Constant Pressure Process of Air

Introduction:
In this problem, we are given that 2kg of air undergoes a constant pressure process. We need to determine the total change of enthalpy and entropy during this process.

Given Data:
- Mass of air (m) = 2kg
- Initial pressure (P1) = 3.03975 MPa = 30 atm
- Initial temperature (T1) = 143K
- Final temperature (T2) = 293K

Assumptions:
- The air is an ideal gas.
- The process is reversible and adiabatic.
- The specific heat capacity (Cp) of air is constant.

Calculations:
1. Change in enthalpy (ΔH):
The change in enthalpy can be calculated using the formula:
ΔH = m * Cp * ΔT
where, m is the mass of the air, Cp is the specific heat capacity of air, and ΔT is the change in temperature.

2. Change in entropy (ΔS):
The change in entropy can be calculated using the formula:
ΔS = m * Cp * ln(T2/T1)

Substituting the given values:
- Mass (m) = 2kg
- Specific heat capacity of air (Cp) = 1.005 kJ/(kg·K) (at constant pressure)
- Change in temperature (ΔT) = T2 - T1 = 293K - 143K = 150K

Calculating ΔH:
ΔH = 2 * 1.005 * 150 = 301.5 kJ

Calculating ΔS:
ΔS = 2 * 1.005 * ln(293/143) ≈ 2.78 kJ/K

Sketch of the Process:
The process can be represented on a temperature-entropy (T-S) diagram. The initial state is at point A with temperature T1 and entropy S1, and the final state is at point B with temperature T2 and entropy S2. The process is a straight line on the T-S diagram.

Explanation:
During a constant pressure process, the pressure remains constant while the temperature changes. In this case, the air is heated at a constant pressure until its temperature reaches 293K. As the temperature increases, the enthalpy of the air also increases. The change in enthalpy (ΔH) represents the heat energy transferred to the air during the process.

The change in entropy (ΔS) represents the increase in disorder or randomness in the air during the process. As the temperature increases, the particles of air move more vigorously, leading to an increase in entropy.

In summary, during the constant pressure process, the air absorbs heat energy and its enthalpy increases. At the same time, the disorder or randomness in the air increases, leading to an increase in entropy.