40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  ATF eLog  Not logged in ELOG logo
Entry  Mon May 3 16:56:59 2021, Stephen, DailyProgress, Cryo vacuum chamber, Cooling power of current setup IMG_8665.JPG
    Reply  Sun May 9 11:14:30 2021, Paco, DailyProgress, Cryo vacuum chamber, Cooling power of current setup strap_1D_heat_transfer.pdf
Message ID: 2562     Entry time: Mon May 3 16:56:59 2021     Reply to this: 2565
Author: Stephen 
Type: DailyProgress 
Category: Cryo vacuum chamber 
Subject: Cooling power of current setup 

StephenA

This log investigates cooling through our current planned copper braid connection (which is standing in for an intended rigid bar linkage that is WIP)

The question is, can we get [cooling power of cryocooler] out of our baseplate through this copper braid?

Copper Braid

Cooner Wire P/N NER 7710836 BOF (oxygen free copper)

  • AWG Size 2/0
  • Circular Mil Area 132300 (conversion: .104 in^2 = 6.71e-5 m^2) - note that a 1 cm x 1 cm bar would have an area of 1e-4 m^2
  • No. of Wires 5292
  • Wire AWG Size 36
  • Construction 7x7x108/36
  • Nominal Diameter .483"
  • Pounds Per MFT 433.

ref. https://www.coonerwire.com/flexible-wire-rope/

Cryocooler

Sumitomo CH-104 (manual from Wiki) has 77K coldhead cooling capacity of 34 W, and from the quote, 50K cooling capacity of just under 40 W.

Adequate cooling power of this setup depends on the radiative heat load and conductive losses; for our purposes, we can imagine that tens of Watts will be needed, and circle back to more precise heat budgeting.

Conductive Heat Transfer

Q = A / L * (Uint_T2 - Uint_T1)

Uint_T = the integral of thermal conductivity between T and 4K, see below table [ETP OFE Copper, W/m]. Note these are values from literature not from our copper braid's spec sheet (no such properties available from vendor).

Table of Thermal Conductivity integral values, between T and 4K. Unit = W/m. Source: Ekin, Appendix 2.1

               20K = 14000, 40K = 40600, 50K  = 50800, 60K = 58700, 70K = 65100, 80K = 70700, 100K = 80200, 120K = 89100, 140K = 97600

A = 6.71e-5 m^2

L = 0.5 m (estimate)

T2 = 123 K (intended workpiece temperature)

T1 = ? (coldhead temperature, unknown, we will pick a value and calculate)

Q(T1_80K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 70700 W/m) = 2.46 W

Q(T1_20K) = 6.71e-5 m^2 / 0.5 m * (89100 W/m - 14000 W/m) = 10.07 W

Conclusion

It appears that the copper braid's capacity for conductive heat transfer will constrain the tens of Watts of cryocooler capacity. This is even before we consider imperfections in the clamping interfaces and similar real losses.

Fixes for this constraint might involve adding parallel linkages (increasing area) or shortening the strap length.

It would be interesting to compare this to the anticipated capacity of the flexible strap in the original design - future work.
 

Attachment 1: IMG_8665.JPG  2.625 MB  Uploaded Fri May 7 11:38:01 2021  | Hide | Hide all
IMG_8665.JPG
ELOG V3.1.3-