ISENTROPIC EXPANSION PROCESS

EXPERIMENT 1: ISENTROPIC EXPANSION PROCESS
Objectives:
1) To demonstrate the isentropic expansion process.

Introduction: In thermodynamics, an isentropic process is a process in which the process takes place from initiation to completion without an increase or decrease in the entropy of the system. One example of a process that approaches being isentropic are the rapid depressurization of gas in a cylinder. The entropy of the system remains in constant. Entropy is a type of energy (like heat, work, and enthalpy) and is by definition energy which is lost in a process.

If a process is both reversible and adiabatic, then it is an isentropic process. An isentropic process is an idealisation of the expansion process which assumes there is no heat transfer between the system and its surroundings (No heat transfer is called "adiabatic").

Note that energy can be exchanged with the flow in an isentropic transformation, as long as it doesn't happen as heat exchange. An example of such an exchange would be an isentropic expansion or compression that entails work done on or by the flow.

Material and Apparatus
1) Pressure Chamber
2) Compressive Pump

Methodology
1) The general start up procedures was performed as stated in appendix A. All valves have been making sure to be fully closed.
2) The hose from compressive pump was connected to the pressurized chamber.
3) The compressive pump was switched on and allows the pressure inside chamber to increase up to about 160kPa. Then, the pump was switched off and the hose was removed from the chamber.
4) The pressure reading inside the chamber was monitored until it stabilizes. The pressure reading P1 and temperature T1 was recorded.
5) Then, valve V 01 was slightly opened and allowed the air to flow out slowly until it reached atmospheric pressure.
6) The pressure reading P2 and temperature reading T2 after the expansion process was recorded.
7) The isentropic expansion process was discussed.

Results

Pressure/kPa
Temperature/oc
Before expansion
157.3
25.1
After expansion
101.5
22.0

Calculations:

By comparing to theoretical value (k =1.40),

= 2.14%

Discussions: In this experiment, the isentropic expansion process happen went both reversible and adiabatic, there will be no heat transferred within the system, and no energy transformation occurs.
Given that,
PVk = constant constant constant

Where, k is constant.

By using the value of temperature and pressure before and after expansion, we can calculate the value of k using the formula shown above. Thus, the calculated value of k in this experiment is 1.43. In this experiment the pressure is drop from 157.3kPa to 101.5 kPa and the temperature also decrease from 25.1 °C to 22.0°C. In this case, the volume inside the pressure chamber was kept constant, causing the temperature and pressure to be decrease. In fact, during contact this experiment, it can be assume that no heat flow occurs in the system and no energy transformation change .Therefore, the change of the gas in entropy also is zero.

However, due to the condition in the surrounding like temperature inside the laboratory and the other factors, the experimental result may be varies by a small degree from the theoretical value. In this experiment, the percentage of error calculated by comparing those results is 2.14%, which is an acceptable value.

Conclusion:
In conclusion, the objectives were achieved. The value or PVk value is always constant for isentropic expansion process. The constant k obtained from this experiment is 1.43.

Limitations:
1) The temperature is not constant. Air conditional or fans should be switched off when conducting the experiment.
2) The hose connecting the pressure chamber and compressive pump must be removed as soon as possible as the pressure reading reach 160.0kPa.

Safety Precautions:
1) We do the general start up procedure before the experiment started.
2) We make sure all the valve is closed when the compressive pump is working.
3) We make sure that the pressure inside the pressure chamber does not exceed 2 bars to prevent the glass cylinder of the pressure chamber to be break.
4) We wait until the pressure readings stabilize before we take the reading.