Sub-ZeroTM pumps achieve 85% efficiency levels - Cryogenic ...

Many factors need to be consideredwhen designing ambient airvaporizers. The environmentaleffect is one such criteria. When designingand specifying fan assisted and naturaldraft ambient air vaporizers, we usefour main climate zones: tropical,Mediterranean, humid continental, andmarine. Each of these zones, however,may contain micro climate zones wherethe climate may be significantly differentthan the weather around it.In discussing climatic effects, a basicunderstanding of the principles of ambientair vaporizers is necessary. Fan-assistedvaporizers utilize forced convective heattransfer where natural draft ambient airvaporizers utilize natural convectiveheat transfer. Natural convective vaporizerstypically are manufactured withthree different fin spacings, dependingon how long the vaporizers are going tobe operated before complete defrost isachieved. Standard spaced vaporizerstypically operate less than 24 hoursbefore complete defrost and have a fintip-to-tip air gap roughly 1.5" (38 mm).(Figure 1.)Wide gap natural convection vaporizersgenerally are designed to operate threeFIGURE 1 FIGURE 2FIGURE 3 FIGURE 4to seven days without defrost and typicallyhave a fin tip-to-tip air gap spacingof 3" (75 mm) or more. (Figure 2.)Super-wide spaced ambient air vaporizersare designed to operate continuously,with the possibility ofmanual defrost required severaltimes per year. These vaporizershave a typical fin tip-to-tipspacing of 10" (254 mm) ormore. (Figure 3.) Forced convectivevaporizers are designed withmaximum heat transfer area in a minimumspace. They typically have fin tipto-tipair gap spacing of less than 1.5"(38 mm). (Figure 4.)Natural draft ambient air vaporizersoperate on the principal of natural convectiveheat transfer. Air is cooled asgravitational force pulls it past the heatexchanger fins. It therefore becomesmore dense and heavier. This densityfurther promotes a downward motiondue to gravitational effects. Forced convectiveheat transfer vaporizers rely onmechanical fan driven forced stimulationmovement of the air, therefore notrelying on gravity.The following are basic vaporizer designconsiderations dealing with the locationand duration of operation of ambient airvaporizers. Certainly other considerationsmust also be reviewed, such aselectrical /fuel requirements and availabilityof land or real estate, proximityto roads, walkways, driveways andoccupied businesses or housing.Tropical Climate ZonesFor the purpose of specifying vaporizers,tropical climate zones include equatorialregions such as Malaysia, Thailand,Indonesia, Panama, Venezuela, andBrazil. Other regions such as Japan andthe southern United States replicate thisclimate zone closely in their summermonths or monsoon season, but aregenerally closer to the humid continentalzone. Tropical climate zones are characterizedby dew point temperaturesgreater than 70 o F (21 o C). Dry bulbtemperatures generally range from 80 o F(27 o C) to 95 o F (35 o C) year round.There typically is not a wide variation inthe temperature between night and day,since the high moisture content of theatmosphere tends to trap the infraredradiation emitted by objects at night,not allowing it to escape to outer space.Both natural and fan-assisted draftambient air vaporizers should be consideredin tropical climates due to thelarge ambient air temperature drivingforce available. Flow rates under 57,000scfh (1500 Nm 3 /hr) are likely to performmore economically with natural4

convection units; flow rates over152,000 scfh (4000 Nm 3 /hr) withforced convection units. The mainadvantage of these systems is maximumvaporization capacity at minimal or nooperation cost coupled with maximumreliability.In order to maintain maximum vaporizercapacity from both types of vaporizersin this zone, the vaporizers should beswitched quite often. Typical switchingcycles would be about every four toeight hours. This is due to the highmoisture content in the atmosphere andtherefore rapid ice growth formation onthe fins which rapidly reduces the overallheat transfer coefficient. Switching lessthan every two hours to obtain evenmore vaporization capacity is bothunrealistic and dangerous. Both the naturaland forced draft vaporizers willdefrost adequately in this climate zonewithout any external energy source aslong as the off cycles are at least half theduration of the on cycles. The fan drivenunits will assist in this process.A system can be designed with a largerapproach temperature (approach temperatureis defined as the differencebetween ambient temperature and dischargegas temperature), because of theconsistently warm temperature at nightand during the day. Resulting in greatercapacity from a system rated for less inother climate zones.Mediterranean Climate ZonesMediterranean climate zoneswould include areas such asthe southern and centralcoast of California, Greece, theAlgerian Coast, and other areaslike Italy and Israel. Typically,these regions are characterizedby precipitation periods ofabout four months per year.This climate zone, like the tropicalclimate zone, is very suited to theambient air vaporizer due to the largeambient air driving force available.Generally, the same rules apply withregards to what flow natural draft andforced draft ambient air vaporizersbecome economical choices.The main difference between this climatezone as compared to the tropicalzone is the low moisture content thatcan exist six to nine months of the year.Several unique weather characteristicsresult from this. Infrared radiation mostlyescapes from the atmosphere at nightresulting in possible colder nighttime orearly morning temperatures; a considerationwhen designing approach temperaturesfor this period and ensuringminimum temperatures remain aboveminimum values. The benefit of thisdrier climate is longer switching cycles.Typically, switching less than every eighthours has little benefit, but switchingshould probably be done before 24hours to obtain maximum efficiency outof the units.Humid Continental Climate ZonesThe humid continental climate zonecovers a vast area. In the northern hemisphere,typical areas include the interiorUnited States, Southern Canada, CentralEurope, and Central Asia. These areasare characterized by somewhat tropicaldew point temperatures in the summerand extended cold, dry periods in thewinter, with a combination of the two inspring and fall.The point where forced draft ambientair vaporizers become more economicalover natural draft vaporizers is muchless apparent and must be analyzed morerigorously due to the larger variations inambient conditions. A phenomenonknown as the freeze period (the periodof time in which ambient temperaturesremain below freezing) is one key tovaporizer specifying.Typically, fan-assisted vaporizers willrequire an external energy source inorder to defrost during their off period.Electrical heater assemblies or gas firedexternal air heaters can be used. Becauseof these additional requirements, the fanambient vaporizers become less attractiveover other vaporizers.Natural draft vaporizers must be sizedsuch that each bank of on-stream andoff-stream vaporizers is capable of operatingfor one half the freeze period. Thiscould be up to several months in partsof Canada or North Central Asia, thusrequiring much more surface area(sometimes as much as four timesmore) than in other climate zones. Dueto the tropical nature that may exist inthese areas during the summer, theswitching cycles of these systems istypically based on summer conditions.Because of the potential for very lowtemperatures during winter months,special equipment additions like gassuperheaters may be required downstreamof the ambient units dependingon pipeline limitations. Lower approachtemperatures are often required duringwinter months. Fluids such as carbondioxide and propane that may be vaporizedin tropical zones by utilizing ambientunits should not be considered in humidcontinental climates since it is morelikely you will be subcooling duringwinter periods.Marine Climate ZonesMarine climate zones pose a uniquechallenge to ambient air vaporizerdesigners. Some areas included in thiszone are Britain, the northwest coast ofthe United States, British Columbia,Canada, the far northeast of the UnitedStates, Maine, Norway, New Zealand,Continued on page 75

Members ofHEADQUARTERS:Cryogenic Industries25720 Jefferson AvenueMurrieta, CA 92562 USAPhone: + 1 909 696-7840FAX: + 1 909 698-7484www.cryoind.comskhall@cryoquip.comCosmodyne and Cryoquip have recentlylaunched web sites to assist their customersin learning more about the companies’product lines and to facilitateelectronic mail inquiries. The sites containcorporate and product profiles, personneldirectories, technical product information,employment opportunities, newsreleases, and links to other relevanthome pages.Visit their web sites at:www.cosmodyne.comwww.cryoquip.comEAST COAST USA:Cryoquip, Inc.Allentown, PA USAPhone: + 1 610 437-1867FAX: + 1 610 770-0766lhimmie@aol.comPACIFIC RIM:Cryogenic IndustriesSelangor, MalaysiaPhone: + 60 (3) 365-9075FAX: + 60 (3) 365-4798sgkellett@aol.comNORTHERN EUROPE AND SPAIN:Cryogenic IndustriesLondon, England UKPhone: + 44 181 932-3100FAX: + 44 181 932-3101cryogenic.uk@btinternet.comSOUTH AMERICA:Cryogenic IndustriesMiramar, FL, USAPhone: + 1 954 450-2700FAX: + 1 954 450-8738ort37@aol.comEAST COAST USA:Cryogenic IndustriesAllentown, PA USAPhone: + 1 610 437-0507FAX: + 1 610 770-0766cryoind@aol.comCHINA:Cryogenic Industries ChinaHangzhou, ChinaPhone: + 86 571-885-9026FAX: + 86 571-885-9025hci@public.hz.zj.cnFRANCE:Cryogenic IndustriesBättwil (Basel), SwitzerlandPhone: + 41 61 731-3832FAX: + 41 61 731-3833EUROPE:Cryoquip. Inc.London, England UKPhone: + 44 181 932-3100FAX: + 44 181 932-3101Tero.Hagelin@btinternet.comTorrance, CA USAPhone: + 1 310 320-5650FAX: + 1 310 320-5688info@cosmodyne.comwww.cosmodyne.comMurrieta, CA USAPhone: + 1 909 677-2060FAX: + 1 909 677-2066bsmith@cryoquip.comwww.cryoquip.comCryopump AGAesch, SwitzerlandPhone: + 41 61 751-6000FAX: + 41 61 751-6260ACD purchased all of theremaining assets of Cryomec,Inc., including intellectualproperty, inventory, tooling,casting patterns and all rightsto the name and patents.Through an earlier purchase,ACD acquired the manufacturingrights for Cryomec’sSG pump, a heavy duty, highpressure/high flow reciprocatingpump.Spare parts for all Cryomecpumps can be purchasedthrough ACD directly orthrough one of our regionalservice centers locatedthroughout the world.For more information, contactRichard Young at ACD.College Park, GA USAPhone: + 1 770-909-0291FAX: + 1 770-909-0694tfarmer@bellsouth.netSanta Ana, CA USAPhone: + 1 714 724-8636FAX: + 1 714 641-1921cryocal@ix.netcom.comSanta Ana, CA USAPhone: + 1 714 261-7533FAX: + 1 714 261-6285acd@acdcom.comwww.acdcom.comImperial, PA USAPhone: + 1 724 695-1910FAX: + 1 724 695-1926pittcryo@ pulsenet.comNorth York, Ontario, CanadaPhone: + 1 416 502-1950FAX: + 1 416 502-1952cryocan@istar.caMelbourne, Victoria, AustraliaPhone: + 61 3 9330-2444FAX: + 61 3 9330-1015rmross1@ibm.netCryopump GmbHBad Bellingen, GermanyPhone: + 49 7635 8105-0FAX: + 49 7635 8965Selangor, MalaysiaPhone: + 60 (3) 365-4800FAX: + 60 (3) 365-4798fychan@tm.net.mySelangor, MalaysiaPhone: + 60 (3) 365-4801FAX: + 60 (3) 365-4798jestes@ pc.jaring.my6

FLUID FLOW (GPM)222018161412108642Sub-Zero efficiencyContinued from page 1system. Initial capital costs for the completepumping system is reducedapproximately 20%. Maintenance of thesystem (operation costs) is reduced byas much as 40% depending on operatingparameters, not including liquid losssavings due to less plumbing and cooldown requirements. Overall, the 3-SZGU pump provides reliability,improved overall performance, andPerformance Curve for "SZGU" Triplex Pump1.625ø x 1.50S (85%), 10000 PSIG MAX WP150135120105907560453015100 200 300 400 500 600PUMP SPEED (RPM)MAXSHAFT HORSEPOWER (10000 PSI)costs 20% less than traditional pumpingsystems for well-service or high flow /high pressure applications for industrialgas usage.ACD’s SZ cold ends are available onother reciprocating pump models specificto cylinder filling, storage filling, andother customer applications where cavitationproblems exist due to low NPSP.The SZ cold ends sub-cool liquid andguarantee positive pressure to thepumping chamber for high efficiency,high performance operation for manyapplications.For more information on the 3-SZGUsystem or SZ pumps for cylinder filling orother high flow / high pressure applications,please contact ACD directly or one of oursales/service centers located regionallythroughout the world.Model:Flow Range:Pressure Range:Pump Speeds:Cold EndDiameters:3-SZGU2-20 gpm (7.5–75 l/m)up to 15,000 psig(1,034 bar)50-600 rpm1.625" (41.28mm)1.25" (31.75mm)Strokes: 1.3" & 1.5"(33mm & 38.1mm)NPSPR:Specifications:1psi (0.069 bar)maximumOperating Requirements:Minimum supply 20 psi (1.4 bar)tank pressure: saturated conditionsClimate affects vaporizersContinued from page 5and the southern coast of Argentina.Although ambient temperatures remainrelatively mild throughout the year, usuallybetween 23 o F (-5 o C) and 70 o F(21 o C), the climate is very moist withdew point temperatures commonly veryclose to the dry bulb temperatures aswell as the freezing point of water. Whattends to result is a substantial amount ofcondensation and added precipitationon vaporizer surfaces that quickly freezeinto dense pockets of ice, reducingvaporizer capacity. Extra surface areamust be added to reduce the effects ofthis atmospheric phenomenon.Likewise, the vaporizers need to beswitched much more often to preventthe formation of very dense ice that willnot defrost during off periods if levelsget too substantial. Often vaporizersmust be sized based on two to three dayratings, but switched every two to sixhours to prevent ice buildup.Micro Climate ZonesMicro climate zones exist in every oneof the zones discussed. They are definedas zones that may result in substantiallydifferent weather conditions and mayexist at distances as close as 31miles(50 km) from one to the other. Microclimate zones may have unique wind orprecipitation design requirements. Anexample is the area downwind of theGreat Lakes region in the United States,where major snow fall accumulationscan occur when dry cold winds moveover warmer moist lake air causing theair to become saturated and creatinglocalized “lake effect” snow. Other commonweather phenomenon such as theChinook winds of Montana, the buranwinds of Russia and Central Asia, thebora winds of the Northern Adriaticcoast of Yugoslavia, and the Santa Anawinds of Southern California may resultin special mechanical design requirementsor height limitations due to thesevere winds caused by the venturieffects of local mountain canyons.Altitude effects need to be considered aswell, with appropriate capacity reductionapplied to the vaporizer models.For more information, contact PatrickBillman at Cryoquip, billp@cryoquip.com.Cosmodyne has commissionedan ASPEN 1000 Series air separationplant in mineral-rich Dares-Salaam,Tanzania. The liquidoxygen, nitrogen and argon plantis owned by TOL Limited, acompany active in the expandingTanzanian economy.7

CALENDAR OF EVENTSMAR 15–17MAR 17APR 1–3APR 21–24APR 26–30MAY 6–8MAY 12–15JUL 7–10JUL 14–17SEP 13–18NWSA 1998 SPRING MANAGEMENT CONFERENCEMiami, FL, USA + 1 215-564-3484, www.nwsa.comCOMPRESSED GAS ASSOCIATION1998 MEMBER BUSINESS EXCHANGEFort Lauderdale, FL, USA, + 1 703-412-0900NWSA 1998 SPRING MANAGEMENT CONFERENCEChicago, IL, USA + 1 215-564-3484, www.nwsa.comINTERNATIONAL CONFERENCE ONCRYOGENICS & REFRIGERATIONHangzhou, China, + 86-571-7951771AMERICAN WELDING SOCIETY Annual MeetingDetroit, MI, USA, + 1 305 443-9353NWSA 1998 SPRING MANAGEMENT CONFERENCEBaltimore, MD, USA + 1 215-564-3484, www.nwsa.comCRYOGENICS ’98 IIR INTERNATIONAL CONFERENCEPraha, Czech Republic, + 420 2 684 08 17THE 4th INTERNATIONAL EXHIBITION & CONFERENCEON VALVES & FITTINGSSingapore, + 65 534 3588ICEC 17th International Cryogenic Engineering ConferenceBournemouth, UK, + 44 (0) 170 357 97621998 APPLIED SUPERCONDUCTIVITY CONFERENCEPalm Desert, CA, USA, + 1 510 486-7241“Until I started getting FrostByte, I neverknew what our company did.”The secretof getting ahead isgetting started. The secretof getting started is breakingyour complex overwhelmingtasks into small manageabletasks, and then starting onthe first one.—Mark Twain25720 Jefferson AvenueMurrieta, CA 92562-9524 USABULK RATEUS POSTAGEPAIDSANTA ANA, CAPERMIT NO. 949Put an ELFin your pump. . .coming in April!