BE - SEMESTER-IV(NEW) — EXAMINATION - SUMMER 2019
Subject Code:2143406 Date:09/05/2019
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Subject Name: Thermo Dynamics and Thermal Engineering
Time:02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Show that internal energy is Property of the system. 03
(b) Write and explain the First Law of Thermodynamics. 04
(c) A fluid system, contained in a piston and cylinder machine, passes through a 07 complete cycle of four processes. The sum of all heat transferred during a cycle is — 340 kJ. The system completes 200 cycles per min.
Complete the following table showing the method for each item, and compute the net rate of work output in kW.
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| Process | Q(KJ/min) | W(KJ/min) | dU(KJ/min) |
|---|---|---|---|
| 1-2 | 0 | 4340 | 0 |
| 2-3 | 42000 | 0 | |
| 3-4 | -4200 | -73200 |
Q.2 (a) Write a short note on Brayton cycle. 03
(b) Write a short note on modified Rankine cycle, 04
(c) Explain Rankine cycle with p-v and T — s diagram and find the efficiency of Rankine cycle. 07
OR
(c) The power developed by a turbine in a certain steam plant is 1200 kW. The heat supplied to the steam in the boiler is 3360 kJ/kg, the heat rejected by the system to cooling water in the condenser is 2520 kJ/kg and the feed pump work required to pump the condensate back into the boiler is 6 kW. 07
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Q.3 (a) Define Effectiveness. 03
(b) One kg of air is compressed polytropically from 1 bar pressure and a temperature of 300 K to a pressure of 6.8 bar and temperature of 370 K. Determine the irreversibility if the sink temperature is 293 K. Assume R = 0.287 kJ/kg K, cp=1.004 kJ/kg K and cv =0.716 kJ/kg K. 04
(c) Derive and Explain Clausius-Claperyon Equation with p-T Diagram 07
OR
Q.3 (a) Define and explain Available and Unavailable Energy 03
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(b) 15 kg of water is heated in an insulated tank by a churning process from 300 K to 340 K. If the surrounding temperature is 300 K, find the loss in availability for the process. 04
(c) Derive Maxwell’s equation 07
Q.4 (a) State and explain Dalton’s law 03
(b) A vessel of 0.35 m3 capacity contains 0.4 kg of carbon monoxide (molecular weight = 28) and 1 kg of air at 20°C. Calculate : 04
- The partial pressure of each constituent
- The total pressure in the vessel, and
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The gravimetric analysis of air is to be taken as 23.3% oxygen (molecular weight = 32) and 76.7% nitrogen (molecular weight = 28).
(c) Prove the following relation: M = S(niMi) 07
where,
ni = Number of moles of an any constituent,
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mi = Mass fraction of the constituent, and
Mi = Molecular weight of the constituent.
OR
Q.4 (a) Show that Cp = ?R/(?-1) 03
(b) Write a short note on Compressibility chart 04
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(c) 4 kg of carbon dioxide at 40°C and 1.4 bar are mixed with 8 kg of nitrogen at 160°C and 1.0 bar to form a mixture at a final pressure of 0.7 bar. The process occurs adiabatically in a steady flow apparatus. Calculate : 07
- The final temperature of the mixture ;
- The change in entropy.
Take value of Cp : for CO2 = 0.85 kJ/kg K and N2 = 1.04 kJ/kg K.
Q.5 (a) A hot plate 1 m x 1.5 m is maintained at 300°C. Air at 25°C blows over the plate. If the convective heat transfer coefficient is 20 W/m2°C, calculate the rate of heat transfer. 03
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(b) Write a short note on Thermal Conductivity 04
(c) The effective temperature of a body having an area of 0.12 m2 is 527°C. Calculate the following : (i) The total rate of energy emission. (ii) The intensity of normal radiation, and (iii) The wavelength of maximum monochromatic emissive power. Take s = 5.67 x 10-8 W/m2K4 07
OR
Q.5 (a) Define black body, white body & gray body. 03
(b) The inner surface of a plane brick wall is at 60°C and the outer surface is at 35°C. Calculate the rate of heat transfer per m2 of surface area of the wall, which is 220 mm thick. The thermal conductivity of the brick is 0.51 W/m°C. 04
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(c) A reactor’s wall 320 mm thick, is made up of an inner layer of fire brick (k= 0.84 W/m°C) covered with a layer of insulation (k =0.16 W/m°C). The reactor operates at a temperature of 1325°C and the ambient temperature is 25°C. (i) Determine the thickness of fire brick and insulation, which gives minimum heat loss. (ii) Calculate the heat loss presuming that the insulating material has a maximum temperature of 1200°C. 07
If the calculated heat loss is not acceptable, then state whether addition of another layer of insulation would provide a satisfactory solution.
Fire brick
Insulation
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