Brayton cycle

Question 1

What are the numbered stages of a closed Brayton cycle

Answer 1

Stage 1: After the condenser Stage 2: After the compressor Stage 3: After the heat exchanger Stage 4: After the turbine

Question 2

Explain the steady flow energy equation

Answer 2

SFEE is used for open systems like an open cycle gas turbine.

Question 3

what does ṁ stand for

Answer 3

ṁ = mass flow rate

Question 4

What is the difference between W and Ẇ in thermodynamics?

Answer 4

W = Work done (energy)

Ẇ = rate of work done (power)

Question 5

What is the difference between Q, q and Q̇?

Answer 5

Q is a quantity of heat (measured in kj)

q is heat per unit of mass (measured in kj/kg)

Q̇ is rate of heat flow (measured in kj/s)

Question 6

What is an isothermal process. Give examples

Answer 6

An isothermal process takes place at a constant temperature. This normal means phase change processes such as evaporation condensation, melting, and freezing

Question 7

What is an idiabatic process

Answer 7

this is a process where energy is not lost from or gained to the system but the form may be changed. Examples include phase change.

Question 8

What is the difference betwee absolute pressure (P) and relative pressure (Pr) of a gas.

Answer 8

Absolute pressure is the force exterted by a gas.

Relative pressure is not really pressure but is a function of temperature. Pr a dimensionless number calculated as the ratio of a gas at standard temperature and a gas at 0ºC. Hence a gas at a given temperature will have the same relative pressure regardless of what the actual pressure is.Gases below 0ºC have Pr values below 1 and gases above 0 have Pr values above 1.

In a compression process the Pr₂ value = P₂/P₁*P_r1. By multiplying the relative pressure at stage one of the cycle by the compression ration you can calculate the relative pressure at the second stage of the cycle from which you can find the temperature in the ideal gas table.