Friday, 25 January 2019

Electrification of a Body (or) Electrification processes of bodies

          A body can be charged or electrified in many ways; the methods are discussed below:
a. Charging by friction
b. Charging by conduction or contact
c. Charging by induction
d. Electrification byh heating
e. Electrification by pressure

a. Charging by friction: When two nutral bodies are rubbed against each other, due to friction one of them losses electrons and hence gets positively charged and the body that ains electrons gets negetively charged.
Experiment: Take a small piece of uncharged plastic rod and cloth, rub against each other this will result both of them get charged. Same thing will happen between rubber rod and fur, Glass rod and silk cloth.

b. Charging by conduction: When a charged body is brought in direct contact with an uncharged body (or nutral body), it shares its charge with it. Thus the uncharged body becomes charged.

c. Charging by Induction: The process of temporary electrification of an initially neutral conductiong body (induced) by bringing a charged body (inducer) close to it without making any actual contact between the bodies is known as charging by induction.

d. Electrification by heating: Certain bodies, when heated, is electrified by presenting contrary electricities names in two diametrically opposite points. The phenomenon is called pyroelectric phenomenon. It is more common in crystalls, such as Tourmaline.

e. Electrification by pressure: Certain bodies, when compressed, is electrified, displaying electricities names against the ends. The phenomenon is called piezoelecttric phenomenon. It is also ore common in crystals, such as Tourmaline, Calcite, and Quartz. 

Thursday, 24 January 2019

Static Electricity

          Electricity is the phenomenon of flow of electric charges. The study related to the charges, when they are at rest is called as "Static electricity". Static electricity generates through friction.
          Greeks found that amber when rubbed with fur attracts small objects. The substances which on rubbing acquire the nature to attract lite objects are called as charged or electrified. The charged bodies possess electric charges by virtue of which they interact with each other. This force of interaction is called as "Electric force".

Some examples of static electricty are:

1) When we brush Dry hair with a plastic comb static electricity is produced. If we done it in a dark room we can also notice sparkles.
2) Similarly when we pass a comb through the dry hair, the hair will starts moving or stand.
3) We rub a plastic pen or a comb and placed near small pieces of paper they will get attracted.
4) Lightining is the best example of static electricity. Lighting causes due to the positive and negetive charges in the cloud.
5) We even can bend a stream of water using static electricity.

There are several practical uses of static electricity, they are

1) Spray painting for car parts
          The spray nozzle is connected to a negetive electrode by this we can charge each droplet of paint. The car body parts is given a positive charge. When the paint is sprayed from a paint gun, the sprayed particles of paint will attracted by the car body parts. There are several more advantages by this method painting they are : (a) Paint goes to the charged body part not to the uncharged or nutral flor,  (b) Paint only attracted by body parts so less wastage, (c) there is no need of skilled labour for painting (d) the paint will distibuteded evenly so job will look neater.

2) Pollution control
          Static electricity is used in pollution control. Static charge is given to the dirt particles in the air and opposite charge is given to the collector. By this the dirt particles which are present in the air are attraced by the collector and pollution is controlled. These devices are called as "Electro static precepitators". Factories and thermal power plants use this kind of technique to reduce pollution coming from their smoke chimnies.

3) In photo copier

Basic Electricity

          The flow of electrons from one place to another is called as Electricity. Electrons can flow through any material, However electron flow is easy in some than in others. How simply it flows is termed as "Resistance". The resistance of material is measured in Ohm's

Basically the mater can be devided into

Conductors: The substances in which the electrons can flow easily. They offer low resistance.
Ex: Copper, Aluminium, Gold , Silver, Mercury, Sea water, Concrete, Steel, Iron.
Semi-conductors: A substance, usually a solid chemical compound, which can conduct electricity under certain circumstances.
Ex: Silicon, Germanium, Antimony, Arsenic, Boron, Carbon, Selenium, Sulfur, and Tellurium. 
Insulators: The substances in which electrons flow with great difficulty. They offer high resistance.
Ex: Pure water, Glass, Air, Dry Wool, Dry Wood, Plastic, Rubber, Diamond,  Asphalt, Oil, Ceramics, Quartz.

Monday, 14 January 2019


          In order to move and increase the pressure of a fluid, power is consumed by a pump, fan or compressor. The power requirement of pump depends upon many factors, including pump and motor efficiency, differencial pressure, density of fluid, viscosity and fluid flow rate. In this article we are going to discuss the relationships to determine the pump power requirement.

Hydraulic power of the pump (kW).
Shaft power of the pump (kW).
Required power to the Motor (kW).
Volumetric flow of fluid through the pump (m3/h).
Density of the fluid being pumped (kg/m3).
Gravity (9.81 m/s2).
Head produced by the pump (m).
Differential pressure across the pump (kPa)
Pump efficiency (%).
Motor efficiency (%).

          Hydraulic power, also known as absorbent power, indicates the power imparted on the fluid which is to be pumped to increase the fluid's pressure and velocity. Hydraulic power can be calcuated using one of the formulae below:

P - kW
Q - m3/h
ρ - kg/m3
g - m/s2
h - m
Ph = Qρgh/3.6 x 10^6
P - kW
Q - m3/hr
dP - kPa
Ph = QdP/3,600​​
P - kW
Q - L/min
dP - kPa
Ph= QdP/60,000​​
P - kW
Q - L/s
dP - kPa
Ph = QdP/1,000​​

          The power supplied by the motor to the pump shaft is called "Shaft power". It is defined as the sum of the hydraulic power and power loss due to inefficiencies in the transmission of power from the shaft to the fluid. The shaft power of pump is generally calculated as the ratio of hydraulic power of the pump to the pump efficiency. 

                        Ps = Ph/ηp
P= Shaft power
Ph = Hydraulic power of pump (dicussed above)
η= Pump efficiency

          The power consumed by the pump motor inorder to turn the pump shaft is called as "motor power". The motor power is the sum of shaft power and power losses while converting electrical energy into kinetic energy. Mthematically motor power is calculated as "shaft power devided by motor efficiency".

Pm = Ps/ηm
P= Motor power
Ps  = Shaft power
η= Motor efficiency

          In addition to the motor we can use some other drive features which will increase the power requirement of pump to transfer a perticular fluid. 
These are :
1) Belt drives 
2) Gear drives
3) VSD's (Variable speed drives)

Tuesday, 1 January 2019

Suction couch roll

Couch roll (also known ascooch) is used in paper machine to remove water by application of vacuum. It acts as the last wrap where the wet web leaves the forming wire (wire part) and enter into the wet-press section (press part). On the surface of the couch roll we found rows of small holes to suck the water. Inside the roll baffles (long and end strips) are present. These baffles direct the vacuum towards the portion of the roll where the wet web of paper is on the fabric. Below of the long baffle strips air tubes are present for strip movement. Below the end baffle strips springs are present to seal the roll for vacuum suction creation. In the vacuum box one shower will present, it cools the rubber material on the roll. In vacuum boxes if we increase the vacuum we need more power to drive the forming fabric. But in couch roll if we applied too high vacuum it produces visible suction-hole “shadows” due to the movement of fines within the sheet.

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