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sladkih [1.3K]
3 years ago
8

An electric resistance heater is embedded in a long cylinder of diameter 30 mm. when water with a temperature of 25°c and veloc

ity 1 m/s flows crosswise over the cylinder, the power per unit length required to maintain the surface at a uniform temperature of 80°c is 38 kw/m. when air, also at 25°c, but with a velocity of 10 m/s is flowing, the power per unit length required to maintain the same surface temperature is 400 w/m. assume unit length. calculate and compare the convection coefficients for the flows of water and air. according to your calculations, which is a better convective heat transfer media, air or water?
Physics
1 answer:
victus00 [196]3 years ago
3 0
KNOWN: Long, 30mm-diameter cylinder with embedded electrical heater; power required to maintain a specified surface temperature for water and air flows.
 FIND: Convection coefficients for the water and air flow convection processes, hw and ha, respectively.
 ASSUMPTIONS: Flow is cross-wise over cylinder which is very long in the direction normal to flow.
 The convection heat rate from the cylinder per unit length of the cylinder has the form
 q' = h*(pi*D)*(Ts-Tinf)
 and solving for the heat transfer convection coefficient, find
 Water
 hw = q'/((pi*D)*(Ts-Tinf))
 hw = (38*10^3 W/m) / ((pi*(0.030m))*(80-25)C)= 7330.77314  W/m^2K
 Air
 ha = (400W/m) / ((pi*(0.030m))*(80-25)C)=<span> 77.166033 </span> W/m^2K
 COMMENTS: Note that the air velocity is 10 times that of the water flow, yet
hw ≈ 95 × ha.
 These values for the convection coefficient are typical for forced convection heat transfer with liquids and gases
 Watter is a better convective heat transfer media than air 

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Any help would be great! Thank you x<br><br><br> Giving brainliest answer xoxo
garri49 [273]

Answer:

A vacuum would have been created. I hope this helps have a great day

3 0
3 years ago
A bottle lying on the windowsill falls off and takes 4.95 seconds to reach the ground. The distance from the windowsill to the g
mr Goodwill [35]

The distance an object falls from rest through gravity is

                         D  =  (1/2) (g) (t²)

            Distance  =  (1/2 acceleration of gravity) x (square of the falling time)

We want to see how the time will be affected
if  ' D ' doesn't change but ' g ' does.
So I'm going to start by rearranging the equation
to solve for ' t '.

                                                      D  =  (1/2) (g) (t²)

Multiply each side by  2 :         2 D  =            g    t² 

Divide each side by ' g ' :      2 D/g =                  t²

Square root each side:        t = √ (2D/g)


Looking at the equation now, we can see what happens
to ' t ' when only ' g ' changes: 

-- ' g ' is in the denominator; so bigger 'g' ==> shorter 't'
                                             and smaller 'g' ==> longer 't' .

-- They don't change by the same factor, because  1/g  is inside
the square root.  So 't' changes the same amount as  √1/g  does.

Gravity on the surface of the moon is roughly  1/6  the value
of gravity on the surface of the Earth.

So we expect ' t ' to increase by  √6  =  2.45 times.

It would take the same bottle  (2.45 x 4.95) = 12.12 seconds
to roll off the same window sill and fall 120 meters down to the
surface of the Moon.
4 0
3 years ago
Read 2 more answers
If a fuse melts, does it create an open circuit, a closed circuit, or a short circuit?
Andrew [12]

Answer:

short circuit

7 0
3 years ago
Read 2 more answers
A student hangs a weight on a newtonmeter. The energy currently stored in the spring in the newton meter is 0.045N. The student
castortr0y [4]

Answer:

5x10^-3

Explanation:

Hooke's Law states that the force needed to compress or extend a spring is directly proportional to the distance you stretch it.

Hooke's Law can be represented as

<h3> F = kx, </h3>

<em>where F is the force </em>

<em>            k is the spring constant</em>

<em>            x is the extension of the material </em>

<em />

Plug values in the equation

Step 1 find the original extension

0.045 = (400)x

x = 1.125x 10^-4 m d

Step 2 find the new extension

0.045+2 = 400(x)

2.045 = 400x

x = 5.1125x10^-3

Step 3 subtract the new extension with original

Total extension of the spring =  5.1125x10^-3 - 1.125x 10^-4 m = 5x10^-3

8 0
3 years ago
Se lanza verticalmente una esfera con una rapidez de 30m/se. Determinar la rapidez de la esfera a una altura de 40m (g=10m/s2)
sergeinik [125]

v^2-{v_0}^2=2a(x-x_0)

dónde v es la velocidad de la esfera, v_0 es suya velocidad inicial, a=-g la aceleración debida a la gravedad, x la posición, y x_0 la posición inicial. Tomamos x_0=0\,\mathrm m a referirse a la posición de la esfera en el momento que la esfera fue lanzada.

Entonces

v^2-\left(30\,\dfrac{\mathrm m}{\mathrm s}\right)^2=2\left(-10\,\dfrac{\mathrm m}{\mathrm s^2}\right)(40\,\mathrm m)

\implies v^2=100\,\dfrac{\mathrm m^2}{\mathrm s^2}\implies v=\pm10\,\dfrac{\mathrm m}{\mathrm s}

Esto nos dice que la esfera alcanza una altura de 40 m en dos momentos - una vez hacia arriba y una vez hacia abajo. Sin embargo, independientemente del signo de la velocidad, sabemos que suya magnitud es 10 m/s, y así tenemos una rapidez de 10 m/s también en ambos momentos.

4 0
3 years ago
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