GATE 2015: MECHANICAL ENGINEERING COACHING IN CHIRANJEEV VIHAR AND GOVINDPURAM GHAZIABAD

GATE 2015

MECHANICAL ENGINEERING COACHING IN

CHIRANJEEV VIHAR AND GOVINDPURAM

THE SALIENT POINTS OF THE COURSE:

• THE COURSE HAS BEEN DESIGNED TO HELP THOSE STUDENTS WHO HAVE DIFFICULTIES IN THE BASIC CONCEPTS.
• AT FIRST THE BASIC CONCEPTS WOULD BE TAUGHT AND THEN ADVANCED CONCEPTS WILL BE INTRODUCED.
• WHILE TEACHING A CONCEPT, SIMULTANEOUSLY MULTIPLE CHOICES QUESTIONS WILL BE SHOWN FROM THAT CONCEPT.
• MORE THAN 2500 MULTIPLE CHOICES QUESTIONS WILL BE DISCUSSED WITH SOLUTIONS.
• PROBLEM SOLVING TECHNIQUES WOULD BE TAUGHT WITH THE HELP OF MASTER CHARTS.
• TWO HOURS PER DAY SIX DAYS PER WEEK CLASSES.
• CLASSES ON IMPROVING LEARNING ABILITIES, INCREASING CONCENTRATION AND THE SCIENTIFIC STUDYING TECHNIQUES WILL BE TAKEN.
• CONCEPTS WOULD BE TAUGHT USING ANIMATIONS, GRAPHS, PICTOGRAMS, MNEMONICS AND OTHER LEARNING ENHANCEMENT TOOLS.
• ONLY 20 STUDENTS PER BATCH TO FOCUS MORE ON THE INDIVIDUAL NEEDS OF THE STUDENTS.
• ASSISTANCES FOR INDIVIDUAL PSU (LIKE ONGC, IOC etc.)
• TRIAL CLASSES ARE THERE TO BE AWARE OF THE PERFORMANCES OF THE CLASSES.
• HIGH TECH STUDY MATERIALS AT AFFORDABLE PRICE.
• COURSE DURATION IS SIX MONTHS.
• INTRODUCTORY PRICES ARE AS LOW AS @₨ 2500 PER MONTH
• CLASSES WILL BE STARTED FROM 25^th JULY; 2014
• CALL AT # +91-9458042791; +91-9555921800; +91-9678534833

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ENGINEERING DRAWING

अर्धबार्षिक परीक्षा प्रश्न पत्र  2013 

इंजीनियरिंग ड्राइंग 

प्रथम वर्ष  यांत्रिक इंजीनियरिंग 

___________________________________________________________________

[ समय : 2 घंटा ]                                                                                   पूर्णांक : 30 

               नोट : किन्ही तीन प्रश्नो के उत्तर दीजिये। प्रश्न संख्या 4 अनिवार्य है। 

                         प्रत्येक प्रश्न के अंक प्रश्न के सामने अंकित है। 

               1 ) 10 mm ऊंचाई के एकल प्रयास उर्ध्वाधर कैपिटल अक्षरों मैं निम्नलिखित वाक्य को        

                    स्वच्छता पूर्वक लिखिए।                                                                        (7. 5 )

                         "CIVIL ENGINEERING IS THE BACKBONE OF CIVILIZATION."

               2 ) एक रेखा AB , HP से 60^o का कोण बनाती है, तथा VP से 25 mm पीछे समानांतर है।  
                    यदि रेखा के सिरा 'A' H.P. से 25 mm निचे है , तथा रेखा की लम्बाई 50 mm है , तब रेखा 
                   के Front  View एबं Top View बनाइये।                                                    (7. 5 )

               3) (1 /50) निरूपक भिन्न (R. F.) वाली एक निकर्ण मापनी बनाइये जिस पर मीटर , 
                   डेसीमीटर तथा सेन्टीमीटर का मापन किया जा सके तथा 9 मीटर लम्बाई तक पढ़ने के 
                   लिए पर्याप्त हो। मापनी पर 6.47 मीटर की दूरी चिह्नित कीजिये।            (7. 5 )


               4) चित्रों मई एक समपरिमन दृश्य (Isometric View) दर्शाया गया है , दी गई दिशाओं से 
                   देखकर इनका अनुविक्षेप (Plan/ Top View) एबं  उत्सेध (Front View) तथा पार्श्व दृश्य 
                   ( Side View ) को III^rd Angle मैं बनाइये।                                                ( 15 )

ME-301: THERMODYNAMICS FOR THIRD SEMESTER; UPTU

SECTION A: Each question carry 2 marks

01) What is point function and path function?

02) Define Enthalpy.

03) What is SFEE?

04) What is internal energy of a system

05) What is vapour dome and dryness factor?

06) What is saturated liquid line and saturated vapour line?

07) What is triple point of water?

08) Define specific heats of ideal gases.

09) Write the reduced form of Vander Waals equation for real gases.

10) Define a thermodynamic system.

11) State with reasoning whether the following systems are closed, open or isolated
i) Refrigerator; ii) Pressure Cooker

12) Distinguish between isolated system and adiabatic system.

13) Explain the concept of flow work

14) What is control volume and control surface?

15) When does a real gas behave like an ideal gas?

16) What are extensive and intensive properties?

17) What is enthalpy of evaporation of steam?

18) Define degree of under-cooling and degree of superheat.

19) What is COP of a heat pump?

20) Define throttling process.

21) Define entropy.

22) Two moles of an ideal gas occupy a volume of 4.24 m³ at 400 K temperature. Find the pressure exerted by the gas.

23) Distinguish between refrigerator and heat pump.

24) What is Free Expansion?

25) Explain Zeroth law of thermodynamics.

26) Explain the concept of compressibility factor?

27) What is PMM-1.

28) What is a superheated steam?

29) Distinguish between universal gas constant and characteristic gas constant.

30) What is Exergy?

31) Distinguish between quasi-static process and reversible process.

32) What is a diathermal system boundary?

33) What is a steady flow open system?

34) What is the difference between latent heat and sensible heat?

35) What is a thermodynamic cycle?

36) Distinguish between restraint and unrestraint process.

37) What is a thermodynamic definition of work?

38) What is work of evaporation?

39) What is a pure substance?

40) What is the concept of continuum?

41) Define thermodynamic state, process and path.

42) Distinguish between thermal equilibrium and thermodynamic equilibrium.

43) What are the conditions for reversible process?

44) Distinguish between heat and work.

45) What are the differences between gas and vapour?

SECTION B: Attempt any three of the following questions. Each question contains two parts of 5 marks each. Total marks In this section is 3x10 = 30

01) a) State Zeroth law of thermodynamics and explain how it leads to the concept of temperature.

b) Explain different types of temperature scale and the relations among them.

02) a) Explain the corollaries of first law of thermodynamics.

b) 2 kg of air is confined in a rigid container of 0.42 m³ at 4 bar pressure. When heat energy of 164 kJ is added, its temperature becomes 127°C.
Find :

i) Work done by the system.
ii) Change in internal energy.
iii) Specific heat at constant volume.

03) a) Derive an expression for heat transfer and work done in a polytropic process.

b) 1.5 kg of oxygen contained in a cylinder at 4 bar pressure and 300 K expands three times its original volume in a constant pressure process. Determine
i) Initial volume, ii) Final temperature, iii) Work done by the gas, iv) Heat added and v) Change in internal energy.
; Assume C_p = 1.005 kJ/kg-K and R = 260 J/kg-K

04) a) Make steady flow energy analysis on a turbine.

b) Find the velocity and diameter at exit of a nozzle if 5 kg/s air at 9 bar and 200°C expands through the nozzle up to pressure at 1.1 bar. Approach velocity is 50 m/s.

05) a) Differentiate between absolute pressure and gauge pressure. What is a manometer?

b) An ideal gas of molecular weight 42.4 has a pressure of 10 bar and occupies a volume of 0.3 m³ at 27°C. Determine the characteristic gas constant for the ideal gas, its mass and number of moles.

06) a) Write the first law of thermodynamics for a flow process. Derive an expression for flow work.

b) Find the total work done and efficiency for a reversible Carnot cycle.

07) a) What is continuity equation in flow process?

b) 3 kg air at 2 bar pressure and 27℃ temperature has been compressed isothermally till the pressure reaches 6 bar. Next it has been heated at constant pressure and thereafter reaches the initial state by expanding adiabatically. Find the maximum Temperature reached in the cycle and total work done by the system.

08) a) Explain the Joule's experiment.

b) Prove that internal energy is a point function.

09) a) What is thermodynamic temperature scale?

b) i) A heat engine running between 300 K and 800 K generates 2000 kJ of energy. Find the total heat extracted from the source.
ii) Determine the power required to run a refrigerator that transfers 2000 kJ/min of heat from a cooled space at 0°C to the surroundings atmosphere at 27°C.

10) a) What is PMM - 2? State Kelvin-Planck statement of second law of thermodynics.

b) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.

11) a) Explain the Vander Waal's gas equation.

b) 4 kg of steam at 16 bar occupies a volume of 0.28 m³. The steam expands at constant volume to a pressure of 8 bar. Determine the final dryness fraction, final internal energy and change in entropy.

12) a) Explain and derive Clausius Inequality.

b) 3 kg of air is heated reversibly at constant pressure of 2.5 bar from 23°C to 227°C. If the lowest available temperature is 20°C determine the increase in the available energy of air due to heating. Take C_p = 1.005 kJ/kg-K.

13) a) What is thermodynamic definitions of work? Distinguish between ∫pdV work and other types of work.

b) 3 kg of air at 1.5 bar pressure and 350 K is compressed isothermally to a pressure of 6 bar. Then heat of 350 kJ is added at constant volume. What will be the maximum temperature of air during the process? Find the total work done in the processes. Also find the change in internal energy of air.

14) a) Write the limitations of second law of thermodynamics. Prove that C_p - C_v = R

b) 10 kg of air at 300 K is stored in a totally insulated cylinder of volume 0.3 m³/kg. If 1 kg air has been taken out of the system, then what will be the value of new pressure?

15) a) Steam at 1.2 bar and a dryness fraction of 0.5 is heated at constant pressure until it becomes saturated vapour. Calculate the heat transferred per kg of steam.

b) Steam at 8 MPa and 500°C passes through a throttling process such that the pressure is suddenly dropped to 0.3 MPa. Find the expected temperature after throttling.

16) a) What are the causes of irreversibility?

b) Distinguish between a quasi-static process and reversible process.

17) a) 3 kg of air at 400 K and 4 bar pressure adiabatically mixed with 4 kg of air at 500 K and 3 bar pressure. Find the change in entropy of the universe.

b) Explain the principle of increase of entropy.

SECTION C : marks 50, 5 questions of 10 mark each. Each question contains 3 parts. Attempt any two parts out of three from each question.

01) a) Steam at 20 bar pressure and 300°C expands isentropically in a turbine to a pressure of 2 bar. Find the final condition of the steam. Also Calculate the work delivered by the turbine.

b) What is isentropic efficiency of a turbine? Calculate internal energy of steam at 6 bar pressure and 300°C.

c) Explain the steam formation process at constant pressure.

02) a) What is adiabatic mixing of two ideal gases? Derive the expressions for final temperature and pressure.

b) 5 kg of steam at 8 bar pressure and 200°C mixed with 3 kg of steam at 5 bar and dryness fraction x = 0.8 adiabatically. Find the final condition of the steam.

c) 5 kg of air at 4 bar pressure is heated at constant pressure from 300 K to 500 K. Find the change in entropy of the system.

03) a) Prove that in an adiabatic process pV^γ = Constant.

b) Polytropic compression of air from state 1 to state 2 where p₁ = 100 kPa and T₁ = 300 K, p₂ = 300 kPa and n = 1.2 where as mass of air is 3 kg. If R = 0.287 kJ/kg-K. Then find

i) heat exchange during the process
ii) change in internal energy
iii) total work done by the air
iv) change in entropy


c) A non flow reversible process occurs for which pressure and volume are correlated by the relation p = (V² + 6V), where V is the volume in m³ and pressure p is in bar. Determine work done if volume changes from 3 to 6 m³.

04) a) A gas expands according to the equation pv = 100, where " p " is the pressure in kPa and " v " is the specific volume. Initial and final pressures are 1000 kPa and 500 kPa respectively. The gas is then heated at constant volume back to it'd original pressure of 1000 kPa. Determine the net work done. Also sketch the processes in p-v coordinates.

b) What is the definition of thermodynamic work?

c) What is the efficiency of a thermodynamic cycle?

05) a) What is paddle work? Distinguish between ∫pdV work and ∫-vdp work.

b) If pV = mRT, determine whether the expression (V/T).dp + (p/T).dV is a property of a system.

c) 2 kg of air at 1 bar pressure and 300 K is compressed adiabatically to a pressure of 6 bar. Then heat of 200 kJ is added at constant pressure. What will be the maximum temperature of air during the process? Find the total work done in the processes. Also find the change in internal energy of air.

06) a) Find the expression for heat transfer in terms of work done in a polytropic process.

b) What is the specific heat C_n for a polytropic process?

c) 2 kg of air at pressure 2 bar and 300 K is compressed reversibly to 4 bar and 650 K temperature in a polytropic process. Determine the polytropic index (n) of the process.

07) a) Find an expression for mechanical work in steady flow process.

b) What is the meaning of - vdp work?

c) Air flows through a gas turbine system at a rate of 5 kg/s. It enters with a velocity of 150 m/s and an enthalpy of 1000 kJ/kg. At exit the velocity is 120 m/s and enthalpy is 600 kJ/kg. If the air passing through the turbine looses 30 kJ/kg of heat to the surroundings, determine the power developed by the system.

08) a) Write the assumptions considered in Kinetic theory of gases? Prove that C_p - C_v = R

b) Explain the law of corresponding states.

c) 10 kg of air at 300 K is stored in a cylinder of volume 0.3 m³/kg. Find the pressure exerted by air using Vander Waals gas equation. Critical properties of air are: P_c = 37.7 bar, T_c = 132.5 K, v_c = 0.093 m³/kg_mole, R = 287 J/kg-K

09) a) What are the limitations of Vander Waals gas equation? Explain reduced properties of a real gas?

b) What is a undercooled liquid and degree of undercooling? Also define enthalpy of water.

c) What are the properties of steam at critical state? Explain sublimation process and triple point line.

10) a) What are the differences between dry saturated steam and superheated steam at a same pressure? Also, explain vapourdome, saturated liquid line, saturated vapour line and critical point.

b) What are the differences between work of evaporation and enthalpy of evaporation?

c) An inventor claims to have developed a refrigeration unit which maintains −10℃ in the refrigerator which is kept at a room where the surrounding temperature is 25℃ and which has COP of 8.5. Find the claim of the inventor is possible or not.

11) a) Prove that the absolute zero temperature is impossible to achieve according to second law of thermodynamics.

b) Two reversible heat engines A and B are arranged in series. A rejects heat directly to B. Engine A receives 200 kJ at a temperature of 421℃ from the hot source while engine B is in communication with a cold sink at a temperature of 5℃. If work output of A is twice that of B, find :
(i) Intermediate temperature between A and B.
(ii) Efficiency of each engine.
(iii) Heat rejected to the sink.


c) Prove that the reversible heat engines are the most efficient.

12) a) Steam at 1 bar and a dryness fraction of 0.523 is heated in a rigid vessel until it becomes saturated vapour. Calculate the heat transferred per kg of steam.

b) Steam at 9 MPa and 600°C passes through a throttling process such that the pressure is suddenly dropped to 0.4 MPa. Find the expected temperature after throttling.

c) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.

13) a) Explain the change of entropy in a perfectly isolated system during a process in the system.

b) Explain the conditions those must be satisfied by a reversible process.

c) Two kg of water at 90℃ is mixed with three kg of water at 10℃ in a perfectly isolated system. Calculate the change in entropy of the system.

14) a) Explain the second law of thermodynamics and prove that no engine can have a 100% efficiency.

b) Explain the theoretical Carnot cycle and derive its efficiency with diagrams.

c) A reversible engine working in a cycle takes 4800 kJ of heat per minute from a source at 800 K and develops 35 kW power. The engine rejects heat to two reservoirs at 300 K and 360 K. Determine the heat rejected to each sink.

15) a) What are the causes of external irreversibility?

b) Write the first and second Tds equations and derive the expression for the change of entropy during a polytropic process.

c) Prove that reversible engines are most efficient.

16) a) Explain the second law of thermodynamics.

b) Derive the Clausius inequality.

c) Steam at 160 bar and 550℃ is supplied to a steam turbine. The expansion of steam is adiabatic with increase in entropy of 0.1 kJ/kg-K. If the exhaust pressure is 0.2 bar, calculate specific work of expansion.

17) a) 5 kg of water at 400 K is isobarically and adiabatically mixed with 3 kg of water at 500 K. Find the change in entropy of the universe.

b) Explain i) Second law efficiency, ii) Effectiveness of a system and iii) Availability of a closed system.

c) Explain the principle of increase of entropy.

18) a) Explain Helmholtz and Gibbs function.

b) Explain the concept of PMM-I and PMM-II.

c) Find an expression of exit velocity C₂ in terms of pressure ratio when air passes through a nozzle from a pressure of p₁ and temperature T₁ to a pressure p₂.

19) a) Distinguish between enthalpy and internal energy.

b) What is absolute or thermodynamic temperature? Explain briefly.

c) Two Carnot engines work in series between the source at temperature 500 K and sink at temperature 300 K. If both develop equal power, determine the intermediate temperature.

20) a) Show that two adiabatic curves on p-V diagram never intersects each other.

b) Define and classify thermodynamic systems.

c) In an isentropic flow through nozzle, air flows at the rate of 600 kg/hr. At inlet to the nozzle pressure is 2 MPa and temperature is 27℃. The exit pressure is 0.5 MPa. Initial air velocity is 300 m/s, determine
i) exit velocity of air
ii) inlet and exit area of the nozzle

THE END

AIR-FUEL MIXTURE AND STOICHIOMETRIC RATIO

AIR-FUEL MIXTURE AND STOICHIOMETRIC RATIO

CHEMICAL COMBUSTION OF FUEL

Subhankar Karmakar
Assistant Professor; SGIT
Jindal Nagar; Ghaziabad

---

Chemical Combustion is basically a rapid oxidation process of hydro-carbon fuel inside thekjm combustion chamber in the presence of air. The oxidation of fuel is basically a Exothermic or heat liberating chemical process.

In SI engines generally we use volatile hydrocarbon as fuel. The intermixing of fuel with air takes place outside the engine and the device that prepares air-fuel mixture of required mixture strength is called CARBURETION and the device is known as CARBURETTOR.

Estimation of air quantity needed for complete combustion of a given fuel

We know that any chemical reaction can be represented by the corresponding chemical equation like
CH₄ + 2O₂ = CO₂ + 2H₂O
here molecular weight of CH₄
μ_CH4 = 12 + 4x1 = 16
μ_2O2 = 2x16x2 = 64
μ_CO2 = 12 + 2x16 = 44
μ_2H2O = 2x(2+16) = 36

For complete combustion of CH₄
16 kg CH₄ needs 64 kg O₂ therefore,
1 kg of CH₄ needs (64/16) = 4 kg of O₂
For 23 kg of O₂ air needed is 100 kg
hence, for 4 kg of O₂ air needed is (100/23)x4 = 17.39 kg of air.
Air-fuel ratio will be 17.39 : 1

The ratio of air fuel mixture, needed for the complete combustion of the fuel or the chemically correct ratio of air fuel mixture required for complete combustion of the fuel is called " Stoichiometric Air fuel mixture. "

If the amount of air in the air-fuel mixture is less than the chemically correct amount of air, then the mixture is called rich mixture, where as if the quantity of air is more than the chemically corrected amount of air it is called lean mixture.

The strength of air-fuel mixture has a profound influences on the process of combustion. The required mixture strength for different operation conditions are different.

Different Operating Conditions	Required air-fuel Mixture Strength
For Max. Efficiency	17 : 1, 16.4% weak
For Max. Power	12 : 1 17.8% rich
For Starting, Idling, & Low load running	11 : 1 ~ 16 : 1 very rich mixture
For accelerated motion	13 : 1 rich mixture
For Part Load running Cruising Range	17 : 1 Lean Mixture Strength

RECIPROCATING COMPRESSORS

Q.2) Classify the compressors
(i) On the basis of operations employed
(ii) On the basis of pressure achieved
(iii) On the basis of pressure ratio
(iv) On the basis of capacity of compressors.

A.2) Depending upon different parameters, compressors can be classified on the basis of operations employed, the delivery pressure achieved, pressure ratio and capacity of compressors as follows.

On the basis of operations employed, compressors are classified into two groups:
i) :Reciprocating compressors : It uses piston cylinder arrangement and due to positive displacement of air in the cylinder, the air is compressed and delivered to a vessel called Receiver. These are capable to produce high delivery pressure with low volume flow rate.
ii) Rotary Compressors : These compressors operate at high speeds, therefore, can handle large volume flow rates compared to reciprocating compressors.

In rotary compressors, the dynamic head is imparted to the gas with the help of very high speed impeller rotating at a confined space so that the air is compressed due to centrifugal action.

On the basis of delivery pressure, compressors are classified into three categories
i) Low Pressure Compressors : Delivery pressure upto 1.1 bar
ii) Medium Pressure Compressors : Delivery pressure upto 7 bar
iii) High Pressure Compressors : Delivery pressure between 7 to 10 bar.

On the basis of pressure ratio, we can classify the devices as follows,
Fans : Pressure ratio upto 1.1
Blower : Pressure ratio upto 1.1 to 4.0
Compressors : Pressure ratio above 4.0

On the basis of capacity, compressors can be classified as follows,
Low capacity compressors : Volume flow rate upto 10 m³/min, or less
Medium capacity compressors : Volume flow rate 10 m³/min to 300 m³/min
High capacity compressors : Volume flow rate above 300 m³/min

Q.3) Find an expression for required work done to drive a compressor, when compression is,
adiabatic in nature
isothermal compression
polytropic compression

A.3) During the analysis of the operations of a reciprocating air compressor, we consider some assumptions to simplify the analysis. They are as follows
i) There is no Clearence Volume
ii) Working substance air is an ideal gas
iii) There is no frictional loss.
iv) There is no wire drawing in the valve or pipe lines.

WORK REQUIRED TO DRIVE A COMPRESSOR

Suppose, we are running a single stage air compressor, which draws air at pressure P₁ and temperature T₁ during the suction or induction process. The air thus drawn inside the cylinder then compressed to achieve a delivery pressure, P₂ by adiabatic process. In the adjacent figure, process a - b is the suction process. Process b - c is the adiabatic compression of the air from pressure P₁ to pressure P₂. Process c - d is the delivery stroke, delivering the compressed air at a pressure P₂.

W_ad = P₂V₂ + {( P₂V₂ - P₁V₁)/(γ - 1)} - P₁V₁

=> (P₂V₂ - P₁V₁){1 + 1/(γ - 1)}

=> {γ /(γ - 1)}P₁V₁ {(P₂V₂)/(P₁V₁) - 1}

=> {γ /(γ - 1)}mRT₁{(P₂/P₁)^{{(γ - 1)/γ}} - 1}

POLYTROPIC WORKDONE IN RECIPROCATING COMPRESSORS

W_poly = P₂V₂ + {( P₂V₂ - P₁V₁)/(n - 1)} - P₁V₁

=> (P₂V₂ - P₁V₁){1 + 1/(n - 1)}

=> {n/(n - 1)}P₁V₁ {(P₂V₂)/(P₁V₁) - 1}

=> {n/(n - 1)}mRT₁{(P₂/P₁)^{{(n - 1)/n}} - 1}

ISOTHERMAL WORKDONE REQUIRED TO DRIVE RECIPROCATING COMPRESSOR

W_iso = P₂V₂ + {P₁V₁ln(V₁/V₂)} - P₁V₁

but as the process is isothermal, P₁V₁ = P₂V₂

W_iso = P₁V₁ln(V₁/V₂)

W_iso = mRT₁ln r_p

V₁/V₂ = P₂/P₁ = r_p (pressure ratio)

THERMODYNAMICS: 2nd MINOR TEST AND ITS SOLUTION.

Topics: First Law of Thermodynamics, SFEE, flow work, Steam, Second Law of Thermodynamics

Total Marks: 30.

Time: 1 hr and 30 min

SECTION A: Attempt all the questions 2x3 = 6

1) What is sub-cooled or undercooled water?

2) What is degree of superheat in case of superheated steam?

3) Write the first law of thermodynamics for a open process.

SECTION B: Attempt all the questions 3x3 = 9

1) 2 kg of saturated water at 8 bar pressure has been supplied 4700 kJ of heat. Find the end condition of the steam produced. Also find the value of specific internal energy and specific entropy of the steam.

2) A stream of air with a mass rate 0.6 kg/s enters a nozzle at a pressure of 8 bar and temperature 200°C at a velocity 1.2 m/s. If the final pressure at exit is 0.3 MPa, then find the value of velocity at exit and inlet and outlet/exit diameter of the nozzle.

3) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.

SECTION C: Attempt any three questions 5x3 = 15

1) What is flow work? Distinguish between flow work and non-flow work. Find the expression for flow work in a open system. What is SFEE?

2) What is quality of steam? Explain the terms "dryness fraction" and "wetness fraction". Calculate the specific enthalpy of steam at 9 bar pressure and 350°C temperature.

3) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.

4) Explain the second law of thermodynamics. Prove that both the statements of 2nd law of thermodynamics are equivalent to each other.

5) Explain the following terms.
i) Vapour Dome,
ii) Saturated Liquid Line,
iii) Critical Point,
iv) Saturation Temperature,
v) Reversible Heat Engine

SOLUTIONS

Topics: First Law of Thermodynamics, SFEE, flow work, Steam, Second Law of Thermodynamics

Total Marks: 30.

Time: 1 hr and 30 min

SECTION A: Attempt all the questions 2x3 = 6

1) What is sub-cooled or undercooled water?

Ans: The boiling point of water is a function of the pressure, as pressure increases, boiling point is also elevated. For a certain pressure, water has a fixed boiling temperature known as saturation temperature and denoted by t_s. If the temperature of water at a given pressure is lower than the corresponding saturation temperature i.e. t < t_s, then the water is called sub-cooled or under-cooled water.

2) What is degree of superheat in case of superheated steam?

3) Write the first law of thermodynamics for a open process.

SECTION B: Attempt all the questions 3x3 = 9

1) 2 kg of saturated water at 8 bar pressure has been supplied 4700 kJ of heat. Find the end condition of the steam produced. Also find the value of specific internal energy and specific entropy of the steam.

2) A stream of air with a mass rate 0.6 kg/s enters a nozzle at a pressure of 8 bar and temperature 200°C at a velocity 1.2 m/s. If the final pressure at exit is 0.3 MPa, then find the value of velocity at exit and inlet and outlet/exit diameter of the nozzle.

3) A heat engine running between two thermal reservoirs of 800 K and 300 K is used to power a refrigerator running between two thermal reservoirs of 325 K and 260 K. If the heat engine draws 5000 kJ heat from reservoirs at 800 K, then find the amount of heat extracted from 260 K reservoir by the refrigerator.

SECTION C: Attempt any three questions 5x3 = 15

1) What is flow work? Distinguish between flow work and non-flow work. Find the expression for flow work in a open system. What is SFEE?

2) What is quality of steam? Explain the terms "dryness fraction" and "wetness fraction". Calculate the specific enthalpy of steam at 9 bar pressure and 350°C temperature.

3) What will be the quality of the steam at the end of adiabatic expansion of steam at 12 bar pressure and 400°C to 1.2 bar in a turbine. Also, find the ideal work out put by the turbine.

4) Explain the second law of thermodynamics. Prove that both the statements of 2nd law of thermodynamics are equivalent to each other.

5) Explain the following terms.
i) Vapour Dome,
ii) Saturated Liquid Line,
iii) Critical Point,
iv) Saturation Temperature,
v) Reversible Heat Engine

COMPRESSORS AND COMPRESSED AIR

COMPRESSORS:

Q.1) What is a Compressor? What is the difference between a Compressor and a Pump? What are the practical uses of Compressed Air?

A.1) A compressor is a device which is extensively used to raise the pressure of a compressible fluid like pure air. In a compressor, the pressure is increased at the expense of work done on the fluid, which is generally provided by an electric motor, IC engines or Gas Turbines. In a compressor, fluids are compressed by reducing the specific volumes of the working fluids. Due to compression, the temperature of the fluid is also increased.

If air is used as the working fluid in a compressor and air is compressed into a high pressure by the application of work on the fluid, then it is known as Air Compressor.

PRACTICAL USES OF COMPRESSED AIR

In industry, compressed air is so widely used that it is often regarded as the fourth utility, after electricity, natural gas and water. Compressed air, commonly called Industry's Fourth Utility, is air that is condensed and contained at a pressure that is greater than the atmosphere. The process takes a given mass of air, which occupies a given volume of space, and reduces it into a smaller space. In that space, greater air mass produces greater pressure. The pressure comes from this air trying to return to its original volume. It is used in many different manufacturing operations.

Compressed air is extensively used in industrial applications like pneumatic machines, as well as in the refrigeration and air-conditioning systems or supercharging CI engines to boost the output of the engine.
01) Compressed air is extensively used to operate pneumatic tools like drills, hammers, rivetting machines etc.
02) It is used to drive Compressed Air Engine.
03) Compressed air is used to spray painting.
04) Compressor is a vital component of Air-conditioning and Refrigeration industry.
05) Very often, compressed air can be used as a means of energy storage.
06) It is used in Gas Turbine power plants.
07) It is used to Super-charging an IC engines.
08) It is used to convey or pump to flow the materials like sand or concrete slurries along a pipe line.
09) It can be used as a means to pump water through the pipe lines.
10) It is used to drive minning machineries in a fire risky zone.
11) It is also used in blast furnaces.

Q.2) Classify the compressors
(i) On the basis of operations employed
(ii) On the basis of pressure achieved
(iii) On the basis of pressure ratio
(iv) On the basis of capacity of compressors.

A.2) Depending upon different parameters, compressors can be classified on the basis of operations employed, the delivery pressure achieved, pressure ratio and capacity of compressors as follows.

On the basis of operations employed, compressors are classified into two groups
i) Reciprocating compressors : It uses piston cylinder arrangement and due to positive displacement of air in the cylinder, the air is compressed and delivered to a vessel called Receiver. These are capable to produce high delivery pressure with low volume flow rate.
ii) Rotary Compressors : These compressors operate at high speeds, therefore, can handle large volume flow rates compared to reciprocating compressors.

In rotary compressors, the dynamic head is imparted to the gas with the help of very high speed impeller rotating at a confined space so that the air is compressed due to centrifugal action.

On the basis of delivery pressure, compressors are classified into three categories
i) Low Pressure Compressors : Delivery pressure upto 1.1 bar
ii) Medium Pressure Compressors : Delivery pressure upto 7 bar
iii) High Pressure Compressors : Delivery pressure between 7 to 10 bar.

On the basis of pressure ratio, we can classify the devices as follows,
Fans : Pressure ratio upto 1.1
Blower : Pressure ratio upto 1.1 to 4.0
Compressors : Pressure ratio above 4.0

On the basis of capacity, compressors can be classified as follows,
Low capacity compressors : Volume flow rate upto 10 m³/min, or less
Medium capacity compressors : Volume flow rate 10 m³/min to 300 m³/min
High capacity compressors : Volume flow rate above 300 m³/min