Showing papers on "Latent heat published in 1985"

Flux-Gradient Relationships in a Forest Canopy

Abstract: Relationships between the flux densities of sensible heat, water vapor and C02 and the appropriate gradients were examined systematically above and within a pine forest, 16–20 m high. Above the forest, the stability functions for heat and water vapor appeared to be identical, but different from those pertaining to smoother surfaces. Consequently, aerodynamic methods for calculating the flux densities of those scalars, which require exact knowledge of the stability functions, were unsuccessful, but the energy balance approach, which requires only that the functions be identical, still proved reliable. However, all gradient-diffusion schemes failed completely within the canopy, where counter-gradient or zero-gradient fluxes were observed for all three scalars. The failure of conventional flux-gradient relationships in that space is due in part to the sporadic penetration of transporting eddies into the canopy and their large scale.

Variation of Bulk-Derived Surface Flux, Stability, and Roughness Results Due to the Use of Different Transfer Coefficient Schemes

Abstract: Ten published bulk transfer coefficient schemes are used with more than 2600 sets of shipboard observations made in the North Atlantic at Ocean Station C over a one-year period. Using the same input data, the differences in the various coefficient schemes were found to produce substantial variations in the resulting flux, stability, and roughness determinations. A conservative analysis found that the scheme-to-scheme differences resulted in a typical maximum variation of 45% for an average stress determination of 0.2 N m−2, 70% for an average sensible heat flux determination of ±25 W m−2, 45% for an average latent heat flux determination of ±40 W m−2, 60% for an average Bowen ratio determination of ±0.06, 500% for an average roughness length determination of 3 × 10−4 m, and 700% for an average roughness Reynolds number determination of 6. It is argued that much of the differences in the various coefficient schemes is due to the widespread use of indirect flux measurements, rather than eddy-correl...

The Atmospheric Heat Source over the Tibetan Plateau: May–August 1979

Abstract: Estimates of the time and space variability of the atmospheric heat source over Tibet are presented for the summer of 1979. These estimates rely on new data from the People's Republic of China allowing a better assessment of the surface heat fluxes, and on new satellite data from Nimbus-7 giving the radiation balance at the top of the atmosphere. The estimates of the atmospheric heat source turned out to be considerably smaller than those provided earlier in the literature, mainly because of different assumptions of the drag coefficient. The atmospheric heat source over Tibet is mainly modulated by the release of latent heat. Over the southeastern and southwestern plateau regions the heat source appears to be in phase with the precipitation yield of the Indian summer monsoon, whereas central Tibet reveals an out-of-phase behavior. Over western Tibet there appears to be hardly any net import of moisture from outside the region, whereas the maintenance of the hydrological cycle over eastern Tibet requires moisture flux convergence from outside the region of up to 40 percent of the mean rainfall, in agreement with what is known about the surface hydrology of Tibet.

Latent heat storage and transfer system and method

Abstract: Heat storage and transfer system and method in which a liquid-solid phase change material and a liquid-vapor phase change material selected for coaction with each other are disposed in a container with a body of the liquid phase of the liquid-vapor material in continuous contact with a body of the liquid phase of the liquid-solid material for superior heat transfer between the materials for giving up and transferring sensible heat and liquid to solid phase change latent heat to vaporize liquid-vapor phase change material and vapor to liquid phase change latent heat to a condenser/heat exchanger and also for superior heat transfer from a heat source such as a solar or electric heater by giving up the heat of condensation of a vapor phase to a solid-liquid material which accepts the heat as sensible heat and as heat of melting.

Bulk heat or cold storage device for thermal energy storage compounds

Abstract: A bulk thermal energy storage device is provided comprising a bulk storage tank containing a latent energy storage material, preferably a phase change material which is subject to repeated melting and freezing during which latent thermal energy is absorbed or released by the phase change material. A plurality of heat exchange devices are generally vertically positioned within the phase change material and at a predetermined distance from each other and from the walls of the storage tank for flow of a heat exchange fluid serially through said passageways in the heat exchange devices. At least one screen is positioned in the storage tank in a generally horizontal position and extending between the walls of the tank and the heat exchange devices for supporting the phase change material when in a frozen condition during the melting cycle of the phase change material to prevent settling of the phase change material to the bottom of the tank. The predetermined positioning of the heat exchange devices and the screen in the storage tank provide for an optimum heat exchange between the heat exchange devices and the phase change material in the tank and prevent the loss of heat exchange efficiency due to a settling-out of frozen particles of the phase change material to the bottom of the tank.

A numerical study of the development mechanisms of polar lows

Abstract: Two well-documented polar lows, one occurring in the Atlantic Ocean and the other in the Pacific Ocean, are modeled numerically. These numerical results are compared with our analytic results in order to determine how the effects of nonlinearity and more complete physics may modify our tentative conclusions. The numerical model used in this study is The Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR), three-dimensional (3-D) primitive equation mesoscale model with a high-resolution planetary boundary-layer parameterization and moist physics. A prediction equation for ground temperature takes into account the existence of variable surface parameters such as albedo, emissivity, thermal inertia. roughness and moisture availability. The Atlantic polar low developed in a shallow but intense baroclinic zone in the Denmark Strait region during the first 24 h of the forecast period. Sensitivity studies with the 3-D model revealed that the baroclinity was sufficient to allow realistic development while the polar low was in the vicinity of this baroclinic zone. However, both convective and non-convective latent heating and the surface fluxes of sensible and latent heat were necessary for the simulation of observed development after this polar low departed from this baroclinic zone and entered the Norwegian Sea. The fact that convective and non-convective latent heating were both essential for simulating the observed development of the Atlantic polar low is consistent with previous analytic-model results. Like the Atlantic polar low, the Pacific polar low developed in an intense baroclinic zone, but this baroclinic zone was deep. Sensitivity studies revealed that baroclinity in conjunction with only non-convective latent heating, overdeveloped the polar low, unlike the analytic results. It was only through the use of the convective parameterization and the convective heating profile that correct development of the simulated Pacific polar low resulted. Surface fluxes played little role in this development. Thus, moist baroclinity and CISK (conditional instability of the second kind) were both important to the observed development of both the Atlantic and Pacific polar lows. DOI: 10.1111/j.1600-0870.1985.tb00444.x

Modelling two dimensional heat and moisture transfer in unsaturated soils, including gravity effects

Abstract: A theoretical model is presented to predict simultaneous transient coupled heat and moisture transfer in partly saturated soils. The formulation is in terms of volumetric moisture content, is two dimensional, includes gravitational flow and takes into account latent heat of vaporization effects. The numerical solution of the problem is accomplished by means of a finite element solution algorithm. Predictions from the numerical model are used to investigate the importance of gravitational flow, for the case of a soil stratum subjected to evaporation losses at the surface. The results achieved show good qualitative agreement with expected behaviour. (Author/TRRL)

Urban-scale variations of turbulence parameters and fluxes

Abstract: Sensible heat (H) and latent heat (LE) fluxes and turbulence statistics in St. Louis, Missouri and the surrounding region are presented. The urban-scale analyses were derived from a series of aircraft transects at 150 m above ground across the metropolitan area during the afternoon convective period. The results revealed that H varied by a factor of two to four in the region; the largest values were associated with the urban heat island. LE varied across the urban area by about a factor of four, but low values of LE overlaid the urban heat island. Consequently, the Bowen ratio (H/LE) exhibited large spatial variability, with a maximum value greater than 1.5 over the city and values less than 0.2 in nonurban areas. The areas along the Mississippi River and adjacent low lying marshland northeast of the downtown area displayed significantly smaller H and Bowen ratio. The derived surface heat storage term (G) for this area as well as for the urban area exceeded either H or LE. The spatial patterns for the standard deviations of the three velocity components (Σ u,v,w ), temperature (Σ T ), and absolute humidity (Σ q ), are also presented. The patterns of Σ u,v,w were similar to the pattern of H. the highest values associated with the urban heat island. The correlation coefficient between the vertical velocity and temperature fluctuations was highest over the city, and a noteworthy minimum was observed in the upwind area over the river and marshland in association with low H. The convective similarity relationships for Σ u,v,w appeared to be approximately valid spatially, as variations were typically less than 10% from theory over the urban area and nonurban region, except for a 40% anomaly in the lowland around the river northeast of the city. Measurements of H from 30-m towers within various land-use areas were contrasted with the aircraft data. Land-use differences in H at the surface were at least as large as those observed at 150 m across the city. This was primarily because of the measurement requirement that the minimum resolvable fetch increases with measurement height.

Theory of natural convection in snow

Abstract: Buoyancy-driven flows of air in show are modeled including the effects of phase change and inclination. Phase change between water vapor and ice is important because of latent heat terms in the energy equation. Upper boundaries of the snow are taken as either permeable or impermeable, with temperature or heat flux specified at the lower boundary. When the ratio of thermal to mass diffusivity is greater than 1, phase change intensifies convection. When this ratio is less than 1, phase change damps convection. The effects of permeable top and uniform heat flux bottom boundary conditions on heat transfer are quantified and described as linear functions of Ra/Racr, where Ra is the Rayleigh number and Racr refers to the critical value for the onset of Benard convection. The slope of each function depends only on the thermal boundary condition at the lower boundary. If a snow cover is inclined, Rayleigh convection occurs for any nonzero Rayleigh number. Velocity profiles for flows in inclined layers with permeable tops are derived, and it is found that velocity is proportional to Ra sin Φ, where Φ is the angle of inclination from the horizontal. The numerical results for different boundary conditions compare reasonably well with experimental results from the literature.

Heat balance components and evapotranspiration from a sedge-grass marsh

Abstract: Daily course of heat balance components (sensible heat, latent heat of evaporation and ground heat fluxes) and evapotranspiration were computed from meterological data recorded in a sedge-grass marsh in South Bohemia, Czechoslovakia. Bowen-ratio method and tank measurements were used, and several comparisons made with parallel aerodynamic measurements. Two simplified empirical formulae for calculating evapotranspiration are suggested: one based on net radiation, the other based on net radiation and on the difference between the mean relative air humidities at the upper and lower levels of the boundary layer above the stand. The seasonal courses and totals of heat-balance components and evapotranspiration obtained in three years (1977 to 1979) are compared and discussed.

Condensation phenomena in supersonic nozzles

Abstract: The heat addition in a Laval-nozzle flow and in a Prandtl-Meyer corner expansion caused by condensation of water vapor in moist air is investigated. In both flow fields at the onset of condensation density, pressure and temperatur increase due to the release of the latent heat of vaporization. Experiments show that the energy addition is related to a relaxation process, and that the changes of the flow parameters can be expected in three different forms. In steady flow the thermodynamic state may change smoothly or it is discontinuous. At high rates of heat addition the flow becomes unsteady and it follows a repetitive cycle. The comparison of steady and unsteady flow fields allows the extraction of simple similarity rules by a dimensional analysis in conjunction with the laws of gasdynamic.

Transverse flow edge heat pipe

Abstract: An edge situated in high speed flow of medium is cooled by a tubular heat pipe having a longitudinal axis situated parallel to the edge. The exterior surface of the evaporator section of the heat pipe forms the edge. The heat pipe contains a working fluid existing in both gaseous and liquefied states. Heat input along the edge evaporates working fluid in the liquid state located in the evaporator section, and the heat is transferred transversely across the longitudinal axis of the heat pipe by the flow of vapor to the condenser section. The vapor condenses in the condenser section and releases its latent heat of vaporization. The condensate flows to the evaporator section by means of wicks composed of capillary material. The heat released into the walls of the condenser section is transferred through the walls by conduction and into another heat transfer device, for example, an active cooling apparatus or the evaporator sections of abutting heat pipes of conventional tubular configuration.

The Distribution of Surface Fluxes and Boundary Layer Divergence in Midlatitude Ocean Storms

Abstract: Surface meteorological observations have been used to calculate the distributions of surface fluxes of momentum, sensible heat, and latent heat and the distributions of surface divergence and curl of surface stress which are characteristic of ocean storms in the Gulf of Alaska. Flux calculations were based on aerodynamic equations which include the effects of high wind speed and stratification of the surface layer. Distributions of divergence determined directly from surface winds were compared with those calculated using the curl of the surface stress. Results indicate that heat fluxes were weak or oven negative for the most intense storms in a band about 300 km wide immediately east of strong cold or occluded fronts. Maximum upward latent heat fluxes occurred to the west of the front, with secondary maxima along the eastern edge of the storm, beyond the 300 km band of weak flux. Surface convergence occurred to the east and divergence to the west of cold or occluded fronts. Vertical velocities c...

Aerosol Formation from Heat and Mass Transfer in Vapour-Gas Mixtures

Abstract: Heat and mass transfer equations and their coupling to the equation for the aerosol size distribution are examined for mixtures in which pressure changes are slow. Equilibrium between an aerosol and its surrounding vapour is shown to be generally fast so that vapour supersaturations are small. Diffusion and conduction control evaporation and condensation on aerosols so that the sign of the aerosol growth term can be determined by the ratio of their relative rates, given by the Lewis number, Le ; for example where Le Cn ( T ), representing the ratio of the rate of heat transport to that of latent heat by vapour diffusion, and which is a strong function of temperature, is introduced to describe the other main controlling physical effect in aerosol formation. Where Cn ≪ 1, as for high-temperature water vapour–air mixtures, the proportion of vapour that can condense as an aerosol is very small. For a fixed total heat transport rate, the maximum aerosol formation rate occurs near Cn ( T ) = 1, which is at T ≈ 4°C for water vapour–air mixtures at 1 atm pressure (101 325 Pa). Specific results in terms of Cn and Le are obtained for the proportion of vapour condensing as an aerosol during the cooling and heating of a mixture in a well-mixed cavity. The assumption of allowing no supersaturations, the validity of which is examined, is shown to lead to maximum aerosol formation. For water vapour–air mixtures predictions are made as to temperature regions in which aerosols will evaporate or not form in cooling processes. The results are also qualitatively applied to some atmospheric effects as well as to water aerosols formed in the containment of a pressurized water reactor following a possible accident. In this context the present conclusion that the whereabouts of vapour condensation is controlled by heat and mass transfer contrasts with previous assumptions that the controlling factor is relative surface areas.

The thermally coupled response of the planetary scale circulation to the global distribution of heat sources and sinks

Abstract: The time-averaged structure of global monsoonal circulations and planetary scale transport processes are determined from the FGGE Level IIIa operational data set generated by the US National Meteorological Center. Through isentropic diagnostics, rotational and irrotational components of the horizontal mass transport and the distribution of heating for the planetary scale are analyzed for the months of January. April, July and October of 1979. The global monsoonal circulations coupled with the planetary scale of differential heating occur in the form of large scale Hadley-type and Walker-type circulations. Net heating within a given region and net cooling in another region in association with latent heat release and differences in boundary flux of energy through the earth's surface and the top of the atmosphere result in forcing of isentropic mass circulations that link energy source with energy sink regions, a result basic to thermally forced circulations. The primary planetary source of energy in the region of Indonesia-Philippines-Southeast Asia is linked through isentropic mass transport with sinks of energy in the regions of the two circumpolar vortices, the Sahara and subtropical anticyclonic circulations. This primary center of the source of energy in the Indonesia-Southeast Asia area moves seasonally from one hemisphere to the other. Other source regions of energy occur over Brazil in January and Central America and Africa in July. Through horizontal transport of mass and energy, the winter Asiatic monsoonal circulation links radiative cooling over Asia to sensible and latent heat release within mid-latitude baroclinic waves and also to latent heat release in the Indonesia, Philippine and New Guinea regions. The role of mid-latitude baroclinic waves in providing for mass and energy exchange between polar and subtropical regions within the time-averaged isentropic structure is briefly discussed. DOI: 10.1111/j.1600-0870.1985.tb00274.x

Heat recovery method and apparatus

Abstract: An improved waste heat-recovery method, and an apparatus embodying the method, are disclosed. Briefly, the improvement relates to recovery of latent heat. An example of how the method improves waste-heat recovery in a conventional solvent-adsorption process is discussed. The conventional process includes introducing steam, which possesses latent heat, into an activated-carbon solvent-adsorption bed to recover solvent from the carbon. A solvent-laden desorbate vapor, which also possesses latent heat, is thereby produced. The desorbate vapor is condensable to an aqueous solvent-laden fluid. The improvement comprises providing a body of liquid water, which is at a temperature lower than the desorbate vapor temperature, and passing the solvent-laden desorbate vapor and the body of liquid water together in a heat-transfer relationship, i.e., preferably through a heat transfer means, to transfer desorbate vapor latent heat into the body of water thereby heating the water. The improvement further includes flashing the heated body of liquid water to vaporize at least a portion thereof. The improvement includes subsequently passing the vaporized heated-water portion into the solvent-adsorption bed whereby a portion of the desorbate latent heat is recovered and re-used in the process.

Transient-temperature and residual-stress fields in axisymmetric metal components after hardening

Abstract: A finite-element method is used to analyse the transient–temperature and residual-stress fields in an axisymmetric metal specimen during quenching. In the calculation of transient-temperature fields it is assumed that an unsteady source of latent heat exists in the specimen when a phase transformation occurs. Factors such as the surface heat transfer coefficient, heat conductivity coefficient, linear expansion coefficient, density, specific heat capacity, latent heat, and so forth are all temperature dependent. The elastic-plastic properties of the specimen are modified according to temperature fields, which are determined; the influence of plastic deformation on the temperature fields is neglected. The agreement between the calculated results and the experimental data shows that the numerical analysis method is reliable. The method may also be applied to the analysis of specimens with other than axisymmetric shape.MST/15

Tidal activity in the middle atmosphere

Abstract: Recent progress in the study of tides in the middle atmosphere ((10÷120) km) includes: i) development of more realistic thermal excitation and numerical simulation models; ii) observational efforts which delineate average seasonal, latitudinal and vertical structures of tides and shorter term variations of these. A survey is presented here of the variation with time and height of atmospheric tides observed at Budrio (45° N, 12° E) in the wind field between 75 and 115 km of altitude during the period 1978–82. Thermal excitation of the tides is mainly due to absorption of solar incident flux by ozone in the stratosphere and water vapour in the troposphere, release of latent heat in clouds, and heat conduction at the ground. The spectral analysis of wind data, obtained at Budrio in a few days of each month of 1978, shows that the semi-diurnal tide is the most easily observable by its regularity and amplitude: consistent amplitudes (around 20 m/s) are recorded in Summer and Winter months at 95 km. The vertical profiles of amplitudes of the diurnal, semi-diurnal and terdiurnal tide observed in zonal winds in some periods of 1979 (January 11–26, March 14–28, July 26–August 4, and September 11–23) demonstrate the great variability of tides not only over a large time scale (seasonal variations) but also on a reduced scale (variations in a few days).