Question

Refrigerant-134a is expanded adiabatically from 100 psia and \(100^{\circ} \mathrm{F}\) to a saturated vapor at 10 psia. Determine the entropy generation for this process, in Btu/lbm-R.

Short answer

Question: Determine the entropy generation during an adiabatic process involving the expansion of Refrigerant-134a from an initial state of 100 psia and 100°F to a final state of saturated vapor at 10 psia. Answer: The entropy generation for this adiabatic process of Refrigerant-134a is equal to the change in specific entropy (\(\Delta s\)), which can be calculated using the property data for Refrigerant-134a and the formula \(S_{gen} = \Delta s = s_2 - s_1\). The final value of entropy generation will be in Btu/lbm-R.

Step-by-step solution

Identify the process and important parameters

Since this is an adiabatic process, there is no heat transfer between the system and its surroundings. Our goal is to calculate the entropy generation during this process. To do so, we need the property data for Refrigerant-134a, which we can find in the tables provided in standard textbooks or online resources.

Determine the initial and final entropy values

Using the Refrigerant-134a tables, we can determine the entropy at the initial and final states. For the initial state (100 psia, 100°F), look up the corresponding specific entropy value (denoted as \(s_1\)) . For the final state (saturated vapor at 10 psia), look up the specific entropy of vapor at 10 psia (denoted as \(s_2\)).

Calculate the entropy change during the process

Now that we have the individual entropy values for both initial and final states, we can calculate the change in specific entropy during the process using the following formula: \(\Delta s = s_2 - s_1\)

Use the adiabatic process relation to find the entropy generation

An adiabatic process implies that the total change in specific entropy should be equal to the specific entropy generation (\(S_{gen}\)) during the process. Thus, we can directly use the computed entropy change (\(\Delta s\)) as the entropy generation: \(S_{gen} = \Delta s\) Now, we have the entropy generation for this adiabatic process of Refrigerant-134a in Btu/lbm-R.