Carbon Dioxide Snow Cleaning
by Applied Surface Technologies
Carbon Dioxide Snow Cleaning systems are for the most part straightforward, they consist of a CO2 source, a nozzle with an internal orifice, an on/off valve, and the means to transport the CO2 from the source to the nozzle. A typical system, such as shown below, consists of a cylinder fitting, tubing, an on/off gun or valve and a nozzle. The units are made with a PTFE lined flexible stainless steel hosing. Available on/off controls include solenoid, pneumatic, or manual valves, or hand guns. Details are below. The units below are aimed at precision cleaning; units for telescopes mirrors and art conservation are on those pages.
Standard unit
The standard unit (K1-10) from Applied Surface Technologies, shown below, is supplied with two nozzles - one asymmetric venturi stainless steel on the unit and a second low velocity nozzle, an on/off gun, a 10 foot flexible PTFE lined stainless steel hose, and a cylinder fitting. Optional submicron sintered stainless steel filter,s and an 0 - 2000 psi pressure gauge can be added. CO2 cylinder fittings for North American (CGA320), Europe (DIN-6), Japan (JIS22R) are available. The DIN-6 is the ISO international standard and works in many other countries. The British BS-8 is also available. We can find a fitting for most countries with your assistance.
High Purity Unit
The high purity unit (K4-10) from Applied Surface Technologies shown below has a packless electropolished stainless steel diaphragm valve to control carbon dioxide flow. Included in the figure are the venturi nozzle, a 10 foot flexible stainless steel PTFE lined hose, and a CO2 cylinder fitting. All fittings for this unit are compression fittings as opposed to NPT fittings for the standard unit shown above. Two stainless steel nozzles also comes with this unit, the asymmetric venturi and a low velocity nozzle. CO2 cylinder fittings for North American (CGA320 or CGA716), Europe (DIN-6), Japan (JIS22R). The DIN-6 is the ISO international standard and works in many other countries. The British BS-8 is also available. We can find a fitting for most countries. Further, the high purity unit valve can be made with VCR or VCO type fittings (K4-10VCR). Optional filters and pressure gauges can be added.
Solenoid Controlled Units
For semiautomatic operation, a 24VDC or solenoid valve (close up of the valve below with compression fittings) can be selected in place of the 90 deg. on/off valve shown above. This unit is referred to as the K4-10S and ia close up of the solenoid valve and nozzle is shown below on the left. The K4-10S comes with the venturi nozzle on the unit, the 24 V Dc normally closed solenoid, 10 feet of a PTFE lined flexible stainless steel braided hose, a CO2 cylinder fitting, a 24 VDC power supply (CE approved with 120 to 250 VAC input), and a foot switch for manual control. Options include an inline filter and pressure gauges. The image to the right shows the first totally portable CO2 Smow Jet, the K4-10S-Port. It can be equipped with Li-ion batteries or the usual footswitch. The battery unit will have a switch on the handle and batteries on the CO2 cylinder.
Portable Units
We introduced two new portable units, the K1-Port and the K4S-Port. The goal was to make refilling easy so it ca be done onsite from a CO2 cylinder (liquid feed) at your site. We now use stainless steel sampling bottles with valves at both ends. Sampling cylinders come with 300, 400, or 500 cubic centimeters volume. The 300 cubic centimeter cylinder has about 250 grams of liquid CO2. Both units have CO2 gas feeds, but the solenoid based unit can be held upside down yielding liquid feed. The solenoid unit comes with a power supply and foot switch.
Close up of solenoid
K4-10S Solenoid unit without foot switch
K1-Port K4S-Port
The Dual Gas Unit
There are dual Gas Unit offers a special nozzle with a compressed gas or nitrogen flow surrounding the carbon dioxide nozzle. This unit assists in reducing moisture condensation problems. The dual gas unit has is based upon the High Purity unit (K4-10S) and an additonal plastic nozzle for the second flow. There are two models - K6-10DG-A uses two solenoids for control along with a dual foot switch. Model K6-10DG-B uses a manual valve for the second dry gas flow.
The photo on the left shows the close up of the Model A nozzle region - there are two solenoids, one for the CO2 and the other for the dry gas. A filter is shown on the CO2 flow. The white polymer nozzle is where the compressed gas enters and exits surrounding the CO2 flow. The Model K6-10DG-B is shown with a top view in the right image. The manual valve control the dry compressed air or nitrogen flow. Optional filters are on both flows. Either unit can be use aheated second gas flow to assist in moisture reduction.
K6-10DG-A with one filter K6-10DG-B with two filters
Nozzles
Two nozzle come with the standard (K1) and high purity units (K4) - one is stainless steel and is the asymmetric venturi, and the second is either a high or low flow nozzle. The venturi nozzle is stable for either gas or liquid carbon dioxide feeds while the second nozzle is stable for liquid carbon dioxide feed.
The venturi nozzle has an internal 400 micron orifice though other diameters ranging from 200 to 1000 microns have been made. The nozzle design is by far the most important factor in performing CO2 snow cleaning. The simplest nozzles are the single expansion nozzles and are usually variations of a Venturi orifice design. The exit side is more typically a nosecone and this chamber is for dry ice nucleation. Its angle and length play an important role in determining the velocity of the stream and the snow size. Other nozzle designs are available including orifices followed by an expansion zone, small diameter orifice tubes, and metering leak valves but they nozzles violate constant enthalpy conditions. These nozzles only form snow with liquid CO2 feed. Different cleaning abilities can result from different designs.
The nozzles from Applied Surface Technologies can operate with gas or liquid CO2 while other nozzle geometries may not. This difference in operation is related to the fact that other commercial nozzles have a sudden expansion internal to the nozzle. This sudden expansion violates the need for a constant enthalpy expansion and causes the enthalpy to decrease enough to exit the mixed gas-liquid phase region shown earlier on the snow formation page under FAQ. When these nozzles are used with a liquid source, snow forms and with proper velocities, they just waste carbon dioxide.
Nozzles for different situations have been made, manifold of many point nozzles, inner diameter tube cleaning, large area nozzles. Large area slot nozzles are problematic above 1 inch and are not available.
