In the wall-hung boiler heat exchanger, in order to effectively transfer the heat of the flue gas to the water, the flue gas must be fully contacted with the surface of the stainless steel coil tubing heat exchanger. In order to achieve this purpose, there are two most commonly used methods at present:
(1) Design the surface of the flue gas side of the stainless steel coil tubing heat exchanger to form many small local swirling flows when the flue gas flows. In this way, the temperature at the center of the channel section of the flue gas flow is too high and the surrounding temperature is too low, forming an excessive temperature gradient from the center of the channel to the wall of the heat exchanger, which is not possible with a smooth and flat wall.
(2) Make the flue gas produce strong turbulence. For improving the heat transfer coefficient, its function is the same as method one, the purpose is to break the temperature gradient in the flue gas channel. The rectangular (or oblate) stainless steel tube is coiled into a spiral shape, and the flue gas from the center of the spiral shape radially flushes the stainless steel spiral tube through a narrow gap with a spiral pitch of only 0.8mm. The flue gas forms a laminar flow in these gaps, which greatly improves the heat transfer coefficient. When the flue gas passes through a 36mm long gap, the temperature can drop from a high to 50°C.
The heat exchanger is divided into two parts by the insulation baffle, which is equivalent to dividing the stainless steel coil tubing heat exchanger into one-stage heat exchange and two-stage heat exchange. In the primary heat exchange, the flue gas flushes the coil from the center outwards; in the secondary heat exchange, the flue gas flushes the coil from the spiral coil to the center.
First, the stainless steel coil is made into a spiral shape with an appropriate diameter, and then squeezed to make each circle of the spiral tube form an oblate cross section, which can increase the heat exchange area. At the same time, the spiral pitch after extrusion is ensured. In order to facilitate the configuration of heat exchangers of different powers, stainless steel spiral tubes are generally processed with a certain power unit (8~10KW). Finally, according to the power of the wall-hung boiler design, several stainless steel spiral tubes are combined into the required stainless steel coil tubing heat exchanger.
The condensed water discharged from the condensing furnace is slightly acidic, with a PH value of about 3 to 4, and must be collected by a plastic collector. This collector also acts as a water seal to prevent the flue gas from being discharged from here. Then, drain the condensate overflowing from the collector to the outside through a special plastic connecting pipe. At the same time, the water in the urban domestic wastewater system is slightly alkaline, with a PH value of about 6.5-10. Therefore, the condensed water can be discharged into the domestic sewage system, which just plays a neutralizing role.
