ALICE TRD AND TPC THERMAL SCREEN COOLING SYSTEM

Transcription

1 ORGANISATION EUROPEENNE POUR LA RECHERCHE NUCLEAIRE EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN-ST/CV-2003-????? February 2003 ALICE TRD AND TPC THERMAL SCREEN COOLING SYSTEM M. Pimenta dos Santos Abstract This document outlines a design proposal for the external cooling system of the Transition Radiation Detector and the TPC thermal screen. For p-p collisions the total power dissipated by the TRD is approximately 55kW. A residual percentage of this heat needs to be removed by a thermal screen in order to ensure an uniform temperature map on the TPC side. The overall design of the cooling system, including piping to and from the detector, plant operation, controls and leak detection are examined. A complete list of components, costs and required manpower is also presented.

2 Index 1.Introduction 3 2.Cooling Circuits Design 3 3.Cooling Plant Design 3.1 Plant description The leakless or sub-atmospheric mode Temperature regulation Cooling System Operation and communication with ECR and TCR Cooling plant layout drawings 10 4.Responsibilities and resources 4.1 Responsibilities Cost estimation 11 Appendix I: Estimation of pressure drop along one MCM cooling circuit 13 TPC Cooling System Page 2 of 13

3 1. Introduction The ALICE Transition Radiation Detector (TRD) aims at providing electron identification at momenta above 1 GeV/c. The segmentation of the TRD follows that of other ALICE detectors, leading to 18 super-modules, each covering 20 degrees in azimuth and aligned along the z direction. Within each super-module, heat is dissipated by a variety of components, the main heat source being the multi-chip modules (MCM). An estimated 55 kw is dissipated for the whole TRD when running with p-p collisions. The interface with the TPC is of particular interest as the temperature map there must be kept as uniform as possible around 20ºC. An actively cooled thermal screen is introduced between the two detectors aiming at removing any residual heat not taken away by the TRD cooling and smoothing out temperature differences at the TPC boundary. The cooling system described herein comprises a water cooling and de-ionization plant, its controls and all the piping to the detector. Figure 1 Cross section of TRD detector within the ALICE space frame 2. Cooling Circuits Design Cooling is provided to each individual super-module as shown in Fig.2 with inlets on RB26 side and outlets on the opposite side. The thermal screen follows the same segmentation as the TRD, i.e. one screen per super-module. Each screen is made of 5 panels cooled in parallel, as shown in Fig.3. The nominal flow rate is 1.5m3/h per super-module and 300L/h per thermal screen. This value was calculated in order to limit the pressure drop within a super-module and enable the so called leakless operation mode (further details in Appendix I). Water temperature at the super-module inlet can be adjusted to any value between 16ºC and 18ºC. The expected water temperature rise (assuming ~3kW heat dissipation per super-module cooled with full efficiency) is less than 2ºC. The thermal screens are meant to remove just the residual heat from the super-modules and smooth out the temperature map on the TPC side. Consequently, the water temperature at the screen inlet should be just under 20ºC, i.e. the temperature aimed for the TPC volume. Assuming a residual heat of 10% from the super-modules, the power to be removed by one screen is approximately 300W. This would lead to a water temperature increase of 0.8ºC. TPC Cooling System Page 3 of 13

4 Figure 2 TRD super-modules cooling circuits. Left: Supply pipes layout around the TRD right: Cooling of one TRD super-module. Figure 3 Thermal screen cooling circuits. Left: Supply pipes layout around the TPC end-cap right: Cooling of one screen 3. Cooling Plant Design 3.1. Plant description A diagram representing the cooling plant as well as some of the piping to the detector is shown in Figure 4 and some components are identified in table 1. The plant consists of a reservoir large enough to contain all the water in the installation (27), a pump (9), one supply manifold for the thermal screen, one supply manifold for the TRD and one common return manifold for both. Given the difference in water temperature required for the super-modules (~16ºC) and the thermal screen (~20ºC), each supply manifold will have its own heat exchanger connected to the ST/CV mixed water network (12 and 13). All 36 circuits can be temperature and flow adjusted. Temperature regulation is done via individual heaters (17 and 18) on the supply manifolds. These heaters are PID controlled using a temperature sensor (14f) immediately downstream as a feedback signal (see section 3.3 for details). Flow adjustment is done manually on balancing valves (21 and 22) during the commissioning of the system, in order to ensure that all circuits get the right flow despite of varying pipe length between the plant and the super-modules or screens. A PID controller adjusts the pump speed via a frequency inverter in order to keep a constant pressure in the supply manifold despite of the number of circuits in service at any given moment. Another PID controller adjusts the flow of mixed water via the 3-way valves (15 and 16) in order to maintain a constant temperature (14d and 14e) at the heat exchangers outlets. All regulation loops and the plant control is done by a Programmable Logical Controller (PLC). A fraction of the total flow (~5%) is by-passed through a mixed bed de-ionizer (11) and its conductivity measured (35). TPC Cooling System Page 4 of 13

5 Flow rate: TRD: m 3 /h Thermal Screen: m 3 /h 16~20 o C TRD supermodule Total flow: 32.4 m 3 /h +5% by-passed demin. Unit. 34m 3 /h Total heat to be removed: ~ 55 kw 18~20 o C Total Volume of water in the installation: ~2000L RB26 side Thermal screen RB24 side Installed Electrical Power: Pump: 11kVA Heaters TRD: 18 x 700VA Heaters Screen: 18 x 3.5kVA Compressed air 30 29b Total Power: 76kVA 28 Range of available water temperature at the Heaters outlet: Super-modules: 16~18ºC Screen: 18~20ºC Mixed Water Consumption: TRD Heat exchanger : ~32..5m 3 /h Screen Heat exchanger: ~4.5m 3 /h 23a f TRD Supply manifold 18 outlets Thermal screen Supply manifold 18 outlets 23b Return manifold 36 inlets a 2a 3a Total consumption: 37m 3 /h 14d 17 25a 18 14e 13 Mixed water 14c b 11 C Figure 4 TRD and Thermal Screen Cooling System 14b a 34 2b 3b 10 29a 1b item Description item Description 1a, 1b Pressure relief valve 14a,b,c,d,e,f Temperature Sensors 2a, 2b Manometer 15, 16 Mixed water Regulation Valve 3a, 3b Pressure transmitters 17, 18 Heaters 4 Ultra sound Level transmitter 19,20,24, 25a,b Pneumatic shut off valves 5 Vacuum pump 21, 22, 31 Balancing Valves 6 3-way Electro-valve 23 a,b Schrader valves 7 Drain valve 26 Visual Level 8 Butterfly Valve 27 Reservoir 9 Circulator Pump 28 Pneumatic distribution array 10 Strainer 29a,b Pressure switch 11 Mixed bed de-ionizer 32,33,34 Flowmeters 12, 13 Heat Exchangers 35 Conductivity transmitter Table 1 Identification of some components in Figure 4 TPC Cooling System Page 5 of 13

6 3.2. The Leakless Operation Mode 1 Consequences of a leak occurring inside the detector are obviously adverse. The risk of such an event can be eliminated if the hydraulics of the system is such that water pressure within the detector is below atmospheric, i.e.p DETECTOR-INLET P ATMOSPHERIC. This is done by keeping the reservoir (22) below atmospheric pressure by means of a vacuum pump (5), but still at a pressure high enough to avoid cavitation in the pump (9). Pressure drops inside the detector and in the return lines are carefully minimized to obey the following condition: 1 2 PDETECTOR + PRETURN _ LINE PATMOSPHERIC PRESERVOIR + ρ U + ρgh (a) 2 Where 1 ρ U 2 (U, flow speed; ρ density) is the dynamic pressure at the detector inlet 2 And ρgh (h, difference in height; g gravitational acceleration) is the hydrostatic pressure difference between the reservoir free surface and the detector inlet. Leak Detection Should a leak occur inside the detector or anywhere downstream to the cooling plant, no water will be spilled out. Instead, air will infiltrate into the system and be flushed down the return line, accumulating inside the reservoir. The pressure sensor in the reservoir (3a) will detect the consequent pressure build up and as soon as a pre-established threshold P 1 is exceeded, the PLC will immediately switch on the vacuum pump (5) and produce a WARNING message. The vacuum pump will run for a maximum period of 10 minutes. If the vacuum pump is able to restore the pressure back to the normal operation pressure P N in less than 10 minutes, it will stop pumping, yet the WARNING message will persist, informing the operator that a small air infiltration has been detected. As long as the air infiltration remains small, the pump is always able to restore the normal operation pressure in less than 10 minutes and the system can run ad infinitum with the pressure in the reservoir swinging between P N and P 1. In these circumstances the user may decide to engage the leak identification procedure to identify the exact leaky circuit, even though this procedure implies stopping the cooling for a while. If the vacuum pump is not able to restore the pressure in less than 10 min or if the pressure in the reservoir rises above a second threshold P 2, then the air infiltration rate into the system is considered to be important. In this case, not a warning but an ALARM message will be generated by the PLC and the cooling will stop. The PLC will also stop the circulator pump (9) and open the by-pass valves (25a and 25b) in order to start recovering all the water back into the reservoir both through supply and return lines. During this whole process, the vacuum pump stays on. Once most of the water has been recovered back into the reservoir, the user may also decide to engage the leak identification procedure. A significant part of the installation, from the pump outlet up to the immediate upstream vicinity of the detector inlet, will be above atmospheric pressure. Water spill out will occur if a leak develops anywhere between these two points. In this case, the ultra-sound level transmitter (4) will detect the loss of water in the reservoir and the PLC will produce an ALARM message and switch off the circulator pump, i.e., the cooling will stop. With the circulator pump switched off, the pressure throughout the installation falls to sub-atmospheric and the water spillage will stop. The by-pass valve (25a and 25b) opens and water recovery can then precede both through supply and return sides. The vacuum pump stays on during the process. Once most of the water has been recovered back into the reservoir, the user may decide to engage the leak identification procedure. Leak identification procedure This is an automatic procedure to identify and isolate the leaky circuit with the intent to restart the installation without intervention. With all supply and return valves closed and the reservoir at subatmospheric pressure, the leaky circuit is identified by successively opening one circuit at a time and monitoring the pressure in the reservoir. Once the leaky circuit has been identified the installation may 1 Leakless systems were developed by Michel Bosteels, CERN ST/CV TPC Cooling System Page 6 of 13

7 resume the cooling for all remaining circuits. The whole procedure is triggered by the Experiment Control Room (ECR) Temperature Regulation The heat dissipated inside a super-module may vary with time, thus some sort of adjustment needs to be undertaken on the cooling if the temperature field at the TPC boundaries is to be preserved. The adjustment suggested here is to modify the temperature of the water at the inlet of the super-modules in order to cope with different heat dissipations. Prior to any physics data taking, the thermal behaviour of a super-module needs to be established experimentally in the form of an empirical relationship between heat dissipation and required water temperature so that in normal running conditions, the ECR will know what water temperature to request from the cooling plant for each individual super-module. The request is communicated from the ECR to the cooling plant PLC where all the PID controllers are implemented. The PID uses as feedback signal the temperature sensor located at the heater outlet and acts on a Solid State Relay which in turns adjusts the heating power. There is of course a long pipe length between the heater outlet and the Super-modules inlet so these pipes are insulated in order to eliminate any thermal disturbance from the surroundings. Heaters are protected with a thermal switch, to prevent damage caused by accidentally overheating when there is little or no flow. The outgoing water temperature acquisition is made using a CERN developed card, the ELMB- Embedded local monitor Board connected to the PLC via CAN fieldbus. Figure 5 depicts the control loop in block diagram language. Water temperature at the heater inlet Water temperature requested by ECR PID controller Triac heater Water temperature at the heater outlet Travel time along supply line Twater at Supermodule inlet PLC Canbus EMLB Pt100 Figure 5 Control loop for water temperature regulation 3.4. Cooling System Operation and communication with ECR and TCR Plant Status The cooling plant can exist in 4 different statuses: stop, test, stand-by and run. In order to transit from one status to another, an input is required and/or certain conditions must be verified. Stop status: All power is off. Maintenance or repair operations can be carried out Test status: Testing the plant s performance and readiness. Filling, emptying and leak testing operations can be carried out. Mixed water may or may not be flowing The plant may or may not contain water The pressure in the reservoir may or may not be sub-atmospheric TPC Cooling System Page 7 of 13

8 Pressure and liquid level readings are available Pneumatic pressure is available so that individual circuits can be shut off for eventual leak testing. Stand-by status: The plant is water filled and waiting for a RUN order from the ECR Return and supply valves are all open (except any previously identified leaky circuit that may remain not repaired). Pressure and liquid level in the reservoir is correct. Circulator Pump is OFF. Temperature Regulation is OFF. Liquid level and Pressure monitoring is ON. Mixed water is flowing at the right temperature and rate. Compressed air is available and at the right pressure Emergency by-pass valve is closed Run status - Cooling is ON Supply and return valves are all open Emergency by-pass valve is closed Pump is running and outlet pressure regulation loop is ON Leak surveillance (reservoir pressure and liquid level monitoring) and is ON Temperature regulation is ON The detector is being cooled. The experiment may switch the detector on Transition between status Test Stand-by: only the local ST/CV SCADA supervisor can order this transition Stand-by Test: only the local ST/CV SCADA supervisor can order this transition. Stand-by Run: only ECR (experiment control room) can order this transition. However, if the stand-by status was the result of an alarm driven transition from run status, the alarms need to be acknowledged and reset first by the ST/CV supervisory SCADA. Upon ordering this transition, the ECR will have the possibility to set the following parameters: 1. Open/Close the water flow for a particular circuit (as long as the circuit hasn t been declared out of order). 2. Temperature set-point for each and every circuit Run Stand-by: this transition can take place as a result of the ECR deciding to stop the cooling to all circuits. The transition may also originate from the PLC as the result of an ALARM and in this case the ECR will promptly receive an alarm message informing of the imminent stopping of the cooling Warnings and Alarms Warnings and Alarms are issued by the cooling plant PLC and transmitted to the Experiment Control Room (ECR) and to the Technical Control Room (TCR). A warning is issued when a parameter is outside its normal range, but the deviation is not significant enough to stop the cooling. If the deviation becomes significant then an alarm is produced and the cooling plant or part of the cooling plant stops. A warning does not necessarily give rise to an alarm. An alarm always implies ceasing of cooling. TPC Cooling System Page 8 of 13

9 List of Warnings: W1) The pressure in the reservoir is above threshold P 1. W2) PID deviation error greater than 0.1 C (set point outlet temperature>0.1 C) for circuit #N W3) PID deviation error greater than 0.5 C (set point outlet temperature>0.5 C) at heat exchanger W4) PID deviation error greater than 100mbar (set point outlet pressure) at pump outlet W5) Circulator pump motor temperature above limit T PM 1 W6) Mixed water temperature is above limit T MW 1 List of Alarms: A1) Pressure in the reservoir is above threshold P 2 or vacuum pump has been running for more that 10 min. A2) Temperature switch has cut off power to heater #N A3) Compressed air failure (pressure insufficient) A4) Liquid pump failure (pressure insufficient at outlet). A5) Circulator pump motor temperature above limit T PM 2> T PM 1 A6) Mixed water failure (temperature either too high or insufficient flow). A7) Drop of water level in the reservoir Communication with ECR and TCR The role of the TCR, regarding this cooling system is assumed to be to receive alarms and to call the appropriate intervention piquet when required. The piquet is the only entitled entity to reset alarms and allow the system to transit back to run status, upon request from the ECR. This is done through the local ST/CV SCADA supervisor. The commands to switch on/off the cooling circuits as well as to modify set points go directly from the ECR supervisory SCADA (PVSS) to the cooling plant PLC (see Figure6). The ECR does not have access to low level commands to act on individual pieces of equipment in the cooling system (valves, pumps, etc.). TCR Cooling plant Status (Stop, Test, Stand-by, Run) Circuits status (Open, Closed) Warnings, Alarms PLC Transition orders Stand-by <=> Run Status Temperature set point for every circuit Open/Close circuits Cooling plant Status (Stop, Test, Stand-by, Run) Circuits status (Open, Closed) Warnings, Alarms Temperature at the heater outlets ECR Transition orders Stand-by <=> Test Status Alarms Reset Definition of Set Points for mixed water and pump outlet pressure PID regulation Definition of warning and alarm thresholds Cooling plant Data Storage Figure 6-Communication with ECR and TCR Local ST/CV Scada Supervisor (Wizcon) TPC Cooling System Page 9 of 13

10 3.5 Cooling plant layout drawings Figure 7 represents a preliminary sketch of the cooling plant physical layout. For transportation purposes, the plant is divided in 6 main volumes: TCR supply manifold, thermal screen supply manifold, return manifold, reservoir, rack containing pump + heat exchanger + filter and finally a rack with control (PLC), electrical equipment (triacs, circuit-brakers, frequency inverters etc ) and pneumatic equipment (electro-valves, etc..). Figure 8 shows a more detailed drawing of one temperature regulated outlet. Figure 7 Layout of the TRD and thermal screen cooling plant Temperature sensor Ball valve Balancing valve To detector From supply manifold Heater Figure 8 Detail of a temperature regulated outlet TPC Cooling System Page 10 of 13

11 4. Responsibilities and resources 4.1. Responsibilities The cooling plant described in this paper will be assembled, tested and first commissioned by ST/CV at the point 2 surface building by December Later on, the plant will be installed in the ALICE Experimental Area, connected to the mixed water network and again commissioned by ST/CV. Cables from the rack to neighbouring control equipment (PLC, etc.) are included, cables to other areas should be laid to ST/CV specifications by the experiment. Documentation (schematics, description, user instruction manuals) and the associated controls will be delivered with the cooling system. The PLC hardware is included in the work package. However, the PC's for the PVSS control are to be supplied by the experimental group. ST/CV will assume responsibility for the maintenance of the cooling plant during the LHC lifetime. A sub-detector expert from the experiment must participate during the commissioning of the cooling system both at the surface building and ALICE cavern Cost Estimation Table 3 Components and Materials Cost breakdown Item Description Manufacturer Quantity Unit cost (CHF) Total (see Fig 4) /model (CHF) 1a,b Pressure Relief valves CERN stores a,b Manometers CERN stores a,b Pressure transmitter Huba Control Ultra sound level transmitter Burkert Vacuum Pump KNF way electrovalve Parker Drain valve Legris Butterfly valve Zuercher/LUG Circulator Pump Grundfos/CRN Filter TECOFI Demineralisation Unit 50L Degremont ,13 Nickel brazed Heat Exchanger Swep ,16 Mixed water regulation valve Sauter Heater 6000W Dimeca Heater 1000W Dimeca Pneumatic Ball valvesdn20 Zuercher/Meca-Inox Pneumatic Ball valvesdn15 Zuercher/Meca-Inox Balancing valve DN20 Ribat/TA hydronics Balancing valve DN15 Ribat/TA hydronics Schrader valves M Paulus Pneumatic Ball valvesdn25 Zuercher/Meca-Inox Pneumatic Ball valvesdn15 Zuercher/Meca-Inox Visual Level CERN stores Reservoir 2000L Depositos Coballes Pneumatic EV array DIMAT Pressure switch Huba control TPC Cooling System Page 11 of 13

12 30 Electrovalve Lucifer Balancing Valve Rohr Flowmeter Aquadis Qmax=50m3/h Actaris Flowmeter Aquadis Qmax=10m3/h Actaris Flowmeter Aquadis Qmax=7m3/h Actaris Conductivity Meter Burkert Supply manifold TRD Tecnodelta Supply manifold thermal screen Tecnodelta Return manifold Tecnodelta rack for pump CERN stores piping, fittings, etc CERN stores 3000 PLC and related add-ons Schneider/TSX Circuit breakers, cabling etc CERN stores 4000 Frequency inverter Omron 3000 Cabling and accessories CERN stores 4000 Triacs for heaters Radiospares Pt100 sensors ELMB acquisition cards Total cost of material and components: CHF Manpower: duration (days) cost/hour (CHF) total cost Mechanical Assembly Electrical/control design Electrical assembly and cabling PLC programming Preliminary tests at CERN Commissioning at surface building point SCADA Wizcon Programming Commissioning in the cavern (including connection to networks, leaktesting, connection to pipes), Total cost of manpower: CHF TPC Cooling System Page 12 of 13

13 Appendix I Estimation of pressure drop along one MCM cooling circuit Pressure drop vs Flow rate for a 2mm ID pipe Pdrop (mbar) Laminar Re<2000 Transition 2000<Re<4000 Turbulent Re> Length=5.6m 200 Length=1.0m Flow rate (L/h) TPC Cooling System Page 13 of 13