Heat-exchange pipe, heat-exchanger unit using same, and condensing boiler using same

A condensing boiler comprising:

• a burner assembly configured to cause a combustion reaction;
• a combustion chamber located downstream of the burner assembly based on a first reference direction that is a flow direction of combustion gas generated during the combustion reaction, flame by the combustion reaction being located in the combustion chamber;
• and
• a heat exchanger unit configured to receive sensible heat generated by the combustion reaction and the combustion gas and to heat water,
• wherein the heat exchanger unit includes:
• a sensible heat exchanging part disposed in a sensible heat exchange area configured to receive the sensible heat generated by the combustion reaction and to heat the water, the sensible heat exchanging part including a sensible heat exchange pipe configured to receive the water and allow the water to flow therethrough;
• a latent heat exchanging part disposed in a latent heat exchange area, the latent heat exchanging part including a latent heat exchange pipe configured to receive the water and allow the water to flow therethrough, wherein the latent heat exchange area is located downstream of the sensible heat exchange area based on the first reference direction and is configured to receive latent heat generated during a phase change of the combustion gas and to heat the water;
• and
• a housing configured to surround the heat exchange areas to define the heat exchange areas therein,
• wherein the latent heat exchange pipe includes a plurality of latent heat straight portions extending along a second reference direction perpendicular to the first reference direction, the plurality of latent heat straight portions being arranged to be spaced apart from each other along a third reference direction perpendicular to the first reference direction and the second reference direction and configured to form a latent heat flow passage through which the water flows and that is connected to the sensible heat exchange pipe,
• wherein interior spaces of the sensible heat straight portions and the latent heat straight portions are formed to be long and narrow such that widths in the third reference direction are smaller than lengths in the first reference direction,
• wherein the latent heat exchange pipe includes a plurality of upstream straight portions and a plurality of downstream straight portions located downstream of the upstream straight portions based on the first reference direction,
• wherein the heat exchanger unit further comprises:
• a sensible heat fin coupled with the sensible heat exchange pipe;
• an upstream fin coupled to the upstream straight portions and arranged to be spaced apart from the sensible heat fin along the first reference direction;
• and
• a downstream fin coupled to the downstream straight portions and arranged to be spaced apart from the upstream fin along the first reference direction,
• wherein cross-sectional areas of the heat exchange areas defined on a plane perpendicular to the first reference direction are referred to as reference cross-sectional areas,
• wherein most upstream side of each fin based on the first reference direction are referred to as an inlet end and the most downstream side of each fin based on the first reference direction are referred to as an outlet end and,
• wherein the housing is provided such that the reference cross-sectional area decreases from the outlet end of the sensible heat fin to the inlet end of the upstream fin, and
• wherein the housing is provided such that the reference cross-sectional area decreases from the outlet end of the upstream fin to the inlet end of the downstream fin along the first reference direction, and
• wherein the housing is provided such that the reference cross-sectional area defined at the outlet end of the downstream fin is smaller than the reference cross-sectional area defined at the inlet end of the upstream fin.