Can mechanical energy be used to do work?
1 answer:
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Answer:
h =12.9 w/m2 k
Explanation:
we know that thermal conductivity of air K at 0 degree celcius = 0.024 w/mk
T_S = 80 Degree celcius
temperature gradient = -43 degree C/mm = - 43*1000 / m
by fourier law
q = 1032 watt/m2
we know that from newton's law
q = h (T_s - T_∞)
1032 = h*(80 - 0)
h =12.9 w/m2 k
Answer:
3.26 secs
Explanation:
Diameter of sphere ( D )= 10 mm
T1 = 75°C
P = 1 atm
T∞ = 23°C
T2 = 35°c
Velocity = 10 m/s
<u>Determine how long it will take to cool the sphere to 35°C</u>
<em>Using the properties of copper and air given in the question</em>
Nu = 2 + (Re)^0.8 (Pr)^0.33
hd / k = 2 + ( vd/v )^0.8 (Pr)^0.33
∴ h ≈ 2594.7 W/m^2k
Given that :
(T2 - T∞) / ( T1 - T∞ ) = exp [ ( -hA / pv CP ) t ]
( 35 - 23 ) / ( 75 - 23 ) = exp [ - 2594.7 * 6 * t / 8933 * 387 * 10 * 10^-3 ]
= ln ( 12/52 ) = -1.466337069 = - 0.45032919 * t
∴ t ≈ 3.26 secs ( -1.466337069 / -0.45032919 )
