Specific moisture evaporation

For drying, a better efficiency parameter is the specific moisture evaporation rate (SMER), defined as... 

Amount of removed moisture Evaporational rate referred to the cross section of the dryer Specific energy consumption... 

The energy performance of a dryer and a drying process is characterized by various indices such as volumetric evaporation rate, surface heat losses, steam consumption, unit heat consumption, and energy (thermal) efficiency. Of all these indices, the energy efficiency / is most frequently quoted in technical specifications. It commonly relates the energy used for moisture evaporation at the solids feed temperature ( , ) to the total energy supplied to the dryer ( ,) ... 

Table 9.2 presents the SEC and drying efficiency values for different microwave-assisted drying processes of food materials, as determined by various research groups. The minimal theoretical value of SEC for a dryer is 2.3 MJ per kg of evaporated water, based on the maximal theoretical specific moisture extraction ratio (SMER) of 1.55 kg per kWh and the latent heat of water evaporation at 100 °C (Holtz et cd., 2009). These results are expected to depend heavily on the scale and design of dryers, as well as on the method used to measure energy consumption (Durance and Wang, 2002). 

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

Evaporative cooling only Increased moisture content and. ipecific volume decreased dry- and wet-biilb tempera turc increased specific enrhalpy and % saturation Washer... 

Rusting indoors and in enclosed spaces Although much of what has been written above is of general application, the experimental data apply specifically to exposure outdoors. The conditions of exposure indoors are somewhat different, because the steel is not exposed to rain and direct sunlight. Rusting depends on the condensation of moisture, which may evaporate from the surface much more slowly under enclosed conditions than outdoors moreover, the rust tends to remain on the surface and may build up in time to a thick scaly layer. 

The physical forms indicated are those which, for each specific type of product, assure product flowability within the reported range of residual moisture they can be achieved by specific mechanical devices operating at the outlet of the evaporator and cooler. 

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