Cooling test results C-side replacement detector

Transcription

1 Cooling test results C-side replacement detector Nikhef number: Item number: Date: 2/10/2011 Page: 1 of MT AA2232 Status: In Work Revision: A.5 Project: LHCb VELO Department: Mechanical Technology Top folder: CO2 cooling Abstract: The quality of the VTCS CO 2 evaporators of the VELO C-side is tested. The CO 2 evaporators are mounted in the VELO C-side and connected to a CO 2 cooling system. The performance tests will be done for the VELO placed in the trolley in vertical orientation and for a horizontal VELO, which is the orientation of the VELO detector in LHCb. Created by: K. de Roo Distribution list: Checked by: Approved by: National Institute for Subatomic Physics Science Park 105, 1098 XG Amsterdam The Netherlands

2 1 ABSTRACT The cooling performance of all CO 2 evaporators of the VELO replacement detector halves is measured with the Nikhef Green Cooler setup. The results are very similar to results of the presently installed VELO detector measured in 2006 at Nikhef with the prototype of a CO 2 cooling system. The CO 2 evaporators perform well, for a total CO 2 mass flow above 6 g/s and for a maximal heat load of 30 W on each of the 23 module heat exchangers (evaporators). The operational conditions for the VELO Thermal Control System at CERN are more comfortable with a total CO 2 mass flow of 10 g/s per detector half and a heat load of 16 W, from the Beetle readout chips, per module. The tests are done in a horizontal orientation of the detector halves as they will be used at CERN and in a vertical orientation as a detector half is mounted in the transport trolley. The CO 2 evaporators perform well even at 4 g/s, apart from the capillaries that are positioned highest in the CO 2 inlet manifold in the concerned orientation. The CO 2 in front of the manifold consists of liquid with a low vapour quality and the vapour enters, due to gravity, the capillaries in the top of the manifold. Due to the small cooling capacity of vaporized CO 2 these capillaries will heat up first at a relative high total CO 2 mass flow. 2

3 Contents 1 ABSTRACT PERFORMANCE CO 2 EVAPORATORS VELO REPLACEMENT C-SIDE TEST SETUP CO 2 COOLING EVAPORATORS GREEN COOLER ENTHALPY CONTROL IN THE GREEN COOLER TEST PROTOCOL LABELS AND NUMBERING OF THE VELO C-SIDE FLOW REDUCTION TEST WITH A POWER OF 15 WATT AND A COOLING TEMPERATURE OF -30 C FIRST MASS FLOW REDUCTION TEST WITH 15 WATT IN THE VELO SECOND MASS FLOW REDUCTION TEST WITH 15 WATT THIRD MASS FLOW REDUCTION TEST WITH 19 WATT FLOW REDUCTION TEST WITH A POWER OF 25 WATT AND A COOLING TEMPERATURE OF -20 C FLOW REDUCTION TEST WITH A POWER OF 30 WATT AND A COOLING TEMPERATURE OF -20 C IN THE VELO FLOW REDUCTION TEST WITH A POWER OF 25 WATT AND A COOLING TEMPERATURE OF -20 C IN A HORIZONTAL VELO FIRST FLOW REDUCTION TEST WITH 25 WATT IN A HORIZONTAL VELO SECOND FLOW REDUCTION TEST WITH 25 WATT IN A HORIZONTAL VELO FLOW REDUCTION TEST WITH A POWER OF 30 WATT AND A COOLING TEMPERATURE OF -20 C IN A HORIZONTAL VELO FIRST FLOW REDUCTION TEST WITH 30 WATT IN A HORIZONTAL VELO SECOND FLOW REDUCTION TEST WITH 30 WATT IN A HORIZONTAL VELO FAST FLOW REDUCTION TEST WITH 30 WATT IN A HORIZONTAL VELO HEAT UP ORDER FOR ALL CO 2 EVAPORATORS CONCLUSION

4 2 PERFORMANCE CO 2 EVAPORATORS VELO REPLACEMENT C-SIDE The VELO contains detectors of silicon, designed to record and reconstruct the positions of traversing particles. The damage to the detectors as a consequence of radiation can be minimized by cooling the detector modules at a cooling temperature of approximately -30 C. The cooling system of the detector modules should be able to cool a minimal heat load of 16 Watt, from the Beetle readout chips, per detector module. A two phase CO 2 cooling system is installed and is operating for the VELO detector halves in operation. Replacement VELO halves are constructed to replace the current halves when necessary. These replacement halves will contain new detector modules and thereby new CO 2 cooling evaporators. The cooling performance of these CO 2 cooling evaporators is tested at Nikhef with a two phase CO 2 cooling system, the Green Cooler. To get an impression of the cooling performance of the CO 2 cooling evaporators the temperature of the evaporators and pressure drop over the VELO is monitored as the total CO 2 mass flow through the VELO cooling system is reduced in steps. When the cooling capacity of an evaporator becomes insufficient due to the low mass flow, the temperature of the evaporator will rise. The increase in temperature of the evaporators must occur well below the 10 g/s of the VELO Thermal Cooling System at CERN. The pressure drop over the VELO gives a view of the quality of the capillaries. When the return line of VELO is connected to the cooling system with the smallest resistance possible, the minimal pressure in the VELO is equal to the pressure of the accumulator of the cooling system. The maximal pressure before the evaporators depends on the resistance of the capillaries. If the resistance of the capillaries is too low, the CO 2 mass flow enters the two phase area before reaching the evaporators. If the resistance of the capillaries differ much, the distribution of the mass flow in the manifold won t be equal and thus the cooling capacity per capillary differs much. The pressure drop over the VELO at a total CO 2 mass flow of 10 g/s, a cooling temperature of -30 C and a power of 25 Watt should be approximately 2.1 bar. 4

5 3 TEST SETUP In Figure 1 the VELO replacement detector mounted on the transport trolley is shown. The replacement detector is connected to the two phase CO 2 cooling system, the Green Cooler by means of two transfer lines. Figure 1: VELO test setup 3.1 CO 2 cooling evaporators The 23 modules of the VELO are cooled with 23 evaporators. A CO 2 flow is led by a capillary through five aluminium cookies, one evaporator. Due to the heat that is transferred from the modules to the evaporators the CO 2 starts to boil. As a consequence of evaporation of the liquid CO 2 the cooling temperature of the fluid remains constant. During the test phase, aluminium blocks are mounted to the evaporators. By means of resistors, which are mounted on the blocks, heat is added to the evaporators. Figure 2: Evaporators with aluminum blocks and resistors 5

6 3.2 Green Cooler A schematic view of the two phase CO 2 cooling system Green Cooler is shown Figure 3. The cooling system consists of a CO 2 cooling system and a primary cooling system. The primary cooling system extracts heat from the CO 2 in the accumulator and the heat exchanger in the CO 2 system. The cooling temperature of an experiment connected to the Green Cooler is controlled by the accumulator. This system is a two phase cooling system, thus controlling the pressure in the system by means of controlling the evaporation temperature of the CO 2 and thereby the cooling temperature in the experiment. By adding or extracting heat from the CO 2 in the accumulator, the pressure is changed in the accumulator and thus in the CO 2 cooling system. The accumulator is placed behind the experiment so that the pressure in the accumulator is equal to the pressure in the experiment if they are in direct contact. The cooling cycle of the Green Cooler is as follows. The pressure of liquid CO 2 is increased by gear pumps and the mass flow is measured with a mass flow meter. The enthalpy of the CO 2 before the experiment is controlled with heater HT105 of the enthalpy control. After passing the enthalpy control the CO 2 reaches the experiment and experiences a pressure drop from a restriction or the capillaries of the experiment. The CO 2 will evaporate in the experiment due to the added heat and the partially evaporated CO 2 is led back to the heat exchanger where it is condensed back to liquid CO 2. The liquid CO 2 is led to the gear pumps. Figure 3: Schematic view of the Green Cooler (Verlaat, 2010) 6

7 3.3 Enthalpy control in the Green Cooler The enthalpy control in the Green Cooler consists of a heater (HT105) which is controlled by an algorithm to reach the set enthalpy. With pressure sensor PT106 and temperature sensor TT106 the enthalpy of liquid CO 2 can be determined by means of a calculation based on the dataset of the NIST Reference Fluid Thermodynamic and Transport Properties (REFPROP) software program. Next the difference between the actual enthalpy and the set enthalpy is calculated, this difference is multiplied with the measured mass flow from the mass flow sensor FT104. The result is the amount of power that is added to the CO 2 in Watt. 7

8 4 TEST PROTOCOL The liquid CO 2 is cooled down to the required cooling temperature and the mass flow is set to 6 g/s. The mass flow in the VTCS is 10 g/s, heating up of the CO 2 evaporators is expected to occur much below a mass flow of 6 g/s and therefore this setting is used. The cooling performance tests are done by means of flow reduction tests. During this test the mass flow is reduced in steps by hand. Due to the power and the reduced mass flow, the temperatures of the evaporators start to increase. When the temperature of an evaporator becomes too high, the power is taken from the concerning heater by removing the heater pin from the plug box. This is continued till all evaporators increased in temperature of the minimal mass flow is reached. A second cooling performance test is done by means of a fast flow reduction test. During this test the mass flow is reduced in steps at a continuous time interval. The heaters will apply heat until the evaporators reach a maximum temperature of 40 C degrees. At this point the concerning heater pin will be removed from the plug box. For the pressure drop test, the mass flow is reduced in continuous steps at a continuous time interval. During the time interval, measuring points are taken while the system is stable. The data is obtained with an automatic RPM scan in PVSS. The cooling performance tests will be done for three different heater powers 15, 25 and 30 Watt on the evaporators and in two different orientations of the VELO replacement halve. Horizontal orientation is equal to the orientation in operation and in vertical orientation equal to the orientation when mounted in the transport trolley. Figure 4: VELO test setup with heater pins in the plug box 8

9 Pin 11 Pin 10 Pin 09 Pin 08 TX_HX027 TX_HX026 TX_HX TX_HX TX_HX021 TX_HX018 TX_HX017 TX_HX016 TX_HX015 TX_HX014 TX_HX013 TX_HX012 TX_HX011 TX_HX010 TX_HX009 TX_HX008 TX_HX007 TX_HX006 TX_HX005 TX_HX004 TX_HX003 TX_HX TX_HX001 Pin 07 Pin 01 Pin 05 Pin 04 Pin 03 Pin 02 Pin Pile up Pile up 002 Pin 24 Pin 23 Pin 22 Pin 21 Pin 20 Pin 19 Pin 18 Pin 17 Pin 16 Pin 15 Pin 14 Pin 13 5 LABELS AND NUMBERING OF THE VELO C-SIDE Figure 5 gives a view of the position of the temperature sensors (0..) on the evaporators (TX_HX ) in the VELO. The pin numbers indicate the heater-pin for the heaters that are mounted on the CO2 evaporators. Figure 5: Evaporators in VELO with the labels for the heater-pins and temperature sensors Figure 6 gives a view of the position and labels of the capillaries in the manifold. In Table 1 can be found which evaporator is connected to which capillary. The labels of the VELO C-side slots, silicon modules, evaporators, capillaries, temperatures sensors in the VELO, temperature sensors in PVSS at Nikhef and the corresponding heater-pins are also given in this table. Upper side in vertical orientation in trolley Figure 6: Capillary label and position in manifold of the VELO C-side 9

10 The slot number is the position of the module on the base. The silicon sensor module label and the heater label are given by the silicon module number. The label of the evaporator in the VELO is given by the TX_HX.../Evaporator number. The capillary in manifold number indicates the label of the position of a capillary in the manifold, also shown in Figure 6. The heater-pin number gives the label of the pin in the plug box for the heaters mounted to the evaporators. The labels of the PT100 sensors in the VELO and in PVSS at Nikhef are given by the TX_TT.../VELO and TT.../PVSS number. Table 1: Labels of the VELO C-side Slot Silicon Module TX_HX... Evaporator Capillary in manifold Heater-pin TX_TT... VELO TT... PVSS 1 1 (pile up) , 002, 003, , (pile up) , 016, 017, , (spare) , 030, 031, ,

11 6 FLOW REDUCTION TEST WITH A POWER OF 15 WATT AND A COOLING TEMPERATURE OF -30 C The results of the quality tests at 15 Watt in the VELO C-side are given in this chapter. In total three tests are done, during the first test only heaters 1-11 and 13 are powered while all the CO 2 evaporators are monitored, during the second test only heaters are powered while all CO 2 evaporators are monitored and during the third test all the heaters are powered and all CO 2 evaporators are monitored. Pressure sensors PT201 and PT202, which measure the pressure before and after the VELO, are not connected and therefore there is no graph which shows the pressure drop over the VELO versus the mass flow. 6.1 First mass flow reduction test with 15 Watt in the VELO The following results are measured at 27 October 2010, from 12:45 to 15:55 with a cooling system temperature of -30 C and the enthalpy control on 140 J/g. A power of 12 Watt is applied to heaters 1-11 and 13. This means that the power supply indicates 13.0 V and 12.3 A. The temperatures of the non-heated CO 2 evaporators are also monitored and shown in Figure 7 and Figure 8. The measurement started with a mass flow of 10 g/s. With a stable cooling system the flow is reduced in steps to a minimal flow of 0.5 g/s. Figure 7: Temperature of the CO 2 evaporators versus the mass flow for the first test with a power of 15 Watt 11

12 Figure 8: Temperature of the CO 2 evaporators versus the time during the first test with a power of 15 Watt The deviation in temperature of CO 2 evaporator HX008 is a consequence of a bad connection of the sensor cable to the Haptas board. The instable cooling temperature of all evaporators is a consequence of the instable accumulator control settings. When the mass flow is reduced the accumulator control starts to adjust the system pressure and thereby the cooling temperature. The mass flows at which evaporators start to heat up are given in Table 2 in the following paragraph. 12

13 6.2 Second mass flow reduction test with 15 Watt The following results are measured at 28 October 2010, from 11:50 to 13:20 with a cooling system temperature of -30 C and the enthalpy control on 140 J/g. A power of 12 Watt is applied to heaters This means that the power supply indicates 13.0 V and 12.3 A. The temperatures of the nonheated CO 2 evaporators are also monitored. The power is turned on at a flow of 10 g/s. After approximately 10 minutes the temperatures of the CO 2 evaporators seems stable and the mass flow is reduced in steps to 6 g/s. During the measurement the mass flow is reduced to a minimal flow of 0.5 g/s. Figure 9: Temperature of the CO 2 evaporators versus the mass flow during the second test with a power of 15 Watt 13

14 Figure 10: Temperature of the CO 2 evaporators versus the time during the second test with a power of 15 Watt A view of the total CO 2 mass flow at which an evaporator starts to increase in temperature is given in Table 2 and Figure 11 gives the distribution of the range at which most evaporators experience an insufficient cooling capacity. Table 2: Heat up mass flow for the second Mass flow test at 15 Watt Heater pin TX_HX... Φ m (g/s) Number of CO 2 evaporators > 5 g/s 4-5 g/s 3-4 g/s 2-3 g/s 1-2 g/s < 1 g/s Figure 11: Number of CO 2 evaporators which heat up at 15 Watt within a mass flow range 14

15 6.3 Third mass flow reduction test with 19 Watt The following results are measured at 28 October 2010, from 15:55 to 17:30 with a cooling system temperature of -30 C, the enthalpy set on 140 J/g and a power of 19 Watt on all heaters (the power supplies indicate 16.1 V, 15.5 A, 16.0 V and 14.0 A). First the nominal flow of 10 g/s is set, at 16:10 the flow is reduced in steps to 6 g/s. Next the mass flow is reduced to a minimal flow of 0.5 g/s. Figure 12: Temperature of the CO 2 evaporators versus the mass flow during the third test with a power of 15 Watt Figure 13: Temperature of the CO 2 evaporators versus the time during the third test with a power of 15 Watt 15

16 First evaporator 5 starts to increase in temperature at a mass flow of 4.5 g/s. Evaporators 3, 7, 9 and 14 heat up within a total CO 2 mass flow range of 3 to 4 g/s. Most evaporators start to increase in temperature at a mass flow below 3 g/s. A view of the total CO 2 mass flow at which an evaporator starts to increase in temperature is given in Table 3. Table 3: Heat up mass flow for the third test at 15 Watt Heater-pin TX_HX... Flow (g/s) Heater- pin TX_HX... Flow (g/s) Figure 13 gives the distribution of the range at which most evaporators experience an insufficient cooling capacity. > 5 g/s 4-5 g/s 3-4 g/s 2-3 g/s 1-2 g/s < 1 g/s Number of CO 2 evaporators Figure 14: Number of CO 2 evaporators which heat up within a mass flow range for the third test at 15 Watt 16

17 7 FLOW REDUCTION TEST WITH A POWER OF 25 WATT AND A COOLING TEMPERATURE OF -20 C The following results are measured at 29 October 2010, from 14:25 to 16:03. The cooling system is more stable at a cooling temperature of -20 C and therefore this cooling temperature is set with the heater control on 150 J/g. A power of 25 Watt (18.5 V is set) is applied to all heaters. The mass flow is set on 6 g/s and next in steps decreased to 1.6 g/s, the mass flow at which all evaporators started to heat up. Figure 15: Pressure drop over the VELO versus the mass flow during the flow reduction test with a power of 25 Watt 17

18 Figure 16: Temperature of the CO 2 evaporators versus the mass flow during the flow reduction test with a power of 25 Watt Figure 17: Temperature of the CO 2 evaporators versus the time during the flow reduction test with a power of 25 Watt 18

19 A view of the total CO 2 mass flow at which an evaporators starts to increase in temperature is given in Table 4. Table 4: Heat up mass flow for the CO 2 at 25 Watt Heater-pin TX_HX... Flow (g/s) Heater- pin TX_HX... Flow (g/s) Figure 18 gives the distribution of the range at which most evaporators experience an insufficient cooling capacity. > 5 g/s 4-5 g/s 3-4 g/s 2-3 g/s 1-2 g/s < 1 g/s Number of CO 2 evaporators Figure 18: Number of CO 2 evaporators which heat up within a mass flow range at 25 Watt 19

20 8 FLOW REDUCTION TEST WITH A POWER OF 30 WATT AND A COOLING TEMPERATURE OF -20 C IN THE VELO The following results are measured at 4 November 2010, from 12:40 to 14:05. These measurements are done with a cooling temperature of -20 C and the heater control on 155 J/g. A power of 30 Watt is applied to all heaters. The mass flow is set on 6 g/s and next in steps decreased to 1.2 g/s. Figure 19: Pressure drop over the VELO versus the mass flow during the flow reduction test with a power of 30 Watt in the VELO C-side 20

21 Figure 20: Temperature of the CO 2 evaporators versus the mass flow during the flow reduction test with a power of 30 Watt Figure 21: Temperature of the CO 2 evaporators versus the time during the flow reduction test with a power of 30 Watt 21

22 In the following table the mass flow is given at which a CO 2 evaporator starts to heat up. This table shows the results from the flow reduction test at 30 Watt. Table 5: Heat up mass flow at 30 Watt Heater-pin TX_HX... Flow (g/s) Heater- pin TX_HX... Flow (g/s) Figure 22 gives the distribution of the range at which most evaporators experience an insufficient cooling capacity. > 5 g/s 4-5 g/s 3-4 g/s 2-3 g/s 1-2 g/s < 1 g/s Number CO 2 evaporators Figure 22: Number of CO 2 evaporators which heat up within a mass flow range at 30 Watt 22

23 9 FLOW REDUCTION TEST WITH A POWER OF 25 WATT AND A COOLING TEMPERATURE OF -20 C IN A HORIZONTAL VELO The results of the quality tests at 25 Watt in a horizontal VELO C-side are given in this chapter. In total two tests are done with equal settings to check the reproducibility of the tests that are done. The mass flows at which the CO 2 evaporators heat up are combined in one table to compare the data. 9.1 First flow reduction test with 25 Watt in a horizontal VELO The following results are measured at 9 November 2010, from 11:50 to 13:10. These measurements are done in a horizontal VELO C-side at a cooling temperature of -20 C, the heater control on 155 J/g and two pumps. A power of 25 Watt is applied to all heaters. The mass flow is set on 6 g/s and next in steps decreased to 1.0 g/s. Figure 23: Pressure drop over the VELO versus the mass flow during the first test with a power of 25 Watt in a horizontal VELO 23

24 Figure 24: Temperature of the CO 2 evaporators versus the mass flow during the first test with a power of 25 Watt in a horizontal VELO Figure 25: Temperature of the CO 2 evaporators versus the time during the first test with a power of 25 Watt in a horizontal VELO 24

25 9.2 Second flow reduction test with 25 Watt in a horizontal VELO The following results are measured at 9 November 2010, from 14:00 to 17:10. These measurements are done in a horizontal VELO C-side at a cooling temperature of -20 C, the heater control on 155 J/g and two pumps. A power of 25 Watt is applied all heaters. The mass flow is set on 6 g/s and next in steps decreased to 1.0 g/s. Figure 26: Pressure drop over the VELO versus the mass flow during the second test with a power of 25 Watt in a horizontal VELO 25

26 Figure 27: Temperature of the CO 2 evaporators versus the mass flow during the second test with a power of 25 Watt in a horizontal VELO Figure 28: Temperature of the CO 2 evaporators versus the time during the second test with a power of 25 Watt in a horizontal VELO 26

27 In the following table the mass flow is given at which a CO 2 evaporator starts to heat up. This table shows the results from the two flow reduction test at 25 Watt in a horizontal VELO C-side. Table 6: Heat up mass flow for the CO 2 evaporators of the VELO C-side in horizontal orientation powered with 25 Watt Heater-pin TX_HX... Flow 1st test (g/s) Flow 2nd test (g/s) > 5 g/s 4-5 g/s 3-4 g/s 2-3 g/s 1-2 g/s < 1 g/s Number CO 2 evaporators Figure 29: Number of CO 2 evaporators which heat up within a mass flow range at 25 Watt in a horizontal VELO 27

28 10 FLOW REDUCTION TEST WITH A POWER OF 30 WATT AND A COOLING TEMPERATURE OF -20 C IN A HORIZONTAL VELO The results of the quality tests at 30 Watt in a horizontal VELO C-side are given in this chapter. In total three tests are done, the first test with the enthalpy control on 155 J/g, the second test with the enthalpy control on 147 J/g and the third test is a fast flow reduction test, which means that power is supplied to the heaters as long as possible before the temperature interlock interrupts the test and the flow is reduced in steps every minute First flow reduction test with 30 Watt in a horizontal VELO The following results are measured at 12 November 2010, from 11:40 to 13:10. These measurements are done in a horizontal VELO at a cooling temperature of -20 C, the heater control on 155 J/g and one pump. A power of 30 Watt is applied to all heaters. The mass flow is set on 6 g/s and next in steps decreased to 0.6 g/s. Figure 30: Pressure drop over the VELO versus the mass flow during the first test with a power of 30 Watt in a horizontal VELO 28

29 Figure 31: Temperature of the CO 2 evaporators versus the mass flow during the first test with a power of 30 Watt in a horizontal VELO Figure 32: Temperature of the CO 2 evaporators versus the time during the first test with a power of 30 Watt in a horizontal VELO 29

30 10.2 Second flow reduction test with 30 Watt in a horizontal VELO The following results are measured at 12 November 2010, from 14:40 to 16:00. These measurements are done in a horizontal VELO at a cooling temperature of -20 C, the heater control on 147 J/g and one pump. A power of 30 Watt is applied to heaters 1 to 11 and 13 to 24. The mass flow is set on 6 g/s and next in steps decreased to 1.4 g/s. The following three graphs give a view of the pressure difference over the VELO C-side as a function of the mass flow, a view of the cookie temperatures versus the mass flow and the CO 2 evaporators temperatures over time. Figure 33: Pressure drop over the VELO versus the mass flow during the second test with a power of 30 Watt in a horizontal VELO 30

31 Figure 34: Temperature of the CO 2 evaporators versus the mass flow during the second test with a power of 30 Watt in a horizontal VELO Figure 35: Temperature of the CO 2 evaporators versus the time during the second test with a power of 30 Watt in a horizontal VELO 31

32 10.3 Fast flow reduction test with 30 Watt in a horizontal VELO The following results are measured at 12 November 2010, from 16:00 to 16:30. These measurements are done in a horizontal VELO at a cooling temperature of -20 C, the heater control on 147 J/g and one pump. A power of 30 Watt is applied to all heaters. The mass flow is set on 6 g/s and next every minute decreased in steps to 0.2 g/s. Figure 36: Pressure drop over the VELO versus the mass flow during the third test with a power of 30 Watt in a horizontal VELO 32

33 Figure 37: Temperature of the CO 2 evaporators versus the mass flow during the third test with a power of 30 Watt in a horizontal VELO Figure 38: Temperature of the CO 2 evaporators versus the time during the third test with a power of 30 Watt in a horizontal VELO 33

34 In the following table the mass flow is given at which a CO 2 evaporator starts to heat up. This table shows the results from the first, second and third flow reduction test at 30 Watt. Table 7: Heat up mass flow for the CO 2 evaporators of the VELO C-side powered with 30 Watt in a horizontal VELO Heater-pin TX_HX... Flow 1st test (g/s) Flow 2nd test (g/s) Flow 3th test (g/s) >5 g/s 4-5 g/s 3-4 g/s 2-3 g/s < 1 g/s Number CO2 evaporators Figure 39: Number of CO 2 evaporators which heat up within a mass flow range at 30 Watt in a horizontal VELO 34

35 11 HEAT UP ORDER FOR ALL CO 2 EVAPORATORS In the table below the heat up mass flows for all CO 2 evaporators are given. For the VELO C-side in vertical orientation, the heat up mass flows at a power of 15, 25 and 30 Watt are given. For the horizontal orientation of the VELO C-side the heat up mass flows at a power of 25 and 30 Watt are given. No test is done with a power of 15 Watt for the horizontal orientation of the VELO due a shortage of time. Table 8: Heat up order for all VELO C-side CO 2 evaporators Heater-pin TX_HX... Evaporator Capillary in manifold Flow (g/s) 15 Watt Flow (g/s) 25 Watt Flow (g/s) 30 Watt Flow (g/s) 25 Watt Tilted Flow (g/s) 30 Watt Tilted The order of dry-out in the capillaries for the VELO in vertical orientation is: The order of dry-out in the capillaries for the VELO in horizontal orientation is:

36 The five first capillaries that heat up in the VELO C-side are indicated in Figure 40. Vertical in trolley Horizontal as in LHCb : Spare or restricted capillary : Order of heating up Figure 40: Heat up order of the capillaries for VELO C-side 12 CONCLUSION The fluctuations in temperature, at a cooling temperature of -30 C, for all CO 2 evaporators are caused by the accumulator control. As the settings weren t correct, the primary cooling wasn t able to cool the total power of the cooling system and the heaters on the evaporators. The test done at a cooling temperature of -20 C didn t experience many fluctuations due to the accumulator control. The first CO 2 evaporators to heat up are the ones connected to the capillaries which are placed in the top part of the manifold. As the CO 2 before the manifold consists of liquid with a low vapour quality, it is possible that all the vapour, due to gravity, enters the capillaries in the top first. As the mass flow decreases, the other evaporators start to heat up. The first evaporators heat up at a mass flow range of g/s. The heat up mass flow of the evaporators is with g/s well below the total CO 2 mass flow of 10 g/s of the VTCS at CERN and the cooling capacity of the VELO C-side is sufficient. 36