SOLAR PHOTOVOLTAIC SYSTEM

                 Solar photovoltaic system                

A photovoltaic power generation is a device which convert the electromagnetic energy directly into electrically. The basic compon-ent in the photovoltaic power generation is the photovoltaic cell. 

The photo-voltaic effect can be described easily for a p-n junction in a semi-conductor material. In a piece of a pure intrinsic semi-conductor such as silicon there are no free electron at absolute zero,since each valance electron of material atom is tied in chemical bond.If this piece of the silicon is doped with phosphorus or arsenic, there will be the ex-cess of electrons leading to a n-type semicon-ductor. Similarly if another piece of the sili-con is doped with boron , there will be a deficiency of electrons leading to a p- type semiconductor. If these two pieces of silicon are connected , a p-n junction is obtained . In tendency will be for the free electron of n-side to flow to the p-side, and the holes of the p-side will tends to flow to the n-region to compensate for their respective deficiencies. Thus a built-in potential barrier is formed.

When light strike on the p-n junction photo-ns with energy above that required to break the covalent bonds will create an electron hole pair. The hole is formed in the valance band,or an electron is added to the conduct-ion band. For a photon in a visible range the diffusion length i.e. average distance which the carrier diffuse before they recombine, has the magnitude of a micron. Those charge carriers that are within a diffusion length of the potential barrier will be trapp-ed by the barriers and caused to flow across it in an attempt to reduce their energy. Therefore a potential energy between the layer is formed and it is used to force the electrons through an external circuit. 

The solar photo-voltaic cells convert incident solar light energy directly to direct current electrical energy. Power delivered depends on intensity of sun light and the load resista-nce. several solar cells can be connected in series on parallel to get desired the voltage, current and power. Solar cells connected in parallel form a module, and the modules are connected in series,parallel ,series-parallel configuration to form a solar PV panel. Solar PV panels are installed outdoors so as to the receive maximum sun light during tha day and thoughtout the year. Solar PV panels are usually fixed type as they à simple ,cheap and maintenance free.

Since solar PV panels deliver DC electrical power only during favourable conditions of  sun light, energy storage batteries as used to supply power during nights and the cloudy weather. For feeding loads t 50 Hz AC supply , DC power supplied by the solar PV panel is converted by means of static inverters to the single phase or three phase. Power conditio-ning unit provided for improving AC wave-form, regulating the voltage, inverting DC to AC and protective control, and monitoring functions. 

Solar energy MCQ-: 01

 Q.1 The diameter of the sun is about ____.

A. 1.2 × 10^4 KM

B. 1.5 × 10^4 KM

C. 2.5 × 10^6 KM

D. 1.39 × 10^6 KM

Ans-: D

Q.2 The mean distance between the sun and the earth is _______.

A. 1.49 × 10 ^8 KM

B. 2.49 × 10 ^6 KM

C. 1.52 × 10 ^5 KM

D. 2.05 × 10 ^4 KM

Ans -: A

Q.3 In the form of electromagnetic radiation from sun, earth receives ______ energy / day.

A. 2.9 × 10 ^13

B. 2.9 × 10 ^11

C. 2.9 × 10 ^15

D. 2.9 × 10^17

Ans-: C

Q.4 A single solar cell has an open circuit voltage of ______.

A. 2.5 to 7.0 V

B. 7.0 to 10.0 V

C. 1.0 to 2.5 V

D. 0.6 to 1.0 V

Ans-: D

Q.5  The solar radiation received per unit area normal to sun rays, in a space outside the earth's atmosphere at earth is called __________.

A. Solar energy 

B. Solar constant

C. Heat energy 

D. Solar collector

Ans-: B

Q.6 Flat-plate collectors are used for _____ temperature applications. 

A. High

B. Constant

C. Low

D. Variable 

Ans-: C

Q.7 Solar power has _____ density.

A. High

B. Low

C. Variable 

D. None of the above 

Ans-: B

Q.8 The solar radiation on a particular location on the earth is affected by _____.

A. Seasonal variation

B. Atmospheric clarity 

C. Daily

D. All of the above 

Ans-: D

Q.9 The solar radiation received outside the earth's atmosphere is called _____.

A. Terrestrial solar radiation 

B. Extra-Terrestrial solar radiation 

C. Outer solar radiation 

D. Non- terrestrial solar radiation 

And-: B

Q.10 The radiation received by the earth is with parallel rays is called ?

A. Beam radiation 

B. Diffuse radiation 

C. Thermal radiation 

D. None of the above 

Ans-: A

SINE BAR

                              SINE BAR 

Sine bar is a accurate instrument for measu-ring angle. Sine bar consist of a rectangular bar made of high quality steel and having steps at the end . A roller is fitted into each step which touch the roller. The Sine bar is specified by the distance between center of two rollers ,i.e. 100 mm , 200 mm , 250 mm and 300 mm . The roller must be of the same diameters. The roller are so fixed that when sine bar is placed on surface plates the sur-face of the bar is exactly parallel to surface plate. 

When component is small size-:

For checking the angle of a component of small size a sine bar is set-up at nominal angle on a surface plates by situable combi-nation of the slip gauge . The component to be checked is pressed over the surface of the sine bar. A dial gauge is carried with surface gauge is move along the upper surface of the component.

When component size is large-:

 The component is placed over a surface plate. The sine bar is placed over the com-ponent. The heights on the rollers are meas-ured by means of vernier height gauge. A dial gauge is used to check the measuring pressure. 

The angle can be found by this formula-:

SINE Ө = H / L

Where, H = Height made by slip gauge.

              L = Distance between roller.

DROP FORGING

 Drop forging-: In drop forging utilizes  a closed impression apply to obtain a desire shape of the component. The shaping is done by the repeated hammering given to the material in the die-cavity. The drop forging sis consist of two-half the lower half of the die is fixed to the anvil of the machine. While the uppr half is fixed to the ramp the heated stock is kept in the die while the ramp 4-5 blows in pick-succession so that a metal spread and completely fill the die-cavity. When the two die half closed the completely cavity form.

The barrier passes used are the following-:

1. Fullering impression 

2. Edging impression 

3. Bending impression 

4. Blocking impression

5. Finishing impression 

1. Fullering impression -: Since drop forging involves only a reduction in cross-section with no up-setting , the very first step is to reduce the stock to the desire size.

2. Edging impression -: This stage is required together the expect amount of material required at each cross-section of the finishing component.

3. Bending impression -: This is required for those parts which have a bend shape. 

4. Blocking impression-: It is very difficult for a material to flow to deep pockets,  Sharp corners etc. Hence before the actual shape obtained the material is allowed to have one or more blocking impressions. Where it requires the shape very near to the final shape.

5. Finishing impression -: This is a final impression there the actual shape required is obtained. 

Cooling tower MCQ -:02

 Q.1 Filling or decking in a cooling tower increases the rate of heat transfer by providing ____.

A. Increase flow of air

B. Increase flow of water

C. A large amount of wetted surface 

D. All of the above 

Ans -: C

Q.2 Which type of fan drive generally cooling towers employ ?

A. Two speed fan drive

B. Multi speed fan drive 

C. Single speed fan drive 

D. Variable speed fan drive 

And-: A

Q.3 The minimum temperature to which water can be cooled in a cooling tower is __.

A. The wet bulb temperature of air

B. The dew point temperature of air 

C. Room temperature 

D. Dry bulb temperature of air

And-: B

Q.4 The performance of an evaporator condenser largely depends on ____.

A. Wet bulb temperature 

B. Dew point temperature 

C. Room temperature 

D. Dry bulb temperature 

Ans-: D

Q.5 In which type of refrigeration system solar energy can be directly used?

A. Vapour absorption 

B. Air refrigeration system 

C. Vapour compression 

D. All of the the above 

Ans -: A

Q.6 What is the means of amount of heat thrown away by the cooling tower in kcal/hr ?

A. Heat load of cooling towers 

B. Drift of cooling towers 

C. Approach of cooling towers 

D. None of the above 

Ans -: A

Q.7 What is mean of cooling range in cooling tower?

A. Amount of heat thrown away by the cooling tower in kcal/hr

B. Difference in temperature of cold water and atmospheric temperature 

C. Difference in temperature of hot water entering and cold water leaving. 

D. None of these

Ans-: C

Q.8 The most commonly used design method for duct size is ?

A. Equal friction method

B. Velocity reduction method

C. Double duct method

D. Static regain method

Ans-: B

Q.9 The process of mixing two or more streams of moist air is called ___.

A. Isothermal 

B. Constant volume 

C. Constant pressure 

D. Adiabatic 

Ans-: D

Q.10 Which type of refrigerating plants not require electricity?

A. Vapour absorption 

B. Vortex tube

C. Air refrigeration 

D. All of the above 

Ans -: A

ROLLING PROCESS

 Rolling process-: The rolling process is a metal forming process in which stock of the material pair of rollers   is passed between one or more pairs of rollers in order to reduce and to maintain the uniform thickness. In other words, it is a process In metal passing through a gap between the rollers rotating in opposite direction. This process is mainly focused on the cross-section of the it not or the metal which is forming.  

 

There are two types of rolling process -:

1. Hot rolling

2. Cold rolling

1. Hot rolling -: Those process working above the recrytalization temperature are termed  as " hot rolling " process.

2. Cold rolling -: Those process working below the recrytalization temperature are termed as cold rolling process. 

Under the action of heat or force when the atom is which a certain higher energy level the new crystal starts forming which is termed as recrytalization. Recrytalization destroy the old grain structure deforming by mechanical working and antaily new crystal which are strain free are formed. In hot working the process may be carried about of the recrytalization temperature with or without actual heating. 

For example-: The recrytalization temperature is below the room temperature and hence working of this metal at room temperature is always hot working. A simple heating is shown in fig. Where the grain start growing after the metal process the recrytalization temperature.  When it is cooled without any hot working the final grain size would be larger then when starts in hot working process.

MACHINE FORGING PROCESS

 Machine forging -: This is also known as up-set forging. Both drop and press forging are also done by machines only up-set forging is reffered as machine forging. Up-set machines are generally horizontal acting. The die-set consist of a die and a corresponding punch. The die consist of two parts one called the stationary greeper die which is fixed to the machine frame and other part is moveable greeper die which moves along with the die slide of the up-setter. The stock help between two greeper die by frition. 

                The two dies when in close position forward the necessary die cavity then the having tool advances against the stock and up-set it to completely fill the die cavity. Having completed the upsetting the heading tools moves back to it's back position. Then the moveable greeper die release the stock by sliding member.

Advantages of machine forging -:

1. High production rate up to 4500 parts per hour.

2. The process can be fully automated.

3. Elimination of the forging draft and flash.

4. High efficiency of material utilization, as the process involves little or no waste