Heat transfer between steel and flowing water

[Breaker]

Hi

Could anyone give me some simple guidelines for some simple calculations on how i could calculate the amount of water and flow rate required to transfer heat from a steel object. Assuming 100% efficiency in heat transfer. The steel object is assumed to be maintained at a fixed temperature. The initial temperature of the water is also known. The heat loss from the steel object for the temperature difference between the steel object and water is also known.

 

[ardilesd]

Hello,

assuming
- the heat to be removed from steel is known (Q kcal/h)
- F is the flow of water ( m3/h)
- T1 inlet temperature (°C)
- T2 outlet temperature (°C)
- Cp = specific heat ( = 1000 kcal/°C.m3)

you have the following equation

Q = F . Cp . ( T2 - T1)

so T2 = T1 + Q / (F . Cp)

With differents values of F, you can determine the T2 set.

Later, you can check thru hear transfer coefficients if this Heat Q can be totally transferred or you need to recalculate it
Regards

 

[poetix99]

I respectfully take issue with your attempt to simplify this problem. Simplification is not objectionable per se; it can be used to establish upper and/or lower bounds to the actual solution of a problem. But you are in a certain sense, placing the cart before the horse when you postulate "100% efficiency of heat transfer".

You cannot arbitrarily chose "T2"; there is an uppper limit that might be significantly less than the bulk temperature of the steel. It is not even a certainty that the steel can be accurately modelled as isothermal. It really must follow from the problem statement & solution.

"Ardilesd" has described what is essentially a (quasi)static heat balance, rather than a heat transfer solution. It is an accurate statement that you "can check thru heat transfer coefficients"; indeed you SHOULD check.

If the steel is effectively an infinite heat source, then the problem is basically to determine the heat transfer coefficient of the water/steel interface. You might use some representative values of "h" from a heat transfer text for an initial guess. Also use a "real world" value of "k" for the steel.

What is the heat transfer area?
What is the water velocity?
What is the particular flow geometry?

I understand that you are looking for a simplified first cut. Be careful of how much you "simplify" your problem.