189:, further increasing the driving force for drying. In the falling rate period, as moisture content falls, the solids heat up and the higher temperatures speed up diffusion of water from the interior of the solid to the surface. However, product quality considerations limit the applicable rise to air temperature. Excessively hot air can almost completely dehydrate the solid surface, so that its pores shrink and almost close, leading to crust formation or "case hardening", which is usually undesirable. For instance in wood (timber) drying, air is heated (which speeds up drying) though some steam is also added to it (which hinders drying rate to a certain extent) in order to avoid excessive surface dehydration and product deformation owing to high moisture gradients across timber thickness.
215:, i.e., passed to the gas phase directly from the solid phase, below the melting point of the solvent. It is increasingly applied to dry foods, beyond its already classical pharmaceutical or medical applications. It keeps biological properties of proteins, and retains vitamins and bioactive compounds. Pressure can be reduced by a high vacuum pump (though freeze drying at atmospheric pressure is possible in dry air). If using a vacuum pump, the vapor produced by sublimation is removed from the system by converting it into ice in a condenser, operating at very low temperatures, outside the freeze drying chamber.
273:
darkening, and drying is not only carried out to inhibit microbial growth, but also to avoid browning during storage. Concerning dried fruits, the reduction of moisture acts in combination with its acid and sugar contents to provide protection against microbial growth. Products such as milk powder must be dried to very low moisture contents in order to ensure flowability and avoid caking. This moisture is lower than that required to ensure inhibition to microbial development. Other products as crackers are dried beyond the microbial growth threshold to confer a crispy texture, which is liked by consumers.
145:. If water removal is considerable, the products usually undergo shrinkage and deformation, except in a well-designed freeze-drying process. The drying rate in the falling-rate period is controlled by the rate of removal of moisture or solvent from the interior of the solid being dried and is referred to as being "mass-transfer limited". This is widely noticed in hygroscopic products such as fruits and vegetables, where drying occurs in the falling rate period with the constant drying rate period said to be negligible.
221:(superheated steam drying) involves steam drying of products containing water. This process is feasible because water in the product is boiled off, and joined with the drying medium, increasing its flow. It is usually employed in closed circuit and allows a proportion of latent heat to be recovered by recompression, a feature which is not possible with conventional air drying, for instance. The process has potential for use in foods if carried out at reduced pressure, to lower the boiling point.
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individual particles that is being removed. The drying rate during this period is mostly dependent on the rate of heat transfer to the material being dried. Therefore, the maximum achievable drying rate is considered to be heat-transfer limited. If drying is continued, the slope of the curve, the drying rate, becomes less steep (falling rate period) and eventually tends to become nearly horizontal at very long times. The product moisture content is then constant at the "
252:
141:", where it is, in practice, in equilibrium with the dehydrating medium. In the falling-rate period, water migration from the product interior to the surface is mostly by molecular diffusion, i.e. the water flux is proportional to the moisture content gradient. This means that water moves from zones with higher moisture content to zones with lower values, a phenomenon explained by the
154:
69:. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of
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takes place when materials are dried with unheated forced air, taking advantage of its natural drying potential. The process is slow and weather-dependent, so a wise strategy "fan off-fan on" must be devised considering the following conditions: Air temperature, relative humidity and moisture content
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In some products having a relatively high initial moisture content, an initial linear reduction of the average product moisture content as a function of time may be observed for a limited time, often known as a "constant drying rate period". Usually, in this period, it is surface moisture outside
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Foods are dried to inhibit microbial development and quality decay. However, the extent of drying depends on product end-use. Cereals and oilseeds are dried after harvest to the moisture content that allows microbial stability during storage. Vegetables are blanched before drying to avoid rapid
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Dielectric drying (radiofrequency or microwaves being absorbed inside the material) is the focus of intense research nowadays. It may be used to assist air drying or vacuum drying. Researchers have found that microwave finish drying speeds up the otherwise very low drying rate at the end of the
242:
In the coatings and adhesives industry, drying is used to cure solvent-based films. In some cases, highly structured films can result. For example, evaporation of solvent from a solution containing helical polymer results in a highly ordered array of squashed toroidal structures.
228:
and temperature of the material being dried. Grains are increasingly dried with this technique, and the total time (including fan off and on periods) may last from one week to various months, if a winter rest can be tolerated in cold areas.
120:(used, for instance, for manufacturing potato flakes), where a heated surface is used to provide the energy, and aspirators draw the vapor outside the room. In contrast, the mechanical extraction of the solvent, e.g., water, by
285:(as part of timber processing), paper, flax, and washing powder. The first two, owing to their organic origins, may develop mold if insufficiently dried. Another benefit of drying is a reduction in volume and weight.
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Indirect or contact drying (heating through a hot wall), as drum drying, vacuum drying. Again, higher wall temperatures will speed up drying but this is limited by product degradation or case-hardening.
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kill, as pathogens can only tolerate a certain dryness level. In addition, drying is required as a process step if the excreta based materials are meant to be incinerated.
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or direct drying). Air heating increases the drying force for heat transfer and accelerates drying. It also reduces air
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classical drying methods. Vacuum microwave drying is used for the US Army's experimental Close Combat
Assault Ration.
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and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and
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In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as
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Genskow, L.R.; Beimesch, W.E.; Hecht, J.P.; Kemp, I.C.; Langrish, T.; Schwartzbach, C.; Smith, (F).L. (2007).
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Onwude, Daniel I.; Hashim, Norhashila; Janius, Rimfiel B.; Nawi, Nazmi Mat; Abdan, Khalina (2016-02-04).
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or lyophilization is a drying method where the solvent is frozen prior to drying and is then
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390:"drying - definition of drying by the Free Online Dictionary, Thesaurus and Encyclopedia"
361:. Mc Graw Hill Professional. pp. Chapter 12 (Evaporative Cooling and Solids Drying).
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Faecal Sludge
Management (FSM) book - Systems Approach for Implementation and Operation
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Carroll, Gregory T.; Jongejan, Mahthild G. M.; Pijper, Dirk; Feringa, Ben L. (2010).
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Removal of water or another solvent by evaporation from a solid, semi-solid or liquid
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Among non-food products, some of those that require considerable drying are
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Strande, L., Ronteltap, M., Brdjanovic, D. (eds.) (2014).
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81:, the solvent to be removed is almost invariably water.
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process consisting of the removal of water or another
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Comprehensive
Reviews in Food Science and Food Safety
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Sludges and fecal materials from sanitation processes
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with drying or considered an extreme form of drying.
128:, is not considered "drying" but rather "draining".
112:), while the vapor thus produced is removed by the
457:"Cooking (and Shrinking) the Modern Combat Ration"
177:The following are some general methods of drying:
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165:. Regular drying is the green arrow, while
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116:system. Another indirect technique is
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34:in the background and duct for
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455:Kord, Tyler (June 29, 2019).
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368:Handbook of Industrial Drying
359:Chemical Engineers' Handbook
143:second law of thermodynamics
139:equilibrium moisture content
100:, where heat is supplied by
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352:. Woodhead Publishing, Ltd.
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315:urine-diverting dry toilets
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790:Electrostatic precipitator
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96:. Other possibilities are
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830:Rotary vacuum-drum filter
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201:belongs in this category.
193:belongs in this category.
873:Aqueous two-phase system
695:Liquid–liquid extraction
370:. Boca RatĂłn: CRC Press.
181:Application of hot air (
770:API oil–water separator
640:Dissolved air flotation
433:10.1111/1541-4337.12196
366:A.S., Mujumdar (1998).
348:Greensmith, M. (1998).
303:sewage treatment plants
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735:Solid-phase extraction
523:. IWA Publishing, UK (
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233:Applications of drying
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855:Vacuum ceramic filter
850:Sublimation apparatus
655:Electrochromatography
615:Cross-flow filtration
350:Practical Dehydration
259:in the production of
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169:is the red arrow and
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805:Fractionating column
600:Acid–base extraction
581:Separation processes
331:Dehydration reaction
219:Supercritical drying
167:supercritical drying
625:Cyclonic separation
685:Gravity separation
519:2017-10-14 at the
492:10.1039/c0sc00159g
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255:Drying of fish in
225:Natural air drying
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30:in a drying room (
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720:Recrystallization
700:Electroextraction
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277:Non-food products
187:relative humidity
149:Methods of drying
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394:. Retrieved
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307:fecal sludge
297:, drying of
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191:Spray drying
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173:is the blue.
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32:dehumidifier
28:clothes line
775:Belt filter
740:Sublimation
630:Decantation
336:Drying room
199:Drum drying
118:drum drying
83:Desiccation
55:evaporation
36:ventilation
864:Multiphase
795:Evaporator
780:Centrifuge
670:Filtration
665:Extraction
605:Adsorption
595:Absorption
486:(4): 469.
376:References
295:sanitation
183:convective
122:filtration
110:microwaves
102:conduction
87:synonymous
63:semi-solid
26:hung on a
878:Azeotrope
588:Processes
500:2041-6520
261:stockfish
106:radiation
914:Category
892:Concepts
883:Eutectic
835:Scrubber
810:Leachate
690:Leaching
635:Dialysis
517:Archived
442:33401820
396:23 April
392:. Farlex
325:See also
319:pathogen
213:sublimed
94:humidity
79:vaccines
866:systems
763:Devices
710:Osmosis
257:Lofoten
85:may be
57:from a
51:solvent
24:Laundry
920:Drying
650:Drying
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114:vacuum
67:liquid
43:Drying
845:Still
416:(PDF)
311:feces
301:from
77:like
59:solid
45:is a
525:ISBN
496:ISSN
438:PMID
398:2011
283:wood
247:Food
108:(or
71:heat
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