer experiment to be incorporated with a larger two-phase flow experiment on Spacelab was designed to confirm (or alter) the results of earth-normal gravity experiments which indicate that the hydrodynamic peak and minimum pool boiling heat fluxes vanish at very low gravity. Twelve small sealed test cells containing water, methanol or Freon 113 and cylindrical heaters of various sizes are to be built. Each cell will be subjected to one or more 45 sec tests in which the surface heat flux on the heaters is increased linearly until the surface temperature reaches a limiting value of 500 C. The entire boiling process will be photographed in slow-motion. Boiling curves will be constructed from thermocouple and electric input data, for comparison with the motion picture records. The conduct of the experiment will require no more than a few hours of operator time

Prediction of Vapor Pressures and Enthalpies of Vaporization Using a COSMO Solvation Model

We have developed a general predictive method for vapor pressures and enthalpies of vaporization based on the calculation of the solvation free energy that consists of three components; the electrostatic, dispersion, and cavity formation contributions. The electrostatic contribution is determined using the quantum mechanical COSMO solvation model. Thermodynamic perturbation theory for hard-core molecules is used for the cavity term, and the dispersion term is modeled using a mean field term proportional to the density and molecular surface area. The proposed model uses one set of van der Waals atomic radii to describe molecular shape, two universal interaction parameters for the electrostatic interaction, one set of atom-specific dispersion coefficients, one universal parameter to scale the atomic exposed surface area, and a single universal parameter for the ratio of the hard-core to atomic radii. The model parameters have been determined using 371 pure substances of varying molecular structure, functionality, and size. The average accuracy of the model for vapor pressures and enthalpies of vaporization at the normal boiling temperature is found to be 76% and 4.81 kJ/mol, respectively, with temperature-independent parameters. The average error in the normal boiling temperature is found to be 16 K for species whose boiling points range from 191 to 610 K

Bubble Behavior and Heat Transfer in Quasi-Steady Pool Boiling in Microgravity

Pool boiling of degassed FC-72 on a plane plate heater has been studied experimentally in microgravity. A quasi-steady heating method is adopted, in which the heating voltage is controlled to increase exponentially with time. Compared with terrestrial experiments, bubble behaviors are very different, and have direct effect on heat transfer. Small, primary bubbles attached on the surface seem to be able to suppress the activation of the cavities in the neighborhoods, resulting in a slow increase of the wall temperature with the heat flux. For the high subcooling, the coalesced bubble has a smooth surface and a small size. It is difficult to cover the whole heater surface, resulting in a special region of gradual transitional boiling in which nucleate boiling and local dry area can co-exist. No turning point corresponding to the transition from nucleate boiling to film boiling can be observed. On the contrary, the surface oscillation of the coalesced bubble at low subcooling may cause more activated nucleate sites, and then the surface temperature may keep constant or even fall down with the increasing heat flux. Furthermore, an abrupt transition to film boiling can also be observed. It is shown that heat transfer coefficient and CHF increase with the subcooling or pressure in microgravity, as observed in normal gravity

A helium-3 refrigerator employing capillary confinement of liquid cryogen

A condensation refrigerator suitable for operation in a zero gravity space environment was constructed. The condensed liquid refrigerant is confined by surface tension inside a porous metal matrix. Helium-4 and helium-3 gases were condensed and held in a copper matrix. Evaporative cooling of confined liquid helium-4 resulted in a temperature of 1.4K. Using a zeolite adsorption pump external to the cryostat, a temperature of 0.6 K was achieved through evaporative cooling of liquid helium-3. The amount of time required for complete evaporation of a controlled mass of liquid helium-4 contained in the copper matrix was measured as a function of the applied background power. For heating powers below 18 mW the measured times are consistent with the normal boiling of the confined volume of liquid refrigerant. At background powers above 18 mW the rapid rise in the temperature of the copper matrix the signature of the absence of confined liquid occurs in a time a factor of two shorter than that expected on the basis of an extrapolation of the low power data

Spray and evaporation characteristics of ethanol and gasoline direct injection in non-evaporating, transition and flash-boiling conditions

© 2015 Elsevier Ltd. Ethanol direct injection plus gasoline port injection (EDI + GPI) represents a more efficient and flexible way to utilize ethanol fuel in spark ignition engines. To exploit the potentials of EDI, the mixture formation characteristics need to be investigated. In this study, the spray and evaporation characteristics of ethanol and gasoline fuels injected from a multi-hole injector were investigated by high speed Shadowgraphy imaging technique in a constant volume chamber. The experiments covered a wide range of fuel temperature from 275 K (non-evaporating) to 400 K (flash-boiling) which corresponded to cold start and running conditions in an engine. The spray transition process from normal-evaporating to flash-boiling was investigated in greater details than the existed studies. Results showed that ethanol and gasoline sprays demonstrated the same patterns in non-evaporating conditions. The sprays could be considered as non-evaporating when vapour pressure was lower than 30 kPa. Ethanol evaporated more slowly than gasoline did in low temperature environment, but they reached the similar evaporation rates when temperature was higher than 375 K. This suggested that EDI should only be applied in high temperature engine environment. For both ethanol and gasoline sprays, when the excess temperature was smaller than 4 K, the sprays behaved the same as the subcooled sprays did. The sprays collapsed when the excess temperature was 9 K. Flash-boiling did not occur until the excess temperature reached 14 K. The fuel temperature changed not only the spray evaporation modes but also the breakup mechanisms

A study of the phase transition in the usual statistical model for nuclear multifragmentation

We use a simplified model which is based on the same physics as inherent in most statistical models for nuclear multifragmentation. The simplified model allows exact calculations for thermodynamic properties of systems of large number of particles. This enables us to study a phase transition in the model. A first order phase transition can be tracked down. There are significant differences between this phase transition and some other well-known cases