A turbofan engine is being designed for a bypass ratio of 6:1. During cruise (M=0.85) at 12,000 km, the ratio of the exit stagnation pressure to ambient pressure po/p„ is 1.6:1 (the same for the fan as for the core engine). The stagnation temperature at exit from the core engine is 600 K; at exit from the fan it is only 340 K. The question is whether: a. The fan and core streams should expand in separate nozzles to ambient pressure, or b. They should first be mixed to uniform stagnation temperature, then expanded in a single nozzle. Determine the rats of thrusts (case a to case b) on the understanding that mixing of the two streams can be done with no loss in stagnation pressure. For simplicity, assume that the specific heat ratio and the gas constant are the same for both streams and that y = 1.4 and R = 0.287 The fuel-air ratio for the core engine is approximately 0.018, and nozzle losses are negligible.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?