ME-601 Thermal Engineering and Gas Dynamics - May 2023 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 high pressure boiler 'Lamont' with neat sketch.
   How to answer

   • Definition and principle of Lamont high pressure forced-circulation boiler
   • Main components and circulation path
   • Working steps
   • Neat labelled sketch
   • Advantages / applications
2. 7 Marks
   bExplain with diagram the effect of boiler and condenser pressure on the efficiency of ranking cycle.
   How to answer

   • Rankine cycle T-s / h-s representation
   • Effect of increasing boiler pressure on efficiency and moisture
   • Effect of lowering condenser pressure on efficiency and work
   • Illustrative diagrams
   • Practical limits
3. 7 Marks
   aExplain three boiler mountings and accessories.
   How to answer

   • Distinction between mountings vs accessories
   • Three mountings with function
   • Three accessories with function
   • Location / sketches if needed
4. 7 Marks
   bA vessel of volume $0.04\, \text{m}^3$ contains a mixture of saturated water and saturated steam at a temperature of $250^{\circ}\text{C}$ The mass of the liquid present is $9\, \text{kg}$. Find the pressure, the mass, the specific volume, the enthalpy, the entropy, and the internal energy.
   How to answer

   • Saturation pressure at $250^{\circ}C$ from steam tables
   • Specific volumes $v_f, v_g$ and vessel specific volume
   • Dryness fraction and total mass
   • Specific enthalpy, entropy, internal energy $h, s, u$
   • Total values by mass
5. 14 Marks
   A two-stage air compressor with perfect intercooling takes in air at $1\, \text{bar}$ pressure and $27^{\circ}\text{C}$. The law of compression in both the stages is $pv^{1.3} = \text{constant}$, the compressed air is delivered at $9\, \text{bar}$ from the H.P. cylinder to an air receiver. Calculate, per kilogram of air,

   1. i)the minimum work done
   2. ii)the heat rejected to the intercooler
   How to answer

   • Intercooler pressure for minimum work with perfect intercooling
   • Work formula for two-stage polytropic compression
   • Heat rejected = $c_p$ times temperature difference in intercooler
   • Numerical substitution per kg of air
6. 14 Marks
   A steam power station uses the following cycle: Steam at boiler outlet - $150\, \text{bar}$, $550^{\circ}\text{C}$ Reheat at $40\, \text{bar}$ to $550^{\circ}\text{C}$ Condenser at $0.1\, \text{bar}$. Using the Mollier chart and assuming ideal processes, find the

   1. a)Quality at turbine exhaust
   2. b)Cycle efficiency
   3. c)Steam rate
   How to answer

   • Locate states on Mollier chart: 150 bar 550C, 40 bar reheat to 550C, 0.1 bar exhaust
   • Read enthalpies and dryness / quality at exhaust
   • Cycle efficiency = net work / heat supplied
   • Steam rate = 3600 / net work per kg
7. 7 Marks
   aExpress the overall efficiency of a steam plant as the product of boiler, turbine, generator and cycle efficiencies. https://www.rgpvonline.com
   How to answer

   • Define boiler, turbine, generator and cycle efficiencies
   • Overall efficiency as ratio of electrical output to fuel heat
   • Multiply component efficiencies
   • Final product expression
8. 7 Marks
   bDerive the conditions for maximum output of a using a reheater and regenerator in a gas turbine.
   How to answer

   • Gas turbine cycle with reheater and regenerator layout
   • Work output and heat input expressions
   • Optimization condition for pressure ratios
   • Condition for maximum output / minimum heat
9. 7 Marks
   aCalculate the velocity of sound in super-heated steam at a pressure of $4\, \text{bar}$ and temperature of $300^{\circ}\text{C}$. The specific volume of steam is $0.338\, \text{m}^3/\text{kg}$.
   How to answer

   • Formula for sound velocity in superheated steam $c = \sqrt{n p v}$
   • Value of adiabatic index for superheated steam
   • Substitute $p=4$ bar, $v=0.338$ m3/kg
   • Compute velocity in m/s
10. 7 Marks
    bDraw and explain vapor Carnot cycle what are its limitations.
    How to answer

    • T-s / p-v diagram of vapor Carnot cycle
    • Four processes: isothermal and isentropic
    • Why pump/compressor and turbine handle mixture
    • Limitations: moisture, work ratio, superheat difficulty
11. 7 Marks
    aExplain the effect of clearance on volumetric efficiency of compressor with diagram.
    How to answer

    • p-V diagram with clearance volume
    • Volumetric efficiency formula $\eta_v = 1 + C - C r^{1/n}$
    • Effect of increasing clearance and pressure ratio
    • Illustrative diagram
12. 7 Marks
    bDerive the condition for minimum work done in a multistage compressor.
    How to answer

    • Total work expression for multistage compression
    • Perfect intercooling assumption
    • Differentiate with respect to intermediate pressure
    • Condition: pressure ratio per stage equal
13. 7 Marks
    aDerive the conditions for maximum discharge in nozzles.
    How to answer

    • Mass flow rate through nozzle as function of pressure ratio
    • Condition d(m)/d(p)=0 for maximum discharge
    • Critical pressure ratio formula
    • Value for steam/air
14. 7 Marks
    bDefine the following terms related to compressor.

    1. i)Isentropic efficiency
    2. ii)Isothermal efficiency
    3. iii)Mechanical efficiency.
    How to answer

    • Definition of isentropic efficiency
    • Definition of isothermal efficiency
    • Definition of mechanical efficiency
    • Formulas in terms of work/power