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Hot combustion gases enter the nozzle of a turbojet engine at 250 kPa, 650°C, and 70 m/s and exit at 80 kPa and 420°C. The mass flow rate is 1.2 kg/s. Assume the heat losses to the surroundings is 90kW and the surroundings is at 27°C. Determine (a) the exit velocity and (b) the decrease in the exergy of the gases. Take k = 1.3 and c, = 1.15 kJ/kg-C for the combustion gases. Qless = 90kW 250 kPa 80 kPa Combustion gases 650°C 420°C 70 m/s m = 1.2 kg/s m = 1.2 kg/s

Hot combustion gases enter the nozzle of a turbojet engine at 250 kPa, 650°C, and 70 m/s and exit at 80 kPa and 420°C. The mass flow rate is 1.2 kg/s. Assume the heat losses to the surroundings is 90kW and the surroundings is at 27°C. Determine (a) the exit velocity and (b) the decrease in the exergy of the gases. Take k = 1.3 and c, = 1.15 kJ/kg-C for the combustion gases. Qless = 90kW 250 kPa 80 kPa Combustion gases 650°C 420°C 70 m/s m = 1.2 kg/s m = 1.2 kg/s

Introduction to Chemical Engineering Thermodynamics
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Hot combustion gases enter the nozzle of a turbojet engine at 250 kPa, 650°C, and 70 m/s and exit at 80 kPa and 420°C. The mass flow rate is 1.2 kg/s. Assume the heat losses to the surroundings is 90kW and the surroundings is at 27°C. Determine (a) the exit velocity and (b) the decrease in the exergy of the gases. Take k = 1.3 and c, = 1.15 kJ/kg-C for the combustion gases. Qless = 90kW 250 kPa 80 kPa Combustion gases 650°C 420°C 70 m/s m = 1.2 kg/s m = 1.2 kg/s
Transcribed Image Text:Hot combustion gases enter the nozzle of a turbojet engine at 250 kPa, 650°C, and 70 m/s and exit at 80 kPa and 420°C. The mass flow rate is 1.2 kg/s. Assume the heat losses to the surroundings is 90kW and the surroundings is at 27°C. Determine (a) the exit velocity and (b) the decrease in the exergy of the gases. Take k = 1.3 and c, = 1.15 kJ/kg-C for the combustion gases. Qless = 90kW 250 kPa 80 kPa Combustion gases 650°C 420°C 70 m/s m = 1.2 kg/s m = 1.2 kg/s
Expert Solution
Step 1

Given nozzel

Chemical Engineering homework question answer, step 1, image 1

At inlet

  • T1=650 C
  • P1=250 kPa
  • V1=70m/s

At exit

  • T2=420 C
  • P2=80 kPa

Data

  • m=1.2 kg/s
  • Heat loss Q=90kW
  • Surrounding temperature=27C
  • Cp=1.15 kJ/(kg C)
  • k=1.3

Find

  1. Exit velocity
  2. Decrease in exergy

 

 

 

Step 2

Specific heat at constant volume

Chemical Engineering homework question answer, step 2, image 1

WHere,

  • Specific heat at constant pressure Cp=1.15kJ/kgC
  • Specific heat ratio =1.3

Gas constant is

Chemical Engineering homework question answer, step 2, image 2

a)

Make the energy balance for a steady flow system

Chemical Engineering homework question answer, step 2, image 3

Chemical Engineering homework question answer, step 2, image 4

Chemical Engineering homework question answer, step 2, image 5

  • Temperature at the inlet T1=650C
  • The temperature at the exit T2=420C
  • Velocity at the inlet V1=70m/s

Chemical Engineering homework question answer, step 2, image 6

Exit velocity V2=619.597 m/s

 

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