A heater assembly includes a flow guide and a plurality of electrical resistance heating elements. The flow guide defines a continuous geometric helicoid disposed about a longitudinal axis of the heater assembly. The flow guide defines a predetermined pattern of perforations that extend in a longitudinal direction through a first longitudinal length of the geometric helicoid. The longitudinal direction is parallel to the longitudinal axis. The geometric helicoid has a first pitch at a first zone along the longitudinal axis and a second pitch at a second zone along the longitudinal axis. The second pitch is shorter than the first pitch. The electrical resistance heating elements extend through the perforations.