ice formation expansion valves

[landrover77]

Gents

Please provide an opinion a collegue and myself are having discussion on the following.

The example below applies to a refrigeration system, in which a small amount of mositure has entered through either poor vacuum processs or air coming into the system.

if we are expanding a saturated refrigerant from 15bar (approx 50degC saturated temperature), to 1bar (-15degC saturated) temperature. we know in the right situation if mostiure is present in a system then hydrates/ice will be formed in the entrance to the valve, and if enough crystals form of large enough size then the valve may block.

But can this occur when the low side saturated pressure/temperature is above zero degC. ie we are expanding a saturated refrigerant from 15bar (approx 50degC saturated temperature), to 8bar (30degC saturated temperature)?
Or will any fine liquid droplets entrained with the refrigerant flow just be maintained a liquid?
Are there local effects of low pressure around the valve that need to be considered?
In the pessure temperature confitions above the water should be present in liquid form.

This ignores the effect the water has on acid formation within the oil.

thanks

 

[TD2K]

Hydrates in hydrocarbon systems will form at temperature above the normal freezing point of water depending on the pressure, temperature and hydrocarbons. If you are below freezing, then any free water can also freeze.

For your system, maybe (you didn't say what type of refrigerant you are using and that could be anything from ammonia to hydrocarbons to conventional R-xxx). For hydrocarbons, hydrates form with methane up to about C4 I believe, larger molecules simply can't fit within a clathrate cage. However, it's been a while since I had worked much with this topic, Zdas, Latexman or others are likely more up on it than I am.