What is Drying: Definition and 33 Discussions

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. 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 heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water. Desiccation may be synonymous with drying or considered an extreme form of drying.
In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as humidity. Other possibilities are vacuum drying, where heat is supplied by conduction or radiation (or microwaves), while the vapor thus produced is removed by the vacuum system. Another indirect technique is drum drying (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 filtration or centrifugation, is not considered "drying" but rather "draining".

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  1. ravindrar

    I Vacuum Drying Vegetables w/ IR Heaters: Investigating Increased Batch Time

    I am working on a project on vacuum drying vegetables using IR heaters. Before winter batch time was around 3 to 4 hours now it has increased to 6 hours. Any logic behind this as though the temperature drops and RH also drop so why has the time increased?
  2. T

    Applications Involving Drying -- Using Kinetic Models

    Hi, I am a mechanical student. I would like to ask are those drying kinetic equations for food drying applicable in drying a paperboard? Thankyou :)
  3. lenilein

    Massflow of steam to be supplied to a drying cylinder

    Good afternoon, I am trying to calculate the massflow of steam required in a cylinder used for paper drying but I think there is a bug in my calculation and I would love to get your help to find where the issue is! Saturated steam is continuously supplied to a cylinder. The steam condenses in...
  4. O

    I Thickness of dark wet spots on drying dishes

    A common observation when doing the dishes is that the wet spots on a drying dish are darker than the dry spots, especially if the dish is held in such a way that it reflects the light of the sky. Evidently the total reflection coefficient is reduced by the water film. The border between dark...
  5. S

    How can we prevent clogging in a drum dryer used for drying liquid digestate?

    I am working on a project to dry liquid digestates (residue from the fermentation process of biogas plants). The liquid digestate has a dry matter (DM) content of about 3%. The digestate is primarily made up of animal manure and maize silage. It is a non-Newtonian fluid having a viscosity of 4...
  6. K

    Help me design a Vacuum Drying system

    Hello all, I've been entrusted a project of developing a Vacuum Drying System for my company. This system will be used for instant drying of automotive parts after washing. Needless to say the parts will be wet and at an elevated temperature (approx 50 degree C). The requirement is to dry the...
  7. C

    I Does moisture escaping from powders decrease chamber vacuum?

    I'm drying some wet powders using vacuum oven and start seeing some condensation on the window after few minutes. The vacuum level stays pretty constant which puzzles me as i thought that the moisture escapes from the powder into the air will increase the chamber pressure or decrease the vacuum...
  8. Peter Hessellund

    How quickly do ocean spray droplets dry into solid salt particles?

    When a bubble in the ocean bursts water drops are thrown into the air. How fast do these water drops dry out creating solid salt particles? There must be a formula for calculating this and I am guessing that the following variables must figure in the formula: - Droplet size - Salt concentration...
  9. S

    Clothes Drying (Evaporation) Equation

    I am trying to find the most efficient way to dry clothes indoors with different evaporation factors 1. Heat/Temperature 2. Airflow 3. Humidity 4. Light (Electromagnetic energy) But I am not sure what equation to use. (mass loss rate)/(unit area) = (vapor pressure - ambient partial...
  10. A

    Pulse Drying of Evaporated Milk

    Hi Guys, I'm new to the forum. I'm an engineering student studying process and chemical engineering. I am currently a member of a group that has been tasked with designing a plant to produce infant formula. The goal is to manufacture a ready-to-feed infant formula product, so that the parent...
  11. copper-head

    Can I Successfully Freeze Dry Phosphoric Acid-Soaked Carbon at Home?

    Hello all. I have carbonaceous material soaking in Phosphoric acid. I'd like to anneal it under an inert environment to activate the carbon. One method used in literature involved freeze drying the mixture and annealing it as is, as opposed to filtering or centrifuging the mixture. However, I am...
  12. irhum31

    How much water remains as ice when wet clothing is dried in dry wind at 0°C?

    Homework Statement Wet clothing at 0°C is hung out to dry when the air temperature is 0°C and there is a dry wind blowing. After some time, it is found that some of the water has evaporated and the remainder has frozen. Estimate the fraction of the water originally present in the clothing which...
  13. P

    Strength of container for vacuum freeze drying

    I have read that freeze drying is the best way to salvage wet books (http://www.ccaha.org/uploads/media_items/technical-bulletin-salvaging-books.original.pdf). However, freeze dryers run in the thousands of dollars, and I don't know anyone who has one I can borrow. Solution: make my own! I...
  14. Jeprox

    Drying or removal of water from turning blanks

    Hi there, I have read an article where osmosis/reverse osmosis could be used to effectively remove water within a piece of wood. What the author has done is submerging a piece of wood under a thick, liquid dishwashing soap. The said soap pulls the water out of the wood which makes it dry...
  15. gfd43tg

    How Can You Calculate the Drying Time of a Spherical Granule?

    Homework Statement Fig. below shows the cross-section of a porous spherical granule of radius a. The pores are initially saturated with water. The granule dries in air at pressure P and temperature T. The drying rate is controlled by diffusion of water vapor through the dry region B; the...
  16. S

    Building a Tray Dryer (Dehydrator)

    Hi All, I know I may be shooting in the dark here but...I was hoping that someone on this forum can assist me. I am trying to build a tray dryer/ medium scale dehydrator. I'm starting a small fruit drying business but cannot afford to buy an commercial dryer. I've heard that some entrepreneurs...
  17. D

    Solve Drying Room Issue: Calculate Air Flow Speed & Mass Flow Rate

    Hello everyone! Here is the problem: The air removal in a drying room is done via a pipe (length 6 m, diameter 100 mm and surface roughness 0,152mm). The pipe system is composed of a sharp edged entrance and 4 standard 90 degrees turns. The excess pressure in the dryer is 50 Pa. Calculate the...
  18. K

    Infrared Drying for firecrackers. Possible?

    Hello. We've been entrusted the job of building a dryer for firecrackers. We were approached by a huge firecracker manufacturing firm here for the job. The current MO of drying is simply laying the product out in the sun and allow evaporation of moisture. But now they plan to go in for a...
  19. B

    How to set up equation for drying agents, and calculating % recovery

    Homework Statement Benzoic acid/biphenyl mixture is mixed with diethyl ethe(CH3CH2-O-CH2CH3). The solution is placed in a separatory funnel and sodium hydroxide is mixed in. The bottom layer, H2O, NaOH and benzoic acid is then placed in a flask where it is mixed with HCl, chilled and then...
  20. G

    Radiator radiation. Which way to place clothes horse for the fastest drying?

    This is not so muc a homework question as settling an argument: I have a clothes horse on which clothes can be hung parallel to each other roughly 50 cm apart. I place the clothes horse perpendicular to the radiator so the heat from the radiates along the length of the wet clothes. However my...
  21. P

    Energy saved from line drying clothes

    Hey everyone, Im trying to calculate how much money can you save by line drying clothes inside a well isolated apartment instead of using an electrical dryer. I just need a kick start on what i need to take in consideration. the apartment has an ac and heater for summer and winter, and the...
  22. J

    Drying rate depending on curvature?

    hi all =D i have a question about evaporation rate depending on curvature. say a droplet of water is placed on a curved surface- one concave, one convex but with the same radius of curvature. will the evaporation rate be different?
  23. J

    What are some factors that affect the drying time of table utensils?

    hi =) i'm doing an experiment on 2011 iypt problem Air Drying. -> "table utensils, after being washed, dry differently. Investigate how the drying time depends on relevant parameters." I've just begun on the experiment and have difficulty figuring out where to start! I'm thinking about...
  24. G

    Drying Timber Logs: Surprising Ease & Benefits

    I am a bit surprised (pleasantly surprised) at how easy it is to dry out logs of timber in the fairly damp ,outdoor and uncovered conditions I leave them out in. And I am wondering if there is something to the drying that I am not aware of. Now I am talking of logs that have the bark on and...
  25. R

    Forces acting on pipe submerged in drying cement

    I need to analyse what's going on when a hexagon pipe is submerged in drying cement. The pipe is hollow with a thickness and is hexagon shape, where the hexagon is pointing up. It is submerged in standard cement, where the top point of the hexagon is about 100mm from the suface. I...
  26. S

    Big project question - salami drying room

    Okay I'm pretty new to all this and this is my first post on this board. I graduated last year from university with a cellular biology degree, and have now taken over my family's italian food business (est. 1968 by my grandfather). We produce both fresh and dry-cured meat products. What I...
  27. J

    Solar Dryer Drying Time Estimation

    Homework Statement The problem is fairly simple (hah): estimate the time it will take for a solar dryer (which I have to design) to dry 50 pounds of fruit from 80% water to 10% water. Homework Equations It seems there are at least a few equations that give an approximation for...
  28. N

    Supercritical Drying with Water

    Do people do supercritical drying with water? The critical temperature and pressure of water - about 375 C and 3500 PSI - don't really seem that high. Some silica aerogels apparently handle temperatures that are much higher than that, and typical oxygen bottles are at 2500 PSI so it seems...
  29. F

    Quicklime: Properties & Uses for Drying Gases

    Quicklime is used to dry gases.It is also basic in nature. It cannot be used to dry acidic gases such as sulphur dioxide and carbon dioxide. Why is this so? Is it because alkali (quicklime) will react with the acidic gases to form salt and water? Please help. Thanks. :smile:
  30. M

    Help with an absorption drying tower

    Can I just say that anyone willing to offer help I will pay them £20+ an hours for their time, I could only really see this happening over msn real time chat though, but I will publish findings on this site. I am studying chemical engineering and am having trouble with a problem, I am only...
  31. A

    Chem - freeze drying & equilibrium

    So I have to use Le Chateliers principle to expalin why low pressure is used in the freeze-drying process (eg in making instant coffee) So here is what I know so far: in freeze drying, they turn solid water right into a gas basically removing all moisture from the food so it keeps for a very...
  32. M

    How can I effectively dry out Iron Chloride?

    I have/had a solution of Iron (III) Chloride. I wanted to extract the Iron Chloride out of solution, so I decided to evaporate all the water off and just collect the crystals that form, right? Wrong, appearently, it is very hygroscopic making it some what difficult to actually dry it. I have...
  33. Ivan Seeking

    U.N. Says Globe Drying Up at Fast Pace

    Also, as a rant: All science aside, this movie is just another example of special effects used in place of substance; be it sci-fi or otherwise. I had the plot figured within the first ten minutes or so. Then, I fail to see why another rendition of plastic miniatures, Styrofoam chunks...