code: def re_rect(FlowRate, Width, DistCenter, Nu, openchannel):
      
      #Checking input validity - inputs not checked here are checked by
      #functions this function calls.
      ut.check_range([FlowRate, ">0", "Flow rate"], [Nu, ">0", "Nu"])
      return (4 * FlowRate
              * radius_hydraulic(Width, DistCenter, openchannel).magnitude
              / (Width * DistCenter * Nu))
docs: Return the Reynolds Number for a rectangular channel.