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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

    2011 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.edu

    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

    9

  • 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

    10

  • 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

    11

  • 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

    12

  • 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

    13

  • 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)

    14

  • 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

    15

  • 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

    16

  • 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)

    17

  • 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

    18

  • 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

    !

    Prad ="#A T4 $Tenv

    4( )

    !

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

    4( )

    19

  • 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

    20

  • 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

    #$Arad

    &

    ' (

    )

    * +

    14

    = 362K

    22

  • 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

    !

    Pint ="#Arad T4 $ Tenv

    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

    26

  • 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

    28

  • 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

    29

  • 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

    30

  • 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

    31

  • 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

    32

  • 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)

    ! whereK=thermal conductivity (W/mK)A=areadT/dx=thermal gradient

    !

    Q = "KAdTdx

    33

  • 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

    34

  • 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

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