rr220802-chemical-engineering-thermodynamics-i

Set No. 1

Code No: RR220802

II B.Tech Supplimentary Examinations, Aug/Sep 2008 CHEMICAL ENGINEERING THERMODYNAMICS-I (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define and explain the terms temperature. Further, compare the various temperature scales. (b) Define work and heat in thermodynamic sense and bring out the comparison between them. [8+8] 2. (a) State the relationship between absolute, guage, atmosphere and vaccum pressures. Rv2 (b) What is work? Show that work in changing volume of a PVT system pdv v1

(c) Is work path function (or) point function? Justify your answer

[6+6+4]

3. What are the various conditions that exit in steady flow process? And explain the various forms of energies that are associated with flow process [16] 4. Five kg mol of an ideal gas (Cp = 7 kcal/kg mol K) initially at 300 K and 2 atm is isothermally compressed to 15 atm and is then heated at constant pressure. The volume of the gas after heating is the same as its volume before compression. Find: (a) The net work done in the overall process (b) The heat transferred during compression (c) The change in internal energy in the overall process

[6+6+4]

5. A pumping station transports 5000 kg/hr of natural gas at 500 kg/cm2 and 200 C through a pipe line of 20 cm O.D. The natural gas has the following composition: Methane : 85% by volume Ethane : 5% by volume Nitrogen: 10% by volume What is the velocity of the natural gas? Data: Tc in K Pc in atm

Methane

Ethane

191

306

45.8

48.2

N2 126 33.5

6. (a) Discuss the various ways to improve efficiency of a heat engine.

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[16]

Set No. 1

Code No: RR220802

(b) A system absorbs 100 kJ energy from a body at 5000 C and does 50 kJ work. If it is required to restore the system to its original state, is it possible to do so by an adiabatic process? [8+8] 7. Show Carnot refrigeration cycle on T-S diagram and show athat it is most efficient. [16] 8. If the thermal efficiency of a reversible power cycle operating between two reservoirs is denoted by ηmax , develop an expression in terms of ηmax for the coefficient of performance of a reversible refrigeration cycle operating between the same two reservoirs. [16] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR220802

II B.Tech Supplimentary Examinations, Aug/Sep 2008 CHEMICAL ENGINEERING THERMODYNAMICS-I (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define and explain the terms temperature. Further, compare the various temperature scales. (b) Define work and heat in thermodynamic sense and bring out the comparison between them. [8+8] R 2. Prove that the work interaction in a steady flow process is given by − P dv . State clearly the assumptions, if any. [16] 3. Explain the application of steady flow energy equation to a nozzle and a boiler. [16] 4. (a) Define heat capacity at constant volume and at constant pressure. (b) An ideal gas is one for which PV/T is a constant, regardless of the changes it undergoes. Such a gas has a volume of 0.02271 m3 /mol at 00 C and 1 bar. In the following problem, air may be considered an ideal gas with the constant heat capacities Cv = (5/2) R and Cp = (7/2) R where R = 8.314 J/mol K. The initial conditions of the air are 1 bar and 250 C. It is compressed to 5 bar and 250 C by the following mechanically reversible process: Cooling at constant pressure followed by heating at constant volume. Calculate the heat and work requirements and ∆U and ∆H of the air for this path [6+10] 5. Define the following: (a) State (b) Process (c) Property (d) Cycle

[4x4]

6. (a) An inventor claims to have developed an engine that takes in 25,000(J)/(s) at a temperature of rejects 12,000 (J)/(s) at a temperature of 200(K), and delivers 15(kW) of mechanical power. Would you advice investing money to put this engine on the market? (b) State the carnot theorems. (c) Write shortnotes on heat engine.

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[7+5+4]

Set No. 2

Code No: RR220802

7. A refrigerated space is maintained at 100 F and cooling water is available at 700 F . The evaporator and condenser are of sufficient size that 100 F minimum temperature difference for heat transfer can be realized in each. The refrigeration capacity is 120,000(Btu)hr−1 . The refrigerant is tetrafluoroethane, for which data are provided below. T(0 F ) P(psia) Liq.Vol. Vap.Enth. Liq.Enth. Liq.Enth. Liq.Enth. Liq.Enth. (f t)3 (lbm)−2 (btu) (Btu) (Btu) (Btu) (Btu) −4 − −4 −1 (lbm) (lbm) 4 (lbm) (lbm) (lbm)−4 −4 (OR) (0 R)−1 10 26.617 0.01202 1.736 15.187 104.471 0.03408 0.22418 70 85.787 0.01312 0.558 34.583 112.652 0.07264 0.22003 (a) What is the value of the coefficient of performance for a Carnot refrigerator ?. (b) Calculate the coefficient of performance for the vapor compression refrigeration cycle provided with an expander. (c) Calculate the coefficent of performance for the vapor compression refrigeration cycle provided with a throttle valve and a compressor efficiency of 0.8. [16] 8. Discuss briefly how liquefaction can be achieved. Write energy balance equation around the separator, valve or cooler for Linde liquefaction process. [16] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: RR220802

II B.Tech Supplimentary Examinations, Aug/Sep 2008 CHEMICAL ENGINEERING THERMODYNAMICS-I (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss the basis of measuring the temperature. Name the different temperature scales in common use. Establish relation between Celsius and Fahrenheit scales. (b) Explain the ideal gas temperature scale.

[10+6]

2. (a) The properties of a closed system undergo change following the relation PV= 4 and P is in bar and V in metre3 . Calculate the work done when P increases from 2.5 bar to 8 bar.

∂T ∂P (b) Show that ∂V = − [8+8] ∂S v s 3. Derive the steady flow energy equation and write the assumptions.

[16]

4. A cylinder closed at both ends contains a free piston, on one side of which is nitrogen and other side air. The initial pressure and volume of each being 1.03 bar and 0.5 m3 respectively. Both the piston and cylinder are perfectly insulated. In the cylinder on the air side of the piston there is an electric heater which is used to heat the air. Heat is added to the air in this manner until the volume occupied by the nitrogen is 0.3 m3 . The initial temperature of each gas is 500 C. Determine (a) the final temperature of air and (b) the heat supplied to air. Assume Cp for air as 1.005 and R for air as 0.287 kj / kg K and γ = 1.4 for nitrogen. Also draw the PV diagram. [16] 5. (a) What is the physical significance of the compressibility factor? Explain. (b) Determine the specific volume of superheated steam at 2 bar and 1500 C using, i. the steam tables ii. the ideal-gas equation of state, and iii. the generalized compressibility chart. What is the error involved in (ii) and (iii)?

[6+10]

6. (a) Derive an expression for the efficiency of reversible heat engine. (b) In thermodynamics cycle the heat and work as follows. Process Q W

1 2 3 4 30 -10 -20 5 3 10 -8 0

Calculate the thermal efficiency.

[8+8] 1 of 2

Set No. 3

Code No: RR220802

7. (a) Present a brief comparison of the Carnot, vapor-compression cycle with reversible compression & expansion and vapor-compression cycle with expansion in a throttle. (b) In a reversed Carnot engine used for refrigeration, the temperature of the refrigerator is kept at −100 C and that of the hot body is 300 C. It is desired to extract 2000 kcal of heat per minute from the refrigerator. Calculate: i. The heat discharged per minute to the hot body. ii. The minimum horsepower of work required. [8+8] 8. (a) Explain Cloude’s process for air liquefaction with neat sketch. Show it by T-S diagram. (b) Obtain the relation for the COP of an absorption-refrigeration process. [8+8] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR220802

II B.Tech Supplimentary Examinations, Aug/Sep 2008 CHEMICAL ENGINEERING THERMODYNAMICS-I (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define and explain the terms temperature. Further, compare the various temperature scales. (b) Define work and heat in thermodynamic sense and bring out the comparison between them. [8+8] 2. Compute the workdone in following cases: (a) 10 kgs of water is evaporated at atmospheric pressure until a volume of 1.25 m3 is occupied. (b) Explain in detail about Maxwell relations.

[6+10]

3. During winter season a room measuring 5 × 6 × 3 m3 is heated electrically from initial temperature of 00 C to 200 C. The air pressure inside the room is the same as that of surroundings and is equal to 74 cm of Hg. The pressure remains constant during the heating process. The heat capacity of furniture and walls is 32 kJ / K. The specific heat of air is 1.005 kJ / kg K. Calculate the amount of electric energy required for heating the room. How much air escapes through gaps and windows during this period? [16] 4. Prepare a comparative statement for a non flow process and a flow process for the work done and heat transfer for the cases (a) constant volume (b) constant pressure process (c) constant temperature process (d) isentropic and polytrophic process.

[4x4]

5. Define the following: (a) State (b) Process (c) Property (d) Cycle

[4x4]

6. (a) Discuss the various ways to improve efficiency of a heat engine. (b) A system absorbs 100 kJ energy from a body at 5000 C and does 50 kJ work. If it is required to restore the system to its original state, is it possible to do so by an adiabatic process? [8+8] 1 of 2

Set No. 4

Code No: RR220802

7. A metal block of specific heat 0.09Kcal/kg 0 C and mass of 10kg is initially at 500 C. (a) 2 kg of water at 350 C is used to quench the block, what is the total entropy change? (b) Repeat if 2 kg of water at 150 C is used. Comment on the above process. [16] 8. A Carnot engine is coupled to a Carnot refrigerator so that all the work produced by the engine is used by the refrigerator in extraction of heat from the heat reservoir at 2700 K at the rate of 4kJ s−1 . The source of energy for the Carnot engine is a heat reservoir at 5000 K. If both devices discard heat to the surroundings at 300 0K, how much heat does the engine absorb from the 5000 K reservoir. If the actual coefficient of performance of the refrigerator is ω = ωCarnot /1.5 and if the thermal efficiency of the engine i η = ηCarnot / 1.5, how much heat does the engine absorb from 5000 K reservoir ?. [16] ⋆⋆⋆⋆⋆

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