Reduced drag combustion pass in a tubular heat exchanger

A HVACR system for heating air, comprising:

• a heat exchanger volume for heating air;
• a heat exchanger tube including a first heat exchange pass, a second heat exchange pass, and a bend fluidly connecting the first heat exchange pass to the second heat exchange pass, the heat exchanger tube being located within the heat exchanger volume;
• and
• a blower that blows outer air into the heat exchange volume towards the heat exchanger tube, wherein
• the first heat exchange pass includes an inlet and is a combustion pass, and
• the first heat exchange pass has a length extending from the inlet to the bend, a majority of the length of the first heat exchange pass being modified to form a modified portion that includes a major diameter and a minor diameter, a cross-sectional area of the heat exchanger tube at the minor diameter and the major diameter being at or about the same area as a circular cross-sectional area that has a single diameter based on equally increasing and reducing the minor diameter and the major diameter, respectively, and
• the heat exchanger tube being configured such that the major diameter of the first heat exchange pass is oriented towards an incoming direction of the blowing air.

A method of making a heat exchanger, comprising:

• constructing a heat exchanger housing with a heat exchanger volume;
• positioning a heat exchanger tube in the heat exchanger volume, the heat exchanger tube including a first heat exchange pass, a second heat exchange pass, and a bend fluidly connecting the first heat exchange pass to the second heat exchange pass, the first heat exchange pass including an inlet and is configured as a combustion pass, the first heat exchange pass having a length extending from the inlet to the bend, a majority of the length of the first heat exchange pass being modified to form a modified portion that includes a major diameter and a minor diameter, a cross-sectional area of the heat exchanger tube at the minor diameter and the major diameter being at or about the same area as a circular cross-sectional area that has a single diameter based on equally increasing and reducing the minor diameter and the major diameter, respectively;
• providing a burner at a tube inlet of the heat exchanger tube, such that when the heat exchanger is in operation, the burner supplies at least a fuel into the first heat exchange pass and the fuel at least partially combusts in the first heat exchange pass;
• providing an inlet and an outlet in the heat exchanger housing for a process fluid such that, when the heat exchanger is in operation, the process fluid flows through the heat exchanger volume and past the heat exchanger tube;
• and
• configuring the first heat exchange pass such that the major diameter of modified portion of the first heat exchange pass is oriented towards an incoming direction of the process fluid.