Showing papers on "Latent heat published in 1981"

Review of Thermal Properties of Snow, Ice and Sea Ice,

Abstract: : This treatise thoroughly reviews the subjects of density, thermal expansion and compressibility of ice; snow density change attributed to destructive, constructive and melt metamorphism; and the physics of regelation and the effects on penetration rate of both the thermal properties of the wire and stress level. Heat capacity, latent heat of fusion and thermal conductivity of ice and snow over a wide range of temperatures were analyzed with regression techniques. In the case of snow, the effect of density was also evaluated. The contribution of vapor diffusion to heat transfer through snow under both natural and forced convective conditions was assessed. Expressions representing specific and latent heat of sea ice in terms of sea ice salinity and temperature were given. Theoretical models were given that can predict the thermal conductivities of fresh bubbly ice and sea ice in terms of salinity, temperature and fractional air content. (Author)

Satellite Estimation of the Surface Energy Balance, Moisture Availability and Thermal Inertia.

Abstract: A method for inferring the distribution of surface heat and evaporative fluxes and the ground moisture availability and thermal inertia (ground conductive capacity) is used to analyze two urbanized areas, Los Angeles and St. Louis. The technique employs infrared satellite temperature measurements in conjunction with a one-dimensional boundary-layer model. Results show that there is a marked reduction of evaporation and moisture availability and a corresponding elevation of sensible heat flux over urbanized areas and over cropped areas with low vegetative cover. Conversely, low heat flux and high evaporation characterize vegetated and, especially, forested areas. Warm urban centers appear directly related to a reduction in vegetation, which normally allows for a greater fraction of available radiant energy to be converted into latent heat flux. The distribution of thermal inertia was surprisingly ill-defined and its variation between urban and rural areas was quite small. Thus, the increased heat storage within the urban fabric, which has been proposed as the underlying cause of the nocturnal heat island, may be caused mainly by enhanced daytime surface heating which occurs because of surface dryness, rather than by large spatial variations in the conductivity of the surface.

The temperature difference across the cool skin of the ocean

Abstract: The temperature difference ΔT across the cool skin of the ocean was determined from radiometric measurements of surface brightness temperature and conventional measurements of temperature at a depth of 1 m. Eleven days of measurements were made from the R/P Flip in February 1974 about 800 miles north of Hawaii (35°N, 155°W). The surface brightness temperature was corrected for nonblackness of the surface to obtain an estimate of the true surface temperature. The constant λ in Saunders' (1967a) formula, ΔT = λvQ/kU* was found to be λ = 6.5±0.6, where v is kinematic viscosity, Q the upward heat flux just below, the interface, k the thermal conductivity, and U* the friction velocity. The constant is independent of wind speed for winds ranging from 3 to 11 m/s. The use of subsurface rather than surface temperature in the bulk aerodynamic formulas results in an increase in the sum of the sensible and latent heat fluxes equal to 4-5% of Q. However, the percentage change in sensible and latent heat fluxes may be much greater. Spectra of surface and subsurface sea temperature exhibit a peak at low frequencies and fall off approximately proportional to ƒ−3/2; with increasing frequency ƒ. The variability of sea surface temperature was caused about equally by the variability of subsurface temperature and the variability of ΔT. Caution should therefore be exercised in the interpretation of radiometric surface temperature measurements as representative of subsurface temperature.

On the Annual Variation in Height of the Tropical Tropopause

Abstract: The existence of an annual variation in height and temperature of the tropopause over tropical regions has long been recognized, but has not been fully explained. In this paper it is proposed that the variation is a fairly direct response to the annual variation in average tropical surface insolation. The variation in insolation causes a corresponding annual cycle in average tropical sea surface temperature with a total range of order 1 K. The consequent variation in absolute humidity in turn produces an annual variation in upper tropospheric potential temperatures, and hence in the height and temperature of the tropopause. The physical link between the surface and the tropopause is provided by convection in the cores of the giant cumulonimbus clouds (hot towers) of the tropical oceanic regions, in which air parcels can achieve the maximum possible heating by release of latent heat. The process is modeled quantitatively in a simplified way, and excellent agreement is found between the predicted a...

Annual Mean Surface Heat Fluxes in the Tropical Pacific Ocean

Abstract: The four components of the long-term annual mean net surface heating of the tropical Pacific Ocean between 30°N and 40°S are calculated and portrayed. These flux elements were derived by using the bulk formulas and about 5 million marine weather reports for the years 1957–76. In addition to illustrating the mean solar, latent heat, infrared radiation and sensible heat fluxes, annual mean values of the atmospheric variables which contribute to those fluxes also are illustrated. A simple error analysis is carried out from which it is concluded that the 95% confidence bands for solar heating, latent heat loss and net oceanic heating are ±29, ±39 and ±49 W m−2, from the respective mean values. The validity of the results for the net heating is partially tested by comparing the horizontal heat transports required by the pattern of heating with independent estimates of those dynamical transports.

On Glacier Energy-Balance, Ablation, and Air-Temperature

Abstract: The paper tries to reconcile the facts that there are often useful correlations between ablation or run-off and air temperature while net radiation is usually the major source of ablation energy. Equations are derived from the energy balance to describe statistics for the ablation-temperature relation in terms of statistics for the relations between individual energy fluxes and air temperature. As examples, statistics are evaluated for four published series from Arctic Canada. Although the net radiation is the largest energy source in all four cases, the ablation rate is moderately well correlated with temperature and poorly correlated with net radiation. This is because the sensible heat flux is more variable than the radiation in three cases and is itself better correlated with temperature in all four cases. The major contributions to the increase of ablation rate with temperature (on average 6.3 kg m−2 d−1 deg−1) are due to sensible heat, followed by latent heat with a small contribution from net radiation. The resulting ablation-temperature model explains about half the variance of ablation rate. The main application of such a simple model is for the estimation of ablation totals in areas where glaciological and hydrological data are sparse.

Latent Heat Release as a Possible Forcing Mechanism for Atmospheric Tides

Abstract: The consequences of the hypothesis of Lindzen (1978) that latent heat release may be a significant excitation mechanism for the semidiurnal atmospheric tide are examined in some detail. Harmonic analysis of hourly rainfall data from 79 tropical stations shows that the semidiurnal variation of rainfall in the tropics is ∼1 mm day−1 and has a phase near 0300 LST, just as Lindzen's theory requires. Analysis of data at 85 midlatitude stations shows that the sermidiurnal rainfall oscillation there has its phase rather later (about 0600). The results of simple classical tidal theory calculations which indicate that the geographical distribution of the surface pressure response to latent heat forcing largely follows that of the forcing itself are presented. This result is then used to suggest a plausible explanation for the observed seasonal cycle of the semidiurnal pressure oscillation in midlatitudes. Further calculations show that the magnitude of the non-migrating components of the semidiurnal barom...

Estimating monthly-averaged air-sea transfers of heat and momentum using the bulk aerodynamic method

Abstract: Air-sea transfers of sensible heat, latent heat and momentum are computed from 25 years of middle-latitude and subtropical ocean weather ship data in the North Atlantic and North Pacific using the bulk aerodynamic method. The results show that monthly averaged wind speeds, temperatures and humidities can be used to estimate the monthly averaged sensible and latent heat fluxes from the bulk aero-dynamic equations to within a relative error of ∼10%. The estimates of monthly averaged wind stress under the assumption of neutral stability are shown to be within ∼5% of the monthly averaged non-neutral values.

Description of transformation kinetics, heat conduction and elastic-plastic stress in the course of quenching and tempering of some steels

Abstract: The first part of the paper deals with the constitutive relations of thermoelastic-plastic bodies during heat treatment when considering phase transformation on the basis of continuum thermodynamics. Interaction between temperature and metallic structures is carefully discussed to obtain the heat conduction equation including latent heat due to phase transformation. Applications of the theory to the cases of quenching and low-temperature-tempering are also presented. Structure and temperature distributions are numerically calculated by a finite element technique after determining the physical properties from the data of dilatation-temperature-time diagrams. Variations of stress and strain are also analysed. Calculated results of the transformation kinetics and residual stress are compared with experimental data for plain carbon and chromium steels measured by micrographs and both method of X-ray diffraction and Sachs' boring out technique, respectively.

Influence of the Tibetian Plateau on cumulative and diurnal changes of weather and climate in summer

Abstract: An investigation of the dynamic and thermodynamic influences of the Tibetian Plateau on the monsoon circulation in southeastern Asia and China is reported. A five-day primitive equation numerical model was used to simulate the influences of the high mountains in the 0-180 deg E and 25-55 deg N region on a typical July day. The equations predicted horizontal motion, heat, the water vapor mixing ratio, and surface pressure. Consideration was given to solar and longwave radiation and the release of latent heat by deep cumulus clouds. A net warming over the Plateau as opposed to the surrounding areas was found to lead to vertical air ascent and the establishment of strong summer monsoon circulation to the south. It is noted that the grid was too coarse to adequately describe the distribution of precipitation on the steep mountains.

Latent heat storage

Abstract: The investigations of materials presumably suitable as storage media for latent heat indicate that water, some salt hydrates and eutectic mixtures of water and salt hydrates possess extreme heats of fusion. Their melting points, ranging from about -50° to + 130°C, fit well for storing low grade heat in residential energy systems. Detailed experimental investigations on a large number of these media show, however, that only a few of them satisfy the quality requirments for practical application in storage units. Flexible flat-plate storage containers especially developed for selected salt hydrates which expand on melting also show satisfactory performance over long periods of operation. In the case of water and selected water-salt hydrate eutectics the volume increases on solidification, and the expansion of solid storage material, being very inhomgeneous, breaks even flexible containers after only a few storage cycles. This ruinous local expansion can be avoided, however, by adding a small amount of special, lower melting salt hydrate eutectics which homogenize the crystallization and solidification of the storage medium.

Evaporation coefficient for the sea surface from eddy flux measurements

Abstract: Eddy correlation measurements of water vapor, heat, and momentum fluxes have been made at a fixed tower near the water's edge on a low, sand island. The evaporation data collected extend the range of conditions to cooler water (larger Bowen ratio) and include cases of stable stratification and downward vapor flux. The evaporation coefficient CE has a value of 1.3 × 10−3 in neutral conditions, varies with stability in accordance with accepted empirical profile laws, and increases significantly with increasing wind speed at this shoal location. The Bowen ratio of sensible to latent heat flux varies widely with meteorological conditions.

Climate sensitivity of a one-dimensional radiative-convective model with cloud feedback

Abstract: The potential complexity of the feedback between global mean cloud amount and global mean surface temperature when variations of the vertical cloud distribution are included is illustrated. This is done by studying the behavior of a one-dimensional radiative-convective model with two types of cloud variation: (1) variable cloud cover with constant optical thickness and (2) variable optical thickness with constant cloud cover. The variable parameter is calculated on the assumption that a correlation exists between cloud amount and precipitation or the vertical flux convergence of latent heat. Since the vertical latent heat flux is taken to be a fraction of the total heat flux, modeled by convective adjustment, the sensitivity of the results to two different critical lapse rates is examined. These are a constant 6.5 K/km lapse rate and a temperature-dependent, moist adiabatic lapse rate. The effects of the vertical structure of climate perturbations on the nature of the cloud feedback are also examined. The model results reveal that changes in the vertical cloud distribution and mean cloud optical thickness can be as important to climate variations as are changes in the total cloud cover.

Occurrence of ice layers at the base of high arctic snowpacks

Abstract: The formation of an ice layer at the base of to dissipate the latent heat released by the reHigh Arctic snowpacks is due to a refreezing freezing process, but through such latent heat of the meltwater percolating to the snow- transfer the warming of the active layer is acground interface. A cold substrate is required celerated.

Observational Analysis of Tropical Cyclone Formation. Part III: Budget Analysis

Abstract: Vertically integrated budgets of moisture, heat, angular momentum and kinetic energy are calculated from the composite data sets of Part I (McBride, 1981). The transition from cloud cluster to typhoon/hurricane is characterized by a warming of the troposphere and increase of tangential wind. Observations are presented to show that these effects are not restricted to the system's inner core region, but rather take place over a volume extending out to at least 6° latitude radius from the system center. Accordingly, in this paper cyclogenesis is investigated by analyzing budgets over this large scale. The heat budget calculations show that the observed warming of the troposphere is an order of magnitude smaller than the other terms in the budget equation. Most of the released latent heat LP0 is exported laterally through the boundaries of the region through conversion to the term ∇·Vs. The portion of LP0 which is released within the volume acts to counter the net radiative cooling QR. All the compos...

Is Evaporation an Important Component in High Alpine Hydrology

Abstract: The knowledge of evaporation in the high mountain areas of the European Alps is still rather poor. It is generally regarded as a component of secondary importance in the water balance. The available mean areal evaporation data are based on conventional water balance estimations and suffer from inaccuracies in the determination of precipitation. This is also obvious from the rate of decrease in mean annual evaporation with altitude indicated by different authors; these values range from 71 mm to 356 mm pro 1,000 m of altitude. From heat balance studies on glaciers it is evident that evaporation/condensation as a process of high specific energy exchange can be a determinative factor in the shortterm variations of melt rates. The scale width of the daily latent heat fluxes reaches at magnitudes equal to or larger than those of net radiation and sensible heat flux.

Heat storage medium for latent heat thermal energy storage unit

Abstract: A heat storage medium for use in a latent heat TES unit is obtained by treating a crystalline polyolefin with ion plasma thereby crosslinking it only in the surface region.

The optimum shape for converting rectangular fins when condensation occurs

Abstract: There may be condensation on the fin surfaces of the air conditioning systems due to the temperature of the fin surfaces being below the dew point temperature of the water vapor in the surrounding air. Heat and mass transfer occur from the saturated air layer to the liquid water film and the latent heat of condensation is transferred to the fin. This study presents a quasilinearization solution for vertical rectangular fins when condensation occurs, assuming that the average convective heat and mass transfer coefficients are constant along the height of the fin. Rectangular fins with and without condensation on the surface have been compared and optimum fin dimensions have been given. The optimum fin length, the fin effectiveness and the average fin temperature in the case of condensation were found to be smaller than in the case of no condensation.

Heat accumulating device

Abstract: PURPOSE:To enable to collect heat from latent heat accumulating materials or to accumulate heat in the materials in a short time by a method wherein a plurality of heat accumulating vessels containing the latent heat accumulating materials of different boiling points, respectively, are disposed within a heat accumulating tank in the flow direction of a fluid in the tank in such a manner that the vessels are arranged in sequence in the order beginning from the vessel having the heat accumulating material of the lowest boiling point and ending with that having the heat accumulating material of the highest boiling point. CONSTITUTION:The fluid 8 of low temperature is flowed from an inlet pipe 4 toward an outlet pipe 5 at the time of heat radiation. In this case, the fluid 8 is heated to an elevated temperature by receiving heat from the heat accumulating materials 2a-2d but since the heat accumulating materials of higher boiling points are arranged in the flow direction of the fluid 8, the difference in temperature between the fluid 8 and the heat accumulating materials is kept substantially constant with respect to the flow direction of the fluid. As a consequence, the amounts of heat radiation from the heat accumulating vessels 1 become substantially equal to one another and the entire amount of heat radiation from the vessels as a whole increases. Therefore, in case where a large amount of heat is required temporarily, this is extremely advantageous and hence it is possible to collect heat from the heat accumulating materials or to accumulate heat in the materials in a short time.

Calculation of sensible and latent heat fluxes, and surface resistance from profile data

Abstract: A set of semi-continuous measurements of temperature, wind and moisture gradients as well as of net radiation and ground heat flux covering a period of about one and a half years has been analysed to give a corresponding set of complete surface energy balance data on an hourly basis. An analysis of the evaporation data so obtained is given.

Mechanistic limitations to the release of latent heat during the natural and artificial glaciation of deep convective clouds

Abstract: The latent heat thermodynamically available in the supercooled water of deep convective clouds is released at rates governed by the glaciation mechanism, presumed here to involve primary nucleation, capture nucleation of rain by small ice particles and secondary ice production (rime-splintering hypothesis). A simple microphysical model of the glaciation shows the importance of regenerative feed-back on the evolution of ice when the primary nucleation and regenerative processes proceed simultaneously, leading to insensitivity to the primary ice nucleus concentration. This allows rapid glaciation and heat release to occur naturally in clouds exhibiting a broad supercooled drop size spectrum. New observational data and model results of artificially induced glaciation are consistent with the idea that the primary microphysical role of seeding is the creation of many small ice particles which substitute for the secondary ice splinters of naturally induced glaciation. the aerodynamic capture of the splinters by the supercooled rain leads to the formation of new graupel particles and the rapid release of fusional heat, shown by calculation to dominate the heat release mechanisms. With a seeding agent acting in the contact mode the small (cloud drop) end of the spectrum is required, since Brownian scavenging of the nuclei by the few large rain drops is inefficient. the quantitative analysis of these glaciation concepts also demonstrates that realistic seeding under conditions conducive to ice multiplication could increase materially the rate of heat release and offer opportunities for artificially invigorating the dynamic structure of a cloud if glaciation is induced to occur within a relatively narrow ‘time window’ for seeding.

Interpretation of Flux-Profile Observations at ITCE (1976)

Abstract: At an International Turbulence Comparison Experiment (ITCE) in Australia (1976), wind, temperature and humidity profiles, plus vertical fluxes of momentum, sensible heat and latent heat were measured for a limited range of unstable conditions, but with a wide variety of instrumentation. Comparisons of like instruments, and of flux and profile measurements via the Monin-Obukhov similarity theory, have been used to assess systematic effects. The scatter about conventional flux-profile formulations varies with choice of stability parameter (z/L or Ri) and this also proves an effective means of identifying the source of the scatter. The cup anemometer results exhibit evidence of errors in calibration factors which are the major source of scatter in the unsmoothed measured gradients. The limited stability range prevents unambiguous solution for all constants in the conventional flux-profile relationships. For momentum transfer, use of Ri as a stability parameter gives least sensitivity to error; adopt...

Limited expansion vapor cycle

Abstract: An apparatus and method for recycling or maintaining the latent heat of vaporization in work producing cycles such as the Rankine cycle by eliminating phase changes by replacing the condenser in such cycles with a compressor and restricting or limiting the expansion to reduce compressor work requirements. The standard compound turbine prevalent today consisting of a single Curtis stage in tandem with pressure compounded stages has been replaced with several two-row Curtis stages. An alternative embodiment utilizes one or several two-row Curtis stages and a condenser as in the Rankine cycle but limits the expansion, maintaining a relatively high pressure typical in exhaust from this type of turbines. The high pressure maintains the temperature of the condensate sufficiently high to eliminate feed water preheating. Sacrifice of low pressure output is compensated in both cases by salvaging latent heat of vaporization which would not be possible economically, if expansion carried to the maximum. Sufficient heat is added in the boiler to restore the vapor to its operating condition and to replace any excess heat removed at the final stage of the turbine.