Showing papers on "Latent heat published in 1986"

Frequency response corrections for eddy correlation systems

Abstract: Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's ‘Hydra’ eddy correlation system. The results show that flux loss from such a system is typically 5 to 10% for sensible and latent heat flux, but can be much larger for momentum flux and variance measurements in certain conditions. A microcomputer program is included which, with little modification, can be used for estimating flux loss from other eddy correlation systems with different or additional sensors.

Eddy fluxes of CO2, water vapor, and sensible heat over a deciduous forest

Abstract: Fluxes of CO2, latent heat and sensible heat were measured above a fully-leafed deciduous forest in eastern Tennessee with the eddy correlation technique. These are among the first reported observations over such a surface. The influences of solar radiation, vapor pressure deficit and the aerodynamic and canopy resistances on these mass and energy exchanges are examined. Following a concept introduced by McNaughton and Jarvis (1983), examination of our data suggest that the water vapor exchange of a deciduous forest is not as strongly coupled with net radiation as is that of agricultural crops. The degree of decoupling is smaller than in the case of a coniferous forest. This difference may be attributable in part to the greater aerodynamic resistance to water vapor transfer in a deciduous forest. It appears that the concept of decoupling may be extended to the CO2 exchange of a deciduous forest as well.

Inertial-dissipation methods and turbulent fluxes at the air-ocean interface

Abstract: The use of high frequency atmospheric turbulence properties (inertial subrange spectra, structure function parameters or dissipation rates) to infer surface fluxes of momentum, sensible heat and latent heat is more practical for most ocean going platforms than direct covariance measurement. The relationships required to deduce the fluxes from such data are examined in detail in this paper and several ambiguities and uncertainties are identified. It is noted that, over water, data on water vapor properties (the dimensionless functions for the mean profile, the structure function parameter and the variance transport term) are extremely sparse and the influence of sea spray is largely unknown. Special attention is given to flux estimation on the basis of the structure function formalism. Existing knowledge about the relevant similarity functions is summarized and discussed in light of the ambiguities identified above.

Mean surface energy fluxes over the global ocean

Abstract: A newly available consolidated data set from the U.S. Navy's Fleet Numerical Weather Central in Monterey, California, is utilized to investigate global energy fluxes at the sea-air interface. Sea surface temperature data from January 1949 to December 1979 were extracted from the data set along with air temperature, sea level pressure, dew point temperature, wind speed, wind direction, and cloud cover. Five degree latitude by five degree longitude spatial averaging and monthly temporal averaging were applied to the parameters in the data set for the purpose of studying long-term large-scale fluctuations. The heat balance of the global ocean surface layer is calculated using bulk flux formulations. Maps of the long-term monthly and annual means of the net surface energy flux together with the four components of the total flux (latent heat flux, sensible heat flux, incoming radiation, and outgoing radiation) for the global oceans are presented. Incoming solar radiation and latent heat flux are the two dominant components that control net surface energy fluxes. Wind speed, cloud cover, and the gradient of specific humidity are the three most important meteorological parameters in determining surface flux. Errors associated with the bulk formula calculations and the significant features of the energy balance at the ocean surface are discussed.

Suburban-rural energy balance comparisons in summer for Vancouver, B.C.

Abstract: Simultaneous energy balance observations at a rural and a suburban site in Vancouver, B.C. during the summer of 1983 are presented. The study is a follow-up to that conducted in 1980. Many of the 1980 results were unexpected and the present study seeks to assess their representativeness. The net radiant, turbulent sensible, and rural soil heat flux densities were measured directly. The suburban heat storage was parameterized and the turbulent latent heat flux densities were resolved as residuals in the energy balances. The 1983 average diurnal energy partitioning for both sites was typical of those quoted in the literature, suggesting that the 1980 results represent an extreme case. Suburban-rural differences showed the suburban area to have a 4% increase in net radiation, a 51% increase in turbulent sensible heat, and a 46% decrease in turbulent latent heat flux density. The values of the average daytime Bowen ratio were 0.46 and 1.28 for the rural and suburban areas, respectively. The sensible heat flux density exhibited relatively large values in the late afternoon and remained directed upward on many summer evenings. Large day-to-day variability in the relative magnitude of the suburban turbulent fluxes may have been due to synoptic influences. In this environment, the turbulent surface and mixed layers are closely coupled because of the low aerodynamic resistance over the rough surface.

A unified approach for prediction of thermodynamic properties of aqueous mixed-electrolyte solutions. Part I: Vapor pressure and heat of vaporization

Abstract: The overall nonideality of an aqueous mixed electrolyte solution is characterized in terms of a newly defined parameter Γ*, called the overall reduced ionic activity coefficient. It is shown that Γ* for the mixed solution is simply related to the properties of single-electrolyte solutions. Γ* is related to the vapor pressure of a mixed-electrolyte solution through well-known thermodynamic equations. This leads to a predictive equation for the vapor pressure of a mixed-electrolyte solution in terms of the vapor pressures of single-electrolyte solutions of the components. This equation is valid over the entire concentration range encountered in practice, without any empirical constants, and has a predictive accuracy of 2%. A predictive equation for the latent heat of vaporization is also developed and tested against experimental data.

Numerical experiments on the genesis of vortices over the Qinghai-Tibet plateau

Abstract: The formation of a vortex and shear line over the Qinghai-Tibet Plateau (QTP) was investigated with numerical experiments using the ECMWF grid point model. The case chosen occurred between 24 and 26 July, 1982, when the south-west monsoon invaded the QTP and a vortex developed. The correct simulation of the vortex in the model shows that it is possible to predict the atmospheric circulation over the QTP and the consequent weather over China. When the simulation was rerun with a dry model (i.e., without the release of latent heat), it was found that only a weak vortex formed. This shows that the release of latent heat is an extremely important factor in the development of the vortex over the QTP, and confirms earlier diagnostic and synoptic studies. The surface sensible heat fluxes, large near the northern and southern flanks of the QTP, appear to have a damping effect on the formation of the vortex; i.e., the vortex was greatly intensified in their absence. It was also found that the intensity of the vortex was dependent upon the height of the QTP: when the mountain height was reduced, the westerly trough invaded the QTP and no vortex formed at 500 mb; when it was increased, the south-west monsoon travelled along the southern boundary of the QTP and intensified the low-level jet south of the vortex area. The results of a 48-h integration with a fine-mesh model (resolution 0.5° of latitude and longitude) showed an improvement in forecasting the location of the vortex with respect to the coarse-mesh model (1.875° of latitude and longitude). However, when compared with the coarse-mesh analysis, the intensity of the vortex was overpredicted. This may be due to mesoscale orographic forcing and exaggerated latent heating. DOI: 10.1111/j.1600-0870.1986.tb00468.x

The Effects of Cumulus Moisture Transports on the Simulation of Climate with a General Circulation Model

Abstract: A hybrid cumulus parameterization was developed to study the effects of cumulus heat and moisture transports on climate simulations. This parameterization consists of a cumulus mass flux representation of the convective fluxes of heat and moisture, and moist adiabatic adjustment representation of the release of latent heat and the removal of moisture by precipitation processes. This hybrid scheme was implemented and tested in the National Center for Atmospheric Research Community Climate Model. Averages over the last 90 days of 210-day simulations made for January and July with the standard moist-convective adjustment scheme were compared with those obtained with the hybrid scheme. The simulations made with the hybrid parameterization resulted in upper-tropospheric temperatures (p ∼ 300 mb) that were as much as 8°C higher than the standard scheme in the tropics. In addition, the tropospheric water content simulated with the hybrid parameterization was considerably greater than that of the standar...

The Effect of Inaccuracies in Weather-Ship Data on Bulk-Derived Estimates of Flux, Stability and Sea-Surface Roughness

Abstract: An analytical error analysis (or sensitivity study) is performed for the momentum, heat, and humidity flux estimates made from weather-ship observations by using the bulk flux method. Bulk-derived stability and roughness errors are also examined. The analysis is performed with two scenarios for the constituent wind speed, air temperature, water temperature, humidity, barometric pressure, and measurement altitude uncertainties. The error scenarios are constructed from published estimates and used to simulate the typical sensor inaccuracies and ship-induced distortions of meteorological measurements made from weather ships. Four bulk transfer coefficient schemes are tested. The combined influence of the sensor inaccuracies and ship-induced distortions is found to result in a typical uncertainty of about 30% for an average stress of 0.2 N m−2, 50% for an average sensible heat flux of ±25 W m−2, 50% for an average latent heat flux of ±40 W m−2, 80% for an average Monin-Obukhov stability of ±0.06, 40%...

Interdependence of Radiation and Microphysics in Cirrus Clouds

Abstract: The important microphysical relationships determining the radiative properties and growth of ice crystals in stratiform cirrus clouds are investigated. A horizontally infinite cloud layer is modeled in the midlatitude upper troposphere. Optical properties of spheres of equal surface area are assumed to represent the scattering characteristics of nonspherical crystals, while the delta-Eddington approximation is used to solve the radiative transfer equations. Classical expressions for ice particle growth and sublimation are coupled to those for radiative energy exchange in order to follow ice particle evolution within the cloud. The radiative properties of the clouds influence the balance among the cloud physical processes within the cloud. In the top 5 percent of optically thin clouds, the ice particle energy balance is essentially between latent and heat diffusion. In the case of clouds with large optical depths, the energy balance is between latent heat and radiation, i.e., radiative cooling enh...

Use of Meteosat for Mapping Thermal Inertia and Evapotranspiration over a Limited Region of Mali

Abstract: In order to determine thermal inertia and latent heat flux from Meteosat data, we propose a model based on a Fourier analysis of the time variation of the surface temperature. This model uses as input the classical meteorological data (temperature, humidity and wind speed) measured in situ from meteorological stations and data obtained from Meteosat records (net radiation and surface temperature). The model is designed in such a way that the heat transfer resistances, which are very local quantities, are calculated by the model. The results of this model have been evaluated by comparison with experimental data and theoretical input data calculated from known in situ parameters. Both the accuracy and stability of these results, and the impact of errors of measurement on the input data will be discussed here. This model has been applied to the mapping of thermal inertia and evapotranspiration over a limited region of Mali within the Group Agro-Meteorological Project (GAMP). Results, on the whole, c...

Carbon dioxide, water vapor and sensible heat exchanges of a grain sorghum canopy

Abstract: With the aid of eddy correlation instrumentation, the components of the energy budget and CO2 flux were measured over grain sorghum grown at Mead, Nebraska. Diurnal patterns of sensible heat, latent heat, CO2 and momentum flux are examined for typical days. On a mostly clear day when the crop leaf area index was 3.7, net radiation reached a mid-day peak of 560 W m-2, while sensible and latent heat fluxes peaked at 50 and 460 W m-2, respectively. The peak CO2 flux occurring just prior to solar noon was 1.5 mg m-2(ground area) s-1. CO2 flux (respiration from plants, soil and roots) in the early evening was about -0.28 mg m-2 (ground area) s-1.

Disposable heat storage unit

Abstract: A disposable heat storage unit comprises a hermetically sealed, heat conductive pouch containing a quantity of a latent heat substance which may be preheated to an initial temperature higher than that of its heat of fusion so that, upon cooling, it releases first its sensible heat followed by the release of the heat of fusion at a constant temperature over a sustained period of time. The unit may be placed in a container within which is positioned an article whose temperature is to be maintained at an elevated level.

Observations of the marine boundary layer thermal structure over the Gulf Stream during a cold air outbreak

Abstract: Thermal structure of the marine boundary layer (MBL) was studied during a five-day cruise over the coastal Atlantic Ocean off North Carolina. Three different synoptic conditions were present: ahead of a low moving along the coast, in the area of a frontal zone and during a cold air outbreak. The marine boundary layer height was deeper (approximately 1500 m) and more sharply defined during the cold air outbreak than when the flow was southwesterly with a long fetch over water; the height was only about 1000 m for the latter case. Latent heat fluxes were significantly larger than sensible heat, but during the cold air outbreak, sensible heat fluxes increased appreciably.

The effect of synoptic-scale advection on the performance of the Priestley-Taylor evaporation formula

Abstract: Measurements of the appropriate parameters for the calculation of the latent heat flux over a black spruce forest in northern Quebec were carried out in August, 1980. Values of the Priestley-Taylor parameter, α, were derived by exploiting the Bowen-ratio-energy-balance (BREB) technique. Derived values of α are then related to synoptic-scale warm air advection, derived from surface synoptic charts and tephigrams of the planetary boundary layer. It is found that when warm air advection is present, α > 1.26, especially when the surface is wet. When advection enhancement is removed, however, values of α approach unity. A new approach to calculating the latent heat flux, when warm air advection is present, is therefore proposed.

Water heater and distiller apparatus

Abstract: A water heater (13) and distiller (49) apparatus is provided in which condensing steam (73) is the distilling portion of the apparatus giving up its latent heat to water (71) which is being heated in the water heating portion of the appa­ratus. In a preferred embodiment, products of combustion which are used to boil water in the distiller boiler, are later passed in heat exchange (67) relation with the water heating tank in the water heating portion of apparatus. It is believed that the present apparatus if both energy efficient and uncomplicated as compared to the prior art.

Prescribed Heating of a Stratified Atmosphere as a Model for Moist Convection

Abstract: The response of a stratified atmosphere to a steady, moving source of heat is explored as a tool for understanding organized, moist convection. The results are shown to depend strongly on the ratio of the vertical wavelength of the forced gravity waves to the depth of the disturbance. The wave-CISK mechanism is understood as a coincidence between heating and low-level upward motion that only occurs for certain values of this ratio. Wave-CISK is shown to require precipitation-induced cooling to work satisfactorily. The cooling suppresses the subsidence wave produced by latent heat release, and allows parcels from near the surface to rise to the level of free convection. Squall lines often have a midlevel jet flowing through them from front to rear. Such a jet is seen in our simulations, and is the result of the oscillatory response of a stratified fluid to a moving beat source. The jet is strongest when evaporative cooling is included.

Thermodynamic properties of lithium nitrate‐ammonia mixtures

Abstract: In this paper, the thermodynamic properties of lithium nitrate-ammonia mixtures are presented. The vapour pressure-temperature correlations are developed by fitting the experimental P-T-x data. The enthalpy of solution, the latent heat of vaporization, the integral heat of solution and the differential heat of solution are presented in appropriate tabular and graphical forms.

Phase change thermal energy storage material

Abstract: A thermal energy storge composition is disclosed. The composition comprises a non-chloride hydrate having a phase change transition temperature in the range of 70°-95° F. and a latent heat of transformation of at least about 35 calories/gram.

Adcumulus growth of the inner core

Abstract: The earth's core is contained in an oxide bottle, the mantle. With regard to any dissolved oxygen, therefore, the outer core (OC) is in a reactive relationship to its container. The mantle contains only trivial amounts of sulfur compared to its solubility in the liquid OC, so the bottle is effectively inert to sulfur. This difference affects whether the diluent convects freely away from the freezing inner core (sulfur) or moves under constraint of saturation at the interface with the container (oxygen). The motion of oxygen is limited by diffusion; it requires double freezing and hence release of latent heat at both top and bottom of the OC, or else (if the top of the OC is a heat sink) no escape of heat to the mantle. The motion of sulfur allows rapid transport of latent heat away from the inner core boundary by compositional convection and implies major heat loss from the core. The velocity of compositional convection (due to sulfur) may be as much as 104 times that of diffusion of oxygen, so sulfur in the outer core should be far more important in driving the dynamo than oxygen.

Basic research on the latent heat thermal energy storage utilizing the contact melting phenomena

Abstract: A latent heat thermal energy storage capsule, having a horizontal heat transfer surface at the bottom and storing the energy by contact melting, is prepared. The time-dependency of the storage heat flux is measured, using n-octadecane as the phase change material. Next, the non-dimensional formula for the contact melting heat flux in the steady state is derived, based on the results of the previous papers. Using the above formula, the time-dependency of the heat flux in the storage process is analyzed generally and the approximate solution is shown to agree well with the experimental results. Then, the effects of the PCM properties and the capsule specifications on the average heat flux are summarized.

Solidification in Convection-Diffusion

Abstract: An energy equation, based on an enthalpy function, representing phase change under convection and diffusion is developed. This equation is easily formulated into the general transport-equation form and its application in the PHOENICS code in the modelling of phase change problems is readily achieved. Two examples of phase change problems are modelled by this approach: i solidification in a square cavity under heat conduction only, ii solidification in a square cavity under heat conduction and natural convection.

Latent heat utilizing heat storage device

Abstract: PURPOSE:To provide a device in which the temperature of a medium is fitted and controlled in conformity with a predetermined heat using condition and which is controlled easily and simply by detecting the actual temperature of a heat transfer medium entering into a heat exchanger on the side of a heat using apparatus at the time of a heat radiation mode and operating the flow quantity of the medium passing through a heat storage tank as an operating signal therefor. CONSTITUTION:In a case where an actually detected temperature (t) of a heat transfer medium at a position 23 on this side of a heat exchanger 7 exceeds a control target set temperature T, a three-way control valve 22 is switched using a deviation DELTAt as an operating signal at the time of a heat radiation so that a part of the medium leaving the heat exchanger 7 is again returned to the heat exchanger 7 via a bypass pipe 21, and the flow quantity of the medium passing through the heat storage tank 8 is adjusted. The ratio between the diameter D of the heat storage tank 8 and the full length L corresponding to the horizontal length is determine in a range 1:3-6 and in the sectioned tank inside 36 are closely accommodated small spherical heat storage bodies 37. Draining means 41 are formed on the lower surface of a drum body 27 so as to permit the passage of the medium within a gap 42 between heat storage bodies 37.

Transition of surface energy budget in the Gobi Desert between spring and summer seasons

Abstract: The surface energetics of the southwest Gobi Desert, including the temporal variations and diurnally averaged properties of the surface energy budget components, was investigated. The field program was conducted during the spring and summer of 1984, with the measurement system designed to monitor radiative exchange, heat/moisture storage in the soil, and sensible and latent heat exhange between the ground and the atmosphere. Results of the analysis reveal a seasonal transition feature not expected of a midlatitude desert. Namely, the differences in both surface radiation exchange and the distibution of sensible and latent heat transfer arise within a radiatively forced environment that barely deviates from spring to summer in terms of available solar energy at the surface. Both similarities and differences in the spring and summer surface energy budgets arise from differences imparted to the system by an increase in the summertime atmospheric moisture content. Changes in the near-surface mixing ratio are shown to alter the effectiveness of the desert surface in absorbing radiative energy and redistibuting it to the lower atmosphere through sensible and latent heat exchange.

Heat accumulating building material

Abstract: PURPOSE: To provide a heat accumulating material which enables a heat dissipating surface temperature to be held approximately at a specified value, by a method wherein latent heat accumulating materials, being different in a base change temperature, are dispersed in a base material so that a phase change temperature on the indoor side is decreased and that on the outdoor side is increased. CONSTITUTION: A heat accumulating material 1 is used as a floor material and has structure in that a finish material 6 is laminated to the surface on the indoor side of the floor material, a base material 2 containing a capsulated latent heat accumulating material is arranged to the interior thereof, a heat generating material 4 and a heat insulating material 5 are laminated to the under surface, forming the indoor side (underfloor side) of the base material. In the base material 2, latent heat accumulating materials 3a, having a low phase change temperature, are dispersed on the indoor side, and latent heat accumulating materials 3b having a high phase change temperature are dispersed on the outdoor side. When a room temperature is decreased and a heat accumulating material is started to dissipate heat, temperature distribution at the interior of the base material is approximately coincided with distribution of the phase change temperature of the heat accumulating material. This constitution enables a heat dissipating surface temperature to be maintained approximately at a specified value, and realizes comfortable heating. COPYRIGHT: (C)1988,JPO&Japio