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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Final Project Discussion Final Report Discussion Thermal Systems Design Overview

1

http://spacecraft.ssl.umd.eduhttp://spacecraft.ssl.umd.edu

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Thermal Systems Design Fundamentals of heat transfer Radiative equilibrium Surface properties Non-ideal effects

Internal power generation Environmental temperatures

Conduction Thermal system components

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Classical Methods of Heat Transfer Convection

Heat transferred to cooler surrounding gas, which creates currents to remove hot gas and supply new cool gas

Dont (in general) have surrounding gas or gravity for convective currents

Conduction Direct heat transfer between touching components Primary heat flow mechanism internal to vehicle

Radiation Heat transferred by infrared radiation Only mechanism for dumping heat external to vehicle

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Thermodynamic Equilibrium First Law of Thermodynamics

! heat in -heat out = work done internally Heat in = incident energy absorbed Heat out = radiated energy Work done internally = internal power used

(negative work in this sense - adds to total heat in the system)

!

Q "W = dUdt

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Radiative Equilibrium Temperature Assume a spherical black body of radius r Heat in due to intercepted solar flux

Heat out due to radiation (from total surface area)

For equilibrium, set equal

1 AU: Is=1394 W/m2; Teq=280K

!

Qin = Is" r2

!

Qout = 4" r2#T 4

!

Is" r2 = 4" r2#T 4 \$ Is = 4#T

4

!

Teq =Is4"#

\$ %

&

' (

14

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Effect of Distance on Equilibrium Temp

Mercury

PlutoNeptuneUranus

SaturnJupiter

Mars

Earth

Venus

Asteroids

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Shape and Radiative Equilibrium A shape absorbs energy only via illuminated faces A shape radiates energy via all surface area Basic assumption made is that black bodies are

intrinsically isothermal (perfect and instantaneous conduction of heat internally to all faces)

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Effect of Shape on Black Body Temps

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Incident Radiation on Non-Ideal Kirchkoffs Law for total incident energy flux on solid

bodies:

! where ! =absorptance (or absorptivity) " =reflectance (or reflectivity) # =transmittance (or transmissivity)

!

QIncident =Qabsorbed+Qreflected +Qtransmitted

!

QabsorbedQIncident

+QreflectedQIncident

+QtransmittedQIncident

=1

!

" #QabsorbedQIncident

; \$ #QreflectedQIncident

; % # QtransmittedQIncident

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Non-Ideal Radiative Equilibrium Assume a spherical black body of radius r Heat in due to intercepted solar flux

Heat out due to radiation (from total surface area)

For equilibrium, set equal

!

Qin = Is"# r2

!

Qout = 4" r2#\$T 4

!

Is"# r2 = 4# r 2\$%T4 & Is = 4

\$"%T 4

!

Teq ="#Is4\$

%

& '

(

) *

14

(\$ = emissivity - efficiency of surface at radiating heat)

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Effect of Surface Coating on Temperature

\$ = emissivity

! =

abs

orpt

ivit

y

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Non-Ideal Radiative Heat Transfer Full form of the Stefan-Boltzmann equation

! where Tenv=environmental temperature (=4K for space)

Also take into account power used internally

!

4( )

!

Is" As + Pint =#\$Arad T4 % Tenv

4( )

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Example: AERCam/SPRINT 30 cm diameter sphere !=0.2; \$=0.8 Pint=200W Tenv=280K (cargo bay

below; Earth above) Analysis cases:

Free space w/o sun Free space w/sun Earth orbit w/o sun Earth orbit w/sun

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

AERCam/SPRINT Analysis (Free Space) As=0.0707 m2; Arad=0.2827 m2

Free space, no sun

!

Pint = "#AradT4 \$ T = 200W

0.8 5.67 %10&8 Wm2K 4

'

( )

*

+ , 0.2827m2( )

'

(

) ) ) )

*

+

, , , ,

14

= 354K

21

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

AERCam/SPRINT Analysis (Free Space) As=0.0707 m2; Arad=0.2827 m2

Free space with sun

!

Is" As + Pint = #\$AradT4 % T = Is" As + Pint

&

' (

)

* +

14

= 362K

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

AERCam/SPRINT Analysis (LEO Cargo Bay)

Tenv=280K

LEO cargo bay, no sun

LEO cargo bay with sun

!

4( )% T = 200W0.8 5.67 &10\$8 W

m 2K 4'

( )

*

+ , 0.2827m2( )

+ (280K)4

'

(

) ) ) ) )

*

+

, , , , ,

14

= 384K

!

Is" As + Pint =#\$Arad T4 % Tenv

4( )& T = Is" As + Pint#\$Arad

+ Tenv4

'

( ) )

*

+ , ,

14

= 391K

23

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

EVA Thermal Equilibrium Human metabolic workload = 100 W Suit electrical systems = 40 W Total heat load = 140 W

24

Q = AT 4 A = QT 4

A =140

(0.8)(5.67 108)(295)4 = 0.41 m2

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

EVA Thermal Equilibrium with Sun Human metabolic workload = 100 W Suit electrical systems = 40 W Total internal heat load = 140 W

25

Q + AIs = AT 4 A =Q

T 4 IsA =

140(0.8)(5.67 108)(295)4 0.2(1394) = 2.2 m

2

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Sublimation Water heat of sublimation = 46.7 kJ/mole @ 18 gm/mole = 2594 W-sec/gm Mass flow for 140 W = 0.54 gm/sec per hour = 194 gm/hr 8 hr total EVA time = 1.55 kg of water @ 2 EVA/day and 180 days = 559 kg of water

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Sitting on a Planetary Surface

27

IsTb

Th

Th

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Radiative Insulation Thin sheet (mylar/kapton with

surface coatings) used to isolate panel from solar flux

Panel reaches equilibrium with radiation from sheet and from itself reflected from sheet

Sheet reaches equilibrium with radiation from sun and panel, and from itself reflected off panel

Is

Tinsulation Twall

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Multi-Layer Insulation (MLI) Multiple insulation

layers to cut down on radiative transfer

Gets computationally intensive quickly

Highly effective means of insulation

Biggest problem is existence of conductive leak paths (physical connections to insulated components)

Is

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Emissivity Variation with MLI Layers

Ref: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 2002

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

MLI Thermal Conductivity

Ref: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 2002

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Effect of Ambient Pressure on MLI

Ref: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 2002

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

1D Conduction Basic law of one-dimensional heat conduction

(Fourier 1822)

!

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

3D ConductionGeneral differential equation for heat flow in a solid

! whereg(r,t)=internally generated heat"=density (kg/m3)c=specific heat (J/kgK)K/"c=thermal diffusivity

!

" 2T ! r ,t( ) + g(! r ,t)K

=#cK\$T ! r ,t( )\$t

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• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Simple Analytical Conduction Model Heat flowing from (i-1) into (i)

Heat flowing from (i) into (i+1)

Heat remaining in cell

TiTi-1 Ti+1

!

Qin = "KATi " Ti"1#x

!

Qout = "KATi+1 "Ti#x

!

Qout "Qin =#cK

Ti( j +1) " Ti( j)\$t

35

• Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Time-marching solution

where

For solution stability,

Finite Difference Formulation

=k

Cv= thermal diffusivityd =

t

x2

Tn+1i

= Tni + d(Tn

i+1 2Tn

i + Tn

i1)

t