4

Define : i) Tonnage of refrigeration ii) Coefficient of performance.

i) Tonnage of Refrigeration – is defined as the amount of refrigeration effect produced by uniform melting of one ton (1000Kg) of ice from and at 00 in 24 hours. .

ii) Coefficient of performance- is the ratio of heat extracted in refrigerator to work done on the refrigerant

4

Explain the working of Watt governor with neat diagram.

4

Explain with sketch, a pneumatic circuit for speed control of bidirectional motor.

Varying the rate of flow of oil will vary the speed of the actuator. Speed control is possible using meter in circuit, meter out circuit, bleed off circuit or by placing flow control before the DCV. Speed control of bi-directional air motor: Bi-directional air motor rotates in clockwise as well as anti-clockwise direction. The speed of bi-directional motor is controlled as shown in fig. The speed control of motor by using variable two flow control valves having built-in check valve and 4x3 DC valve having zero position or central hold position with Pilot S1 and S2. ( Lever / Push button / Solenoid may be used ) When Pilot S2 is operated, port P will be connected to port A of air motor and motor will start rotating in clockwise direction. Its speed can be controlled by using variable flow control valve F1. Port B of motor will be connected to exhaust R and air in motor will be exhausted through port R via DC valve. When Pilot S1 is operated, pressure port P will be connected to port B of motor and naturally motor will start rotating in anticlockwise direction. Port A will be connected to port R and air in the motor will be exhausted through port R via DC valve.

4

Define following terms with respect to springs : 1) Free length 2) Solid height 3) Spring rate 4) Spring index

Definition of 1) Free length-it is a length of spring in unloaded condition 2) Solid height-it is a length of spring in fully loaded condition 3) Spring rate-load per unit deflection 4) Spring index- ratio of mean diameter of coil to diameter of wire

8

List the factors to be considered for selecting the pipe while designing the pneumatic system. Give specification of pipes for the pneumatic system.

List the Factors to be considered for selecting the pipe while designing pneumatic system. Give specification of pipes for the pneumatic system. Factors to be considered while selecting the pipe for pneumatic system 1. Pressure of compressed air in the line. 2. Total flow rate per unit time through the line. 3. Permissible pressure drop in the line. 4. Type of tube material and type of line fittings. 5. Length and diameter of tube or other pipelines. 6. Working environment. Pipe Size Specifications: Generally pipe size is specified in three ways 1. Nominal Pipe Size (NPS) : This number indicates the base diameter of pipe in inches. e.g. : ½ inch, ¾ inch, 1 inch, 1 ½ inch etc. 2. Schedule Number (SCH): This number is based on wall thickness, greater the SCH, greater will be the wall thickness of pipe. A schedule number indicates the approximate value of SCH = 1000 * P / S where P – service pressure & S – Allowable stress SCH Number 40, 80 and 160 are widely used. 3. Pipes are also classified as Standard (STD), Extra strong (XS) size, Double Extra strong (XXS) size based on strength

8

(i) The extension springs are in considerably less use than compression springs. Why?

(i) it is easier to overextend the extension spring. Compression springs will bottom out before the overextend. Also it seems like the tensile strength will be weaker at the attachment point for the extension spring, making it generally larger and more cumbersome to correct the deficiency

4

Draw speed control of single acting cylinder pneumatic circuit using 3 × 2 DC valve

4

Define following terms : Fluctuation of energy, co-efficient of fluctuation of energy, co-efficient of fluctuation speed, maximum fluctuation of energy.

Fluctuations of energy: The variations of energy above and below the mean resisting torque line are called fluctuations of energy.

Coefficient of fluctuation of energy: It may be defined as the ratio of the maximum fluctuation of energy to the work done per cycle. Mathematically, Coefficient of fluctuation of energy, E = Maximum fluctuation of energy/Work done per cycle

Coefficient of fluctuation of speed: The difference between the maximum and minimum speeds during a cycle is called the maximum fluctuation of speed. The ratio of the maximum fluctuation of speed to the mean speed is called the coefficient of fluctuation of speed.

Maximum fluctuation of energy: Δ E = Maximum energy – Minimum energy = (E + a1) – (E + a1 – a2 + a3 – a4) = a2 – a3 + a4

2

State the function of flywheel in I.C. Engine.

A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply. In other words, a flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.

4

Draw a neat block diagram of “vapour compression cycle”. Show the direction of flow ofrefrigerant.

Block diagram of Vapour Compression cycle :-

8

Develop a pneumatic circuit for operation of two DA cylinders such that one operates after other using travel dependant sequencing.

Answer: a pneumatic circuit for operation of two DA cylinders such that one operates after other using travel dependant sequencing as shown in fig.

4

Explain the following terms :- i) Daltons law of partial pressures  ii) Relative humidity

4

Sketch a psychrometric chart and show the following properties of air on it. i) DBT lines ii) WBT lines iii) Specific volume lines iv) Relative humidity lines

4

State any four area of Application of spring:

1) To cushion, absorb or control energy to external load : Car springs, Railway buffers 2) To store Energy : Watches Toys 3) To Measure forces : Spring Balances, Gauges ,Engines 4) To provide clamping force in Jigs & fixtures. 5) To apply forces as in brakes, clutches & spring loaded valve.

2

Define: (i) Coefficient of fluctuation of speed. (ii) Coefficient of fluctuation of energy.

(i) Coefficient of fluctuation of speed: Coefficient of fluctuation of speed is defined as the  ratio of the maximum fluctuation of speed to the mean speed. It is denoted by C s.
Mathematically,
C s = (N 1 – N 2 ) /N
Where, N 1 = maximum speed in rpm;

N 2 =minimum speed in rpm; N = mean speed in rpm

(ii) Coefficient of fluctuation of energy: Coefficient of fluctuation of energy may be defined as the ratio of the maximum fluctuation of energy to the work done per cycle. It is denoted by Ce.
Mathematically,
Ce = Maximum fluctuation of energy/ Work done per cycle.

8

Represent following processes on Psychrometric chart. i) Heating with humidification ii) Sensible heating. iii) Sensible cooling iv) Evaporative cooling.

4

State any four applications of spring.

1) To cushion, absorb or control energy to external load : Car springs, Railway buffers 2) To store Energy : Watches Toys 3) To Measure forces : Spring Balances, Gauges ,Engines 4) To provide clamping force in Jigs & fixtures. 5) To apply forces as in brakes, clutches & spring loaded valve.

8

Explain with neat block diagram the working of ‘Vapour Absorbtion Cycle’.

Working of Simple Vapor absorption system: A Simple Vapor absorption system consists of evaporator, absorber, generator, condenser, expansion valve, pump & reducing valve. In this system ammonia is used as refrigerant and solution is used is aqua ammonia. Strong solution of aqua ammonia contains as much as ammonia as it can and weak solution contains less ammonia. The compressor of vapor compressor system is replaced by an absorber, generator, reducing valve and pump. The heat flow in the system at generator, and work is supplied to pump. Ammonia vapors coming out of evaporator are drawn in absorber. The weak solution containing very little ammonia is spread in absorber. The weak solution absorbs ammonia and gets converted into strong solution. This strong solution from absorber is pumped into generator. The addition of heat liberates ammonia vapor and solution gets converted into weak solution. The released vapor is passed to condenser and weak solution to absorber through a reducing valve. Thus, the function of a compressor is done by absorber, a generator, pump and reducing valve. The simple vapor compressor system is used where there is scarcity of Electricity and it is very useful at partial and full load. -------

4

Draw a neat sketch of leaf spring of semi-elliptical type and name its parts.

Sketch of Leaf Spring of semi elliptical Type ….Diagram+ Names :

4

Explain single cylinder 4-stroke I.C. engine using turning moment diagram.

A turning moment diagram for a four stroke cycle internal combustion engine, we know that in a four stroke cycle internal combustion engine, there is one working stroke after a crank has turned through two revolution i.e.7200 . Since the pressure inside the engine cylinder is less than the atmospheric pressure during suction stroke therefore a negative loop is formed. During the compression stroke, the work is done on gases, therefore a higher negative loop is obtained.

During the expansion or working stroke, the fuel burns and the gases expand, therefore a positive loop is obtained. In this stroke the work done is by the gases. During exhaust stroke, the work is done on the gases, therefore negative loop is formed. It may be noted that effect of inertia forces on the piston is taken is account.

2

Define fluctuation of energy and coefficient of fluctuation of energy.

a) Fluctuation of energy -- The difference of maximum and minimum kinetic energy of flywheel is known as Fluctuation of energy

b) Coefficient of fluctuation of energy -- - It is defined as the ratio of the maximum fluctuation of energy to the work done per cycle. It is denoted by ke = (E1 - E2)/work done per cycle

4

Define i) Humidity ratio, ii) Specific humidity

Specific humidity : It is defined as the ratio of mass of vapor to the mass of dry air in a given sample of moist air . It is denoted by ω 

4

Distinguish between flywheel and governor.

8

Design a helical compression spring with ground ends. The spring index is 12. Maximum load on the spring is 100N and deflection under maximum load is 15 mm. Allowable shear stress of the material is 100 MPa and modulus of rigidity is 4 MPa. Find wire and spring diameters, number of coils and stiffness of spring.

4

Define (i) Dew point temp. (ii) Wet bulb temp

i) DPT – Dew point temperature tDP - It is the temperature at which air water vapour mixture starts to condense. D.P.T. of mixture is defined as the temperature at which water vapours starts to condense.

Ii) WBT - Wet bulb temperature - tWB - It is the temperature recorded by thermometer when its bulb is covered with wet cloth known as wick and is exposed to air.

4

Draw neat sketch of split air conditioner and name the parts.

Split Air-conditioner labeled Diagram 02 for figure 02 for labeling

2

State the function of Governor in an I.C. engine.

The function of a governor is to regulate the mean speed of an engine, when there are variations in the load e.g. when the load on an engine increases, its speed decreases, therefore it becomes necessary to increase the supply of working fluid. On the other hand, when the load on the engine decreases, its speed increases and thus less working fluid is required. The governor automatically controls the supply of working fluid to the engine with the varying load conditions and keeps the mean speed within certain limits.

8

Explain vapour compression refrigeration (for dry saturated state of refrigerant) cycle with the help of P-h and T-s charts.

Processes in VCR cycle 1) The point 1 represents condition of refrigerant at entry of compressor which is wet. Process 1 – 2 – Isentropic compression of refrigerant vapour till it becomes dry and saturated. Process 2 – 3 – Condensation of vapour refrigerant up to saturated liquid condition at constant pressure. Process 3 – 4 – Expansion of liquid refrigerant by expansion device. This reduces pressure as well as temperature of liquid refrigerant. Process 4 – 1 – Evaporation of liquid refrigerant in the evaporator thus establishing required refrigerating effect. Thus it completes one cycle of refrigeration. Refrigerating effect = RE = m (h1 – h4) Compressor power = m (h2 – h1) Where m = mass flow rate of refrigerant in kg/sec.

4

Explain with sketch working of hartnell governor.

4

Explain the concept of fluctuation of energy related with turning moment diagram with sketch.

4

Explain the working of window air conditioner with neat sketch.

The low pressure and low temperature refrigerant vapour from evaporator is sucked by compressor. The compressor compresses the vapour to high pressure and high temperature and discharges to the condenser. On the condenser the refrigerant vapour condenses by dissipating heat to the cooling medium (air) the liquid refrigerant coming out of condenser passes through filter, dryer into capillary tube where it is again throated back to the evaporated pressure. The low pressure low temp liquid refrigerant then flows to evaporator which it boil off by extracting heat from air to be circuited to the conditioned space.

2

State the function of flywheel in IC engine.

A flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.

A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply.

8

Explain sensible heating and cooling with dehumidification by sketching it on outline diagram of psychrometric chart

Heating with Dehumidification process : By this process, specific humidity of air decreases and its dry bulb temperature increases. This type of process is suitable for industrial air conditioning where low relative humidity is required. This process is achieved by passing a stream of air over chemicals which have an affinity for water. The process is shown in figure. 

  Cooling with Dehumidification process : This process is used when atmospheric condition is hot and humid. To decrease the humidity of air it is passed over a cooling coil whose temperature is less than dew point temperature of air. As the air passes over the cooling coil, the moisture in air condenses and its temperature is also decreased

4

: (1) Spring index (2) Spring stiffness (3) Free length of spring (4) Solid length of spring

8

Explain construction and working of ice plant with neat sketch.

The main cycle used for ice plant is vapor compression cycle with ammonia as the refrigerant in primary circuit and brine solution in secondary circuit. Brine solution takes heat from water in secondary circuit and delivers the heat to ammonia in primary circuit. Thus, the indirect method of cooling is used in ice plant. In secondary circuit brine is cooled in evaporator and then it is circulated around the can which contains water. The heat is extracted from the water in the can and is given to the brine. The brine is contentiously circulated around the can with the help of brine pump till entire water in the can is converted into ice at -6 0 C. Ammonia vapor coming out of evaporator is compressed to high pressure and then these vapors are condensed in the condenser. High pressure liquid ammonia is collected in the receiver and it is passed through the expansion valve to reduce its pressure and temperature as per requirement. The throttle liquid ammonia at low temperature & low pressure enters in evaporator, which are the coils dipped in brine tank. The liquid ammonia absorbs heat from brine and gets converted into vapors, which are drawn by suction line of compressor.

4

Represent subcooling and superheating on P-h and T-S diagram in refrigeration also give its effect on C.O.P. of refrigeration.

Superheating

Due to superheating suction temperature of compressor increases , increasing compressor power but it also increases the refrigerating effect therefore COP of system remains more or less constant. The superheating is not done to increase the refrigerating effect or COP but it is done to increase the life of compressor.

The process of cooling refrigerant below condensing temperature for a given pressure is known as sub-cooling. Due to sub-cooling the refrigerating effect increases or for same refrigerating effect the circulation rate refrigerant decreases and therefore COP of system increases. Thus sub-cooling is desirable & is done to increase refrigerating effect & COP of system.

8

A semi-elliptical carriage spring of 1200 mm length withstands a load of 60 kN with maximum deflection of 90 mm. Assume breadth to thickness ratio as 8. Design the spring if bending stress of spring material is 540 MPa and E = 2 × 105 N/mm2.

8

Define: 1) DPT 2) WBT 3) DBT 4) moist air.

DPT – Dew point temperature tDP - It is the temperature at which air water vapour mixture starts to condense. 01 D.P.T. of mixture is defined as the temperature at which water vapours starts to condense. WBT - Wet bulb temperature - tWB 01 - It is the temperature recorded by thermometer when its bulb is covered with wet cloth known as wick and is exposed to air. DBT – Dry bulb temperature - tDB 01 - It is the temperature of air recorded by a ordinary thermometer and it is not affected by the moisture present in air. Moist Air – It is the mixture of dry air and water vapour

4

List any four applications of refrigeration.

i. To produce Ice in ICE Plant ii. To Store Vegetable or Domestic materials in Domestic Refrigerator. iii. To Transport Fish, Fruits etc. in Cold Storage. iv. To Cool Water in Water cooler. v. Processing of food products. vi. Processing of textiles, printing work, photographic materials etc. vii. Storage of ice, blood and medicines etc. viii. Preservation of photographic films , archeological documents etc

4

Distinguish between central A/C and unitary A/C systems with respect to following parameters: (i) vibration (ii) noise (iii) power consumption (iv) operating cost (v) ducting (vi) failure problem (vii) initial cost (viii) maintenance cost

8

Explain working principle of simple vapour absorption refrigeration system. Represent it on the block diagram.

Working of Simple Vapor absorption system: A Simple Vapor absorption system consists of evaporator, absorber, generator, condenser, expansion valve, pump & reducing valve. In this system ammonia is used as refrigerant and solution is used is aqua ammonia. Strong solution of aqua ammonia contains as much as ammonia as it can and weak solution contains less ammonia. The compressor of vapor compressor system is replaced by an absorber, generator, reducing valve and pump. The heat flow in the system at generator, and work is supplied to pump. Ammonia vapors coming out of evaporator are drawn in absorber. The weak solution containing very little ammonia is spread in absorber. The weak solution absorbs ammonia and gets converted into strong solution. This strong solution from absorber is pumped into generator. The addition of heat liberates ammonia vapor and solution gets converted into weak solution. The released vapor is passed to condenser and weak solution to absorber through a reducing valve. Thus, the function of a compressor is done by absorber, a generator, pump and reducing valve. The simple vapor compressor system is used where there is scarcity of Electricity and it is very useful at partial and full load.

8

Explain with neat sketch working principle of Ice plant.

Working of Ice plant: The main cycle used for ice plant is vapor compression cycle with ammonia as the refrigerant in primary circuit and brine solution in secondary circuit. Brine solution takes heat from water in secondary circuit and delivers the heat to ammonia in primary circuit. Thus, the indirect method of cooling is used in ice plant. In secondary circuit brine is cooled in evaporator and then it is circulated around the can which contains water. The heat is extracted from the water in the can and is given to the brine. The brine is contentiously circulated around the can with the help of brine pump till entire water in the can is converted into ice at -6 0 C. Ammonia vapor coming out of evaporator is compressed to high pressure and then these vapors are condensed in the condenser. High pressure liquid ammonia is collected in the receiver and it is passed through the expansion valve to reduce its pressure and temperature as per requirement. The throttle liquid ammonia at low temperature & low pressure enters in evaporator, which are the coils dipped in brine tank. The liquid ammonia absorbs heat from brine and gets converted into vapors, which are drawn by suction line of compressor.

4

Give the classification of air conditioning systems.

Air conditioning systems are classified as

1) Classification as to major function- i) Comfort air-conditioning - air conditioning in hotels, homes, offices etc. ii) Commercial air-conditioning- air conditioning for malls, super market etc iii) Industrial air-conditioning – air conditioning for processing, laboratories etc

2) Classification as to season of the year- i) Summer air-conditioning - These system control all the four atmospheric conditions for summer comfort. ii) Winter air-conditioning – This system is designed for comfort in winter. iii) Year round air-conditioning – These system consists of heating and cooling equipments with automatic control to produce comfortable condition throughout the year 3)According to equipment arrangement-Unitary and Central air conditioning.