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Desiccant Drying and Cogeneration
Published in Bernard F. Kolanowski, Small-scale Cogeneration Handbook, 2021
Desiccants use either adsorption or absorption to attract water molecules to accumulate at the desiccant. Adsorption desiccants include zeolites and silica gel. Absorption desiccants include hygroscopic salts, such as lithium bromide.
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Published in Frank R. Spellman, Fundamentals of Wastewater-Based Epidemiology, 2021
Total solids are measured by weighing the amount of solids present in a known volume of sample; this is accomplished by weighing a beaker, filling it with a known volume, evaporating the water in an oven and completely drying the residue, then weighing the beaker with the residue. The total solids concentration is equal to the difference between the weight of the beaker with the residue and the weight of the beaker without it. Since the residue is so light in weight, the lab needs a balance that is sensitive to weights in the range of 0.0001 g. Balances of this type are called analytical or Mettler balances, and they are expensive (around $3000). The technique requires that the beakers be kept in a desiccator, a sealed glass container that contains material that absorbs moisture and ensures that the weighing is not biased by water condensing on the beaker. Some desiccants change color to indicate moisture content. Measurement of total solids cannot be done in the field. Samples must be collected using clean glass or plastic bottles, or Whirl-pak® bags and taken to a laboratory where the test can be run.
Mold: Potential Threats Sprout in a Watery World
Published in Ed Bas, Indoor Air Quality, 2020
Desiccants are materials with a very high affinity for moisture that pull water vapor from humid air through a process known as sorption. The most common commercial desiccant systems employ wheel technology in which a rotor made of a lightweight honeycomb-shaped matrix impregnated with solid desiccant material rotates between two air streams. As outside supply air passes through one section of the wheel, it comes into contact with the desiccant material, which draws out the moisture. The wheel rotates slowly into a second opposing reactivation air stream where the desiccant is dried, and the process repeats itself. The desiccant is never “used up” in the process. This is adsorption, which does not change the material in any way, and differs from absorption, in which the substance soaks up moisture and holds onto it, like a sponge.
Mathematical modelling of solar drying of a novel composite desiccant
Published in International Journal of Ambient Energy, 2019
Anish Malan, Vikrant Kamboj, Ashwani Kumar Sharma, Avadhesh Yadav
Humidity is a great concern in the tropical region of the earth. Controlling humidity is not only important for human comfort, but also necessary for monitoring the quality of air to be used in industries (e.g. drying industries) or for preserving food nutrition. One alternative for dehumidification of air is the use of desiccant materials. Desiccant is a material that attracts and holds the moisture from its vicinity and induces a state of dryness usually at room temperature. Desiccant drying is an isothermal process which not only produces dry air but also increases the temperature of dehumidified air. Dehumidification at low temperature can solely be carried out by desiccant materials; another method produces dry air at high temperature only. The air heating for dehumidification requires a complex and costly control system which impedes its practical, low-cost drying usage on village/farm applications.
Investigation on the performance of LDDS using biomass-based wood shaving as the packing material
Published in International Journal of Sustainable Energy, 2022
Sampath Suranjan Salins, S.V. Kota Reddy, Shiva Kumar, Sreejith Sanal Kumar
The process in which moisture removal occurs due to the absorption by a desiccant is called desiccant dehumidification. Packing is an important medium for dehumidification. Its material property and configuration decide wettability. Desiccant is a chemical substance that absorbs moisture and its performance depends upon its concentration, flow rate, and temperature. When desiccant encounters the air, it absorbs moisture. During that process, the heat of condensation will be liberated and because of this, both air and desiccant will receive sensible energy. Therefore, the DBT of the outlet air rises. Figure 1 shows the representation of the counter flow process using a psychometric chart which indicates dehumidification and heating.
Modeling the effect of a superabsorbent polymer material as desiccant in maize drying using CFD
Published in Drying Technology, 2019
Franz Román, Duncan O. Mbuge, Oliver Hensel
For several decades, studies have been carried out dealing with the drying of grain and other products with the help of solid desiccants. Common desiccant materials have been silica gel and bentonites. Due to their hygroscopicity, these materials adsorb water vapor from the surrounding air, thus lowering its vapor pressure and facilitating grain drying, even (to some extent and depending on the mass ratio) in the absence of airflow. Sturton et al.[7] and Watts et al.[8] used bentonites to dry grain in closed systems where an intimate contact existed between the materials and with desiccant:grain ratios of 0.5:1 to 2:1. Falabella et al.[9] also used bentonite to dry maize, although with higher ratios of up to 10:1 and both in static closed containers and well as containers mixed by rotation. However, at the conditions employed there was no difference in the drying rate between treatments. Yamaguchi and Kawasaki[10] dried rough rice with silica gel in closed systems, both in intimate contact and in a divided bed system with silica gel at the bottom and rice at the top. The latter system proved to be inappropriate due to the slow driving mechanism of vapor diffusion in both beds which translated in low drying rates and large moisture gradients forming along both beds. Seyhan and Evranuz[11] dried mushroom slices in closed containers with silica gel, with the slices hanging above the desiccant and with a material ratio of about 50:1. Li et al.[12] dried soybean using silica gel in 100 ml containers at ratios of 0.25:1–0.75:1. An issue with most of the studies mentioned above is that they were conducted only on laboratory scale with a food sample mass ranging from a few grams to a few kilograms. Moreover, the dessicant:product ratios in most cases were relatively high and, therefore, difficult to implement at larger scales.