Thermal Loading Calculations (Updated January 12, 2009)

The thermal loads are calculated and shown in the file ThermalLoadTotals7pixel.XLS with the 15K to 300 K arrangement : 5" of copper WR42 output waveguide, 9" of SS WR42 output waveguide, a sliding waveguide joint, and a wr42 thermal gap (14 total).

Waveguide Window Leakage

The attached page summarizes the leakage rates for various waveguide window materials. A vacuum 10^-5 Torr increases the convection loading of Helium (1st stage loading of ~ 4 Watts). The table includes the number of days to reach this vacuum based on measured leak rates of materials and assumes a typical 0.51/101323 pressure of He. This may be an underestimate since He is the coolant for the GM refrigerators and may raise the ambient level. Charcoal traps effectively adsorb the He and extend this time

Waveguide Window Outgassing

April 2008 out gassing measurements of Ecco Foam PS102 are given here :TestSummary.xls. The test dewar measured 12.75" diameter x 21.5" height. The sample was cylindrical with dimensions 6.25" diameter x 3" height. From these measurements the rate is: 1.1 10^-3 atm cm^3/s or flux assuming STP as 1.41772*10^-6 atm cm^3/cm^2-s.

Taking into account the surface area of all the windows(14 wr42 windows and 7 circular windows) and the presumed outgassing ratio of 0.51/101323 for He gives 3.7 atm cm^3/s leak rate, or 236 days to reach 10^-5 Torr( 13 10^-9 atm)

Charcoal Adsorption

This paper charcoalcurves.pdf gives Langmuir curves for charcoal adsorbent. The fractional coverage for a monolayer of adsorbed gas as a function of pressure P is given by the equation, v/vm = B P/(1 + BP). A fit to the Langmuir curves gives B = 300 atm^-1 and vm = 50 atm cc/g of material for He adsorption at 10 K. The constant B scales exponentially with inverse temperature giving a correction of .8 for B at 20K. A total of 67 grams for one year of adsorbate is needed. With a bulk density of 0.4 g/cm^3, a total of 838 cm^2 area of 2 mm charcoal is required, or a ~6 inch square plate with charcoal on both sides.

Topic attachments
I Attachment Action Size Date Who Comment
CRYORadiative7p_SI.xlsmxlsm CRYORadiative7p_SI.xlsm manage 54 K 2010-11-11 - 10:35 StevenWhite  
CRYORadiativeLoading.XLSXLS CRYORadiativeLoading.XLS manage 61 K 2007-12-17 - 15:36 StevenWhite  
CRYORadiativeLoading7pixel.XLSXLS CRYORadiativeLoading7pixel.XLS manage 111 K 2009-12-22 - 10:39 StevenWhite  
CRYOtermalconduction.XLSXLS CRYOtermalconduction.XLS manage 94 K 2009-12-22 - 10:40 StevenWhite  
ThermalLoadTotals.pdfpdf ThermalLoadTotals.pdf manage 14 K 2007-12-13 - 14:28 StevenWhite  
ThermalLoadTotals.xlsxls ThermalLoadTotals.xls manage 48 K 2007-12-17 - 15:36 StevenWhite  
ThermalLoadTotals7pixel.pdfpdf ThermalLoadTotals7pixel.pdf manage 16 K 2009-01-15 - 09:55 StevenWhite  
ThermalLoadTotals7pixel.xlsxls ThermalLoadTotals7pixel.xls manage 402 K 2009-12-22 - 10:40 StevenWhite  
ThermalLoadTotalsSS.pdfpdf ThermalLoadTotalsSS.pdf manage 20 K 2007-12-17 - 15:33 StevenWhite  
ThermalLoadTotalsSmallDewar.pdfpdf ThermalLoadTotalsSmallDewar.pdf manage 16 K 2008-05-22 - 09:40 StevenWhite  
ThermalLoadTotalsWG.pdfpdf ThermalLoadTotalsWG.pdf manage 21 K 2008-03-04 - 14:12 StevenWhite  
Windowleaks.pdfpdf Windowleaks.pdf manage 6 K 2008-05-14 - 08:59 StevenWhite  
Windowleaks.xlsxls Windowleaks.xls manage 37 K 2008-05-14 - 08:59 StevenWhite  
charcoalcurves.pdfpdf charcoalcurves.pdf manage 354 K 2008-05-14 - 15:57 StevenWhite  
cryosorbentDay_10.pdfpdf cryosorbentDay_10.pdf manage 48 K 2008-05-16 - 16:48 StevenWhite  
Topic revision: r60 - 2010-11-11, StevenWhite
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