Abstract: A simple and reliable method for the efficient inactivation of metabolism and for quantitative metabolite extraction from yeast cells is presented. It is based on the use of a boiling solution made of 75% ethanol (volume/final volume) buffered with 70 mM-Hepes (final concentration), pH 7.5, to guarantee the stability throughout the whole procedure of a large variety of metabolites, including all glycolytic intermediates, nucleotides, pyridine nucleotides and organic acids compounds. The extraction is fast, requiring only 3 min incubation of yeast cells in the ethanol-buffered mixture maintained at 80 degrees C. It can be carried out either directly by spraying the cells into the boiling mixture, or after quenching the whole culture in 60% methanol kept at -40 degrees C. Extracts are subsequently concentrated by evaporation under partial vacuum and the residue is resuspended in a small volume of water. This concentration step and the use of a highly sensitive analytical method allow us to quantify metabolites in less than 10 mg dry weight cells. This method, which can be applied to other fungi, could be very helpful for the determination of true metabolites in mutants generated through the EUROFAN programme and for metabolic flux analysis.

Abstract: This review considers the many techniques that have been developed to enhance convective heat transfer. After introducing the techniques, the applications to most of the modes of heat transfer (single-phase forced convection, including compound techniques, pool boiling, convective boiling/evaporation, vapor-space condensation, and convective condensation) are described. Comments are offered regarding commercial introduction of this technology and the generations of heat transfer technology : advanced enhancement represents third-generation heat transfer tehnology.

Abstract: Modifications of the entropy of boiling term and heat capacity change upon boiling term are made to the Yalkowsky−Mishra vapor pressure equation. These modifications eliminate a systematic error and enable the pure component vapor pressure estimation of complex organic compounds, including those that are hydrogen bonding. The new vapor pressure equation, which requires only the knowledge of transition temperatures and molecular structure, is shown to be more accurate than the Yalkowky−Mishra equation for a wide variety of compounds over a wide range of temperatures (vapor pressures from 1 atm and below).

Abstract: The past efforts in applying linear Taylor instability theory to the prediction of heat transfer during film boiling on a horizontal surface have suffered from the fact that empirical correlations must be used to define the shape of vapor-liquid interfaces and to determine the transport of mass and heat across these interfaces. The objective of this study is to clarify the physics of film boiling and to predict heat transfer coefficients through complete numerical simulation of the evolving interface between superposed layers of immiscible fluids. A coordinate transformation technique supplemented by a numerical grid generation method and a second-order projection method are combined to solve for the flow and temperature fields associated with an evolving interface. From the numerical simulation, the film thickness and, in turn, the heat transfer coefficient are found to vary both spatially and temporally. Increased wall superheat not only thickens the vapor film in the valley but also enlarges the vapor bulge. The effect of increased system pressure is to slow down the growth of the interface.

Abstract: This review considers the many techniques that have been developed to enhance boiling heat transfer. After introducing the techniques, the applications to pool boiling are described. Comments are offered regarding commercial introduction of this technology and the generations of heat transfer technology; advanced enhancement represents 3rd generation heat transfer technology.

Abstract: Pool boiling experiments using R-113 were conducted in the microgravity of space on a flat heater, consisting of a semitransparent gold film sputtered on quartz substrate, 19.05 x 38.1 mm (0.75 x 1.50 in.). Transient measurements of both the mean heater surface temperature and input heat flux are used to compute the mean heat transfer coefficient at the heater wall. Steady-state pool boiling is achieved in microgravity under conditions in which a large vapor bubble somewhat removed from the heater surface is formed, which acts as a reservoir for the nucleating bubbles. The steady nucleate boiling heat transfer is enhanced materially in microgravity relative to that in Earth gravity, whereas the heat flux at which dryout occurs is considerably less. Using quasisteady data obtained during periods in which some significant portions of the heater surface were dried out, it was possible to construct two distinct composite approximate microgravity pool boiling curves for R-113, one for the higher level of subcooling and one for the lower level of subcooling. These are compared with a reference curve for pool boiling at a/g = +1, constructed from available data and correlations deemed to reasonably represent the circumstances present.

Abstract: This paper is basically the text of the Kern Lecture for 1991 (the 1990 Kern Award). The paper begins with some remarks about Dr. Kern. By way of introduction to heat transfer enhancement, historical notes and the evolution of literature in this area are presented. Comments are made about the increasing practical applications of enhancement technology. Developments in single-phase convection are presented, with particular emphasis on offset strip fins and twisted-tape inserts. Pool boiling and flow boiling (particularly microfin tubes) are then considered in some detail. It is concluded that enhancement represents a powerful technology to improve heat exchanger performance.

Abstract: The influence of the roughness of a heating surface on the heat transfer coefficient has been investigated by experiments with propane boiling on single horizontal copper and steel tubes with different surface roughnesses (emery ground, fine or rough sandblasted). The results can be correlated in a preliminary manner by no longer separating the influence of surface roughness from the other parameters in an empirical prediction method. A detailed description of the three surfaces on the steel tube examined is given, with surface profiles, quasi three-dimensional topography presentation, SEM photographs, and with a statistical analysis of a selected roughness parameter. The size distributions of active nucleation sites have been determined using the model assumptions of Schomann of the heat transfer near growing and departing bubbles. The calculated results have been compared to experimental investigations by high speed video techniques. New measurements of the departure diameter dA and frequency f of the bubbles at the same conditions as for the heat transfer measurements show that dA and f are influenced by the azimuthal position of the active nucleation sites on the tube, and that the calculated results react sensitively on the input data for dA and f.

Abstract: NMR imaging has been used to study the boiling and steaming of intact wheat grains by mapping the distribution of water on the central cross section of grains after various cooking times. The results show different distributions of water occurring with boiling and steaming. Boiled grains showed a front of moisture which gradually moved towards the centre of the grain, although some water was able to diffuse ahead of the front. Steamed grains showed no such front, but showed a homogeneous distribution of water which gradually increases with cooking time. The different results for boiling and steaming imply that different mechanisms control the influx of water in each case, and provide important data for modelling these processes. It is postulated that absorption of water during steaming is slowed by the grain temperature rising above that of the steam temperature as a result of the latent heat associated with the condensation of steam being taken up by the grain.

Abstract: Intube flow boiling experiments for refrigerant R-134a mixed with a lubricating oil are reported for a plain, horizontal tube. The tests were run at a nominal inlet pressure of 340 kPa over a wide range of vapor qualities at mass velocities of 100, 200, and 300 kg/(s·m2) (73,500, 147,000, and 220,500 lb/h·ft2) for inlet oil concentrations from 0 to 5 mass % oil. At low to intermediate vapor qualities (0.2 < x < 0.60), the oil tended to increase the local boiling coefficient, while significant deterioration in boiling performance occurred at high vapor qualities for the higher concentrations. As opposed to similar tests with a microfin tube, no evidence of oil holdup inside the plain tube test sections was noted. However, the effect of flow pattern appears to be important; the effect of local physical properties on the heat transfer coefficient at high vapor qualities was confirmed.

Abstract: This report describes a theoretical and experimental study of the boundary layer boiling and critical heat flux phenomena on a downward facing curved heating surface, including both hemispherical and toroidal surfaces. A subscale boundary layer boiling (SBLB) test facility was developed to measure the spatial variation of the critical heat flux and observe the underlying mechanisms. Transient quenching and steady-state boiling experiments were performed in the SBLB facility under both saturated and subcooled conditions to obtain a complete database on the critical heat flux. To complement the experimental effort, an advanced hydrodynamic CHF model was developed from the conservation laws along with sound physical arguments. The model provides a clear physical explanation for the spatial variation of the CHF observed in the SBLB experiments and for the weak dependence of the CHF data on the physical size of the vessel. Based upon the CHF model, a scaling law was established for estimating the local critical heat flux on the outer surface of a heated hemispherical vessel that is fully submerged in water. The scaling law, which compares favorably with all the available local CHF data obtained for various vessel sizes, can be used to predict the local CHF limits on large commercial-size vessels. This technical information represents one of the essential elements that is needed in assessing the efficacy of external cooling of core melt by cavity flooding as a severe accident management strategy. 83 figs., 3 tabs.

Abstract: Critical heat flux (CHF) in nucleate pool boiling of binary mixtures was newly measured with a horizontal platinum wire, 0.5 mm in diameter, and heated by DC, over the full range of concentrations. Seven mixtures were selected with the intent to cover various types of mixtures: methanol/water, ethanol/water, methanol/ethanol, ethanol/n-butanol, methanol/benzene, benzene/n-heptane and water/ethylene glycol, each in the saturated state at atmospheric pressure. Total 311 raw CHF data were obtained at 75 concentrations including pure components. Aqueous mixtures of methanol and ethanol revealed significant increase of CHF compared to either CHF linearly interpolated between pure components or CHF predicted from a single component correlation with use of the mixture properties. Three organic mixtures showed more or less the same level as an interpolated CHF, while the remaining two mixtures of methanol/benzene and water/ethylene glycol gave the reduced CHF by 20% and 50% at most, respectively. Marangoni number was introduced as a controlling variable to explain the observed increased, invariable, or reduced CHF, and an empirical correlation was developed.

Abstract: In this first in a series of three papers, a formal treatment is presented for the development of property correlations for homologous series of compounds. The theoretical basis for asymptotic behavior is discussed, and the methodology used to regress parameters is described. The equations developed are quite general and can be extended to other properties or homologous series. Parts 2 and 3 of this series present correlations developed for n-paraffins and n-olefins (1-alkenes) to predict PVT related properties, normal boiling and melting points, critical temperature, pressure, and volume, acentric factor, liquid molar volume, and vapor pressure (part 2); thermal properties, ideal-gas enthalpy and free energy of formation, ideal-gas heat capacity, enthalpy of vaporization, and liquid heat capacity (part 3); transport properties: liquid viscosity, thermal conductivity, and surface tension (part 3). It is demonstrated that these correlations are accurate, consistent, and yield reasonable extrapolations. Th...

Abstract: Heat transfer coefficients in nucleate pool boiling of five binary mixtures were measured under atmospheric pressure on an upward-facing heated surface for a wide range of heat flux from about 15 percent of the critical heat flux to close to it. Mixtures were : methanol / water, ethanol / water, methanol / ethanol, tehanol / n-butanol, and methanol / benzene. As has been observed in many previous experiments, heat transfer coefficients of mixtures were reduced in comparison with interpolated values between their constituent components. This reduction was a function of the mixture composition and became more pronounced with an increase in heat flux. To provide a simpler and more reliable prediction of heat transfer coefficients of mixtures, Thome correlation was modified so as to include the effect of heat flux in a dimensionless form. A newly developed correlation in this way was verified to predict heat transfer coefficients for the present five mixtures well within ±20 percent accuracy lines.

Abstract: The laser drilling process is a complex phenomenon. This is especially true after the evaporation process starts. It is experimentally evident that liquid ejection occurs due to drag forces developed around the solid cavity and/or explosion resulting from nucleation of vapour bubbles in the liquid zone. Therefore, study into the ejection of liquid due to vapour bubble formation is necessary. Consequently, the present study examines the liquid ejection mechanism experimentally and possible saturated nucleate boiling is treated theoretically. In the experimental study, streak photography is introduced while a kinetic theory is adopted for the heat transfer model. This enables us to obtain the surface and internal temperature rise due to the laser heating pulse. It is found that the time measured for the liquid expulsion from the heated zone is identical with the time computed corresponding to possible saturated nucleate boiling.

Abstract: The boiling of pure fluids has been experimentally studied in several types of compact heat exchanger channels. Plate fin and corrugated heat exchangers have been studied (seven geometries). Controlling the flow parameters (mass flux and vapour quality), the heat flux and measuring the wall temperature, have allowed characterization of the local heat transfer coefficient. The results clearly show that the dominant mechanisms occurring could be nucleate or convective boiling. The transition between these two mechanisms depends on the flow characteristics and also on the channel geometry. Based on these measurements, an objective criteria can be established to identify the flow boiling regime. The knowledge of such a criteria is useful if we want to extend the use of compact heat exchanger to boiling of mixtures.