Showing papers on "Latent heat published in 1976"

Parameterization of Air-Sea Interface Fluxes of Sensible Heat and Moisture by the Bulk Aerodynamic Formulas

Abstract: The parameterizations of the sensible heat and moisture fluxes by the bulk aerodynamic formulas are determined from a compilation of existing data, together with some new results. The data set comprised 152 determinations of the sensible heat flux and 30 of the moisture flux from experiments in which the fluxes were measured directly over water with suitable turbulence instrumentation. Least-square-error fits were performed on the data. The moisture flux (and therefore the latent heat flux) is adequately described by the bulk formula with a coefficient of 1.32 × 10−3. The parameterization of the sensible heat flux is complicated, for the data show 1) a small positive heat flux for zero temperature difference between the air and sea surface, 2) the coefficient for stable conditions is smaller than for unstable conditions, and 3) the coefficient appears to increase at high wind speeds, as shown by the data of Smith and Banke (1975). Separate bulk formulas are presented for the sensible heat flux fo...

Evaporation and advection I: evaporation from extensive homogeneous surfaces

Abstract: The process of modification of the Bowen ratio, with distance downwind of a change in surface wetness, is considered to establish the ratio of the fluxes of sensible and latent heat when unaffected by surface inhomogeneity. The case of steady-state two-dimensional advection is considered. It is shown that the coupled, simultaneous, diffusion equations for heat and moisture transfer from natural vegetated or wet surfaces can be used to generate two independent diffusion equations in composite variables. The vegetated surface is represented as an extensive single leaf. The height integral of the reciprocal effective eddy diffusivity is assumed to become indefinitely large with height so that heat and moisture continuously accumulate within the overpassing air. As a result equilibrium does not obtain. However, the surface latent heat flux approaches a quasi-equilibrium value given, in conventional symbols, by LE = (s/(s+γ)) (Rn −G). For terrestrial surfaces, where the available energy depends only slightly on surface temperature, the Bowen ratio approaches γ/s. For deep water bodies and melting snow the heat flux into the surface also evolves with distance and the above relationship is approached only in the trivial sense that Rn = G and LE = 0. This model for terrestrial surfaces is consistent with some recent experimental observations.

Calculating the high-temperature vapour line by Monte Carlo

Abstract: A combination of canonical and grand-canonical ensemble Monte Carlo calculations, together with the virial expansion, have been used to calculate the thermodynamic properties of the liquid/vapour co-existence curve of the (6 : 12) Lennard-Jones fluid for reduced temperatures, [Ttilde] ⩽ 1·1. The results for the liquid density and energy and the latent heat of vaporization are believed to be precise, with the exception of the point at [Ttilde]=1·1 which may lie outside the range of the function fitting the liquid phase Monte Carlo data. The liquid density and the saturated vapour pressure are in very good agreement with the results of perturbation theory. The latent heat of vaporization does not agree well with the experimental data for argon though the fit to liquid density and internal energy is good.

Parameterization of the Moisture and Heat Transfer Process over the Ocean under Whitecap Sea States

Abstract: The mechanics of evaporation from the ocean under whitecap sea states was analysed by taking into account the water droplets produced by sea sprays and popping of entrained air bubbles. The theory proves that the droplets are a major source of moisture for the humidity field, and at the same time the latent heat of evaporation from the droplets is a dominant heat sink for the temperature field. Many known atmospheric conditions over the ocean can be correctly simulated by the present theory. From these results, an analytical expression for the rate of vertical flux of water vapor was obtained.

A thermal study of the formation of oceanic crust

Abstract: Summary. The temperature distribution beneath an ocean ridge with a magma chamber solidifying to form the crustal layer 3 has been investigated by numerical methods. Assuming that water circulation rapidly cools layer 2 but does not penetrate deeper, it is found that a magma chamber forms provided that the half spreading rate exceeds about 0.45 cm y-' ; for slower rates instantaneous dyke-like solidification occurs down to the Moho beneath the ridge axis. Numerical models show that the width of the magma chamber and the thickness of the dyke complex depend on half-spreading rate. The width is about 20 km for 3 cm y-'. If there is significant crystal settling to form cumulates, the chamber width is much reduced. The resulting heat flow pattern is as follows: an outer zone where latent heat effects are negligible; a middle zone about twice as wide as the magma chamber where latent heat significantly contributes to the heat loss; a narrow axial zone where quenching of magma to form layer 2 provides the main heat loss. The computations support Cann's petrological model and suggest that the depth of water penetration at the accretion boundary defines the layer 2-layer 3 boundary.

A Comparison of Two Optical Methods for Measuring Line Averages of Thermal Exchanges Above Warm Water Surfaces

Abstract: Line averages of the vertical transports of sensible and latent heats in the surface boundary layer are determined above a warm water surface by the use of two optical, line-of-sight, remote-sensing techniques. In one method, the amount of atmospherically-induced blurring of images is observed visually with the aid of a small portable astronomical telescope. The other method utilizes unaided observations of the formation of inferior mirages, in particular the heights of distant objects that appear to be partially hidden behind the mirage. In the present application above industrial cooling ponds, lines of sight are within 1 m of the water surface and 0.4 to 1.5 km in length. The evaluation of the heat fluxes also requires estimates of the surface friction velocity and the ratio of the sensible to latent heat fluxes, each of which can be obtained with sufficient accuracy over a warm water surface from relatively simple measurements of temperatures and wind speeds. The direct visual measurements ar...

Eddy flux measurements above a pine forest

Abstract: Estimates of sensible and latent heat flux measured above a Pinus radiata forest plantation, 11km north of Mt Gambier in South Australia, by eddy-correlation instrumentation, were found to satisfy the forest energy budget to within 20% provided the mean windspeed was greater than about 2ms−1. In lighter winds these two fluxes were severely underestimated. A study of the higher windspeed data when the forest canopy was externally dry and transpiration the only water loss, gave a Bowen ratio of 0.8 ± 0.1 during the day, with a diurnal trend similar to that for shorter vegetation types. In these conditions the hourly change in canopy heat storage was a significant component of the energy budget. When the canopy was wet from intercepted rainfall, the Bowen ratio was generally less than 0.3 and often negative. Incoming sensible heat and a cooling canopy provided energy for evaporation when the net radiation was low or negative.

Specific heat of normal and superfluid $sup 3$He on the melting curve

Abstract: A method has been developed for determining the specific heat of liquid $sup 3$He on the melting curve as a function of temperature and magnetic field. This approach depends on the accurate measurement of pressure and volume responses to heat pulses applied to the $sup 3$He in a Pomeranchuk cell. Analysis of a number of different experiments at a particular melting pressure yields both the specific heat of the liquid and its temperature. The thermodynamic determination of the temperature has been separately discussed in another publication. Measurements were performed between 1.1 and 23 mK in magnetic fields up to 8.8 kOe. From the normal-fluid specific-heat data the low- temperature value of the effective mass at the melting curve was found to be m*/m = 5.5 +- 0.2. This is substantially smaller than that reported by Wheatley. Specific-heat discontinuities at the A, A$sub 1$, A$sub 2$, and B superfluid transitions have been measured. These give values for certain combinations of the coefficients of the fourth-order invariants in a Ginzburg-Landau expansion. Comparison was made with the predictions of spin-fluctuation theories. It was found that these alone cannot account for the behavior of $sup 3$He at melting pressures. The entropy difference between themore » A and B phases was calculated from the specific-heat data and compared with that calculated from (i) measurement of the latent heat at the B $Yields$ A transition, and (ii) measurement of the suppression of the B transition by magnetic field, B phase susceptibility data, and a magnetic Clausius-Clapeyron equation. The different methods give a consistent picture in which the thermal differences between A and B phases are quite small. The A-phase specific heat at T/T/subc/ approx. 0.5 appears to have a weaker dependence on temperature than that expected for the limiting low- temperature behavior of the Anderson-Brinkman-Morel state. (AIP)« less

Observational constraints on the generation process of the earth's magnetic field.

Abstract: Summary The most likely origin of the Earth's magnetic field is a dynamo process acting in the liquid core, with motions of the fluid driven by thermal convection. This hypothesis is examined in relation t o the constraints imposed by a knowledge of the surface magnetic field, the surface heat flux, and also to some extent the properties of the core. Assuming the Weidemann—Franz relation between the electrical and thermal conductivities for the core, it is possible to obtain lower bounds on the heat flux through the base of the mantle. The minimum heat flux from the core is found to be 2.1010W, independent of either the electrical conductivity or the temperature gradient. By requiring that these bounds be less than the surface heat flux, the product of the electrical conductivity and the temperature gradient may be bounded both from above and from below. The heat flux estimates are improved by considering ohmic heating from the toroidal magnetic field, which cannot be observed directly, and the convected heat flux. An expression is obtained for a bound of the ohmic heating of the toroidal field in terms of the radial fluid velocity. A comparison with existing dynamo models reveals that the true value of the ohmic heating is much larger than the ideal bound. This is evidence against the existence of a toroidal field as large as, say, 10 mT. The heat fluxes are larger for heating by uniformly distributed heat sources than for latent heat from growth of the inner core. Unless the adiabatic gradient is below about 0.1 K km−1, it is not possible to generate the magnetic field by distributed heat sources. The latent heat case does not suffer the same difficulty, but then it is possible for the outer regions of the core to be density-stratified. Gravitational energy released by accretion of the inner core may also be an appreciable or even dominant factor.

Process and apparatus for heat exchange

Abstract: A process and apparatus is provided for storing thermal energy and subsequently releasing and extracting the stored thermal energy upon demand. At least one sealed container of salt hydrate is agitated continually and is positioned in heat exchange relationship with a heat exchange liquid which is passed between a thermal energy source and a container enclosing or partially enclosing the sealed container(s) for the salt hydrate. Agitation of the container(s) of salt hydrate prevents or minimizes salt separation and supercooling so that the latent heat of fusion of the salt hydrate can be stored and extracted by the heat exchange liquid upon demand, in addition to the sensible heat of the salt hydrate composition.

Reversible latent heat storage method, and reversible latent heat accumulator

Abstract: Utilization of latent heat stored in a crystalline liquid heat storage medium subject to super-cooling by continuously circulating the storage medium past a heat exchanger positioned in the upper portion of an enclosed space containing a body of such storage medium to effect super-cooling thereof, then past a bed of seed crystals in the lower portion of such space to effect partial crystallization thereof, and then back past the heat exchanger.

Methods and apparatus for heating articles

Abstract: Articles are heated in a condensation heat transfer facility to effect soldering thereof by transporting said articles into a body of hot saturated vapor within the facility. The hot saturated vapor condenses on, and gives up latent heat of vaporization to, the articles to effect solder reflow. The articles are subsequently quenched in a liquid prior to the withdrawal of the articles from the facility.

The Effects of Released Latent Heat in Growing Baroclinic Waves.

Abstract: The effects of released latent heat on the development of baroclinic waves are explored using two numerical experiments in which these waves are allowed to grow from small perturbations on a flow that initially was zonally constant. In one experiment the effects of released latent heat were excluded; in the other, these effects were included and the initial zonally constant flow was considered saturated everywhere. In the moist experiment the growth rates of all wavelengths were found to be significantly increased over the corresponding growth rates in the dry experiment. However, the wavelength of maximum growth rate (wavenumber 15) was the same in both the dry and moist experiments. At the time of maximum development of wavenumber 15, the kinetic energy structure in the moist experiment was quite different from that in the dry experiment. In the moist experiment there was a distinct double maximum in the vertical; while in the dry experiment most of the kinetic energy of wavenumber 15 was near ...

Does Mercury have a molten core

Abstract: The question of whether or not Mercury could contain a molten metallic core is investigated by studying the possible thermal evolution of a metallic core in that planet. The calculations involve the solution of the equation of heat conduction for a spherically symmetric body with internal heat sources, modifications to take account of the latent heat of fusion as well as the redistribution of radioactive heat sources as a consequence of melting, the terrestrial Fe/U ratio, and a Th/U ratio of 3.7. The temperature profile predicted by the calculations for a period of 4.6 billion years indicates that the inner 1400 km of the core would now be solid while the outer 500 km would be molten. It is emphasized that this result is a direct consequence of a discontinuity in melting temperatures at the core-mantle boundary and that although a dynamo is possible, it would have to be driven mechanically rather than by thermal convection.

Kinetic analysis of the problem of evaporation and condensation

Abstract: The mass transfer between a vapor and its condensed phase (liquid or solid) is considered on the basis of the reduced, linearized BGK equation as the governing equation and the finite element method as a tool. The results obtained for the vapor flow between two interfaces show that the parameter related to the latent heat of phase transition plays an important role in determing the flow characteristics.

Effects of aerosol on the local heat budget of the lower atmosphere

Abstract: SUMMARY The convergence of heat below subsidence inversions was estimated from radiosonde ascents on fine summer days. Sensible heat input from the ground was estimated from measurements of heat fluxes and net radiation over a wheat field. Absorption and back scattering of solar radiation by aerosol throughout the atmosphere were calculated from measurements of solar radiation at the ground. Radiation absorbed by aerosol in the thermal boundary layer heated the lower atmosphere at an average rate of 3.3degC day-’ (60Wrn-’), about twice as fast as estimated for gaseous constituents. An equation is derived to show how the net effect of aerosol on the lower atmosphere depends on the reflection coefficient of the surface and on the aerodynamic and surface resistances to vapour transfer. Over the wheat, the net effect was almost zero when the crop was transpiring fast, but when the crop was mature, aerosol caused net cooling. I. INTRODUCTION As part of a wider attempt to identify possible causes of climatic change, attention has recently been directed to the absorption and scattering of solar radiation by aerosol, processes which modify the heat balance of the atmosphere and the radiation budget at the earth’s surface. Calculations by Mitchell (1971), and by others, demonstrate that aerosol may be responsible either for cooling or for heating the lower atmosphere depending on factors such as the height, thickness and optical properties of the layer and the relative inputs of sensible and latent heat from the ground. The main sources of uncertainty in predicting thermal effects of aerosol in the atmosphere are an incomplete knowledge of (i) optical properties and distribution of aerosol, and (ii) the relationship between net radiation and sensible heat flux at the earth’s surface. We have made direct measurements, during summer anticyclonic conditions in Britain, of heat storage in the lower atmosphere, coupled with measurements of surface radiation and heat fluxes. In the first instance, the measurements were analysed to show the importance of radiant energy absorbed by aerosol in determining the energy budget of the lower atmosphere. The analysis was then extended to estimate the influence of atmospheric aerosol on the input of sensible heat to the atmosphere from the ground. It appears that aerosol may be responsible for a net heating or cooling of the lower atmosphere at a rate which depends on surface reflectivity and on the ratio of aerodynamic and surface resistances to vapour transfer. 2. THEORY During anticyclonic weather in Britain, inversions formed by subsidence are common at heights between 1 and 2km. Below the main inversion, the atmosphere is heated by radiation and by an input of sensible heat from the ground. Heat may also be entrained from the warmer air above the inversion as discussed by Cattle and Weston (1975). For simplicity, we shall consider the heat budget of a ‘thermal boundary layer’ defined as that layer of the atmosphere above which there was no measurable change of temperature due 95

Thermophysical properties of foodstuffs

Abstract: Minimum overall nutritional deterioration of foodstuffs is generally attained by maximizing the rate of heat input and minimizing the duration of heating. Measurement of thermophysical data for foodstuffs is discussed in terms of specific heat, latent energy, enthalpy, thermal conductivity, thermal diffusivity, and density. Since phase change in foodstuffs occurs over a temperature range rather than at a discrete temperature, enthalpy is preferred over sensible and latent energy measurements as it can be used to fix the state of a sample very accurately; also, in the fusion process there is no precise way of separating sensible and latent energies. The first step in determining property data for foodstuffs is to describe the material in conventionally accepted terms. Future work should be concentrated in the area of thermal diffusivity and enthalpy measurements.

A Classification of the Structure of the Tropical Atmosphere and Related Energy Fluxes

Abstract: Meteorological data from the tropics have been classified according to a scheme based on the rate of moist convection obtained indirectly from cloud photos. The degree of convection has been categorized into six modes ranging from severely depressed to severely enhanced. Simultaneous high-resolution measurements of tropospheric static energy, longwave radiation, and sensible and latent heat fluxes across the air-sea interface were categorized accordingly. The specific results clearly reveal many of the physical processes associated with the observed changes in the variables which are discussed. They also emphasize the complex interaction of the various processes and scales of motion, which suggests application of classification techniques in parameterization of variables.

Hemispheric asymmetry of oceanic heat budget in the Equatorial Atlantic and Eastern Pacific

Abstract: The oceanic heat budget is studied on the basis of ship observations during 1911–70 compiled by one degree square areas. The clockwise turning cross-equatorial surface air flow is conducive to upwelling to the South and downwelling to the North of the Eastern Pacific and Atlantic Equator, particularly during Northern summer. The wind-induced vertical motion field is considered a factor in maintaining the cold water tongues immediately to the South, and the strong temperature increase northward across the Equator. Net radiation is only slightly higher in the Southern hemisphere equatorial zone, but sensible and latent heat flux are greatly reduced in the cold water regions, especially in Northern summer. As a result, the ocean exports heat at the rate of 53 and 62 W m -2 to the South of the Atlantic and Pacific Equator, respectively, compared to an export of only 29 and an import of 3 W m -2 in the Northern hemisphere equatorial zone. DOI: 10.1111/j.2153-3490.1977.tb00764.x

Survey of high temperature thermal energy storage

Abstract: A survey of current technology relating to high temperature thermal energy storage is presented. The motivation for this study resulted from the need for energy storage in solar thermal applications; however, the results have much wider application. The generic classes of storage concepts considered are sensible heat, latent heat, and heat of reversible chemical reaction. The study includes a review of the basic thermodynamic aspects of thermal energy storage; a summary of storage concepts which have been conceptualized and/or built and tested, including comparisons of system characteristics within the generic classes; and, finally, specific technology surveys within the areas of materials problems, heat transfer and fluid mechanics problems and systems application. It is shown that the design and engineering of thermal storage systems have not progressed beyond the most simple concepts and that there has been only a limited effort in the design and construction of large scale systems. Current technology appears adequate to support the development of most sensible heat concepts and simple latent heat concepts while some degree of technology advancement will be required to develop advanced latent heat concepts and heat-of-reaction concepts. Specific recommendations for future research and development work are presented.

Energy exchange within individual layers of a meadow.

Abstract: Measurements of the radiation extinction in a meadow at Baumkirchen (Tyrol) show that the decrease in the photosynthetically active radiation (PhAR: 400–700 nm) is different to that of the total net-radiation in a characteristic way. The photosynthetically active radiation is distributed evenly to all vegetation layers, the “active surface” comprises practically the entire 90 cm high canopy. The total radiation energy (net-radiation) is absorbed and 45% is converted into sensible and latent heat only in a 25 cm wide layer, i.e., between 30 and 55 cm within the canopy. A second “active surface” lies in the lowermost 10 cm of the meadow and at the soil surface where additional 28% of the radiation energy is transformed into heat.

An Example of Polar Air Modification over the Gulf of Mexico

Abstract: A satellite picture shows many aspects of modification of continental air over warm water. The estimated average vertical flux of sensible and latent heat over 24 h was 103 W m−2 (1.44 cal cm−3 min−1 Maximum rates were estimated to be an order of magnitude higher.

An Application of Two Tropical Parameterization Schemes of Convective Latent Heat Release in Middle Latitudes

Abstract: Models developed by Krishnamurti et al. (1973) and Kuo (1974) for parameterizing the convective latent heat release in synoptic–scale tropical systems are slightly modified and applied to a case study in which Tropical Storm Candy (1968) interacts with a developing extratropical baroclinic frontal system over the United States. Stable latent heat release is also computed, although much of the reported weather activity is unstable. The convective and stable components of latent heat are converted to precipitation rates and compared to the observed precipitation rate. The results show that Krishnamurti's scheme does not produce reliable patterns. Reasons for this failure are discussed. Kuo's scheme, on the other hand, shows better agreement with observed precipitation rates, although discrepancies still exist.

On the theory of the steady perturbations in the troposphere

Abstract: The linear steady-state response of a hemispheric two-level primitive equation model to forcing by heat sources and by topography is studied. Realistic forcing is considered for January where the zonal variation of the release of latent heat and of the sensible heating dominates the radiational heating. The response to each of these heat sources is discussed and an attempt is made to understand the computed patterns by aid of a simple quasigeostrophic theory. The combined topographical and thermal forcing induces standing waves which verify favourably against observations. At 400 mb, the ridge on the windward side of the Himalayas and the trough over north-eastern Asia appear to be induced by the orography whereas the heat sources play an almost dominant role over North America and determine the position of the ridge over the Atlantic. At 800 mb, the linear model fails to simulate the Aleutean low but is rather satisfactory elsewhere. The northward transport of heat and momentum by the standing waves is discussed. DOI: 10.1111/j.2153-3490.1976.tb00688.x