MICE absorber and Window / flow Design

Wing Lau, Giles Barr & Stephanie Yang

Oxford University

MICE MeetingBerkeley, Oct 2002

This talk is in two parts;

Firstly (presented) we will go through briefly the progress and results on the MICE Convective Window design and flow simulation;

Secondly (slides at the end, but no time to present them) about the Lithium Window calculations from John Cobb.

Window Design and Convective Flow analysis

The design of the bellow window geometry is such that it is possible to scale the standard design geometry to suit any window dimension without the need to do any FE calculation and still keeping the same pressure rating, i.e. burst pressure at 120 psi.

As far as the pressure rating is concerned, we believe that the development on the window geometry has now reached its most optimum state.

Future effort should be spent in studying the absorber safety. In that we need to identify and quantify the various loads introduced during either normal operation or at fault conditions.

The mechanical design of the Window

This includes, but not limited to:

• Thermal loads caused, possibly, by uneven temperature distribution of LH2 during operation;

• Differential thermal loads at Window anchor points;

• Eddy current and magnet quench effect, if applicable;

• Cyclic loads during the start up and shut down of the experiment etc.

With the installation of CFX-5, we now have the correct software to do 3-D buoyancy calculations on convective thermal models.

Our fluid model has been tested and compared well with benchmark results.

We will discuss how the simulation results compare with KEK’s LNe test;

Our goal is to construct a set of simple rules / graphs to enable designers to establish the thermal capacity of the Window at various operating and environmental conditions without doing any complex FE calculation -- similar to what we did on the Window geometry design method;

We will also look at how design details of the Absorber vessel could be changed to improve its thermal performance. A case in time would be the fitting of an internal baffle to separate the current flow inside the absorber vessel, as suggested by Mike Green. This will enhance the buoyancy velocity and will improve the heat absorption capacity;

The convective heat flow

LH2

LHe in

LHe out LHe out

LHe in

Absorber

Internal Baffle

Internal baffle to improve current circulation – suggested by Mike Green

The following slides show our simulation on a convective flow inside the Absorber filled with liquid Neon.

A dummy coil, producing 60 watts of heating power is modelled as a fluid sub-domain so that its presence does not affect the buoyancy flow of the fluid.

Two boundary conditions were applied; one with the outer wall kept at 10K, and the other at 24.5K. The intention was to see how sensitive the results are to the imposed wall temperature

Heating Coil

Liquid Hydrogen

KEK’s test set-up

The Fluid grid model

LNe, dummy heater: 60w. BC=10K

LNe, dummy heater: 60w. BC=10K

LNe, dummy heater: 60w. BC=10K

LNe, 60W, BC=24.5K

LNe, 60W, BC=24.5K

29 K 29 K

Solid Ne were visible in the lower absorber

29 K

KEK’s results

Dummy heater

Temperature probe readings

Boiling occurred here

A cross check:

Material and thermal properties of Liquid Neon:

Density of Liquid Neon: 1204 Kg / M^3

Specific Heat of liquid Neon: 1080J / Kg /K

Volume of the absorber is approx. 7 litre or 0.007 m^3

This requires a total thermal energy of approx. 910J to heat up the Liquid Neon inside the absorber by 1 K;

A heat source of 60W will take 15 second to do this, when the window wall is assumed adiabatic, i.e. no heat exchange across the absorber wall.

What we have assumed in our simulation is that the wall are being fully kept to a lower temperature at all time. We need to investigate whether the results would make any difference if the walls are being cooled by a fixed volume of coolants circulating from the bottom to the top of the absorber.

We are still investigating the cause of this difference with KEK

Why different?

A study on the Lithium Window

Lithium thermal calculation

• Less dangerous:– Nearly as good (particularly in early

stages of cooling channel).– Contacts in Chemistry

• Consider Lithium– ~2.5x worse equilibrium emmitance– John Cobb thermal calculations

• MICE proposal: running with alternate absorbers (Li, plastic).– Design to fit into place of LH absorber

window

Beam time structure

Temperature rise

Temperature profiles2e13 /bunch, rms beam size 1 cm.