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+clear;

+clc;

+printf("\t\t\tExample Number 7.7\n\n\n");

+// calculation with simplified relations 

+// Example 7.7 (page no.-338-339) 

+// solution

+

+// this example is calculation of heat transfer with simplified relations for example (7.5) so we use the data of example 7.5

+

+d = 0.3048;// [m] diameter of pipe

+Ts = 250;// [degree celsius] surface temperature of pipe 

+Ta = 15;// [degree celsius] temperature of air 

+// we first determine the Grashof-prandtl number product and then select the appropriate constants from table 7-1(page no.-328) for use with              equation (7-25) 

+// the properties of air are evaluated at the film temperature:

+Tf = (Ts+Ta)/2;// [degree celsius]

+// the properties of interest are thus

+v = 26.54*10^(-6);// [square meter/s]

+k = 0.03406;// [W/m degree celsius]

+Pr = 0.687;// prandtl number

+Beta = 1/(Tf+273);// [K^(-1)]

+g = 9.8;// [square meter/s] acceleration due to gravity

+// in example (7.5) we found that a rather large pipe with a substantial temperature difference between the surface and air still had a GrPr product of  1.57*10^(8)<10^(9), so laminar equation is selected from table 7-2(page no.-339). the heat transfer coefficient is given by 

+h = 1.32*((Ts-Ta)/d)^(1/4);// [W/square meter degree celsius]

+// the heat transfer is then 

+q_by_L = h*%pi*d*(Ts-Ta);// [W/m]

+printf("heat transfer is %f kW/m",q_by_L/1000);

+

+

+