Small vacuum storage tanks (up to 11 m{sup}3 capacity) are generally used for applications, where, for logistics optimization, the re-filling periods are longer, typically two-three weeks. With long retention time the bulk of liquid becomes warmer and doesn't accept so much heat leak, which is transformed more into vaporization, then. In high pressure tanks with relief pressure set to 37 bar and operating pressure close to the critical pressure of nitrogen at 33 bar, as encountered at laser applications, e.g., the heat of vaporization is very low. Any heat leak causes large vaporization and holding times are very short. Minimization of heat leak is very important, then. Holding time and nominal evaporation rate was improved by using of multi-layer insulation at the new multi-layer insulated EVT tanks in sizes 3, 6 and 11 m{sup}3,. Measurement of temperature distribution in a cryogenic pallet tank 600 liters at high operating pressure proves warming up of the bulk of liquid. Recommendations for prolongation of the holding time of high pressure tanks are presented.
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