Calculating Local Heat Flux in a Pipe: Is h = Nu*(k/x) the Correct Formula?

[evoke1l1]

I am a little unsure how to get started with a homework question.

Essentially, I have to calculate the local heat flux at a distance 1.2m (x) along a pipe. I have the fluid's properties and have calculated the Reynolds number, for which I've determined the flow to be turbulent and therefore do not see to consider the distance as part of the Nusselt number calculation. From here, I know how to calculate the average heat flux per unit length, but I am unsure how to calculate the local heat flux for a pipe.

If I determine the Nusselt number, would the local heat transfer coefficient calculation be h = Nu*(k/x) for determining the local heat flux? Where h is the local heat transfer coefficient, Nu is the Nusselt number, k is thermal conductivity and x is the distance along the pipe. I could then plug these values into q = h(T1-T2) for the local heat flux. Would this be correct?

 

[Chestermiller]

No. The characteristic length for the Nussult number in this situation is the diameter. But, the temperature driving force is changing along the pipe. You need to use the local temperature difference at x, T(x)-T2 to calculate the local heat flux.

 

[evoke1l1]

No. The characteristic length for the Nussult number in this situation is the diameter. But, the temperature driving force is changing along the pipe. You need to use the local temperature difference at x, T(x)-T2 to calculate the local heat flux.

Thank you for this. T(x) is already specified in the question with a uniform temperature for the pipe surface so I have the two temperatures to plug in, so in my instance, would the below be correct or have I misunderstood?

h = Nu*(k/d) and q = h(T(x)-T2)