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For the surface temperature, what I have done is that the main equation was rearranged to get surface temp in terms of wall & bulk temp. This gives me the maximum surface temp for the assumed flow rate, film temp and bulk temp. With my current parameter, the maximum well below the 500C I had...

The analysis is taking a good shape now. Thank you everyone for the valuable inputs. One query to @georgeverghese, For the resistance in the thermal cement, I have assumed a concentric thermal cement where the copper tube is buried (as you suggested previously). R = ln(r4/r3)/(2*pi*kcement*L)...

Thanks. If the water flow is laminar say Reynolds number is around 1000, according to wikipedia a Nu of 3.66 is assumed for constant surface temperature for circular tubes or 4.36 with uniform surface heat flux for circular tubes. How valid is this assumption? I would like to check a case of low...

Thank you for the correction. I think assuming a concentric conductive cement where the Cu tube is buried makes it easier to calculate U. As you mentioned earlier, after the converged Twall consequently Tfilm is achieved, if it is higher than the boiling temperature can we say that the current...

I have used a conservative approach to calculate the copper tube wall temp. Does this method seem logical? It is an iterative process. Any suggestion would be helpful. TIA.

I was thinking if direct contact of copper tubes with combustion gases would cause more corrosion, oxidation etc.

Should the thermal conductivity and other thermal properties be calculated at the bulk fluid temp or as you mentioned at film temp.? If the film temp is say 150C, then the k value would be for steam...

It seems there are couple of assumptions to make: Film temp. and flow velocity for Reynolds number (for Dittus-Boelter eq. it has to be turbulent?). My aim is to find the flow rate at which water would not boil i.e. achieve bulk fluid temp. of say 40C or 80C (this can be impractical to achieve...

For the time being, it is assumed to burn wood and the combustion gases flow upwards. It is a part of a bigger system. I want to extract some of the heat from that combustion gases to heat the water flowing through the copper tubes at a specific temp. Unfortunately,I do not know what temp. the...

Thank you for the reply. I have some initial values of the pitch, no. of turns, OD, ID for copper tube. The targeted water temp. can be within 60C to 80C. The contact area is minimal in the above arrangement. My aim is to get some flow rate figures, to achieve that Tmax. If the figure is...

Many thanks for your the replies with Some really useful suggestions. The contact between the cylinder and tube is not that good. Therefore, burying the tube is a good suggestion. I apologise for not mentioning that it is an open loop system for the water flowing through the tubes. That is...

I have a copper coil wrapped around a stainless steel cylinder (please see attached). The temp. of inner surface of the cylinder is assumed to be 500C. Water will flow through the copper coil, entering at 20C and leaving at 60C (therefore the average water temp is 40C). Now for the heat...