Question

For a vertical surface, h, btu/h · ft² · °F = 87(?T °F)¹?? q/A, btu/h · ft², < 1000 h, W/m² · K = 537(?T K)¹?? q/A, kW/m², < 3 h, btu/h · ft² · °F = 0.240(?T °F)³ 1000 < q/A, btu/h · ft², < 20 000 h, W/m² · K = 7.95(?T K)³ 3 < q/A, kW/m², < 63 where ?T = T_w - T_sat K or °F. If the pressure is p atm abs, the values of h at 1 atm given above are multiplied by (p/1)??. Equations (4.8-1) and (4.8-3) are in the natural convection region. For forced convection boiling inside tubes, the following simplified relations can be used (J3): h = 2.55(?T K)³ e^{p/1551} W/m² · K (SI) h = 0.077(?T °F)³ e^{p/225} btu/h · ft² · °F (English) where p in this case is in kPa (SI units) and psia (English units). 3. Film boiling. In the film-boiling region, the heat-transfer rate is low for the temperature drop used, which is not utilized effectively. Film boiling requires considerable theoretical analysis. Bromley (B3) gives the following for the heat-transfer coefficient in the film-boiling region on a horizontal tube:

          For a vertical surface,
h, btu/h · ft² · °F = 87(?T °F)¹??  q/A, btu/h · ft², < 1000
h, W/m² · K = 537(?T K)¹??  q/A, kW/m², < 3
h, btu/h · ft² · °F = 0.240(?T °F)³  1000 < q/A, btu/h · ft², < 20 000
h, W/m² · K = 7.95(?T K)³  3 < q/A, kW/m², < 63
where ?T = T_w - T_sat K or °F.
If the pressure is p atm abs, the values of h at 1 atm given above are multiplied by (p/1)??. Equations (4.8-1) and (4.8-3) are in the natural convection region.
For forced convection boiling inside tubes, the following simplified relations can be used (J3):
h = 2.55(?T K)³ e^{p/1551} W/m² · K (SI)
h = 0.077(?T °F)³ e^{p/225} btu/h · ft² · °F (English)
where p in this case is in kPa (SI units) and psia (English units).
3. Film boiling. In the film-boiling region, the heat-transfer rate is low for the temperature drop used, which is not utilized effectively. Film boiling requires considerable theoretical analysis. Bromley (B3) gives the following for the heat-transfer coefficient in the film-boiling region on a horizontal tube:

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For a vertical surface,
h, btu/h · ft² · °F = 87(?T °F)¹?? q/A, btu/h · ft², < 1000
h, W/m² · K = 537(?T K)¹?? q/A, kW/m², < 3
h, btu/h · ft² · °F = 0.240(?T °F)³ 1000 < q/A, btu/h · ft², < 20 000
h, W/m² · K = 7.95(?T K)³ 3 < q/A, kW/m², < 63
where ?T = Tw - Tsat K or °F.
If the pressure is p atm abs, the values of h at 1 atm given above are multiplied by (p/1)??. Equations (4.8-1) and (4.8-3) are in the natural convection region.
For forced convection boiling inside tubes, the following simplified relations can be used (J3):
h = 2.55(?T K)³ e^p/1551 W/m² · K (SI)
h = 0.077(?T °F)³ e^p/225 btu/h · ft² · °F (English)
where p in this case is in kPa (SI units) and psia (English units).
3. Film boiling. In the film-boiling region, the heat-transfer rate is low for the temperature drop used, which is not utilized effectively. Film boiling requires considerable theoretical analysis. Bromley (B3) gives the following for the heat-transfer coefficient in the film-boiling region on a horizontal tube:

Added by Barbara T.

Chemistry: Structure and Properties

Nivaldo Tro 2nd Edition

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Solved by Expert Supratim Pal

12/15/2022

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- The rate of water boiling is 30 kg/h. - The pan has a diameter of 30 cm. - The boiling occurs at atmospheric pressure, indicating nucleate boiling conditions. - We are asked to estimate the temperature of the bottom surface of the pan. Show more…

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Water is boiled at a rate of 30 kg/h in a copper pan, 30 cm in diameter, at atmospheric pressure. Estimate the temperature of the bottom surface of the pan, assuming nucleate boiling conditions and the rate of heat transfer. NOTE: Use the Simplified Empirical Equations and not by Rohsenow.

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Transcript

00:01 Hello and welcome to this video solution of new madrid.

00:04 So here it's given that a pot of 25 centimeter diameter.

00:07 So this diameter of the pot is 25 centimeters, which is equal to 0 .25 meters, right? this pot is made of stainless steel, which is having value of k that is equal to 15 watt per meter degrees celsius, right? and it contains boiling water at 98 degrees celsius.

00:31 The bottom of the pan is having a thickness of 0 .6 centimeters which is equal to 6 times of 10 to the part of minus 3 millimeters sorry yes the surface temperature on the bottom of the pan in contact with water is 105 degrees celsius we can take this as t1 that is 105 degrees celsius and it is given that the heat transfer through the bottom of the pan is 600 watt so this queue is 600 watt we have got now you have to determine the outside surface temperature of the pan that is export to the exposed to the heating stove right so this is pretty simple so here we have q the heat transfer will be equal to k a delta t over the thickness right so this is the expression of heat transfer the rate of heat transfer actually this is 600 q k is given as 15 a is pi by 4 d square right because it's a circular one right 5 by 4 d is 0 .25 squared delta t is a t minus sorry t minus of t 1 right t is the surface which is in sorry which is in contact with the stove right okay so what i do is t1 i plug it as 105 and finally you will have the thickness as six times of 10 to the power of minus 3 right so let's evaluate and see how much we're getting for this t this is around 110 degrees celsius right so this is the temperature on the surface of this pan which is in contact with the water itself sorry the stove next the second question is you have to determine the convective heat transfer coefficient of the boiling water so this is pretty simple.

02:39 So the temperature of the boiling water is given as 98 degrees celsius, right? fine.

02:49 So here we have the q will be equal to h .a...

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