Showing papers on "Latent heat published in 1979"

The turbulent heat flux from arctic leads

Abstract: The turbulent transfer of heat from Arctic leads in winter is one of the largest terms in the Arctic heat budget. Results from the AIDJEX Lead Experiment (ALEX) suggest that the sensible component of this turbulent heat flux can be predicted from bulk quantities. Both the exponential relation N = 0.14R x 0.72 and the linear relation N = 1.6 × 10−3 R x+ 1400 fit our data well. In these, N is the Nusselt number formed with the integrated surface heat flux, and R x is the Reynolds number based on fetch across the lead. Because of the similarity between heat and moisture transfer, these equations also predict the latent heat flux. Over leads in winter, the sensible heat flux is two to four times larger than the latent heat flux. The internal boundary layer (IBL) that develops when cold air encounters the relatively warm lead is most evident in the modified downwind temperature profiles. The height of this boundary layer, δ, depends on the fetch, x, on the surface roughness of the lead, z 0 and on both downwind and upwind stability. A tentative, empirical model for boundary layer growth is % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaadaWcaaqaaiabes% 7aKbqaaiaadQhadaWgaaWcbaGaaGimaaqabaaaaOGaeyypa0JaeqOS% di2aaeWaaeaacqGHsisldaWcaaqaaiaadQhadaWgaaWcbaGaaGimaa% qabaaakeaacaWGmbaaaaGaayjkaiaawMcaamaaCaaaleqabaGaaGim% aiaac6cacaaI4aaaaOWaaeWaaeaadaWcaaqaaiaadIhaaeaacaWG6b% WaaSbaaSqaaiaaicdaaeqaaaaaaOGaayjkaiaawMcaamaaCaaaleqa% baGaaGimaiaac6cacaaI0aaaaaaa!472D!\[\frac{\delta }{{z_0 }} = \beta \left( { - \frac{{z_0 }}{L}} \right)^{0.8} \left( {\frac{x}{{z_0 }}} \right)^{0.4} \] where L is the Obukhov length based on the values of the momentum and sensible heat fluxes at the surface of the lead, and Β is a constant reflecting upwind stability. Velocity profiles over leads are also affected by the surface nonhomogeneity. Besides being warmer than the upwind ice, the surface of the lead is usually somewhat rougher. The velocity profiles therefore tend to decelerate near the surface, accelerate in the mid-region of the IBL because of the intense mixing driven by the upward heat flux, and rejoin the upwind profiles above the boundary layer. The profiles thus have distinctly different shapes for stable and unstable upwind conditions.

Advectively-assisted evapotranspiration from irrigated urban vegetation

Abstract: The energy balance of an irrigated suburban lawn in Vancouver, B. C. during fair summer weather is presented. The results indicate that the evapotranspiration regime is assisted by advected energy from drier surfaces. Areal estimates of the suburban energy balance suggest that the latent heat flux from such irrigated surfaces is sufficient partially to compensate for the decrease in evapotranspiring areas by urbanization.

Aircraft observations of the structure of the lower boundary layer over the sea

Abstract: Results from an investigation of the turbulence structure of the lower half of the convective boundary layer over the sea around the UK in a wide variety of meteorological conditions are presented. The data were obtained on eight flights made by the Hercules aircraft of the Meteorological Research Flight. Differences in structure between boundary layers over sea and over land are emphasized, the most notable being the relatively increased importance of mechanically driven mixing over the sea. This means that a more general scaling scheme is required which retains both u* and zi as scaling parameters. Such a scheme orders the results quite effectively. Dimensionless profiles of momentum, sensible heat and latent heat fluxes are presented, together with dimensionless variance profiles. Excellent agreement is found between these and theoretical predictions from numerical models. Surface fluxes are estimated and compared with bulk aerodynamic formulae. The turbulence statistics are shown to be in good agreement with those published by other workers.

Variability in the Annual Fields of Large-Scale Atmospheric Water Vapor Transport

Abstract: Annual mean holds of the zonal and meridional components of the vertically integrated water vapor flux in the atmosphere have been computed objectively from six years of Northern Hemispheric upper air data. Emphasis is placed on the longitudinal structure of these fields in order to identify regional contributions to the annual variations of the zonally averaged moisture fluxes. These temporal changes, particularly those associated with the meridional transport of latent heat. appear large enough to impact significantly on the maintenance of the atmospheric energy balance. While the distribution and quality of some upper air data make it difficult to estimate the degree to which the analyses precisely duplicate atmospheric behavior everywhere, this study provides documentation of a wide range of interannual variability. In this regard, the behavior of one of the years chosen for study contrasts sharply with that of the rest of the sample, as was similarly noted for other quantities evaluated by R...

Mathematical model for lumber drying. I. Principles involved

Abstract: The various processes involved in moisture movement in wood are described, and appropriateequations with parameters are presented. The processes are: 1) heat transfer through the boundary layer in response to a temperature differential; 2) heat conduction in wood in accordance with Fourier's equations; 3) bound-water diffusion in response to a vapor pressure gradient; 4) capillary flow in response to net surface tension forces determined by the free-water differential; 5) evaporation from the wood surface due to a vapor pressure differential between a wood surface and the kiln atmosphere; and 6) the transport of latent heat (activation energy) by diffusing and evaporating molecules. Equations for vapor pressure, RH, and heat conductivity are obtained from the literature and, where necessary, parameters determined by least-squares fit of published data. Boundary layer heat and moisture transfer coefficients are calculated from drying rate data when the surface MC exceeds fiber saturation point. Equations and parameters involved in capillary flow, and the relationship between moisture diffusion coefficient and MC are determined indirectly from experimental data. -- AATA

Water Loss and Canopy Resistance of a Young Sitka Spruce Plantation

Abstract: Transpiration of a 7 m-high Stika spruce forest was investigated using measurments of net radiation, sensible heat and ground heat fluxes in an energy balance to give latent heat flux, and hence canopy resistance from the Penman-Monteith equation. Sensible heat flux was measured by the eddy-correlation method using a Fluxatron circuit.

a Numerical Investigation of New England Coastal Frontogenesis.

Abstract: A three-dimensional, primitive equation, boundary-layer model is used to investigate wintertime mesoscale frontogenesis along the New England coast. Some features included in the model are a terrain-following coordinate system to study the effects of irregular terrain, a stable beating scheme to allow for the release of latent heat and to estimate precipitation, and an upper boundary condition on pressure which permits interaction with the synoptic-scale circulation. Numerical experiments with the model have verified the hypothesis that coastal fronts form when a cold anticyclone is located just to the north or northeast of New England, and a wave disturbance at 700 mb approaches the northeast from the midwest United States. Polar continental air flowing southwestward around the eastern side of the anticyclone is modified rapidly by sensible and latent heat transfer from the relatively warm Atlantic Ocean. As the 700 mb trough approaches the northeast, surface winds over the ocean veer from north...

On the two-dimensional, hydrostatic flow of a stream of moist air over a mountain ridge

Abstract: The small perturbation of a steady, two-dimensional horizontal stream of a moist inviscid, Boussinesq fluid is treated analytically by use of an asymptotic method when a certain parameter ∊ is small and numerically by use of an iterative method for general values of ∊. This parameter is a measure of the difference between dry and wet adiabats in the model atmosphere, which is absolutely stable and which contains a moist layer near the ground. Vapour condenses (evaporates) where the vertical displacement of a fluid particle exceeds the ascent condensation level and the vertical motion is upward (downward). The condensation of vapour and release of latent heat are nonlinear phenomena which are treated, but otherwise the equations of motion and boundary conditions are linearized. We limit our attention to an airflow of uniform properties over a mountain ridge. The hydrostatic approximation is made. As a result, the horizontal wavelengths must be long compared to the vertical ones and lee waves are a...

Shallow Convection on Day 261 of GATE/ Mesoscale Arcs

Abstract: Cloudy convection in the moist layer of a cloud cluster growing in the GATE ship array is examined. Analyses suggest that the moist layer was dominated by features of horizontal dimension roughly 40 km and lifetime roughly 2 h, with arc patterns triggered by dense downdraft air accompanying rainfall, and composed of many small cumulus clouds. Aircraft recorded data on thermodynamic quantities and winds, indicating that the arcs persisted as mesoscale circulations driven by the release of latent heat in the clouds, rather than being driven by the original density current at the surface. It is also suggested that the mesoscale cloud patterns of the moist layer play a primary role in heat transfer upward within this layer, and contribute to the forcing of showering midtropospheric clouds.

Turbulence Measurements above a Pine Forest

Abstract: Eddy fluxes of momentum, sensible and latent heat, and turbulence spectra measured over the Thetford Forest during 10 days in the Spring of 1973 are described. The measured total heat flux (H + λE) for 122 20-min periods agreed closely on average with independent estimates from an energy balance method. There was evidence that the energy balance data gave small systematic overestimates of available energy during the hours before noon, compensated by slight underestimates for the remainder of the day. A comparison of measured wind speeds and friction velocities in neutral stability confirmed the validity of the aerodynamic method for estimating momentum fluxes at heights of a few roughness lengths above the canopy. In stable conditions the log-linear wind profileU = (u */k)(ln ((z -d)/z o) + α (z -d -z o)/L) with α = 3.4 ± 0.4 provided a good fit to the data. Spectra in unstable conditions were generally more sharply peaked than those measured by other workers over smoother terrain: differences were less marked in the case of vertical velocity in stable conditions. Temperature spectra in these stable conditions showed high energy at relatively low wavenumbers, andwT cospectra showed a cospectral gap; both of these results were associated with an intermittent sawtooth structure in the temperature fluctuations.

Analysis of the Convectively Modified GATE Boundary Layer Using in situand Acoustic Sounder Data

Abstract: A boundary-layer categorization scheme based on GATE acoustic sounder data stratifies surface data and tethered balloon data from the NOAA research ship Oceanographer. The results indicate a clear increase in the sensible heat flux across the sea surface during disturbed conditions (the gravity current and storm wake of the disturbance) but no conclusive differences of latent heat and momentum fluxes. The tethered balloon profiles show a near disappearance of the mixed layer within the gravity current and, in the storm wake, a very shallow and cool mixed layer capped by a strong stable layer relative to the undisturbed category. We calculate the vertical motion due to buoyancy-driven entrainment for a range on entrainment parameters after exploiting the categorized tethered balloon profiles to obtain mean gradients at the top of the mixed layer. Because we and others have observed that the shallow mixed-layer depth remains nearly constant with time in the storm wake, this calculated entrainment-i...

Latent Heat-of-Fusion Energy Storage: Experiments on Heat Transfer from Cylinders During Melting

Abstract: Melting from an array of three staggered, electrically heated cylinders imbedded in a paraffin (n-octadecane) has been studied. The shape of the melting front has been determined photographically, and the local heat transfer coefficients were measured using a shadowgraph technique. The experiments provide conclusive evidence of the important role played by natural convection on the timewise variation of the melt shape, the surface temperature and the instantaneous local as well as circumferentially averaged heat transfer coefficients around the imbedded heat sources. After a common solid-liquid interface is formed around the cylinders, natural convection circulation around each cylinder interacts strongly with the other two cylinders. The arrangement of heat sources affects significantly the melt shape but the circumferentially averaged instantaneous heat transfer coefficients differ only by about 10 percent for the two arrangements studied. The experimental findings indicate that natural convection effects are important and should be considered in analysis and design of systems involving phase change.

Model for Energy Exchange of a Pine Forest Canopy

Abstract: The CANOPY model describes energy exchange in a sparse pine forest stand at Jadraas, central Sweden in order to evaluate simple formulas for regional forest evapotranspiration. It incorporates latent and sensible heat exchange, long- and shortwave radiation balance, heat conduction and storage in trees and ground, and interception of precipitaion and dew. Self-sustained modules for different parts of the system are connected through the main program. This program structure enables each process to be studied separately, incorporation of various degrees of interaction, and direct comparison of different theories for the various processes. Required driving variables, given with a resolution of an hour or less, are global radiation, atmospheric longwave radiation, air temperature, relative humidity, wind speed, and precipitation. Simulation results indicate that penetration of shortwave radiation is more governed by gaps in the canopy than by reflection and transmission properties of the crowns. Evapotranspiration is almost fully determined by the surface (i.e., stomatal) resistance. This resistance is successfully predicted as a function of global radiation and vapour pressure deficit using a semiempirical equation with physiological basis. The aerodynamic regime of the forest is important only in the case of dew or precipitation. A successful prediction of interception is therefore necessary. Additional index words : Evaporation, interception, latent heat flow, longwave radiation, sensible heat flow, shortwave radiation, stomatal resistance, transpiration.

Structure and dynamics of ammonia adsorbed on graphitized carbon black. Part 1.—Adsorption isotherms and thermodynamic properties

Abstract: Isotherms of ammonia on a graphitized carbon black (Vulcan III) have been measured at temperatures of 163.4, 172.6, 182.0, 191.5, 201.5 and 211.0 K, using a microbalance. They are all of Type III. Values of isosteric heats and differential entropies of adsorption have been determined. The isosteric heat is comparable with the latent heat of evaporation of the liquid but much less than the latent heat of sublimation of the solid. This has the effect that, below the melting point of bulk ammonia, the amount adsorbed at a given relative pressure decreases with decreasing temperature. This type of behaviour is uncommon and seems to be characteristic of systems in which heterogeneous nucleation takes place.

Preheating system for IC engine - stores waste heat as latent heat and uses salt solution changing from crystalline to liquid form releasing heat to oil circuit

Abstract: The preheating system for an internal combustion engine stores the waste heat obtd. when the engine is in operation. It uses a latent heat store, which functions as a heat exchanger to supply or absorb the necessary energy. It also includes a switch to release the required heat. The latent heat store is incorporated in the coil circuit. The latent heat store (6) uses a salt solution, which changes from a crystalline form to a liq. form thus releasing the latent heat. The heat is given off to the coil circuit of the engine via the oil pump (4) driven by a motor (15), which pumps lubricating oil whose viscosity will be reduced. This will therefore reduce the consumption of the starter.

Latent heat storage material of encapsulated wax in liquid medium - allowing heat transfer by convection

Abstract: A heat storage material functioning by phase conversion using its latent heat, consists of paraffin wax particles coated with a plastics, metal foil or glass film, with a fluid, e.g. water, filling the spaces between the particles. Used in hot water, central heating and solar energy storage systems. Heat storage and release takes place over a narrow temp. range and heat transfer occurs by convection, with only short paths through the coating dependent on conduction.

Specific heat of the two dimensional antiferroelectric squaric acid

Abstract: The heat capacity of a single crystal of the two dimensional antiferroelectric squaric acid was measured particularly near the phase transition. In a wide temperature range belowTc a strong temperature dependence of the anomaleous specific heat is found which can be described by a critical exponentα′=0.5. The behaviour close toTc is determined by a latent heat thus indicating the phase transition to be of the first order. Near the phase transition the thermal behaviour can be described by a Landau type theory. The smallness of the transition entropy detected may be ascribed possibly to proton tunneling.

Separation of an aqueous solution by the improved vacuum freezing high pressure ice melting process

Abstract: In the Improved Vacuum-Freezing High Pressure Ice Melting Process, an aqueous solution is flash vaporized under a reduced pressure to simultaneously form a low pressure water vapor and ice crystals. The ice formed is first purified in a counter-washer and then melted inside of heat conductive conduits under a high pressure (e.g. 600 atm.) and the low pressure water vapor is desublimed to form desublimate (ice) on the outside of the conduits. The latent heat of desublimation released is utilized in supplying the heat needed in the ice-melting operation. The desublimate is removed intermittently by an in-situ dissolution operation utilizing an aqueous such as the feed solution or the concentrate; about an equivalent amount of ice is formed inside of the conduits by an exchange freezing operation. The ice so formed is also melted by the high pressure ice melting operation described. The process uses components that are available commercially and can be reliably operated. The process is highly energy efficient and cost competitive with other desalination processes and conventional evaporation processes. The process is useful in desalination of brackish water and sea water and in concentrating industrial aqueous solutions.

Changes in dimensions, stresses and gravitational energy of the Earth due to crystallization at the inner-core boundary under isochemical conditions

Abstract: Summary. If the inner-core boundary (ICB) is a phase boundary, not a chemical boundary, changes in core temperatures will lead to changes in the size of the inner core with corresponding changes in the size of the Earth. We have investigated theoretically some effects of crystallization at the ICB due to slow cooling of the core. The earth model consists of a homogeneous inner core, outer core and mantle, and the calculations are for the elastic and viscoelastic case, including self-gravitation. Complete solidification of the core is connected with a decrease of the Earth's radius by 5 km and with additional pressures in the core and mantle of the order of several kbar, under the assumption that the density change at the ICB is 1 per cent. Part of the released gravitational energy is converted into deformational energy, distributed throughout the Earth. The main part, more than 70 per cent, is converted into heat at the ICB: this is the work done by the hydrostatic pressure during contraction of the crystallizing material. It forms a part of the latent heat of crystallization that in previous estimates has been neglected. Assuming that: (1) the density change at the ICB is 1 per cent, (2) the radius (volume) of the inner core has grown to its present value in 4 x 109yr, we obtain as an estimate for this part of latent heat 5.82 x 10" (1.94~ 10") watt. This is 1.9 (0.6) per cent of the Earth's heat flux. If crystallization of the core would actually take place, the concentrated heat source at the ICB would delay cooling of the core and possibly maintain for long times temperature gradients in the outer core which are sufficient 'for thermal convection. The critical parameter for all effects studied is the (so far unknown) density change of core material upon crystallization under high pressures.

Deep freeze system with latent heat storage - utilises low tariff electricity operating storage utilising latent heat of freezing

Abstract: The deep freezing refrigerator has an electrically driven refrigerator unit, and has a refrigerating storage arrangement making use of latent heat. This storage utilises the cheaper electric power supplied during the night. This arrangement is connected to an electrical switch which connects the refrigerator or in relation to the current tariff or depending on the time of the day. The refrigerator is disconnected at the temperature below the freezing point of the material used in the storage arrangement.

Diabatic Heating and Generation of Available Potential Energy in a Tornado-Producing Extratropical Cyclone

Abstract: Diabatic heating by latent heat release and longwave radiation and corresponding generation of available potential energy have been computed for a tornado-producing cyclone system. Also, the contributions of two subareas, encompassing the immediate cyclone vicinity and the convection area, to the cyclone system generation are examined applying the concepts of limited region baroclinic and barotropic generation. Heating values, which are dominated by convective latent heat release, are generally in good agreement with observed weather features and cyclone development. The resulting positive cyclone system generation is comparable with previous studies and is strongly influenced by the contributions made by the two subareas. In turn, the latter are dominated by their. barotropic components, indicating that the heating fields in these subareas contribute more effectively to increasing or maintaining the baroclinicity of the cyclone system than of the subareas themselves.

Discharging a latent-heat accumulator

Abstract: A latent heat accumulator gives up its heat when a heat exchange medium isassed through the accumulator and around a circuit containing an external heat sink. The heat storage medium in the accumulator changes its state from liquid to solid as it gives up heat. In order to prevent heat exchange medium from being trapped by the heat storage medium as it solidifies, the exchange medium is always introduced directly into a zone where the storage medium is liquid.

Temperature and Pressure Study of 8S5

Abstract: We have studied the liquid crystal phase transitions of 4-n-pentylbenzenethio.4′-n-octyloxybenzoate (8S5) as a function of pressure and temperature. There were no pressure induced anomalies. We measured the latent heat at the N-1 transition (.5±.1 calories/gram) but were not able to observe any evidence of a latent heat for both the A-N and C-A transitions. We speculate that the continuous nature of these transitions may be linked to the flexibility of the polar part of 8S5.

Individual Time Period Analyses over the GATE Ship Array

Abstract: Diagnostic moisture and dry static energy budgets for the GATE A/B-scale area are performed for individual time periods using rawinsonde and satellite data. The data are sufficiently accurate to permit quantitative analysis of that area with 3–6 h time resolution. Each budget is used to estimate the net condensation rate for every time period. The budget condensation rates slightly exceed radar rainfall estimates for the GATE master array and the radar values lag the budget condensation by 4–6 h during major rainfall episodes. Storage of liquid water and unsampled vapor in clouds can account for a large portion of the observed lag. The present results indicate that observed 3–6 h lags between, low-level mass convergence and echo growth during GATE result primarily from the lag between condensation and precipitation during convective system evolution. The release of latent heat in a tropical convective system appears to be closely related to the instantaneous mass convergence below 700 mb. Budget-...

Process for storing calories

Abstract: A process for storing heat in the form of fusion/solidification latent heat which comprises passing a thermo-conductive fluid into a thermally insulated storage element containing a substance having a melting point that corresponds to the supply and heat consumption temperatures, characterized in that said fusible substance is absorbed on a microporous carrier which forms a granular bed in which the thermo-conductive fluid circulates.

Upslope Enhanced Extreme Rainfall Events over the Canadian Western Plains: A Mesoscale Numerical Simulation

Abstract: A limited-area numerical model, previously applied to the study of cold easterly circulations over the Canadian Western Plains, is used to simulate upslope enhanced extreme rainfall events over the Saskatchewan River and adjacent drainage basins. Following Lavoie (1972) the atmospheric structure was represented by three layers: a constant flux layer in contact with earth's surface, a well-mixed planetary boundary layer capped by an inversion, and a deep stratum of overlying stable air. The governing primitive equations were averaged through the depth of the mixed layer with interactions between the mixed layer and both the underlying and overlying air being suitably parameterized. A 47.6 km grid mesh of 1369 (37×37) points covering the Canadian Prairie Provinces was used to represent the variables. The governing equations were solved numerically for the mixed layer with terrain influences, surface roughness, temperature variations, moisture fluxes and the release of latent heat allowed to perturb...