Cryocooler Contamination (Cryogenics Refrigerators, Coolers, Engines)

HOW TO USE THIS WEB SITE: This web site is divided into 21 main sites as represented by the twenty one yellow buttons on the top of each page. The user can surf from one main site to another using these bottons. Within each main site use the vertical navigation bar on the left hand side to navigate from one page to another. Use the search command on the upper left to find what you are looking for.

Join these leading companies today!

China Hotels & China Tours
China Tours Tailor
China Tours and Cruises
China Tours & China travel
China Expetition Tours,China Holidays, China Family Tours & China Travel Guide
Kiseido,Yutopian.net

China Tours & Yangtze Cruises
Your Advertisement here
Mahjong Solitaire
China Culture Tour, Private China Tours, China City Tours

China Tours, China Hotels, China Flights and YangtzeCruise,
China Tours, China Flights, Hotel in China, Beijing Tours
Beijing Tours & Tour of Beijing

For advertising information, please click here

Please Visit Our Sponsor

Gift Shop

Cryocooler Contamination (Cryogenics Refrigerators, Coolers, Engines)

If you like the contents of our webpage, you will love our new Cryogenics book (only $20) the materials in this book has been taught in a Cryogenics course at UCLA. It is packed with >200 pages of information and references, with an index for easy lookup.

As the mean time to failure (MTTF) of cryocoolers approaches and surpasses 10,000 hours, contamination becomes a crucial factor that impacts cooler's life. Cooler manufacturers are faced with the task of further reducing the beginning-of-life contaminant levels so that the end-of-life levels will yield performance that meet the specification. This translates to longer bake-out time at elevated temperatures. To shorten the process time, bake-out at a higher temperature is called for. This requires knowledge of outgassing as a function of temperature.

Outgassing properties of various gaseous and liquid contaminants in cryocoolers have been investigated in Reference 1. Due to the lack of outgassing data as a function of temperature, a linear function was adopted, assuming desorption of gases from a monolayer. Further testings indicated that the temperature dependence of outgassing is nonlinear. The test setup and procedure are described in Reference 1, except that the test chamber temperature was varied between 23 C and 100 C. An exponential dependence of concentration on temperature was found, with much higher outgassing rates at elevated ambient temperatures (Reference 2).

The high outgassing rate at elevated temperature was first attributed to the possibility of phase transition. >As the boiling points of the liquids are exceeded, vaporization of the liquids may have resulted in the high contents of concentrations being measured. Further testing on the outgassing property of air shows that it exhibits similar exponential behavior. This confirms that the exponential outgassing property as a function of temperature is intrinsic to all gases and liquid tested.

Using a least squares curve approach, the above data can be fitted with the following equation.

m = K₁ exp ^(BT) + K₂......................................Eq. (1)

Where m is the concentration, T is the ambient temperature, B, K₁, and K₂ are constants.

Knowing the temperature dependence of the outgassing property, one can then combine with the time dependence function reported in Reference 1 to arrive at the following equation.

m = m_o exp ^(BT) [1-exp ^(-t/A)]..............................Eq. (2)

Where m_o is a function of the initial contaminant level in the system (i.e., the larger the value of m_o the higher the contamination level), B is the temperature dependence constant found in Equation (1), and A is the time dependent constant found in Reference 2. The values of these constants are listed in Table 1.

Table 1- Outgass parameters of acetone, alcohol and water.

	m_o(PPM)	B (dimensionless)	A (dimensionless)
Acetone	22.69	0.0384	100
Alcohol	0.111	0.0666	36.4
Water	0.607	0.0512	45.0

Care must be taken in applying values in Table 1 for Equation 2, for the contamination level inside a cooler is a function of the amount of gas in the cooler.

References:

"Cryocooler Contamination Study", in the proc. of Adv. in Cryogenic Engineering, vol. 45A, P275, 1999. (with D.T.Kuo and A.S. Loc) Abstract Download

"Cryocooler Contamination Study: Temperature Dependence of Outgassing", to be published in the proc. of the 11^th International Cryocooler Conference, 2000. (with D.T.Kuo) Abstract Download

Do You Know Someone Who Needs A Job in Engineering, Physics or Chemistry?

About the author- Dr. Sidney Yuan is a consultant in the field of Low Temperature Physics and Cryogenics, and has written a Book on Cryogenics and published extensively in the field. E-Mail.

Bookmark This Page

Send This Page To A Friend