The sizing of cryogenic safety relief devices requires detailed knowledge on the evolution of the pressure increase in cryostats following hazardous incidents such as the venting of the insulating vacuum with atmospheric air. Based on typical design and operating conditions in liquid helium cryostats, the new test facility PICARD, which stands for Pressure Increase in Cryostats and Analysis of Relief Devices, has been constructed. The vacuum-insulated test stand has a cryogenic liquid volume of 100 liters and a nominal design pressure of 16 bar(g). This allows a broad range of experimental conditions with cryogenic fluids. In case of helium, mass flow rates through safety valves and rupture disks up to about 4 kg/s can be measured. Beside flow rate measurements under various conditions (venting diameter, insulation, working fluid, liquid level, set pressure), the test stand will be used for studies on the impact of two-phase flow and for the measurement of flow coeffcients of safety devices at low temperature. This paper describes the operating range, layout and instrumentation of the test stand and presents the status of the commissioning phase

Grohmann, Steffen

Heidt, Carolin

Schön, H.

Stamm, M.

IOP Conference Series Materials Science and Engineering

English

KITopen

IOP Conference Series: Materials Science and EngineeringPAPER • OPEN ACCESSCommissioning of the cryogenic safety test facilityPICARDTo cite this article: C Heidt et al 2015 IOP Conf. Ser.: Mater. Sci. Eng. 101 012161 View the article online for updates and enhancements.Related contentFirst experimental data of the cryogenicsafety test facility PICARDC Heidt, A Henriques, M Stamm et al.-Recent citationsFirst experimental data of the cryogenicsafety test facility PICARDC Heidt et al-This content was downloaded from IP address 129.13.72.197 on 10/10/2017 at 12:35Commissioning of the cryogenic safety test facilityPICARDC Heidt1,2, H Schön1, M Stamm1 and S Grohmann1,21 Karlsruhe Institute of Technology, Institute for Technical Physics,Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany2 Karlsruhe Institute of Technology, Institute for Technical Thermodynamics andRefrigeration, Kaiserstrasse 12, 76131 Karlsruhe, GermanyE-mail: carolin.heidt@kit.edu, heinz.schoen@kit.edu, michael.stamm@kit.edu,steffen.grohmann@kit.eduAbstract. The sizing of cryogenic safety relief devices requires detailed knowledge on theevolution of the pressure increase in cryostats following hazardous incidents such as the ventingof the insulating vacuum with atmospheric air. Based on typical design and operating conditionsin liquid helium cryostats, the new test facility PICARD, which stands for Pressure Increasein Cryostats and Analysis of Relief Devices, has been constructed. The vacuum-insulated teststand has a cryogenic liquid volume of 100 liters and a nominal design pressure of 16 bar(g). Thisallows a broad range of experimental conditions with cryogenic fluids. In case of helium, massflow rates through safety valves and rupture disks up to about 4 kg/s can be measured. Besideflow rate measurements under various conditions (venting diameter, insulation, working fluid,liquid level, set pressure), the test stand will be used for studies on the impact of two-phase flowand for the measurement of flow coefficients of safety devices at low temperature. This paperdescribes the operating range, layout and instrumentation of the test stand and presents thestatus of the commissioning phase.Keywords: Cryogenics, liquid helium, safety, test setup, heat flux, relief flow rate1. IntroductionThe dimensioning of cryogenic safety relief devices requires detailed knowledge on the evolutionof the pressure increase in cryostats following hazardous incidents such as the venting of theinsulating vacuum with atmospheric air. However, the process dynamics are often not consideredin the established design codes. Rather, the codes are based on constant (maximum) heat fluxdata, yielding safe but potentially oversized dimensions of safety devices. General design stepsare the following:(i) Determination of the maximum heat flux to the cryogenic fluid from experimental data,e.g. for helium (He) found in• Lehmann and Zahn [1]: heat transfer to He I, with and without multi-layer insulation(MLI), venting of the insulating vacuum with air,• Harrison [2]: heat transfer to He II, with and without composite insulation, venting ofthe insulating vacuum with air,• Bosque et al. [3]: heat transfer to He II, without MLI, venting of the insulating vacuumwith gasous nitrogen.CEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/012161Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd 1(ii) Determination of the resulting discharge mass flow rate, e.g. from models based on• Varghese and Zhang [4]: Calculation of the maximum discharge mass flow rate fromthe maximum heat flux1,• Chorowski et al. [6]: Calculation of the time-dependent discharge mass flow rate fromthe maximum heat flux2.(iii) Determination of the required discharge diameter of the safety relief device, e.g. based onDIN EN ISO 4126 [8], API 520-1 [9] or AD-2000 [10][11].The analytic approach presented in [12] is based on theoretical considerations and differentialequation modeling and includes a time-dependent heat flux caused by desublimating air3. Byconsideration of the process dynamics between step (i) and (ii), a reduction of the requireddiameter of safety relief devices is possible. Besides savings in both spending and space, asmaller diameter also reduces gas leakage through safety relief devices, which especially in liquidhelium cryostats contributes significantly to the overall leakage.The model [12] contains some simplifying assumptions concerning the kinetics ofdesublimation, heat transfer and thermal equilibrium in the inner vessel. Therefore, the newtest facility PICARD, which stands for Pressure Increase in Cryostats and Analysis of ReliefDevices, has been constructed. This paper discusses the aims and possibilities of measurementsat PICARD, presents the design and construction of the experimental setup and instrumentationbefore giving an overview on the status of the commissioning and an outlook on the R&Dcollaboration between KIT and CERN.2. Purpose and Operating RangeWith a cryogenic liquid volume of 100 liters and a nominal design pressure of pN = 16 bar(g), thecryogenic test facility PICARD allows a broad range of experiments. In order to complementthe existing data on the processes following hazardous incidents, detailed flow rate and heat fluxmeasurements under various conditions will be conducted. In the course of the experiments,the impact of the venting diameter, the insulation, the liquid level and the set pressure onthe heat flux and hence on the process dynamics will be investigated. The results will be1 This model is used in DIN EN 13648 [5].2 This model was used for the dimensioning of the safety relief devices at the KATRIN experiment [7].3 This model is used in DIN SPEC 4683 [13].Table 1. Scope of the planned experiments at the PICARD test facility.Parameter RangeVenting diameter 1 . . . 40 mmInsulation 0 . . . 30 layers of superinsulation, with/without radiation shieldLiquid level 20 . . . 80 %Set relief pressure 2 . . . 12 bar(g)Cryogenic fluid Helium, nitrogen, neon, argonVenting fluid Air, nitrogenSafety relief device Safety valve, rupture disk, control valveHeating With/without simulating the quench of a superconducting magnetRelief mass flow Single-phase, two-phaseDischarge coefficient Of different safety relief devices at 4 . . . 300 KCEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/0121612filling line assembly jigfor inner vesselto reliquefactionexhaust gas linequench gas linevent linevacuum pumpswater bath heaterrupture discrupture discsventuri tubeventilation cross-sectionsafety valvecontrol valvedewarcryostatto purification andreliquefactionFigure 1. Overview of the PICARD test facility.implemented in the form of fit parameters in the analytic model [12]. Experiments with differentworking fluids such as helium and nitrogen as well as with the venting fluids air and gaseousnitrogen will complement the data set. Specifically, a detailed investigation on the occurance andeffects of two-phase flow during helium discharge will be conducted. Furthermore, the dischargecoefficients of safety relief devices in a temperature range between T = 4 . . . 300 K and with reliefpressures between p = 2 . . . 12 bar(g) will be investigated. In case of helium, mass flow ratesthrough safety valves and rupture disks up to about 4 kg/s can be measured. Additionally, theblow-off at constant pressure through a control valve shall be studied as an alternative to theestablished safety valves, where the pressure fluctuates because of constant relief cross sections.The scope of the planned experiments is summarized in table 1.3. Design and Construction3.1. Experimental SetupFigure 1 shows a CAD drawing of the PICARD test setup with its main components: thecryostat, the piping, the dewar and the assembly jig. From the dewar, cryogenic liquid istransferred through a filling line into the inner vessel of the cryostat. A picture of the innervessel is shown in figure 2(a). The dimensions of the cryostat are given in table 2.During the filling process, the evaporating cryogenic fluid cools down the inner vessel andthe exhaust gas line. In order to avoid air condensation, the exhaust gas is heated up in a waterbath heater. When the required liquid level in the inner vessel of the cryostat is reached, thefilling line is disconnected manually.CEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/01216134· TITI TILITITITI TI TILITITITITITIPIPIPIPIPICPICPDIPDITIPITITIMITITITIventuri tubeoptional MLIvacuum pumpscryogenic vesselradiation shieldvacuum vesseltemperature sensor measurementinsertair inletthrough orificefilling lineexhaust gas linevent linefilling lineoptional orificequench gas line vent line(a) (b)Figure 2. (a) Picture of the PICARD inner vessel mounted on the assembly jig and connectedto the radiation shield and to the lid of the vacuum vessel by the vent line. (b) P&ID ofthe PICARD experiment that is equipped with 18 TVO temperature sensors (TI), three fastpressure transducers (PI) where one is connected to the control valve (PIC), two vacuum pressuretransducers (PI) where one controls the closure of the vacuum valve in order to protect the turbopump from pressure surge when venting the insulating vacuum (PIC), two manometers (PI), twofast differential pressure transducers (PDI) for mass flow measurements, two liquid level probes(LI), and one combined temperature-humidity probe (TI with MI). The instrument symbols incircles indicate a display on site, those in combs specify that the sensors are connected to acomputer where the data is recorded and processed with the LabviewTM software [14].Different measures have been taken to prevent fast evaporation of the cryogenic fluid insidethe cryostat due to unwanted heat inleak caused by convection, conduction and radiation.The vacuum pumping station is flanged to one side of the vacuum vessel and provides aninsulating vacuum of p = 10−6 mbar. The inner and outer surfaces of the cryogenic vessel havebeen electropolished. An additional radiation shield made of aluminum is cooled by thermalconduction through contact with the vent line. Depending on the type of experiment, either theradiation shield or the MLI can be attached to the inner vessel at the assembly jig.During the experiments, the cryogenic fluid is released through a safety valve. The setpressure is at least 20 % below the nominal design pressure of 16 bar(g), considering the tolerancesof the rupture disk and the safety valve. The escaping cryogenic fluid is conducted through aquench gas line to be collected in the helium facilities of the Institute for Technical Physics(ITEP). The ultimate safety device of the pressurised volume is a rupture disk with a burstpressure of p = 16 bar(g).CEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/0121614Table 2. Dimensions of the main PICARD components.Component Parameter ValueInner vessel Height 900 mmDiameter 400 mmTypical liquid volume 100 lNominal pressure 16 bar(g)Outer vessel Height 1500 mmDiameter 600 mmVacuum volume 300 lNominal pressure 10 bar(g)Radiation shield Height 1050 mmDiameter 500 mmVent line Inner diameter 60 mmQuench gas line Inner diameter 100 . . . 150 mm3.2. InstrumentationIn order to perform heat flux and flow rate measurements under various specified conditions,studies on the impact of two-phase flow and measurements of flow coefficients of safety devicesat low temperature, a variety of valves, orifices, venturi tubes, temperature sensors, (differential)pressure transducers and liquid level probes have been installed at the PICARD test stand. ThePiping and Instrumentation Diagram (P&ID) is shown in figure 2(b).An overview of the different TVO temperature sensors that have been calibrated at thecalibration facility at ITEP is given in figure 3(a)-(d). For fast temperature measurements, sevenplain TVO temperature sensors (figure 3(a)) have been chosen and fixed at the measurementinsert shown in figure 3(e). Four of them are attached to horizontal wings of the measurementinsert that unfold once having passed through the vent line. They are complemented by threeadditional plain TVO sensors hanging freely at different heights of the measurement insert toverify the simplifying assumption of a homogenious temperature profile within the cryogenicfluid.The design of eight additional TVO sensors for surface temperature measurements is shown infigure 3(c). The copper blocks were mounted on the top, bottom, left and right side of the outersurface of both the inner vessel and the radiation shield. The temperature measurement at theouter surface of the inner vessel shall provide information concerning the heat transfer resistancewithin the inner vessel. Three more TVO sensors were prepared for in-tube temperaturemeasurements of the cryogenic fluid inside the vent line and quench gas line (figure 3(d)).A capacitive level sensor, attached to the measurement insert shown in figure 3(e), wasdesigned for experiments with e.g. nitrogen. For helium level measurements, an additionalsuperconducting level sensor has been installed.Due to fast pressure and temperature changes and the possible ocurrence of two-phase flow,two different methods are applied for measuring the discharge mass flow. The first method is aflow measurement with a venturi tube according to DIN EN ISO 5167-4 [15]. The venturi tubewas installed right before the safety valve, since the expected two-phase flow after the safetyvalve would make a downstream measurement impossible. The second method is based on themeasurement of the temperature T and the pressure p inside the inner vessel. By means ofthermodynamic correlations and fluid property data [16], the changes in the mass within theinner vessel m over time τ (and therefore also the discharge mass flow ṁ) can be calculated withCEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/0121615TVO sensorTVO sensorconnection to flangesuperconductinglevel sensorcapacitive levelsensorTVO sensors(a) (b)(c)(d) (e)Figure 3. (a) Picture of a plain TVO sensor for fast temperature measurement of the cryogenicfluid inside the inner vessel, and (b) of a TVO temperature sensor casted into a copper case.(c) Picture of a casted TVO temperature sensor that has been inserted into a copper block tobe mounted on the surface of the inner vessel and the radiation shield. The copper block isprotected from heat radiation by an aluminum shield. (d) Picture of a casted TVO temperaturesensor at the tip of a stick to measure the temperature of the cryogenic fluid inside the vent lineand the quench gas line. (e) CAD drawing of the measurement insert with TVO temperaturesensors as well as capacitive and superconducting level probes.a constant total volume V and the time-dependent density ρ by:ṁ(τ) =dm(τ)dτ=d(V · ρ [p(τ), T (τ)])dτ. (1)The expected uncertainties in the range of 20 % were judged sufficiently accurate under thedifficult conditions. However, large temperature gradients within the cryogenic fluid could makean evaluation difficult, if not even impossible following this procedure.For the air or nitrogen venting mass flow rate in the vacuum vessel, an orifice measuringsection has been chosen. Since both critical and subcritical flow is expected, the measured datawill be evaluated based on calibration. The composition of the ambient air will be measured witha combined hygrometer and temperature sensor in order to consider the influence of humidity.Using orifices of different diameters, the heat flux into the pressure vessel can be adjusted.4. Status and OutlookAll components have been manufactured and assembled. Their specified leak tightness and thepressure resistance have been verified. Within the next month, the approval by the notifiedbody is scheduled. The further commissioning with measurements of the evaporation ratesand temperature gradients during stand time will be conducted, before first data of ventingCEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/0121616experiments will be taken. Later this year, the experiments will concentrate on the occurrenceand the influence of two-phase flow, which is the focus of a R&D collaboration between KITand CERN.AcknowledgmentsWe would like to acknowledge the support from the Karlsruhe School of Elementary Particleand Astroparticle Physics: Science and Technology (KSETA).References[1] Lehmann W and Zahn G 1978 Proc. Int. Cryog. Eng. Conf. 7 569–579[2] Harrison S M 2002 IEEE T. Appl. Supercon. 12 1343–1346[3] Bosque E S, Dhuley R C and Van Sciver S W 2014 AIP Conf. Proc. 1573 260–267[4] Varghese A P and Zhang B X 1991 Adv. Cryog. Eng. 37 1487–1493[5] DIN EN 13648-3 2003 Cryogenic vessels - Safety devices for protection against excessive pressure - Part 3:Determination of required discharge - Capacity and sizing[6] Chorowski M, Fydrych J, Polinski J and Süßer M 2006 Proc. Int. Cryog. Eng. Conf. 21 141–144[7] Angrik J et al 2004 KATRIN design report Tech. rep. Karlsruhe[8] DIN EN ISO 4126-1 2004 Safety devices for protection against excessive pressure - Part 1: Safety valves[9] API 520-1 2000 Sizing, selection, and installation of pressure-relieving devices in refineries - Part 1: Sizingand selection[10] AD 2000-Merkblatt A 1 2006 Sicherheitseinrichtungen gegen Drucküberschreitung - Berstsicherungen[11] AD 2000-Merkblatt A 2 2012 Sicherheitseinrichtungen gegen Drucküberschreitung - Sicherheitsventile[12] Heidt C, Grohmann S and Süßer M 2014 AIP Conf. Proc. 1573 1574–1580[13] DIN SPEC 4683 2015 Cryostats for liquefied helium - Safety devices for protection against excessive pressure[14] National Instruments 2014 LabVIEW Professional Development System 14.0f1th ed[15] DIN EN ISO 5167-4 2004 Measurement of fluid flow by means of pressure differential devices inserted incircular cross-section conduits running full - Part 4: Venturi tubes[16] Lemmon E W, Huber M L and McLinden M O 2010 NIST Standard Reference Database 23: Reference FluidThermodynamic and Transport Properties - REFPROP 9th edCEC 2015 IOP PublishingIOP Conf. Series: Materials Science and Engineering 101 (2015) 012161 doi:10.1088/1757-899X/101/1/0121617

Commissioning of the cryogenic safety test facility PICARD

C Heidt

H Schön

M Stamm

S Grohmann

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Commissioning of the cryogenic safety test facility PICARD

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