1. Studies in zeotropic C2F6/C3F8 blends for reduced temperature cooling of the ATLAS SCT and pixel detectors + HTC measurements in these blends
G. Hallewell
Aix Marseille Université, CNRS/IN2P3,
CPPM UMR 7346, 13288, Marseille, France
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

2. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

3. Reason for the C2F6/C3F8 blends study
Radiation damage growth in leakage current can provoke positive feedback-driven thermal runaway in silicon detector substrates;
ATLAS guidelines (see Viehhauser, Viehhauser & Beck) :
maintain module temperature at -15 ⁰C at for sufficient protection
factor against radiation damage induced thermal after exposure to
highest expected ( « 10 year ») ∫I.dt :
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

4. Some relevant papers relating to thermal runaway…
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

5. Reason for the C2F6/C3F8 blends study
Radiation damage growth in leakage current can provoke positive feedback-driven thermal runaway in silicon detector substrates;
ATLAS guidelines (see Viehhauser, Viehhauser & Beck) :
maintain module temperature at -15 ⁰C at for sufficient protection
factor against radiation damage induced thermal after exposure to
highest expected ( « 10 year ») ∫I.dt :
Evolution of ∫I.dt in ATLAS:
ATLAS ID TDR for 10 years’ LHC operation 1000 fb-1 :
 later summer conf. figures  750 fb-1  630 fb-1 :
now 350 fb-1 before HL-LHC upgrade, unless upgrade delayed
Si module temperatures typically ⁰C higher than tube temperature below module  -25⁰C required:
Not achievable in ATLAS barrel SCT in C3F8 due to higher-than-expected pressure drops in exhaust heaters, heXs etc.
C2F6/C3F8 blends are a thermodynamic sidestep…
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

6. C2F6/C3F8 blending and circulation machine built for these studies
Single stage compressor + vane liquid pump  same liquid
output pressure & vapour aspiration pressure as the installed
ATLAS C3F8 compressor C3F8 circulation system
(c)
(d)
(e)
Sonar analyzer/flowmeter
to verify C2F6/C3F8 blends
(a)
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

7. Back Pressure Regulator (evaporation pressure)
Tests in an SCT bistave at total power 0, 3, 6, 9 & 10.5 W /module (0, 144, 288, 432 & 504 W total power on the 48 modules)
Liquid pressure
regulator
30 m
Coiled tube
Back Pressure Regulator
(evaporation pressure)
P_A2
P_B2
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

8. at total powers 0, 288 & 504 W (0, 6 & 10,5 W/module (48))
Pressure-enthalpy diagrams for evaporation of pure C3F8 & 75% C3F8/25% C2F6 in a thermal model of an SCT bistave
at total powers 0, 288 & 504 W (0, 6 & 10,5 W/module (48))
Note zeotropic temperature “glide” 
in the C3F8/C2F6 blend
Pressure(barabs)
Enthalpy (kJ/kg): C3F8
Enthalpy (kJ/kg): 75%C3F8/25%C2F6
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

9. Tests in an SCT bistave at total power 0, 3, 6, 9 & 10
Tests in an SCT bistave at total power 0, 3, 6, 9 & 10.5 W /module (0, 144, 288, 432 & 504 W total power) : total tube length 3 m
Reduction in average tube temp with
Increasing C2F6 concentration
24 station temperature profile comparison
Pure C3F8 and 75% C3F8/25% C2F6
10,5W DT = 8.5 C
6W DT =10 C
0 W DT = 12C
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

10. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

11. Electrically-heated Cu/Ni tube of same ID (4.08mm) as SCT barrel
total power 36 142W:
equivalent to 5.3  21.1W per barrel SCT “module station”
(= 6.2cm module length + 6 cm space) along an SCT barrel tube
2 Capillaries: 3 flow combinations
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

12. Similar reductions in average tube temperature with increasing
C2F6 concentration: heated tube length 820 mm
Equivalent power
per 12.2 cm length
equivalent of a
barrel SCT
“module station” 
0 W DT = 11C
5,3 W DT = 10C
7.7 W
11.8 W DT =10C
15.2 W
21.1 W
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

13. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017
Expect to see temperature profiles characteristic of at least some of these evaporation regimes, depending on (3 different) mass flows, (5 different) applied powers & (5 different) C2F6 – C3F8 compositions
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

14. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017
LOW & INTERMEDIATE POWER, LOW FLOWS ( g/s)
TOP
OF TUBE
BOTTOM
OF TUBE
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

15. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017
LOW & INTERMEDIATE POWER, INTERMEDIATE FLOWS ( g/s)
TOP
OF TUBE
BOTTOM
OF TUBE
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

16. Tracker mechanics forum, CPPM Marseille, July 3-5, 2017
INTERMEDIATE & HIGH POWER, HIGH FLOWS ( g/s)
TOP
OF TUBE
BOTTOM
OF TUBE
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

17. HTC COMPARISON IN ANNULAR FLOW REGIME WITH BOILING MODELS
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

18. COMPARISON OF HTC IN ANNULAR FLOW REGIME
WITH BOILING MODELS (1) From Paper accepted for HEFAT2017
1224
data points
5.3 W/
Module:
Kandlikar:
Fluid specific parameter set
to f=1.53
11.8 W/
module
Liu-Winterton correlation with suppression factor for boiling zeotropic mixtures gave best agreement (~5% dev.) with our data
covering the annular flow regime
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

19. COMPARISON OF HTC IN ANNULAR FLOW REGIME
WITH BOILING MODELS (2)
2 capillaries open: high flow ( g/s) : density reduction with increasing C2F6 content
5.3 W/
module
station
5.3 W/
module
station
11.8 W/
module
station
11.8 W/
module
station
15.2 W/
module
station
15.2 W/
module
station
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017

20. Conclusion of zeotropic C2F6/C3F8 blends & HTC measurement studies
The SCT barrel can be adequately cooled (9 ⁰C cooler) with a blend containing 25% C2F6,using existing pipework and infrastructure up to an accumulated radiation dose of at least 750 fb-1,
even at worse case power-per-module expectation of 10.5 W);
HTC studies have shown this enhanced cooling is achievable with modest HTC values in the range W.m-2.K -1 ;
HTC comparisons with predictive models look reasonable, despite sparse data on this radiation-resistant zeotropic combination;
Sonar studies with custom electronics integrated into the ATLAS DCS has demonstrated C2F6/C3F8 molar blend resolution of ± 0.3%. This instrumentation in use in various parts of the ATLAS ID evaporative cooling system (A. Madsen)
The temperature gain using C2F6/C3F8 blends can be added to the extra reduction (headroom) given by the new ATLAS thermospihon (talk of C. Rossi)
Tracker mechanics forum, CPPM Marseille, July 3-5, 2017