Hot-wire mass flow sensor with low-loss bypass passage

A mass fluid flow sensor comprising:

• a housing adapted to be inserted in a fluid flow, the housing including an internal passage having an inlet in opposition to a primary direction of fluid flow and an outlet disposed at a predetermined angle with respect to the primary direction such that a minimum pressure drop is developed at the outlet relative to the inlet as fluid flow in the primary direction passes over the housing, wherein the passage includes, in series,
• a first section converging along a first axis to define an annular nozzle having a nozzle diameter,
• a generally-right-cylindrical second section adjacent to the first section and extending along the first axis, the second section having a diameter greater than the nozzle diameter and defining a radial step immediately downstream of the nozzle,
• a third section adjacent to the second section and defining a generally-semi-spherical chamber centered on the first axis in opposition to the radial step, the third section having an effective radius substantially equal to one half of the diameter of the second section, and
• a fourth section adjacent to at least one of the first and second intermediate sections, the fourth section converging along a second axis to a minimum diameter, the second axis being disposed at a first, nonzero angle with respect to the first axis;
• and
• a sensing element supported by the housing within the passage proximate to the radial step.