Question

Water at 20oC, with a free-stream velocity of 1.5 m/s, flows over a circular pipe with diameter of 2.0 cm and surface temperature of 80oC. Calculate the average heat transfer coefficient and the heat transfer rate per meter length of pipe.\

Answer 1

Average heat transfer coefficient = 31 kw/m^2 k

Heat transfer rate per meter length of pipe = 116.808 KW

Step-by-step explanation:

water temperature = 20⁰c,

free-stream velocity = 1.5 m/s

circular pipe diameter = 2.0 cm = 0.02 m

surface temperature = 80⁰c

A) calculate average heat transfer coefficient

we apply the formula below :

m = αAv

A (area) =
`\pi /4 (d)^2`

m = 10^3 *
`\pi / 4 ( 0.02)^2` * 1.5

= 10^3 * 0.7857( 0.0004) * 1.5

= 0.4714 kg/s

Average heat transfer coefficient

h =
`(m(cp))/(A)` , A =
`\pi DL`

L = 1 m , m = 0.4714 kgs , cp = 4.18

back to equation

h =
`(0.4714*4.18)/(\pi * 0.02 )` = 1.970 / 0.0628 = 31.369 ≈ 31 kw/m^2 k

B) Heat transfer rate per meter length of pipe

Q = ha( ΔT ), a =
`\pi DL`

= 31 * 0.0628 * ( 80 - 20 )

= 31 * 0.0628 * 60 = 116.808 KW