Showing papers on "Latent heat published in 1975"
01 Jan 1975
TL;DR: Parametric designs for two latent heat materials (sodium thiosulfate pentahydrate and a paraffin wax) and for a sensible heat material (a 1:1 mixture of water and ethylene glycol) were compared as to cost, performance, and space requirements.
Abstract: Latent heat thermal energy storage materials suitable for solar heating and off-peak air conditioning were investigated and evaluated in terms of criteria developed to judge their usefulness. The often recommended sodium sulfate decahydrate and its mixtures were shown to have undesirable melting properties, causing a reduction in storage capacity upon repeated cycling. Materials more suitable at present are paraffin waxes for solar heating and paraffin waxes and tetrahydrofuran hydrate for off-peak air conditioning. Sensible heat storage has the economic advantage of not requiring heat transfer surfaces between storage and collection and between storage and delivery. Latent heat storage provides operational advantages of smaller temperature swings and lower, more efficient solar collector temperature, smaller size and lower weight per unit of storage capacity. The optimization of the thermal energy storage subsystem is dependent on the collection and delivery characteristics of the system. Parametric designs for two latent heat materials (sodium thiosulfate pentahydrate and a paraffin wax) and for a sensible heat material (a 1:1 mixture of water and ethylene glycol) were compared as to cost, performance, and space requirements. The conditions of equal cost for latent heat and sensible heat storage systems were determined as functions of latent heat capacity, thermal conductivity, and the temperature swing allowed in the sensible heat storage tank. The comparative designs include the cost of the heat exchanger required for latent heat storage and the operating penalty due to storage temperature swings inherent in sensible heat storage.
112 citations
TL;DR: In this paper, the effect of parent phase ordering in depressing the T 0 temperature has been satisfactorily explained using a quasichemical approach and a consequent difference in bonding enthalpies.
99 citations
TL;DR: In this paper, a numerical model for the study of the interactions of dynamics, photochemistry and radiation in the stratosphere and mesosphere is presented. But the model is not applicable to momentum fluxes: these are currently specified from observations made mainly from the selective chopper radiometer on the Nimbus V spacecraft.
Abstract: The paper sets out the detailed formulation of a numerical model whose purpose is the study of the interactions of dynamics, photochemistry and radiation in the stratosphere and mesosphere. Two integrations of the model for 900 days are described in which many features of the atmosphere are reproduced but with important differences of detail.
The dependent variables are zonal means of the relevant meteorological quantities, held as functions of time, latitude and height (log pressure) with a resolution of μ/19 in latitude and 0.5 in pressure scale height.
Eddy fluxes of heat and matter are treated by large-scale diffusion coefficients. This treatment is not applicable to momentum fluxes: these are currently specified from observations made mainly from the selective chopper radiometer on the Nimbus V spacecraft.
Radiative coolings due to CO2 and O3 emission are computed from simplified expressions which are essentially cooling-to-space approximations with emissivities obtained by curve-fitting against the results of more elaborate treatments. Absorption of solar radiation by ozone is obtained from tabulations of absorption against ozone amount traversed. Radiation and latent heat release in the troposphere are specified climatologically.
The photochemistry in the integrations described here is the classical ozone scheme but, with a view to investigating possible stratospheric pollution problems, integrations have been performed with the inclusion of reactions involving nitrogen and hydrogen compounds. These will be described in a later paper.
99 citations
TL;DR: The Bowen-ratio profile method for calculating total carbon dioxide, latent heat, and sensible heat flux density above a corn crop was used by measuring temperature, water vapor, and CO2 concentrations at several heights in the aerodynamic boundary layer of the crop as mentioned in this paper.
Abstract: The Bowen-ratio profile method for calculating total carbon dioxide, latent heat, and sensible heat flux density above a corn crop was used by measuring temperature, water vapor, and CO2 concentrations at several heights in the aerodynamic boundary layer of the crop. The ratio (α) of sensible heat flux density to carbon dioxide flux density as well as the Bowen ratio (β) were used in the computations. The two ratios, α and β were determined graphically from the slopes of linear plots of temperature vs CO2 concentration and vs water vapor. Each of the energy flux densities was computed from the two ratios and net radiation minus soil heat flux density. An analysis of probable error was performed on the Bowen-ratio profile method to evaluate the accuracy of the flux density estimates. Less than 10% error was found for latent heat flux density and less than 15% for carbon dioxide flux density under normal midday conditions for the instrumentation used. However, the carbon dioxide flux density error increased to over 40% when the sensible heat flux was small.
87 citations
TL;DR: In this paper, two methods of pararmeterizing expressions for ground surface evaporation rate that are used in planetary boundary layer models have been examined and the analysis was performed by running a planetary boundary layers numerical model several times, using at each time either Method A or B with different specifications of M and h.
Abstract: Two methods of pararmeterizing expressions for ground surface evaporation rate that are used in planetary boundary layer models have been examined. In one method (Method A) the surface evaporation rate is proportional to M (Qs − Q1). In the other (Method B) the surface evaporation rate is proportional to hQs − Q1. Here Qs is the surface saturation mixing ratio, Q1 the mixing ratio at the lowest level of the atmospheric model, M the moisture availability parameter, and h the relative humidity immediately above the ground. The analysis was performed by running a planetary boundary layer numerical model several times, using at each time either Method A or B with different specifications of M and h. The calculated diurnal surface temperature and surface latent heat flux were examined. Specific results are: 1) for equal M andh, Method B results in higher surface temperatures than Method A; 2) the surface evaporation rate calculated using Method A is less sensitive to changes in M, than the surface eva...
47 citations
39 citations
TL;DR: In this paper, a model of the energy exchange between the atmosphere and a vegetated surface has been developed and used to investigate the sources of energy available for evaporation of precipitation intercepted by a forest canopy.
Abstract: A model of the energy exchange between the atmosphere and a vegetated surface has been developed and used to investigate the sources of energy available for evaporation of precipitation intercepted by a forest canopy. Simulations with this model have demonstrated that a forest canopy wetted by rainfall will partition more of the absorbed radiant energy into latent heat exchange than an unwetted canopy in the same environment. This energy diversion creates a decrease in sensible heat transfer from the canopy to the atmosphere and a smaller decrease in a long-wave radiation emitted by the canopy.
38 citations
TL;DR: In this article, the energy and angular momentum budgets for a three-dimensional model hurricane described by Kurihara and Tuleya are analyzed for a 3D model hurricane, where the mean flow dominates the transport by importing those quantities into the inner area and exporting potential energy.
Abstract: Energy and angular momentum budgets are analyzed for a three-dimensional model hurricane described by Kurihara and Tuleya. Eddies which developed in the model are maintained in the mature stage by energy supply from both mean kinetic and total potential energy. In the evolution of eddies during the early development stage of the storm, the supply from potential energy is more important. Eddies export latent, internal, kinetic energy and relative angular momentum from the storm core region. They also contribute to the outward transfer of energy through pressure work. However, the mean flow dominates the transport by importing those quantities into the inner area and exporting potential energy. The energy and angular momentum budgets are primarily controlled by the mean flow, though the role of eddies is not negligible for the budgets of angular momentum, kinetic and latent energy in the inner region. For the maintenance of mean kinetic energy in the inner area, both generation and advection make p...
34 citations
TL;DR: The Bowen ratio as mentioned in this paper is the ratio between sensible and latent heat lost by the ocean, which depends in part on the sea surface temperature, and is defined as the amount of available energy that leaves the oceans as sensible, rather than latent heat.
33 citations
TL;DR: In this article, it was shown that the fraction of absorbed radiation transferred into the ambient gas by collisions changes significantly with particle size and altitude, and that the dependence of the heating rate, characterizing the exchange of energy between particles and gas, on various factors such as the planetary albedo may have a bearing on upper atmospheric behavior.
29 citations
TL;DR: This paper made a synthesis of atmospheric conditions for 20,000 yr BP based on fairly standard palaeoclimatological data and procedures from mean zonal conditions at 20° latitude intervals from 80°N to 80°S.
Abstract: WE have made a synthesis of atmospheric conditions for 20,000 yr BP based on fairly standard palaeoclimatological data and procedures From mean zonal conditions at 20° latitude intervals from 80°N to 80°S we have computed radiative heating rates and the energy balance of atmospheric columns We find that net cooling of the atmosphere by radiative processes was smaller at 20,000 yr BP than it is now The total heating of the air, which sums to zero in the annual average except during periods of climatic change, is the sum of heating by latent heat liberation, heating by conduction and convection from the boundary layer, and radiative cooling (see for example Fig 7 in ref 1) Because the change in radiative cooling is comparable to boundary layer heating itself, we postulate that the decrease in cooling is accompanied primarily by a decrease in heating from rainfall and therefore that global rainfall was smaller at 20,000 yr BP than it is now Examination of the magnitudes of the three components suggests that the decrease in rainfall was about 10%
TL;DR: In this article, the authors used an instrumented light aircraft and radio-sondes to investigate the structure and development of the boundary layer over southern England during two periods of active, shallow convection.
Abstract: Observations of the convective boundary layer over southern England using an instrumented light aircraft and radio-sondes enable its structure and development to be described for two periods of active, shallow convection. Budgeting is used to deduce the sensible heat flux as a function of height, showing a downward flux in the upper part of the boundary layer associated with entrainment of warmer air from above. For the two occasions studied results indicate that the entrained sensible heat flux is about 0·3 of the sensible heat flux at the ground. For one of the occasions a moisture budget was possible yielding a value of the mean latent heat flux at the ground.
01 Apr 1975
TL;DR: In this article, a global circulation model (GCM) developed at the National Center for Atmospheric Research (NCAR) has been used to simulate the large-scale features of the Asian-African summer monsoon.
Abstract: A global circulation model (GCM) developed at the National Center for Atmospheric Research (NCAR) has been used to simulate the large-scale features of the Asian-African summer monsoon. The model has 6 vertical layers of 3-km thickness with a 2½° horizontal latitude-longitude grid. The physical processes incorporated are solar and infrared radiation, with cloudiness explicitly calculated from a model-generated relative humidity distribution. The latent heat released from precipitation is derived from stable lifting and cumulus convection. Also included in the model are subgrid-scale vertical and horizontal transports of momentum, sensible heat, and latent heat. We compare the computed sea-level pressure, wind, cloudiness, and precipitation patterns with. observed data and, in particular, concentrate on the strong low-level monsoon jet near eastern Kenya and Somalia. The model correctly simulates this jet in position; however, the wind maxima are weaker than observed. Because of the relatively coa...
Journal Article•
TL;DR: In this paper, the development of the propagating and the stationary bands in a three-dimensional model of a hurricane was investigated, and the results of two experiments, one in which the so-called nonconvective release of latent heat in the upper troposphere was included and the other in which this heating was not incorporated, were compared.
Abstract: The developments of the propagating and the stationary bands in a three-dimensional model of a hurricane (Isbell, 1964) are investigated. Propagating bands in the vertical motion fields in the middle and the upper troposphere form in the regions of strong heating in the upper troposphere and weak cooling in the middle troposphere. The structures of the wind, temperature and pressure fields in these bands are similar to those observed in the outer radar bands of hurricanes. Strong, nearly stationary bands form close to the center in the intense storm stage. Results of two experiments, one (M1) in which the so-called nonconvective release of latent heat in the upper troposphere is included and the other (M2) in which this heating is not incorporated, are compared. Convective release of latent heat is included in both experiments. The stationary bands in which form in M1, also develop in M2. The propagating bands which form in M1, however, do not develop in M2. The rate of intensification of the sim...
TL;DR: In this paper, the influence of free surface conditions on the fluxes under near neutral stability conditions was analyzed in a wind-water-wave channel with four variations of the interfacial conditions.
Abstract: Wind, temperature and humidity profiles obtained in a wind-water-wave channel with four variations of the interfacial conditions were analyzed in order to assess the influence that the free surface conditions have on the fluxes under near neutral stability conditions. The dimensionless humidity gradient remained essentially constant at 1.2 for all surface variations except for the case of suppressed waves where its value was 0.86. On the other hand, the dimensionless temperature gradient demonstrates a definite response to changes in surface conditions and ranges from 0.73 for the suppressed wave case to as high as 1.41 for the larger wind speed (11 m/s), wind-wave cases. Comparing the results from the suppressed surface and wind-wave cases for U∞ = 10 m/s it was observed that the total energy (sensible plus latent heat) transfer remained constant. However, sensible heat flux increased with the suppression of the wind waves whereas latent heat flux decreased.
TL;DR: In this article, measured current waveforms in an RLC circuit are used as a basis for obtaining information on the behavior of wire material at various stages of the explosion, where resistance and energy are derived from the measured current.
Abstract: Measured current waveforms in an RLC circuit are used as a basis for obtaining information on the behavior of wire material at various stages of the explosion. In the premelt region, there is, as expected, complete agreement between measured current and current calculated on the assumption that temperature and resistivity are linear with energy input. After absorption of an energy which under static condition leads to solid−liquid transition, the fit is unsatisfactory but can be improved by treating the wire as a superheated solid for a period of about 20 nsec. During the vaporization stage, resistance and energy are derived from the measured current. If all the energy input is assigned as latent heat of vaporization, the calculated current deviates drastically from the measured current, indicating that for all capacitor voltages used in this study, the process is far from static condition. Furthermore, the higher the energy input rate, the greater the containment forces and the more energy is required to...
TL;DR: In this article, it is shown that long-term average fluxes of sensible and latent heat from clean water surfaces at equilibrium temperature can be expressed analytically in terms of the emissivity, the Stefan-Boltzmann constant, and the surface temperature only.
Abstract: It is proposed that a body of water required to dissipate a fixed quantity of heat (derived from all sources including insolation) will come to an equilibrium temperature essentially determined by the maximization of the evaporation rate, By using this hypothesis and one of several simple expressions for the Bowen ratio versus surface temperature dependency it is shown that long-term average fluxes of sensible and latent heat from clean water surfaces at equilibrium temperature can be expressed analytically in terms of the emissivity, the Stefan-Boltzmann constant, and the surface temperature only. Data obtained in two different field experiments are found to be in good agreement with predictions made by this simple model.
TL;DR: In this article, a linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above Tm with-out loss of heat storage capability.
Abstract: Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures Tm ≥ 100°C can provide fully reversible heats of fusion ΔHm ≥ 35 cal/gm under programmed heating-cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above Tm with-out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non-expendable, heat storage materials.
TL;DR: In this article, a variational principle is applied for initial boundary value problems of unsteady heat flow, and the finite elements method is used to generate approximate solutions to plane and axisymmetic problems.
Abstract: The finite element method has an excellent solution capability for problems requiring transient temperature distribution under time-dependent temperature initial and boundary conditions. Some exceptional features in handling are: space variations of temperature-dependent material properties, irregular boundary geometries of problem regions, temperature and heat flux boundary conditions at any point in the problem region, and freedom in varying the size of the finite discretization within the problem region. This paper presents a general computer-oriented solution technique for geotechnical problems of heat condition, including the effect of latent heat generation and absorption. A variational principle is applied for initial boundary value problems of unsteady heat flow, and the finite elements method is used to generate approximate solutions to plane and axisymmetic problems. Variation in physical and thermal properties of materials with both temperature and space, and functional relationships between the amount of water frozen and the temperature are taken into account automatically during the process of heat condition. /ASCE/
01 Jan 1975
TL;DR: In this paper, the authors investigated the effects of cumulus clouds on the temporal and spatial characteristics of atmospheric energy content, and showed that changes in energy content of the cloud environment and the flux of energy are shown as functions of height and radial distance from the cloud axis.
Abstract: : The report investigates the effects of cumulus clouds on the temporal and spatial characteristics of atmospheric energy content. Changes in energy content of the cloud environment and the flux of energy are shown as functions of height and radial distance from the cloud axis. Energy related to water vapor accounts for most of the energy change in the cloud's vicinity. In the outer region, changes in water-vapor enthalpy are counterbalanced by changes in dry-air enthalpy, but potential energy change dominates. The total energy used in attempting to to decrease conditional atmospheric instability is given by the total amount of energy produced by the condensate formed, regardless of whether it falls as rain. The study presents data which, together with reasonable assumptions about the natural occurrence of cloud cells, leads to an estimated relaxation time of convection of about ten hours.
TL;DR: The turbulent fluxes of momentum, sensible heat and latent heat associated with a cold frontal passage of October 8, 1972 over Lake Ontario are examined in this article, and the effects on the lake surface temperature are discussed.
Abstract: The turbulent fluxes of momentum, sensible heat and latent heat associated with a cold frontal passage of October 8, 1972 over Lake Ontario are examined. There are marked increases in the momentum and moisture fluxes after the frontal passage but the effects on the sensible heat flux are more complicated. The effects on the lake surface temperature are discussed.
01 Jan 1975
TL;DR: In animals with an external insulation in the form of feathers or fur, the resistance to heat flow can be increased in the cold by piloerection, or fluffing up the coat, with the result that the amount of trapped air is increased as discussed by the authors.
Abstract: Although the temperature of the body core in mammals and birds is maintained at a fairly constant level, the temperature of the peripheral tissue may vary widely The effect of these variations in temperature, which are usually associated with changes in the thickness of the peripheral shell, is to modify the resistance to heat loss (Chapter 2) In animals with an external insulation in the form of feathers or fur, the resistance to heat flow can be increased in the cold by piloerection, or “fluffing up” the coat, with the result that the amount of trapped air is increased In man a similar effect is obtained when he wears extra clothes Within the peripheral tissue, heat conductance is modified by variations in the flow rate of blood that transfers heat from deep in the core to the skin surface Even under thermoneutral conditions, however, external insulation is already near its minimum On exposure to heat, therefore, an increased peripheral blood flow plays an important role in increasing the rate of heat loss In animals that sweat, and particularly in man with his very high rate of cutaneous moisture loss, the increased blood flow provides both the latent heat of vaporization and a supply of water for evaporation