Review:thermal resistance Comparison of the steady state heat flow equation with Ohm's Law for current flow through a resistor, --分）台1-) Analogies: Heat Flow, 2 台 Current,I Temperature Difference,T-T2 台 Voltage Difference,V-V2 Thermal Resistance, 台 Electrical Resistance,R △x RT= kA
Review: thermal resistance Analogies: Comparison of the steady state heat flow equation with Ohm's Law for current flow through a resistor, Heat Flow, Current, I Temperature Difference, T1 - T2 Voltage Difference, V1 - V2 Thermal Resistance, Electrical Resistance, R kA x R T
Thermal resistance method:Steady state,no volumetric heating arC四A=-k,T型A=-2 q=-k-dx L kA T2 △TL 9-kAl K/W] L Plane wall T--T2 L kA
Thermal resistance method : Steady state, no volumetric heating L Plane wall
T1>T2,9g=0 Ky k2 2 T Rcond= L1+ k A k2A k1>k2 T2 k1<k2 q=-klaA=-名0对4 L2 Ti-M12 L1 L2 k1A A (in series)
(in series)
=0 Ti| K k2 T2 A2 A2+A3=A1 q2+q3=91 3 q3 急 名4 -Ww T- T2 - 3 In parallel k3
In parallel
Contact Resistance T-T哇 Rt.c= 7 L T2 q"A Unit area contact resistance is: k2 R2-,m2-Km Thus T-MT2 L1 RtcA L2 kA k2A
Contact Resistance Unit area contact resistance is: Thus
Heating Source:not volumetric heating Qe T T2 k1 k2 0x习 T-MMMT2 L1 Rtc A RtczA L2 k1A Qe k2A L2 Ultra thin electric heater
Heating Source: not volumetric heating Ultra thin electric heater
Convection Thermal Resistance qconv T 9- Ts-Too 1 Rconv= Aconv hA(T;-T)=halk/W] Too,h qconv Ts-MMTo
Convection Thermal Resistance
Radiation Resistance Tsur Arad,net Ts-Tsur 1 Rrad Ts-Tsu= Ts-Tsur Qrad eo(T-T )A-h(T-T )A=hAlk/W] hr =E(T+Tsur)(Ts +Tsur)
Radiation Resistance
Overall Tsur Aconv hA 习 T WT∞ Acond Acond L- M Tsur Qrad 1 hrA
Overall
Thermal resistance in radial systems Cylindrical 2 2πLK Spherical (侣)
Thermal resistance in radial systems Cylindrical Spherical