1. LATLAT Tower T/V MGSE Memo 11 th November 2004 1 GLAST Program Analysis Memo TKR Tower Thermal-Vacuum Test MGSE Nicola Saggini SSAL @ INFN – Pisa nicola.saggini@pi.infn.it

2. LATLAT Tower T/V MGSE Memo 11 th November 2004 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. LATLAT Tower T/V MGSE Memo 11 th November 2004 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. LATLAT Tower T/V MGSE Memo 11 th November 2004 4 Proposed Solution (1 of 2) Color – Material Legenda: Blue: Al Orange: Cu Yellow: G-10 500 ~ 350 180

5. LATLAT Tower T/V MGSE Memo 11 th November 2004 5 Proposed Solution (2 of 2) Structural stiffness provided by four columns (  = 40 mm) Heat transfer to an from Cold Plate provided by four Thermal Sidewalls (2 mm thick) and Cold Ring (20 mm thick) (Two Thermal Sidewalls not shown or clarity)

6. LATLAT Tower T/V MGSE Memo 11 th November 2004 6 Description of the Thermal Model Mesh 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. LATLAT Tower T/V MGSE Memo 11 th November 2004 7 Description of the Thermal Model Boundary 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/(m 2 K) 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/(m 2 K) (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/(m 2 K) Later, the whole interface was replaced by a time-varying temperature directly on the Thermal Sidewall feet surface boundary

8. LATLAT Tower T/V MGSE Memo 11 th November 2004 8 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. Description of the Thermal Model Approximations

9. LATLAT Tower T/V MGSE Memo 11 th November 2004 9 Results 1of2

10. LATLAT Tower T/V MGSE Memo 11 th November 2004 10 Results 2of2

11. LATLAT Tower T/V MGSE Memo 11 th November 2004 11 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 Final Comments