Question

An experiment to determine the convection coefficient associated with air flow over the surface of a thick steel casting involves insertion of thermocouples in the casting at distances of 10 and 20 mm from the surface along a hypothetical line normal to the surface. The steel has a thermal conductivity of 15 W/m.K. If the thermocouples measure temperatures of 50 and 40℃ in the steel when the air temperature is 100℃, what is the convection coefficient?

Answer 1

please foolow me amd mark me brainlist

Answer 2

Given:-

• L1= 10mm L2=20mm (thermocouple distances)
• k= 15W/mK (steel thermal conductivity)
• T1= 50C T2= 40C
• air temp(T')= 100C

To find:-

• Convection Coefficient

Solution:-

Assuming there are no other energy sources, the energy balance equation is given as:-

Ein=Eout  and q''in=q''out

Since conduction is only one-dimensional total heat rate transferred can be found from Fourier's law for surfaces 1 and 2.

q''cond = k*(T1-T2)/(L2-L1) = 15*(50-40)/(20-10) = 15W/mm^2 = 15000 W/m^2.

The temperature at the surface for steel is considered as 60C as the gradient is linear in this case of conduction. For the convection factor, we will use Newton's Law of Cooling.

Substituting the values we get,

q''conv = h(T'-Ts) -> h = q''conv/(T'-Ts) = 15000/(100-60)

h= 375 W/m^2K

The convecton coefficient is 375 W/m^2K.