Boil-off rate

In the event of faults developing (as indicated by high boil-off rates or external frost), cease using the equipment. 

Truck boil-off rate Truck capacity Fuel economy Average speed Load/unload time Truck availability Hour/driver... 

AVERAGE BOIL-OFF RATES FOR PHOSGENE FROM UNDERLYING CONCRETE [557]... 

Industrial gases sold in small quantities are liquefied at the point of manufacture, stored in cryogenic storage vessels, shipped over the road, and stored as a liquid at the point of use until needed. When required, the product is drawn from storage, vaporized, and used in the customer s process. Cryogenic storage involves the use of high performance vessels that reduce the boil-off rate of product to less than 0.1%per day [1]. 

The costs associated with liquefied hydrogen storage are determined by the production rate, storage time, and boil-off rate. Equation (5) is used to determine the net production accounting for the losses incurred from the boil-off effect... 

Storage Vessel The boil-off rate of hydrogen from a liquid hydrogen storage vessel due to heat leaks is a function of the size, shape and thermal insulation of the vessel. Theoretically, the best shape is a sphere, since it has the least surface to volume ratio and because stress and strain are distributed uniformly. However, large... 

For the ground-hold condition, the pressure in the test chamber was maintained at atmospheric, while the insulation was evacuated to within the range of 5 to 10 /i Hg. The pressure within the test tank itself was kept at 0.3 5 psig by means of a back-pressure regulator. The flow rate of the hydrogen gas was measured by an 0.1955-in.-diameter Venturi meter and data recorded for a period of 10 hr before the test was terminated. For the second run, the test chamber w as evacuated to a pressure of about 10 atm and the insulation to 0.5 /it Hg. Continuous boil-off data was recorded for a period of 220 hr, with a wet-drum gas meter used in place of the Venturi to measure this lower flow rate. Finally, a series of tests was conducted at several test chamber pressures from 0.29 to 5 psia, which provided corresponding compressive loads on the insulation. The boil-off rate was allowed to stabilize for at least 8 hr at each external pressure condition before data were recorded. Each test lasted 12 to 24 hr. 

Answer by Author During the test a large leak occurred when an evacuation line was inadvertently opened. The liquid hydrogen boil-ofF rate increased considerably during the time air was condensed in the insulation. However, we successfully warmed the tank and removed all the air from the insulation with no difficulty or damage to the insulation. 

Variation of boil-off rate with heater input. 

Reproducibility. The overall accuracy of the thermal conductivity apparatus is estimated to be 10%. This estimate is based on the accuracy of measuring the volume of boil-off gases, controlling the gas pressures above the crypgenic liquids in the measuring and guard vessels, the effect of atmospheric pressure changes on the boil-off rates, and the temperature measurement of the cold and warm surfaces. The estimate is supported by the electrical heater calibration tests. 

In addition, several calibration tests of the heat chamber were conducted to determine the heat flux to the liquid for the different electrical power levels employed. The general method used for this calibration was to operate the heat chamber for several minutes while the sensible-heat gain of the liquid (temperature rise) and the latent-heat increase (boil-off rate) were monitored. 

Data Reduction. Repeatability test data were reduced and plotted as shown for a hypothetical case in Fig. 4. The slope of the lines shown depicts the boil-off rate for a particular run. All reasonable wet and dry points fall within the respective bands. The total band encompasses all readings, dry and wet. The dead band is the area where no readings fall. The dead band is caused by intentional tolerances associated with the sensor triggering point and such considerations as differences between output relay pull-in and drop-out currents, and by other experimental uncertainties. Overlap of dry and wet readings were also observed in some cases these may be partially explained by meniscus and surface-tension effects. Response times were taken directly from the recorder charts and tabulated. 

It must have a gas permeability rate substantially lower than the anticipated boil-off rate of the vessel or tank. 

The third polyurethane specimen, Last-A-Foam, exhibited good thermal performance for approximately 800 cycles (approximately 3 years of airline service) before experiencing a large degradation in thermal performance. The failure of the Last-A-Foam was first detected by a significant increase in the hydrogen boil-off rate. Visual examination of the warm insulation at that time revealed only a few very fine tributary type cracks. When the insulation was examined immediately after the next test period. 

Visual examination of both insulation systems after a week of cyclic testing showed that the specimens were completely covered with frost within 7.6 (3 in) of the edge of the samples. The cold surface was in complete agreement with the high boil-off rate recorded for these insulations, initially the exterior vapor barrier of the ADL Upjohn system appeared relatively smooth (Fig. 14c). 

Foam thickness was scaled to simulate stress conditions encountered by insulation on a large diameter tank. Insulation specimens were bonded to a thin, flat aluminum tank, which had separate compartments for six specimens. The tests were conducted by filling the compartments with liquid hydrogen and exposing the outer surface of the insulations to a cyclic thermal environment representative of repeated subsonic aircraft flight. The boil-off rate in each compartment indicated insulation thermal performance. 

EMISSIVITY OF ALUMINUM SHIELDS AND APPARATUS SURFACES. Tests on the small samples were conducted with the same single-guarded cold plate thermal conductivity apparatus as was used in previous investigations [2]. This apparatus was found useful in establishing the mean emissivities of foils and films. To obtain measurements, the foil was glued to the cold and warm surfaces of the apparatus, keeping one surface at 46 F and the other at -320 F. The space between the surfaces, 1/4 in., was evacuated to 3.10 mm Hg, so that radiation was the major factor in the heat transferred. The heat flux between the surfaces was calculated from the observed boil-off rate on the assunaption that the emissivities of the warm and cold surfaces were equal. The mean emissivity was established by means of the Stefan-Boltzmann equation ... 

Vaporization rates were determined utilizing the same basic container maintained at the full level of liquid oxygen. In this case, however, the vaporized liquid was vented through a wet-test meter which was equipped with a helical potentiometer and sufficient circuitry to record the volume boil-off rate. Unit area heat transfer rates were then determined from these data. The temperature of the container skin, Ts, was recorded with the use of a thermocouple soldered to the container wall during the length of the test. All tests of this nature were performed for times of 3 hr. 

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