JP7821673B2 - Vacuum water heater - Google Patents

Description

The present invention relates to a vacuum water heater, and in particular to a vacuum water heater equipped with a sound-absorbing structure.

Conventionally, vacuum water heaters have been known that heat transfer water sealed in a sealed container under reduced pressure and in a near-vacuum state, heating it to a boil at a low temperature of 100°C or less, and then using the resulting steam as a heat source to heat water and generate hot water.

Fig. 8 shows a conventional vacuum water heater. The vacuum water heater 100 shown in Fig. 8 includes a sealed container 101, heat transfer water W sealed in the sealed container 101, a combustion chamber 102 that is submerged in the heat transfer water W and forms a heating device for heating the heat transfer water, a combustion burner 103 that radiates a flame into the combustion chamber 102, a reduced pressure space 104 formed above the heat transfer water W, a heat exchanger 105 disposed in the reduced pressure space 104, and a group of water tubes 106 that penetrate the combustion chamber 102. The pressure inside the sealed container 101 is reduced to below atmospheric pressure by an automatic air extraction device (not shown) to create a near-vacuum state. In this state, the combustion burner 103 heats the combustion chamber 102, boils the heat transfer water W, and generates steam in the reduced pressure space 104 that has the same temperature as the heat transfer water W at that time. The steam condenses on the surface of the heat exchanger 105, heating the water _H1 in the heat exchanger 105 and producing hot water _H2 .

In this type of vacuum water heater, subcooled boiling occurs during low-pressure heating when the heat transfer water temperature is relatively low at the start of operation. The boiling steam suddenly condenses and disappears as it rises to the water surface. When the boiling steam suddenly disappears, a high-level impact noise similar to a metallic crackling sound is generated, which is thought to be due to pressure waves generated when liquid-liquid collisions occur. This impact noise is transmitted to the wall of the sealed vessel 2, generating unpleasant noise. This noise tends to increase as the temperature of the heat transfer water W decreases. This is because the lower the temperature, the larger the specific volume of saturated steam, making it more likely to condense rapidly, and the greater the degree of subcooling (the difference between the saturated temperature at the surface of the combustion chamber and the temperature of the heat transfer water surrounding the combustion chamber). Normally, in a sealed vessel decompressed to near vacuum, this impact noise almost disappears once the heat transfer water temperature reaches 65°C or higher. Therefore, a challenge for vacuum water heaters has been how to complete warm- up operation without generating noise at low temperatures.

To solve this problem, a sound-absorbing structure is known in which the bottom and side walls of the sealed container have a double structure to absorb the impact noise generated (Patent Document 1).

A noise-absorbing structure is also known in which a baffle plate with a bubble flow opening and a condensed water inlet opening is provided in the heat transfer liquid to control the flow of steam bubbles generated by the boiling of the heat transfer liquid and the flow of condensed water from the steam that has lost heat in the heat exchanger, thereby silencing noise (Patent Document 2).

Furthermore, a pressure-reducing heater is also known that has a guide member for guiding boiling steam inside the side wall of the sealed container, which guides the boiling steam that rises between the side wall and the heating device toward the heating device, thereby suppressing noise generation (Patent Document 3).

Japanese Patent Application Publication No. 8-219402 Japanese Patent Application Publication No. 8-189605 Japanese Patent Application Laid-Open No. 2005-69569

However, the sound deadening structure of Patent Document 1 was insufficient in its noise suppression effect against impact noise generated near the water surface. Furthermore, while Patent Documents 2 and 3 are effective in reducing impact noise caused by the rapid condensation of boiling steam generated near the surface of the heat transfer water, they are unable to suppress impact noise caused by the rapid condensation of steam generated during subcooled boiling on the surface of the combustion chamber that constitutes the heating device.

The primary objective of the present invention is to provide a vacuum water heater that can adjust the degree of subcooling on the surface of the heating device of the vacuum water heater and suppress noise when it starts operating.

To achieve the above object, one aspect of the present invention provides a vacuum water heater comprising: a sealed container whose interior is maintained at a pressure lower than atmospheric pressure and in which heat transfer water is sealed; a heating device that is submerged in the heat transfer water and heats and evaporates the heat transfer water; a heat exchanger that is positioned in a reduced-pressure space above the heat transfer water and heats the water circulating inside by indirect heat exchange with the steam from the heat transfer water; and a shielding plate that covers the heating device and has a heat transfer water inlet on its lower side and a steam outlet on its upper side that opens above the surface of the heat transfer water.

The system may further include a first temperature detector that detects the temperature of the heat transfer water inside the shielding plate, a second temperature detector that detects the temperature of the heat transfer water outside the shielding plate, and a control unit that calculates the temperature difference between the temperatures detected by the first temperature detector and the second temperature detector and controls the heating device so that the temperature difference becomes a set temperature.

The system may have a combustion chamber and a group of water tubes that vertically penetrate the combustion chamber, with the upper portions of the water tubes of the group of water tubes positioned above the surface of the heat transfer water.

The surface of the heat transfer water may be located between the heating device and the shielding plate.

The steam outlet may be positioned so as to avoid being vertically below the heat exchanger.

The shielding plates may have a multi-layer structure, allowing the heat transfer water to flow between each shielding plate.

The water pipe may also have a double pipe structure.

According to the present invention, the degree of subcooling on the surface of the heating device can be adjusted, and the boiling steam generated on the surface of the heating device can be released into a reduced pressure space without coming into contact with the surrounding cold heat transfer water, thereby reducing the sudden condensation of the boiling steam and reducing noise when operation starts.

1 is a longitudinal sectional front view showing a vacuum type hot water machine according to a first embodiment of the present invention together with a partially enlarged view. FIG. 10 is a longitudinal sectional front view showing a vacuum type water heater according to a second embodiment of the present invention together with a partially enlarged view. FIG. 10 is a partially enlarged vertical sectional top view of a vacuum type water heater according to a third embodiment of the present invention. FIG. 10 is a longitudinal sectional front view showing a vacuum type water heater according to a fourth embodiment of the present invention together with a partially enlarged view. FIG. 5 is a vertical cross-sectional side view taken along the line VV in FIG. 4. FIG. 10 is a vertical sectional top view of a vacuum type water heater according to a fifth embodiment of the present invention. FIG. 7 is a vertical cross-sectional side view taken along line VII-VII of FIG. 6. FIG. 1 is a longitudinal sectional front view of a conventional vacuum type water heater.

Embodiments of a vacuum water heater according to the present invention will be described with reference to the drawings. Note that in the following description, identical or similar components are designated by the same reference numerals throughout all drawings and embodiments.

Referring to FIG. 1, the vacuum water heater 1 according to the first embodiment comprises a sealed container 2 whose interior is maintained at a pressure lower than atmospheric pressure and in which heat transfer water W is sealed; a heating device 3 that is submerged in the heat transfer water W and heats and evaporates the heat transfer water W; a heat exchanger 5 that is disposed in a reduced pressure space 4 above the heat transfer water W and heats water H circulating therethrough by indirect heat exchange with the steam from the heat transfer water W; and a shielding plate 8 that covers the heating device 3 and has a heat transfer water inlet 6 on its lower side and a steam outlet 7 on its upper side that opens above the surface of the heat transfer water W.

The heating device 3 includes a combustion chamber 9 and a group of water tubes 10 that vertically penetrate the combustion chamber 9. The combustion chamber 9 has a cylindrical portion 9a and a rectangular tubular portion 9b that is connected to the cylindrical portion 9a and through which the group of water tubes 10 penetrates. The combustion chamber 9 is submerged in heat transfer water W. The combustion chamber 9 is not limited to a cylindrical shape, but can also be a rectangular parallelepiped (box-shaped). The bottom of the combustion chamber 9 is spaced apart from the bottom surface of the sealed container 2. A combustion burner 11 is attached to the combustion chamber 9 to form a furnace. The combustion burner 11 radiates a combustion flame into the combustion chamber 9 to heat the interior of the combustion chamber 9. A smoke chamber 12 is connected to the combustion chamber 9, and a flue 13 extends from the smoke chamber 12. Combustion gas G generated in the combustion chamber 9 is discharged from the smoke chamber 12 through the flue 13.

By covering the heating device 3, the shielding plate 8 forms a jacket-structured first heating area 14 around the heating device 3, into which the heat transfer water W enters. In this embodiment, the shielding plate 8 is formed in a cylindrical shape that surrounds the cylindrical portion 9a of the combustion chamber 9, and the first heating area 14 is formed between the combustion chamber 9 and the shielding plate 8. The heat transfer water inlet 6 opens at the bottom of the first heating area 14, and the steam outlet 7 protrudes in a cylindrical or rectangular tubular shape at the top of the first heating area 14, with its upper end projecting above the heat transfer water W.

The heat transfer water W in the first heating range 14 is heated by the combustion burner 11, generating boiling steam on the outer surface of the combustion chamber 9. However, because it is covered by the shielding plate 8, the subcooling degree (the difference between the saturation temperature of the heat transfer water W on the combustion chamber surface and the temperature of the surrounding heat transfer water) is small, preventing sudden condensation of the steam. Even if an impact noise due to sudden condensation of the steam is generated, the shielding plate 8 reduces the unpleasant noise. The steam generated in the first heating range 14 is then released into the reduced pressure space 4 through the steam outlet 7. Because the steam temperature in the reduced pressure space 4 is lower than the steam temperature generated in the first heating range 14, the steam released into the reduced pressure space 4 is cooled and condensed. However, because the heat quantity per unit volume of steam is smaller than that of liquid, condensation occurs more slowly than when cooled with heat transfer water of the same temperature, and the impact noise can be reduced.

When the heat transfer water temperature in the first heating range 14 becomes high, subcooled boiling also occurs on the outer surface of the shielding plate 8 in the second heating range 15 outside the shielding plate 8. Therefore, the heat transfer water temperature in the first heating range 14 and the heat transfer water temperature in the second heating range 15 are measured, and using these measured values, the combustion amount of the combustion burner 11 is adjusted to achieve a predetermined subcooling degree (here, the difference between the saturation temperature on the outer surface of the shielding plate 8 and the heat transfer water temperature around the outside of the shielding plate 8), and warm-up operation is performed until the heat transfer water temperature reaches 65°C or higher.

Specifically, it includes a first temperature detector 16 that detects the temperature of the heat transfer water inside the shielding plate 8, a second temperature detector 17 that detects the temperature of the heat transfer water outside the shielding plate 8, and a control unit 18 that calculates the temperature difference ΔT between the temperature detected by the first temperature detector 6 and the temperature detected by the second temperature detector 17 and controls the heating device 3 so that the temperature difference ΔT becomes a preset temperature. In this embodiment, the control unit 18 controls the amount of combustion in the combustion burner 11 by controlling the amount of fuel supplied to the combustion burner 11 and the amount of air blown by the blower fan 19.

The inner surface of the shielding plate 8 can be considered to be at the temperature of the first temperature detector 16, but the outer surface of the shielding plate 8 is always cooled by the heat transfer water W in the second heating range 15. Therefore, the temperature detected by the first temperature detector 16 plus a few degrees Celsius can be considered to be the temperature of the outer surface of the shielding plate 8. Therefore, by controlling the temperature difference ΔT, the degree of subcooling in the second heating range 15 can be controlled, suppressing the sudden condensation of steam generated by subcooled boiling and reducing noise.

As a means of reducing noise and shortening warm-up time, as shown in Figure 2, the vacuum water heater 1 of the second embodiment is equipped with double shielding plates 8a and 8b. This forms a first heating area 14 between the combustion chamber 9 and the inner shielding plate 8a, where the heat transfer water W enters; a second heating area 15 between the inner shielding plate 8a and the outer shielding plate 8b, where the heat transfer water W enters; and a third heating area 20 outside the shielding plate 8b. Each of the shielding plates 8a and 8b is formed with a heat transfer water inlet 6a, 6b and a steam outlet 7a, 7b. The principle of noise reduction is the same as above, but because the shielding plates 8a and 8b have a double structure, the combustion area of the combustion burner 11 can be increased, thereby shortening the warm-up time.

In the first and second embodiments described above, subcooled boiling also occurs inside the water tubes 10a, but the water tubes 10a are selected to have an inner diameter (e.g., approximately 53 mm or less) that does not increase the degree of subcooling, and the upper ends of the water tubes 10a are positioned above the surface of the heat transfer water W. This suppresses impact noise for the same reasons as the shielding plate 8 of the combustion chamber 9 described above.

However, if the degree of subcooling cannot be adjusted by selecting the inner diameter of the water tube 10a, the degree of subcooling can be adjusted by making the water tube 10a a double-pipe structure and placing heat transfer water W between the outer tube 10a1 and the inner tube 10a2, as shown in the third embodiment in Figure 3.

In the first embodiment, the first heating area 14 is submerged in the heat transfer water W. However, as shown in a fourth embodiment in Figures 4 and 5, the surface of the heat transfer water W may be located between the upper surface of the combustion chamber 9 and the shielding plate 8 constituting the heating device 3, so that the surface of the heat transfer water W is in the first heating area 14. In the fourth embodiment, the surface of the heat transfer water W is lower than in the first embodiment, so the length of the portion of the water pipe 10a that protrudes above the combustion chamber 9 can be shorter than in the first embodiment, making it easier to weld the water pipe 10a to the combustion chamber 9. Furthermore, in the fourth embodiment, the amount of heat transfer water W can be reduced compared to the first embodiment, so that the warm- up operation can be completed more quickly.

During steady-state operation, the heat transfer water boils vigorously, and if this boiling water splashes onto the heat exchanger 5, it will impede the condensation heat transfer of the water vapor. Therefore, the heat exchanger is generally placed at a certain distance from the surface of the heat transfer water W to avoid being affected by the boiling water, or the heat exchanger 5 is designed to be larger to take into account the reduction in heat transfer caused by splashing of boiling water, and in either case the tube body (sealed container) will be larger.

As shown in Figure 5, by arranging the steam discharge port 7 in a position that avoids being vertically below the heat exchanger 5, it is possible to prevent the heat transfer water W from scattering into the heat exchanger 5, and the sealed container 2 and heat exchanger 5 can be designed compactly.

The present invention should not be construed as being limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

For example, while the heating device is exemplified as a furnace equipped with a combustion burner, it can also be a fire-tube heating device that uses high-temperature exhaust gas emitted from an engine or the like as a heat source, or an electric heater instead. Figure 6 is a longitudinal front view showing a fire-tube heating device 3 as a fifth embodiment, and Figure 7 is a cross-sectional view taken along line VII-VII in Figure 6. The fire-tube heating device 3 is composed of a fire-tube group 21 consisting of multiple fire tubes 21a through which high-temperature exhaust gas Ga emitted from an engine or the like passes, and this fire-tube group 21 is entirely covered by a shielding plate 8. The amount of heat input to the fire-tube heating device 3 can be controlled by adjusting the flow rate of the inflowing exhaust gas Ga using a control valve or the like (not shown).

In addition, while the above embodiment illustrates a vacuum water heater with a water tube structure and a combustion chamber, the furnace tube that constitutes the heating device can also be covered with a shielding plate in a vacuum water heater with a flue and smoke tube structure.

In addition, in the above embodiment, the shielding plate has one heat transfer water inlet and one steam outlet each located in the center, but their positions can be changed appropriately, taking into account areas where boiling is likely to occur (for example, areas close to the flame) and areas where steam is likely to accumulate (for example, upper areas close to the flame), and multiple outlets can also be provided. The steam outlet can also be provided in areas where steam is likely to accumulate, such as the corners between the shielding plate 8 and the sealed container 2. Alternatively, the steam outlet can be provided above the area where boiling is difficult, and the heat transfer water inlet can be provided below the area where boiling is likely to occur, to create a steam flow in the first heating range and promote heat absorption by the heating device.

In addition, while the shielding plate in the above embodiment has a double structure, it can also have a multi-layer structure such as triple or quintuple.

REFERENCE SIGNS LIST 1 Vacuum water heater 2 Sealed container 3 Heating device 4 Reduced pressure space 5 Heat exchanger 6 Heat transfer water inlet 7, 7a, 7b Steam outlet 8, 8a, 8b Shielding plate 9 Combustion chamber 10 Water tube group 10a Water tube 11 Combustion burner 14 First heating range 15 Second heating range 16 First temperature detector 17 Second temperature detector 18 Control unit 20 Third heating range W Heat transfer water

Claims (7)

a sealed container whose interior is maintained at a pressure lower than atmospheric pressure and in which heat transfer water is sealed;
a heating device that is submerged in the heat transfer water and heats and evaporates the heat transfer water;
a heat exchanger disposed in a reduced pressure space above the heat transfer water, for heating water circulating therein by indirect heat exchange with steam of the heat transfer water;
a shielding plate that covers the heating device and has a heat transfer water inlet on a lower side and a steam discharge port that opens above the water surface of the heat transfer water on an upper side;
A vacuum water heater equipped with: a first temperature detector for detecting the temperature of the heat transfer water inside the shielding plate;
a second temperature detector for detecting the temperature of the heat transfer water outside the shielding plate;
a control unit that calculates a temperature difference between the temperature detected by the first temperature detector and the temperature detected by the second temperature detector during a warm-up operation , and controls the heating device so that the temperature difference during the warm-up operation becomes a set temperature;
The vacuum water heater according to claim 1 , further comprising: the heating device has a combustion chamber and a group of water tubes that vertically penetrate the combustion chamber,
An upper portion of the water tube of the water tube group is located above the water surface of the heat transfer water.
The vacuum water heater according to claim 1. A vacuum water heater as described in claim 1, wherein the surface of the heat transfer water is located between the heating device and the shielding plate. A vacuum water heater as described in claim 1, wherein the steam discharge port is disposed in a position that avoids being vertically below the heat exchanger. A vacuum water heater as described in claim 1, wherein the shielding plates have a multi-layer structure and are configured so that the heat transfer water can flow between each shielding plate. 4. The vacuum water heater according to claim 3, wherein the water pipe has a double pipe structure.