Trying to solve a set of equations in matlab result gives NaN instead of values,

Question

Trying to solve a set of equations in matlab result gives NaN instead of values, can't figure out why. Code is pasted below:

clc

clear all

deltax=0.008;

kAL=237;

kCu=401;

h=60;

Tsur=20;

Ax=3.1416*(0.005/2)^2;

As=2*3.1416*(0.005/2)*0.008

T1=100;

T21=150;

syms T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20

eq1=((kCu*Ax/deltax)*(T1-2*T2+T3))+(h*As*(Tsur-T2))==0;

eq2=(kCu*Ax*(T2-T3)/deltax)+(kCu*Ax*(T4-T3)/deltax)+(h*As*(Tsur-T3))==0;

eq3=(kCu*Ax*(T3-T4)/deltax)+(kCu*Ax*(T5-T4)/deltax)+(h*As*(Tsur-T4))==0;

eq4=(kCu*Ax*(T4-T5)/deltax)+(kCu*Ax*(T6-T5)/deltax)+(h*As*(Tsur-T5))==0;

eq5=(kCu*Ax*(T5-T6)/deltax)+(kCu*Ax*(T7-T6)/deltax)+(h*As*(Tsur-T6))==0;

eq6=(kCu*Ax*(T6-T7)/deltax)+(kCu*Ax*(T8-T7)/deltax)+(h*As*(Tsur-T7))==0;

eq7=(kCu*Ax*(T7-T8)/deltax)+(kCu*Ax*(T9-T8)/deltax)+(h*As*(Tsur-T8))==0;

eq8=(kCu*Ax*(T8-T9)/deltax)+(kCu*Ax*(T10-T9)/deltax)+(h*As*(Tsur-T9))==0;

eq9=(kCu*Ax*(T9-T10)/deltax)+(kCu*Ax*(T11-T10)/deltax)+(h*As*(Tsur-T10))==0;

eq10=(kCu*Ax*(T10-T11)/deltax)+(kCu*Ax*(T12-T11)/deltax)+(h*As*(Tsur-T11))==0;

eq11=(kCu*Ax*(T11-T12)/deltax)+(kAL*Ax*(T13-T12)/deltax)+(h*As*(Tsur-T12))==0;

eq12=(kAL*Ax*(T12-T13)/deltax)+(kAL*Ax*(T14-T13)/deltax)+(h*As*(Tsur-T13))==0;

eq13=(kAL*Ax*(T13-T14)/deltax)+(kAL*Ax*(T15-T14)/deltax)+(h*As*(Tsur-T14))==0;

eq14=(kAL*Ax*(T14-T15)/deltax)+(kAL*Ax*(T16-T15)/deltax)+(h*As*(Tsur-T15))==0;

eq15=(kAL*Ax*(T15-T16)/deltax)+(kAL*Ax*(T17-T16)/deltax)+(h*As*(Tsur-T16))==0;

eq16=(kAL*Ax*(T16-T17)/deltax)+(kAL*Ax*(T18-T17)/deltax)+(h*As*(Tsur-T17))==0;

eq17=(kAL*Ax*(T17-T18)/deltax)+(kAL*Ax*(T19-T18)/deltax)+(h*As*(Tsur-T18))==0;

eq18=(kAL*Ax*(T18-T19)/deltax)+(kAL*Ax*(T20-T19)/deltax)+(h*As*(Tsur-T19))==0;

eq19=(kAL*Ax*(T19-T20)/deltax)+(kAL*Ax*(T21-T20)/deltax)+(h*As*(Tsur-T20))==0;

S=solve(eq1, eq2, eq3, eq4, eq5, eq6, eq7, eq8, eq9, eq10,eq11, eq12, eq13, eq14, eq15, eq16, eq17, eq18, eq19)

T2_=eval((S.T2))

T3_=eval(S.T3)

T4_=eval(S.T4)

T5_=eval(S.T5)

T6_=eval(S.T6)

T7_=eval(S.T7)

T8_=eval(S.T8)

T9_=eval(S.T9)

T10_=eval(S.T10)

T11_=eval(S.T11)

T12_=eval(S.T12)

T13_=eval(S.T13)

T14_=eval(S.T14)

T15_=eval(S.T15)

T16_=eval(S.T16)

T17_=eval(S.T17)

T18_=eval(S.T18)

T19_=eval(S.T19)

T20_=eval(S.T20)

Explanation / Answer

clc

clear all

deltax=0.008;

kAL=237;

kCu=401;

h=60;

Tsur=20;

Ax=3.1416*(0.005/2)^2;

As=2*3.1416*(0.005/2)*0.008

T1=100;

T21=150;



syms T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20



eq1=((kCu*Ax/deltax)*(T1-2*T2+T3))+(h*As*(Tsur-T2))==0

eq2=(kCu*Ax*(T2-T3)/deltax)+(kCu*Ax*(T4-T3)/deltax)+(h*As*(Tsur-T3))==0;

eq3=(kCu*Ax*(T3-T4)/deltax)+(kCu*Ax*(T5-T4)/deltax)+(h*As*(Tsur-T4))==0;

eq4=(kCu*Ax*(T4-T5)/deltax)+(kCu*Ax*(T6-T5)/deltax)+(h*As*(Tsur-T5))==0;

eq5=(kCu*Ax*(T5-T6)/deltax)+(kCu*Ax*(T7-T6)/deltax)+(h*As*(Tsur-T6))==0;

eq6=(kCu*Ax*(T6-T7)/deltax)+(kCu*Ax*(T8-T7)/deltax)+(h*As*(Tsur-T7))==0;

eq7=(kCu*Ax*(T7-T8)/deltax)+(kCu*Ax*(T9-T8)/deltax)+(h*As*(Tsur-T8))==0;

eq8=(kCu*Ax*(T8-T9)/deltax)+(kCu*Ax*(T10-T9)/deltax)+(h*As*(Tsur-T9))==0;

eq9=(kCu*Ax*(T9-T10)/deltax)+(kCu*Ax*(T11-T10)/deltax)+(h*As*(Tsur-T10))==0;

eq10=(kCu*Ax*(T10-T11)/deltax)+(kCu*Ax*(T12-T11)/deltax)+(h*As*(Tsur-T11))==0;

eq11=(kCu*Ax*(T11-T12)/deltax)+(kAL*Ax*(T13-T12)/deltax)+(h*As*(Tsur-T12))==0;

eq12=(kAL*Ax*(T12-T13)/deltax)+(kAL*Ax*(T14-T13)/deltax)+(h*As*(Tsur-T13))==0;

eq13=(kAL*Ax*(T13-T14)/deltax)+(kAL*Ax*(T15-T14)/deltax)+(h*As*(Tsur-T14))==0;

eq14=(kAL*Ax*(T14-T15)/deltax)+(kAL*Ax*(T16-T15)/deltax)+(h*As*(Tsur-T15))==0;

eq15=(kAL*Ax*(T15-T16)/deltax)+(kAL*Ax*(T17-T16)/deltax)+(h*As*(Tsur-T16))==0;

eq16=(kAL*Ax*(T16-T17)/deltax)+(kAL*Ax*(T18-T17)/deltax)+(h*As*(Tsur-T17))==0;

eq17=(kAL*Ax*(T17-T18)/deltax)+(kAL*Ax*(T19-T18)/deltax)+(h*As*(Tsur-T18))==0;

eq18=(kAL*Ax*(T18-T19)/deltax)+(kAL*Ax*(T20-T19)/deltax)+(h*As*(Tsur-T19))==0;

eq19=(kAL*Ax*(T19-T20)/deltax)+(kAL*Ax*(T21-T20)/deltax)+(h*As*(Tsur-T20))==0;

[T2_, T3_, T4_, T5_, T6_, T7_, T8_, T9_, T10_, T11_, T12_, T13_, T14_, T15_, T16_, T17_, T18_, T19_, T20_]=solve(eq1, eq2, eq3, eq4, eq5, eq6, eq7, eq8, eq9, eq10,eq11, eq12, eq13, eq14, eq15, eq16, eq17, eq18, eq19, T2, T3, T4, T5, T6 ,T7, T8, T9, T10, T11, T12, T13 ,T14,T15, T16, T17, T18, T19 ,T20)

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