Thermodynamics compressor Question

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SUMMARY

The discussion centers on a thermodynamics problem involving a compressor where air enters at 14.7 psi and 70°F with a volumetric flow rate of 500 ft³/min. The exit pressure is 120 psi, and the process follows the relationship pv1.34 = constant. Participants are tasked with calculating the exit temperature in Fahrenheit, the diameter of the exit pipe in inches, and the isentropic efficiency of the compressor. Key insights include the necessity of demonstrating work for effective assistance and understanding the relationships between temperature and pressure in a polytropic process.

PREREQUISITES
  • Understanding of polytropic processes in thermodynamics
  • Familiarity with the ideal gas law
  • Knowledge of isentropic efficiency calculations
  • Basic skills in fluid dynamics, particularly mass flow rate
NEXT STEPS
  • Calculate the exit temperature using the polytropic process equation
  • Determine the diameter of the exit pipe based on flow rate and velocity
  • Analyze the isentropic efficiency of the compressor using relevant formulas
  • Explore the relationship between temperature and pressure in ideal gas processes
USEFUL FOR

Students studying thermodynamics, engineers working with compressors, and anyone involved in fluid dynamics or energy systems analysis will benefit from this discussion.

Jason Brooks
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Homework Statement



Air enters a compressor operating at a steady state with a pressure of 14.7 psi, a temperature of 70 F , and a volumetric flow rate of 500 ft^3/min. The air velocity in the exit pipe is 700ft/s and the exit pressure is 120 psi. If each unit mass of air passing from the inlet to the exit undergoes a process described by pv^1.34= constant determine the exit temperature on F and the diameter of the exit pipe in inches. What is the isentropic efficiency of the compressor?


Homework Equations





The Attempt at a Solution

 
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Jason, Welcome to the PF, but do NOT post multiple threads with the same question in other forums. I've deleted the two other copies of this question, and left this one here in the homework forum where it belongs. You are also receiving a warning via the PF warning system.

You also need to show your work so far in order for us to help you (PF rules).
 
I moved this thread to the Intro Physics homework forum where it will probably get more looks. Jason -- you still need to post some work for us to help you.
 
Part 1: What can you say about relationships between temperature and pressure in a polytropic process for an ideal gas?

Part 2: What can you say about the mass flow rate of air entering and leaving the compressor?
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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