VTCS evaporator block design and prototyping. Status report July 2004

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1 VTCS evaporator block design and prototyping Bart Verlaat, Luc van Diepen & Martin Doets (NIKHEF) Frans Mul (VU) 30-Jul-04 1

2 VTCS evaporator block design (1) Detail of cooling block mounted onto the VELO module Evaporator block is 30-Jul-04 situated underneath the module cables 2

3 VTCS evaporator block design (2) Evaporator header Ø6x1 pipe Orbital TIG weld Laser weld Ø1.5x0.25 pipe Aluminum cooling block 30-Jul-04 3

4 VTCS evaporator block design (3) 1. A NIKHEF/VU developed aluminum casting method allows embedded piping to be of any shape, with a full thermal contact over the entire pipe area. 2. Casting under vacuum (<10-4 mbar) gives that the aluminum is floating perfectly in the mould and sticks itself to the stainless steel pipes, by the formation of intermetallic phases. 3. A good thermal contact of the cooling block to the pipe is expected due to the following properties: The CTE difference of aluminum and stainless steel gives a strong crimping force of the block around the pipe No intermediate filing material with low thermal conductivity is needed (glue, solder, etc) around the pipe The aluminum tends to stick to the stainless steel pipes when melted under vacuum (See note 2). 30-Jul-04 bverlaat@nikhef.nl 4

5 30-Jul-04 5

6 Cooling block connection detail Aluminum potting in the paddle base top area makes the laminate symmetric to minimize bi-metal forces. 30-Jul-04 6

7 VTCS evaporator block prototyping Optimal process parameters (So far known): Evacuate the vacuum chamber before heating Setting the oven to be 700 C for 1 hour After sensor in casting mould has reached 700 C the Argon is inserted (oven time is approx. 30 minutes) Solidifying is obtained with a closed oven Melting under vacuum and solidifying under Argon gives the best results Perfect floating of the aluminum in the mould Aluminum / Stainless steel sticking Magnesium containing alloys seemed unusable due the vaporizing of the magnesium under vacuum conditions, but applying pressure after the melting eliminates most of the vapor bubbles. The bottom part (Which is the final part) shows the best results. Optimal material (so far) is AL99.5 or AlMg4.5Mn. 30-Jul-04 bverlaat@nikhef.nl 7

8 Oven Vacuum vessel Vacuum/Argon Inlet Control Casting mould with cooling pipes Casting set-up in vacuum vessel Vacuum pump 30-Jul st Prototype cooling block casting set-up

9 1 st Prototype casted aluminum cooling block Cooling block is machined after casting process 1 st prototype is melted and solidified under vacuum Magnesium vapor bubbles 30-Jul-04 bverlaat@nikhef.nl 9

10 2 nd Prototype casting block mounted on a prototype module Cooling block 2 nd prototype is melted under vacuum and solidified under 1 bar Argon In & outlet tube 30-Jul-04 bverlaat@nikhef.nl 10

11 Detail of the casted evaporator block. The shown side is the molded side, which needed no post machining. 30-Jul-04 11

12 Due to the possibility of free forming the embedded tube, a new cooling block is under investigation. This block has 5 separate cooling blocks casted to the pipe in 1 casting cycle. The separation shall eliminate the forces in the module occurred by the differences in CTE. The production of a prototype of this cooling block is ongoing. The mounting interface is the same for both designs. The disadvantage of this cooling block is worse thermal performance as the strait version. Also handling seems less practical. 30-Jul-04 bverlaat@nikhef.nl 12