GLAST Program Analysis Memo TKR Tower Thermal-Vacuum Test MGSE Nicola Saggini SSAL @ INFN – Pisa nicola.saggini@pifn.it

1. GLAST ProgramAnalysis MemoTKR Tower Thermal-Vacuum Test MGSENicola SagginiSSAL @ INFN – Pisanicola.saggini@pi.infn.it

2. Overview • Statement of the problem • Proposed Solution • Analysis - Description of thermal model: • Mesh • Boundary conditions • Thermal couplings • Simplifications/Approximations • Analysis - Results • Final Comments

3. Statement of the problem • A large (1200x1200 mm) Cold Plate with recirculation of fluid (+120°C -60°C) is provided to control the Test Article temperature. (Very little is know about convective loop performance). • The TKR Tower needs to be raised over the plate at least 300 mm in order to accomodate TEM+PS underneath. • Efficiency and rapidity in heat conduction needs to be ensured. CONSTRAINTS/CONDITIONS • TKR Tower dissipates 10 W at nominal power level. • Inner Guard Shield that surrounds TKR Tower has heaters that dissipate 10 W at nominal power level. • TKR Tower temperature gradient must not exceed ±20°C/hr

4. Proposed Solution (1 of 2) ~ 350 • Color – Material Legenda: • Blue: Al • Orange: Cu • Yellow: G-10 500 180

5. Proposed Solution (2 of 2) Heat transfer to an from Cold Plate provided by four Thermal Sidewalls (2 mm thick) and Cold Ring (20 mm thick) Structural stiffness provided by four columns (f = 40 mm) (Two Thermal Sidewalls not shown or clarity)

6. Description of the Thermal ModelMesh Geometry of model was simplified dropping all parts not thermally coupled to MGSE To ease computational time, all parts were meshed using shell (2-D) elements of appropriate thickness

7. Description of the Thermal ModelBoundary Conditions Non-geometric element representing TKR+IGS with a thermal mass of 26000 J/K Coupled with cold ring using a thermal conductance of 1000 W/(m2K) Total power input on Cold Ring of 20 W Thermal couplings within Thermal Sidewalls parts and between Cold Ring and Thermal Sidewalls modeled with a thermal conductance of 7500 W/(m2K) (Thermally Conductive Grease present) Cold Plate initially modeled as non-geometric element at constant temperature and thermal conductance at interface with thermal sidewalls of 7500 W/(m2K) Later, the whole interface was replaced by a time-varying temperature directly on the Thermal Sidewall feet surface boundary

8. Description of the Thermal ModelApproximations • TKR Tower and IGS heat load on Cold Ring has been supposed uniform on its surface, actual configuration has two different frames (one for the Tower, the Other for IGS in contact with Cold Ring) • The decision to replace actual interface between Cold Plate and Thermal Sidewalls was made in order to overcome a simulation program shortcoming (i.e. the impossibility to model a non-geometric element with a time-varying temperature), but results of early simulation with actual interface modeled (constant temperature non-geometric cold plate) were comforting (given the very high thermal conductance). • No radiation losses/inputs have been taken into account yet.

9. Results 1of2

10. Results 2of2

11. Final Comments • Use of thermally conductive grease at Cold Plate to T/SW, within T/SW, and at Cold Ring to T/SW interfaces is strongly recommended. • Time required to change temperature should be greater, by at least an hour, than what has been experienced in the Thermal Vacuum chamber (EM heritage) . • Convective loop performance of Cold Plate could further increase the time required to change temperature. Things to do: • Accuracy of simulation could be increased once radiation losses and inputs are taken into account. • “Stiffness” of the system to small perturbation is still to be ascertained