Equilibrium moisture basis

Analyses reported on a dry basis are calculated on the basis that there is no moisture associated with the sample. The moisture value (ASTM D-3173 ISO 331 ISO 589 ISO 1015 ISO 1018 ISO 11722) is used for converting as determined data to the dry basis. Analytical data that are reported on a dry, ash-free basis are calculated on the assumption that there is no moisture or mineral matter associated with the sample. The values obtained for moisture determination (ASTM D-3173 ISO 589) and ash determination (ASTM D-3174) are used for the conversion. Finally, data calculated on an equilibrium moisture basis are calculated to the moisture level determined (ASTM D-1412) as the equilibrium (capacity) moisture. 

Equilibrium moisture basis data calculated to the moisture level established as the equilibrium moisture (ASTM D-1412 ASTM D-3180). 

Strips of a material 10 mm thick are dried under constant drying conditions from 28 per cent to 13 per cent moisture in 25 ks. If the equilibrium moisture content is 7 per cent, what is the time taken to dry 60 mm planks from 22 to 10 per cent moisture under the same conditions, assuming no loss from the edges All moisture contents are expressed on the wet basis. The relation between E, the ratio of the average free moisture content at time t to the initial free moisture content, and the parameter / is given by ... 

A wet solid is dried from 40 to 8 per cent moisture in 20 ks. If the critical and the equilibrium moisture contents are 15 and 4 per cent respectively, how long will it take to dry the solid to 5 per cent moisture under the some drying conditions All moisture contents are on a dry basis. 

The moisture content of a material is usually expressed in terms of its water content as a percentage of the mass of the dry material, though moisture content is sometimes expressed on a wet basis, as in Example 16.3. If a material is exposed to air at a given temperature and humidity, the material will either lose or gain water until an equilibrium condition is established. This equilibrium moisture content varies widely with the moisture content and the temperature of the air, as shown in Figure 16.1. A non-porous insoluble solid, such as sand or china clay, has an equilibrium moisture content approaching zero... 

Thus, to classify coal, the calorific value and a proximate analysis (moisture, ash, volatile matter, and fixed carbon by difference) are needed. For lower-rank coals, the equilibrium moisture must also be determined. To calculate these values to a mineral-matter-free basis, the Parr formulas are used (ASTM D-388). 

The equilibrium moisture of seeds is modified upon dehulling. Equilibrium moisture values for undehulled sunflower seeds, hulls, and kernels are compared as a function of the relative humidity of the surrounding air at 25°C (Figure 16). The initial moisture content of all seeds was 5% (dry basis). Those samples stored at a relative humidity below 33% reached the equilibrium by desorption, and those at a relative humidity above 33% reached the equilibrium by adsorption (51). 

Equilibrium moisture content EMC, %EMC, Wo.eq, Ww.eq The moisture content (sometimes expressed on a percentage basis) at equilibrium under specified conditions of temperature, pressure, and vapor composition. 

Falling-Rate Kinetics To correct from a calculated constant-rate (unhindered) drying time ten to first-order falling-rate kinetics, the following equation is used, where Xi is the initial, X2 the final, and X the equilibrium moisture content (all must be dry-basis) ... 

X is the equilibrium moisture content and Xln, in units of g/100 g dry basis, is the B.E.T. monomolecular moisture content for the food listed in Table 3.2. However, there are nearly as many equations to sorption isotherms as there are researchers in this field. 

Figure 63.1a shows the equilibrium moisture content (dry basis) at the different a for the desorption experiments (obtained from samples dried by hot air) and also for the adsorption experiments (obtained from the freeze-dried samples). Both isotherms are very similar and no hysteresis phenomenon was observed. Hysteresis is justified by assuming that during... 

Consider the drying of a wet solid under fixed drying conditions. In the most general cases, after an initial period of adjustment, the dry-basis moisture content X decreases linearly with time t following the start of the evaporation. This is followed by a nonlinear decrease in X with t nntil, after a very long time, the solid reaches its equilibrium moisture content X and drying stops. In terms of free moisture content, defined as... 

Example 24.1. A filter cake 24 in. (610 mm) square and 2 in. (51 mm) thick, supported on a screen, is dried from both sides with air at a wet-bulb temperature of 80°F (26.7°C) and a dry-bulb temperature of 120°F (48.9°C). The air flows parallel with the faces of the cake at a velocity of 3.5 ft/s (1,07 m/s). The dry density of the cake is 1201b/ft (1922 kg/m ). The equilibrium-moisture content is negligible. Under the conditions of drying the critical moisture is 9 percent, dry basis, (a) What is the drying rate during the constant-rate period (b) How long would it take to dry this material from an initial moisture content of 20 percent (dry basis) to a final moisture content of 10 percent Equivalent diameter is equal to 2 ft. 

A continuous countercurrent dryer is to be designed to dry 800 lb of wet porous solid per hour from 140 percent moisture to 20 percent, both on the dry basis. Air at 120°F dry bulb and 70°F wet bulb is to be used. The exit humidity is to be 0.012. The average equilibrium-moisture content is 5 percent of the dry weight. The total moisture content (dry basis) at the critical point is 40 percent. The stock may be assumed to remain at a temperature 3°F above that of the wet-buib temperature of the air throughout the dryer. The heat-transfer coefficient is 12 Btu/ft -h-°F. The area exposed to the air is 1,1 ft per pound of dry solids. How long must the solids remain in the dryer ... 

Table 3.1. Equilibrium Moisture Contents (percentage wet basis) for Soybeans...

Biological resistance of fiber-based materials can be improved by several methods. Bonding chemicals to the cell wall polymers increases resistanee due to the lowering of the equilibrium moisture content point below that needed for microorganism attack and by changing the conformation and configuration requirements of the enzyme-substrate reae-tions. Toxic chemicals can also be added to the composite to stop biologieal attack. This is the basis for the wood preservation industry. 

Brown coals, like the hard coals, are also defined in terms of their calorific value (see the previous text) and were also recognized as potential fuels. The International System for the classification of brown coals is based on two inherent characteristics which indicate the value of brown coals as fuels (1) the total moisture (ash-free basis) and (2) the yield of tar (daf basis). Thus, the six classes of brown coal based on the ash-free, equilibrium moisture content are divided into groups according to the yield of tar on a dry, ash-free basis (Table 2.14). This system indicates... 

---