Ecal regulating circuit Proposal

31/08/2001

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=> Introduction

=> Known parameters and Assumptions

=> Determination of other parameters

=> Regulating Loops, PLC

=> Recommendation for SM size circuit

Introduction

Following the Principle Review (link), some more work has been done concerning the regulating circuit of ECAL. A new draft of the hydraulic circuit contains more informations about flow rates and temperature. The goal is to have a more precise idea of the circuit as it will be built. Even if some value have a possibility to change (mainly the power dissipated by the electronics), it will allow us to settle some technical specifications and also to make a reasonable estimation of the costs.

First proposal

Schema ECAL

Schema Super module size

The design and calculations were made for the final circuit and applied to a super-module size (1/36) with as much as possible the same technical solutions.
The cooling circuit at a super module size will be suitable for the crystals calibrations of every super module, it will also be used as a "Test facility" for the final circuit, to give a good understanding of the cooling process and regulation.

Known parameters and Assumptions

For Ecal Regulating circuit (EE+EB), we know the power dissipated and the flow rate.

Power dissipated in the detector (computed with 1.7 W/channel + 15%margin): EE=3 kW and EB= 13 kW
Total: 16 kW

Flow rate: EE= 10 l/s and EB= 50 l/s
Total: 60 l/s

It is also important to know the heat dissipated by the pump, the head loss has been estimated to 40..50 m (link) which make a power dissipated of 50 kW (link).

Tin= 18șC and Tc= 17.8șC.
We assume a precision of ±0.1șC on Tc, and the resistance will reach the final precision of 0.05șC.

Determination of other parameters

From there we can calculate the temperature encountered in the circuit that includes the detector.

It gives us the value of the total heat to be removed by the heat exchanger (PHE2).
Heat to remove: 125 kW

The immersion heater will have to heat the fluid between 0.1 and 0.3șC, wich makes a power of 26 to 78kW.
Resistance power: 80kW

The flow conditions (flow rate, temperatures...) in the intermediate loop depends on:
- the flow rate and the heat to release in PHE2
- the flow conditions in the primary circuit (chilled or mixed water available in CERN facilities)
- the technical solutions available

The usual heat exchanger used in ST-CV installation are Gasketed Plate Heat Exchanger (GPHE), for their compacity, their evolution capacity, and the different materials available for the plates.
The society Alfa Laval was contacted and proposed a solution using GPHE that presents the advantage to be the same for the Super Module size circuit and the final circuit.

Intermediate Loop:

The flow rate is already determined by the choice of the heat exchanger. To size up the pump, we need to know the pressure drop inside the circuit. It is known in the heat exhanger and after, we consider 10 m of pipe and 6 elbows.

Regulating Loops, PLC

There are two control loops in the circuit, one for the resistance and the other for the valve. They both regulate the temperature of the process.
The type of controller forseen is a PID (Proportionnal Integral Derivative). Some controllers exists in a bloc form, but it seems better to use a PLC (Programmable Logic Controller) instead.
It will ensure the regulation loop, as well as the monitoring of the different values in the process. It will also ensure the communication to a supervision software.

Recommendation for SM size circuit

- Variable speed pump
The head loss will be difficult to determine accurately for the prototype, and some new applications can be asked to the circuit (it is a direct experience of the Module 0 activity). A pump over dimensionned with a variable speed drive could give a lot of flexibility to the system in terms of flow and head loss.

Pressure drop estimation
15 m + 10 elbows.

In a first approach, we can consider that the pump will have to deliver a flow of 1.7 l/s with a pressure drop between 1 and 3 bars.

- HE over-dimentionnned
The heat that will be removed by the regulating circuit is supposed to be 10% of the heat produced by the electronics. If this value was changed, it will lead to an increase of the flow rate in the intermediate loop and in the primary circuit and also another operating point point for the regulating valve.

- Process monitoring
The flow conditions, temperature, pressure and flow rate will have to be monitored in several points of the circuit.

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