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A rigid tank contains 5 kg of refrigerant-134ainitially at 20°C and 140 kPa. The refrigerant isnow...

A rigid tank contains 5 kg of refrigerant-134ainitially at 20°C and 140 kPa. The refrigerant isnow cooled while being stirred until its pressure
drops to 100 kPa. Determine the entropy changeof the refrigerant during this process.

I know how to do this question, but the point that confuesd is why specific volume of refrigerant-134 does not change when its pressure drops. And in what condition that the specific volume of a system does no change?

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Answer #1

If we assume that the rigid tank does not expand or contract significantly with the temperature and pressure change, we have is a constant volume process. We can find the entropy change from the initial state, where we are given the temperature and pressure and the final state where we know the temperature or pressure and we also know that the specific volume will be the same as it is at the initial state. We can also use the information on the rigid tank volume to find the system mass.

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