Dewar Flasks Made of Glass
Construction and Function of Dewar Flasks
Dewar flasks are double walled vacuum insulated flasks made of glass or metal, which have the task to thermally insulate a therein-stored product (LN2; CO2 etc.) against the ambient temperature. Dewar flasks consist of an inner and an outer recipient, whichare connected on top at the filling port. The space between the inner and the outer flask is vacuum insulated, to stop the heat contact between the product stored in the Dewar flask and the ambient temperature (contact warmth). Additionally, Dewar flasks made of glass have a silver coating in the vacuum space, in order to minimise the warmth radiation. The best possible insulation could be received by reducing the contact warmth and the radiation warmth.
Admissible Operation Conditions for Standard Glass Flasks
Temperature range Dewar -200°C to +200 °C Temperature range other components -10°C to +80 °C Pressure range depressurised
Standard -Dewar flasks are not appropriate for the use of liquid and gaseous helium. Special design is available on request.
Standards and Guidelines
All of the EMCLAB glassware are manufactured considering —Guideline of pressure devices", directive 97/23 EC and DIN 12492 "Equipment with vacuum insulation". Under the condition that there are any standards for joint parts such as spherical ground joints or conical ground joints, those will be utilised (e.g. DIN 12242-1 and DIN 12244-1).
Verifications
Each of the EMCLAB products is subject to individual verification and identification, as well as the documentation of all manufacturing data.
Testing device for measurement of the LN2 evaporation rate Helium leak test device Ultrasonic wall thickness measuring instrument Vacuum measuring and calibration device Temperature measuring and calibration device Water and compressed-air testing device for reaction vessels Temperature testing device for columns
For the evaporation rates of Dewar flasks mentioned in the catalogue, the flasks were covered with the appertaining lid respective plug, and were verified with the coolants (liquid nitrogen, or dry ice) mentioned in the catalogue. The figures (evaporation rate) are stated in the catalogue in L/h (litres per hour) or as holding time in hours.
Material - Glass
All the glassware from EMCLAB are made of borosilicate glass 3.3 DIN/ISO 3585. The glass has the following characteristics:
Chemical characteristics hydrolytic resistance : according to DIN-ISO 719 (98°C) acid resistance : according to DIN12116, acid class 1 acid resistance : according to DIN-ISO 1776 alkaline resistance : according to DIN 52322 alkaline resistance class : according to DIN 52322-A2 :according to ISO 695-A2
Optical characteristics spectrum region, where the : 310-200 mm absorption is negligible low
Physical characteristics linear expansion factor : 3,3 x 10-6 1/K (at 20°C-300°C)
density : 2,23 g/cm3
specific thermal capacity : 910 J/kg K
transformation temperature : 525 °C
Application
flexible applications in laboratory
cooling of small samples
storage: liquid nitrogen (LN2), dry ice (CO2), other coolantsas insulating flask
Advantages
high insulating ability, easy handling, made of Borosilicatglass 3.3, deliverable: fully silvered (standard), not silvered, silvered with viewing stripes, shortened
Versions
C: blue coated metal cover
G-C: blue coated metal cover incl. side grip
Application
tempering of round bottom flasks
cooling of small samples
suitable as a hot or cold bath
suitable on magnetic stirrer
Advantages
easy handling, aluminium cover: antimagnetic, stainless
made of Borosilicatglass 3.3 fully silvered
Application
storage and transport of temperature-sensitive goods e.g. dry ice (CO2)
flexible applications in laboratory
cooling of small samples
as high quality insulating flask
when storing liquid nitrogen (LN2) a hole (Ø ca. 2 mm) in centre of the lid is necessary
Advantages
robust design, made of Borosilicatglass 3.3, incl. insulated lid held by two spring clips, incl. handle made of aluminium
Versions
B: blue coated metal cover
BE: stainless steel cover
Application
storage and transport of temperature sensitive goods e.g. dry ice (CO2)
suitable as insulating flask
Advantages
robust design, large opening, made of Borosilicatglass 3.3, insulated lid (incl. grip), handle or two grips
deliverable: fully silvered (standard), silvered with viewing stripes, incl. quick release clamp, shortened
Version
C: blue coated metal cover
Application
storage and transport of liquid nitrogen (LN2)
Advantages
low evaporation rate, good tipping stability, made of Borosilicatglass 3.3, incl. loose lied lid, incl. handle, deliverable: fully silvered (standard), silvered with viewing stripes
Version
AL: aluminium cover, brushed
Application
flexible applications in laboratory
cooling of small samples
storage and transport of: liquid nitrogen (LN2), dry ice (CO2), other coolants
suitable as insulating flask
Advantages
good resistance to breaking, easy handling, made of stainless steel, side grip and carrying handle (except DSS 500/GSS 500: no carrying handle)
Application
tempering of liquids
the tempering medium is pumped round the double walled casing with the aid of a thermostat
Advantages
made of Borosilicatglass 3.3, operating temperature max. 300 °C for Type T and max. 120 °C for Type T-GL,
coolant ram pressure max. 0,5 bar, high thermal resistance, very good chemical resistance, transparency, deliverable various special jacket joints, special dimensions
Versions
T: with hose connectors
T-GL: with screw hose connectors
Application
tempering of liquids
the tempering medium is pumped round the double walled casing with the aid of a thermostat.
Advantages
made of stainless steel, good resistance to breaking, stainless, operating temperature max. 200 °C (further temperatures by request), coolant ram pressure max. 0,5 bar, olive welded
Construction, Operation And Principles
Cold traps are used in conjunction with vacuum pumps to collect condensation produced from humidity or solvents and these cold traps can be used for many different tasks. The most common application is collecting condensation produced from humidity or solvents from rotating discs, vacuum pumps or high vacuum systems that use oil diffusion or turbo-molecular pumps. In this case a common coolant such as liquid nitrogen (LN2) or dry-ice (CO2) with acetone is normally used.
Cold traps can be manufacturer from glass or metal. The use of glass is advantageous in the chemical sector and when producing condensation from solvents, due to its resistance to chemicals. The cold traps listed in our catalogue are produced solely from 3.3-type borosilicate glass, in compliance with DIN/ISO (DURAN made by Schott). The mechanically design takes into account the wall thickness for use under vacuum.
Cold Traps – Different Versions
Simple cold traps, which are also known as cold finger condensers, are used in standard applications in conjunction with vacuum pumps and the condensation is forced out of the humidity or solvents used in the chemical applications. The cold trap is used to protect the vacuum pump in this case and the speciality of this type of construction is that the user does not need to use a stand to hold the cold trap. The cold trap has a rim, which is hung inside the Dewar-flask's support ring. The cold trap can be changed very quickly without any problems arising.
Cold Traps Fitted With A Spout
An upgraded version is a cold trap fitted with a spout. These cold traps are constructed in the same way as standard cold traps but have a GL 32 glass thread together with a screw-on cap, which is the actual spout. This spout enables the condensation to be simply poured out of the cold trap and the cold trap is also simple and easy to clean.