Problem specification
5 kg of air is contained in the piston-cylinder device, initially at pressure of 2MPa and a specific volume of 0.08m^{3}/kg. The air then expands, as an ideal gas, through a polytropic process, with variable values of n, to a final specific volume of 0.30m^{3/}kg.
Objective:
prepare the MATLAB code to solve for pressure and temperature variation throughout the expansion process and to find out work and heat produced in processes for variable values of n.
Procedure:
1) Begin by defining the temperature at the initial state and then define the temperature and pressure at the final state. Sketch rough graph of what the process looks like on P-v coordinates. prepare out by hand the equations and steps you would take to determine the actual P, T, and v at all points along the process. Identify unknowns, equations, constants, and calculation orders.
2) Using your hand calculations as guide, prepare the simple MATLAB m-file to find out properties at points along the process (minimum of 20 points, but must be a variable which can be changed) using one of the values of n (I recommend using n=1.5). Plot P-v and T-v diagrams for the process using MATLAB.
3) find out work performed for process by integrating the curve of pressure versus specific volume. Use the “trapezoidal area method” for calculating integral.
4) Assume that specific internal energy for the air in this problem can be defined as the function of temperature as follows:
u(T)=(1.0344∗10^{−4})∗T^{2}+(6.4476∗10^{−1})∗T+(1.3727∗10^{2})
Add code to your MATLAB program to find out the specific internal energy for process using the information of the pressure and specific volume at each state.
5) Using conservation of energy and the work find outd, determine amount of heat transferred for each process.
6) prepare the loop in the code to analyze the different values of n, or run the code for the different values of n asked for below.
Deliverables
1) MATLAB code (m-file) that find outs the state variables P, v, T, and u for the defined process, and that find outs the work and heat for each process.
2) On the same graph, plot of P-v for this process with 4 different values of n: 1, 1.4, 1.5, 1.8.
3) Plot of P-v and T-v for n=1.5 on a single graph. Use the function plotyy.
5) Table summarizing results of work and heat as a function of n.
6) A brief paragraph detailing what you learned in this exercise and how useful you think these skills will be for your future as an engineer.