New Home

TABLE OF CONTENT

• INTRODUCTION
• CRYO—-
• TYPES OF CRYOGENIC TREATMENTS
• ABSOLUTE ZERO
• PRODUCTION OF LOW TEMP
• METHODS OF LIQUIFICATION OF AIR
• APPLICATIONS
• CRYOGENS
• CONCLUSION
• CRYOGENIC LABORATORY

INTRODUCTION

• Cryogenics – the study and use of materials at extremely low temperatures

• Inputs from three major disciplines, namely PHYSICS , MECHANICAL ENGINEERING, CHEMICAL ENGINEERING

•  Such low temperatures cause changes in the physical   properties of materials that allow them to be used in unusual engineering, industrial, and medical applications
•  For example, in the cryogenic temperature range, air becomes a liquid—or even a solid—and living tissue freezes instantly

• Cryobiology: Branch of biology involving the study of the effects of low temperatures on organisms
• Cryosurgery: Branch of surgery applying very low temperatures (down to -196 °C) to destroy malignant tissue, e.g. cancer cells.
• Cryonics: The emerging medical technology of cryopreserving humans and animals with the intention of future revival.
• Cryoelectronics: Field of research regarding superconductivity at low temperatures.
• Cryotronics: Practical application of cryoelectronics.

TYPES OF CRYOGENIC TREATMENT

•  SHALLOW CRYOGENICS, the objects are cooled down to temperature of approximately -85^oC
• FLOODING, first the object is taken to -85^oC, then the chamber is flooded with liquid nitrogen to reduce the temperature furthur
• DEEP CRYOGENICS TREATMENT, Subjects the objects to the temperature of approximately    -185^oC

ABSOLUTE ZERO

• Absolute zero is a temperature marked by a 0 entropy configuration. It is the coldest temperature theoretically possible and cannot be reached by artificial or natural means

PRODUCTION OF LOW TEMPERATURE

• HEAT CONDUCTION: When bodies are in contact, heat flows from the body with the higher temperature to the body with a lower temperature. Can occur between any and all forms of matter. It is essential in the production of cryogenic temperatures and environments.

• EVAPORATIVE COOLING: Humans lose heat by this mechanism. Atoms and molecules in the gaseous state are moving faster than the atoms and molecules in the liquid state. Adding heat energy to the particles in a liquid makes them gaseous

• THE JOULE-THOMSON EFFECT:  Allowing a gas to expand very rapidly causes its temperature to drop dramatically. Reducing the pressure on a gas accomplishes the same effect.
• Ordinary house hold refrigerators and air conditioners operate on this principle.

METHODS OF LIQUIFICATION OF AIR

• Linde’s System also known as Hampson System
• Claude’s System

LINDE’S SYSTEM

• Clean dry air is taken from the atmosphere and is compressed up to 200 bar
• The high pressure enters into counter flow air to air heat exchanger and is then throttled to atm – pressure
• The J-T cooling up to expansion causes a lowering of temperature and this cool air is passed through heat exchanger where it cools the incoming high section
• Thus the temperature at the valve is progressively lowered until the liquefaction temperature is reached

CLAUDE’S SYSTEM DIAGRAM

• Claude’s System yields more efficient cycle than Linde’s System
• The expansion through an expansion valve is an irreversible process.
• In Claude’s System energy is removed from the gas stream by using an expansion engine or expander.
• The expansion process is isentropic and much lower temp is attained then isenthalpic expansion
• In Claude’s System the gas is first compressed to pressure of the order 4 Mpa.

How Claude’s System is more efficient than Linde’s System

• The advantage of the Claude’s System is, it operates at low compression ratio      compared with Linde’s process.
• Secondly the temperature of air before coming to the expansion valve in Claude system is lower than the Linde system.

Cryogenic Devices

APPLICATION OF CRYOGENICS

•   Aerospace-cryogenic engines
•  Medical Field
•  Manufacturing field
•  Electronics Field
•  Fuels research
•  Miscellaneous uses

CRYOGENIC ENGINES IN AEROSPACE

• First operational Cryogenic Rocket Engine is 1961 NASA designed  RL-10 LOX LH2 rocket engine

• The second-stage Pratt & Whitney RL10B-2 engine is based on the 30-year heritage of the reliable RL10 engine

• At Mahendragiri in Tamil Nadu, is the LPSC. The system involves materials working at 23K and pumps at speeds of 40,000 rpm. Complex metering, monitoring, integrating technologies involved. The engines required to fire for  700 seconds during the final stage of a launch providing 7 tones of thrust

• Engine works on ‘Staged Combustion Cycle’ with an integrated turbo pump running at 42,000rpm. Also equipped with two steering engines developing a thrust of 2 kN each to enable three-axis control of the launch vehicle during the mission

• Closed loop control of both thrust and mixture ratio, which ensures optimum propellant utilization for the mission
• To know how cyrogenics plays vital role in space shuttle.. watch this video :

              https://www.youtube.com/watch?v=LjG-4oR7JxI

CRYOSURGERY

• Cryosurgery- Use of extreme cold produced by liquid nitrogen (or argon gas) to destroy abnormal tissue.
• Used to treat external tumors, such as those on the skin.
• For internal tumors, liquid nitrogen is circulated through a hollow instrument called a Cryoprobe.
• Used since many years in the treatment of skin cancer

CRYOGENICS IN MANUFACTURING FIELD

• Cryogenic treatment works on Reamers, Tool bits, Tool punches, Carbide Drills, Carbide Cutters, Milling Cutters, Files, Knives, Reciprocating Blades, Dies and cutting tools
• Stress relieved ferrous and non ferrous castings and forgings for enhanced dimensional stability and surface finish

CRYOGENICS IN ELECTRONICS FIELD

• Super conducting electronic devices like SQUID (Super conducting quantum interference device) are used in sensitive digital magnetometers and voltmeters
• Zero friction bearings use magnetic field instead of oil or air, derived from the Meissner Effect associated with super conductivity.
• Super conducting electric motors are constructed approaching zero electric loses

Nuclear Magnetic Resonance Spectroscopy (NMR)

Most common method to determine the physical and chemical properties of atoms by detecting the radio frequency absorbed and subsequent relaxation of nuclei in a magnetic field. Strong magnetic fields are generated by supercooling electromagnets. Liquid helium(BP  4K) is used to cool the inner coils. Cheap metallic superconductors can be used for the coil wiring. So-called high-temperature superconducting compounds can be made to superconduct with the use of liquid nitrogen(BP 77K)

Magnetic Resonance Imaging (MRI)  :

Complex application of NMR where geometry of the resonances is deconvoluted and used to image objects by detecting the relaxation of protons that have been perturbed by a radio-frequency pulse in the strong magnetic field. Mostly used in health applications

Electric Power Transmission:

• Superconductors could be used to increase power throughput. Require cryogenic liquids such as nitrogen or helium to cool special alloy-containing cables to increase power transmission. Field is the subject of an agreement within the International Energy Agency.

Frozen Food:

• Transportation of large masses of frozen food. Food is freezed in war zones, earthquake hit regions, etc. Cryogenic food freezing is also helpful for large scale food processing industries

Forward looking infrared (FLIR)
Many infra-red cameras require their detectors to be cryogenically cooled

Blood banking
Certain rare blood groups are stored at low temperatures, such as −165 °C

Special effects
Liquid nitrogen and CO₂ has been built into nightclub effect systems by Kryogenifex to create a chilling effect and white fog that can be illuminated with colored lights.

• Inert Gases: Do not react chemically to any great extent. Do not burn or support combustion. Includes Nitrogen, Helium, Neon, Argon and Krypton

• Flammable Gases: Some cryogenic liquids produce a gas that can burn in air. Includes Hydrogen, Methane and Liquefied Natural Gas

• Oxygen: Many non-combustible materials can burn in the presence of Liquid Oxygen. Organic materials react explosively with Liquid Oxygen. Hazards and handling precautions of liquid oxygen is considered separately from other cryogenic liquids

FACILITIES AT OUR CRYOGENICS LABORATORY

• Oil Diffusion Vacuum Pumping System with Measuring Guages, Trolley Heater & Oil

• Dewar vessels ( Model T-26-A 0110 capacity – 25 Lt. ) ( Model T-55-A 0110 capacity – 50 Lt. )

• VPF 100 Liquid Nitrogen variable temperature Dewar with Controller & Trolley

• Servotronic Digital (6 digit) Temperature Indicator ( PT-100 -200C to 100C six channel 230 VAC )

• Piezo-Electric Transducer with Accessories

• Data Logger with Software for online display ( ModelNo: MICROLOG 6102 + CST 27)

• Helium Compressor

Projects on Cryogenics

• QUASI-ISOTHERMAL EXPANSION ENGINE FOR CRYOGENIC AUTOMOTIVE PROPULSION

• CRYOGENIC ENGINE IN ROCKET PROPULSION

• DEEP SPACE COOLING TO ELIMINATE CRYOGENIC VENTING

• APPLICATION OF CRYOTREATMENT FOR ENHANCEMENT IN TOOL LIFE

Hey 2^nd Yearites . !!  As you are in 4^th sem so first of all you might be thinking  what chemical engineering is…. We are not definitely studying it the way we used to study chemistry in XI or XII standard,instead of that we are with subjects like Electrical Technology, TMMD, Solid mechanics. I’ll tell you why these subjects are important. As chemical engineer you will be able to come up with technical solutions for problems and issues in relation to process and product technology. In finding these solutions, chemical engineers work closely with experts from other specializations, taking into account the related economical, social, environmental and ethical aspects of the problem they’re dealing with. To understand it let us see one practical situation wherein you have task to build up a transportation pipeline from point A to point B  and no qualified person is with you to help except one or two labourers. Your area of concern will be : 1) Angle of elevation of point A and point B from horizontal. 2) Diameter,length of pipe and which type of joints should be there? — So here comes Theory of machines and machine designing. 3) From what material pipe is to be made ? and what are the possibilities of failure of such a  structure? If pipeline is to be made underground then the nature of soil needs to be understood to avoid corrosion problems— So here comes Chemical Engineering Materials. Finally let’s say you have carefully made all arrangements and the pipeline is ready to use. And as you switch on the pump, you may not see the fluid coming out from the pipe!!Then what will you do??? What is the problem??? Problem was that you may not used proper motor which will provide you exact power or you have purchased correct HP motor but it is consuming more power, then you will go and see whether my motor is delta or star connected because every connection has its advantages and disadvantages. So if you have studied electrical engineering basics then you would have easily identified the problem.

• Please don’t take any subject lightly or for the sake of getting marks. Strictly speaking what I think  from my experience is that an engineer should have the know of  basics of all disciplines of engineering. Now you may ask is coding and programming is going to help a chemie?? The answer is yes, because chemical process calculations are not as simple as solving an two variable equation and finding the answers. Practically any chemical  process or  even a small unit operation will have ‘n’ no. of variables so how you can solve them. So we need simulation software to handle these large no of variables. Now if you have basic “funda” clear in your mind that how it was designed and programmed.. You can handle the software much better than your colleague. But again I am not saying that you should be ‘phoodu’ in programming but basics are compulsory.
• So, Chemical or process engineering is an interdisciplinary science comprising elements of mechanical Engineering, chemistry and technical physics.
• The difference between chemical Engineering and process engineering lies in the emphasis of the degree course: while chemical engineers concentrate mainly on chemical processes, process Engineers deal primarily with the plants needed for this, their design and technical solution.
• For General Chemical Technology (GCT) please watch you tube animation videos, NPTEL lectures. Also you can distribute these topics among your friends and then have a discussion for e.g. one can prepare about paper and pulp industry , other one on sugar industry and discuss among themselves.

I hope you are clear what are the application and importance of these subjects in the life of chemical engineer.

• For first yearites : Observe the chemical processes occurring in day to day life and analyze them. See corrosion problems , how thermodynamics is playing in your home kitchen, analyze how propulsion systems works , analyze how energy sources like batteries, fuel cells, solar cells works.
• Study alternate sources of energies such as bio diesel ( Jatropha seeds).Go through some basic outline of industries such as:Sugar industry, paper and pulp industry, soap and detergent industry….etc.
• If possible visit as many industries as possible.
• At the end of first year try to learn Microsoft Excel Software as much you can and C programming language in summer vacations.

• For second yearites.. We dont have core chemical engineering subjects in 2nd year… So in 2nd year have active  participation  in techfests of various colleges; this will give you experience, direction , boost up your confidence and   will definately gives practical knowledge which helps when you will study core subjects such as (HTO, MTO, Thermo, CRE..etc)
• You can participate in events like chemical car competition and chemistry related quizzes in 2nd yearand then in 3rd year you can participate in heat exchanger event …(I am saying this because there is a separate topic on heat echanger in 5th semester,so it is better to participate in this event later on in 3rd year.) … Do as per your interest.
• Read magazines these are available in library, watch NPTEL lectures they are very good.
• There are some free online courses available online these are given by profs of MIT , Harvard, Oxford, Stanford.. So make use of them. Most recommended courses are EDX and Stanford university online course.
• My advice to you all is that don’t do industrial training in 2nd year.Instead  go to your seniors, profs and work under them  and learn as much you can from them. The best places for summer training  in chemical engineering some are: IITs, IISC , ISER, NCL, ICT, CSMCRI etc and in Private colleges we have very good Nanotechnology Lab at DDIT college in Nadiad. and in our college itself we have summer training programme so apply for that .

Some preferred courses: EDX

1. our energetic earth
2. Introduction to water treatment 
3. Solar energy
4. Introduction to solid state chemistry
5. Thermodynamics

6. Introduction to Drinking Water Treatment

STANFORD ONLINE COURSE

1. Solar: Solar Cells, Fuel Cells and Batteries.
2. Reservoir Geomechanics

Video : CEV TALK_3: DATA STRUCTURES- SEGMENT TREE

Data Structures are a way to store data in such a way that we can operate on them efficiently. The way we are organizing our data matters a lot. If we manage our data in the right way, we can reduce the running time of our operations on the data by a lot.

This talk is about such a data structure known as segment tree.

First lets see why we need segment trees. I demonstrate it using a problem statement:

You are given an array of n integers (a[0] to a[n-1]).

You have to answer m queries.
In each query, you are given two integers, l and r ( 0<=l,r<=n-1 ). Your job is to print the largest number in the range a[l], a[l+1], a[l+2],…., a[r-1], a[r].
n is in the order of 10^6
m is in the order of 10^5.

Iterate from l to r and keep track of the maximum number found.
Eg. For query 2 7, look at all the numbers from 2 till 7. Easy to find the max number this way.
In form of a ‘for’ loop:
int max=array[l];
for(i=l;i<=r;i++)

{

if(array[i]>max)

max=array[i];
}
Though very simple to understand, this method is very time consuming.
For each query, it does (r-l+1) operations. For n=1000000, and a query where l=0 and r=999999, 10^6 iterations will take place. As I mentioned earlier, there can be 10^5 queries like this. So, the total operations required to answer all queries will be 10^5 X 10^6= 10^11.

For n=1000000 and m=100000, this method will take 120 seconds to run. And this is a lot!

The better way to solve this problem is using segment tree.

The principle of segment tree is:
If we have two arrays
{3,5,2} and {6,22,1,6,10}.
And the maximum integer of these arrays is m1=5 and m2=22 respectively. Then, the maximum of the array obtained by combining both these array {3,5,2,6,22,1,6,10} is MAX(m1,m2)=MAX(5,22)=22.
i.e. We don’t need to look at the whole combined array again. We can deduce the maximum of the whole array just by looking at the maximum of the individual arrays

Segment tree for the array {30,9,62,2,6,39,22,77,67,51,83,12,19,49,3,99} is as follows:

Using this segment tree, we can reduce the number of nodes that we have to look at to answer a query. For eg.
for the query 4 15, we have to look at the two nodes labelled 4-7 and 8-15. And the answer for the query 4 15 will be the MAX of the value of the two abovementioned nodes i.e. MAX(77,99)=99.
For the query 4 13, we will look at the three nodes labelled 4-7 and 8-11 and 12-13. And similarly find that the answer to the query is MAX(77,83,49)=83.
You may observe that you never have to look at more then 2 X log2(n) nodes for answering any query.
So, for n=1000000, m=100000, the number of operations required to answer all queries is 2 X log2(1000000) X 100000 = 4 X 10^6 operations.
And indeed, this algorithm runs on the same input in only around 0.35 seconds!

Click the following to download the .pdf on segment trees used during the Talk.

CEV TALK SEGMENT TREES

If 20th century was the century of war, then question arises : what’s gonna happen next ? Firstly, why we mark past century only by war, although they brought only miseries to the world? But if we deeply introspect the journey of technological advancement in world, (the technology which makes our life easier today) all came through furious bloody wars of 20th century. It was the time of World War I and World War II when the world saw technological advancement like never before. Each country wanted to utilize their resources up to the zenith. It was the environment of agony and competition which made some bright minds to invent something out of the box every time to stay ahead…
As we have entered in 21st century to some tiny extend, it’s time to think how we are going to shape this century. This past decade has pushed us to the world of internet, open source knowledge, liberation and globalization. Now we can easily judge, by undertaking the ongoing research works, what is going to happen next!!
We are witnessing a trend in which all hardware’s size are on decrease. Computers which were made short ago to occupy a whole room, now finds our pockets big enough. Punching cards were replaced by buttons and now buttons are all set to be replaced by the Sixth Sense technology (yeah that’s what is the best of Pranav Mistry). But wait, that’s just a start of 21st century. Research shows us that we are going to replace all these sort of thing by just developing or realizing the power of human brain.
We are near the times when we will be able to control all our daily stuffs by just thinking in our brain.Electronics and Computing will collaborate with Neural Science to bring technological advancement which we even can’t think about. We will be able to store out memories out our body, we will be able to control remote machine or robots by just a couple of thoughts. These times will witness competition between countries about the extent of human brain study and research.
Today, we are not having any substantial and structured theory of human brain. But through extensive research going over it’s study by using Brain-Computer Interface (BCI) and taking case study of many medical cases, we can hope of such theory coming soon. Looking to the potential of field many parts of world has started research in this area. In University of Pittsburgh, scientist had succeeded in a experiment over a monkey, in which monkey controls a robotic arm by brain signals assisted by BCI. There are various cases in which scientist are able to bring back the lost sense or body parts by using BCI through which the patients were able to control a electronic sense or organ just as a normal human do it by his brain. In commercial world, a game company has already launched a product in which a player can control a game just by thoughts (www.emotiv.com). Further, IBM predicts it will be making “mind-controlled” PC’s within next five years. So now we can definitely hope for drastic future development. And projects like Human Brain Project of European Countries (www.humanbrainproject.eu ) will boost the research work to unlock various mysteries of human brain.
Below are some links to show you some glimpse of that. So be ready to witness the century where it is all about to study the huge potential of THE HUMAN BRAIN.

Wikipedia: Brain-computer Interface

Solar energy has enormous potential and it is highest among all the available sources of energy available whether it is renewable or non renewable sources. It is free, it is renewable and it is clean source of energy.

Now to begin, let’s start with one practical situation:

Assume that you have told to set up a solar power plant in India and you have given sufficient fund and land.  So what you will do??!!

Following are the points which you should think:

1) first you have to find a place in India where maximum solar power is hitting (Solar Ir-radiance ).

2)      Lets say you have decided to put solar power plant in Gujarat. Now in Gujarat you have to see at what location exactly what amount of solar energy is hitting per square area.

Now we will  understand how it is calculated:

Any body which is above 0K  temperature will emit radiation according to planks law which is

given by:

Above expression is for a body which is at particular  temperature and emitting radiation of a particular wavelength  but as we know body is  emitting radiations of all wavelengths from 0 to infinity. So we have to integrate that expression E(ƛ)d(ƛ) from o to infinity to find total emissive power emitted by the body.

Similarly consider sun as the source of solar radiations and earth is intercepting those radiations .the amount of solar radiation hitting on some area of earth will depend upon solid angle multiplied total emissive  power of sun.

So by doing integration of solar irradiance expression (emissive power) multiplied by solid angle of whole earth considering no atmosphere we will get a fix value known as solar flux and that is equal to 1367 W/m2.

Solar flux: The total energy flux (energy per time per area) incident on a unit area perpendicular to a beam outside the Earth’s atmosphere.

Air mass factor(AM): Air mass factor gives you idea about the relative position of sun w.r.t. to earth.

AM = 1/ CosƟ , where Ɵ equal to angle from vertcle line when sun is directly overhead to us.

For e.g.  AM 1.5 = 1/CosƟ  => Ɵ=48.2*

AM0 means no atmosphere.

Now you have to calculate the solar flux which is hitting on your area in Gujarat. What you will do you will first of all find latitude of that area.

After finding latitude we have to multiply that solar power density which is coming parallel to plane of equator with cosine of latitude because we want those photons which are hitting perpendicular to our solar cell.

3) So we have decided the location of power plant by calculating the exact solar flux hitting that area.

4) Now what next?? Before installing the solar panels we have to understand how solar cell works:

Working

• The main part of solar cell is p-n junction. When p type and n type material are joined there is formation of space charge region/depletion region and It stays localized at the P-N junction and an electric field has been created.
• If the solar cell is put in the sun, photons will strike the surface of the Silicon and pass their energy on to electrons. A typical photon can eject one electron from its nucleus creating a free electron and a vacancy. These free electrons will feel the effect of the electric field. They are pushed towards the junction on the N-side and away from the junction on the P-side. Likewise, the vacancy, which has a net positive charge, will be pulled towards the junction on P-side and pushed away from it on the N-side.
• So there is current flowing from p type to n type material. This current is known as photo induced current and denoted by I_L

• This photo induced current generates voltage around load, but this voltage generation will also forward biased our p-n junction and there is another current  flows  through load known as forward biased current I_F . so we will have net current I=I_L  – I_F   flows through our load.
• Current vs voltage characteristics of our p-n junction is shown below:

• We can see from the graph that there is point where we are getting maximum power. so our aim is to find that point. This can be easily calculated by simple differentiation technique.
• If still not clear , watch this video: https://www.youtube.com/watch?v=1gta2ICarDw

Efficiency

• Efficiency is most important thing to any type energy system. We have reached maximum efficiency of  44% in case of solar cell.(search and find what are the efficiency of other sources of energy)
• How to find efficiency of our solar cell???…

To find efficiency we have to first follow above procedure and calculate J_max and V_max

Above numerator term is J_max* V_max

Denominator is solar power denoted by P_s   at some AM value.

For e.g. P_s value at AM= 1.5 means

1367W/m² *cos(41.8) =1000 W/m²

  5) After learning basics of solar cell, let’s build solar cell. Before we discuss the components of real solar cell,( just think what can be most imp building blocks of solar cell !!!  )

Following are the main components of solar cell:

• P-n junction : Every p-n system is characterized by its unique band bap( ΔE_g) or    forbidden energy gap.
• Anti Reflecting Coating:  If ray of light incident on any surface ,some part is reflected and some part is transmitted.  we have to have maximize the transmittance .so we are applying the layer of such a material whose refractive index is the geometric mean of mediums which are above and below of anti reflective coating.

• Glass: glass is used for two purposes first to concentrate the beam of light secondly to have self cleaning property so that any dust particle or any organic impurity can be washed off easily.

So to have self cleaning property of glass, two methods are used:

1. We can coat a hydrophobic layer on glass which will make the contact angle for water – glass system to very large and consequently a spherical drop of water will from, which rolls down due to gravity taking away dust .
2. We can coat a super hydrophilic coating on glass e.g. coating of TiO₂. The glass cleans itself in two stages. The “photo catalytic” stage of the process breaks down the organic dirt on the glass using ultraviolet light and makes the glass super hydrophilic (normally glass is hydrophilic. During the following “super hydrophilic” stage, rain washes away the dirt, leaving almost no streaks, because water spreads evenly on super hydrophilic surfaces

• Conducting wires: these are used to connect small -small solar cells into series and parallel.

Watch the below link to know how solar cell is manufactured. This video is of company- ‘’Sun Tech Power”.

https://www.youtube.com/watch?v=IAufbqbUS6k

6) Now you have installed solar cells and production is started. Now you have to know what maintenance is required and what are the factors which affects the performance of my cell.

Following are the factors which affects the efficiency of solar cell:

• Loss of photons which are below the band gap:

This loss is highest among all losses. We know that light which is hitting contains photons of various energies but out of 100% photons only 30% are capable of generating current because a p-n junction is fixed for photon which have energy equal to band width rest are of no use.

There are multiple p-n junction kept one below the another and of variable band gaps.

• Loss of energy from relaxation of carriers to band edges:

To understand this lets go to atomic level of p type material. This material when irradiated with some light electron will make jump from valence band to conduction band. Now this electron from the conduction band of p type goes to conduction band of n type via space charge region and during this journey electron losses its potential energy and relax at the band edges which results in dissipation of heat   as shown in fig:

• Resistance losses (shunt and series resistances) which will decrease Voc and photo current:

This is the second largest loss after loss of photons. Generally two types of resistances are there series and shunt .These resistances arises because of:

Series: 1. Resistence of connecting wires.

2. Contact resistances.

Shunt (parallel) : These are mainly due to impurities phases lying from  p type to  n type material .

•  Junction recombination: electrons which are generated by light, some of them will lost while going through depletion region.
• Optical losses :
• Dirt accumulation on the glass :
• Effect of temperature:  There is optimum range of temperature in which solar cell works efficiently ,Increasing temperature will decrease the cell efficiency.
• Carrier recombination at defects: This effect is due to grain boundaries resulting in decrement of light current.

7) At last these are materials used in solar cell technology with their efficiencies:

In India we have largest solar park of Asia at Charanka village, Patan district, Gujarat. There is video on it : https://www.youtube.com/watch?v=kIhHy8X0kCg

Refrences:

Stanford university free online course: “solar cell, fuel cell and batteries”

 Equipment Identity Register(EIR) –

-database located near the MSC and containing information identifying cell phones which are stolen or which are cloned.

Authentication unit:-

-This unit holds the security concerns that hover around the all channels, authenticating even the correct base station not the ones held for data recovery by some external agents.

-dedicated channel for sending ack,tracking call,tracking messages,other control signals

-only control data ;no voice

-for only voice transmission

CALLING & RECEIVING :-

Download materials:-

CELLULAR COMMUNICATION

Basic Communication:-

Types of Hand-offs:-

OFDM is of great research interest in laboratories all over the world. It has already been accepted for the new wireless local area network. Also, it is expected to be used for wireless broadband multimedia communications as well. 

         Data rate is really what broadband is all about. The new standard specifies bit rates of up to 54 Mbps. Such high rate imposes large bandwidth, thus pushing carriers for values higher than UHF (Ultra High Frequency) band. For instance, IEEE802.11a has frequencies allocated in the 5- and 17- GHz bands.

         OFDM, orthogonal frequency division multiplex is a rather different format for modulation to that used for more traditional forms of transmission. It utilises many carriers together to provide many advantages over simpler modulation formats.

 What is OFDM? – The concept

                       An OFDM signal consists of a number of closely spaced modulated carriers. When modulation of any form – voice, data, etc. is applied to a carrier, then sidebands spread out either side. It is necessary for a receiver to be able to receive the whole signal to be able to successfully demodulate the data. As a result when signals are transmitted close to one another they must be spaced so that the receiver can separate them using a filter and there must be a guard band between them. This is not the case with OFDM. Although the sidebands from each carrier overlap, they can still be received without the interference that might be expected because they are orthogonal to each another. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period.

To see how OFDM works, it is necessary to look at the receiver. This acts as a bank of demodulators, translating each carrier down to DC. The resulting signal is integrated over the symbol period to regenerate the data from that carrier. The same demodulator also demodulates the other carriers. As the carrier spacing equal to the reciprocal of the symbol period means that they will have a whole number of cycles in the symbol period and their contribution will sum to zero – in other words there is no interference contribution.

Advantages

• Can adapt easily to bad channels.
• Robust against crosstalk between channels that are close together.
• Robust against Inter-symbol interference (ISI) and fading caused by multipath propagation
• High spectral efficiency
• There are good implementations available
• Few problems with errors that come from time synchronization.
• Tuned sub-channel receiver filters are not required (unlike conventional FDM).

Disadvantages

• Problems with Doppler shift.
• Synchronizing frequencies can be problematic.
• Sensitive to frequency synchronization problems.
• High peak-to-average-power ratio (PAPR). This needs linear transmission circuits; they need a lot of power.
• Loss of efficiency caused by Cyclic prefix/Guard interval.

Application

With OFDM, high data rate is achieved .So it is basically used in Digital audio and terrestrial TV broadcasting, Wireless LAN’s (802.11a,g and n), High-speed cellular data etc.

Sanjay Mangal

B.Tech III (ECE)

mangalsanjay25@gmail.com

What is OPTIMIZATION?

– Choosing a best solution among a set of many solutions
– It is about fulfilling the objective with certain limitations
– It is not about a perfect solution, it is about doing the best you can with limited resources
– Optimization can only be applied when we have a set of options. Optimization is meaningless when we have only one option. 

e.g. Suppose you want to arrange a trip to Mumbai. In this trip you want to visit following 4 places: Juhu beach, Bandra bandstand, Marine lines and Gateway of India. You have two options: first, you take following sequence to cover those 4 places:

Juhu->Bandra->Marine lines->Gateway of India

Second, you take following sequence:

Juhu->Marine lines->Bandra->Gateway of India

Which option you will take?? Of course, you will take option first because it minimizes your time and cost. Here our objective was to visit 4 places, which is fulfilled and that too with minimum time and money.

APPLICATION:

1. CIVIL ENGINEERING

– Designing of road networks
– Design of civil engineering structures such as frames, foundations, bridges, towers, chimneys and dams for minimum cost.
– Designed of minimum weight structures for earth quake, wind and other types of random loading.
– Design of water resources systems for obtaining maximum benefit.
– Optimal plastic design of structures.

2. Electronics Engineering
– Optimum design of circuit boards

Eg: While designing a circuit board, we need to place components such that solder path is not shorted. Circuit should run after it is developed on GCB(Genreal Circuit Board). Here, limitation is the size of circuit board. Circuit boards are available in certain fixed sizes in market. Moreover, for embedded application, size of circuit board should be as small as possible. So, we need to place components such that we find a clear path for soldering without much complexities.

3. Mechanical Engineering
– Optimum design of linkages, cams, gears, machine tools, and other mechanical components.

– Selection of machining conditions in metal-cutting processes for minimizing the product cost.– Design of pumps, turbines and heat transfer equipment for maximum efficiency

– Design of material handling equipment such as conveyors, trucks and cranes for minimizing cost.

4. Computer Science
– Program and software optimization

5. Chemical Engineering
– Optimum design of chemical processing equipments and plants
– Design of optimum pipeline networks for process industry
– Selection of a site for an industry

6. Electrical Engineering
– Optimum design of electrical machinery such as motors, generators and transformers
– Optimum design of electrical networks.
– Optimal production planning, controlling and scheduling.
– Optimizing location of a power plant
– Optimum design of control systems.

Eg: Power plant should be located such that it is close to consumer( to reduce transmission losses) and close to the fuel source(to reduce transportation cost). But it is rarely possible that consumer site and fuel source are located near each other. In India, fuel sources are located in Jharkhand,  MP, Chattisgarh. While big consumers( heavy industries) are located in western region(Gujarat, Maharashtra). So we need to have a compromise in chosing location of power plant. It should be at optimum distance from fuel source and consumer site. 

7. Commercial Application
– Allocation of resources or services among several activities to maximize the benefit
– Inventory control
– Controlling the waiting and idle times in production lines to reduce the cost of production.
– Planning the best strategy to obtain maximum profit in the presence of a competitor

ADVANCED TECHNIQUES:

These techniques are developed in last 15-20 years. They heavily rely on power of computation. They are based on the natural phenomena. Few examples are:
– Genetic Algorithm
– Ant Colony Optimization
– Teaching Learning Based Optimization
– Particle Swarm Optimization (PSO)
– Mosquito behavior based optimization

REFERENCES:
– civil.iisc.ernet.in/~nagesh/…/LN01_1_Optimization_Intro_history.pdf?
– Short Term Training Programs (STTPs)
– Video lectures on NPTEL by G. Srinivasan sir (IIT Madras)
– OCW- MIT
SIMULATION SOFTWARES:
– MATLAB
– Maple
– Mathematica
– Nexus
– TOMLAB
– Labview
– Excel

                                                       

A satellite is one of the most complex machines ever built by mankind. It is a great challenge to make a satellite because of the harsh conditions of space, the shock waves, vibrations of launch, the varying temperatures (from -250 degrees to > 100 degrees warm), making adjustments in the orbit and dealing with space debris, solar flare and radiation, making it last for about 5-10 years. Sophisticated electronics are used which can withstand these harsh conditions, Apart from it there are no repair/ reservice  options either – one part damaged or malfunctioned , then goodbye satellite forever..!!

It has its own communication system module often termed as payload to receive the signal from earth (UPLINK) and filters the signal from noisy components, amplify it and send it back to earth where an antenna receives the signal (DOWNLINK). It does this work with the help of a transponder, which is an integrated radio signal receiver and antenna. The frequency is generated by a quartz resonator, which is the heart of satellite.

Classification of Satellites :

Satellites are orbiting the earth in three different orbits : Low Earth Orbit (LEO), Medium Earth Orbit (MEO) and Geosynchronus Earth Orbit(GEO).LEO satellites work at an altitude between 160 km and 1,600 km  above Earth. MEO satellites operate from 10,000 to 20,000 km .GEO satellites are positioned 35,786 km (22,236 miles) above Earth and they complete one orbit in 24 hours.

LEO Satellites

• Advantages:
  • Reduces transmission delay
  • Eliminates need for bulky receiving equipment.
• Disadvantages:Subdivisions: Little, Big, and Mega (Super) LEOs.
  • Smaller coverage area.
  • Shorter life span (5-8 yrs.) than GEOs (10 yrs).

Little LEO Satellite

• 0.8 GHz range
  • Small, low-cost
  • Vehicle tracking, environmental monitoring and two-way data communication. Used for short, narrowband communications.

Super LEO Satellite

• 2 GHz or above range
• Can offer global services, which can be subject to regulatory requirements.
• Used for technology devices such as high-speed, high-bandwidth data communications, and video conferencing. They carry voice and high-speed data services. The main uses are data communications and real-time voice delivery to hand-held devices.

MEO Satellite :

• MEO satellites have a larger coverage area than LEO satellites
• A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network
• A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite

Satellite use very high frequency range of signals for effective communications. The lower GHz frequency range bands are  L band,S band, C band extending upto Ku,Ka, X and Vbands which extend upto 50GHz range. The L,S,C bands have low power and Ku,Ka, X and V bands have high power.

GEO Satellite :

• Orbit is synchronous with the earth’s rotation.
• From the ground the satellite appears fixed.
• Altitude is about 23,000 miles.
• Coverage to 40% of planet per satellite.
• Geostationary satellites are commonly used for communications and weather-observation.
• The typical service life expectancy of a geostationary satellite is 10-15 years.
• Because geostationary satellites circle the earth at the equator, they are not able to provide coverage at the Northernmost and Southernmost latitudes.
• Advantages:
  • Weather images can be displayed.
  • Television broadcasts are uninterrupted.
  • Used to track major developments such as hurricanes 24 hours a day.
• Disadvantages:
  • It takes longer for the signal to get to earth and back to satellite (Delay of .22 s).
  • Increased difficulty of telephone conversations.
  • GEOs are not positioned in the farthest northern and southern orbits.

Satellite Components :

Bus Mainframe  :

It is the frame of the system. It contains antenna dishes, transponders, thrusters, fuel cylinders, engine, position control system,solar panels etc. It is made of aluminium and carbon fibre.

Command Control and Telemetry :

The station from earth monitors the health of satellite including its vital parameters continuously which ensure the satellite is operable for many years. They have a separate antenna and separate frequency to monitor and establish radio diagnostics and control (RDC).

Power System :

Photovoltaic cells are employed on solar panels which have a conversion rate of 20%.They power up the circuitry on board and recharge batteries. The panels are foldable and are constantly positioned for maximum collection of sunlight on panels. Apart from that on board Ni-Cd  batteries that have best power weight ratio and are used on eclipses, where shadow of the planet causes block in sunlight.

Orbital Position System:

The gravitational fields of earth and moon have effect on the orbit of the satellite. The fuel in satellite system, hydrazine is thrusted out to maintain on its elliptical path (Attitude Control System). The attitude and orbit control subsystem consists of sensors to measure vehicle orientation; control laws embedded in the flight software; and actuators (reaction wheels, thrusters) to apply the torques and forces needed to re-orient the vehicle to a desired attitude, keep the satellite in the correct orbital position and keep antennas positioning in the right directions.

Antenna and Receivers :

Every satellite has got a different range of antennas on it. Medium gain antenna , high gain antenna etc. are employed for various purposes. Different radiating power is needed for these antennas.LEO satellites need big antenna dish because of low power and low frequency and due to high frequency range of GEO satellites, need a small antenna system. They have carbon fibre skins bound on Kevlar honeycomb. They don’t have a smooth surface.

The Thermal Control Subsystem

The thermal control subsystem helps protect electronic equipment from extreme temperatures due to intense sunlight or the lack of sun exposure on different sides of the satellite’s body (e.g. Optical Solar Reflector).Vacuum deposited aluminium on kapton is used for thermal insulation too.

Transponder :

The second major module is the communication payload, which is made up of transponders. A transponder is capable of :

• Receiving uplinked radio signals from earth satellite transmission stations (antennas).
• Amplifying received radio signals
• Sorting the input signals and directing the output signals through input/output signal multiplexers to the proper downlink antennas for retransmission to earth satellite receiving stations .

After serving its term the small thrusters fire off  the satellite using the last of on board fuel to its graveyard orbit away from earth in to the deep space.