Question

Water flows on the inside of a steel pipe with an ID of 2.5 cm. The wall thickness is 2 mm, and the convection coefficient on the inside is 500 W/m2 · ◦C. The convection coefficient on the outside is 12 W/m2 · ◦C. Calculate the overall heat-transfer coefficient. What is the main determining factor for U

Answer 1

U = 11.67 W/m² °C

Step-by-step explanation:

Inner diameter, d = 2.5 cm = 0.025 m

Thickness of the wall, t = 2 mm = 0.002 m

thus, the outer diameter, D = d + 2t = 0.025 + 2 x 0.002 = 0.029 m

`h_i =500 W/m^2.^oC`

`h_0 =12 W/m^2.^oC`

Now, based on outside convection heat transfer

we have

`(1)/(UA_o)=(1)/(h_iA_i)+(1)/(h_oA_o)`

on rearranging, we get

`(1)/(U)=(1)/(h_i)(A_o)/(A_i)+(1)/(h_o)`

where,
`A_i\ \textup{and}\ A_o` are the perimeter respective to inner and and outer diameter

on substituting the values, we get

`(1)/(U)=(1)/(500)(0.029^2)/(0.025)+(1)/(12)`

or

U = 11.67 W/m² °C