"What is the heat flow rate [...]?" 1. The problem statement, all variables and given/known data The problem is: "A copper tube (length, 3.0 m; inner diameter, 1.500 cm; outer diameter, 1.700 cm) extends across a 3.0-m long vat of rapidly circulating water maintained at 20 °C. Live steam at 100 °C passes through the tube. (a) What is the heat flow rate from the steam into the vat? (b) How much steam is condensed each minute? (For copper, ##k_T## = 1.0 cal/s ⋅ cm ⋅ °C.)" The solution is attached as TheSolution.jpg. 2. Relevant equations ##ΔQ/Δt = ####k_T## ##A## ##ΔT/L## 3. The attempt at a solution When looking at the provided solution, I am, basically, confused about the assumptions made and the geometries involved. To elaborate, I am confused as to why the solution deemed it was necessary to approximate the tube wall as a flat sheet. (Also, how exactly does a tube WALL look like? - I wasn't able to find anything useful on Google Images.) Also, it is probably because I am having trouble visualizing the geometries in this problem but, I don't see why the inner and outer surface areas are being averaged. Lastly, I don't see why we're assuming the hypothetical plate has a thickness of 0.100 cm. Any help in understanding how this problem is done would be greatly appreciated!