code: def baffle_S(self):
          
          return ((self.BAFFLE_K /
                  ((2 * self.expansion_H * (self.vel_grad_avg ** 2) *
                   pc.viscosity_kinematic(self.temp))).to_base_units()) ** (1/3) *
                 self.Q / self.channel_W).to(u.cm)
docs: Return the spacing between baffles.
          :returns: Spacing between baffles
          :rtype: int