JPS5997455A - Heat exchanger for water heater - Google Patents

Abstract

PURPOSE:To accelerate dewing and enhance efficiency in recovering latent heat, by a construction wherein the ratio of a heat-transmitting area on a combustion gas side and that on the circulating water side is gradually reduced from the upstream side to the downstream side of a combustion gas, and a passing area of the combustion gas is also gradually reduced. CONSTITUTION:The combustion gas is sequentially passed through a heat exchanger as indicated by arrows, while circulating water flows sequentially in the order of heat exchangers 12C, 12B and 12A. In the heat exchanger 12A comprising water-passing pipes 15 fitted with fins 14, the heat-transmitting area on the gas side is set to be about 10 times of that on the circulating water side, and the heat exchanger 12B is provided with annular finned water-passing pipes 16 having a gas-side heat-transmitting area of smaller than that of the fins 14, and the height and the pitch span of the fins are set to be so large that drops do not fill up the spaces between the fins. The heat exchanger 13C constituted of a bare pipes 17 has a reduced pitch and a restricted gas passage so that the area for contact of the gas becomes large and dewing occurs easily. Dewing is accelerated by removing sensitive heat of the combustion gas on the upstream side and removing latent heat of the gas on the downstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heat exchanger that heats water using the heat of combustion gas in an instantaneous water heater.

Conventional structure and its problems Conventionally, this type of high-efficiency heat exchanger for recovering H2O latent heat in combustion gas has a knob with one fin on the combustion gas side, as shown in Figure 1. 2, the inner surface of the pipe 2 is the heat transfer area on the water flow side, and the combustion gas combusted by the burner 3 is transferred from the combustion chamber 4 on the upstream side of the combustion gas passage to the heat exchanger. Pass through fin 1 and pipe 2,
The water in the water pipe 2 reaches the exhaust box 6 on the downstream side of the combustion gas passage, and the water in the water pipe 2 flows from the combustion gas to the fin 1. Noku Eve 2
The structure is such that the pipe 2 receives heat from the inner surface of the pipe 2 and becomes hot water. In this case, the H20 latent heat in the combustion gas is
Then, heat is recovered by pipe 2, and the H2Q steam condenses to become drain water and drips downward.

The fin 1 with which the combustion gas in the combustion chamber 4 comes into contact with high combustion gas whose temperature is 800°C to 1oOo°C and the exhaust box 50 fin 1 with which the combustion gas reaches around 50°C are common, and the heat transfer area on the combustion gas side The ratio of the heat transfer area on the water flow side and the heat transfer area on the water flow side is constant. Therefore, the fins on the downstream side of the combustion gas, where the temperature is low, are unnecessarily large, and the heat transfer from the high temperature fins on the upstream side of the combustion gas causes the H2
The amount of condensation of O vapor is small, and the combustion gas passage area is the same on the upstream and downstream sides of the combustion gas, so the high-temperature gas becomes colder on the downstream side, the volume decreases, and the flow rate of the combustion gas decreases to 3rd place, so the condensation water There is a drawback that a bridge is formed between the fins 1 due to surface tension, which prevents dew condensation from accelerating. Since there are still many fins on the downstream side of the combustion gas, a large amount of heat is radiated from the fins to the outside of the aircraft, and it also has the disadvantage of having a large volume as a heat exchanger for latent heat recovery.

Purpose of the Invention The present invention aims to eliminate these conventional drawbacks, and provides a compact heat exchanger that promotes dew condensation, increases latent heat recovery efficiency, allows easy dripping of condensed water, and reduces heat radiation loss. It is something.

Structure of the Invention In order to achieve this object, the present invention has a structure in which combustion gas is forcibly exhausted downward, and from the upstream side to the downstream side of the combustion gas passage, the heat transfer area on the combustion gas side and the water flow side are The structure is such that the heat transfer area ratio is sequentially reduced, and the combustion gas passage area is also sequentially reduced.

With this configuration, when sensible heat is taken from the high-temperature combustion gas on the upstream side of the combustion gas, the heat transfer area on the combustion gas side with a low heat transfer coefficient is large, resulting in a compact fin-equipped heat exchanger configuration for sensible heat recovery. Combustion gas temperature decreases, H2 in combustion gas
As the latent heat ratio of O component increases, the heat transfer area on the combustion gas side is reduced, and by configuring the ratio to the heat transfer area on the water flow side to be small, the heat transfer surface on the combustion gas side near the low temperature water flow source is temperature, condensation occurs on contact with the combustion gases, increasing the rate of latent heat recovery. Moreover, since the fin area on the combustion gas side is also reduced, it is possible to have more water pipes than on the upstream side of the combustion gas, and the passage area for the combustion gas is also narrower, making it easier for condensed water to drip at a faster flow rate, and the area is reduced. There is little heat loss,
It becomes a compact heat exchanger for latent heat recovery. In addition, by stacking heat exchange units that sequentially reduce the ratio of the combustion gas side heat transfer area to the water flow side heat transfer area from the upstream side of the combustion gas side, heat transfer to the upstream fins is prevented and the downstream fins are kept at a low temperature. The structure makes it easy to maintain and recover latent heat. At the same time, corrosion-resistant surface treatments on the high temperature side and the latent heat recovery side of condensation can be freely selected. -1: By arranging bare water pipes without fins in a staggered manner in the passages where the combustion gas temperature is below 120°C, condensation water drips down the water pipes on the cylinder and dew condensation treatment is carried out. In addition, since the flow of combustion gas always hits the water pipe, it is easy to remove the latent heat of condensation, and it is also easy to perform corrosion-resistant surface treatment on the bare pipe.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 2. A heat exchanger 12 and a hot water outlet 13 communicate with a water supply port 10 and a water pressure response unit 11 that generates a pressure difference by water flow and turns on a switch.
The heat exchanger 12 that constitutes the water circuit of the water heater is a finned heat exchanger 12 that has a water pipe 15 with a large number of fins 14.
Heat exchanger 1 composed of ~A and annular finned water pipe 16
The heat exchanger 12 is constructed by stacking a heat exchanger 12-B and a heat exchanger 12-C composed of bare tubes 17. On the other hand, the burner 18 is connected to a fuel supply port 19 and a fuel valve 20 that is linked to the hydraulic response part 11, a combustion chamber 21, a heat exchanger 12, and an exhaust box 2.
2 constitutes a combustion section.

23 is a motor fan that forcibly exhausts combustion gas, 2
4 is an exhaust port, and 26 is a H2O condensed water discharge port.

In this configuration, the combustion gas combusted downward in the burner 18 sequentially passes through the heat exchanger as shown by the arrows, exchanges heat with the flowing water, and becomes hot water. Water passes through heat exchanger 12-C → 12-B → 1
Flows in the order of 2 to A. In this case, the fins 14 on the upstream side of the combustion gas are made of copper fins with high fuel conductivity because they come into contact with the high temperature (800°C to 1000°C) combustion gas, and absorb heat.
Since the heat transfer coefficient on the combustion gas side is considerably higher than that on the water flow side, it is recommended that the heat transfer area on the combustion gas side, including the water flow pipes 15 and fins 14, be approximately 10 times the heat transfer area on the water flow side. The heat exchanger 12-A is an element designed to be compact as a heat exchanger for high-temperature combustion gas, and is used in a normal water heater heat exchanger. Next, the heat exchanger of 12-B is
The combustion gas passes through the annular finned water pipe 16, which has a smaller heat transfer area on the combustion gas side than the fins 14 of 12-A, but in this case, the water pipe surface is often below 50°C, and the dew point temperature of the combustion gas is 50 to 60. ℃, the H2O content in the combustion gas condenses on the surface of the annular finned water pipe 16, generating latent heat and causing water droplets to adhere. In order to prevent these water droplets from adhering and filling the spaces between the fins, the fins are configured to have a wide height and a wide fin pitch, so that dew condensation and water easily drip. The combustion gas, which is further heated and has a low temperature (below 120 degrees Celsius), enters the heat exchanger 12-C made up of bare tubes 17, and since the combustion gas directly touches the surface of the bare tubes, a water supply source (5 to 26 ℃) condenses on the tube wall, generates latent heat, and becomes water droplets. H2 in combustion gas
The amount of latent heat of O component is around 1° of the calorific value of fuel, so it is important to increase the number of cold heat transfer wall surfaces rather than increasing the heat transfer area in the combustion gas, and by narrowing the pitch of bare tubes, the combustion The gas passage is also narrow to increase the area in contact with the combustion gas, making it easier for dew to form, and at the same time, it has a bare tube shape that allows condensed water to easily drip along the flow. Figure 3 shows that the bare tubes 17 of the 12-C heat exchanger are arranged in two stages in a staggered manner, and since water drops occur from the lower end of the center of the tubes, the dripping water does not touch the bare tubes below, and the uncondensed components This shows an example where the combustion gas touches the bare tube below and improves the latent heat recovery rate.

In this way, a heat exchanger 12 having a water pipe 16 with fins 14 is installed.
-A to 12-B- and 12-C, the heat transfer area on the combustion gas side is successively reduced, and the ratio with the heat transfer area on the water flow side is decreased, and the number of water flow pipes is increased to the second level. As shown in the figure, by gradually increasing the combustion gas passage area in the direction of flow of the combustion gas and decreasing the combustion gas passage area, the warm surface close to the water passing temperature increases, and as shown in Figure 4, the amount of sensible heat decreases to several inches at around 20℃. The temperature above 90% is latent heat, and the condensation of H2O is important.
The low-temperature combustion gas comes into contact with the bare tube at around 20°C and condenses, giving a greater effect of imparting latent heat to the bare tube, reducing the passage area, increasing the flow rate of the combustion gas, promoting the dripping of condensed water, and creating a circular shape. Because it is a bare tube, the water continues to drip without being held as water droplets like in the case of fin plates, and has the effect of removing latent heat one after another. In addition, the heat exchangers are stacked in three stages from the high temperature side of the combustion gas to the low temperature side, so 12-A and 1
2-B was performed by pb seeding surface treatment, and 12-B on the low temperature side
C can be adequately covered with silicone coating, and has the effect of being able to practically handle surface treatments that are resistant to acids such as sulfuric acid or nitric acid in dew condensation water depending on the temperature. Also, fin 14, annular finned water pipe 1:6, Since the bare tubes 17 are separated from each other, there is no temperature increase in the low temperature side fins due to heat conduction from the high temperature side fins, unlike in the conventional case, and 12-B and 12-C are folded to maintain a low temperature surface suitable for latent heat recovery. As shown in Figure 6A, latent heat recovery works effectively. Even if the heat transfer area on the combustion gas side is increased as shown in characteristic B of the conventional finned heat exchanger, the thermal efficiency can only be gradually increased; This has the effect of increasing the thermal efficiency as shown by curve A by decreasing the number of water pipes and decreasing the heat transfer area on the combustion gas side. In this example, the diameter of the water pipes was kept the same, but
On the other hand, it goes without saying that the same effect can be obtained even if the fins are common and the diameter of the water pipe is increased and the ratio of the heat transfer area on the combustion gas side to the heat transfer area on the water side is sequentially decreased. In this way, it is possible to reduce the heat transfer area on the combustion gas side, increase thermal efficiency, and achieve a more compact design.

Effects of the Invention As described above, according to the water heater heat exchanger of the present invention, the ratio of the heat transfer area on the combustion gas side to the heat transfer area on the water flow side is gradually decreased from the upstream side of the combustion gas toward the downstream side. Since the structure is such that the combustion gas passage is gradually lowered, the sensible heat of the combustion gas is taken away on the upstream side and the latent heat is taken away on the downstream side, promoting dew condensation and increasing the latent heat recovery efficiency. Because there is less heat transfer area on the combustion gas side in the low temperature part on the side, there is less heat radiation loss.
Since the heat transfer area on the combustion gas side can be reduced, it has the effect of allowing for a more compact design. By arranging the bare tubes in a staggered manner, it is easy for dew condensation water to drip, and the combustion gas hits the tube wall and flows along the circumference of the tube, making it easier to remove latent heat. In addition, thermal division is achieved by sequentially stacking heat exchangers.
There is no heat conduction from the upstream heat exchanger, so recovery of latent heat on the downstream side is promoted, and there is also the effect that corrosion-resistant surface treatment can be freely selected for high-temperature or low-temperature condensation depending on the combustion gas temperature.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional water heater, FIG. 2 is a block diagram of one implementation of the present invention, and FIG. 3 is a characteristic diagram showing another latent heat recovery heat exchange system. 12... Heat exchanger, 13... Tap water outlet,
14...Fin, 15...Water pipe, 1
6... Water pipe with annular fin, 17... Bare pipe, 18... Burner. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 2.5 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) In a water heater heat exchanger that recovers H2O latent heat in combustion gas, the combustion gas is forcibly exhausted downward, and the combustion gas side is transferred from the upstream side to the downstream side of the combustion gas passage. A heat exchanger for a water heater, which has a structure in which the ratio of the heat area to the heat transfer area on the water flow side is sequentially reduced, and the combustion gas passage area is also sequentially reduced. (2) Claim 1 in which bare pipes for water passage without fins are arranged in a staggered manner in the passage where the combustion gas temperature is 120°C or less.
Heat exchanger for the water heater described. (3) The heat exchanger for a water heater according to claim 1, which is constructed by stacking heat exchange units that sequentially reduce the ratio of the heat transfer area on the combustion gas side to the heat transfer area on the water flow side.