Question

Problem 1 (30 pts): a. Differentiate between the higher and lower heating values of fuels. Explain with the aid of an equation. b. Assume steady-flow, no heat transfer, no work, one entrance, and one exit and neglect elevation changes. Show that the stagnation enthalpy is constant throughout a nozzle. c. Recall that the pressure ratio that maximizes the net work for the simple Brayton cycle and makes Ta = T2. What happens if the regenerative Brayton cycle operates at a pressure ratio larger than this ratio? The pressure ratio that maximizes the net work is given by: 4,121-12 HT

Answer 1

Solution @ Highes, and lawer heating values of fuels The numerical difference between the LHV and HHV of a fuel is roughly earuivalent to the amount of latent heat of vaporization The numerical value of HHW is always greater than or arnal to the LHV. 6 flow through nozzle Steady flow Energy Eruations FD hi +1 q² + gz, tal cu = hz +26² +9 zz=Wkw Nov = Wew=0 & Z=22 hitta2 = hat £6² Where ho- Stagnation enthalty WN = t(1)-((-1) COTI where & H=C t = 3 for any given value oft, there must be an obtimum pressure ratio to give a maximum specific output. This can be found by differentiating the ann with respect toC and earuating it to zero noi o P2=8 Pi

Sopt Saluaring bath sides t= (87) VK or 8= Eu llence proved Effect of subcooling and superheating on the refrigeration effect Superheat occurs when the rapor is heated above gits boiling point Super keat = Current Temperature - Bolling point Subcooling is when that livuil is cooled below the temperature at which it turns into a linvuod Subcooling = Boiling point - Cussent Temperature Effect Super Reating Effect of subcooling R It is used to accelerate a hot, pressurized gas passing Righer supersonic Speed in the axial derest 72 어 1 41 h through it to a by converting the heat energy of the show in to kinetic energy