07a40802 Chemical Engineering Thermodynamics-i

Code.No: 44064

R07

SET-1

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD II B.TECH II SEM SUPPLEMENTARY EXAMINATIONS FEBRUARY - 2010 CHEMICAL ENGINEERING THERMODYNAMICS – I (CHEMICAL ENGINEERING) Time: 3hours Max.Marks:80 Answer any FIVE questions All questions carry equal marks --1.a)

b)

Compute the work done in following cases: i) 10kg mass of water is evaporated at atmospheric pressure until a volume of 1.25 m3 is occupied. ii) Steam admitted to cylinder of a engine of stroke = 35 cm and bore = 18 cm at a constant pressure of 100 kgf/cm2. Explain the concept of continuum. (10+6)

2.a) b)

What is enthalpy? Is enthalpy a path function? The piston of a piston cylinder device containing a gas has a mass of 75 Kg. Diameter of piston is 250 mm. The local atmospheric pressure is 0.97 bars, gravitational acceleration is 9.8 m/s2. i) Determine the pressure inside the cylinder. ii) If some heat is transferred and its volume doubles, do you expect the pressure inside the cylinder to change? (4+12)

3.

If one kmole of methane is stored in 0.31 m3 tank at 301 K, estimate the pressure of the gas using Redlich-Kwong equation of state. The critical constants of methane are Pc = 4.60 MPa and Tc=190.6K. (16)

4.a) b) c)

Draw the entropy versus enthalpy curve for compressor and explain them. Define turbine efficiency and compressor efficiency Write expression to calculate enthalpy and entropy in a pump used for liquids. (4+8+ 4)

5.a) b)

State and prove Carnot’s theorem. Prove that it is not possible to obtain zero degrees on thermodynamic temperature scale. Heat is transferred from a vapour at 4200c to water to evaporate at 2500C. The steam so generated is used in a power cycle to reject the heat to atmosphere at 350C. What is the loss in an available energy while the heat is transferred over a finite temperature difference during evaporation of water? (4+4+8)

c)

6.a) b)

A kilogram of water at 273 K is brought into contact with a heat reservoir at 373 K. When the liquid water has reached 373 K, what is the entropy change of the water and that of the reservoir? What is ∆Stotal? Derive the expression for change of entropy for an ideal gas (8+8)

7.a) b)

Explain absorption compression cycle and derive the relation for the COP It is proposed to use a reversed Carnot cycle for cooling and heating. The work supplied to the unit is 10 kW. If the COP = 3.5 for cooling, determine the ratio of temperatures of the reservoirs between which the device is working, the rate of refrigeration and the COP for heating. (8+8)

8.a)

Show that

b)

.

A system has the equation of state as PV = ZRT, show that *******

. (6+10)

Code.No: 44064

R07

SET-2

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD II B.TECH II SEM SUPPLEMENTARY EXAMINATIONS FEBRUARY - 2010 CHEMICAL ENGINEERING THERMODYNAMICS – I (CHEMICAL ENGINEERING) Time: 3hours Max.Marks:80 Answer any FIVE questions All questions carry equal marks --1.a)

b) 2.a)

b)

Water falling from a height of 100 m at a rate of 5000kg/hr is used to feed turbine in a hydroelectric power station. What is potential energy? Assuming 10% loss of electrical power, the power is sufficient to keep a 200 watt bulb burning. How much % of potential energy is converted into electrical energy? Explain briefly the sign convention for heat and work (10+6) The piston of a piston cylinder device containing a gas has a mass of 75 Kg. diameter of piston is 250 mm. The local atmospheric pressure is 0.97 bars gravitational acceleration is 9.8 m/s2. i) Determine the pressure inside the cylinder. ii) If some heat is transferred and its volume doubles, do you expect the pressure inside the cylinder to change? Differentiate between Open system and Closed system (12+4)

3.

It is desired to design a tank to store 10 kmole methane at 6.0MPa and 300K. Determine the size of tank using the Redlich-Kwong equation of state. The critical constants of methane are Pc=4.60MPa and Tc=190.6K. (16)

4.a) b)

Differentiate between nozzles and turbines. Draw entropy verses enthalpy curve for adiabatic expansion process in a turbine and explain briefly. (6+10)

5.a)

A Carnot engine I operate between two reservoirs at temperatures 1920K and T K while a second Carnot engine II operates between two reservoirs at T K and 300 K. It is found that both the engines have the same efficiency. Determine the value T. Explain in detail the Carnot cycle of the heat engine and applicability of second law of thermodynamics (8+8)

b) 6.a) b)

State and explain third law of thermodynamics A steel casting [Cp = 0.5 kJ kg-1 K-1] weighing 40 kg and at temperature of 4500C is quenched in 150 kg of oil [Cp = 2.5 kJ kg-1 K-1] at 250C. If there are no heat losses, what is change in entropy of (i) the casting, (ii) the oil and (iii) both considered together. (8+8)

7.a) b)

8.a) b)

What modifications are made in the Carnot refrigerator in devising a technically feasible vapor-compression refrigerator? A house has a winter heating requirement of 30kJ/s and a summer cooling requirement of 60 kJ/s. Consider a heat pump installation to maintain the house temperature of 200C in winter and 250C in summer. This requires circulation of the refrigerant through interior exchanger coils at 300C in winter and 50C in summer. Underground coils provide the heat source in winter and the heat sink in summer. For a year- round ground temperature of 150C, the heat-transfer characteristics of the coils necessitate refrigerant temperatures of 100C in winter and 250C in summer. What are the minimum power requirements for winter heating and summer cooling? (6+10) Prove that A particular thermodynamic system has the following fundamental relation U= CS2/VN, where C is a constant. Transform the given fundamental relation into the enthalpy representation. (6+10) *******

Code.No: 44064

R07

SET-3

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD II B.TECH II SEM SUPPLEMENTARY EXAMINATIONS FEBRUARY - 2010 CHEMICAL ENGINEERING THERMODYNAMICS – I (CHEMICAL ENGINEERING) Time: 3hours Max.Marks:80 Answer any FIVE questions All questions carry equal marks --1.a)

b) 2.a) b)

3.

4.

5.a) b) c)

The turbines in a hydroelectric plant are fed by water falling from a 40 m height. Assuming 93% efficiency for conversion of potential to electrical energy and 9% loss of the resulting power in transmission, what is the mass flow rate of water required to a power a 150 watt light bulb? What you understand about force, energy, pressure and temperature? (8+8) What is the difference between the Continuity equation and the Bernoulli’s equation? One Kg of water at 30 0C and 100 KPa are continuously heated in the open atmosphere till it is completely evaporated. Determine the heat and work interactions. Data: At 30 0C: Sp. Vol. of water = 0.001004 m3/Kg. Sp. Vol. of water vapor = 1.6949 m3/Kg. Heat content of vapor and water liquid are 2675.47 and 125.6 KJ/Kg respectively. (6+10) Gas leaving a fermenter at close to atmospheric pressure and 25 0C has the following composition Nitrogen: 78.2% Oxygen: 19.2% Carbon dioxide: 2.6%. Calculate a) The mass composition of fermenter off gases. b) The mass of carbon dioxide in each cubic meter of the gas leaving the fermenter using Vander Waals equation of state with the following coefficients. a=363.077KNm4/Kmole, b=0.043m3/Kmole. (16) Explain briefly a) Throttling b) Converging/diverging nozzles c) Sonic and subsonic flow pipe

(4+6+6)

What is Carnot principle? A cyclic heat engine operates between a source temperature of 7500C and a sink temperature of 280oC. What is the least rate of rejection per KW net output of engine? Explain briefly second law of thermodynamics (4+6+6)

6.a)

b)

Show whether or not the following process is possible: Air at 7x105 N/m2 and 20oC enters an apparatus which is well insulated from the surroundings. One half the air issues from the apparatus at 27oC and the other half at -40oC, both at 1x105 N/m2. No work is done on or by the apparatus and exit steams have the same composition as the entering air. Take Cp constant at 7 and assume air to be an ideal gas. Write short notes on entropy from microscopic view point. (8+8)

7.a) b)

What are the common methods used for Refrigeration? Explain briefly A refrigeration system requires 1.5 kW of power for a refrigeration rate of 4kJ/s. (i) What is the coefficient of performance? (ii) How much heat is rejected in the condenser? (iii) If heat rejection is at 400C, what is the lowest temperature the system can possibly maintain? (8+8)

8.a)

A lump of 1000 kg steel at 1180 K is to be cooled to 398 K. If it is desired to use the steel as a source of energy, calculate the available energy and unavailable energy. The ambient temperature is 301 K and the specific heat capacity of steel is 0.5 kJ kg-1K-1.

b)

Show that

(10+6) *******

R07

Code.No: 44064

SET-4

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD II B.TECH II SEM SUPPLEMENTARY EXAMINATIONS FEBRUARY - 2010 CHEMICAL ENGINEERING THERMODYNAMICS – I (CHEMICAL ENGINEERING) Time: 3hours Max.Marks:80 Answer any FIVE questions All questions carry equal marks --1.a) b)

Discuss open U-tube manometer indicating gauge pressure. The pressure of a gas in a pipe line is measured with a mercury manometer having one limb open to the atmosphere. If the difference in the height of mercury in the two limbs is 650 mm, calculate the gas pressure. The barometer reads 760 mm Hg, the acceleration due to gravity is 9.79 m/s2, and the density of mercury is 13460 Kg/m3. (8+8)

2.a)

A lean and thin man, who can lift a body of mass 100 Kg where g= 9.81 m/s2, claims that he can lift a body of mass 150 Kg. his friend did not agree and both went in to a bet. They go high in space to a H, height where the lean and thin man lifts the body of mass 150 Kg. If ‘g’ decreases at the rate 0.01 cm/s2 per 1000 m of ascent, what is the value of H? Differentiate between closed system and isolated system giving proper explanations. (10+6)

b) 3.

Hydrogen gas is contained in two constant volume vessels, each having a capacity of 500litres. The pressure and temperature in vessel A are 5 bar and 300K respectively, while in vessel B the values are 1.7bar and 310K. A valve connects the two vessels. The valve is now opened and the system is allowed to reach thermal equilibrium with the surroundings. If the surrounding temperature is 290K. What is the final pressure in the vessel? (16)

4.a)

Show that the critical pressure ratio reached at the throat of the converging-diverging ( ( r / ( r -1) )

b)

⎛ P2 ⎞ ⎛ 2 ⎞ nozzle is: ⎜ ⎟ = ⎜ ⎟ ⎝ P1 ⎠ ⎝ r + 1 ⎠ Write short notes on expanders.

(10+6)

5.a) b)

Derive the expression for the efficiency of the heat engine. A reversible heat engine interacts with four reservoirs at 1000 K, 600 K, 400 K and 300K. It absorbs 2000 kJ energy as heat from the reservoir at 1000K, rejects 600 kJ energy as heat to the reservoir at 300 K and delivers 1200 kJ work. Determine the energy interaction with the other two reservoirs. (10+6)

6.a) b)

What is entropy and explain briefly with the examples 1.8 kgs of oxygen at 480c are mixed with 6.2 kgs of nitrogen at the same temperature. Both oxygen and nitrogen are at pressure of 102 kpa before and after mixing. Find the increase in entropy? (8+8)

7.a) b)

8.a) b)

Write and explain various ways to achieve low temperature? An industrial unit wishes to install a refrigeration unit based on Carnot cycle with plant capacity of 10 tons. The refrigeration unit employs water as refrigerant. The temperature in the evaporator and condenser are 20C and 250C, respectively. Compute the C.O.P and circulation rate. Assume heat capacity of water as 4.18 J/gm K. (8+8)

⎛ ∂V ⎞ Prove TdS = C p dT − T ⎜ ⎟ dP ⎝ ∂T ⎠ P Define availability and the does the availability depends upon the conditions of system and surroundings (8+8) *******