/* ----------------------------------------------------------------------------
**  Figure 23.5: The heat transfer module, heat.c
** 
**  A pipe of radius p is to be insulated with a material having a conductivity 
**  k.  A heat transfer analysis gives the following equation for the radius of
**  the outer insulation layer for a specified heat loss per unit length:
**  
**      (1/k)*ln(r/p) + 1/r = 2.0/p 
**  
**  Find the solution of this equation (the radius r) to within ~.01% error.
** ----------------------------------------------------------------------------- 
*/
#include "tools.h"
#include "ffam.h"

/* These variables are global within this module but hidden from other modules. */
static double conductivity;     /* thermal conductivity */
static double pipe;             /* radius of pipe (feet) */

/* --------set up parameters for the heat transfer equation------------------ */
void 
setup( void )      
{   
    printf( "\n Thermal conductivity of insulation (BTU/h ft F): " );
    scanf( "%lg", &conductivity );

    printf( "\n Enter radius of pipe (feet): " );
    scanf( "%lg", &pipe );
}

/* --------- function to compute heat transfer discrepency ------------------ */
double 
f( double r )      
{   
    if (r < pipe) 
        fatal( " Error--radius received is inside pipe dimensions." );
    return log( r/pipe ) /  conductivity + 1.0/r - 2.0/pipe; 
}