Temperature differentials, moisture

Moisture. Moisture is usually determined by a vacuum oven-dry method at 80°C. Moisture levels of more than 0.05% are likely to lead to caking or lumping problems which can make storage and transfer of bulk sugar difficult. The usual standard is 0.03%, which manufacturers can easily meet. Care must be taken to avoid temperature differentials ia storage which cause moisture to migra te and estabUsh pockets of unacceptably high moisture levels. 

There are substantial differences in the rates at which water vapor and other gases can permeate different plastics. For instance, PE is a good barrier for moisture or water vapor, but other gases can permeate it rather readily. Nylon, on the other hand, is a poor barrier to water vapor but a good one to other vapors. The permeability of plastic films is reported in various units, often in grams or cubic centimeters of gas per 100 in.2 per mil of thickness (0.001 in.) of film per twenty-four hours. The transmission rates are influenced by such different factors, as pressure and temperature differentials on opposite sides of the film. 

Moisture. As anticipated, moisture contents of the powder samples decreased with decreasing temperature differentials between inlet and exit air temperatures when either inlet or exit air temperature was held constant (Figure 2). The sample with the highest temperature differential ( T=120 C) and lowest exit air temperature (T=80 C) had the highest moisture content (7.8%) of all the powder samples. The role of temperature differential on product moisture content is apparent from either data series in Figure 2. While the sample dried at 280 C inlet and 105 C exit air temperatures had the greatest temperature differential, the... 

In summary, we have found that the optimum (within the limits of this study) a for shelf-life is 0.54. In addition, the dryer inlet and exit air temperatures had no effect upon oil retention and perhaps only a minor effect upon shelf-life. If there is a significant effect it is that the higher inlet air temperature actually yielded a better shelf-life. A higher temperature differential means that dryer throughput also is increased and operating costs are cut. The more product that can be produced per hour, the lower the production costs. A larger temperature differential also results in a higher final product moisture. 

Another factor augmectting the heat conductivuty of plastic foams under conditions is the absorbed moisture. For example, for CCljF-foamed polyurethane at 25 °C and a relative humidity of 65%, the ambient moisture diffusion rate is 10-20 g/m for 24 h. Especially strong is the effect of moisture on heat conductivity if the temperature differential across the sample is considerable. For example, in plastic foams used in cryogenic technology, the inner layers are exposed to low temperatures the water vapor first condenses and is then convected into ice. Since the thermoconductivity of water and ice are 0.5 and 1.5 kcal/m x h °C, respectively, even minor tunounts have a considerable detrimental effect of the heat insulating capacity of a foam material... 

An analyzer with a range of 0.1 to 10 p.p.m. of ozone is being used in the Biochemistry Research Section of the foundation. Another prototype with a range of 0.01 to 1 p.p.m. was found to be subject to drift. The drift was traced to temperature differentials between the various elements of the bridge circuit and leakages due to superficial condensation of atmospheric moisture. An improved instrument is being assembled in which all the elements of the circuit, except the balancing potentiometer, are enclosed in the thermostatically controlled bath. 

As seen from relations (62.30a-c), the stresses are temperature and moisture content dependent. Thus, to determine the state of stress, the distributions of moisture content and temperature have to be determined first. To this aim the differential equations (62.23) and (62.27) are adopted to the cylindrical geometry... 

The depth-type filter elements are used when the oil is free from water, and when particles sizes to be removed are in the five-micron and greater range. Generally, the depth-type element is water-sensitive, and when oil is contaminated with moisture, this element type will absorb the water and produce a rapid increase in differential pressure across the filter. The desired maximum differential pressure across a filter with clean elements is five psig at normal operating temperature. 

The problem with a conventional system that relies on heat exchangers (i.e. aftercoolers) for moisture removal is temperature. The aftercooler will remove only liquids that have condensed at a temperature between the compressed air and cooling water temperature. In most cases, this differential will be about 20 to 50° lower than the compressed air temperature or around 70 to 90°F. As long as the compressed air remains at or above this temperature range, any remaining vapor that it contains will remain in a vapor or gaseous state. However, when the air temperature drops below this range, additional vapor will condense into water. 

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