Showing papers on "Latent heat published in 1978"

Melting of a Prairie Snowpack.

Abstract: An energy budget approach is used to study the melt of a prairie snowpack. Air temperature, humidity and wind speed are measured at seven levels in the first 2 m above the snow surface. Evaporation and melt are measured directly with a weighing lysimeter. In the analysis this enables all the terms of the energy budget to be determined independently. On the basis of results from three spring melt periods the net radiation flux is shown to be the major source of energy for the melt of a continuous snowcover. In the absence of local advection, the sensible heat flux is shown to be a function of the energy content of the air mass and more closely related to the 850 mb temperature than to temperatures near the snow surface. The latent heat flux responds to the radiation flux with daytime evaporation and nighttime condensation; however, the net daily flux is usually evaporative.

Properties of melting 3He: Specific heat, entropy, latent heat, and temperature

Abstract: A sequence of experiments has been performed to measure thermal properties of liquid and solid 3 He between the temperatures 1 and 25 mK at melting curve densities. A two-phase mixture of 3 He sample was self-cooled by the Pomeranchuk method. A heat pulse technique was used, combined with measurements of pressure and volume, to yield separate determinations of liquid and solid properties: the specific heat of liquid 3 He in the normal Fermi liquid and superfluid phases; the entropy of solid 3 He above and through a nuclear magnetic transition at 1.10 mK; and an absolute thermodynamic temperature scale based on measurement of latent heat of conversion of liquid to solid.

Numerical Simulation of Tropical Cyclone Development with Latent Heat Release by the Resolvable Scales I: Model Description and Preliminary Results.

Abstract: Axisymmetric hurricane simulators with a hydrostatic model, in which the release of latent heat occurs totally in convective elements that are explicitly resolved on a 20 km horizontal grid, are presented. It is shown that there is good reason to believe that the failures of earlier attempts in this direction were due to model and experimental design. A fairly complete description of the model is given. The solutions do not depend upon overly large lateral mixing coefficients nor upon artificial numerical smoothing procedures. The relationship between this work and CISK theories of hurricane development is discussed. The impact of this work on cumulus parameterization studies is also discussed.

Measurements of the Energy Fluxes Involved in the Energy Budget of a Snow Cover

Abstract: Measurements of the various energy components involved in an energy balance of a snow cover were made at the Elora Research Station, University of Guelph during the winter of 1976. A pressure sphere anemometer and a sonic anemometer-thermometer in conjunction with fast response, fine wire, resistance thermometers and Lyman-alpha humidiometers were used to measure the fluxes of sensible and latent heat by eddy correlation techniques. A net radiometer and soil heat flux plates measured the radiative and soil heat fluxes. The data allowed a complete energy budget to be calculated including the energy stored in the snowpack and/or utilized in the fusion process, determined as a residual. The data indicated the absence of any close relationship between the net radiation and sensible and latent heat fluxes during the diurnal cycle. The flux of heat into the snowpack was found to be a major component of the energy balance. Maximum evaporation from the snow surface was observed to occur following the rep...

Phase change material heat exchanger

Abstract: A phase change material heat exchanger wherein the latent heat of a substance as its physical state changes from solid to liquid, and vice versa, is utilized as a heat storage medium. Structure is also disclosed whereby a heat transfer fluid is intimately associated with the phase change material so as to accomplish the desired heat exchange between the phase change material and the heat transfer fluid. As a result of the construction utilized for the heat exchanger, the addition of homogenizing agents to the phase change material is not required.

The influence of water vapor fluctuations on turbulent fluxes

Abstract: The influence of water vapor fluctuations on vertical turbulent fluxes is examined. It is shown that effects on density and, consequently, buoyancy are insignificant. However, because specific heat of air is a function of specific humidity, these fluctuations are found to influence sensible heat flux significantly. The critical parameter is the Bowen ratio, and a formulation relating the heat flux assuming dry air to the true value is given. The implications of this analysis to flux-gradient relationships in the surface layer are commented on.

Comparison of theoretical and observed temperature profiles in Devon Island ice cap, Canada

Abstract: Summary. A non-steady-state theoretical model is used to predict the present variation of temperature with depth in two boreholes in the Devon Island ice cap, Arctic Canada. The boreholes are 300 m apart and one of them reaches bedrock. The heat transfer equation is solved numerically with the record of past temperatures obtained from measurements of the variations of oxygen—isotope ratio with depth in the cores as surface boundary condition. The effects of ice advection, refreezing of meltwater percolating from the surface (the amount of which is recorded in the cores), heating due to firn compaction and ice deformation, and heat flow in the bedrock below the ice sheet are all included in the model. The free parameters are geothermal heat flux, present surface temperature and heat loss at the surface which depends on the depth of meltwater penetration and other factors. Agreement between observed and predicted temperature—depth profiles is very close. Latent heat released by percolating meltwater is the predominating factor in determining the temperature distribution in the upper half of each borehole. The temperature distribution is insensitive to the value of the factor used to convert oxygen—isotope ratio to temperature.

Thermal storage method and system utilizing an anhydrous sodium sulfate pebble bed providing high-temperature capability

Abstract: Anhydrous sodium sulfate has been shown to have higher thermal content than any other low cost solid material because of its high density, high specific heat, and additional reversible latent heat of solid-to-solid crystal phase change at around 465° F. By compressing anhydrous sodium sulfate into pellets and then forming a bed of these pellets and passing a heated fluid through the bed a relatively great quantity of heat energy may be economically stored in a relatively small volume. Moreover, a rapid rate of heat transfer into or out of the pebble bed can be achieved, up to 400,000 Btu per hour per cubic foot. The same heat transfer fluid may be used to withdraw the heat from the bed for use in space heating or other purposes. The fluid may be air, other inert gases, or a non-acqueous heat transfer liquid which does not react with sodium sulfate, such as a modified terphenyl or a high temperature oil. Advantageously, a thermal storage system embodying this invention can store a relatively great quantity of heat energy per unit volume, for example up to at least 45,000 Btu per cubic foot in a pebble bed containing thirty percent voids, and even higher when the pebbles are smaller and the percentage of voids is lower. This amount of stored heat energy per unit volume with rapid charging and discharging rates is considerably greater than in any practicable arrangement heretofore proposed.

Extreme Evapotranspiration by Irrigated Alfalfa: A Consequence of the 1976 Midwestern Drought

Abstract: The rate of evapotranspiration by irrigated alfalfa at Mead, NE (41°09′N; 96°30′W, elevation 354 m) reached record levels in 1976. Evapotranspiration was measured with precision weighing lysimeters in a field 1.9 ha in size. Evapotranspiration ranged during the growing season from 4.75 to 14.22 mm day−1 and exceeded 10 mm day−1 on one-third of the days studied. On each day of study the ratio of latent heat flux density (LE) to the sum of the net radiation and soil heat flux densities (Rn + S) was such that LE/(Rn + S) > 1, indicating the occurrence of significant sensible heat advection. On clear days during mid-summer the net radiation provides energy sufficient for evaporation of no more than 7 mm day−1. Sensible heat advection provided the remaining energy consumed in evapotranspiration. The unusually strong sensible heat advection likely was due to the generally dry condition of surrounding regions during the drought of 1976.

Analysis of the Tropical Marine Boundary Layer during GATE Using Acoustic Sounder Data

Abstract: An acoustic sounding system placed on the NOAA Ship Oceanographer during GATE provided a unique meteorological data set. Examples of three distinct boundary-layer situations are discussed as they appear on the facsimile records of backscattered acoustic intensity: 1) ubiquitous plume echoes associated with undisturbed conditions, 2) cool-air outflows (or wakes) from either squall-line or isolated cumulonimbus activity associated with disturbed conditions and 3) “hat”- or “hummock” -shaped echoes associated with low-level cumulus clouds usually occurring during weakly disturbed conditions. Profiles of potential temperature and mixing ratio from radiosonde flights launched from the Occonograph are compared with the acoustic data. Convective plumes observed during GATE were less vigorous than those seen over land. Bulk aerodynamic fluxes of surface sensible and latent heat varied in time with the passage of thermal plumes. This indicates a minimum averaging time for valid flux estimates of about 30 ...

Condenser and 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 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 to 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.

Heat storage apparatus and method

Abstract: A heat storage apparatus and method including a heat storage medium encapsulated within a container and heat exchange apparatus for exchanging thermal energy with the heat storage medium. The heat storage medium may include a salt having a relatively high latent heat of reaction at a relatively low temperature range. The dehydration reaction of sodium sulfate decahydrate appears to the most promising reaction for this application. Other suitable salts and salt mixtures for other temperature ranges may also be used. The apparatus includes, where necessary, techniques for stirring the heat storage medium to inhibit stratification of the salt during cycles of dissolution and recrystallization or fusion.

Boundary-layer evolution and nocturnal inversion dispersal—Part I

Abstract: The evolution of boundary layers capped by nocturnal inversions has been studied with an instrumented aircraft. A large sample of the original data obtained on two of the four observation days is presented. Profiles of temperature, humidity and sensible and latent heat flux are compared with the results of numerical models. The sensitivity of simple models for the prediction of nocturnal inversion dispersal is discussed in relation to certain measured input parameters.

Eddy flux measurements over the ocean and related transfer coefficients

Abstract: Eddy correlation measurements of vertical turbulent fluxes made during AMTEX 1975 are used to assess the reliability of flux prediction from established bulk transfer relations, using both surface-layer and planetary boundary-layer formulations. The surface-layer formulae predict momentum and latent heat fluxes to an accuracy comparable to the direct eddy correlation method, using transfer coefficients of CDN (at 10m and in neutral conditions) increasing with wind speed, and a constant CEN ∼- 1.5 × 10−3. The data suggest CCHN, for sensible heat, increases significantly with wind speed and is on average 30% lower than CCEN The boundary-layer drag coefficient, CGD, agrees within about 40% of recently published values using a vertically averaged geostrophic wind to the height of the lowest temperature inversion, corrected for trajectory curvature. Values of θ*/δθ from which CCGH is derived, are in excellent agreement if the published values are modified to account for inappropriate surface temperatures used in their derivation. Preliminary values of CGE are also presented.

Mass and Energy Budgets of a 1 km High Atmospheric Box over the GATE C-Scale Triangle during Undisturbed and Disturbed Weather Conditions

Abstract: Using vertical wind, temperature and humidity profiles in the C-scale triangle during GATE from 2–5 September 1974, the budgets of mass, latent heat and dry and moist static energy are calculated in the lowest kilometer of the atmosphere. The computations are performed for intervals of 3–6 h. Using radar pictures the results are classified as “undisturbed” or “disturbed” with respect to the convective activity. The horizontal flow near the sea surface is nearly always convergent. During disturbed situations the low-level convergence (∼10−4 s−1) is about one order of magnitude larger than during undisturbed conditions. When relating the convection (radar echo covergage) to the low-level convergence it is found that a certain background value of convergence must be exceeded before radar echoes (raining convection) develop and that the convection reacts with a delay of 3–4 h to variations of the low-level divergence. During disturbed situations the subgrid-scale flux of moist static energy at the se...

The structural phase change in s-triazine. II. Specific heat measurements

Abstract: For pt.I see ibid., vol.11, p.1761 (1978). The specific heat of s-triazine has been measured using an adiabatic calorimeter in the temperature range 100-335K. A rapid rise in the specific heat, followed by a small latent heat discontinuity was observed at around 198K and this is identified with the quasi-continuous structural phase transition observed in previous X-ray diffraction studies. A mean-field model is shown to account for the main part of the anomaly, but significant features remain which are attributed to fluctuation effects. A further specific heat anomaly was observed around 268K and this is briefly discussed.

Numerical simulation of an industrial cumulus and comparison with observations

Abstract: A two-dimensional field-of-flow numerical model of cloud development is used to study a cloud that formed over a refinery as a result of heat dissipated to the atmosphere. The observed vertical structure of the atmosphere provided initial conditions. The wind necessarily was simplified to a unidirectional flow. The cloud-initiating perturbation consisted of sensible and latent heat equal to the waste heat rejected to the atmosphere by the refinery. When conditions were matched to those reported, the simulated cloud agreed in most particulars with the observations. Sensitivity tests showed that the simulated cloud depends too strongly on ambient wind speed and shear. This perhaps is a generic defect of two-dimensional formulations. The response of the simulated cloud to expected changes in heat flux density appears more realistic than its response to small changes in ambient wind. The cloud evolution consists of bubbles forming and breaking away from the main cloud mass, then moving downwind and d...

Molten-Salt Thermal-Energy Storage Systems

Abstract: The feasibility of storing thermal energy at temperatures of 450 C to 535 C in the form of latent heat of fusion was examined for over 30 inorganic salts and salt mixtures. Alkali carbonate mixtures were chosen as phase-change storage materials in this temperature range because of their relatively high storage capacity and thermal conductivity, moderate cost, low volumetric expansion upon melting, low corrosivity, and good chemical stability. Means of improving heat conduction through the solid salt were explored.

Mechanics of Multiphase Fluxes Over the Ocean

Abstract: The study of multiphase fluxes of water over the ocean has long been recognized by scientists (Roll, 1965) as being important to the understanding of the exchange process between the ocean and the atmosphere. Recently, Ling and Kao (1976) have successfully obtained a preliminary solution showing how water droplets produced by both the whitecaps and sea sprays play a major role in the transport of energy and moisture from the ocean. The evaporating water droplets produce a large moisture source for the humidity field, while the latent heat of evaporation contributes to a large heat sink for the temperature field. The resultant temperature stratification further influences the stability of the wind field which in turn affects the exchange processes. Thus the problem was solved by a set of coupled equations governing both the wind, the droplet concentration, the humidity, and the temperature fields. In addition, one must further consider the coupling effect between the surface layers of the atmosphere and the ocean. Under high sea states most of the forces produced between the wind and the sea are through the form drag on the waves. This produces a surface (drift) layer of water to move faster than the orbital velocity of the wave crest, thus causing the crest to break.

Energy transfer in the tropical subcloud layer measured with DC‐6 aircraft during GATE

Abstract: Turbulent fluxes of heat and moisture measured during the GARP Tropical Atlantic Experiment of 1974 (GATE) are analyzed with respect to magnitude, distribution with height, intercorrelation and relation to synoptic weather systems. Sensible heat transport on the average is small, whereas latent heat transport is large and nearly always directed upward. In and near convective cloud masses both fluxes become very large compared to clear air, especially sensible heat transfer. A qualitative model of cold and warm downdrafts is presented. There are not only warm, moist updrafts, but also warm, dry downdrafts sinking against buoyancy so that sensible heat fluxes up and down nearly cancel. The role of enhanced fluxes in the general circulation is discussed. DOI: 10.1111/j.2153-3490.1978.tb00869.x

Stability Analysis of Deep Cloud Streets

Abstract: Linear stability analysis of cloud streets is investigated by including the latent heat and considering a few types of wind profiles. The release of latent heat follows the wave-CISK hypothesis. The results indicate that as the buoyance force released by latent heat becomes dominant, the most unstable mode is stationary relative to the mean wind, and the orientation of cloud streets is parallel to the direction of the wind shear. On the other hand, if the conversion of kinetic energy becomes important, the cloud streets which are perpendicular to the wind shear and propagating relative to the mean wind become most unstable. Results also show that the wavelength, growth rate and orientation angle of the most unstable mode are very sensitive to the height of cloud tops, the strength of wind shear, static stability and the environmental moisture profile. These results compare well with other theoretical results and observations.

Storage of heat for subsequent use - using reversible chemical reaction with greatly reduced ambient losses

Abstract: The periodic storage and discharge of heat uses at least one heat transformer contg. a working medium. This undergoes an endothermic reversible reaction to give a solid and a gaseous component. In the storage phase, heat is added to the absorber/releaser and the medium yields the gaseous component, which flows into the condenser/evaporator section. Here it condenses releasing heat. In a heat release mode, the condensate in the condenser/evaporator section is evaporated. This then releases heat in the absorber/release zone by reacting with the solid phase which absorbs it. Solar or electric energy can be used as sources of heat. The energy released by condensation is released to atmosphere or to a latent heat store. The heat released during the release mode is used for water heating or space heating. For use in storing solar energy or electrical energy during the night.

Condensation soldering facility

Abstract: A first vessel is mounted within and spaced from a second vessel A primary heat transfer liquid is introduced into the first vessel and a secondary heat transfer liquid introduced into the second vessel Heating coils immersed in the secondary heat transfer liquid are energized to boil the secondary liquid to form a body of secondary vapor, a portion of which condenses on the outer surface of the first vessel to heat said vessel and boil the primary liquid therein to form a body of primary vapor An article having previously applied solder thereon is immersed in said body of primary vapor and the solder caused to melt and flow due to the latent heat of vaporization transferred thereto by the primary vapor condensing thereon Additionally, a tertiary body of vapor is formed above the primary vapor to substantially preclude the loss of the primary vapor to the atmosphere

On the general circulation of the atmosphere without clouds

Abstract: An experiment has been performed with an 18-level, hemispheric, stereographic general circulation model to clarify the radiative role of clouds in the general circulation of the atmosphere. All cloud properties were removed from the radiation scheme in the model, and it was then integrated to generate a new set of quasi-equilibrium atmospheric statistics which were compared with a control run. Apart from an expected warming of the surface and troposphere the overall changes to the general circulation characteristics following the removal of clouds were surprisingly small. For example, the zonal mean latitude-height distributions of the zonal wind and eddy kinetic energy were almost identical to those of the control run, while synoptic distributions of most model variables revealed little change in character attributable to the removal of cloud. The largest modification occurred in the mean meridional stream function, with corresponding effects in surface pressure. This result was explicable in terms of the enhanced role of latent heat in the model which occurred at the expense of sensible heat. Despite the individual variations in latent and sensible heat, the poleward flux of total heat by large-scale eddies was essentially unchanged in the two models. This surprising result indicated that the forcing function for the general circulations of the two models was also unchanged, and moreover that this forcing function was independent of cloud cover. Where possible, explanations are advanced to account for the limited response of the model to the removal of cloud. It appears that the major function of clouds in radiative calculations, at least in extended general circulation simulations, is to provide an obscuration or blocking effect, rather than a more subtle radiative-dynamical coupling mechanism.