55 Cooling method for gas turbines. Refer to the Journal of Engineering for Gas Turbines and Power (Jan. 2005) study of a high-pressure inlet fogging method for a gas turbine engine, presented in Exercise 25 . Recall that you fit a firstorder model for heat rate ( y ) as a function of speed (x1), inlet temperature (x2), exhaust temperature (x3), cycle pressure ratio (x4), and air mass flow rate (x5) to data saved in the GASTURBINE file.

a. Researchers hypothesize that the linear relationship between heat rate ( y ) and temperature (both inlet and exhaust) depends on air mass flow rate. Write a model for heat rate that incorporates the researchers’

theories.

b. Use statistical software to fit the interaction model you wrote in part a to the data in the GASTURBINE file.

Give the least squares prediction equation.

c. Conduct a test (at a = .05 ) to determine whether inlet temperature and air mass flow rate interact to affect heat rate.

d. Conduct a test (at a = .05 ) to determine whether exhaust temperature and air mass flow rate interact to affect heat rate.

e. Interpret practically the results of the tests you conducted in parts c and d .