The invention concerns a condensing heat exchanger designated for central heating and utility water installations.

Known are heat exchangers featuring a set of tube elements for the flow of hot fumes, fitted between two sieve walls in a chamber encased in an external jacket, where the heated water is supplied to the chamber through the inlet stub tube fitted in the lower section of the outer jacket and is discharged through the outlet stub tube fitted in the upper section of the outer jacket, and thus circulates inside the chamber. In these heat exchangers the combustion chamber is placed above the upper sieve bottom, and under the lower sieve bottom there is a condensate collecting bowl.

Known from patent application PL216290 B l is a heat exchanger comprising an outer jacket which encases a set of vertical tubee elements anchored in sieve walls on both ends, a gas combustion chamber positioned over the upper sieve wall, and baffles which are mounted perpendicular to the tube elements, with openings through which the tube elements run, plus liquid inlet and outlet stub tubes fitted in the side wall of the outer jacket.

The purpose of the invention is to improve heat exchange

parameters of the heat exchanger and reduce the exchanger size. In particular, the purpose of the invention is to develop a flue tube for a fired condensing heat exchanger which would intensify the heat exchange process, at the same time reducing the combustion gas flow resistance and retaining the condensing nature of the processes which occur in the exchanger, all of which would allow to reduce the heat exchanger size. A condensing heat exchanger comprising a combustion chamber fitted in its top section which features an opening for inserting the burner, as well as flue tubes anchored in the sieve bottoms and encased in an outer jacket, where the jacket is fitted with stub tubes for the supply and discharge of the heated fluid, and inside the jacket there is a chamber for the heated liquid, a condensate container fitted with the condensate discharge stub tube and a stub tube for the discharge of fumes to the vent, according to the invention is characterised in that the flue tubes feature dents formed along the length of the tube, and said dents are pointed towards the centre of the tube, and said dents are positioned opposite each other, and two opposite dents mark out a section, where the distance between the lowest points in the dents measured inside the tube in the section is 1.0 mm or less, and the ratio of the length of the tube to the tube cross section circumference around which the combustion gases flow falls within the range from 2.5 to 6.5.

Preferably, the flue tube is cylindrical in shape in its top and/or bottom section(s).

Preferably, the length of the cylindrical top section of the flue tube ranges from 0.25 to 1.5 of the tube's cross section circumference around which the combustion gases flow.

Preferably, the adjacent dent sections are arranged otherwise than collinearly to each other along the flue tube length, in particular at the angle of 90°.

Preferably, the dent sections are arranged at even distances along the flue tube length, or the distances between the dent sections decrease along the flue tube length.

Preferably, the dents are circular, oval, or drop-like in shape.

Preferably, the cross section of the flue tube in the fragment between the adjacent sections is circular, oval, or square in shape, with rounded apexes and sides indented towards the axis.

The designed proportions between the flue tube dimensions and the shape and arrangement of the dents according to the invention ensures retaining the condensing nature of the processes which occur in the exchanger while reducing the flow resistance of the combustion gases inside the tubes and increasing the flow turbulences.

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

In the drawings:

Fig.l shows the flue tube in the isometric projection with drop-shaped dents arranged at even distances along the tube length;

Fig.2 and Fig.3 show the flue tube as in Fig. 1 in side view;

Fig.4 depicts the flue tube as in Fig. 1 in bird's eye view;

Fig.5 and Fig.6 illustrate the flue tube as in Fig. 1 in axial section;

Fig.7 shows the flue tube as in Fig.1 in cross section;

Fig, 8 shows the flue tube in the isometric projection with circular dents arranged at even distances along the tube length;

Fig.9 and Fig.10 show the flue tube as in Fig. 8 in side view;

Fig.l 1- depicts the flue tube as in Fig. 8 in bird's eye view;

Fig.12 and Fig, 13 illustrate the flue tube as in Fig. 8 in axial section;

Fig.14 shows the flue tube as in Fig.8 in cross section;

Fig.15 shows the flue tube in the isometric projection with oval dents, arranged at even distances along the tube length;

Fig.16 and Fig.17 show the flue tube as in Fig. 15 in side view;

Fig.18 depicts the flue tube as in Fig. 15 in bird's eye view;

Fig.19 and Fig.20 illustrate the flame pipe as in Fig. 15 in axial section; Fig.21 shows the flue tube as in Fig.15 in cross section;

Fig.22 shows the flue tube in the isometric projection with drop-shaped dents arranged at even distances along the tube length in another variant;

Fig.23 and Fig.24 show the flue tube as in Fig. 22 in side view;

Fig.25 depicts the flue tube as in Fig. 22 in bird's eye view;

Fig.26 and Fig.27 illustrate the flue tube as in Fig. 22 in axial section;

Fig.28 shows the flue tube as in Fig.22 in cross section;

Fig.29 - shows the flue tube in the isometric projection with circular shaped dents arranged at even distances along the tube length in another variant;

Fig.30 and Fig.31 show the flue tube as in Fig. 29 in side view;

Fig.32 depicts the flue tube as in Fig. 29 in bird's eye view;

Fig.33 and Fig.34 illustrate the flue tube as in Fig. 29 in axial section;

Fig.35 - shows the flue tube as in Fig.29 in cross section;

Fig.36 shows the flue tube in the isometric projection with oval dents arranged at even distances along the tube length in another variant;

Fig.37 and Fig.38 show the flue tube as in Fig. 36 in side view;

Fig.39 depicts the flue tube as in Fig. 36 in bird's eye view;

Fig.40 and Fig.41 illustrate the flue tube as in Fig. 36 in axial section;

Fig.42 shows the flue tube as in Fig.36 in cross section;

Fig.43 shows the flue tube in the isometric projection with drop-shaped dents arranged at uneven distances along the tube length;

Fig.44 and Fig.45 show the flue tube as in Fig. 43 in side view;

Fig.46 depicts the flue tube as in Fig. 43 in bird's eye view;

Fig.47 and Fig.48 illustrate the flue tube as in Fig. 43 in axial section;

Fig.49 shows the flue tube as in Fig.43 in cross section;

Fig.50 shows the flue tube in the isometric projection with circular dents arranged at uneven distances along the pipe length; Fig.51 and Fig.52 show the flame pipe as in Fig, 50 in side view;

Fig.53 depicts the flue tube as in Fig. 50 in bird's eye view;

Fig.54 and Fig.55 illustrate the flue tube as in Fig. 50 in axial section;

Fig.56 shows the flue tube as in Fig.50 in cross section;

Fig.57 shows the flue tube in the isometric projection with oval dents arranged at uneven distances along the tube length;

Fig.58 and Fig.59 show the flue tube as in Fig. 57 in side view;

Fig.60 depicts the flue tube as in Fig. 57 in bird's eye view;

Fig.61 and Fig.62 illustrate the flue tube as in Fig. 57 in axial section;

Fig.63 shows the flue tube as in Fig.57 in cross section;

Fig.64 shows the flue tube in the isometric projection with drop-shaped dents arranged at uneven distances along the tube length in another variant;

Fig.65 and Fig.66 show the flue tube as in Fig. 64 in side view;

Fig.67 depicts the flue tube as in Fig. 64 in bird's eye view;

Fig.68 and Fig.69 illustrate the flue tube as in Fig. 64 in axial section;

Fig.70 shows the flue tube as in Fig.64 in cross section;

Fig.71 shows the flue tube in the isometric projection with circular dents arranged at uneven distances along the tube length in another variant;

Fig.72 and Fig.73 show the flue tube as in Fig. 71 in side view;

Fig.74 depicts the flue tube as in Fig. 71 in bird's eye view;

Fig.75 and Fig.76 illustrate the flue tube as in Fig. 71 in axial section;

Fig.77 shows the flue tube as in Fig.71 in cross section;

Fig.78 shows the flue tube in the isometric projection with oval dents arranged at uneven distances along the tube length in another variant;

Fig.79 and Fig.80 show the flue tube as in Fig. 78 in side view;

fig.81 depicts the flue tube as in Fig. 78 in bird's eye view;

Fig.82 and Fig.83 illustrate the flue tube as in Fig. 78 in axial section; Fig.84 shows the flue tube as in Fig.78 in cross section;

Fig.85 shows the heat exchanger in axial section.

In the exemplary embodiment, a heat exchanger comprises, in its top section, a combustion chamber 3 which features an opening for inserting the burner, as well as flue tubes 1 anchored in the sieve bottoms 4, 5 and encased in an outer jacket 6, inside which the is a chamber 7 for the heated liquid, where the jacket is fitted with inlet stub tube 8 and outlet stub tube 9 for the supply/ discharge of the heated liquid. In the bottom section of the outer jacket 6 there is a condensate container 10 fitted with a condensate discharge stub tube 11 and a stub tube for the discharge of fumes to the vent 12, as shown on Fig.43 and Fig. 44. The flue tubes 1 feature dents 2 pointing towards the centre of the flue tube 1. At the predetermined point there are two dents 2 made in the flue tube 1 opposite each other, which mark out a section. The distance between the lowest points in the dents 2 measured inside the flue tube in the section is 0.5 mm, and the ratio of the length L of the flue tube 1 to the tube cross section circumference around which the combustion gases flow is 3.5. The adjacent sections of the dents 2 are mutually arranged along the length of the flue tube 1 at the angle of 90°. In the top section, the flue tube 1 is cylindrical in shape and the length H of the top section amounts to 1,0 of the tube cross section circumference around which the

combustion gases flow.

In the exemplary embodiments shown on Figs. 1 to 7 and Figs. 22 to 28, the dents 2 are drop-like in shape; in other variants which are shown on Figs. 8 to 14 and Figs. 29 to Fig. 35 dents 2 are circular in shape, and in further embodiments shown on Figs. 15 to 21 and Figs. 36 to 42 the shape of the dents 2 is oval.

In the invention embodiment variants referred to above the sections of dents 2 are arranged at even distances along the length L of the flue tube 1.

In the remaining invention embodiment variants shown on Figs. 43 to 49 and Figs. 64 to 70 (drop-shaped dents 2); Figs. 50 to 56 and Figs. 71 to 77 (circular dents 2); and Figs. 57 to 63 and Figs. 78 to 84 (oval dents), the sections of dents 2 are arranged at uneven distances along the length L of the flue tube in such a way that the distance S between the sections reduces along the tube length.

In the invention embodiment variants described above and shown on Figs. 1 to 21 , and Figs. 43 to 63, the flue tube 1 in the fragment between the adjacent sections is circular in cross section, and in the variants illustrated on Figs. 22 to 42, and Figs. 64 to 84 the shape of the tube cross section is square with rounded apexes and sides indented towards the axis.

In other embodiment variants the flue tube 1 between the adjacent sections can be oval in cross section.

In other embodiment variants described above the distance between the lowest points in the dents 2 measured inside the flue tube 1 in the section cannot be larger than 1.0 mm and the ratio of the length L of the flue tube 1 to the tube cross section circumference around which the combustion gases flow ranges from 2.5 to 6.5, and the length of the cylindrical flue tube 1 in its top section ranges from 0.25 to 1.5 of the tube cross section circumference around which the combustion gases flow. It has been found that with the combustion gas temperature at the flue tube inlet ranging from 1450 to 1550 °C, the flow of the combustion gas in the flue tube between 0.83 and 0.89 kg/h (for natural gas, C0 ₂ = 9%), and the initial temperature of 30 °C and dT=20K of the heated liquid in counterflow of 22-26 1 h per tube, the combustion gas reaches the dew point at the distance of 155-225 mm from the tube inlet, and the pressure drop does not exceed 375Pa.