An experimental study of heat transfer and pollutant emission characteristics at varying distances between the burner and the heat exchanger in a compact combustion system

The effect of the distance between the burner and the heat exchanger on the heat transfer characteristics and NOx and CO emission characteristics in a compact combustion system was studied. The premixed burner was installed in front of a heat exchanger, and the distance between the burner and the heat exchanger was varied from 30 mm to 50 mm to experimentally investigate the effect of distance for the counter flow and the parallel flow conditions. Distances in the type A, type B and type C heat exchangers were 30 mm, 40 mm and 50 mm, respectively. The results showed that NOx concentration increased at the same equivalence ratio for both flow conditions as the distance between the burner and the heat exchanger increased. On the other hand, CO emission increased for both flow conditions due to the quenching effect as the distance between the burner and the heat exchanger decreased. In the experimental range, the optimal equivalence ratio of heat exchanger type A was 0.75 to minimize pollutant emission. At this condition, the NOx and CO emissions were 32.3 ppm and 85.6 ppm, respectively, and the effectiveness was 0.797.