Static evaporation rate measurement: What is the purpose of the vent valve in cryogenic equipment?
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What is the purpose of the vent valve in cryogenic equipment? To measure the static evaporation rate, the container must be filled; there is definitely pressure inside when it’s full. If the valve is opened, won’t the liquefied gas inside escape? How can static evaporation rate still be measured? Excerpted from GB/T18443.5 \"Test Methods for the Performance of Vacuum Insulated Cryogenic Equipment\" – Seek expert assistance to resolve doubts!
The evaporation rate is generally measured under normal pressure using liquid nitrogen, rather than under operating conditions.
Opening the valve allows the liquefied gas inside to evaporate; only after pressure returns to normal can the measurement of the static evaporation rate be taken...
“Liquid nitrogen: at standard pressure, its temperature is -196°C. “Taken from encyclopedias.” By opening the vent valve, can the temperature inside be kept at -196 degrees? If it’s above -196 degrees, wouldn’t liquid nitrogen turn into gaseous nitrogen?
“Liquid nitrogen: at standard pressure, its temperature is -196°C. “Taken from encyclopedias.” By opening the vent valve to reach atmospheric pressure, can the temperature inside be maintained at -196 degrees? If it’s above -196 degrees, wouldn’t liquid nitrogen turn into gaseous nitrogen? In that case, it would be impossible to measure the evaporation rate. For example, in tanks for liquefied natural gas, the temperature isn’t that low either – it’s not at -196 degrees.
Please understand carefully that \"liquid nitrogen, at normal pressure, has a temperature of -196\"℃“
The vent valve must be opened to allow the liquefied gas inside to evaporate; only after normal pressure is reached and a new equilibrium is established can the measurement of the static evaporation rate be taken. The static evaporation rate refers to the rate at which liquid nitrogen evaporates under normal pressure
Thanks to the answers from the three of you above, I now understand a bit more. Thank you! By standard, liquid nitrogen is generally used as the testing medium; in other words, liquid natural gas can also be used. It’s probably because natural gas is considered less safe, and moreover, letting it evaporate over 48 hours would be a waste.