Sardar Vallabhbhai National Institute of Technology 2012 B.Tech Mechanical Engineering Thermodynamics - Question Paper
Thermodynamics paper at end sem examination of SVNIT
Total Marks 50
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY, SURAT DEPARTMENT OF MECHANICAL ENGINEERING IV SEMESTER B TECH (ENDSEM EXAMINATION) 2011- 12
Thermodynamics
Q.l a) What are intensive and extensive properties?
b) What is a quasi- static process? What is its characteristics feature?
c) Which is the property introduced by the first law of thermodynamics? Can you show that it is a point function?
d) What are the different solid, liquid and gaseous fuels used in industry? Also mention calorific values
e) How ultimate analysis of fuel is different than proximate analysis
Q.2 a) A domestic refrigerator is loaded with food and the door is closed. During a certain period the machine consumes 1 kW h of energy and the internal energy of the system drops by 5000 kJ. Find the net heat transfer for the system.
b) At the inlet to a certain nozzle the enthalpy of fluid passing is 2800 kJ/kg and the velocity is 50 m/s. At the discharge end the enthalpy is 2600 kJ/kg. The nozzle is horizontal and there is negligible heat loss from it.
(i) Find the velocity at exit of nozzle
(ii) if the inlet area is 900 cm and specific volume at inlet is 0.187 m /kg, find the mass flow rate
(iii) If the specific volume at the nozzle exit is 0.498 m3/kg, find the exit area of nozzle.
Q.3 a)
What amount of heat would be required to produce 4.4 kg of steam at a pressure of 6 bar and temperature of 250 C from water at 30 0 C? Take Cp for superheated steam as = 2.25 kJ/kg K.
(b) Two boilers one with superheater and other without superheater are delivering equal quantities of steam into a common main. The pressure in the boilers and main is 20 bar. The temperature from a boiler with a superheater is 350 0 C and temperature of steam in the main is 250 0 C. Determine the quality of steam supplied by the other boiler. Take Cp = 2.25 kJ/kg K.
Q.4 Attempt any Two [6]
(i) Differentiate between a heat engine, heat pump and refrigerator with simple schematic and expression for efficiency / COP.
(ii) List the causes of irreversibility. *
(iii) Differentiate between the first law and second law of thermodynamics.
(iv) Explain Clausius inequality.
Q.5 A reversible engine, as shown in Fig. 1 during a cycle of operations draws 5 MJ from the [6] 400 K reservoir and does 840 KJ of work. Find the amount and direction of heat interaction with other reservoirs.
400 K
300 K
Qi
03
W* 840 kJ
OR _ ___--
Q.5 (a) An aluminum block (cp = 400 J/kg K) with a mass of 5 kg is initially at 40C in room air [6] at 20C. It is cooled reversible by transferring heat to a completely reversible cyclic heat engine until the block reaches 20C. The 20C room air serves as a constant temperature sink for the engine. Compute (i) the change in entropy for the block (ii) the change in entropy for the room air (iii) the work done by the engine.
Q.6 Two reversible heat engines A and B are arranged in series, A rejecting heat directly to B. [6] Engine A receives 200 kJ at a temperature of 421 C from a hot source, while engine B is in communication with a cold sink at t temperature of 4.4C. If the work output of A is twice that of B, find (a) the intermediate temperature between A and B, (b) the efficiency of each engine and (c) the heat rejected to the cold sink.
OR
Q.6 A heat pump is to be used to heat a house in winter and then reversed to cool the house in [6] summer. The interior temperature is to be maintained at 20C. Heat transfer through the walls and roof is estimated to be 0.525 kJ/s per degree temperature difference between the inside and outside. If the outside temperature is winter is 5C, what is the minimum power required to drive the heat pump?
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