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Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDFinal Project Discussion Final Report Discussion Thermal Systems Design Overview1 2011 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.eduhttp://spacecraft.ssl.umd.eduhttp://spacecraft.ssl.umd.eduFinal Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDThermal Systems Design Fundamentals of heat transfer Radiative equilibrium Surface properties Non-ideal effects Internal power generation Environmental temperatures Conduction Thermal system components9Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDClassical 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 vehicle10Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDThermodynamic 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 = dUdt11Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDRadiative 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#T4! Teq =Is4"# $ % & ' ( 1412Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEffect of Distance on Equilibrium TempMercuryPlutoNeptuneUranusSaturnJupiterMarsEarthVenusAsteroids13Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDShape 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)14Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEffect of Shape on Black Body Temps15Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDIncident 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; % # QtransmittedQIncident16Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDNon-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)17Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEffect of Surface Coating on Temperature$ = emissivity! = absorptivity18Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDNon-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 $Tenv4( )! Is" As + Pint =#$Arad T4 % Tenv4( )19Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDExample: 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/sun20Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDAERCam/SPRINT Analysis (Free Space) As=0.0707 m2; Arad=0.2827 m2 Free space, no sun! Pint = "#AradT4 $ T = 200W0.8 5.67 %10&8 Wm2K 4' ( ) * + , 0.2827m2( )' ( ) ) ) ) * + , , , , 14= 354K21Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDAERCam/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= 362K22Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDAERCam/SPRINT Analysis (LEO Cargo Bay) Tenv=280K LEO cargo bay, no sun LEO cargo bay with sun! Pint ="#Arad T4 $ Tenv4( )% T = 200W0.8 5.67 &10$8 Wm 2K 4' ( ) * + , 0.2827m2( )+ (280K)4' ( ) ) ) ) ) * + , , , , , 14= 384K! Is" As + Pint =#$Arad T4 % Tenv4( )& T = Is" As + Pint#$Arad+ Tenv4' ( ) ) * + , , 14= 391K23Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEVA Thermal Equilibrium Human metabolic workload = 100 W Suit electrical systems = 40 W Total heat load = 140 W24Q = AT 4 A = QT 4A =140(0.8)(5.67 108)(295)4 = 0.41 m2Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEVA Thermal Equilibrium with Sun Human metabolic workload = 100 W Suit electrical systems = 40 W Total internal heat load = 140 W25Q + AIs = AT 4 A =QT 4 IsA =140(0.8)(5.67 108)(295)4 0.2(1394) = 2.2 m2Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDSublimation 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 water26Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDSitting on a Planetary Surface27IsTbThThFinal Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDRadiative 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 panelIsTinsulation Twall28Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDMulti-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)Is29Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEmissivity Variation with MLI LayersRef: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 200230Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDMLI Thermal ConductivityRef: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 200231Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDEffect of Ambient Pressure on MLIRef: D. G. Gilmore, ed., Spacecraft Thermal Control Handbook AIAA, 200232Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLAND1D Conduction Basic law of one-dimensional heat conduction (Fourier 1822)! whereK=thermal conductivity (W/mK)A=areadT/dx=thermal gradient! Q = "KAdTdx33Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLAND3D 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( )$t34Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLANDSimple Analytical Conduction Model Heat flowing from (i-1) into (i) Heat flowing from (i) into (i+1) Heat remaining in cellTiTi-1 Ti+1! Qin = "KATi " Ti"1#x! Qout = "KATi+1 "Ti#x! Qout "Qin =#cKTi( j +1) " Ti( j)$t35Final Project Discussion And Thermal DesignENAE 697 - Space Human Factors and Life SupportU N I V E R S I T Y O FMARYLAND Time-marching solutionwhere For solution stability,Finite Difference Formulation =kCv= thermal diffusivityd =tx2Tn+1i= Tni + d(Tni+1 2Tni + Tni1)t