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Study of the Cooling System with Study of the Cooling System with FluorFluorooinert Refrigerants inert Refrigerants V. Vinš, V. Vacek, M.Doubrava, M. Galuška
CTU, Faculty of Mechanical Engineering, Department of Applied Physics
Technická 4, 16607 Praha 6
©2004 V. Vinš & V. Vacek
ABSTRACT:ABSTRACT:
The goal of our project was an elaborate study of a lubricant-free cooling circuit working with a fluoroinert refrigerant. The cooling power of the studied circuit was set to be around 5 kW and the temperature in the evaporator around -20°C. A capillary behavior study was included into the project as well.The Department of Applied Physics has been participating in design of cooling systems and consecutive measurements on prototypes of Pixel and SCT detectors at the international nuclear research center CERN (Geneva) for several past years. Main interest of current work is the design of cooling system for the Inner Detector of the ATLAS experiment. The fluoroinertrefrigerants, having the chemical structure CnF (2n+2), were considered according to specific needs of the cooling system. These refrigerants are non-conductive, have low viscosity and low impact on an environment. Prior to design of the cooling circuit, it was necessary to collect basic thermo-physical data of refrigerants. Our study has concentrated on the C3F8 (octofluoro-propane) and C4F10 (perfluoro-butane). Manufacturers, suppliers and scientific conference’s web pages were essential sources of information about the refrigerants. Using the Benedict-Webb-Rubin equation (MBWR) that contains 34 constants the log p-h and log p-T diagrams were prepared. Respecting all analyses one can conclude that the final design of ATLAS cooling system will use the C3F8 the most likely.Our study of the cooling circuit proposal assumes the use of non-lubricated compressor, sub-cooling of refrigerant in inter-heat exchanger and ideal phase changes were considered. The circuit consists of following main parts: non-lubricated (~ dry) compressor, condenser, sub-cooler, pressure reduction element (capillary) and evaporator, all of them connected with the appropriate pipelines. The refrigerant undergoes following phase changes: isentropic compression in the compressor, isobaric condensation in the condenser, isobaric sub-cooling in the recuperative heat exchanger, adiabatic throttling in the capillary, isobaric evaporation in the evaporator and isobaric super-heating in recuperative exchanger. The projected mass flow through the circuit should be around 65 g/s.
A computational algorithm was made for all main components of the cooling circuit by use of MS-Excel. The input data can be simply changed to obtain optimal condenser, evaporator and recuperative exchanger parameters. We have been also involved in pilot type measurements on the test prototype of the cooling system installed at CERN. The main goal of our work was to design and test the various prototypes of the recuperative exchanger in which the refrigerant superheated vapor, leaving the evaporator, cools down the inlet liquid arriving from the condenser. Two main designs were studied. In the first case, the heat exchanger consisted of two capillaries (containing inlet liquid) coiled around the support tube (filled with outlet vapor). In the second case, there were three capillaries coiled inside of the support tube.As a supplementary part of the project, an experimental set-up for the measurement of capillary characteristics has been installed in the Prague laboratory. Data obtained from experiments on this set-up should provide better understanding of pressure-drop through a capillary as a function of its length and inner diameter. This knowledge is essential for the optimal design of cooling circuit that uses the capillary as the only pressure reduction element. The set-up consists of a DARI air compressor providing a maximum of 9 bars absolute, a pressure tank manufactured at the faculty workshop, capillary to be tested, scale for measurement of refrigerant mass flow, and connecting tubes with operating valves. Two temperature sensors Pt100 and one differential pressure sensor DMD 331 were installed to monitor changes of running parameters along the capillary. All sensors were connected to a mobile DAQ system MIC 2000 using Advantec cards and Eflab software.The set-up can be operated at normal room conditions (temperature, pressure) and with convenient testing medium (C8F18…or even with water). A similar test stand will be also installed at CERN for checking the reference capillaries that will be later delivered to the Inner detector assembly sites.
This research has been supported by FRVŠ grant No. FRV 2417-G1.
Design of the cooling circuitSet-up for the measurement of capillary characteristics
Results from Measurements
Summary:Summary:
• Basic thermo-physical data of fluoroinert refrigerants (C3F8, C4F10) has been collected; Using the MBWR equation the log p-h and log p-T diagrams were prepared
• The study of non-lubricant cooling system working with fluoroinert refrigerants has been elaborated; Cooling power has been 5kW and temperature in the evaporator -20°C
• An experimental set-up for the measurement of capillary characteristics has been installed in the laboratory
•We have been participating in design of the heat exchanger and testing measurements on the prototype of the cooling system installed at CERN
Air escape
& safety valve
Liquid
Air
Capillary
AirLiquid
Measuring
cylinder
Filling valve
Stopwatch
Differential pressure
sensor (app. 0 - 17 bar)Set-up for measuring the
pressure drop along the capillary
Liquid
Filter
Air compressor
(app. 18 bar)
Needle
valve
Scale
Differential pressure sensor DMD331
Pressure drop along stainless capillary (ID=1.0mm)
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
1,5 2,5 3,5 4,5 5,5 6,5
mass flow [g/s]
dp [bar]
L=1.84m, C8F18 L=1.63m, C8F18L=1.39m, C8F18 L=1.18m, C8F18L=0.98m, C8F18
Pressure drop along copper capillary (ID=0.8mm)
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0
mass flow [g/s]
dp [bar]
L=1.72m, C8F18 L=1.0m, C8F18
L=0.7m, C8F18 L=1.07m, C8F18 weird
L=1.05m, C8F18 weird L=1.07m, H2O
Working layout of the “eflab” program
based on TestPoint software
Photo of the test stand
Measurements at CERN
Scheme of the cooling set-up installed at CERN
Compressors1: increase to ~ 2 bar
2: increase to ~ 15 bar
(absolute)
Pressure
control valve
AC
Temperature
control
Chilled water
as coolant
1 2
Pump
CondenserAC
Heating -
warming the
outlet vapour
Vacuum pump - used to
evacuate the system after use
Water
as
coolant
Heat
Exchanger
AC
Heating -
warming the inlet
liquid
Two capillaries
Heat Exchanger
Set-up for temperature control of the inlet liquid
Cold box
Pixel barrels
Loop 8
Loop 9Heat exchanger between
the inlet and outlet pipe -
outlet vapor cools inlet fluid
Cross
section:
solder
Liquid
in
Vapor
out
Liquid
in
Flow
meter
Study of flouroinert
refrigerants
Log p-T diagram for C3F8
P - T Diagram for C3F8
p = 2E-08.T4 + 9E-06.T
3 + 0,0016.T
2 + 0,1351.T + 4,1531
0,1
1
10
100
-70 -50 -30 -10 10 30 50 70
Pressure [bar]
Temperature [C]
∑ ∑= =
−
−+
=
9
1
15
10172
expn n
nnc
nn
v
a
v
v
v
aP
Benedict-Webb-Rubin equation:
17°C
46°C
2'
1'
345
6
1p = 2 bar
p = 8.7 bar
Qk/m
Qd/m
Qd/m
Qo/m
Qo = 5000 W
Qd = 1797 W
Qk = 6093 W
m = 0.0635 kg/s
KondenzátorDochlazovač
Kapilára
DochlazovačVýparník
Kompresor
Log p-h diagram for C3F8 with marked
working points
( )skg
hh
Qm o /0635.0
102007.278
50003
61
=⋅−
=−
=
••
WhhmhhmQ
WhhmQ
d
k
1797)2003.228.(0635.0).().(
4.609310).3.2283.324.(0635.0).(
5411
3
42
=−=−=−′=
=−=−′=•••
••
Mass flow:
Power in the condenser and heat exchanger: Water as
coolant
Compressor
Staves with pixels
(evaporator)
Cold box
Condenser
vapour
(or two-phase flow)
vapour
Capillary
vapour
liquidliquid
Heat
Exchanger
Results from CERN (capillaries coiled around the heat exchanger)
Scheme of studied cooling circuit
Various PT 100
sensors
Pt 100 attached to the
capillary outlet
Scheme of the test stand
installed in the laboratory
