…ue36_CoaxialPipes

…onvective heat transfer coefficient for circular pipe by interpolation

…ki (2013)

…ntation

It is not yet clear if this second borehole thermal resistance function
will be necessary. I will not know until I have completed this and
Massimo reviews it to see if he could use his own techniques to make it
happen.

I plan to make use of this function to calculate the effective borehole
thermal resistance for a concentric (coaxial) pipe arrangement.

A new file has been included with an example. The file is included for
reviewal purposes by Cimmino.

The calculation has now been checked versus GLHEPRO, two errors were
found:

- The Reynolds number (Re) was improperly being calculated inside of the
  annulus, thus leading to improper convection coefficients and the
  resulting resistances inside of the annulus (contains inner and outer)

- The hyperbolic cotangent in the uniform borehole wall temperature
  effective resistance was not returning the proper value. This user
  believed that the function "arctanh" in numpy meant hyperbolic
  cotangent. Apparently, it does not. The solution is 1 divided by the
  "tanh" function.

I'll push this so you can see what I did to find that _Rd[0, 0] value
to make the methods solve for the same effective borehole resistance.

@MassimoCimmino

These are general formatting changes along with variable name changes to
align with the rest of the `pipes` module and the
`convective_heat_transfer_coefficient_circular_pipe` function.

The definition of each pipe type now has its own section in the script.
The mass flow is prescribed instead of the volume flow rate as is done in
the other examples. A mistake was corrected in the call to
`borehole_thermal_resistance()`: the borehole mass flow rate should be
provided (as opposed to the pipe mass flow rate). Pipes in single and
double U-tube boreholes are moved closer to the borehole wall and the
fluid is changed to propylene glycol 20%.