Hi,
I am working in the oil & gas pipeline industry, where I do mechanical integrity test & I precommissioned the pipelines before being put to service. Part of the precommissionig process is to perform hydrostatic test as the strength test, and then the water used during the test have to be get rid off the system.
Dewatering and drying the pipelines are basically performing some straight forward mechanical operations. Only towards the particular drying operations, vacuum dying is being applied. The principal is to evacuate the air + moisture within the pipeline utilizing vacuum pump, bring it down to a pressure where moistures inside the pipeline will evaporate.
Moistures at their saturated vapor pressure will boil and be evacuated from the pipeline. Now here's my question. It sounds silly to me, but I need some help on it.
While operating the vacuum pumping, at the stage where water is boiling off (around 5 milibar absolute) - it happens to me that the hoses connecting the pump to the pipeline is freezing cold with ice. It seems like there is ice block formed inside the hoses. I am trying to find scientific explaination to this.
I understand that the water moistures are all well above the saturated vapor pressure inside the pipeline & hoses, how can I be formed at this pressure?
Hello Halda
You are observing the basic principle of refrigeration. The vacuum causes the water to evaporate and heat is absorbed in the process. Expanding gases absorb heat cooling the lines and the gases inside (the water vapor). In a refrigeration cycle the gases are compressed which causes them to give up the heat they have acquired during the expansion cycle.
QUOTE (halda+Nov 28 2006, 03:26 AM)
While operating the vacuum pumping, at the stage where water is boiling off (around 5 milibar absolute) - it happens to me that the hoses connecting the pump to the pipeline is freezing cold with ice. It seems like there is ice block formed inside the hoses. I am trying to find scientific explaination to this.
I understand that the water moistures are all well above the saturated vapor pressure inside the pipeline & hoses, how can I be formed at this pressure?
Yeah, when you have a phase transition such as this it takes a certain amount of thermal energy to initiate it. Lower pressures mean less thermal energy needed to initiate this change. The liquid water in the reduced pressure system will begin to evaporate, but since the thermal energy required is much less it will essentially begin to cool its environment and ice will form. Essentially it is refrigeration, but the refigerant freezes because of the 'high' freezing point.
QUOTE (fizzeksman+Dec 1 2006, 04:25 AM)
Hello Halda
You are observing the basic principle of refrigeration. The vacuum causes the water to evaporate and heat is absorbed in the process. Expanding gases absorb heat cooling the lines and the gases inside (the water vapor). In a refrigeration cycle the gases are compressed which causes them to give up the heat they have acquired during the expansion cycle.
I get the refrigeration part, but as the lines maintains at vacuum, the water will not be condensated / solidified as what I experienced.
You are observing the basic principle of refrigeration. The vacuum causes the water to evaporate and heat is absorbed in the process. Expanding gases absorb heat cooling the lines and the gases inside (the water vapor). In a refrigeration cycle the gases are compressed which causes them to give up the heat they have acquired during the expansion cycle.
I get the refrigeration part, but as the lines maintains at vacuum, the water will not be condensated / solidified as what I experienced.
Hi halda
Could the velocity of the water vapor through the hoses cause a pressure differential leading to ice formation within the hoses?
Could the velocity of the water vapor through the hoses cause a pressure differential leading to ice formation within the hoses?
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