Fridge Gases

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Big Pete
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Fridge Gases

Postby Big Pete » Fri Sep 14, 2012 10:31 am

I have just joined a new ship. The ship's A and domestic fridge plant use the new ozone friendly fridge gases which are a blend of gases. Discussing the fridge plant with the previous Chief, he told me that if we had any leaks we could not top up the remaining gas in the system but had to dump all the gas in the system and completely recharge it. He thought that if there was a leak the proportions of the different gases in the blend would change and therefore the operating characteristics. I have never heard of this before. What does everybody else think?

BP
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JK
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Re: Fridge Gases

Postby JK » Sat Sep 15, 2012 3:03 am

Sort of defeats the stable gas the companies advertise, you would think. I have never heard of it and really can't see it. The gas would be chemically blended.
I have heard the same thing about biodiesel as well, that it will separate. Not true.

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Big Pete
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Re: Fridge Gases

Postby Big Pete » Sat Sep 15, 2012 9:16 pm

Thanks JK, Confirms what I thought. You will love this, which I found in the C/E file on the ER computer!!!!!

As they say on TV, DO NOT TRY THIS AT HOME!!

Instructions to top up refrigeration systems with R404 & R407
R407 - to be used for A/C systems
R 404 - to be used for fridge systems
Both gases (R404 & R407) are made with 3 different components and they are settled in the bottles in 3 different levels.
If any system requires a top up of gas, this must be done as follow:
1- IT HAS TO BE CHARGED AS LIQUID NOT AS A GAS. If the bottle does not have a liquid discharge we have to turn it upside down and use the gas discharge..
2- Connect one hose from the bottle to the pressure gauges
3- Connect another hose from the gauges to the suction line on the compressor in use.
4- Top up while the compressor is running. It must be done very carefully to not damage the compressor as we are using liquid on the suction side.
5- It must be done just a little bit at a time opening the valve from the pressure gauges to the compressor.
6- When the sight glass is full of liquid passing through it the system is fully charged.

Note: The procedures above were observed while an AIKEN service engineer was onboard for the ECR A/C repairs.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: Fridge Gases

Postby JK » Sun Sep 16, 2012 3:14 am

I dug into this a bit more, it appears that I unintentionally gave you the wrong info. I apologize.
This is why I have the Fridge contractor on speed dial at work :oops:

The gases are blends and can fractionate.
Here is some info:
http://www.3dair.co.uk/download-files/r407c-guide.pdf
4.11The refrigerant R407C is a blended refrigerant,
being a mixture of R32, R125 and R134A, and is
known as a ZEOTROPE fluid, and at a given
pressure each component part of the blend will
boil at a different temperature.
4.12 The pure refrigerant fluids R32 and R125 boiling
points are -52oC and -51oC respectively, and are
more volatile than R134a - boiling point -27oC.
4.13 Consequently R32 and R125 exert a higher vapour
pressure than R134a and should there be any
leaks in the system, the partial loss of one
component would result in the total remaining
blend being of the incorrect composition.
4.14 The magnitude of the leak is significant, but the
amount of the leak usually impossible to establish.
Small changes in the refrigerant quality / composition
may not noticeably affect the equipment
performance in the short term. However, the
leakage effect is irreversible and at some point,
the refrigerant has to be reclaimed and returned
to the manufacturers for reblending or disposal,
and the system would require evacuating and
completely recharging.
6.6 Individual HFC's have differing miscible properties
with oils and under certain conditions of temperature
and pressure can cause fractionation of a HFC blend
eg. R407C. Under these exceptional circumstances
the fractionation can lead to a change in composition
of the circulating blend and a change in system
performance. However, these circumstances are
unlikely to arise with equipment operating at
temperatures and pressures of typical refrigeration
systems used in building air conditioning systems.

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Big Pete
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Re: Fridge Gases

Postby Big Pete » Sun Sep 16, 2012 9:39 am

Thanks JK, I wish I had your speed dial numbers!

Trying to get to practical basics, I assume that:-

1) there is no need to replace the entire charge unless the performance has deteriorated.
2) that if the 3 liquid components of the the Refrigerant have different densities, and hence stratify in storage, the storage cylinder should be shaken to mix them before charging,
3) charging liquid instead of vapour makes sense if the mixed liquids each have a different evaporation temperature.
4) However I still can't understand charging liquid into the compressor suction, that just flies in the face of common sense, surely it has to be charged into the liquid line with the condenser outlet shut? (as normal)


BP
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JK
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Re: Fridge Gases

Postby JK » Mon Sep 17, 2012 6:36 am

Refrigeration is akin to voodoo magic for me.
My pratical work with it was long before the new gases. I hope someone with more recent background in it will answer your questions.

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Big Pete
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Re: Fridge Gases

Postby Big Pete » Mon Sep 17, 2012 10:08 am

Thanks for the help JK.
I will have to dome research online, or even buy myself a new reefers for dummies book.
The Earth's atmosphere is made up of different gases with different densities and vapour pressures, but we dont suffocate in pure CO2 at sea level and have to live on mountain tops and breath pure oxygen to live, and aircraft engines don't stop at a certain altitude because they are ingesting pure Nitrogen.
I would have thought the circulating velocity of gas in a reefer plant would create sufficient turbulence to ensure that the gases were always evenly mixed, even without the natural tendency of each individual gas to spread out and fill the entire volume of the space it is in.
I assume the main problem would be if part of the system was at a temperature and pressure that permitted some components of the gas to be liquid while permiting the others to be gas.
More knowledge and understanding urgently required!!

BP
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: Fridge Gases

Postby JK » Mon Sep 17, 2012 10:57 am

In the link I posted, they have some comments on charging in section 9.10

This is one of those times I get frustrated that we have engineers read and not posting their experience!


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