Improving Temperature Uniformity at –86 °C in a ... - Biomedical

T E C H N I C A L A R T I C L EImproving Temperature Uniformity at –86 °C in aMechanically Refrigerated Ultralow Freezer:Reducing Compressor Discharge Temperatures and ApportioningEnergy Management Between Low- and High-Stage CoolingCircuitsby Joseph Laporte and Deepak MistryThe development of an application-specific refrigerationcompressor for use in a mechanically refrigeratedcascade system results in lower compressor dischargetemperatures, more balanced workload between highandlow-stage compressor systems, and more efficientlocation of evaporator systems around the interiorchamber in the –86 °C ultralow temperature freezer.As a result, the freezer delivers better chamber temperatureuniformity necessary for stability of storedproduct, better viability of frozen biological materials,and more accurate monitoring of operating anomaliesthat may warrant investigation by service personnel inadvance of maintenance problems. This article examinesnew compressor technology developed specificallyfor use in the ultralow temperature freezer, andhow this new technology will enable biorepositoriesand laboratories to comply with new recommendedpractices emerging from federal agencies such as thoseexpressed in First Generation Guidelines for NCISupported Biorepositories. 1Enhancing the viability of biochemical and biomedicalproducts is essential in today’s life science market.Depending on desired protocols, preservation of biologicalmaterials requires storage at temperatures rangingfrom –10 °C to –40 °C, –86 °C, and as low as –150°C or colder. Because material stored in these freezersis of such a high value, or irreplaceable altogether, thepotential for freezer failure is no longer considered anacceptable risk in the life science community.Simple refrigerationprinciplesA mechanical refrigeration system is designed to removeheat (or move energy) from one location and transferit to another. Key components in a refrigeration systeminclude a compressor, a cabinet for the stored perishableproduct, evaporator, condenser, and refrigerant. Theevaporator is wrapped around the top, sides, and backwall of the interior chamber within the cabinet insulation.The compressed refrigerant liquid passes throughthe evaporator, where it flash-expands into a vapor andabsorbs heat. The compressor moves refrigerant throughthe system and compresses the vapor into a high-pressureliquid in the condenser. The condenser releases the heatto the ambient environment and the process continueson demand from the controller so that the interiorchamber remains at the desired setpoint.Basic ultralow temperaturerefrigeration systemDue to the significant temperature differencesbetween ambient (room temperature) and the freezer(–86 °C), two systems are required for incorporatingindividual compressors and refrigerants with differentboiling points for absorption and dissipation ofheat. A single refrigerant does not have the physicalproperties to cover such a wide temperature range.Thus, ultralow temperature freezers employ a cascaderefrigeration technique whereby two independentrefrigeration circuits operate in a “high-stage” and“low-stage” configuration (see Figures 1 and 2).In the cascade process, the low-stage system removesheat from the product located in the interior chamber.These products typically include vials, bags,canisters, or other commonly used storage containersor labware selected for archival use. Heat fromthis stored product is absorbed by refrigerant gas inthe evaporator tubing wrapped around the interiorchamber and concealed in the insulation. This heatis transferred to an interstage heat exchanger whereit is passed off to the high-stage system and ultimatelyreleased to the ambient as room air is circulatedthrough the condenser coils by a motor/blower/fan assembly. The interstage heat exchanger servesas the evaporator for the high-stage system.CompressorThe most important component of any mechanicalrefrigeration system is a reliable compressor. Becauseultralow freezers require two compressors workingtogether, these compressors are particularly critical tothe operation. Most ultralow freezer manufacturersacquire their compressors on the open market fromcommercial suppliers who also market their productsto air conditioning, refrigeration, supermarket, foodand beverage, consumer goods, and other commercial/industrial OEM customers. In terms of unit production,compressors sold for ultralow temperature applicationscomprise a very small fraction of overall compressorproduction worldwide. As a result, ultralow freezermanufacturers must make concessions to adapt openmarket compressors to highly refined ultralow systems.Because relative demand and economies of scale dictatehow compressor manufacturers serve their markets,manufacturers of ultralow freezers, classified as OEMcustomers, have little leverage in compressor design and/or adaptation to mass-produced product required to overcomeheat and lubrication challenges presented in theultralow environment. In some cases, compressor manufacturerswill not warrant their products to the OEM customerif the compressors are used in high-stress ultralowapplications. This in turn affects the scope and nature ofthe freezer manufacturers’ warranty to the customer.Cause and effectThe challenges of maintaining reliability in anultralow refrigeration system relate to the system as awhole, and most specifically to the compressor, compressormotor, and wrist pins integral to the design.• Commercial air-conditioning compressors are notdesigned for ultralow temperature (ULT) applications.In ultralow circuits, these compressors aresubjected to higher-than-normal operating pressuresrequired to achieve and sustain evaporatortemperatures. Operating pressures generate heat.These pressures demand more compressor motortorque to accommodate startup and to maintainultralow temperatures, thus adding stress andpotentially more heat into the system.• Some ULT freezer manufacturers increase thecompressor motor horsepower in an attempt toovercome these issues. If the total refrigerationsystem is not properly balanced, however, excessmotor capacity simply adds heat to the system.• Refrigeration oil required to lubricate internalcompressor components can break down chemicallyover time, resulting in poor componentlubrication, additional heat, and a reverse cascadeeffect of heat generating more heat.• Operating conditions in laboratories, hallways,mechanical rooms, and repositories are less thanideal. Most freezer installations are compromisedby lack of air conditioning in laboratories or hallways,low voltage at the freezer connection, voltagefluctuations and power surges, high ambienttemperatures and lack of adequate ventilation,dust and particulate buildup on condenser finssurrounding condenser tubing, frequent freezerdoor openings, and poor technique such as introductionof large amounts of warm or room temperatureproduct without prefreezing.• Despite advances in refrigerant chemistry, oils,and lubricating additives, today’s environmentallyfriendly non-CFC refrigerants are not as efficientas earlier CFC-based ozone-depleting refrigerantsof the past.SANYO compressordevelopmentSince mechanically refrigerated ultralow temperaturefreezers were adopted into the mainstream scientificcommunity in the late 1940s, research investigatorshave learned that storing biological materialsat colder temperatures enhances cell viability byreducing metabolic activity. Biological products canbe sustained for longer storage periods at lower temperaturesprovided protocols for sample preparationand pulldown to storage temperature match scientificmethods.A proprietary refrigeration compressor was developedspecifically for ultralow freezer applications. Bypassingthe commercial air conditioning sourcing model,SANYO (Bensenville, IL) has successfully testedand refined its own compressor to meet the physicalchallenges of ultralow temperature operation using00 / SEPTEMBER 2007 • AMERICAN BIOTECHNOLOGY LABORATORY

T E C H N I C A L A R T I C L EFigure 1 The SANYO cascade refrigeration system employs twoindependent refrigeration circuits indirectly connected by an interstageheat exchanger. The company’s proprietary integrated lubricating oilcoolingsystem (patent pending) automatically apportions the workloadbetween compressors and permits both compressors to operate well withinthe expanded performance envelope. 1) Freezer cabinet with evaporator:The evaporator coil is strategically wrapped around the interior chamberand concealed within the composite wall of vacuum insulation panelsand conventional foamed-in-place urethane insulation. 2) Low-stageheat exchanger: Energy is absorbed by the refrigerant gas and transferredto the low-stage heat exchanger to cool discharge gas. 3) Low-stagecompressor: The compressor pumps refrigerant through the low-stagecircuit. 4) Low-stage oil reservoir: High-stage refrigerant passes throughthe low-stage oil sump to cool lubricating oil, resulting in high-stagecompressor energy being used to minimize the workload on the low-stagecompressor. 5) Interstage heat exchanger: Energy is transferred to thehigh-stage circuit. 6) Low-stage capillary tube: Liquid refrigerant underpressure is passed through the capillary tube where it flash-evaporates inthe low-stage evaporator to absorb energy (heat) from the product storedin the freezer. 7) High-stage compressor: The compressor pumps refrigerantthrough the high-stage circuit. 8) High-stage oil reservoir: High-stagerefrigerant passes through the high-stage sump to cool lubricating oil enroute to the low-stage compressor through the air-cooled precondenser.9) Air-cooled precondenser: Removes energy (heat) from the high-stagerefrigerant en route to the low-stage compressor. 10) Main condenserand motor/fan assembly: The motor/fan assembly blows ambient airacross condenser coils to move energy (heat) from the high-stage refrigerantto the ambient environment. 11) High-stage capillary tube: Liquidrefrigerant under pressure is passed through the capillary tube where itflash-evaporates in the interstage heat exchanger to absorb energy (heat)from the low-stage refrigerant circuit. 12) Air-cooled precondenser:Removes energy (heat) from the high-stage refrigerant en route to thehigh-stage oil reservoir. 13) High-stage refrigerant: Commonly availableworldwide. A combination of R134a and R410a (Puron ® ) selected foroptimum cooling performance in compliance with international environmentalprotection laws. 14) Low-stage refrigerant: Commonly availableworldwide, R508. 15) Instrumentation (not shown): Temperature andpressure sensors throughout the high- and low-stage circuits transmitinformation to the Status 3 central controller for operation, monitoring,and interpretation.new, environmentally safe refrigerants. Collaboratingwith industry leaders in refrigeration chemistry,lubrication pathways, natural and synthetic oils, andcabinet insulation technologies, SANYO engineershave created a highly reliable ultralow temperaturefreezer based on the performance of compressorsdoing the work they were specificallydesigned to do.Cabinet designprerequisitesConcurrent with refrigeration system research,SANYO pioneered the development of a compositecabinet wall based on a combination ofconventional, high-density foamed-in-placeinsulation and new, state-of-the-art vacuuminsulation panels (SANYO VIP ® , U.S. patentno. 6,260,377) permitting a thinner wall profileand increased interior volume. This design optimizesuse of available laboratory space by allowingmore storage in the same footprint.Since the original VIP design was introduced,company researchers developed proprietaryimprovements in the open cell panel technique,creating better matrices to support a sustainablevacuum, and giving manufacturing engineersmore latitude in composite orientation withconventional foam. As a result, evaporator coilswithin the thin-wall cabinet are arranged foroptimal interior uniformity and best heat removal(energy transfer), further reducing the burden onthe cascade refrigeration system. A byproductof the design permits a hot gas bypass to circulatearound the peripheral edges of the cabinetdoor gasket, warming the gasket to mitigate thebuildup of moisture to prevent ice formation ormold on external services (see Table 1).Vertical componentintegrationThe concept of vertical component integrationis central to the company’s entire product line.SANYO manufactures its own oil separators,circuit boards, and vacuum insulation panels,and designs its own compressors. This integratedsupply chain ensures component quality fromsource to application, and permits the companyto evaluate and improve its own componentswithout third-party involvement.Together with other refrigeration system componentssuch as filter dryers, heat exchanges,condenser and evaporator tubing, meteringdevices, motor windings, and sophisticatedmicroprocessor-based electronic controls, thecompany has created a holistic solution to biologicalpreservation.Key compressor componentsEach component of the SANYO compressorhas been electronically designed and modeledin stereolithographic beta form to exceedactual operating conditions. Pistons, connectingarms, valve plates, and wrist pins aredesigned to handle high load capacities. Alltesting is performed in a +35 °C ambient.*Proper delivery and return of lubricants is a key factorin extending component life. Compressor motor sizingis predicated on refrigerant flow as well as energyrequired for initial pull-down, and then sustainedultralow temperature with reserve capacity. Motorwindings are configured to accommodate fluctuatingelectrical supplies in many institutional settings. Atthe same time, SANYO’s commitment to “greenproducts” is expressed through more efficient motoroperation with reduced energy consumption.A better compressor yieldsbetter uniformity andimproved reliabilityHeat from multiple sources contributes to compressorwear. Heat is generated by compressors working tocompress low-density refrigerants required in the lowstage of the cascade loop. Additional heat is absorbedby room-temperature product placed into the freezer,as well as migration from the ambient environment.In the SANYO research and development laboratory,prototype compressors were tested under harshenvironmental conditions to exceed actual freezeruse in typical laboratories. Because the companycontrols its own compressor design, all amendmentsand reengineering options were explored as needed,with new prototypes brought into test quickly. Lifetesting and tear-downs delivered critical data toSANYO engineers, permitting beta test results to besynthesized into the complete design program in supportof the global ultralow freezer program.Design mandate: reducedischarge temperatureThe ultralow temperature compressor employs anorientation of conventional components to reducedischarge temperatures and compressor heat whileusing commercially available refrigerants and lubricants.Heat reduction results range from as low as 25°C below previous SANYO compressors and morethan 40 °C below leading-brand compressors used bynumerous competitors.At the heart of the solution is a compressor oilcoolingloop that reapportions the working heatbyproduct between the low-stage compressor and thehigh-stage compressor. Due to low molecular weightsin low-stage refrigerant formulations, low-stage compressorsmust work harder to achieve cooling targets.The SANYO technique uses existing lubricating oilto cool the low-stage compressor, passing the resultingheat load to the high-stage compressor, which,by design, is already doing less work.By shifting a portion of the burden from the lowstage to the high stage, the load on both compressorsis balanced while reducing operating pressuresand keeping heat loads and discharge temperatureswell within tolerances required to prevent chemicalbreakdown of oils and refrigerants. As a result,refrigeration capacity is expanded and structuralengineers have more latitude in strategic applicationof evaporator coils around the interior chamber, akey to temperature uniformity and, ultimately, tocell viability.Applying the benefitWith lower compressor discharge temperatures and pressures,newer refrigerants can be more effective. Combinedwith VIP insulation, the migration of ambient*Testing and evaluation: Consumer Advisory Performance testing and published data on SANYO ultralow temperature freezers is based on extensive testing in a +35 °C ambient to simulate worstcaseconditions. When comparing performance of competitive ultralow freezers, it is important to establish and verify conditions under which tests are performed. Tests performed at temperaturesbelow +35 °C may exhibit lower compressor discharge temperatures; these discharge temperatures are not typical of real-world conditions, however, and should be used with caution when evaluatingnew or replacement freezer selection. For summary information on test conditions contact SANYO (Table 2).00 / SEPTEMBER 2007 • AMERICAN BIOTECHNOLOGY LABORATORY

T E C H N I C A L A R T I C L EIf a condition self-corrects (as most do in highly fluctuatingenvironments), the signal will switch off. Ifthe condition persists, however, the signal will notifythe user that a professional assessment of freezer performanceis required. Often, this assessment can beinitiated by a quick query of on-board data from thecontroller, conducted by in-house facilities maintenancepersonnel familiar with standard ultralowfreezer operations.Figure 2Ultralow refrigeration system benefits.Table 1 Comparison chart: uniformity/noisePerformance SANYO Brand N Brand R Brand FTemperature uniformity 4.2 °C 9.0 °C 12.5 °C 7.7 °Crange (setpoint @ –80 °C)Temperature, top of chamber –86.0 °C –77.5 °C –81.4 °C –81.4 °C(setpoint @ –86 °C)Maximum warming point –75.0 °C –34.3 °C –57.7 °C –76.8 °C(10-sec door opening)Noise level (1 meter from unit) 43.8 dB(A) 51.7 dB(A) 52.0 dB(A) 72.0 dB(A)Storage volume efficiency 2.7 cu. ft./sq. ft. 2.67 cu. ft./sq. ft. 2.28 cu. ft./sq. ft. 2.19 cu. ft./sq. ft.(volume/sq. ft. floor space)Table 2 SANYO ultralow temperature freezer testing protocolAmbient temperature +35 °C. Important: Performance testing and published data on SANYO ultralowduring testtemperature freezers are based on extensive testing in a +35 °C ambient to simulateworst-case conditions. When comparing performance of competitive ultralowfreezers, it is important to establish and verify conditions under which tests areperformed. Tests performed at temperatures below +35 °C may exhibit lowercompressor discharge temperatures; these discharge temperatures are not typical ofreal-world conditions, however, and should be used with caution when evaluatingnew or replacement freezer selection. For summary information on test conditionscontact SANYO.Voltage range during test Variable. For 220 V ac, 60-Hz models testing is conducted over voltage rangesstarting as low as 202 V to simulate brown-out conditions typical of real-worldinstallations.Freezer load during test Variable. Thermal mass of a fully loaded freezer at equilibrium under normalultralow temperatures yields the best performance data. SANYO freezers are testedunder empty, half-load, and full-load conditions.heat from the laboratory to the interior is minimized.Evaporator wrapping concealed within the compositewall is wrapped around the interior chamber to achievebest energy transfer and leverage common physical propertiesof cold air density within the storage area.Smart refrigerationmonitoring systemWhile compressor improvements have led tomore efficient refrigeration performance, SANYOengineers have tapped the company’s extensiveresources in electronics and controls to develop theStatus 3 control, alarm, and security system. Morethan just a controller, the system collects internaldata from waypoints deep within the cascade refrigerationsystem, and processes this information bycomparing to normative values written to the onboardalgorithm. This continuous, self-diagnosticprotocol is automatic. If values range beyond thosewritten to the factory-based performance permissions,the freezer will display an advisory signal onthe main control panel.Status 3 functions1. High ambient conditions• The Status 3 system tracks high ambient (roomor hallway) conditions that can occur periodically,but are not recommended for long-termoperation. These usually constitute ambienttemperatures at or above +35 °C. Repeatedexcessive ambient readings will activate thewarning and the user must investigate thereason for the high ambient condition. TheSANYO freezer will continue to function, butsubjecting the freezer to extreme ambient conditionsresults in longer refrigeration run timeand higher energy costs.2. Low voltage• Low voltage is common in many laboratoriesdue to increased power demand in clinicaland research environments, drug discovery,storage, and processing. These conditions aremost common in older institutions or thosethat have been retrofitted for laboratory use.• Often, freezer users mistakenly assume thatproper power (120 V or 208/230 V) is readilyavailable and sustainable at the wall electricaloutlet. Often, however, supply voltageis erratic and usually lower than desired forproper freezer operation. The Status 3 detectslow voltage and warns the user through thefreezer control panel monitoring system.When this notification occurs, building maintenanceor facilities engineering personnelshould be contacted to investigate the issue.• To protect the valuable stored product, SANYOultralow freezers with voltage enhancementsystems will automatically correct the voltagethrough an internal transformer and boost thevoltage to the proper level.Run time dataHigh ambient temperatures, numerous or prolongeddoor openings, and introduction of warm or roomtemperatureproduct into the freezer storage compartmentcan cause prolonged refrigeration systemrun time. The Status 3 monitors compressor run timeand performs diagnostics based on ambient temperatures,door openings, voltage, and other usage factors.If the low-stage compressor run time is inordinatelyhigh, the Status 3 will notify the user that thesystem and installation should be reviewed. Thesecalculations are based on the following:• Length of time from previous door opening• Operating time below setpoint• Ambient temperature.In simple terms, the freezer senses when it is overloadedor operating under stress. The Status 3 warningsystem will alert the user of this condition inadvance of any pending performance issues.Compressor run time/powerconsumptionThe SANYO ultralow system employs a high-stage andlow-stage compressor controlled by the Status 3 micro-00 / SEPTEMBER 2007 • AMERICAN BIOTECHNOLOGY LABORATORY

T E C H N I C A L A R T I C L Eprocessor control system. By design, the high-stage compressorruns 100% of the time, permitting the low-stagecompressor to cycle on demand for cooling from theinterior chamber, reducing high head pressures on thelow-stage system, permitting easier startup and reducingenergy demand. Since conventional cascade refrigerationsystems cycle both systems on and off, the highandlow-stage compressors must “step start” nearly simultaneouslyor with a slight delay. This requires a high powerdemand for two systems to start, and can trip a circuitbreaker during periods of high electrical demand.The phenomenon of high-temperature “in-rush currents”over time can weaken and degrade compressorwindings, resulting in compressor failure. SANYOcompressors feature oversized windings designed toanticipate and accommodate in-rush currents withinthe normal performance envelope to mitigate compressordegradation due to frequent startups.Thinking green, thinkingsafe*SANYO is conscious of the need to protect our environmentand conserve energy. As a corporate pioneerin life science laboratory equipment and appliances,and as a global source of solutions ranging from energymanagement to solar power and alternative energies,the company remains committed to providing thebest possible laboratory equipment for research andclinical needs. This commitment was demonstratedwhen it took the initiative to revamp and redesignnewer refrigeration systems that would employ new,environmentally friendly refrigerants throughout thelaboratory without compromising performance.1. CFC-free refrigerants• SANYO was the first ultralow freezer manufacturerto employ non-HCFC R508 lowstagerefrigerant, now recognized as today’sindustry standard and widely available.This nonproprietary refrigerant is availableto refrigeration service professionals on theopen market.• The high-stage refrigeration system is a mixtureof R134a and R410a (Puron), availableto refrigeration professionals on the openmarket as well.2. RoHS compliance• In 2006, RoHS (Restriction of HazardousSubstances) legislation (EU Directive2003/95/EU) became effective. RoHS relatesto the restriction of hazardous substances andreductions in environmental pollution.• Through RoHS legislation, the EU and otherparticipating countries are banning toxicsubstances in electrical equipment such aslead, cadmium, mercury, chromium 6+, polybrominatedbiphenyls (PBBs), and polybrominateddiphenyl ethers (PBDEs).• While compliance with this legislation hasposed a significant challenge for SANYO, allof its ultralow freezers and components arenow 100% compliant to RoHS standards.3. Electrical standards• All SANYO products, including ultralowtemperature freezers, are tested and certifiedby Entela 2 NRTL (National Recognized TestingLaboratory) to ensure compliance withU.S. and international standards for electricalsafety prescribed in 29 CFR 1910.7(c).SANYO has selected Entela for independenttesting to accelerate testing on new productswhile maintaining the highest standards forquality, safety, and performance.4. Noise reduction• Ultralow freezers are often located withinresearch and hospital laboratories or productionfacilities. Users prefer close proximity foreasy access to valuable stored products.• If operating noise from refrigeration compressorsis excessive and/or compoundedby installation of multiple freezers in adjacentlocations, the working environment isseverely compromised.• SANYO has included advanced noise abatementin all contemporary ultralow freezersand noise reduction levels are well belowthose of competitive freezers. (Data are availableupon request.)5. Inventory management• Those familiar with the technical designof the SANYO ultralow freezer can draw aquick connection between lower compressordischarge temperatures and better, more efficientinventory management.• Because benefits of the SANYO compressordesign extend to evaporator tubing surroundingthe interior chamber, and the interior chamber ispart of the thin-wall composite based on the patentedVIP cabinet, the company can offer moreuseable storage volume within the same squarefootage of floor space than competitive models.• The concept of high-density storage isenabled by advances in SANYO compressordesign. The cost per cubic foot (or liter) ofinterior storage space is significantly lowerin a SANYO ultralow freezer, generatingimmediate return on investment based onfirst costs, operating costs, and maintenancecosts over time.• Additionally, the placement of evaporatorsurfaces within the cabinet walls achievesdocumented ultralow temperature uniformity,thereby permitting investigators morefreedom in placing valuable cell lines andbiologicals within the interior cabinet, andensuring uniform cell viability when harvestingproducts from the ultralow archive.ConclusionBy apportioning the oil-cooling function betweenspecially designed SANYO compressors, and byemploying cooler oil to minimize compressor operatingtemperatures, the SANYO ultralow temperaturefreezer refrigeration system is balanced to decreasecomponent stress, increase system longevity and reliability,and improve temperature uniformity necessaryfor better cell viability regardless of where thespecimen is stored within the chamber.References1. Fed. Reg. vol. 71, no. 82/Fri., Apr. 28, 2006/NoticesRe: Department of Health and Human Services,National Institutes of Health, First-Generation Guidelinesfor NCI Supported Biorepositories. Agency:National Institutes of Health (NIH), National CancerInstitute (NCI).2. Fed. Reg., Entela, Inc., Expansion of Recognition.64:11501-11502; publ. date: 03/09/1999; publ.: notice;Fed. Reg.: 64:11501–11502; standard number: 1910.7;1919.7; title: Entela, Inc., Expansion of Recognition.U.S. Department of Labor, Occupational Safety andHealth Administration, docket no. NRTL-2-93.Mr. Laporte is Service Manager, and Mr. Mistry is MarketingManager, SANYO Commercial Solutions, A Divisionof SANYO North America Corp., 1062 Thorndale Ave.,Bensenville, IL 60106, U.S.A.; tel.: 800-858-8442; fax:630-238-0074; e-mail: DMistry@SSS.Sanyo.com.*SANYO has established a corporate-wide initiative, Think GAIA, to emphasize its commitment to energy conservation and environmental integration. GAIA, which stands for “the livingearth,” suggests that the earth is a green organism where mankind and all livings things exist in harmony. By treating the earth as a living organism, SANYO is creating products needed to promoteharmony with the planet. In practice, GAIA is a threefold approach consisting of action on environmental, energy, and lifestyle fronts. In each of these areas, SANYO is redefining conventionalideas and taking advantage of unique technological resources to propose global solutions for the earth and all living things.00 / SEPTEMBER 2007 • AMERICAN BIOTECHNOLOGY LABORATORY

Improving Temperature Uniformity at –86 °C in a ... - Biomedical

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