Showing papers on "Latent heat published in 1977"

Evaporation from the wet canopy of a pine forest

Abstract: Measurements of the energy budget of a pine forest were made on 70 days when the canopy was wet. Out of 245 20-min periods when the canopy was wholly wet, 173 were occasions when the latent heat flux exceeded the net radiation, the additional energy being provided by a downward flux of sensible heat. Under the same level of radiation the average rate of evaporation of intercepted precipitation has been found to be three times the average rate of transpiration, so that the loss by evaporation of intercepted precipitation is only partly compensated by the suppression of transpiration. It is concluded that reliable estimates of the water resources of forested areas require a separate calculation of the interception and transpiration components of the total evaporation loss.

Engineering Properties of Snow

Abstract: The general properties of snow are described with a view to engineering applications of data. Following an introduction and a short note on the origins of snow, data are given for fall velocities of snow particles, and for mass flux and particle concentrations in falling snow and blowing snow. Notes on the structural properties of deposited snow cover grain size, grain bonds, bulk density, overburden pressure, and permeability. A section on impurities deals with stable and radioactive isotopes, chemical impurities, insoluble particles, living organisms, acidity, and gases. Mechanical properties are treated only selectively, and the reader is referred to another paper for comprehensive coverage. The selective treatment deals with stress waves and strain waves, compressibility, effects of volumetric strain on deviatoric strain, and specific energy for comminution. The section on thermal properties covers heat capacity, latent heat, conductivity, diffusivity, heat transfer by vapor diffusion, heat transfer and vapor transport with forced convection, and thermal strain. The section on electrical properties opens with a brief discussion on dielectric properties of ice, and proceeds to a summary of the dielectric properties of snow, including dielectric dispersion, permittivity, dielectric loss, and d.c. conductivity. There are also notes on the thermoelectric effect and on electrical charges in falling and blowing snow. The section on optical properties deals with transmission and attenuation of visible radiation, with spectral reflectance, and with long-wave emissivity. The review concludes with some comments on engineering problems that involve snow, and the requirements for research and development.

Numerical analysis of lava lake cooling models; Part II, Application to Alae lava lake, Hawaii

Abstract: The numerical formulation of Shaw, Hamilton, and Peck (p. 384-414 of this issue) using the method of explicit cell balances was applied to the cooling of Alae lava lake, Hawaii. Temperatures in this 15-m-thick, ponded basalt flow were measured over a 4-yr period from 1 week after it formed in August 1963 at a temperature of 1140 degrees C until temperatures throughout the lake had fallen to below 100 degrees C. Representative temperature profiles in the thicker central part of the lake can be reproduced with average deviations of 21 degrees C using one-dimensional models with a lake thickness of 14.6 m, a constant diffusivity of 0.006 cm 2 /sec, a latent heat of 90 cal/g, and a heat withdrawal of 620 cal/cm2 of measured rainfall using the average measured density of basalt in the lake in the calculations. Average differences between computed and observed temperature profiles were decreased to 2 degrees C by using all the following modifications of the initial model: (1) diffusivity was allowed to vary according to the calculated increase of the heat capacity with temperature, the variations of the measured density of the lava with depth in the lake, and the variations of conductivity with temperature and lava porosity; (2) heat loss to rainwater was computed using the measured density structure of the lake; (3) the lake thickness was increased to 14.9 m, a better approximation of the deepest part of the lake, and the latent heat of the basalt was accordingly decreased; and (4), low conductivity and density values were assigned to one of the cells to simulate the highly vesicular and cavernous zones found at shallow depth in the lake. The best results were obtained using a latent heat of 80 + or - 10 cal/g (from 80 percent crystallization of the lava) and a conductivity that increased with temperature at a rate of 0.06 + or - 0.01 percent of its value at room temperature per degree C. Computations using a two-dimensional model indicate that marginal cooling decreased temperatures in the lake more than 1 degrees C only in the outer 15 m of the lake until a year after the eruption and only in the outer 45 m during the final year of cooling. The values for latent heat and conductivity derived from the thermal modeling are in good agreement with values determined directly in the laboratory and calculated from laboratory data.

Substantiation of the Priestley and Taylor Parameter α = 1.26 for Potential Evaporation in High Latitudes

Abstract: Summertime latent heat flux values determined by the energy budget approach are compared to equilibrium model estimates for two shallow lakes and two sedge meadow surfaces in northern Canada. Comparison of energy budget values with equilibrium estimates for each surface show that the latent heat flux can be accurately determined by the Priestley and Taylor (1972) model, where α the ratio of actual to equilibrium evaporation equals 1.26. Results suggest that the Priestley and Taylor parameter is generally applicable to saturated surfaces in high latitudes.

Thermal Energy Exchange Model and Water Loss of a Barrel Cactus, Ferocactus acanthodes

Abstract: The influences of various diurnal stomatal opening patterns, spines, and ribs on the stem surface temperature and water economy of a CAM succulent, the barrel cactus Ferocactus acanthodes, were examined using an energy budget model. To incorporate energy exchanges by shortwave and longwave irradiation, latent heat, conduction, and convection as well as the heat storage in the massive stem, the plant was subdivided into over 100 internal and external regions in the model. This enabled the average surface temperature to be predicted within 1 C of the measured temperature for both winter and summer days.Reducing the stem water vapor conductance from the values observed in the field to zero caused the average daily stem surface temperature to increase only 0.7 C for a winter day and 0.3 C for a summer day. Thus, latent heat loss does not substantially reduce stem temperature. Although the surface temperatures averaged 18 C warmer for the summer day than for the winter day for a plant 41 cm tall, the temperature dependence of stomatal opening caused the simulated nighttime water loss rates to be about the same for the 2 days.Spines moderated the amplitude of the diurnal temperature changes of the stem surface, since the daily variation was 17 C for the winter day and 25 C for the summer day with spines compared with 23 C and 41 C, respectively, in their simulated absence. Ribs reduced the daytime temperature rise by providing 54% more area for convective heat loss than for a smooth circumscribing surface. In a simulation where both spines and ribs were eliminated, the daytime average surface temperature rose by 5 C.

Geothermal heat recovery system

Abstract: A system for recovering heat from a geothermal well includes a quantity of heavy drilling mud filling the bottom of the geothermal well. A hollow heat absorber is disposed within the drilling mud in the well bottom. The heat absorber is supplied with a working fluid such as freon through a supply pipe extending from the top of the well, the pressure head of the working fluid at the heat absorber being commensurate with the depth of the well. A high pressure gas delivery pipe extends from the heat absorber to the top of the well, and is connected to a heat exchanger disposed within a water boiler. The outlet of the heat exchanger is connected to a working fluid supply tank, which is connected in turn to the upper end of the supply pipe. A thermostatic valve interposed between the supply tank and the supply pipe controls the amount of working fluid entering the heat absorber in accordance with the temperature and heat demands of the water boiler. The amount of working fluid in the heat absorber is computed to fill the absorber to the proper height for efficient heat transfer. The working fluid vaporizes in the heat absorber at a pressure equal to the pressure head of the supply pipe, and the pressure and temperature of that vapor causes the vapor to rise at a very high rate and disperse its latent heat into the water boiler.

Properties of some salt hydrates for latent heat storage

Abstract: For the utilization of low-grade heat the latent storage of thermal energy is of great advantage because the heat can be preserved at a constant temperature perfectly matched to the special purpose of application. Investigations on the heat capacities, enthalpies of fusion, densities, crystallization behaviour and other chemical and physical properties have shown that the following salt hydrates are especially suitable media for storing low-grade heat. The eutectic mixture of water and 3.92% by weight of sodium fluoride, melting point (MP) = - 3.5°C, is extremely convenient and cheap for refrigerating or other cooling purposes. Lithium chlorate trihydrate, LiClO3. 3H2O, MP = +8.1°C has an extremely high storage capacity and other advantageous properties as a storage medium in cooling systems, but a very high price will limit its application. Calcium chloride hexahydrate, CaCl2. 6H2O, MP = + 29.2°C, is a suitable and cheap storage medium for heating purposes. For the same application disodium hydrogen phosphate dodecahydrate, Na2HPO4. 12H2O, MP = + 35.2°C, is even better because of the larger storage capacity per unit volume and other advantages which largely compensate the higher material cost. the unique properties of potassium fluoride tetrahydrate, KF. 4H2O, MP = +18.5°C, make it especially suitable for storing low-grade heat. It can directly function as an energy sink and as an energy reservoir in heat collecting and consuming systems. Examples of the practical applicability for residential heating, temperature levelling and cooling are described.

On the Bowen Ratio and Surface Temperature at Sea

Abstract: Gradients of temperature and humidity above water surfaces are analyzed in order to determine the dependence of the long-term average Bowen ratio ..beta.. (the ratio of sensible to latent heat flux) on surface temperature. The least-squares fit that results from investigation of six such bodies of data, and which is supported by recent direct measurements of the fluxes by eddy correlation techniques, can be expressed as ..beta.. = 0.63 ..gamma../s - 0.15, where ..gamma.. is the ratio of the specific heat of air at constant pressure to the latent heat of vaporization of water and s is the slope of the saturated specific humidity curve at the surface temperature. This expression forms the basis of a model which can be used to determine the average surface temperature from routine observations of air temperature and humidity at sea.

Snowmelt: A Two-Dimensional Turbulent Diffusion Model

Abstract: The melt from a ripe snowpack due to sensible and latent heat flux is considered. The problem is two- dimensional; the snow field has a well-defined leading edge. The equations that describe the airflow over the snow are the conservation of momentum, sensible heat, and water vapor. The turbulent diffusion is formulated by semi-empirical turbulence theory. The solution shows the manner in which the point melt varies downwind from the leading edge and the average melt varies with the fetch of the snowpack for varying degrees of atmospheric stability conditions. The results indicate that a reasonably accurate estimate of total melt can be achieved by using the one-dimensional formulae with temperature, humidity, and velocity measurements taken over the central part of the snow field.

Thermodynamic process and latent heat engine

Abstract: The invention involves thermodynamic processes, heat engines, and ways of making gaseous fluid jets by using primarily the latent heat of condensation for the energy required. A vapor such as water vapor is mixed with a gaseous fluid such as air, and the mixture is expanded in a nozzle sufficiently to condense a substantial portion of the vapor and transform the latent heat of the condensation into kinetic energy of the gaseous fluid. The process can be used to form a gaseous fluid jet, which can be used to drive the turbine of a heat engine for either open-cycle or closed-cycle operation. Moist ambient wind can be used as the energy source for producing a jet that drives a wind turbine, or a boiler can be used to form saturated vapor mixed with the gaseous fluid and directed into the nozzle. For closed-cycle systems, the gaseous fluid exhausted from the turbine and the liquid from the condensation of the vapor are both recompressed, the liquid is revaporized, and the vapor and compressed gaseous fluid are recombined. The process is efficient enough so that electric energy from the turbine output can be used to heat a liquid supply for storing energy that is later reconverted to electricity, and operating pressures and temperatures are low enough so that a wide variety of energy sources become usable, including many that are impractical with present heat engines.

Simultaneous determinations of the sensible and latent heat transfer coefficients for tree leaves

Abstract: The heat and mass transfer coefficients for exchange across the fluid dynamic boundary layer over tree leaves were simultaneously determined in a controlled environment chamber. The mass transfer coefficients were calculated from measured values of evaporation, air specific humidity and a value of leaf specific humidity at leaf temperature. The heat transfer coefficients were calculated from measured values of air temperature, leaf temperature and an estimate of the sensible heat flux density calculated as the measured net radiation at the leaf surfaces minus the latent heat flux density. The experiments described in this paper indicate that the equations based on laminar boundary-layer theory can give reasonable estimates of the transfer coefficients of real tree leaves for the velocities most commonly experienced in plant canopies, if they are adjusted by a constant multiplier greater than one. Calculations of local mass transfer coefficients based on temperature measurements at three locations at different distances from the leading edge of the leaves, indicate that the deviation from theory is probably the result of transition to turbulent boundary-layer flow at some distance from the leading edge.

Computation of Surface Fluxes from Climatological and Synoptic Data

Abstract: The effect of using climatological and synoptic atmospheric data commonly available at oceanic locations on the computations of surface fluxes was examined. The data used in this study are a 10-year time series of surface meteorological measurements from Ocean Weather Station P (50°N, 145°W). Examination of the cumulative covariances of the quantities used in bulk transfer calculations of fluxes show that to estimate the stress and sensible heat flux requires measurements at intervals of 2 days or less but that long- term averages or less frequent samples may be used to estimate the latent heat flux. A comparison of the values of monthly wind stress and latent beat flux as calculated from the data organized into the format of the Marine Climatic Atlas with the directly calculated values show good agreement between the two methods. The sensible heat flux deviates more seriously, particularity in months of small fluxes. The effect on computing surface fluxes from surface weather chart data was exam...

Heat Balance in the Ablation Area of the Ampere Glacier (Kerguelen Islands)

Abstract: The heat balance at the surface of the Ampere Glacier (69°E, 49°S) was studied from 8 January to 2 March 1972. The validity of the logarithmic model was verified up to a height of 3 m for wind speed and 2 m for temperature. The energy conservation equation in the heat exchange layer was verified to 2%. On an average, net radiation is responsible for 58% of the melting. However, during periods when turbulence is particularly high, the eddy fluxes of sensible heat and latent heat are responsible for 56% of the melting. The ocean environment manifests itself by fluxes of latent heat which are generally directed toward the surface.

Heat exchange method and apparatus including two non-mixable media

Abstract: Heat exchange method and apparatus are disclosed which include the use of o non-mixable media of different temperatures that are brought in direct contact with each other to effect the transfer of heat from the heating medium to the heat storage medium One of the media is normally a fluid and the other is preferably a substance -- such as a crystalline material -- which is operable between solid and liquid phases, whereby the latent heat produced by the phase transition is utilized in the heat exchanging process Owing to the non-mixability of the two media, the first medium is bubbled through the second in direct heat exchanging contact when the second medium is in the liquid phase A supply conduit including a submerged perforated portion is used to introduce the first medium within the second, an imperforate by-pass conduit being also provided for conveying the first medium in heat transfer relation through the second medium when the supply conduit is clogged by the second medium when it is in its solid phase

Hot water system

Abstract: This invention relates to a hot water system which utilizes heat from the refrigerant of a refrigeration system to produce hot water. The utilized heat consists of the superheat of the refrigerant vapor, the heat of condensation or latent heat, and part of the sensible heat of the liquid refrigerant. The water passing through a water-cooled condensing unit, which is part of the refrigeration system, is heated to a selected temperature by removal of both the latent heat and superheat and part of the sensible heat from the refrigerant as it passes through the condenser unit. The condensing unit has a water inlet and an outlet between which is connected a hot water storage tank. As the water in the condensing unit is heated by absorption of latent and superheat and part of the sensible heat from the refrigerant passing therethrough, the heated water rises and flows by convection into the storage tank. Eventually the storage tank may fill completely with water of a selected temperature. A temperature responsive flow restriction device, or thermostat, is located between the water outlet of the condenser and the storage tank, which restricts the flow of water below a preselected temperature. The heated water, being lighter than the balance of the water in the tank, will remain stratified at the top of the tank and may be drawn off as needed.

Energy Budget by an Eddy Correlation Method

Abstract: A digital data logging system, controlled by a newly designed twin-propeller vane anemometer, was developed and measurements of the energy budget over grasslands were carried out to evaluate an eddy correlation sampling technique. The combined fluxes of sensible and latent heat were underestimated under light wind conditions (0–2 m s−1) and overestimated on another occasion when the sensors probably extended beyond the boundary layer characteristics of the crop. It now appears that with more optimization of the design of the vertical wind sensor, this relatively simple sampling technique has good potential for measuring the energy budget of crops.

Latent and Sensible Heat Flux Calculations at the Air-Sea Interface During AMTEX 74

Abstract: Computations of latent and sensible heat flux at the air-sea interface using the bulk-aerodynamic method are presented for the period of the 1974 Air Mass Transformation Experiment (AMTEX) conducted over the East China Sea. Results show quantitatively the impact of the outbreak of cold and dry polar air over the warm Kuroshio Current as sensible and latent heat flux increased, respectively, from minima of 49 and 182 cal cm−2 day−1 to maxima of 485 and 1099 cal cm−2 day−1. Correspondingly, the total heat flux (sensible and latent) from the sea to the atmosphere from the warm to cold periods increased from 231 cal cm−2 day−1 to 1584 cal cm−2 day−1 which should be a representative range of extreme values for weak and strong heat flux associated with air-sea interaction. Some discussion is given as to the effect of this strong increase in heat flux during air mass modification on the evolution of cyclones over the Kuroshio Current and the Gulf Stream.

Hot water system and condensing unit therefor

Abstract: This invention relates to a hot water system which utilizes heat from the refrigerant of a refrigeration system to produce hot water. The utilized heat consists of the superheat of the refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant. The water passing through a water-cooled condenser, which is part of the refrigeration system, is heated to a selected temperature by removal of both the superheat of refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant as it passes through the condenser. The condenser has a water inlet and an outlet between which is connected a hot water storage tank. As the water in the condenser is heated by absorption of the superheat of the refrigerant vapor, the latent heat of condensation, and part of the sensible heat of the liquid refrigerant passing therethrough, the heated water rises and flows by convection into the storage tank. Eventually the storage tank may fill completely with water of a selected temperature. A temperature responsive flow restriction device, or thermostat, is located between the water outlet of the condenser and the storage tank, which restricts the flow of water below a preselected temperature. The heated water, being lighter than the balance of the water in the tank, will remain stratified at the top of the tank and may be drawn off as needed.

Thermal energy storage and release utilizing combined sensible heat and latent heat of fusion

Abstract: A method for the storage and retrieval of thermal energy is disclosed, which in a two phase, two component system is able to utilize both the sensible heat of water (always one of the components) and the heat of fusion of the second component (a salt which forms a hydrate). The system to be employed must be graphically definable in a phase diagram including a liquidus, the compositional range of the system being selected so as to lie within the compositional range of the liquidus along which the system is to operate during both the heating and cooling cycles.

Domestic appliance system with thermal exchange fluid

Abstract: A domestic appliance system and method are provided for storing and processing food by exchanging heat between the food and a latent heat storing material by forced circulation of a liquid thermal exchange fluid. A plurality of appliances, each having a single heat exchanger for receiving the thermal exchange fluid, connect across supply and return mains which contain the thermal exchange fluid at a differential pressure. Hot supply and return mains are part of a liquid thermal exchange fluid circuit which also includes a heat exchanger for exchanging heat with latent heat storing material in a hot reservoir, a pump, and the appliance heat exchangers with selector and regulator valves to control flow and temperature of thermal exchange fluid within the appliances. Cold supply and return mains are part of a similar liquid thermal exchange fluid circuit for exchanging heat between a cold latent heat storing material and a plurality of appliances. Moderate temperature supply and return mains are part of another similar circuit for exchanging heat in auxiliary heat sinks to deliver the thermal exchange fluid at moderate temperatures to a plurality of appliances during temperature transitions between hot and cold to conserve energy. As the thermal exchange fluid is forced to circulate between selected appliances and independently selected thermal reservoirs or auxiliary heat sinks, food associated with the appliances is subject to programmed temperatures. The thermal reservoirs are charged at off-peak hours and have large thermal capacity and peak thermal delivery capability.

Generation of Available Potential Energy of an Extratropical Cyclone System

Abstract: Generation of available potential energy of an extratropical cyclone system moving across the United States is computed for the period 20–21 March 1962 using standard rawinsonde data. A quasi-Lagrangian frame of reference is used and only the baroclinic component of generation, which is based on specification of a reference state and efficiency factors for the cyclone system, is considered. Parameterization schemes are used to estimate diabatic heating distributions due to convective and stable latent heat release and long-wave radiation. The heating fields are found to be in good agreement with observed weather patterns and computed kinematic parameters. Available potential energy generation estimates appear to be more representative than those from other similar studies of extratropical cyclones. Longwave radiation is a dominant source of available potential energy generation during the system's early development in the southwestern United States. Latent heat release rapidly becomes the major s...

A simple model for estimating the evaporation from a shallow water reservoir

Abstract: A simple model of the energy fluxes of a well-mixed water reservoir is presented based upon its energy and mass budget. The heating processes due to atmospheric-radiative and hydrological forcing are separated and parameterized in terms of two characteristic temperatures. Accordingly, two related time scales can be deduced which describe the energetical response of the reservoir on the two forcing mechanisms. Three different approximations for the latent heat fluxes are introduced. The model which includes the complete energy balance is applied to the Salton Sea (California) and shows good agreement with the observations. DOI: 10.1111/j.2153-3490.1977.tb00753.x

Numerical simulation of cold easterly circulations over the Canadian Western Plains using a mesoscale boundary-layer model

Abstract: Arctic outbreaks over the Canadian Western Plains during the late spring period frequently take the form of a cold east-northeasterly flow over a warmer, sloping surface A mesoscale numerical model is developed in an attempt to simulate such circulations Following Lavoie (1972) the atmospheric structure of the cold air mass is represented by three layers: a constant flux layer in contact with the earth's surface, a well-mixed planetary boundary layer capped by an inversion, and a deep stratum of overlying stable air Averaging the set of governing primitive equations through the depth of the mixed layer yields predictive equations for the horizontal wind components, potential temperature, specific humidity, and the height of the inversion Time-dependent calculations are limited to this layer by parameterizing the interactions between the mixed layer and both the underlying and overlying layers Precipitation from limited convective clouds, and latent heat within the layer are included in terms of mesoscale variables

Product drying apparatus

Abstract: An apparatus for removing moisture from a moisture containing product in which the improvement consists of removing latent heat from the moisture removed from the product and reintroducing the latent heat as sensible heat to heat the air stream which is used to remove the moisture from the product, thus providing a continuous closed cycle drying process which includes its own heat supply.

A Model of the Greenhouse with a Storage-Type Heat Exchanger and its Verification

Abstract: A model describing the heat exchange in the plastic greenhouse with a storage-type heat exchanger was made in order to examine the feasibility of the storage-type heat exchanger for controlling the temperature and humidity in the plastic greenhouse. Relatively good agreement was obtained between measured and calculated environmental conditions in the plastic greenhouse with the storage-type heat exchanger.The magnitude of the heat storage ratio, defined as the ratio of the amount of heat accumulated in water as a heat accumulator to the amount of heat transferred from crop and soil surfaces into the house, was considerably influenced by factors such as short-wave irradiance, ventilation rate and difference in the operation of air circulation system. Sample calculations indicated clearly that under high irradiance the latent heat due to the condensation of water vapor on the inside surface of heat exchange pipes plays an important role for the accumulation of heat.

Process for the recovery of energy and in particular for the recovery of heat on the heat pump principle

Abstract: A body of still water is confined in heat exchange with one or more ambient heat sources whose temperature is usually above but may drop near 0° C. Heat is withdrawn from the body according to the heat-pump principle. If the temperature of the heat sources drops near zero the withdrawal of heat from the body results in the formation of ice in the body and the latent heat of fusion liberated during the ice formation is also withdrawn, so that the time periods during which the temperature of the ambient sources is near 0° C. can be bridged. When the temperature of the ambient sources rises again their heat is used to re-melt the ice in the body of water.