Hey, I want to know how I can de

[zineb boucif]

Hey,

I want to know how I can determine the flow and the pressure values of the cooling water to use to reach a certain temperature on the surface of a rolling cylinder (to cool it), is there a mathematical method or i have to try to solve it numerically ?
Thank you

 

[SandCounter]

Zineb, you need to first determine how much heat you need to remove to cool the cylinder down to an acceptable temperature. Then calculate how much water is required to transfer the heat form the cylinder's surface. Then apply that flow to your system to determine the pressure, if an existing system, or design a new system and select a pump that will accommodate your required flow.

Here are some links to get you started:

Heat Transfer Coefficient
Heating system flow rates
Darcy-Weisbach Pressure and Head Loss Equation

I used to count sand. Now I don't count at all.

 

[zineb boucif]

Hey,thank you first for your helpful answer
So to determine the amount of heat I need to remove I am confused between 2 methods and I do not know which one is correct
first method
The Heat lost Q (J) by the cylinder when its temperature decreases from Ti = 400 °C to Tf= 100 °C is:

Q= mc∆T = m c (T_i-T_f)​

Where
[ul]
[li]m is the mass of the roll Kg[/li]
[li]c is the Specific heat of cast iron roll J/kg K[/li]
[li]T_i Initial temperature of the cylinder[/li]
[li]T_f Final temperature of the cylinder[/li]
[/ul]

and I divide the amount heat Q by the contact time and I replace it in the equation (*)

second one
the hate rate flow is given by

Q⁄t=hA(T_f-T_s)​

[ul]
[li]h heat transfer coefficient, W/(m²•K)[/li]
[li]A surface area where the heat transfer takes place, m²[/li]
[li]T_f temperature of the surrounding fluid[/li]
[li]T_s temperature of the solid surface[/li]

--------------
once the heat to be evacuated is calculated I will pass to the determination of the flow rate of cooling water whose calculation is done as follows

The volumetric flow rate in a heating system can be expressed as

D_v=(Q⁄t)/(ρ cp ∆T) (*)​

Where

[li]D_v = volumetric flow rate (m³/s)[/li]
[li]Q⁄t = heat flow rate (J/s, W)[/li]
[li]cp = water specific heat (J/kg°C)[/li]
[li]ρ = water density (kg/m³)[/li]
[li]∆T=T_f-T_i = temperature difference (°C)[/li]
water's Initial temperature T_i
waterer's Final temperature T_f
[/ul]

except that for this 2nd stage I do not know the temperature that the water will have after the heat exchange

Thank you !

 

[IRstuff]

Yes, you do, or you should. I would express the last relationship as a flow-rate*delta-T product, as that embodies the conservation of energy aspect. You can have a high flow rate, which would result in a lower delta-T, or a low flow rate, which would result in a high delta-T. Typically, you will have constraints on how much water you are willing to dump down the drain or into some other heat exchanger, or you have constraints on how hot the effluent water is allowed to be.

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[zineb boucif]

Apparently I would have a constraint on the temperature of the water returned because it will undergo a subsequent recycling so I will try to estimate the tempéarture admissible for the treatment of water. for the flow rate it's up to me to find the optimal value and then I would have a single variable to determine.
For the heat to be evacuated do you have an idea by which relation I can determine it ?
thank you