1. COMPRESSIBLE FLOW IN NOZZLES Alberto L. Pérez Dávila Est. # 60423 Thermal Engineering Laboratory WI-15-ME4111-35 Prof. Eduardo Cabrera February -13-2016

2. Outline Objectives Main Concept of Experiment Equipment Description Experimental Procedures Examples of Calculation

3. OBJECTIVE The purpose of this experiment is the behavior characterization of compressible flow through a nozzles.

4. Main Concept of Experiment Visual demonstration of nozzle choking Visual demonstration of under expansion and over expansion with re-compression(shock wave).. Investigation of the relationship between inlet pressure and mass flow rate. Investigation of the relationship between outlet pressure and mass flow rate for:- A convergent nozzle, and convergent-divergent nozzle. Investigation of the pressure distribution in convergent and convergent-divergent nozzles over a variety of overall pressure ratios.

5. F810 Nozzle Pressure Distribution Unit

7. F810 Nozzle Pressure Distribution Unit (Cont.)

8. EXPERIMENTAL PROCEDURES

9. Steps to change a Nozzle 1)Close the air inlet valve. 2)Unscrew all the knurled unions on the nozzle. 3)Remove the nozzle and place it in the box provided. 4)Select another nozzle and ensure that the '0' rings are in place. 5)Fit the nozzle in position and loosely connect the knurled unions. 6)Starting at No.1 tapping, connect the No.1 flexible tube to the nozzle body and firmly tighten the small knurled union. 7)Make all the remaining connections in order - rotating the nozzle as needed. 8)Push any unused connections back into the panel. 9)Lighten the large knurled unions. 10)Display the appropriate nozzle profile on the panel. NOTE: No tools are necessary for the above.

10. Visual demonstration of the phenomenon of choking Choked flow is a limiting condition which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed. Assuming ideal gas behavior, steady-state choked flow occurs when downstream pressure falls below a critical value. That critical value can be calculated from the dimensionless critical pressure ratio equation where is the heat capacity ratio of the gas (also called the adiabatic index, also sometimes denoted ) and is the upstream pressure.heat capacity ratioadiabatic index When the gas velocity is choked, the equation for the mass flow rate in SI metric units is:mass flow rate

11. Visual demonstration of the phenomenon of choking

12. k=1.4 R=287.1 J/kg K T=293K

13. Visual demonstration of the phenomenon of choking Critical Pressure Equation Po=700kPa K=1.4 For constant pressure of 700kPa the critical pressure or the pressure where the choke occur is 369.80kPa. This pressure is pretty import because at this point star a lot of change in the graphic pattern.

14. Visual demonstration of the pressure distribution in nozzles which are over and under expanding

15. Over expanded Under expanded

16. Demonstration of the effect of backpressure on the position of the shock and recompression in convergent-divergent nozzles  The position (x) of the shock wave and recompression changes when the pressure ratio (Po/Pi) changes (Po/Pi < [Po/Pi]chocked).  Plot Po/Pi Versus x (mm)

17. Demonstration of the effect of backpressure on the position of the shock and recompression in convergent-divergent nozzles

18. Demonstration of the effect of inlet pressure on the mass flow rate with constant backpressure  The objective is to demonstrate that the mass flow rate in an ideal nozzle varies similarly to the equation 4.3  After the experiment plot mdot versus Pi for calculated values and for the measured values.

19. Demonstration of the effect of inlet pressure on the mass flow rate with constant backpressure Theoretical and Actual Mass Flow Rate

20. Determine the pressure distribution in nozzles  The objective of this task is to demonstrate that the pressure distribution in nozzles follow an isentropic behavior with the added effect of the shock waves.  Plot Px/Pi versus position x, mm to nozzle A & C

21. Determine the pressure distribution in nozzle A

22. Determine the pressure distribution in nozzle C

23. Questions?