Dear Students:  Meet me tomorrow in class room # C 005 at 10am.

Important for 1st Ssessional-Sept 2012

Dear Students,
Revise the following:
1)    Sheet # 1 sectioning first 3 figures & identification of surfaces
2)    Limits, Fits & Tolerances sheet # 2
3)    Gears' calculation-to find design data and types of gears
4)    Types of couplings-freehand sketches
5)    To show the fits' examples
6)    Bring geometric box all instruments except drafter
7)    All explained in class 

One TR

One ton of refrigeration is defined as the refrigerating effect that freezes One ton of liquid water(2000 lbs) during 24 hrs. Water and ice Are both on 0 degree C. 2000 lbs=2000/2205=907 kg Enthalpy of fusion of water at 0 degree=333.43 kJ/kg 1 ton of refrigeration= 907x333.43/24x60=210kJ/min = 3.5kJ/sec=3.5kw

Best of luck

Dear students I have posted revision points key go through before sleep. Good luck and good night 

SC Malhotra

1.Lathe machine...fig, parts, operations difference between shaper and planer, operation of milling. 2.NC and CNC complete 3.laws of thermodynamics, Zeroth law 4.Heat pump, heat engine and refrigerator 5.what is entropy, enthalpy(total heat) 6.Properties of steam, Calorimeters, Mollier chart and steam table 7.Rating of Refrigeration I.e. TR, COP, simple refrigeration vapour compression cycle. 8.psychometric chart, human comforts 9.Classification of turbines their brief description, pumps and clutches 10.Power transmission by belt, rope, chain and gear velocity ratio and mechanical advantage And power transmitted by belt 11 All types of stresses, strain as in blog, hook's law, poisson's ratio, elastic constants, Their relationship. Modulus of elasticity,rigidity, bulk modulus, lateral &leaner strain etc 12.Stress-strain diagram digm and description of each points A, B, C, D, E and F,

Exam eve

Dear students are u studying? Ok see the blog in between.

Good luck

Dear students Psychometric chart it is a graphically representation, which gives mainly humidity percentages for designing refrigeration and air-conditioning units. It gives the values of vapour pressure, enthalpy, sensible heat specific humidity specific volume depending on dry bulb temperature& wet bulb temperature. Draw rough chart to explain. Mollier chart it is a graphical representation of steam table I.e. The values of steam table are plotted. Specific entropy is on ordinate (X axis) and specific enthalpy on Y axis(abscissa). A Mollier chart has following lines. Dryness fraction lines Constant specific lines Constant pressure lines Constant temperature lines. I will be typing pl go through before sleep. Best of luck.

Syllabus for Sessional Test (APR-12)

SYLLABUS FOR SESSIONAL TEST TO BE HELD ON 23.4.12

1. Machine tools- Lathe, Milling, Shaper-parts & operations. Also read specification’s requirements.

2. CNC & NC full chapter as told in the class.

3. Manufacturing System, Chips- formation & types.

4. Entropy, Enthalpy and Internal Energy.

5. Stress-Strain Diagram elastic constants and relationship.

6. Types of belts, chain, pumps, turbines, gears and clutches.

7. Main-main descriptions of above types.

8. Mollier, psychrometric, VCR cycle, use of steam tables, formulae.

9. Numerical as done in class e.g. manometer, gas laws, stresses & strains.

10. Values from steam table.

See syllabus on blog –Section B. C & D

Gears' Details

Psychrometric Chart

Psychrometric Chart

Transmission of Power by belt/ chain

Transmission of Power by Belt/ chain

Human Comforts

University QP

University QP

Relationship between Elastic Constants

Relationship between Elastic Constants

Stresses/ Strain Contd & Principle of Superposition

Stresses & Strains in bar of diff length and dias

FLUID MACHINES

FLUID MACHINES

There are various fluid machines in which the fluid flows and energy conversion takes place. The machines may convert hydraulic energy to mechanical energy and vice versa, e.g. turbines, pumps, compressors, fans, hydraulic couplings and torque converters etc.

TURBINES: are prime movers in which change of momentum of a fluid is utilized to create rotation of a shaft. Rotary motion is obtained by centrifugal forces resulted by change in direction of motion of high velocity jet.

Classification of turbines:

1. On basis of process of energy conversion

a) Impulse turbine b) Reaction turbine

a) Impulse turbine: In Impulse turbine hydraulic energy available is first converted in kinetic energy by means of efficient nozzles. The high velocity jet from nozzle strikes a series of buckets fixed on rotor shaft. The buckets are designed to split the change of direction of motion of jet. It results the change in moment of momentum of rotor shaft and shaft rotates. Examples are pelton wheel, Girad turbine, Banki turbine, Jonval turbine etc.

b) Reaction turbine: In reaction turbines some part of the total available energy is converted into kinetic energy, and remaining part still in form of potential energy. As the water flows through the runner, the water under pressure goes on changing pressure energy to kinetic energy. Examples Francis, Kaplan, Propeller,Fourneyron turbines etc.

2. On basis of direction of flow of water in the runner:

a) Tangential flow turbine (Pelton Wheel)

b) Axial or parallel flow turbine (Kaplan Turbine)

c) Mixed-radial & axial turbine (Modern Francis Turbine)

d) Outward radial flow turbine (Fourneyron Turbine)

e) Inward radial flow turbine (Old Francis Turbine)

Construction details are to be discussed in BME Lab.

· Specific Speed of turbine:

· Specific Speed (Ns) N√P/H⁵⁄⁴

· Where N= Speed of actual turbine

P= Power in kw

H= Head in metres

Refer classification of pumps on this Blog

TYPES OF CLUTCHES

TYPES OF GEARS

TYPES OF PUMPS

SIMPLE VAPOUR COMPRESSION REFRIGERATION CYCLE

Refer simple vapour compression cycle on Blog:

Vapour compression refrigeration is most important and practical form of refrigeration system for domestic & commercial utility. The working fluid (refrigerants) used are CO2, NH3 and Feron etc are liquid gas mediums, which at normal temperature may exit either as a liquid or a gas depending upon pressure.

The system comprises namely compressor, condenser, expansion valve or capillary tube and evaporator. The refrigerant is not allowed to leave the system, but is circulated again & again alternately condensing and evaporating.

The sequence of operation of the cycle is:

1. Reversible adiabatic compression (1-2): The vapour at low temperature T1 & pressure p1 preferably dry (state1) is drawn from evaporator during suction stroke of compressor. Vapour is compressed isentropically to a higher pressure p2 and temperature T2. At compressor exit, the vapour may be wet, dry or superheated. Compressor creates the pressure difference for maintaining continuous flow of refrigerant in system by raising the pressure.

2. Constant pressure condensation (2-3): The vapour refrigerant at high temperature and pressure (state2) coming from the compressor is delivered to the condenser, where the condensation is at constant pressure. The condenser first absorbs the heat of superheat and temperature of the vapour falls to saturation temperature. Subsequently the refrigerant loses its latent heat and changes to high pressure liquid (state3)

3. Throttling (3-4): Expansion of high pressure liquid refrigerant is done by throttling process. During expansion pressure drops, but enthalpy remains constant. Due to pressure drop, the liquid starts boiling and required heat is provided by refrigerant itself. Refrigerant is mixture of liquid and vapour. Throttling is an irreversible process( shown by dotted line)

4. Constant pressure evaporation(4-1): The wet vapour after throttling passes through evaporator coils placed in the medium (usually brine), which is to be cooled. The temperature of vapour is below that of brine. It absorbs latent heat from the brine and gets evaporated at constant pressure (state1) the refrigerant may remains wet, dry saturated or slightly superheated.

Notes:

Rotary type compressor…………… for domestic refrigerators.

Reciprocating type compressor……for large plants & machines.

Centrifugal compressor……………..for plants over 50 tons.

Cooling medium atmosphere………for domestic refrigerators.

Cooling medium steam of water …for large units refrigerations.

The components of the system are connected by pipes:

Suction line from evaporator to compressor, delivery line from compressor to condenser and liquid line from receiver tank to expansion/ throttling----(i.e. capillary tube, thermostatic expansionvalve or automatic expansion valve.

Types of Steam

Specific Enthalpy, Entropy & IE

VCR Cycle

VCR Cycle

Heat Engine, Pump & Refrigerator

Types of Steam

Saturation points of steam and units of specific Enthalpy, Emtropy & IE

REFERIGERATION & AIR-CONDITIONING

REFRIGERATION

Science of providing and maintaining temperatures below that of surroundings.

· Deals with the chilling or freezing of a substance by removing some of its heat.

· Transfer of this heat to another system at high temperature.

· For this mechanical work must be performed to satisfy the second law of thermodynamics.

AIR CONDITIONING refers to simultaneous control of temperature, humidity, cleanliness and air motion within a confined region.

Separating Calorimeter

Separating & Throttling Calorimeter

Throttling Calorimeter

measuring quality of steam

Measurement of Quality of Steam

For pure substances –in-dependant properties such as pressure and temperature are needed (if pressure is known, temperature can be found)

We need specific volume, enthalpy or quality of mixture(liquid & vapour)

For measuring specific volume of mixture (quality) calorimeters are used.

a) Separating Calorimeter

b) Throttling Calorimeter

c) Separating & Throttling Calorimeter

d) Barrel Calorimeter

e) Electric Calorimeter

a) Separating Calorimeter:

Fig

X = M/ (M+m)

M=Mass of dry steam read from gauge of condenser

M=Mass of water separated in specified time interval

x= Dryness fraction or quality of steam

b) Throttling Calorimeter

Fig

x1= (h-hf1)/ hfg1

Let P1 = Initial Pressure

x1 = Dryness Fraction

hf1 = Enthalpy of water at P1

hfg1 = Enthalpy of vaporization

Cps = Sp heat of superheated steam after throttling..kJ/ kg

Tsat = Saturation temp at P2

During throttling process, the enthalpy remains constant.

Enthalpy of steam at P1 before throttling= Enthalpy of steam at P2 after throttling

hf1 + x1 hfg1 = hg2 + Cp (T2-Tsat)

x1 hfg1= hg2 + Cp (T2-Tsat) - hf1

x1= hg2 + Cp (T2-Tsat) - hf1/ hfg1

= h- hf1/ hfg1

h = sp enthalpy at state 2 from superheat read from table