timmonskids2681

27.07.2021 • 

Physics

A decorative plastic film on a copper sphere of 10 mm diameter in an oven at 750C. Upon removal from the oven, the sphere is subjected to an air stream at 1 atm. , and 230C having a velocity of 10 meter/sec. Estimate how long it will take to coal the sphere to 350C? Density of copper is 8933 kg/m3 , thermal conductivity k = 399 W/m.K and specific heat Cp = 387 J/kg.K. for Air at an average temperature of T[infinity] = 296 K has viscosity µ= 181x10-7 N.s/m2 , kinematic viscosity ν = 15.36x10-6 m2/s and thermal conductivity k = 0.0258 W/m.K and Prandtl No. Pr = 0.709 and air at surface temperature Ts = 328 K will have viscosity µs = 197x10-7 N.s/m2

Ответ:

gissell30

26.08.2021

Physics

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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

Determine how long it will take to cool the sphere to 35°C

Using the properties of copper and air given in the question

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 )

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Ответ:

KillerSteamcar

27.11.2020

Physics

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If a coil of wire is placed in a changing magnetic field, a current will be induced in the wire. This current flows because something is producing an electric field that forces the charges around the wire. (It cannot be the magnetic force since the charges are not initially moving). Idk if this helps :)

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