Thermal Control
Robert Manning
AAE450
Spring 2007
Outline
Fundamentals
 Thermal Control Devices
 Heat Shield (TPS)
 Resources & Considerations

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/m2)
 Area is ALWAYS normal to transfer.
 Three method of heat transfer:
radiation, conduction, & convection.
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Fundamentals: Conduction
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Simple one dimensional condition:
dT
q  K
dx
q12
T1  T2
K
x
K = Thermal conductivity (W/m/K)
 dt/dx = Temperature gradient (K/m)
 Derivative can be approximated
using two temperature (T1 and T2)

Fundamentals: Convection

Newton’s Law of cooling:
q12  h(T1  T2 )
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h = Transfer Coefficient (W/m2-K)
Empirical equation. Use Nusselt number
correlations to determine h.
Laminar/Turbulent?
Free convection/external/internal?
Boiling/Condensation?
Fundamentals: Radiation
qout  T
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4
q absorb  qincident
Heat emitted is governed by StefanBoltzmann Law.  is emissivity.  is
5.67x10-8 J/(K4-m2-s)
Heat absorbed is governed by the
absorbitivity coefficient .
Use view factor relationship (Incropera
Chapter 13)
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:

x
R
KA
T
Q
R
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
Multi-layer Insulation
Outer Cover
Spacer
Spacer
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………………………………
………………………………
Cover &
Structure
MLI is typically part of micrometeorite
protection.
Use Effective Emmittance(~0.005):
 *A(T  T )  Q
4
H

Reflector
4
C
Chapter 13.2.5 from Incropera
Pumped-Loop Systems
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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
Radiators
Active Control
 Used in conjunction with pumpedloops to radiate heat into space.
 Two types:
body-mounted or deployable
 Use Flash Evaporators when not
deployed

Thermal Protection System
Difficult. Ask Prof. Schneider!
 Establish characteristics of entry:

Velocity-altitude profile
bluff or streamlined body
Knudsen number
ablative vs. no ablation
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Consider using existing data or
codes!
TPS: Flow characteristics
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Chemical reaction at high temperatures
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Oxygen: T > 2000 K, Nitrogen: T > 4000 K
Possible ionization
Turbulent, separated, shock interactions
Convection vs. Radiation
Knudsen: kn > 0.1 => no continuum
kn 

  mean free path
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  characteri c length
Resources: Books
1)
2)
3)
Excellent Thermal Design Book:
David G. Gilmore. Spacecraft Thermal
Control Handbook.
Incropera, DeWitt, et al. Fundamentals
of Heat and Mass Transfer.
Anderson, John. Modern Compressible
Flow or Hypersonic and High
Temperature Gas Dynamics.
Resources: Web
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Code for aero-thermal modeling:
http://roger.ecn.purdue.edu/~aae450s/
methods.pdf
TPSX:
http://tpsx.arc.nasa.gov/
Resources @ Purdue
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SODDIT:
Sandia One-Dimensional Direct and
Inverse Thermal Code
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Newton’s Method:
Predicts Cd and Cl for high mach numbers

Prof. Schneider