Most foods will not support the growth of bacteria if their water activity is less than 0.85, because at this water activity there is not enough water available for the bacteria to grow.
However, yeasts can grow at water activities as low as 0.70, while some molds will grow even at water activities as low as 0.60!
Foods with water activities in this range usually have preservatives added to prevent the growth of yeasts and molds.
Acidic foods with a pH less than 4.6, such as tomato sauce, retard the growth of microorganisms. Thus an acidic food with a water activity less than 0.85 is relatively shelf stable, especially if it is stored in the refrigerator.
In this case, low pH, water activity and temperature combine to provide good insurance against the growth of harmful pathogens.
Water activity and different instruments to determine AwAbel Jacob Thomas
This presentation includes water activity, its importance, equations, food sorption isotherm, different instruments to determine the water activity of a food product.
Water activity is the moisture content of the food which is available for microbial growth.By controlling water activity the food can be preserved for longer duration
Water activity and different instruments to determine AwAbel Jacob Thomas
This presentation includes water activity, its importance, equations, food sorption isotherm, different instruments to determine the water activity of a food product.
Water activity is the moisture content of the food which is available for microbial growth.By controlling water activity the food can be preserved for longer duration
Applications for Water Activity and Sorption Isotherms in PharmaceuticalsLabFerrer LabFerrer
The pharmaceutical industry has been measuring moisture for decades.
Why? Because most people think water is the enemy of API stability. Turns out they're only partly right.
Design Of Freezing Equipments in Food Industry.Shahnaz Mol. S
Freezing, or solidification, is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. Food freezing equipments can be classified depending on the heat transfer medium
Thermal processing is defined as the combination of temperature and time required to eliminate a desired number of microorganisms from a food product.
The term "thermal" refers to processes involving heat.
Heating food is an effective way of preserving.
The basic purpose for the thermal processing of foods is,
to reduce or destroy microbial activity,
reduce or destroy enzyme activity,
and to produce physical or chemical changes,
to make the food meet a certain quality standard.
The detailed description on theory of dryer, mechanism of drying and stages of drying. Water activity, types of dryers used in food processing industry, concept of osmotic dehydration of foods is discussed.
Refrigeration and freezing of foods (control of microorganisms) Ihsan Wassan
It is necessary to avoid the contamination of microorganisms in food products and the storage life of fresh perishable foods such as meats, fish, vegetables, and fruits can be extended by cooling or by reducing temperature.here are two important method to avoid the growth of microorganisms one is Refrigeration and other one is Freezing.
In this 30 minute webinar, food scientists Mary Galloway and Zachary Cartwright talk about how to get answers to your shelf life questions. Learn how to:
-Troubleshoot issues and complaints to find out why shelf life is ending sooner than expected
-Predict how recipe changes will impact shelf life
-Compare the effect of different ingredient options
-Evaluate whether a specific packaging option will help you achieve or improve shelf life
Applications for Water Activity and Sorption Isotherms in PharmaceuticalsLabFerrer LabFerrer
The pharmaceutical industry has been measuring moisture for decades.
Why? Because most people think water is the enemy of API stability. Turns out they're only partly right.
Design Of Freezing Equipments in Food Industry.Shahnaz Mol. S
Freezing, or solidification, is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point. Food freezing equipments can be classified depending on the heat transfer medium
Thermal processing is defined as the combination of temperature and time required to eliminate a desired number of microorganisms from a food product.
The term "thermal" refers to processes involving heat.
Heating food is an effective way of preserving.
The basic purpose for the thermal processing of foods is,
to reduce or destroy microbial activity,
reduce or destroy enzyme activity,
and to produce physical or chemical changes,
to make the food meet a certain quality standard.
The detailed description on theory of dryer, mechanism of drying and stages of drying. Water activity, types of dryers used in food processing industry, concept of osmotic dehydration of foods is discussed.
Refrigeration and freezing of foods (control of microorganisms) Ihsan Wassan
It is necessary to avoid the contamination of microorganisms in food products and the storage life of fresh perishable foods such as meats, fish, vegetables, and fruits can be extended by cooling or by reducing temperature.here are two important method to avoid the growth of microorganisms one is Refrigeration and other one is Freezing.
In this 30 minute webinar, food scientists Mary Galloway and Zachary Cartwright talk about how to get answers to your shelf life questions. Learn how to:
-Troubleshoot issues and complaints to find out why shelf life is ending sooner than expected
-Predict how recipe changes will impact shelf life
-Compare the effect of different ingredient options
-Evaluate whether a specific packaging option will help you achieve or improve shelf life
Water activity, not moisture content, determines the lower limit of “available” water for microbial growth. Since bacteria, yeast, and molds require a certain amount of “available” water to support growth, designing a product below a critical water activity level provides an effective means to control growth.
Water quality index with missing parameterseSAT Journals
Abstract This paper presents the efficient modifications in calculating formula of water quality index. Water quality index provides us a single number which expresses overall water quality at a certain location and time which is based on several quality parameters. The objective of an index is to turn complex water quality data into information that is understandable and usable by the public. In this paper a formula will be found to calculate water quality index when the numerical value of some of it’s quality parameters are missing. The standard formula to calculate water quality index has nine water quality parameters- biochemical oxygen demand, dissolved oxygen, pH, nitrate, phosphate, faecal coliform, turbidity, total dissolve solids and temperature. Sometimes it becomes very difficult to find out the values of all these parameters because of lack of time or because of failure in testing. In that case the formula with missing parameters will help us to calculate water quality index. Index Terms: Water quality index, q- values, weight factors, weighted mean.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
The basic food law is intended to assure consumers that foods are pure and wholesome, safe to eat, and produced under sanitary conditions. Generally, food law prohibits importation and distribution of food products that are adulterated, or have labels that are false or misleading in any context.
Soil and water conditions. ...
Keep an eye on the forecast for heavy rainfall events. ...
Calibrate, inspect, and maintain manure application equipment. ...
Separation distances for land application. ...
Irrigation of manure sources. ...
Savvy stockpiling and dry manure management.
Based on the mode of action, the major food preservation techniques can be categorized as: (1) slowing down or inhibiting chemical deterioration and microbial growth, (2) directly inactivating bacteria, yeasts, molds, or enzymes, and (3) avoiding recontamination before and after processing.
Food processing waste is derived from the processing of biological materials and is, in the main, biodegradable. Biowaste is defined in the landfill directive as 'waste capable of undergoing anaerobic or aerobic decomposition such as food and garden waste, and paper and cardboard
Water has a wide variety of uses in food production, for cleaning, sanitation, and manufacturing purposes. In addition to being an ingredient in many foods, it may be used for various other operations, such as for growing, unloading, fluming, washing, brining, ice manufacture, and in sanitation and in hygiene programs.
The environmental damage of food production from conventional agriculture is not limited to deforestation and pollutants associated with crop growth. Harvesting the crop represents a significant amount of nutrients, water, and energy being taken from the land.
The basis for sanitation is the removal of soils from the manufacturing environment. There are many benefits to this process. From a food safety standpoint, there is the removal of pathogenic organisms, prevention of the formation of biofilms and removal of potentially harmful chemicals from food contact surfaces.
Food packaging is defined as enclosing food to protect it from tampering or contamination from physical, chemical, and biological sources, with active packaging being the most common packaging system used for preserving food products.
Sugar, salt, nitrites, butylated hydroxy anisol (BHA), butylated hydroxyl toluene (BHT), tert-butylhydroquinone (TBHQ), vinegar, citric acid, and calcium propionate are all chemicals that preserve foods. Salt, sodium nitrite, spices, vinegar, and alcohol have been used to preserve foods for centuries.
Sugaring is a food preservation method similar to pickling. Sugaring is the process of desiccating a food by first dehydrating it, then packing it with pure sugar. This sugar can be crystalline in the form of table or raw sugar, or it can be a high sugar density liquid such as honey, syrup or molasses.
Removing the moisture from food helps prevent bacterial and fungal growth which would ruin stored foods. Smoking is a method of drying that also imparts flavor to the food (usually meat items), and smoke helps keep bacteria-carrying-insects away during the drying process.
Microwave penetrates inside the food materials resulting in entire internal cooking of whole volume of food rapidly and uniformly reducing the processing time and energy. This fast heat transfer in turn results in preservation of nutrients, vitamins contents, flavor, sensory characteristics, and color of food
Food irradiation (the application of ionizing radiation to food) is a technology that improves the safety and extends the shelf life of foods by reducing or eliminating microorganisms and insects. Like pasteurizing milk and canning fruits and vegetables, irradiation can make food safer for the consumer
Food irradiation is the process of exposing food and food packaging to ionizing radiation, such as from gamma rays, x-rays, or electron beams. Wikipedia
Low dose (up to 1 kGy): Inhibit sprouting (potatoes, onions, yams, garlic)
Lowering the temperature of food so that microbes and enzymes are inactivated.
Moisture is changed to ice and microbes become inactive without water.
Packaging food maintains the colour, flavour and texture.
Fast freezing (-25ºC) helps maintain nutritive value and texture of food.
Chilling is an important activity in food processing. Foods are chilled to extend shelf life by reducing biochemical reactions and microbial activity. Temperature control is essential in order to prevent spoilage and food safety concerns during storage.1
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.
Food drying is a method of food preservation in which food is dried (dehydrated or desiccated). Drying inhibits the growth of bacteria, yeasts, and mold through the removal of water.
Dehydration has been used widely for this purpose since ancient times; the earliest known practice is 12,000 B.C. by inhabitants of the modern Middle East and Asia regions. Drying is a simple method for preserving food.
Dried foods make great healthy and tasty snacks. They are good for lunches, travel, backpacking, hiking, and camping plus many other activities. Most types of foods can be dried. Drying is an ancient method of food preservation.
Sorption is a physical and chemical process by which one substance becomes attached to another.
Sorption includes both adsorption & absorption
e.g., liquids being absorbed by a solid or gases being absorbed by a liquid, cotton dipped in ink.
Sorption the process in which one substance takes up or holds another; adsorption or absorption
Sorption is a process in which a solute moves from a fluid to a particulate solid.
The food sorption isotherm describes the thermodynamic relationship between water activity and the equilibrium of the moisture content of a food product at constant temperature and pressure. ...
The typical shape of an isotherm reflects the way in which the water binds the system.
Water plays many very important roles in food. It affects texture (dry and brittle versus moist and soft), enables the activity of enzymes and chemical reactions to occur (acts as a solvent), supports the growth of microorganisms, makes it possible for large molecules like polysaccharides and proteins to move about and interact, and conducts heat within food.
Many foods such as meat, poultry, seafood, fruits and vegetables are composed of 75% and more water, so water is the most abundant component in many fresh foods. Other foods such as dairy products, and fresh baked goods also contain high levels of water (about 35% or more). Foods that are high in moisture are at
risk of contamination from the growth of microorganisms such as bacteria, yeast and mold, while dry foods like pasta generally have long shelf lives.
Dry heat acts by protein denaturation, oxidative damage and toxic effects of elevated levels of electrolytes. The moist heat acts by coagulation and denaturation of proteins.
Moist heat is superior to dry heat in action.
Temperature required to kill microbe by dry heat is more than the moist heat.
Thermal death time is the minimum time required to kill a suspension of organisms at a predetermined temperature in a specified environment
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
In this session I delve into the encryption technology used in Microsoft 365 and Microsoft Purview. Including the concepts of Customer Key and Double Key Encryption.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Welocme to ViralQR, your best QR code generator.ViralQR
Welcome to ViralQR, your best QR code generator available on the market!
At ViralQR, we design static and dynamic QR codes. Our mission is to make business operations easier and customer engagement more powerful through the use of QR technology. Be it a small-scale business or a huge enterprise, our easy-to-use platform provides multiple choices that can be tailored according to your company's branding and marketing strategies.
Our Vision
We are here to make the process of creating QR codes easy and smooth, thus enhancing customer interaction and making business more fluid. We very strongly believe in the ability of QR codes to change the world for businesses in their interaction with customers and are set on making that technology accessible and usable far and wide.
Our Achievements
Ever since its inception, we have successfully served many clients by offering QR codes in their marketing, service delivery, and collection of feedback across various industries. Our platform has been recognized for its ease of use and amazing features, which helped a business to make QR codes.
Our Services
At ViralQR, here is a comprehensive suite of services that caters to your very needs:
Static QR Codes: Create free static QR codes. These QR codes are able to store significant information such as URLs, vCards, plain text, emails and SMS, Wi-Fi credentials, and Bitcoin addresses.
Dynamic QR codes: These also have all the advanced features but are subscription-based. They can directly link to PDF files, images, micro-landing pages, social accounts, review forms, business pages, and applications. In addition, they can be branded with CTAs, frames, patterns, colors, and logos to enhance your branding.
Pricing and Packages
Additionally, there is a 14-day free offer to ViralQR, which is an exceptional opportunity for new users to take a feel of this platform. One can easily subscribe from there and experience the full dynamic of using QR codes. The subscription plans are not only meant for business; they are priced very flexibly so that literally every business could afford to benefit from our service.
Why choose us?
ViralQR will provide services for marketing, advertising, catering, retail, and the like. The QR codes can be posted on fliers, packaging, merchandise, and banners, as well as to substitute for cash and cards in a restaurant or coffee shop. With QR codes integrated into your business, improve customer engagement and streamline operations.
Comprehensive Analytics
Subscribers of ViralQR receive detailed analytics and tracking tools in light of having a view of the core values of QR code performance. Our analytics dashboard shows aggregate views and unique views, as well as detailed information about each impression, including time, device, browser, and estimated location by city and country.
So, thank you for choosing ViralQR; we have an offer of nothing but the best in terms of QR code services to meet business diversity!
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
2. CONTENTS
Introduction
Definitions
Definitions
Concept of Water Activity
Why Water Activity is important?
Methods for measuring water activity
Factors affecting Water Activity
Microbial Growth of aw
Minimum aw for some bacterial growth
Examples of aw values of several foods
Advantages & Disadvantages of aw
3. •Most foods will not support the growth of bacteria if their water activity is less than 0.85, because at this water
activitythereisnot enoughwateravailableforthebacteriato grow.
•However, yeasts can grow at water activities as low as 0.70, while some molds will grow even at water activities
aslowas 0.60!
•Foods with water activities in this range usually have preservatives added to prevent the growth of yeasts and
molds.
•Acidic foods with a pH less than 4.6, such as tomato sauce, retard the growth of microorganisms. Thus an
acidic food with a water activity less than 0.85 is relatively shelf stable, especially if it is stored in the
refrigerator.
•In this case, low pH, water activity and temperature combine to provide good insurance against the growth of
harmfulpathogens.
Introduction
4. Definitions
Food scientists measure the amount of water that is available for the growth of microorganisms, as well as
enzymeandchemicalreactions,througha numberknownas wateractivity(aW).
Water activity is a measure of the amount of free and adsorbed water in food, and is measured on a
dimensionlessscaleof zeroto one.
Water activity is the ratio of the vapor pressure (P) of water in food divided by the vapor pressure of pure
water(P0)at thesametemperature.
Thewateractivityof purewaterisequalto 1.0.
Another way of determining water activity is by measuring the relative humidity (RH) of the atmosphere in
equilibriumwiththefood:RH (%)= 100 x aW.
5. Food Moisture% Water Activity
Fresh meat 70 0.98
Bread 40 0.95
Flour 14 0.70
Pasta 10 0.45
Potato chips 2 0.10
Inotherwords,wateractivityisa measureof thewaterthatis availableto be convertedto vapor.
Thereis a generalcorrelationof themoisturecontentof foodwithitswateractivity, asshowninthe table
below.
6. Conceptof WATERACTIVITY
The concept of aw has been very useful in food preservation
and on that basis many processes could be successfully adapted
and new products designed.
Water has been called the universal solvent as it is a
requirement for growth, metabolism, and support of many
chemical reactions occurring in food products.
Free water in fruit or vegetables is the water available for
chemical reactions, to support microbial growth, and to act as a
transporting medium for compounds.
In the bound state, water is not available to participate in
these reactions as it is bound by water soluble compounds such
as sugar, salt, gums, etc. (osmotic binding), and by the surface
effect of the substrate (matrix binding).
These water-binding effects reduce the vapour pressure of the
food substrate according to Raoult’s Law.
7. Comparing this vapour pressure with that of pure water (at the
same temperature) results in a ratio called water activity (aw).
Pure water has an aw of 1, one molal solution of sugar - 0.98,
and one molal solution of sodium chloride - 0.9669.
A saturated solution of sodium chloride has a water activity of
0.755. This same NaCl solution in a closed container will develop
an equilibrium relative humidity (ERH) in a head space of 75.5%.
A relationship therefore exists between ERH and aw since both
are based on vapour pressure.
The ERH of a food product is defined as the relative humidity of
the air surrounding the food at which the product neither gains nor
loses its natural moisture and is in equilibrium with the
environment.
aw=ERH
100
8.
9.
10.
11.
12.
13. Why is water activity important?
Water activity is a critical factor that determines shelf life.
While temperature, pH and several other factors can influence if
and how fast organisms will grow in a product, water activity may
be the most important factor in controlling spoilage.
Most bacteria, for example, do not grow at water activities
below 0.91, and most molds cease to grow at water activities
below 0.80.
By measuring water activity, it is possible to predict which
microorganisms will and will not be potential sources of spoilage.
14. Water activity--not water content--determines the lower limit
of available water for microbial growth.
In addition to influencing microbial spoilage, water activity can
play a significant role in determining the activity of enzymes and
vitamins in foods and can have a major impact their color, taste,
and aroma.
It can also significantly impact the potency and consistency of
pharmaceuticals.
15. METHODSFORMEASURINGWATERACTIVITY
Methods are based on the colligative properties of solutions.
Water activity can be estimated by measuring the following:
1. Vapour pressure
2. Osmotic pressure
3. Freezing point depression of a liquid
4. Equilibrium relative humidity of a liquid or solid
5. Boiling point elevation
6. Dew point and wet bulb depression
7. Suction potential, or by using the isopiestic method
8. Bithermal equilibrium
9. Electric hygrometers
10. Hair hygrometers
16. Water activity is expressed as the ratio of the partial pressure of
water in a food to the vapour pressure of pure water with the
same temperature as the food.
Thus, measuring the vapour pressure of water in a food system is
the most direct measure of aw.
The food sample measured is allowed to equilibrate, and
measurement is taken by using a manometer or transducer device
(Vapour pressure manometer).
This method can be affected by sample size, equilibration time,
temperature, and volume.
This method is not suitable for biological materials with active
respiration or materials containing large amounts of Volatiles.
1. Vapourpressure
17.
18. 2. Osmotic pressure
Water activity can be related to the osmotic pressure (p) of a solution
with the following equation:
p = RT/Vw ln(aw)
where Vw is the molar volume of water in solution, R the universal gas
constant, and T the absolute temperature.
Osmotic pressure is defined as the mechanical pressure needed to prevent
a net flow of solvent across a semi-permeable membrane. For an ideal
solution, Equation can be redefined as:
p = RT/Vw ln(Xw)
where Xw is the molar fraction of water in the solution. For non-ideal
solutions, the osmotic pressure expression can be rewritten as:
p = RTfnmb(mwVw)
where n is the number of moles of ions formed from one mole of
electrolyte, mw and mb are the molar concentrations of water and the
solute, respectively, and f the osmotic coefficient, defined as:
f = -mw ln(aw)/nmb
19.
20. 3. Freezing point depression of a liquid
This method is accurate for liquids in the high water activity range but is
not suitable for solid foods (Barbosa-Cánovas and Vega-Mercado, 1996).
The water activity can be estimated using the following two expressions:
Freezing point depression:
-log aw = 0.004207 DTf + 2.1 E-6 DT2
f (1)
where DTf is the depression in the freezing temperature of water
Boiling point elevation:
-log aw = 0.01526 DTb - 4.862 E-5 DT2
b (2)
where DTb is the elevation in the boiling temperature of water.
21. 4. Equilibriumrelativehumidityof a liquidor solid
The relative humidity is the water vapor pressure (numerator) divided
by the equilibrium vapor pressure (denomator) times 100%. The
equilibrium vapor pressure occurs when there is an equal
(thus the word equilibrium) flow of water molecules
arriving and leaving the condensed phase (the liquid or ice).
If the water vapor pressure is greater than the equilibrium value
(numerator is greater), there is a net condensation (and a cloud could
form, say).
And that is not because the air cannot hold the water, but merely
because there is a greater flow into the condensed phase than out of it.
Relative humidity describes the amount of water vapor actually in the
air (numerator), relative to the maximum amount of water the air can
possibly hold for a given temperature (denominator).
22. One important consequence is that when air masses change in temperature,
the relative humidity can change, even if the actual amount of water vapor
in the air does not (the numerator in our equation, which is defined by the
saturation curve, stays the same, but the denominator changes with
temperature).
If the relative humidity (RH) is 100%, this means that condensation
would occur. On a typical hot muggy summer day, RH might be around
60-80%. In a desert, RH is commonly around 15-25%.
It is expressed as a percentage:
RH=H2OactualH2OmaxThis equation is not rendering properly due to an
incompatible browser. See Technical Requirements in the Orientation for a
list of compatible browsers.
23. When an air mass contains the maximum amount of water it can hold, it is
saturated with water vapor. This is shown graphically in the plot above as
the black solid curved line in Figure .With increasing temperature (x-axis),
the air can hold more water vapor (y-axis), as indicated by higher
saturation values (solid black curved line).
In general, it is not possible to have water contents that exceed
saturation (i.e. relative humidity is 100%). In other words, the maximum
relative humidity is generally not greater than 100% (i.e. not above the
solid black curved line). Another way to think about relative humidity is
that it describes how close the air is to saturation.
In the example shown, the actual water vapor content is about 40% of
that at saturation (i.e. the blue point is about 40% of the way to
saturation) – meaning the RH = 40%.
24.
25.
26.
27. 5. Boilingpointelevation
oBoiling-point elevation describes the phenomenon that the boiling point of
a liquid will be higher when another compound is added, meaning that a
solution has a higher boiling point than a pure solvent.
oThis happens whenever a non-volatile solute, such as a salt, is added to
a pure solvent, such as water.
oThe boiling point elevation is a colligative property, which means that it
is dependent on the presence of dissolved particles and their number,
but not their identity.
oIt is an effect of the dilution of the solvent in the presence of a
solute.
oIt is a phenomenon that happens for all solutes in all solutions, even in
ideal solutions, and does not depend on any specific solute–solvent
interactions.
oThe boiling point elevation happens both when the solute is
an electrolyte, such as various salts, and a nonelectrolyte.
28. In thermodynamic terms, the origin of the boiling point elevation
is entropic and can be explained in terms of the vapor
pressure or chemical potential of the solvent.
In both cases, the explanation depends on the fact that many solutes are
only present in the liquid phase and do not enter into the gas phase
(except at extremely high temperatures).
Put in vapor pressure terms, a liquid boils at the temperature when its
vapor pressure equals the surrounding pressure.
For the solvent, the presence of the solute decreases its vapor pressure
by dilution.
A nonvolatile solute has a vapor pressure of zero, so the vapor pressure
of the solution is less than the vapor pressure of the solvent.
Thus, a higher temperature is needed for the vapor pressure to reach
the surrounding pressure, and the boiling point is elevated.
29. Put in chemical potential terms, at the boiling point, the liquid phase and
the gas (or vapor) phase have the same chemical potential (or vapor
pressure) meaning that they are energetically equivalent.
The chemical potential is dependent on the temperature, and at other
temperatures either the liquid or the gas phase has a lower chemical
potential and is more energetically favorable than the other phase.
This means that when a nonvolatile solute is added, the chemical
potential of the solvent in the liquid phase is decreased by dilution, but
the chemical potential of the solvent in the gas phase is not affected.
This means in turn that the equilibrium between the liquid and gas phase
is established at another temperature for a solution than a pure liquid,
i.e., the boiling point is elevated.
30. The phenomenon of freezing-point depression is analogous to boiling point
elevation.
However, the magnitude of the freezing point depression is larger than
the boiling point elevation for the same solvent and the same
concentration of a solute.
Because of these two phenomena, the liquid range of a solvent is
increased in the presence of a solute.
The extent of boiling-point elevation can be calculated by
applying Clausius–Clapeyron relation and Raoult's law together with the
assumption of the non-volatility of the solute.
The result is that in dilute ideal solutions, the extent of boiling-point
elevation is directly proportional to the molal concentration (amount of
substance per mass) of the solution according to the equation:
ΔTb = Kb · bB
where the boiling point elevation, is defined as
Tb (solution) - Tb (pure solvent).
31. Kb, the ebullioscopic constant, which is dependent on the properties of the
solvent. It can be calculated as Kb = RTb
2M/ΔHv,
where R is the gas constant, and Tb is the boiling temperature of the pure
solvent [in K], M is the molar mass of the solvent, and ΔHv is the heat of
vaporization per mole of the solvent.
bB is the molality of the solution, calculated by taking dissociation into
account since the boiling point elevation is a colligative property, dependent
on the number of particles in solution.
This is most easily done by using the van 't Hoff factor i as bB = bsolute · i. The
factor i accounts for the number of individual particles (typically ions) formed
by a compound in solution.
32. 6. Dewpointandwetbulbdepression
For warmer temperatures than 60, the cooling is between about 1/3
and 1/2 the dew-point depression.
If the temperature was 42 with a dew-point of 15 and it started
raining, the temperature and dew-point would wet-bulb out to a chilly
33 degrees Fahrenheit.
A quick technique that many forecasters use to determine the wet-bulb
temperature is called the "1/3 rule".
The technique is to first find the dew-point depression (temperature
minus dew-point).
Then take this number and divide by 3. Subtract this number from the
temperature. You now have an approximation for the wet-bulb
temperature.
33. Vapour pressure can be determined from the dew point of an air-water
mixture.
The temperature at which the dew point occurs is determined by
observing condensation on a smooth, cool surface such as a mirror.
This temperature can be related to vapour pressure using a
psychrometric chart.
The formation of dew is detected photoelectrically
Suppose the temperature is 42 degrees Fahrenheit with a dew-point of
15 degrees Fahrenheit.
The dew-point depression is 42-15 = 27. Now divide 27 by 3 = 9. Now
subtract 9 from the original temperature of 42. 42 - 9 = 33.
For temperatures between 30 and 60 degrees F, the 1/3 rule works
quite well.
For warmer temperatures than 60, the cooling is between about 1/3
and 1/2 the dew-point depression.
34. If the temperature was 42 with a dew-point of 15 and it started raining,
the temperature and dew-point would wet-bulb out to a chilly 33 degrees
Fahrenheit.
As dew-point depression or temperature increase, the evaporation
potentialincreases.
This technique does not give the exact wet bulb temperature but it does
give a pretty close approximation.
Warmer air will cool at a greater rate than colder air since more water
vapor can evaporate into warm air.
Evaporation is a cooling process that absorbs latent heat, therefore the
more evaporation the more cooling.
35.
36. 7. Suctionpotential,or by usingtheisopiesticmethod
The isopiestic method consists of equilibrating both a sample and a
reference material in an evacuated desiccator until equilibrium is reached
at 25°C.
The moisture content of the reference material is then determined and
the aw obtained from the sorption isotherm.
Since the sample was in equilibrium with the reference material, the aw
of both is the same.
37. 8. Bithermalequilibrium(ThermocouplePsychrometer)
Water activity measurement is based on wet bulb temperature
depression.
A thermocouple is placed in the chamber where the sample is
equilibrated. Water is then sprayed over the thermocouple before it is
allowed to evaporate, causing a decrease in temperature.
The drop in temperature is related to the rate of water evaporation from
the surface of the thermocouple, which is a function of the relative
humidity in equilibrium with the sample.
38. 9. Electrichygrometers
Most hygrometers are electrical wires coated with hygroscopic salts or
sulfonated polystyrene gel in which conductance or capacitance changes
as the coating absorbs moisture from the sample.
The major disadvantage of this type of hygrometer is the tendency of
the hygroscopic salt to become contaminated with polar compounds,
resulting in erroneous aw determinations.
39. 10. Hairhygrometers
Hair hygrometers are based on the stretching of a fibre when exposed to
high water activity.
They are less sensitive than other instruments at lower levels of activity
(<0.03 aw) and the principal disadvantage of these types of meters is the
time delay in reaching equilibrium and the tendency to hysteresis.
Today we find many brands of water activity meters in the market. Most
of these meters are based on the relationship between ERH and the food
system, but differ in their internal components and configuration of
software used.
One of the water activity meters most used today is the AcquaLab
Series 3 Model TE, developed by Decagon Devices, which is based on the
chilled-mirror dew point method.
40. This instrument is a temperature controlled water activity meter that
allows placement of the sample in a temperature stable environment
without the use of an external water bath.
The temperature can be selected on the screen and is monitored and
controlled with thermoelectric components.
Most of the older generations of water activity instruments are based
on a temperature-controlled environment.
Therefore, a margin of error greater than 5% can be expected due to
temperature variations.
This equipment is highly recommended for measuring water activity in
fruits and vegetables since it measures a wide range of water activity.
The major advantages of the chilled-mirror dew point method are
accuracy, speed, ease of use and precision.
The AquaLab's range is from 0.030 to 1.000aw, with a resolution of
±0.001aw and accuracy of ±0.003aw.
41. Measurement time is typically less than five minutes.
Capacitance sensors have the advantage of being inexpensive, but are
not usually as accurate or as fast as the chilled-mirror dew point
method.
Capacitive instruments measure over the entire water activity range 0 to
1.00 aw, with a resolution of ±0.005aw and accuracy of ±0.015aw.
Some commercial instruments can complete measurements in five minutes
while other electronic capacitive sensors usually require 30 to 90 minutes
to reach equilibrium relative humidity conditions.
The hair hygrometer uses the characteristic of the hair that its length
expands or shrinks response to the relative humidity. ...
The length of human hair from which liquid are removed increases by 2
to 2.5% when relative humidity changes by 0 to 100%.
42. Principleof Hairhygrometer
Due to humidity, several materials undergo a change in physical,
chemical and electrical properties.
This property is used in a transducer designed and calibrated to
directly read the relative humidity.
Certain hygroscopic materials, such as human hair, animal membranes,
wood, paper, etc., undergo changes in the linear dimensions when they
absorb moisture from the surrounding air.
This change in the linear dimension is used as the measurement of the
humidity present in the air.
43. Workingof hairhygrometer:
When air humidity is to be measured, this air is made to surround
the hair arrangement and the hair arrangement absorbs moisture from
the surrounding air and expands or contracts in the linear direction.
This expansion or contraction of the hair arrangement moves the arm
and the link and, therefore, the pointer to a suitable position on the
calibrated scale and, therefore, indicates the humidity present in the
air / atmosphere.
These Hair hydrometers are called membrane hydrometers when the
sensing element is a membrane.
44. Human hair is used as a humidity sensor.
The hair is arranged on a parallel beam and separated from each other to
expose them to the surrounding air / atmosphere.
Number of hairs are placed in parallel to increase the mechanical strength.
This hair arrangement is placed under a small tension by the use of a
tension spring to ensure proper functioning.
The hair arrangement is connected to an arm and a link arrangement and
the link is attached to a pointer rotated at one end. The pointer sweeps
over a calibrated scale of humidity.
45. Applicationof Hairhygrometer
These hydrometers are used in the temperature range of 0’C to 75’C.
These hydrometers are used in the range of relative humidity (relative
humidity) from 30 to 95%.
Limitations of the hydrometer for the hair
These hydrometers are slow in response
If the hair hydrometer is used constantly, its calibration tends to
change.
50. Advantages
The main advantages of this technology are its rather low cost
and a greater insensitivity to volatile substances such as alcohol
and propylene glycol.
Disadvantages
The main disadvantages of this technology are the loss of
efficiency of the sensor over time and fouling issues.
Advantages& Disadvantagesof WaterActivity