ME-601 Thermal Engineering and Gas Dynamics - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDescribe with a neat sketch the working of "Loeffler boiler".
   How to answer

   • Definition and type of Loeffler boiler - forced circulation, high pressure water-tube boiler
   • Neat labelled sketch showing economiser, evaporating drum, superheater, Loeffler pump, furnace
   • Working steps: feed heating, pumping saturated steam, evaporating tubes, superheating and circulation
   • Advantages / applications in power plant
2. 7 Marks
   bWhat are super critical boilers? Give their advantages.
   How to answer

   • Definition of supercritical boiler - pressure above critical pressure 221.2 bar
   • Principle: once-through, no drum, water directly to superheated steam
   • Main types / features
   • Advantages: higher efficiency, compact, quick start, less fuel consumption
3. 7 Marks
   aDraw a Carnot cycle and state the practical difficulties encountered in applying it to a power plant.
   How to answer

   • Draw Carnot cycle on p-V and T-s diagrams with four reversible processes
   • Brief description of isothermal and adiabatic processes
   • Practical difficulties: isothermal heat addition, isentropic compression of wet mixture, pump and turbine limitations
   • Conclusion why Carnot not used in power plant
4. 7 Marks
   bWhat is the effect of superheat on the efficiency of Rankine cycle?
   How to answer

   • Effect of increasing superheat temperature at same pressure on heat added and work
   • T-s / h-s representation of superheated Rankine cycle
   • Increase in mean temperature of heat addition and efficiency
   • Effect on turbine dryness, work and moisture problems
5. 14 Marks
   In a Rankine cycle, the steam inlet pressure is 30 bar and exhaust pressure is 0.20 bar. Determine : Assume flow rate of 15 kg/sec.

   1. i)Pump work
   2. ii)Turbine work
   3. iii)Turbine power
   4. iv)The cycle efficiency
   5. v)The condenser heat flow
   6. vi)Dryness at the end of expansion
   How to answer

   • Obtain steam properties at 30 bar and 0.20 bar from steam tables
   • Calculate pump work $w_p = v_f \Delta p$ and turbine work $w_t = h_1-h_2$
   • Calculate turbine power, heat supplied, cycle efficiency
   • Calculate condenser heat rejection and dryness $x_2$ at end of expansion
6. 7 Marks
   aWhat is a stagnation state? What do you mean by stagnation properties?
   How to answer

   • Definition of stagnation state - isentropically decelerated to zero velocity
   • Expressions for stagnation temperature, pressure and density
   • Meaning of stagnation properties and their use in compressible flow
   • Example / illustration
7. 7 Marks
   bFind the velocity of bullet fired in standard air if the Mach angle is $30^{\circ}$. Take $R = 287.14$ J/kg K and $k = 1.4$ for air. Assume temperature as $15^{\circ}C$.
   How to answer

   • Relation between Mach angle $\mu$ and Mach number $M = 1/\sin\mu$
   • Calculate speed of sound $a = \sqrt{kRT}$ at $15^{\circ}C$
   • Calculate Mach number from $30^{\circ}$ angle
   • Calculate bullet velocity $V = M \times a$
8. 7 Marks
   aWhat are rotary compressors? How are rotary compressor classified?
   How to answer

   • Definition of rotary compressors - positive displacement / dynamic type
   • Classification: roots blower, vane, screw, scroll, centrifugal, axial
   • Brief working of each type
   • Sketch / applications if needed
9. 7 Marks
   bDetermine the minimum work required to compress 1 kg of air from 1 bar and $20^{\circ}C$ to 18 bar in two stages, if the inter-cooling is perfect. The compression law process follows $PV^{1.35} = C$ and Take $R = 287$ J/kg K.
   How to answer

   • Condition for minimum work with perfect intercooling: pressure ratio per stage equal
   • Formula for two-stage polytropic work $W = 2n/(n-1) mRT_1[(p_2/p_1)^{(n-1)/2n}-1]$
   • Substitute $p_1=1$ bar, $p_2=18$ bar, $T_1=293$ K, $n=1.35$
   • Compute minimum work per kg
10. 14 Marks
    A single acting reciprocating air compressor has a cylinder diameter and stroke of 200 mm and 300 mm respectively. The compressor sucks air at 1 bar and $27^{\circ}C$ and delivers at 8 bar while running at 100 rpm. Find the following. The compression follow the law $PV^{1.25} = C$, Take R as 287 J/kg K.

    1. i)Indicated power of the compressor
    2. ii)Mass of air delivered by the compressor per minute
    3. iii)Temperature of air delivered by the compressor
    How to answer

    • Calculate swept volume from $D=200$ mm, $L=300$ mm and $N=100$ rpm
    • Indicated work per cycle using polytropic law $n=1.25$ and indicated power
    • Mass delivered per minute using $pV=mRT$
    • Delivery temperature $T_2 = T_1(r_p)^{(n-1)/n}$
11. 7 Marks
    aDiscuss the back pressure of steam condensers and its effect on power plant performance.
    How to answer

    • Definition of back pressure / condenser pressure
    • Effect of lowering back pressure on work, heat rate and efficiency
    • Limits: moisture, air leakage, cooling water temperature
    • Impact on power plant performance and capacity
12. 7 Marks
    bThe following observations were recorded during a test of steam condenser. Barometer reading = 760 mm of Hg Vacuum at steam inlet to condenser = 690 mm of Hg Hot well temperature = $32^{\circ}C$ Calculate the vacuum efficiency of the condenser.
    How to answer

    • Calculate absolute condenser pressure from barometer minus vacuum
    • Obtain saturation pressure at hot well temperature $32^{\circ}C$ from steam tables
    • Vacuum efficiency = actual vacuum / ideal vacuum
    • Substitute 760 mm Hg and 690 mm Hg values and compute
13. 14 Marks
    Write short notes on any three of the following.

    1. a)Cooling towers
    2. b)Ash handling of thermal power plant
    3. c)Mach number
    4. d)Steam nozzles
    How to answer

    • Select any three topics from given list
    • For each: definition, working principle / significance, neat sketch where applicable
    • Key equations / functions in power plant or gas dynamics
    • Advantages / applications