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+// Display mode

+mode(0);

+// Display warning for floating point exception

+ieee(1);

+clear;

+clc;

+disp("Engineering Thermodynamics by Onkar Singh Chapter 12 Example 2")

+h1=40;//average heat transfer coefficient at inner surface in KJ/m^2 hr oc

+h6=50;//average heat transfer coefficient at outer surface in KJ/m^2 hr oc

+deltax_steel=2*10^-3;//mild steel sheets thickness in m

+deltax_wool=5*10^-2;//thickness of glass wool insulation in m

+k_wool=0.16;//thermal conductivity of wool in KJ/m hr

+k_steel=160;//thermal conductivity of steel in KJ/m hr

+T1=25;//kitchen temperature in degree celcius

+T6=5;//refrigerator temperature in degree celcius

+disp("here thermal resistances are")

+disp("R1=thermal resistance due to convection between kitchen air and outer surface of refrigerator wall(T1 & T2)")

+disp("R2=thermal resistance due to conduction across mild steel wall between 2 & 3(T2 & T3)")

+disp("R3=thermal resistance due to conduction across glass wool between 3 & 4(T3 & T4)")

+disp("R4=thermal resistance due to conduction across mild steel wall between 4 & 5(T4 & T5)")

+disp("R5=thermal resistance due to convection between inside refrigerator wall and inside of refrigerator between 5 & 6(T5 & T6)")

+disp("overall heat transfer coefficient for one dimentional steady state heat transfer")

+disp("(1/U)=(1/h1)+(deltax_steel/k_steel)+(deltax_wool/k_wool)+(deltax_steel/k_steel)+(1/h6)")

+disp("so U=1/((1/h1)+(deltax_steel/k_steel)+(deltax_wool/k_wool)+(deltax_steel/k_steel)+(1/h6))in KJ/m^2hr oc")

+U=1/((1/h1)+(deltax_steel/k_steel)+(deltax_wool/k_wool)+(deltax_steel/k_steel)+(1/h6))

+U=2.8;//approx.

+disp("rate of heat transfer(Q)=U*A*(T1-T6)in KJ/m^2 hr")

+disp("wall surface area(A) in m^2")

+A=4*(1*0.5)

+Q=U*A*(T1-T6)

+disp("so rate of heat transfer=112 KJ/m^2 hr ")

+disp("Q=A*h1*(T1-T2)=k_steel*A*(T2-T3)/deltax_steel=k_wool*A*(T3-T4)/deltax_wool")

+disp("Q=k_steel*A*(T4-T5)/deltax_steel=A*h6*(T5-T6)")

+disp("substituting,T2=T1-(Q/(A*h1))in degree celcius")

+T2=T1-(Q/(A*h1))

+disp("so temperature of outer wall,T2=23.6 oc")

+disp("T3=T2-(Q*deltax_steel/(k_steel*A))in degree ")

+T3=T2-(Q*deltax_steel/(k_steel*A))

+disp("so temperature at interface of outer steel wall and wool,T3=23.59 oc")

+disp("T4=T3-(Q*deltax_wool/(k_wool*A))in degree celcius")

+T4=T3-(Q*deltax_wool/(k_wool*A))

+disp("so temperature at interface of wool and inside steel wall,T4=6.09 oc")

+disp("T5=T4-(Q*deltax_steel/(k_steel*A))in degree celcius")

+T5=T4-(Q*deltax_steel/(k_steel*A))

+disp("so temperature at inside of inner steel wall,T5=6.08 oc")

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