Example 14.5-3 Combined Radiation and Convection

>  restart;
>  Qr := e1*A1*sigma*(Twater^4); Radiation loss of the water 
assuming the radiation is emitted to the sky where the temperature 
is very low.
>  Qconv := h*A1*(Tair-Twater); Convective heat absorbed by the 
water.
>  e1 := 0.95; sigma:=0.1712e-8*Btu/hr/ft^2/R^4; 
Twater := 492*R: h :=0.2*((Tair-Twater)/R)^(1/4)*Btu/hr/ft^2/R;
 Given in the problem. Note that we try to find Tair in the untis of 
R so (Tair-Twater)/R will be a pure number.
>  eq:=simplify((Qr-Qconv)/(A1*Btu/hr/ft^2)); Setting up the 
balance equation to be solved.
>  Tair:=x*R;eq:=simplify(eq,assume=positive); Deciding to use 
a numerical solution for the unitless number x.
>  eq:=unapply(eq,x);
>  plot(eq(x),x=492...700); There is obviously a root near 600R.
[Maple Plot]
>  x:='x';
>  T:=fsolve(eq(x),x)*R; Without specifying the interval, Maple 
does not find a root.
>  T:=fsolve(eq(x),x,500....700)*R; This is better.
[Maple Math]