Question about Refrigerants used within a Heat Pump

[Martin Harris]

I've been given the following 2 questions (please see below), and I've been asked to come with answers and arguments for my decision for the proposed answer, since there is just 1 correct answer per question. (so you can see my attempt below)

Q1)The refrigerants have to:

a)Vapourise at high temperatures and low pressures close to the atmospheric pressure
b)To be soluble in water
c)To be soluble towards the compressor lubrication oil.

Q2) The refrigerants have to:

a) Be Carbon-less such as not to contain Carbon
b)Not to dissolve in oil
c)Vapourise at low pressures and high temperatures

I think the correct answer for Q1 would be a) but don't know about high temperatures to vapourise, though low pressures would make sense, the same goes for Q2 as my answer would be c)

Are these answers even correct though? So I can know if I can start the arguments

 

[Chestermiller]

My answer to Q1 is c. https://www.achrnews.com/articles/9...ts-with-a-knowledge-of-refrigerant-oil-basics

My answer to Q2 is, of course, c

 

[Martin Harris]

My answer to Q1 is c. https://www.achrnews.com/articles/9...ts-with-a-knowledge-of-refrigerant-oil-basics

My answer to Q2 is, of course, c

Thanks for the quick reply!

Right, I thought the answer for Q1 would be a)

I thought mixing with oil is a big no-no...I will give way to your knowledge...just that coolant dissolving in the compressor oil sounds like a nightmare...like doing things like vapour locking your oil cooling/cleaning system...or gassing off at random times "There was a low pressure transient and our compressor lubricant started boiling"

Why would the answer from Q2 c) be feasible for Q1 a), it's basically the same answer, I am thinking that Q2 is either b) or c), leaning more towards b)..so it doesn't dissolve in your compressor oil...and gas off at the least convenient moment

 

[Chestermiller]

Thanks for the quick reply!

Right, I thought the answer for Q1 would be a)

I thought mixing with oil is a big no-no...I will give way to your knowledge...just that coolant dissolving in the compressor oil sounds like a nightmare...like doing things like vapour locking your oil cooling/cleaning system...or gassing off at random times "There was a low pressure transient and our compressor lubricant started boiling"

Why would the answer from Q2 c) be feasible for Q1 a), it's basically the same answer, I am thinking that Q2 is either b) or c), leaning more towards b)..so it doesn't dissolve in your compressor oil...and gas off at the least convenient moment

Q1a confines it to pressures near atmospheric pressure.

 

[Martin Harris]

Q1a confines it to pressures near atmospheric pressure.

Thanks for the reply, please find attached the notes that I've been provided.
These refrigerants should be used within a heat pump application

Having had a look over them I think it could be Q1)b) Q2)b)

1)b) seems a special case for heat pumps with absorption installation thus producing cold from the heat pump

2)b) would help to extract more heat from the refrigerant I think since it won't be soluble with the lubricating oil.

What's your opinion though?

On the 1st page of the notes I'm being told insolubility between the refrigerant and the lubricating oil and on the 2nd page of the notes there is a disadvantage for ammonia for having low solubility in the lubricating oil...

 

[Martin Harris]

I think based on the notes that refrigerants shouldn't be soluble with lubricating oil... however there is a contradiction on page 1) with page 2) because low solluvility of Ammonia with lubricating oil is considered a disadvantage