# Tutor profile: Teresa B.

## Questions

### Subject: Basic Math

What is pi, and where does it come from?

Pi, which is approximately 3.14, is a very interesting number! If you take a string of length equal to the diameter of a circle, and try to use this string to go around the circumference of said circle, it will take pi times that string to go around!

### Subject: Mechanical Engineering

Why is the temperature of saturated water constant during a constant pressure heat addition process, assuming that the water remains in the saturation region during this process?

The temperature remains constant because this heat that is being transferred *to* our system (at constant pressure) is simply causing phase change from saturated liquid to saturated vapor, without changing the temperature!

### Subject: Aerospace Engineering

Let us analyze an ideal Brayton cycle, assuming it is a closed cycle and we are reusing the same substance going into our compressor, heat exchangers, and turbine. What is the thermal efficiency for this Brayton cycle in terms of rate of energy transfer?

The thermal efficiency for an ideal, closed Brayton cycle is the net power of the cycle divided by the rate of heat transfer going into the cycle. Therefore, the thermal efficiency is equal to the power of the turbine minus the power required by the compressor, and then this number divided by the rate of heat transfer going into the heat exchanger that follows the compressor.