Humidity Control(2)

HUMIDIFIERS

A humidifier is a device that increases humidity (moisture) in a single room or an entire building.  A humidifier works by adding water vapor to the indoor air. Humidifiers accomplish this by one of the following four methods or variations/combinations of producing vapor from the water.

NOTE: Humidifiers can also be attached to the ductwork.

TYPES OF HUMIDIFIERS

Some types of humidifiers are:

1.Central Humidifiers;

2.Portable Humidifiers.

CENTRAL HUMIDIFIERS:

These types o humidifiers are attached to the ductwork and add moisture to the airspace before it leaves the supply grill to the space to be conditioned.

They can be installed ;

1.Via bypass ductwork

2.Directly into the return or supply ductwork

Some types of central humidifiers are;

BYPASS HUMIDIFIER: Just as the name suggests, it is used to bypass air flowing from the supply air plenum. Not all the conditioned air follows this bypass route. The air that is bypass is humidified.

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EVAPORATIVE HUMIDIFIERS: This type of humidifier add moisture to the air through evaporation. It contains an element that is kept damp.

Some of the moisture in the element  evaporates as air is forced through the humidifiers thereby increasing the humidity of the air.

The types of evaporative humidifiers are;

Plate humidifiers

Fixed filter humidifiers

Rotating drum humidifiers(Used for restricted spaces)

Rotating disk humidifiers

PORTABLE HUMIDIFIERS

Portable humidifiers are standalone units that are placed in the spaces where the humidity level is to be maintained. They are used for room control humidity and not building humidity control.

Many portable humidifiers add moisture by circulating air across a wet filter, though some units ultrasonic humidification.

Portable Humidifiers

Portable humidifiers are easy to maintain. The water tank and the wet filter can be removed and cleaning or replaced depending on the conditioned.

It uses a float-operated switch that turns on an indicator light when the water level in the water pan gets too low. Most of the units must be refilled manually.

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Humidity Control (1)

Humidity is concerned with the physical properties of mixtures of air and water vapor. humidity, which is the amount of water vapor in the air, can make hot temperatures even more unbearable than they already are.

Humidity is an important factor to understand because it affects both weather and climate as well as global climate change. Humidity also affects indoor environments, so understanding it can help you determine the best place to store your books, clothing and other important items in your house.

WHY CONTROL HUMIDITY? 

  • Comfort: This is why air conditioners were introduced in the first place.
  • Storage and Preservation.
  • To prevent corrosion.
  • Mildew and Mould prevention.
  • To prevent condensation

Humidistat:

A humidistat is a control device that responds to changes in humidity and activates and deactivates parts of the humidity control systems.

These humidity control systems include:

1.Humidifiers

2.Dehumidifiers

3.Air mixers

NOTE: Humidistats are available with analog dial adjustments or incremental digital adjustments for controlling relative humidity

Trading Bloc

A trade bloc is a type of intergovernmental agreement, often part of a regional intergovernmental organization, where barriers to trade (tariffs and others) are reduced or eliminated among the participating states. It is a group of countries within a geographical region that protect themselves from imports from non-members. A group of countries who have joined together to promote trade. This might be through relaxing protectionist barriers or even having a common currency.

Examples of trading blocs include :

EU-European Union), NAFTA -North American Free Trade Agreement), ASEAN-Association of Southeast Asian Nations, EEA – The European Economic Area, CEFTA -The Central European Free Trade Agreement.

Types of trade Bloc

Preferential Trade Area: Preferential Trade Areas (PTAs) exist when countries within a geographical region agree to reduce or eliminate tariff barriers on selected goods imported from other members of the area. This is often the first small step towards the creation of a trading bloc.

Free Trade Area: Free Trade Areas (FTAs) are created when two or more countries in a region agree to reduce or eliminate barriers to trade on all goods coming from other members.

Customs Union: Countries that belong to customs unions agree to reduce or abolish trade barriers between themselves and agree to establish common tariffs and quotas with respect to outsiders.

Common Market: This is a customs union in which the members also agree to reduce restrictions on the movement of factors of production – such as people and finance – as well as reducing barriers on the sale of goods

Advantages of Trade Bloc
• Firms can enjoy economies of scale, in a trading bloc, firms can produce goods and services with a lower average cost because trading blocs allows firm to have large scale of production
• Trading blocs brings firms closer to each other and create greater competition, consumers will be benefited with better quality of goods and services in a lower price, they will have more choices
• Firms within the bloc can enjoy a tariff free environment
• Countries within the trading bloc can have more international bargaining power

Disadvantages of Trade Bloc
• unfair against countries out of the Trading Blocs –
• Groups not within the Blocs have to pay Tariffs in order to transfer goods
• Countries within the Blocs have to pay higher price to buy goods input from countries out of the Blocs
• May take over local producers
• Workers are often exploited by global companies and paid low wages for long hours

 

Introduction to Macroeconomics 1

WHAT IS MACROECONOMICS ALL ABOUT?

Macroeconomics is a branch of economics that focuses on the behavior and decision-making of an economy as a whole. It describes and explains economic processes that concern aggregates. An aggregate is a multitude of economic subjects that share some common features. By contrast, microeconomics treats economic processes that concern individuals.
For example, the decision of a firm to purchase a new office chair from company
X is not a macroeconomic problem. The reaction of Austrian households
to an increased rate of capital taxation is a macroeconomic problem.

From the foregoing, macroeconomists study aggregated indicators such as GDP, unemployment rates, and price indices to understand how the whole economy functions.  They develop models that explain the relationship between such factors as national income, output, consumption, unemployment, inflation, savings, investment, government spending and international trade.

Though macroeconomics encompasses a variety of concepts and variables, but there are three central topics for macroeconomic research on the national level: output, unemployment, and inflation.   Macroeconomics investigates aggregate behavior by imposing simplifying assumptions (“assume there are many identical firms that produce
the same good”) but without abstracting from the essential features.
These assumptions are used in order to build macroeconomic models. Typically,
such models have three aspects: the ‘story’, the mathematical model,
and a graphical representation.

ISSUES ADDRESSED BY MACROECONOMICS

The issues addressed by macroeconomics are as follows;

  • What determines a nation’s long-run economic growth?
  • What causes a nation’s economic activity to fluctuate?
  • What causes unemployment?
  • What causes prices to rise?
  • How does being a part of a global economic system affect nations’ economies?
  • Can government policies be used to improve economic performance?

 

Thermal Comfort 1

What is Thermal Comfort?

Thermal comfort describes the human satisfactory perception of the thermal environment. It refers to a number of conditions in which the majority of people feel comfortable. Thermal comfort is rated amongst the most important conditions for improving comfort and satisfaction of occupants with their indoor environment, based on a review of various studies

It is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation. Thermal comfort is the occupants’ satisfaction with the surrounding thermal conditions and is essential to consider when designing a structure that will be occupied by people.

Buildings.

Factors Affecting Human Comfort

There are six factors to take into consideration when designing for thermal comfort. Its determining factors include the following:

  • Metabolic rate (met): The energy generated from the human body
  • Clothing insulation (clo): The amount of thermal insulation the person is wearing
  • Air temperature: Temperature of the air surrounding the occupant
  • Radiant temperature: The weighted average of all the temperatures from surfaces surrounding an occupant
  • Air velocity: Rate of air movement given distance over time
  • Relative humidity: Percentage of water vapor in the air

The environmental factors include temperature, radiant temperature, relative humidity, and air velocity. The personal factors are activity level (metabolic rate) and clothing.

Thermal comfort is calculated as a heat transfer energy balance. Heat transfer through radiation, convection, and conduction are balanced against the occupant’s metabolic rate. The heat transfer occurs between the environment and the human body, which has an area of 19 ft(1.81 m2) .  If the heat leaving the occupant is greater than the heat entering the occupant, the thermal perception is “cold.” If the heat entering the occupant is greater than the heat leaving the occupant, the thermal perception is “warm” or “hot.”

A method of describing thermal comfort was developed by Ole Fanger and is referred to as Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD).

Ref: Autodesk 2017 and ecophon group

INTRODUCTION TO THERMODYNAMICS 2

CLOSED, OPEN AND ISOLATED SYSTEMS

A thermodynamic system, or simply system, is defined as a quantity of matter or a region in space chosen for study.  The region outside the system is called the surroundings.  The real or imaginary surface that separates the system from its surroundings is called the boundary.  The boundary of a system may be fixed or movable.

Surroundings are physical space outside the system boundary.

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Systems may be considered to be closed or open, depending on whether a fixed mass or a fixed volume in space is chosen for study.

A closed system consists of a fixed amount of mass and no mass may cross the system boundary.  The closed system boundary may move.

Examples of closed systems are sealed tanks and piston cylinder devices (note the volume does not have to be fixed).  However, energy in the form of heat and work may cross the boundaries of a closed system.

Picture3

An open system, or control volume, has mass as well as energy crossing the boundary, called a control surface.  Examples of open systems are pumps, compressors, turbines, valves, and heat exchanger.

Picture4

An isolated system is a general system of fixed mass where no heat or work may cross the boundaries.  An isolated system is a closed system with no energy crossing the boundaries and is normally a collection of a main system and its surroundings that are exchanging mass and energy among themselves and no other system.

 

Introduction to Thermodynamics 1

What is thermodynamics:

Thermodynamics is a science and, more importantly, an engineering tool used to describe processes that involve changes in temperature, transformation of energy, and the relationships between heat and work.

Thermodynamics is concerned with the ways energy is stored within a body and how energy transformations, which involve heat and work, may take place.  One of the most fundamental laws of nature is the conservation of energy principle.  It simply states that during an energy interaction, energy can change from one form to another but the total amount of energy remains constant.  That is, energy cannot be created or destroyed.

PROPERTIES OF A SYSTEM

Any characteristic of a system in equilibrium is called a property.  The property is independent of the path used to arrive at the system condition. Some thermodynamic properties are pressure P, temperature T, volume V, and mass m.

Properties may be intensive or extensive.

Extensive properties are those that vary directly with size or extent of the system. Some Extensive Properties

  1. mass
  2. volume
  3. total energy
  4. mass dependent property.

Intensive properties are those that are independent of size or the amount of material in the system

Some Intensive Properties

  1. temperature
  2. pressure
  3. age
  4. color
  5. any mass independent property

Picture1

Extensive properties per unit mass are intensive properties. For example, the specific volume v, defined as

Picture2

and density ρ, defined as;

Picture3

are intensive properties.

AIR CONDITIONING: AIR PURITY(1)

Maintaining the proper air quality level is essential for keeping compressed air energy costs down and to ensure reliable production. Poor air quality can have a negative effect on production equipment and can increase energy consumption and maintenance needs. The quality of air produced should be guided by the quality required by the end-use equipment

AIR CLEANING DEVICES.

  1. Dust collectors
  • Electrostatic precipitator
  • Fabric collectors
  • Wet collectors
  • Dry centrifugal collectors

2. Air filters

SELECTION OF AIR FILTRATION EQUIPMENT

The selection of air filtration equipment is based on;

  • Efficiency
  • Dust holding capacity
  • Pressure drop

METHODS OF AIR FILTRATION

Straining:  straining occurs when a particle is larger than the opening between fibers and cannot pass through. It is a very ineffective method of filtration because the vast majority of particles are far smaller than the spaces between fibers.

Impingement:  when air flows through a filter, it changes direction as it passes around each fiber. Larger dust particles, however, cannot follow the abrupt changes in direction because of their inertia. As a result, they do not follow the air stream and collide with a fiber. Filters using this method are often coated with an adhesive to help fibers retain the dust particles that impinge on them.

Interception:  interception is a special case of impingement where a particle is small enough to move with the air stream but, because its size is very small in relation to the fiber, makes contact with a fiber while following the tortuous air flow path of the fiber.

Diffusion:  diffusion takes place on particles so small that their direction and velocity are influenced by molecular collisions. These particles do not follow the air stream, but behave more like gases than particulate. Diffusion is the primary mechanism used by most extremely efficient filters.

Electrostatic:  A charged dust particle will be attracted to a surface of opposite electrical polarity. Most dust particles are not electrically neutral, therefore,  electrostatic attraction between dust particle and filter fiber aids the collection of efficiency of all barrier type air filters.

PLANE STRESS AND STRAIN (1)

A REVIEW ON FORCE:

A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force is the newton*, N. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are so small.

The three main types of mechanical force that can act on a body are:

(i) tensile

(ii) compressive and;

(iii) shear

Tensile is a force that tends to stretch a material.A tensile force, i.e. one producing tension, increases the length of the material on which it acts.

Compression is a force that tends to squeeze or crush a material.A compressive force, i.e. one producing compression, will decrease the length of the material on which it acts.

Shear is a force that tends to slide one face of the material over an adjacent face. A shear force can cause a material to bend,slide or twist.

 

Image result for tensile shear force

 

 

Radioactivity(1)

The Nucleus.

Strong nuclear force holds neutrons and protons together to form a nucleus

Review of Atomic Terms •

Nucleons – particles found in the nucleus of an atom – neutrons and protons

  • Atomic Number (Z) – number of protons in the nucleus
  • Mass Number (A) – sum of the number of protons and neutrons
  • Isotopes – atoms with identical atomic numbers but different mass numbers
  • Nuclide – each unique atom.

KEYNOTE: Each Isotope has its own characteristic half-life. The rate of decay for an isotope is constant. It is unaffected by pressure, Temperature, Magnetic and Electric field, Chemical Reaction…

Radius Of the Nucleus.

Image result for radius of a nucleus

  Where A is the Atomic Mass, Fm is femtometer, it stands for 10 raised to the power of -15

The diameter of a Nucleus is D = 2r

Radioactivity.

Radioactivity was discovered in 1896 by the French physicist, Henri Becquerel working in Paris. In 1896, Henri Becquerel discovered, almost by accident, that uranium can blacken a photographic plate, even in the dark.

Radioactivity is the process by which nuclei emit particles and rays These penetrating particles and rays are called radiation.

Radioactivity is a phenomenon that occurs naturally in a number of substances. Atoms of the substance spontaneously emit invisible but energetic radiations, which can penetrate materials that are opaque to visible light. The effects of these radiations can be harmful to live cells but, when used in the right way, they have a wide range of beneficial applications, particularly in medicine.

Unstable isotopes can become stable by releasing different types of particles.

  • This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

Therefore, Radioactive decay is a process by which the nuclei of a nuclide emit α, β or γ rays. A few naturally occurring isotopes and all of the man-made isotopes are unstable.

Uranium emits very energetic radiation – it is radioactive.