Eurizon.eu

Organization: CEA-Saclay

Location: Gif-sur-Yvette, France

Field: Thermal engineering

Requirements:

PhD or equivalent in Engineering;
ENGLISH and FRENCH: good
The candidate must have a PhD in experimental fluid mechanics / two-phase / heat transfer with expertise in physical modeling

Abstract:

For large superconducting magnets at liquid helium temperature, cooling systems are often based on two-phase gravity circulation loops...

Description:

For large superconducting magnets at liquid helium temperature, cooling systems are often based on two-phase gravity circulation loops. Their main interest is to create a flow of high stability with large cooling capacities without any pressurization system. These magnets have large heat load (100 W) and require a liquefaction system burdensome and costly to ensure the vapor recondensation. For smaller power systems (1 W) it is proposed to develop a circulation loop coupled with a cryocooler to recondense vapors.
A 4 K cryocooler will be used as a heat sink for the condenser. The experimental loop includes a condenser, the heat exchanger part and the loop. The loop will be instrumented with various sensors to achieve the characterization of the heat exchanges, the thermal-hydraulic of the flow and the thermodynamic of the entire loop. The candidate will be responsible for final assembly of the loop, experimental sessions and the analysis results.
 
For large superconducting magnets at liquid helium temperature, used in detectors for high energy physics, such as the CMS detector at CERN (Geneva) or R3B at GSI (Darmstadt), cooling systems are often based on two-phase gravity circulation loops (two-phase thermosyphon). Their operating principle is based on an imbalance in weight between the two branches of the loop due to a phase change of the fluid in the "heat exchanger" part. Their main interest is to eliminate any pressurization system, cost in use and maintenance, to create a flow of high stability with large cooling capacities (h~1000 W/m.K). These magnets have large heat load (~ 100 W) and require a systematic liquefaction system burdensome and costly to ensure the recondensation of the cryogenic fluid vapors in the loop. For cryo-magnetic system of smaller size and average power (~ 1 W or 100 W helium in nitrogen), the Cryogenics Laboratory Testing Stations (LCSE) proposes to develop a circulation loop coupled with a cryocooler to recondense vapors and create a closed loop. This coupling combines the advantages of a "self-propelled" circulation loop and recondensation of vapors by a compact device closer located to the loop, synonymous with a significant energy gain (no transfer and loss of cryogen). We see the value of such an autonomous system for detectors located in places difficult of access, but also for applications with higher operating temperatures using, for example, high critical temperature superconductors such as cables electricity transmission or electromagnets new generations.

Initially, a cryocooler a power of 1.5 W at 4.2 K will be used as a heat sink for the condenser. It is optimized to operate at temperatures of liquid helium and therefore the first measurement campaigns will be conducted with liquid helium coolant. A change in the course of study might be conducted after the test campaigns with helium to adjust the loop with liquid nitrogen. The experimental loop includes a condenser, the heat exchanger part and the buckle. The entire loop will be instrumented with various sensors to achieve a characterization of wall heat exchanges of exchanger, a thermal-hydraulic characterization of the flow and thermodynamic characterization of the entire loop. The entire experimental system is controlled by different control loops for pressure and temperature. The data acquisition system is a low level scanning system on 16bit that allows data acquisition with good sensitivity (1 mK for temperatures and pressures to 1 Pa).

The candidate will be responsible for final assembly of the loop, mainly instrumentation, operation, experimental sessions and the analysis results. A thermal-hydraulic modeling of the loop is provided using the Comsol software. Within the LCSE, it will be supported by a senior technician and the scientist in charge of the program.

Deadline: 01-07-2011

Contacts:

Link: http://irfu.cea.fr/Sacm/en/index.php

Email: bertrand.baudouy@cea.fr

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