1. Thermal Control Robert Manning AAE450 Spring 2007

2. Outline Fundamentals Thermal Control Devices Heat Shield (TPS) Resources & Considerations

3. Fundamentals: Steady-state thermal modeling is simply an energy balance. Q is heat flux or transfer (Watts) q is heat flux per unit area (W/m 2 ) Area is ALWAYS normal to transfer. Three method of heat transfer: radiation, conduction, & convection.

4. Fundamentals: Conduction Simple one dimensional condition: K = Thermal conductivity (W/m/K) dt/dx = Temperature gradient (K/m) Derivative can be approximated using two temperature (T 1 and T 2 )

5. Fundamentals: Convection Newton’s Law of cooling: h = Transfer Coefficient (W/m 2 -K) Empirical equation. Use Nusselt number correlations to determine h. Laminar/Turbulent? Free convection/external/internal? Boiling/Condensation?

6. Fundamentals: Radiation Heat emitted is governed by Stefan- Boltzmann Law.  is emissivity.  is 5.67x10 -8 J/(K 4- m 2- s) Heat absorbed is governed by the absorbitivity coefficient . Use view factor relationship (Incropera Chapter 13)

7. Fundamentals: Tricks Area is projected area of radiation. If no heat is generated in body, temperature can be controlled by examining /. We can treat thermal conductance as an electrical resistor:

8. Thermal Control Devices Passive Thermal Control: System without any moving parts or electrical input Active Thermal Control: Anything that has moving parts and/or electrical input

9. Multi-layer Insulation MLI is typically part of micrometeorite protection. Use Effective Emmittance(~0.005): Chapter 13.2.5 from Incropera Outer Cover Spacer Reflector Cover & Structure ………………………………

10. Pumped-Loop Systems Active Control Transfers heat from one location to another using a pumped liquid. Typically use water for human habitat. Ammonia or Freon used for external or non-habitat portions. Use counter-flow heat exchangers! Chapter 11 of Incropera

11. Radiators Active Control Used in conjunction with pumped- loops to radiate heat into space. Two types: body-mounted or deployable Use Flash Evaporators when not deployed

12. Thermal Protection System Difficult. Ask Prof. Schneider! Establish characteristics of entry: Velocity-altitude profile bluff or streamlined body Knudsen number ablative vs. no ablation Consider using existing data or codes!

13. TPS: Flow characteristics Chemical reaction at high temperatures Oxygen: T > 2000 K, Nitrogen: T > 4000 K Possible ionization Turbulent, separated, shock interactions Convection vs. Radiation Knudsen: kn > 0.1 => no continuum

14. Resources: Books 1) Excellent Thermal Design Book: David G. Gilmore. Spacecraft Thermal Control Handbook. 2) Incropera, DeWitt, et al. Fundamentals of Heat and Mass Transfer. 3) Anderson, John. Modern Compressible Flow or Hypersonic and High Temperature Gas Dynamics.

15. Resources: Web Code for aero-thermal modeling: http://roger.ecn.purdue.edu/~aae450s/ methods.pdf TPSX: http://tpsx.arc.nasa.gov/

16. Resources @ Purdue SODDIT: Sandia One-Dimensional Direct and Inverse Thermal Code Newton’s Method : Predicts Cd and Cl for high mach numbers Prof. Schneider