Specific evaporation heat

In addition to volume changes the effect of temperature is also important. Thus the specific latent heat of vaporization of a chemical is the quantity of heat, expressed as kJ/kg, required to change unit mass of liquid to vapour with no associated change in temperature. This heat is absorbed on vaporization so tliat residual liquid or tlie sunoundings cool. Alternatively an equivalent amount of heat must be removed to bring about condensation. Thus the temperature above a liquefied gas is reduced as tlie liquid evaporates and tlie bulk liquid cools. There may be consequences for heat transfer media and the strength of construction materials at low temperatures. 

Carbonate op Strontia is found native as stron-tianite, both massive, and in forms belonging to the square prismatic system. It is most readily prepared pure by precipitating the nitrate or chloride with carbonate of ammonia, The artificial carbonate is beautifully white and soluble in one thousand five hundred and thirty-six parts of boiling Water. It is more soluble in aqueous solution of carbonio acid, and separates in needles when, evaporated. Heated to bright redness in a stream of watery vapor it loses its carbonic acid, and becomes changed into strontia. The symbol is SrO, CO Eq. 74-00 specific gravity, 3 605. 

NN have also been used in the design of refrigerants. In Ref. the authors have studied the prediction of the specific volume of refrigerant-absorbent couple in the function of system composition, pressure, and temperature using NN. The objective was to determine the properties of the couple such as ensuring zero ozone depletion, thermal resistance, high evaporation heat at low pressure, low specific volume of vapor, low solidification, and high critical temperatures. 

These evaporators are necessarily precision machines and therefore are more expensive than other types, particularly so if compared strictly on equivalent heat transfer area. When the performance for a specific evaporation duty is the basis of comparison, the thin-film evaporator is often the more economical choice because the larger heat transfer coefficient and higher driving force mean much less surface is required than for other evaporators (A = Q/U AT). Thin-film evaporator cost per unit area decreases significantly with unit size, and the largest available unit has 430 square feet of active heat transfer surface. 

The vacuum calorimeter described by Schwers and me has been further developed recently in a few respects by Gunther (107), who used it for many important measurements reference may therefore be made to the description given by Gunther for a more detailed account. The vacuum calorimeter has been used by Eucken (105) with marked success to determine the specific heats of gases at constant volume, and also for the measurement of heats of evaporation, heats of fusion, and heats of transformation at low temperatures (cf. also Chapter V). 

Empirical fits to the specific latent heats of evaporation AHv and of melting AHm are as follows for temperature T in K ... 

Corresponding quantities of heat required for the change of state are called specific latent heat of melting or solidification (333.3 kJ kg" ) and evaporation or boiling (2257 kJ kg ). 

Typical specific steam consumption of the drum dryer varies from 1.3 to 1.5 kg steam per kg water removed or a steam economy of 0.66-0.76 kg water removed per kg steam. It means that the specific heat consumption is typically about 3000-3500 kJ/kg water removed. The specific evaporation rate is 10-30 kg water evaporated per mVh for difficult to dry materials and 40-50 kg water evaporated per mVh for easy to dry materials. Recent studies have increased the understanding of the processes in the drum dryer but it is still a long way before the drum dryer can be modeled completely. 

Specific requirement of gas Specific requirement of heat Specific evaporation... 

W, and W, i are the moisture contents dry basis for MFD cycles k and k-, respectively L is the latent evaporation heat of water Cp d and Cp are the specific heat of dry product and water, respectively... 

For a saturated liquid, as it often occurs in process engineering applications, the specific isobaric heat capacity does not make much sense, as a supply of heat does not yield a temperature increase but causes evaporation. Therefore, a specific heat capacity along the saturation line is used (c ), which is only a function of... 

This book contains tables of the properties of water and steam from 0 to 800 and from 0 to 1000 bar which have been calculated using a set of equations accepted by the members of the Sixth International Conference on the Properties of Steam in 1967. Properties which are tabulated include the pressure, specific volume, density, specific enthalpy, specific heat of evaporation, specific entropy, specific isobaric heat capacity, dynamic viscosity, thermal conductivity, the Prandtl number, the ion-product of water, the dielectric constant, the isentropic exponent, the surface tension and Laplace coefficient. Also see items [43] and [70]. 

According to scheme b), the steam side of the generator is included in the node and the streams 3 resp. 4 represent feed water resp. produced stream. We approximate the specific heat of liquid water also by a constant, Cp, and let L be the evaporation heat at temperature 7 we neglect the pressure dependence for liquid water enthalpy. Then, by (6.1.1)... 

The heat input to diyers is to a gas and as such takes place over a range of temperatures. Moreover, the gas is heated to a temperature higher than the boiling point of the liquid to be evaporated. The exhaust gases from the dryer will be at a lower temperature than the inlet, but again, the heat available in the exhaust will be available over a range of temperatures. The thermal characteristics of dryers tend to be design-specific and quite difierent in nature from both distillation and evaporation. 

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