docs: def S_isothermal_pipe_to_two_planes(D, Z, L=1.):
      r'''Returns the Shape factor `S` of a pipe of constant outer temperature
      and of outer diameter `D` which is `Z` distance from two infinite
      isothermal planes of equal temperatures, parallel to each other and
      enclosing the pipe. Length `L` must be provided, but can be set to
      1 to obtain a dimensionless shape factor used in some sources.
  
      .. math::
          S = \frac{2\pi L}{\ln\frac{8z}{\pi D}}
  
      Parameters
      ----------
      D : float
          Diameter of the pipe, [m]
      Z : float
          Distance from the middle of the pipe to either of the planes, [m]
      L : float, optional
          Length of the pipe, [m]
  
      Returns
      -------
      S : float
          Shape factor [m]
  
      Examples
      --------
      >>> S_isothermal_pipe_to_two_planes(.1, 5, 1)
      1.2963749299921428
  
      Notes
      -----
      L should be much larger than both diameters. L should be larger than W.
  
      .. math::
          Q = Sk(T_1 - T_2) \\ R_{\text{shape}}=\frac{1}{Sk}
  
      References
      ----------
      .. [1] Shape Factors for Heat Conduction Through Bodies with Isothermal or
         Convective Boundary Conditions, J. E. Sunderland, K. R. Johnson, ASHRAE
         Transactions, Vol. 70, 1964.
      .. [2] Bergman, Theodore L., Adrienne S. Lavine, Frank P. Incropera, and
         David P. DeWitt. Introduction to Heat Transfer. 6E. Hoboken, NJ:
         Wiley, 2011.
      '''
      return 2.*pi*L/log(8.*Z/(pi*D))