Showing papers on "Latent heat published in 1980"

Correction of flux measurements for density effects due to heat and water vapour transfer

Abstract: When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.

The Fair Weather Boundary Layer in GATE: The Relationship of Subcloud Fluxes and Structure to the Distribution and Enhancement of Cumulus Clouds

Abstract: The structure of the convective atmospheric boundary layer and the characteristics of the associated turbulent mixing processes in undisturbed conditions over the tropical ocean are investigated using data collected during the GARP Atlantic Tropical Experiment (GATE). The data were obtained by a number of aircraft equipped with turbulence measuring instrumentation. The fluxes of momentum, sensible and latent heat throughout the subcloud layer are presented for four cases considered in detail. It is shown that the sensible and latent heat fluxes at the top of the mixed layer (and therefore the distribution of heating and moistening in the boundary layer) are strongly affected by the presence or absence of cumulus convection while the virtual heat flux remains unaffected. Features of this cloud-subcloud interaction are discussed in the light of Betts (1976) coupled cloud-subcloud layer model. An examination of the spectra (and cospectra) of subcloud-layer variables shows that with the exception of ...

Estimation of Heat and Mass Fluxes Over Arctic Leads

Abstract: Recent work on the turbulent transfer of scalar quantities following a step increase in the surface value of the scalar is directly applicable to the problem of estimating heat and mass transfer from Arctic leads in winter. If the turbulent flux is nondimensionalized as a Nusselt number N and the flow regime over the lead is parameterized by the fetch Reynolds number Rr, either the exponential transfer relation N = 0.08 × Rr0.76 or the linear relation N = 1.8 × 10−3Rr + 1100 describes the available data. Because N can be the Nusselt number for sensible heat, latent heat or condensate flux, Nusselt numbers of these scalar fluxes are equal for a given lead—Rr. The transfer relations and this Nusselt number equality are powerful estimation tools. With the transfer relations, turbulent fluxes can be computed from standard meteorological observables; and from the Nusselt number equality, partitioning of the turbulent fluxes can be evaluated— in particular, the partitioning of the heat flux between sen...

The photoacoustic effect at first-order phase transition

Abstract: Thermal properties are essentially involved in the acoustic response of a liquid or solid sample to the absorption of chopped light. Recently, the first experimental observation of the photoacoustic effect at first‐order phase transitions has been published. In the present work we calculate the temperature variation in the gas at the surface of a sample and determine its amplitude and phase angle. Therefore we solve the differential equation of conduction of heat for a medium exhibiting a temperature gradient superposed by a temperature oscillation due to absorption of light with sinusoidal varying intensity. In the medium there exist two regions of different thermodynamic phases separated by an interface at transition temperature. The latent heat for phase transition is taken into account via a boundary condition for the heat flow at the interface. We have assumed the optical‐absorption coefficient to be much larger than the thermal‐diffusion coefficient realized in strongly absorbing materials. The appl...

Pressure Dependence of the Specific-Heat Jump at the Superfluid Transition and the Effective Mass of He 3

Abstract: The specific heat of liquid $^{3}\mathrm{He}$ has been measured from 1 to 10 mK between 0 and 32.5 bars. The values implied for the effective mass are considerably smaller than the currently accepted ones. Near zero pressure the specific-heat jump is close to the BCS value 1.43, and at 32.5 bars it has reached 1.90 in the $B$ phase and 2.04 in the $A$ phase. The temperature dependence of the specific heat in the $B$ phase agrees with a model of Serene and Rainer. The latent heat at the $A\ensuremath{-}B$ transition has been measured.

Short term thermal energy storage

Abstract: The present paper reviews the problem of short term thermal energy storage for low temperature solar heating applications. The techniques of sensible and latent heat storage are discussed, with particular emphasis on the latter. Requirements for hot water storage subsystems are provided and the importance of stratification in hot water storage tanks is described. Concerning latent heat storage, both material and heat exchanger aspects are considered in detail. The example of a passively operating latent heat store employing a finned heat pipe heat exchanger is used to elaborate upon the heat transfer problems in the generally poorly conducting phase change heat storage materials. Finally, some data pertaining to the current economics of heat storage are presented.

Process for distilling water and distillation apparatus

Abstract: A process and an apparatus for distilling water in which a heat receiving plate member and a plurality of cooling plate members have a means for holding water to be treated on each reverse side thereof and are arranged in parallel spaced relationship with each other, and the water vapor produced by heating the heat receiving surface of the heat receiving plate member is condensed on the condensing surface of the adjacent cooling plate member, while giving the latent heat of the condensation to the cooling plate member and heating a water held on its back to produce the water vapor which is condensed on the condensing surface of the next cooling plate member, such evaporation by the latent heat and condensation being conducted according the number of rooms partitioned by adjacent two cooling plate members. There are apparatuses of two types, i.e. thermal diffusion type and convection type, and they are availably employed for purifying impure water or desalting sea water in high heat efficiency by utilizing various heat sources such as solar heat.

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...

Microdroplets and Transport of Moisture from Ocean

Abstract: The complex moisture and heat exchange process over the ocean was studied as a strongly coupled system of momentum, heat, moisture, and microwater droplets. Many unusual temperature profiles observed over the ocean can be naturally explained through the latent heat of evaporation of microwater droplets produced by the breaking waves. It is hoped that this preliminary analysis will lead to a better understanding of the complex sea-air interface and provide a more accurate means for estimating the rate of evaporation and heat transfer over large bodies of water.

Physical influences on east coast cyclogenesis

Abstract: Three examples of cyclogenesis off the east toast of North America are studied using an 8‐level primitive equations model. The model includes input of sensible and latent heat from the sea surface, both parameterized convective and large‐scale precipitation and release of latent heat, surface frictional drag and orography. The grid size is 190 km. Twenty‐four‐hour prognoses were made for four time periods with similar results: orography and fluxes of sensible and latent heat from the ocean were of little consequence, while the effect of the land‐water roughness contrast was significant. The lack of appreciable orographic influences is attributable to the fact that the Lows studied crossed the Appalachians south of the highest terrain. The cyclones formed along well‐developed frontal systems where the difference between air or dew‐point temperature and sea temperature in the warm sector was small or negative. Consequently fluxes of both sensible and latent heat near the Low centres during cyclogen...

Heat flow in an aluminium sample undergoing melting and resolidification under irradiation by a nanosecond laser pulse

Abstract: The characteristic times and lengths involved in the problem of heat flow through a semiinfinite Al sample irradiated with nanosecond laser pulses are discussed with reference both to the underlying physics and to the numerical solution of heat diffusion equation. Laser pulse energies allow sample melting, but no vaporization. The numerical solution proceeds via subdividing the sample into layers of thickness Δx. After describing the mechanism of heat flow through these layers, the Δx-dependence of some significant quantities is discussed and found negligible. The temperature time behaviour at different sample depths is given, showing latent heat effects; results for the solid-liquid interface motion, cooling rates, energy deposition in the front layer are presented and their dependence on the laser pulse parameters discussed qualitatively. Finally the connection of the present calculations with some recent experiments is discussed and the conditions under which neglecting of undercooling effects...

Solar power system

Abstract: Various control methods and means are disclosed for varying the temperature of vaporization of a solar-powered system so that the instantaneous power delivered by the heat engine of this system, or by a device driven by this engine, is a maximum for given conditions external to the power system, or to the power system and the driven device, respectively, while ensuring that dry saturated vapor, or vapor with a preselected amount of superheat is supplied to the heat engine. The power system uses a Rankine power cycle whose working fluid is either vaporized in the absorber of a solar collector, or in a heat exchanger by a separate fluid which absorbs heat by flowing through the solar collector absorber. Also, various methods and means are disclosed for controlling the foregoing separate heat-transfer fluid so that it absorbs sensible and latent heat in the absorber of the solar collector in essentially the same ratio as the power-cycle working fluid absorbs sensible and latent heat from this heat-transfer fluid.

Phase transitions in DyVO4 and DyAsO4

Abstract: This paper reports on optical, magnetic, and specific heat experiments at low temperatures on DyVO4 and DyAsO4, including a summary of previous works on these two substances. The crystallographic phase transition in DyVO4 is second order, whereas in DyAsO4 there is a latent heat at the distortion temperature. In contrast to the results of neutron diffraction experiments, no evidence for a canted antiferromagnetic structure in DyAsO4 below the magnetic transition temperature was found. Magnetically, DyAsO4 behaves almost identically to DyVO4.

Phase Behavior of some Condensed Polycyclic Aromatics

Abstract: This letter reports phase behavior for 11 polycyclic aromatics. Although melting temperatures for these materials have been published elsewhere, no previous latent heat data are known to us. The experimental methods of Ref. 1 were used. Both transition temperatures and latent heats were obtained by differential scanning calorimetry (DSC). By taking appropriate precautions it was possible to study transitions at temperatures as high as 770K.

A Three-Dimensional Tropical Cyclone Model with Release of Latent Heat by the Resolvable Scales

Abstract: Preliminary results are presented for a new three-dimensional tropical cyclone model that is unusual because the cumulus parameterization has been replaced by release of latent heat by scales of motion that are resolved by the grid. As a result, deep convective cells are formed in the model. Essentially all of the convective cells occur on the fine (10 km) mesh of a triply nested grid. These Cells form in clusters that propagate downwind. As the vortex grows, the clusters become organized into an eyewall and sometimes into spiral bands. Spiral bands without convection are also present. A model vortex is integrated from tropical storm strength to a mature hurricane. The maximum low-level wind is 82 m s−1 and the minimum sea level pressure is 880 mb in the mature stage.

Parameterization of the vertical flux of latent heat at the earth's surface for use in statistical-dynamical climate models

Abstract: A formula is developed expressing the vertical flux of latent heat at a saturated point of the earth's surface (e. g., ocean, or a Piche evaporimeter on land),Hs(4P)↑, as a function of surface temperature, relative humidity, wind speed, and the vertical flux of sensible heat. The formula generalizes and improves upon one applied in several statistical-dynamical climate models.

Stomatal response to humidity: implications for transpiration

Abstract: . Transpiration rates from apple leaves are analysed in terms of the ratio of latent heat flux (λE) to leaf net radiation (Q1) and the climatological resistance (ri). Increases in stomatal resistance with increasing leaf to air vapour pressure gradient (D), described by an empirical model, are incorporated in the analysis. This humidity effect causes the proportion of energy dissipated as latent heat to fall as Q1 increases, so that leaf transpiration rates in high energy environments are likely to be similar to those in lower energy environments. Boundary layer resistance (ra) exerts an increasingly important effect on transpiration rates as Q1 increases. At constant Q1 stomatal closure in response to increasing D results in very small changes in leaf temperature (T1) across a wide range of ambient vapour pressure deficits (δe); ra is then the major factor determining T1. The implications of these results are discussed.

Latent heat recirculating system

Abstract: The latent heat of condensation released by condensing a process vapor is captured in a fluid contained in a latent heat recirculating system; the captured heat is returned by the fluid to the body of process liquid for continued vaporization.

The respective effects of water vapor and temperature on the turbulent fluxes of sensible and latent heat

Abstract: Various aspects of the Brook correction for the effects of moisture fluctuations or gradients on atmospheric specific heat and, consequently, on the vertical flux of sensible heat are discussed, and additional forms of the complete and approximate equations are derived. Corollary expressions for the influence of temperature fluctuations or gradients on vertical latent heat flux are presented. Errors due to neglecting these temperature and moisture effects on the respective fluxes are compared in terms of the Bowen ratio. Either of these normally neglected effects can change the direction (sign) and very substantially affect the magnitude of the corresponding flux. The effects sometimes compensate in the total, sensible plus latent, heat flux. Calculations include practical examples from the very different climates of the tropical Atlantic Ocean and the Great Plains of Nebraska.

Heat storage capability of a rolling cylinder using Glauber's salt

Abstract: SYNOPSIS Glauber's salt has been melt-refreeze cycled to store heat at 90.3°F in a laboratory sized rolling cylinder surrounded by a calorimeter. The quantitative results show: 1. Complete phase change. 2. Theoretical latent heat release. 3. Repeatable performance over 150 cycles. 4. High heat release rates. 5. High internal heat transfer rates. 6. High heat exchanger surface temperatures. 7. Acceptability of commercial source salts. 8. Uniform freezing. Based on these measurements the rolling cylinder continues to be a prospective high performance thermal storage device. No technical barriers to further development were discovered.

Waste water heat storage process - passes fluids through series of latent heat units operated by different temperature levels

Abstract: The process extracts heat from warm fluids and transfers it to cold fluids at other times with the aid of latent-heat storage units The fluids flow in succession through a series of such units, which are operated at different temperature levels The number of such units can be from two to fifteen preferably from five to ten A number of different currents of fluid, yielding up and absorbing heat and with different inlet and outlet temperatures, can be incorporated in the system

Apparatus for rapid heat transfer and efficient heat storage

Abstract: Heating of intermittent users, such as domestic appliances, may require a rapid transfer of heat during an operating period. But hot reservoirs based on transitions between liquid and crystalline phases are least effective during rapid discharge since the crystalline latent heat storing material forming on encapsulating heat transfer surfaces increases thermal impedence. Various means for shortening thermal paths through the crystalline material, such as penetrating conductors, undesirably decrease thermal energy density. In order to provide both rapid heat transfer capability and a large thermal energy density, the invention uses prolonged idle periods between the operating periods for passive recharging within a hot reservoir of a first latent heat storing material by a second latent heat storing material which has a higher melting point so that the first latent heat storing material melts while the second crystallizes as the hot reservoir approaches a uniform equilibrium temperature. The first latent heat storing material is encapsulated in assemblies having short thermal paths for rapid heat transfer and has sufficient thermal capacity for one of the operating periods. The second latent heat storing material is encapsulated in assemblies having a large thermal energy density and has a thermal capacity which is sufficient to recharge the first for a plurality of the idle periods. Accordingly, the hot reservoir includes a first latent heat storing material assembly for rapid discharge and a second latent heat storing material for a large energy density and passive recharging of the first latent heat storing material.

Characterization of glass transition in a-As2Se3 by heat of vaporization

Abstract: The glass transition in evaporated amorphous As 2 Se 3 films was investigated by measuring the vaporization rate from a free surface of the film. Samples were heated or cooled at a very slow rate (0.02 deg./min.). Arrhenius plot of the vaporization rate had two asymptotic lines with different gradients below and above the glass transition temperature (Tg = 174.2 °C). We determined the heat of vaporization E g and E s l of the glass and supercooled liquid regions, respectively. The latent heat of glass transition E g -E s l is approximately equal to 15R Tg/2, where R is the gas constant. We conclude that the glass transition in a-As 2 Se 3 is the first order phase transition.

Heat recovery system.

Abstract: Apparatus for heat recovery from stacks and chimneys, using a heat exchanger scroll (2) mounted at the apex of such stacks, which consists of paired plates, spaced by deformed portions (21, 22) to define channels for flow of a liquid to be heated. A jacket (3) surrounds the scroll (2) is closed by a dome (5) having a filler cap (6). The scroll (2) is connected to the dome (5) by piping and a dome outlet (8) connected to a pump which circulates the heated water to a heating system by supply lines (11) or to other areas returning the liquid to the scroll (2) by return line (12). Sensible heat as well as latent heat of moisture in the fuels together with vapor produced as a combustion product can be scrubbed out. The use is to effect economies and to reduce environmental contamination wherever fuels are fired.