code: def h_x(self, L, theta, Ts, **statef):
          
  
          Nu_x = self.Nu_x(L, theta, Ts, **statef)
          k = self._fluid.k(T=self.Tr)
          return Nu_x * k / L
docs: Calculate the local heat transfer coefficient.
  
          :param L: [m] characteristic length of the heat transfer surface
          :param theta: [°] angle of the surface with the vertical
          :param Ts: [K] heat transfer surface temperature
          :param Tf: [K] bulk fluid temperature
  
          :returns: [W/m2/K] float