At a given location in a double-pipe heat exchanger, the bulk temperature of the fluid in the annulus is 100°C, and the bulk temperature of the fluid in the inner pipe is 20°C. The tube wall is very thin, so the resistance due to the metal wall may be ignored. Likewise, fluid fouling resistances may also be ignored. The individual heat transfer coefficients at this point in the heat exchanger are h = 100 W/m²/K and h_o = 500 W/m²/K 

What is the temperature of the wall at this location?

What is the heat flux across the wall at this location?

If there was a fouling resistance of 0.001 m K/W on the inside surface of the inner pipe, what would the temperature of the wall be at this location?