Thermal Analysis of short bake out jacket

version 112-Nov-2013

Bake out jacket without outer cover and cooling lines

PTFE frame with stainless heater support with 3 heater rods on a side

Simplified model of bake out jacket for thermal analysis

outer stainless jacket with fixed temperature cooling ribs/tubes

insulation layer

stainless heater supports

naked Be beam pipe

naked Aluminum beam pipe

6 mm dead air layer between heater support tube and beam pipe

The beam pipe wall thickness and outer stainless shell have been scaled up by a factor of 5 and the thermal conductivities have been scaled down by a factor of 5 to compensate. This was to facilitate meshing and reduce solving time.

The analysis was done by adjusting the heater power input to raise the beam pipe temperature to approximately 250 deg at the center.

The ambient temperature was adjusted to give approximately zero power into the air. That is the heat into the air by convection from hotter elements is equal to the heat out by convection to the cooled surface.

Two cases were run with different conditions. Case 1 did not have radiative heat transfer between the beam pipe and the heater jacket while Case 2 did. The convective parameter is a factor of 2 higher in Case 1 than Case 2. Case 2 has a higher temperature for the cooling tubes.

Boundary conditions and results for SolidWorks Thermal Simulation

parameters & boundary conditions case 1 case 2

convection parameter 20 W/(m^2 K) 10 W/(m^2 K)cooling tube temperature 22 deg. C 32 deg. Cbeam pipe end temperature 250 deg. C 250 deg. Cheater power 150 W 125 Wradiative coupling between heater tube & beam pipe emissivity: 0 emissivity: 0.9

conductivities W/(m K) W/(m K)

Stainless 18 18Insulator 0.082 0.082Dead air layer 0.027 0.027Aluminum 167 167Beryllium 216 216

Results

beam pipe min (deg. C) 168 204beam pipe max (deg. C) 247 258beam pipe spread (deg. C) 79 54

stainless heater rod support min (deg. C) 206 208stainless heater rod support max (deg. C) 303 276

ambient air temperature (deg. C) 41 50

convective heat loss from naked beam pipe sections 90 W 51 W

beam pipe temperature distribution

Case 1

Case 2

Stainless heater support temperature distribution

Case 1

Case 2

End region temperature distribution

Case 1

Case 2

Outer jacket temperature distribution

Case 1

Case 2

Power entering beam pipe ends from jacketed beam pipe sections set at 250 deg C

Power slightly different for the two ends since one pipe is Beryllium and one is Aluminum. Also the wall thicknesses are not the same.

Case 1Total 72 W

Case 2Total 39 W

Case 1 Cooling ribs/tubes power transfer

total for all ribs: 222 W

Case 2 Cooling ribs/tubes power transfer

total for all ribs: 159 W

Convective heat loss from the naked sections of the beam pipe.

Case 1Total 90 W

Case 2 Total 51 W

Summary of results and comments

The spread in temperature on the beam pipe is 168 deg C to 247 deg C for 150 watts of heater power in case 1. For case 2 the input heater power is 125 watts with a spread in beam pipe temperature from 204 deg C to 258 deg C. The more uniform beam pipe temperature in case 2 is the result of choosing a reduced convection parameter thus reducing the convective heat loss from the naked portions of the beam pipe. The reduced temperature of the stainless heater in case 2 is because of the increased coupling of between beam pipe and heater that results from including radiative heat transfer.

As these two cases demonstrate there is uncertainty in the heat loss from the naked portions of the beam pipe, since one can’t know in this limited model what the correct convective heat loss is. A factor of 2 uncertainty can be expected. In either case however there is significant heat transfer from the naked sections to the surrounding air. So it makes sense to arrange some exchange of air in the PST region, rather than trying to absorb all of the heat with the cooling jacket as has been done in this simulation.

The model does not include the PTFE (Teflon) ribs which have a factor 3 higher conductivity than the insulation, but the ribs are some what isolated from the hot stainless heater carrier. This is important because the stainless heater support tube reaches 280 deg C and the melting point of PTFE is 327 deg C. Decomposition sets in at a lower temperature.

It is expected that the ambient air temperature will be somewhat lower that indicated in the simulation, because there will be additional heat loss to the PST walls which have not been included in this model.