Dessicant definition by Babylon’s free dictionary Wikipedia Dictionaries English Wikipedia - The Free Encyclopedia A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its vicinity. Commonly encountered pre-packaged desiccants are solids that adsorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams. See more at Wikipedia.org... What does desiccant mean? a medicine or application for drying up a sore Origin: [L. desiccans, p. pr. of desiccare. See Desiccate.] Freebase(0.00 / 0 votes)Rate this definition: Desiccant A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container. A humectant is also a hygroscopic substance, but it is used to help a product retain water. Both are frequently used in food and cosmetic products.

Glycerine is often used as a humectant. Commonly encountered pre-packaged desiccants are solids which work through absorption or adsorption of water, or a combination of the two. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. Pre-packaged desiccants are most commonly used to remove excessive humidity that would normally degrade or even destroy certain products which are sensitive to moisture. Some commonly used desiccants are: silica gel, activated charcoal, calcium sulfate, calcium chloride, montmorillonite clay, and molecular sieves. The numerical value of desiccant in Chaldean Numerology is: 2 Pythagorean Numerology Drying agents Monday, March 21, 2016 Drying Agents Drying agents (also called desiccants) come in various forms and have found widespread use in the foods, pharmaceuticals, packing, electronics and many manufacturing industries. A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its vicinity. Ideally, it is chemically stable and chemically inert (i.e., silica).

Unfortunately, this is not always the case in the chemistry lab because the drying agent comes into direct contact with the solvent and the chemical. Many organic solvents are immiscible with aqueous solutions, but they are able to dissolve significant amounts of water because of their polarity i.e., diethyl ether dissolves 7 % of its weight in water while tetrahydrofuran is completely miscible with water (Why?). Unfortunately, water is a compound that is very difficult to remove from many compounds, because they are either holding on to it well (i.e., alcohols) or the compound itself is steam volatile. Bottom-line is that the more polar the solvent is, the more hygroscopic it will usually be because it dissolves the water better. Thus, removing water and other impurities from a solution can become an arduous task but is necessary if the reagents are also sensitive towards water i.e., Grignard reagents or in cases where water has a detrimental effect on the yield or rate of the reaction.

In those cases, drying agents like calcium hydride (CaH2), sodium metal (in combination with benzophenone) or lithium aluminum hydride (LiAlH4) are used to chemically destroy the water in the solvent. Those compounds are relatively reactive and difficult to handle and usually not used in lower division undergraduate laboratories (see below). Use of Conventional Drying Agents Commonly used drying agents in organic laboratories are calcium chloride (CaCl2), sodium sulfate (Na2SO4) calcium sulfate (CaSO4, also known as Drierite) and magnesium sulfate (MgSO4), all in their anhydrous form. How do they work? All four of them readily form hydrates at low temperatures according to Their efficiency is measured by intensity, capacity and velocity can greatly vary from one solvent to the other. Capacity refers to the maximum numbers of moles of water that the drying agent can bind (n). Another parameter of importance is the efficiency, which refers to the amount of water left in the organic solution after the drying process is completed (e). 1.

Calcium chloride (n=6, e=1.5 mg/L) is a very good drying agent for a broad variety of solvents but is generally not compatible with hydroxy (alcohol, phenol), amino (amine, amide) and carbonyl (acid, ketone, ester) functions due to basic impurities such as Ca(OH)2 and CaCl(OH). In addition, it tends to form adducts with some of those compounds as well. It is often used in drying tubes because it also is available in granular form. 2. Calcium sulfate (n=0.5, e=0.004 mg/L) is a neutral and good drying agent. However, it does not have a high capacity, which makes it useless for very wet solutions. The commercially available Drierite® contains about 2 % cobalt chloride as indicator, which can be leached out into various solvents i.e. ethanol, DMSO, DMF, ethers, etc. Drierite is often used in desiccators . If the compound is pink, the water can be removed by heating the compound to 210 oC for an hour.

Dry (blue) Wet (wet) 3. Magnesium sulfate (n=7, e=2.8 mg/L) is a slightly acidic drying agent. It works well in solvents like diethyl ether, but not as well for ethyl acetate. It is a fast drying agent, in part because it comes as a fine powder with a large surface area. 4. Sodium sulfate (n=10, e=25 mg/L) has a very high capacity and is mainly used for very wet solutions. It is very efficient in ethereal solutions, but it also absorbs other polar compounds like alcohols, etc. In addition, it is slower compared to magnesium sulfate, etc. 5. Potassium hydroxide (KOH, n= high, e=0.1 mg/L) and potassium carbonate (K2CO3, n=2, e=moderate) are both of basic nature and often used to dry basic solutions containing amines. They cannot be used to dry acidic compounds since they react with them. 6.

Sulfuric acid (H2SO4, e=0.003 mg/L) and phosphorous pentoxide (P4O10) are both acidic drying agents that are mainly used in desiccators and not in direct contact with the solution since they are very aggressive reagents. Both have a very high capacity. Sulfuric acid forms hydrates while phosphorous pentoxide is ultimately converted into phosphoric acid. P4O10 + 6 H2O ----- > 4 H3PO4 7. Molecular sieves are alumino silicates with a three-dimensional network with different pore sizes (3-5 Å). They have to be activated prior use and also can be regenerated at higher temperatures (~180 oC - 260 oC, 1-2 hours).

Class of Compounds The Gibbs free energy for the following reaction Na2SO4 + 10 H2O ---- > Na2SO4 * 10 H2O can be described by ΔG = ΔH - TDS = -77.8 kJ/mol - T (-261 J/mol*K) Based on this equation, it can be estimated that the reaction reverses at 298 K or 25 oC (ΔG =0). The drying process itself is slightly exothermic (ΔH for the process is negative) but the entropy decreases during the drying process. The solution often times warms up a little bit when the drying agent is added. Practical Aspects for the Use of Conventional Drying Agents One of the main problems is that many drying agents do not only absorb water, but also other polar compounds. Hence, an excess of drying agent should be avoided in order to prevent the absorption of the target compound, particularly if the compound was polar as well. Even though water usually has a higher affinity towards the drying agent, excess can also lead to significant loss of product. Note that the presence of other polar compounds i.e.

alcohols, etc increase the solubility of water in the organic solvent. How do I know that I added enough drying agent? Before a drying agent is added, the organic layer has to be separated as thoroughly as possible from the aqueous layer. It does make very little sense to add the drying agent if there is a second layer on the bottom (or the top depending which organic solvent is used). The experimenter has to make sure that the "organic layer" is really the organic layer. The drying process does take some time to complete. Most students are not patient enough and add too much drying agent right from the start and often lose a significant amount of their product this way. The best protocol is to add a small amount first. The mixture is swirled and then allowed to settle. If the solution is translucent and there is still drying agent flowing around in the mixture, the solution is reasonably dry. If this is not the case, the mixture is allowed to sit a couple of minutes and then re-examined. If the mixture is still not translucent, a little bit more drying agent is added and the procedure above repeated. Wet solution Dry solution Why does my solution start to "boil"?

Depending on how much water remained in the solution, the solvent can boil if too much drying agent was added at once. This is particularly a problem for low boiling solvents like diethyl ether and dichloromethane, where one can often observe the formation of bubbles in the solution due to this problem. All of these drying agents should preferably be used after the organic solution is treated with a saturated sodium chloride solution, which already removed the a lot of the water from the organic layer. It is also imperative that the organic layer and the aqueous layer are separated well! How do I know that the solution is dry? Small water droplets cause the mixture to be kind of milky in the beginning. Most of the time, the solution becomes translucent if it is dry. In addition, the drying agent does not clump up anymore and floats in the solution as well when the mixture is swirled. What do I do if the solution is dry? Since the drying process is reversible at higher temperatures, the solution and the drying agent have to be separated. This can be done using a Pasteur pipette if small solvent quantities are used (<5 mL). For larger quantities, a careful decanting works best and it is also relatively fast.

In some cases, a simple gravity filtration is best to remove the drying agent. Afterwards the solvent can be removed or the liquid be distilled. Important Pointers 1 One of the main problems in the drying process is that the above equilibrium is shifted to the left if the mixture is heated (increase in entropy!). Therefore, the drying agent has to be removed (by filtration or decanting) from the dry solution prior to removing the solvent. 2. The drying agent is only working if it is still anhydrous. This implies that YOU close the container that is used to store it right after you removed what you need for yourself. 3. Students usually tend to add way too much drying agent. The proper way of using a drying agent is as follows: a. Separate the organic layer cleanly from the aqueous layer. You should not observe any visible water droplets or a second layer in your beaker/Erlenmeyer flask that holds the solution to be dried. If there are droplets present, you will need to transfer the solution again. b. Add a small quantity of drying agent (~2-4 microspatulas for micro-scale setup) and swirl the mixture. The mixture should become translucent and the drying agent is still free flowing.

c. If not, wait for ~2-3 minutes and check again. If the solution is not translucent and/or all your drying agent is clumped up, add an additional (small) quantity of drying agent. d. When the solution is dry, decant (=pour) the liquid part into another dry container and leaving the solid behind in the first flask. Alternately use a gravity filtration using a Pasteur pipette with a cotton ball (not vacuum filtration!) to remove the drying agent. e. Remove the solvent by evaporation in a water bath or on a hot plate (depending what the procedure asks for). 4. Try to avoid a large excess of drying agent since it will inevitably lead to the loss of product. There is a competition of water or your compound absorbing on the drying agent. Generally, water has a higher affinity towards the drying agent, but a large excess of drying agent also causes the target compound to absorb. Thus, it might be good protocol to extract the drying agent with some clean solvent. This solvent should be combined with the first part. 5. The proper way of describe the step in your report is "the solution was dried over [drying agent X]". What is wrong with this picture?

Dessicant : Wikis (The Full Wiki) The Full Wiki Related topics Dessicant: Wikis Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles . (Redirected to Desiccant article) From Wikipedia, the free encyclopedia A desiccant is a hygroscopic substance that induces or sustains a state of dryness ( desiccation ) in its local vicinity in a moderately well-sealed container. Commonly encountered pre-packaged desiccants are solids, and work through absorption or adsorption of water , or a combination of the two. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. Pre-packaged desiccant is most commonly used to remove excessive humidity that would normally degrade or even destroy products sensitive to moisture. Drierite , Silica gel , calcium sulfate , calcium chloride , montmorillonite clay , and molecular sieves are commonly used as desiccants.

Rice is a common " low-tech " alternative frequently used, for example, in salt-shakers to maintain granularity of table-salt for effective pouring or shaking. Rice, however, is not a good general purpose desiccant since, unless immersed in an organism-hostile environment like pure salt, over time may be eaten by creatures that might in turn contaminate the product that is being preserved. Salt itself is another effective desiccant, used for millennia in preparation of dried food and also to mummify corpses. A specific usage of a desiccant would be in double glazing where it is placed inside the spacer between the air space and window edge. This prevents moisture condensation between the panes. Contents 10 External links Toxicity A desiccant may be chosen for a particular task based not only on its effectiveness at drying, but also perhaps for any natural antibiotic , fungicidal , pesticidal or virucidal effect, or for a lack of harmful effect on humans. For instance, table salt has a natural antibiotic and anti-fungal effect and is not harmful to humans when consumed in moderate quantities, and is thus commonly used as a drying agent in the preparation of dried foods.

Chemical reactivity Because of their common use in preservation, it is usually desirable for a desiccant to be substantially chemically stable or chemically inert , and a number of useful desiccants with this property have been identified and are in common use, such as silica gel, chalk and clay-based desiccants. Performance efficiency One measure of desiccant efficiency is the ratio (or percentage ) of water storable in the desiccant, relative to the mass of desiccant (ie weight ). Another measure is the residual relative humidity of the air or other fluid being dried. The performance of any desiccant varies with temperature and both relative humidity and absolute humidity . To some extent, desiccant performance can be precisely described, but most commonly, the final choice of which desiccant best suits a given situation, how much of it to use, and in what form, is made based on testing and practical experience. Coloured saturation indicators Often some sort of humidity indicator is included in the desiccant to show, by color changes, the degree of water-saturation of the desiccant. One commonly used indicator is cobalt chloride (CoCl2). Anhydrous cobalt chloride is blue.

When it bonds with two water molecules, (CoCl2•2H2O), it turns purple. Further hydration results in the pink hexaaquacobalt(II) chloride complex [Co(H2O)6]Cl2. Desiccant regeneration Most useful desiccants can be recycled by thermally -induced drying, for example, in a conventional kitchen oven , or with solar energy . A cost-effective, low-energy, continuous-cycle desiccant dehumidifier or desiccant regeneration system can be easily designed from off-the-shelf component parts. Drying of solvents Toluene is refluxed with sodium and benzophenone to produce dry, oxygen-free toluene. The toluene is dry and oxygen free when the intense blue coloration from the benzophenone ketyl radical is observed. See also: air-free technique Desiccants are also used to dry solvents , typically used for moisture free reactions (e.g. the Grignard reaction ). While various desiccants are used in a variety of ways, the method generally involves stirring the desired solvent with the drying agent.

Often, the drying agent will react with moisture to form an insoluble solid in the solvent being dehydrated, thus the precipitate can be removed by filtration. For more demanding applications, requiring very pure, anhydrous solvents a distillation still is used to remove moisture and other impurities simultaneously. See also Des-Case Breather | DesCase Disposable Breathers DesCase Disposable Breathers DC-BB DesCase Disposable Breather DC-BB Air Breather is available in Sharon, PA. From the core standpipe to the tough polycarbonate exterior, every element of Des-Case’s disposable standard breather has been designed to stand up to the wide variety of industries and applications taking advantage of Des-Case’s contamination control expertise. Des-Case breathers attack the cause of contamination, allowing your equipment and lubricants to run longer and harder. DC-BB DC-BB How the Product Works As wet, dirty air is drawn through the unit, multiple 3-micron polyester filter elements remove solid particulate and the color-indicating silica gel extracts moisture. When air is expelled from the container, the top foam pad prevents oil mist from contacting silica gel or entering the atmosphere.

The breather is outfitted with a resilient nylon standpipe and a clear polycarbonate body which allows for easy monitoring of the high-contrast silica gel. DC-BB Features 3-micron absolute particulate filter elements Color indicator for easy system monitoring Prevents water contamination in oil and related fluids. Prevents rust and corrosion inside the container. Prevents chemical reactions or spoilage. Increased oil and oil filter life. Reduced abrasive wear, downtime, and repair costs. Improved lubricant performance. Unit Height 3.9″ (9.9 cm) Diameter 2.5″ (6.4 cm) Amount of Silica Gel: 2 oz. (57 g) Adsorption Capacity: 0.8 fl.oz. ( 23 ml ) Max. Flow Rate (cfm): 3 @ 1 PSID Filtration: 3µ (absolute) Operating Temp.

Range: -20°F to 200°F (-29°C to 93°C) Hydrophilic Agent: Silica Gel Connection Size : 3/8″ NPT DesCase Desiccant Breathers Designed to replace the standard breather cap on gearboxes, hydraulic reservoirs, storage and process tanks, our Breather incorporates a patented design that filters water and particulate contamination for optimum system performance. The breathers are available in a variety of sizes and materials to meet the needs of virtually any industry application. Common features of all units include the use of a hygroscopic agent to prohibit water ingression and a patented filter media to capture and backflush particulate. An industry exclusive airflow pattern ensures maximum saturation and a partial regeneration of all desiccant crystals, which extends the life of the breather. A visual indicator allows the user to easily recognize when the breather must be changed or rebuilt. A wide variety of adapters are available for quick and easy replacement of factory installed breather caps. Disposable Hygroscopic Breathers Removes moisture from incoming air, extending fluid and system life. Captures particles as small as 0.5 micron (73.5% eff.) or 3 micron absolute.

Disperses air evenly over filter media and silica gel. Allows for easy activation of the unit without tools and controlled breathing. Allows for adaptation to virtually any system. Disposable hygroscopic Breathers remove moisture and particulate before it enters the fluid containing reservoir keeps it clean. The hygroscopic breather elements are state-of-the-art in design and function, and are the industries best choice for assuring maximum machine performance. Disposable breathers are for general use filters from 1 to 40 cfm. Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing substance becoming physically changed somewhat. This could be by an increase in volume, boiling point, viscosity or other physical characteristic and properties of the substance, as water molecules can become suspended between the substance’s molecules in the process. A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its vicinity. Commonly encountered pre-packaged desiccants are solids that adsorb water.

Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams. The DC-BB is a hygroscopic desiccant air breather employing both of these technologies to remove moisture from your lubricants. Breathers, also known as emission control filters, filter fresh air that’s drawn into the engine’s crankcase. Because the engine must breathe to purge itself of fuel and water vapors, breathers are used in conjunction with the PCV valve. Other Products in this area Desiccant Dehumidifiers - What are Zeolites? Molecular sieve (zeolites) Calcium oxide Some desiccant materials can be regenerated (i.e. purged of contaminants and then re-used), whereas some cannot. This depends on the change in the physical structure of the desiccant and the deleterious effects of regeneration on the material. Our desiccant dehumidifiers use Zeolite – and for a very good reason, too. Zeolites are highly efficient at removing moisture from the air.

They are also capable of regeneration, meaning your Ionmax dehumidifiers need little to no maintenance at all! So, what are zeolites? Zeolites are a form of naturally occurring volcanic rock composed of hydrated aluminosilicates of the alkali earth metals. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or other zeolites. This is why naturally occurring zeolites are excluded from important commercial applications where uniformity and purity are essential. For commercial use, synthetic zeolites are used. Produced into a uniform, phase-pure state, synthetic zeolites and hold some key advantages over their natural form, namely being in a uniform, phase-pure state. Zeolites have a high affinity for water and are capable of adsorbing and desorbing it without damaging its crystal structure. This property makes them very efficient at removing excess moisture from the air [1] . Are Zeolites safe? As explained by ExplainThatStuff.com , zeolites are very stable solids that resist the kinds of environmental conditions that challenge many other materials. Here are some of zeolites’ properties [2] : Can withstand high temperatures.

Zeolites don’t burn and they have high melting points (over 1000°C) Resistant to high pressures Don’t dissolve in water or other inorganic solvents Don’t oxidise in air Do not cause health problems through skin contact or inhalation Unreactive and, being based on naturally occurring minerals, they’re not believed to have any harmful environmental impacts How do zeolites work in the dehumidifier? How do zeolites regenerate? The zeolites are used in the desiccant wheel of our dehumidifiers. When a zeolite is placed in an air stream, it will adsorb moisture up to its maximum capacity (or saturation point) and will not adsorb any more moisture. When the zeolite has reached its saturation point, the dehumidifier runs a stream of hot air through it and vents the moisture away from it. This moisture collects in the dehumidifier’s water tank. This is necessary to prevent the captured moisture from being reintroduced into the conditioned space. After this, the zeolite can begin to adsorb moisture and the cycle is repeated. This is the process of the zeolite regenerating itself.

Why do the desiccant dehumidifiers produce heat? This is the only way zeolites are used to control humidity levels in conditioned spaces. Desiccant dehumidifiers need to have a heating element to heat the zeolite in order to regenerate it. Heating the zeolite discharges the absorbed water into the water tank. The zeolite regenerates itself during the heating process and is then able to adsorb more water. But the amount of heat produced by the dehumidifiers is not significant – usually only 3 ~ 5°C higher than room temperature at most. How does a desiccant dehumidifier compare to a compressor type dehumidifier? Desiccant dehumidifiers are preferred due to their ability to perform at low temperatures, even close to freezing point. For example, our 7-litre Ionmax ION612 desiccant dehumidifier would be able to extract 7 litres per day even at 5°C, provided there is enough moisture in the air. Desiccant dehumidifiers are also able to dry to humidity levels below 40%RH if required, something that compressor dehumidifiers can hardly achieve.

Additionally, desiccant dehumidifiers can be quite energy efficient, as most of the energy consumed is returned to the room as warm air. This can reduce the amount of energy used by other sources to the heat the room. With a high efficiency in removing moisture from the air, the ability to regenerate itself, and little to no maintenance required, desiccant dehumidifiers are becoming one of the top dehumidifier choices in Australia, especially in cooler climates. Check out our posts on Dehumidifier Buying Guide and Desiccant Dehumidifiers vs Compressor Dehumidifiers for more information on their differences. P.S. Our Ionmax ION612 and ION632 desiccant dehumidifiers were reviewed by CHOICE and both have been recommended again! CHOICE is formally known as the Australian Consumer’s Association (ACA) and is an independent publisher of consumer information. They conduct rigorous and scientific product reviews across a range of goods and services. With over 160,000 members, CHOICE is the number one advocate of consumer rights in Australia.

Check out the full Choice Dehumidifier Review here and view the Ionmax ION612 and Ionmax ION632 desiccant dehumidifiers on our website . Notes: Information from this article was researched from the following sites. Please visit the sites below if you’d like to learn more 🙂 [1] Zeolites, Atomic Scale Design Network (ADSN), [2] Zeolites, Explainthatstuff.com, This article also incorporates public domain material from the United States Geological Survey document: “Zeolites” (PDF): Chalk as DIY Dehumidifier | Achoo! Blog Chalk as DIY Dehumidifier Shifrah We love portable dehumidifiers for small, damp spaces like under sinks, in poorly ventilated bathrooms, and in closets. But did you know there's a very inexpensive and easy yet effective way to absorb low levels of moisture in your closet and other similar spaces? Using chalk as a makeshift ‘dehumidifier’ of sorts can actually make the difference between moisture-damaged clothes and a nice, dry closet.

Martha Stewart, famous guru of home care, recommends such a chalk dehumidifier, and suggests tying a bundle of chalk with an attractive ribbon and hanging it in the closet from a hook. Interestingly, the Riverwalker's Stealth Survivor blog offers a similar dehumidifying tip, although this time in reference to ammo storage. The Riverwalker describes how to pound chalk into a powder and then place it in an old stocking. Tie the stocking in a knot and place it in a plastic container. Punch holes in the container and place with your ammo. When the chalk clumps or gets moist, place the chalk-filled stocking outside in sunlight to let it dry out and it's ready to re-use.

Indeed, chalk is a known dessicant , which is defined by Wikipedia as ‘a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately well-sealed container.’ The Wikipedia article further describes that ‘because of their common use in preservation, it is usually desirable for a desiccant to be substantially chemically stable or chemically inert, and a number of useful desiccants with this property have been identified and are in common use, such as silica gel, chalk and clay-based desiccants.’ To read more about dehumidification, see the articles below: What are Desiccants What are Desiccants? 11/8/2013 7:51:53 AM | by Anonymous Desiccants are hygroscopic substances that draw in moisture from their surrounding environment or induce a state of dryness in its vicinity. There are a number of uses for desiccants. They range from preparing the chemicals in a chemical plant in order to protect the moisture sensitive items during the shipment. Some common desiccants would include sodium perchlorate, activated carbon, silica gel and calcium sulfate.

Salt and rice are also both common desiccants used around the house. They have been used for their desiccating properties by many cultures historically. Salt for instance was a key component used in the mummification in Egypt. They use it to draw the water out of the bodies to reduce the speed of the rate of decay or even to completely stop the decay from happening. For industrial uses, desiccants are widely used to control the level of water in the gas streams. Dryness is often a largely sought after desired property. Many objects are allowed to dry through evaporation however the water loss slows as the evaporation reduces the moisture content of the object that of the surrounding environment. Once an object is as moist as the surrounding environment, it no longer has the means to lose any more water. Thus, this is where desiccants come in useful. It encloses the object in a container with a desiccant that will allow it to lose more water as the desiccant sucks the fluid out. Due to their common use in preservation, desiccants are chemically stable or inert. A number of them have been identified and are in common use. The two types of desiccants are those that are for performance efficiency and for coloured saturation indicators.

One measure of desiccant efficiency is the ratio of water that is storable in the desiccant relative to the mass of the desiccant. Another measure is the residual humidity of the air or fluid that is being died. Another type of desiccant is that it has a humidity indicator included in it to show by the colour changes, the degree of water saturation of the dessicant. One commonly used indicator is the cobalt chloride. The anhydrous cobalt chloride is blue when it bonds with paper, it changes to purple. One of the common uses for desiccants is in the shipment of goods. This is where things may get damaged when they come into contact with water or become moist. Desiccants are also included in the packaging to help draw the excess water out. They can be discarded once the objects have arrived at their destination for use. These products are also typically used in dehumidifiers. They bring down the moisture in the air by drawing in the water. Desiccant cooling systems also take advantages of this useful train to lower the humidity in order to make the warm temperatures feel less extreme than it really is. On top of being drying, desiccants also have many other properties.

Some are antimicrobial, antiviral, antifungal which makes them extremely useful for the variety of applications. Many of which are not safe for consumption and have labels placed to warn people not to get confused. Some are treated with materials that will possible stain as the desiccants attract water. This allows people to see when the maximum amount of water has been absorbed. In some cases, a desiccant sachet or bag can be refreshed for use again by heating it to forcefully release the water in it. This allows them to reuse the desiccant bags to prevent wastage. Some others are of single uses only. They are needed to be discarded once they have fulfilled their function accordingly. It is always important to select the desiccant which is appropriate to the task. This is because most people want to avoid chemical reactions, corrosion and other problems that may occur due to the wrong substance being used as the desiccants. Examples would be like salt. It cause metal corrosion which then makes it unsuitable for the settings wherever metal is present. Thus, it is important to be aware of what substances are not suitable to another. Tags: Desiccant Terminology, Desiccant Definitions, Desiccant Information - Drytech Inc.

Desiccants Important Terminology Relative humidity is the ratio of the partial pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a prescribed temperature. The relative humidity of air depends not only on temperature but also on the pressure of the system of interest. This is the ratio expressed as a percentage of the amount of water vapor in the air to the amount, which would saturate it at the same temperature and pressure. RH = Water Vapor Pressure / Saturation Water Vapor Pressure x 100% Air will always contain moisture in the form of water vapor unless specially prepared (temperature reduced to -273°C). At any particular temperature the air can hold a limited amount of moisture but the higher the temperature the greater its capacity. When this capacity is reached it is said to be saturated. If unsaturated air is cooled the temperature will eventually be reached at which it becomes saturated and if the temperature is lowered further still, the air will no longer be able to hold all of the moisture and some will be deposited. This is said to be the Dewpoint of the gas. Relative humidity of the atmosphere is the dominating factor in determining whether corrosion or mold growth occurs.

This applies equally to both inside and outside an equipment, the former being most significant. Humidity The presence of water vapor in the atmosphere or gas Absolute Humidity This is the unit weight of water vapor present per unit volume of gas. Water Vapor Pressure This is the fundamental measure of humidity. Water vapor in a gas can be treated as a gas itself and behaves in accordance with the standard gas laws. The total pressure of the gas (Pt) is composed of the partial pressure of the gas (Pg) plus the partial pressure of the water vapor (Pw) Pt = Pg + Pw Vapor Pressure This is sometimes referred to as partial pressure. This is the part of the total pressure, which is contributed by the water vapor. PPmV (Parts per million by volume) PPmW (Parts per million by weight) This is the number of parts of water to one million parts of dry gas. Parts per million terminology is generally only used up to about 10,000. This is not a direct unit reading. It is calculated from either dewpoint or relative humidity (R.H.) Take note of the severely NON-LINEAR relationship between dewpoint and PPM scales.

Usable Scales: It is worth looking at this comparative table to see how when one scale is near the end of its usefulness the others are still usable. (Ex.) Dewpoint (°F) : -14°F R.H. (@70°F) : 5% PPM (V) : 1020 However, it must be remembered should the ambient temperature at which the measurement is being made, then the R.H. value will change but the other two will remain the same because they are measuring absolute humidity. Temperature the effect temperature has upon gases ability to carry moisture is best illustrated on a standard psychometric chart. It can be seen that with an increase in temperature a gases ability to carry moisture increases. Pressure The effect pressure has upon a gas, its dewpoint, is best shown on a dewpoint/pressure conversion chart. See charts . You will notice that with a change of pressure the dewpoint changes, whereas the PPM remains unchanged. Leakrates Leakrates are potentially the easiest way for water vapor to enter an equipment which is essentially sealed. The rate of diffusion will depend upon: the nature of the leak and its configuration, and the pressure differentials present.

Ideally, to maintain an effective long term sealed system a leakrate of the order of 1 x10-3cc per second or lower should be achieved. As a rough guide this equates to an equipment being pressurized and completely immersed under water, no bubbles should be evident. Key points – Temperature stability is vital for accurate results. Not only could th results be inaccurate but also in extremes it could be possible for water to ingress into the container. You also have to differentiate between a slight leak and bubbles trapped in any possible holding places on the equipment Moisture Vapor Transmission Rate (MVTR) moisture will enter an equipment via gaskets, seals, connectors, and even through the material the equipment is made of. As a good rule of thumbs, all non-metals have a degree of hygroscopicity and therefore have an MVTR. MVTR is relative to the partial pressure, which exists across the container or reservoir. If an equipment has a leakrate of 1 x 10-3cc per second or lower then MVTR is probably going to be the main way water vapor will enter. This is one of the main considerations when calculating the desiccant life expectancy. Dew Point A measure of atmospheric moisture.

It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant). A higher dew point indicates more moisture present in the air. It is sometimes referred to as Dew Point Temperature, and sometimes written as one word (Dewpoint). PPMv – Parts per million is a close up measure of indicating the amount of moisture within a system. One part per million (ppm) denotes one part per 1,000,000 parts, one part in 106, 1/1,000,000 * 100% = 0.0001% (or 1% = 10,000 ppm), and a value of 1 × 10−6. This is equivalent to one drop of water diluted into 50 liters (roughly the fuel tank capacity of a compact car) or about 32 seconds out of a year. Desiccants A desiccant is a hygroscopic substance that induces or sustains a state of dryness ( desiccation ) in its local vicinity in a moderately well-sealed container.

One measure of desiccant efficiency is the ratio (or percentage ) of water storable in the desiccant, relative to the mass of desiccant. This is typically represented by an adsorption percent by weight. Another measure is the residual relative humidity of the air or other fluid being dried. The performance of any desiccant varies with temperature and both relative humidity and absolute humidity . To some extent, desiccant performance can be precisely described, but most commonly, the final choice of which desiccant best suits a given situation, how much of it to use, and in what form, is made based on testing and practical experience.

Question: A dessicant is a hygroscopic substance used to produce (What?) in its vicinity?
Answer: Dryness