Question

Thermodynamics

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 network for the simple Brayton cycle and makes T = 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: 112-11 d. Explain the effect of subcooling and superheating on the refrigeration effect. Explain with the aid of a P-h diagram. e. Converging diverging nozzles are used to accelerate gases to supersonic speeds. Explain briefly how supersonic speed is achieved. What is the Mach Number at the throat? I

Answer 1

The sub cooli cooling reduces the flashing of the liquid during expansion expansion andinere and increases the r refring erating effect ( from Chin ha) to Chi ha) without super heating). so if both super heating and subcooling are there then refrigerating effect increases more i.e. from Chi ha ) to the ha). e) see the attached figure. when PEY Pb yo Po = Back Pressure the flow in the diverging PE = Prem wor at the exit plane as shown in section is supersonic and the fhund expands without normal shock within the nozzle. The Mach no (Ma) ent the throat is 1. the figure.

Throat Po IP V, 0) PA Po PA B A) Subsonic flow PB at nozzle exit ci (no shock) Pc D P* Subsonic flow PD at nozzle exit (shock in nozzle) Sonic flow at throat IPE 1 1 1 Shock E, EGIPO IPE Supersonic flow at nozzle exit (no shock in nozzle) in nozzle 0 Inlet Throat Exit Ma 1 Shock in nozzle Sonic flow! at throat E, F, G Supersonic flow at nozzle exit (no shock in nozzle) DI Subsonic flow at nozzle exit (shock in nozzle) Subsonic flow at nozzle exit (no shock) B 0 Inlet Throat Exit