FOR

WATER HEATER

FIELD OF THE INVENTION

This invention relates to energy efficient water heaters, especially for the storage type water heater used on combustion heat sources. BACKGROUND

The water heater is a basic appliance in our daily lives. People use hot water for taking showers, washing hands, cooking food, washing foods, washing dishes, etc; space heating in houses for both humans and farm animals, and in many industrial applications. The hot water supply to a household is typically provided by a storage tank water heater. In a storage water heater, heat is provided to a tank of water by electrical heating elements or by combustion flames. Despite the increased efficiency of the electrical water heater, the combustion type heating water heater is still very popular. In the areas without access to electricity, people use wood, tree leaves, natural gas, liquid propane gas or other combustible material as a heat source. A primitive form of water heater is a large pot. To improve efficiency it is proposed by US patent 1706416 to construct a water heater by having a flame tube going through a water tank. Although there have been many improvements found in water heaters since then, such a configuration is still the basis for most of the storage tank water heaters, ranging from the basic water heater to more advanced condensing water heaters.

However this configuration of the water heater is not the optimal design from a heat transfer point of view. Therefore the water heater tends to be tall to have sufficient efficiency. This can be an issue where space is limited for installing the water heater.

As the water is heat up to desired temperatures, the water is stored in the water tank, waiting for the demand of hot water. Therefore, there is need to insulate the water heater from losing heat. A tall format of water heater takes more insulation material to achieve good thermal insulation to reduce heat loss. Therefore there is an inherent need to further improve the current water heater design.

It is objective for the current invention to provide heat exchange designs for better heat transfer for storage tank water heater. It is another objective to provide improved designs of the tank to reduce the heat loss, and therefore reduce the amount of insulation material required. It is another objective to provide a means to embed the burner inside the water heater tank to improve the capture of the heat from the flame.

It is another objective to provide an energy efficient vessel to cook large quantities of liquid based food.

BRIEF DESCRIPTION OF THE FIGURES

Objectives and advantages disclosed herein will be understood by reading the following detailed description in conjunction with the drawing, in which:

FIG.l is a perspective view of a conventional water heater.

FIG.2 is a perspective view of a water heater with a rectangular flame flue.

FIG.3 is a perspective view of a water heater with a rectangular flame flue and baffles. FIG.4 is a perspective view of a water heater with an embedded burner assembly.

FIG.5 is a perspective view of a water heater with a wavy flame flue.

FIG.6 is a perspective view of a stock pot with a flame flue.

DETAILED DESCRIPTION

Although the following detailed description contains many specifics for the purpose of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alternations may be made. A typical water heater has a storage tank to hold water and a burner under the tank to provide heat to heat up the water. Since the invention of US patent 1706416, storage water heaters are designed with a flame flue running upward through the water to provide good heat transfer to the water. The flue is a circular pipe of about 4 inches to 6 inches. Some designs of water heaters have coiled piping that improves the path to improve efficiency. Some designs even utilize the condensation of the hot flame flow to achieve a high degree of efficiency. However, fundamentally, the circular flame flue design is not the most efficient design in term of heat transfer capability.

Figure 1 shows a typical design of a storage tank water heater. Water heater 100 consists of a water storage tank 110, a flame flue 120 and a burner 130 placed under the flame flue. Burner 120 can run natural gas, and other fuels, or it can be replaced simply by burning woods and other combustion sources. The heat from the flame will heat up the dome base 140 of the storage tank. As the flame travels upward through the flue 120, the heat will transfer to the wall of the flue and further heat up the water inside the tank. Materials used to make the water heater typically are stainless steels, steels, aluminum, copper, and specially coated versions of them.

Typically the water tank is cylindrical in shape, and the flue is also a circular pipe.

Normally the cylindrical water tank is thermally insulated from the outside air by an insulation layer 150. The circular cross-section design of the water tank 120 is good for preventing heat loss from the side wall, because for a given cross-sectional area, the circular shape has the smallest peripheral circumference compared with other cross- sectional shapes, such as a square or rectangle. Therefore for a given volume of water to store, the cylindrical tank requires less tank material and insulation material than a rectangular or square one.

However, the same principle will apply to the flame flue 130. Because the conventional flue is designed with a circular cross-section as well, it provides the smallest surface area for heat transfer for a given cross-sectional area and the length of the flue. The lack of efficient heat transfer from the flame flue to the water forces the water tank to be made taller than necessary. A taller water tank requires more tank wall material and insulation material, and occupies more space. In some situations where the ceiling space is limited, for example, when installing a water heater under the staircase, a tall water tank may pose difficulty in installation. Mathematically, if we define circumference factor that reflects the effectiveness of a particular cross-sectional shape for heat transfer. Let this be the ratio between the square of the perimeter to the cross-sectional area; for example, for a circle the ratio is 4π, and for an n-sided polygon the ratio is 4n * tan (^ . π is a mathematical constant defined as the ratio of a circle's circumference to its diameter. In general, the larger the circumference factor, the more suitable the cross-sectional shape is for heat transfer. Therefore, it is proposed here to use an optimized cross-sectional shape for the flame flue for more energy efficient heat transfer from the flame to the water. One simple embodiment is shown in FIG 2: Water heater 200 consists of a water tank 210, a flame flue 220 and a gas burner 230. The flame flue 220 has a rectangular cross-sectional area. The long side of the rectangle 221 has a length of about 10 times of the length of the short side 222. The shape of the burner 230 has a linear format rather than the conventional donut shape. The flame from a linear burner will couple well with the rectangular flame flue. The heat transfer coefficient of a rectangular flame flue is calculated to be about 1.5 times that of a circular flue for a given cross-sectional area. At this situation, the circumference factor is 48.4 way larger than the 12.57 of a circular shape. Using this configuration, the water tank can be made shorter while keeping the same efficiency. A shorter tank will have a smaller outer surface area for heat loss, therefore requiring less insulation material. Other cross- sectional shapes can be used as well such as a triangle shape, star shape, and other concave polygons.

A linear design is also good for completeness of combustion. For a conventional ring burner where the flame ports are arranged in a ring structure, the air supply comes inward in a radial direction. For the flame along the ring, the air supply comes only from the inward direction. On the other hand, in the linear flame pattern, the flame along the linear line will receive air from both sides of the line. Therefore, the linear flame will have better air supply for better combustion. This will improve the exhaust air quality, and will extract more energy from the fuel.

To further improve heat transfer efficiency, a set of baffles can be placed inside the rectangular flame flue. As show in FIG 3, the water heater 300 consists of a water tank 310, the flame flue 320 and a burner 330. The water tank in thermally insulated by insulation layer 340. To improve the heat transfer, a set of support baffles 321 is placed inside the flue. The baffle 321 is a set of metal plates that connects the two larger walls of the flame flue. By connecting the two large walls, the support baffles provides support to the two larger walls of the flame flue against the water pressure in the water tank. The support baffle is oriented such that it will displace the flame flow from the center of the flue to the two ends of the narrow rectangular cross-section, to take full advantage of the wall's large surface area for heat transfer. Also, the presence of the baffles can create turbulence to further improve the heat transfer. Alternatively a baffle set 322 is arranged such that it pushes flame flow to flow zig-zag upwards along the large walls of the flame flue 320. Baffles can have holes and other features to create turbulence. Different other types of baffles can be used to enhance the flame interaction with the wall improving heat transfer. Furthermore, fins or serpentine posts can be put on the walls and the bottom of the water tank to further improve the heat transfer.

As seen in FIG 1, burner 130 is typically placed under the water tank. When the burner is on, there will be heat transferred downwards and sideways that is not transferred to the water. This reduces the efficiency of the water heater. To improve this, a linear flame configuration can be designed like in FIG 4. The water heater 400 consists of the cylindrical water tank 410 and a rectangular flame flue 420. The whole burner assembly unit 450 is embedded in the water tank 410. There is water around the burner assembly 450. Therefore the heat emitted from the burner 430 will be transferred through the wall 450 of the burner assembly unit to the water without losing much heat to the outside environment. This arrangement can further improve the efficiency of the water heater.

As an alternative design, the flame flue can be curved so that the flame path is longer.

Shown in FIG.5, the water heater 500 consists of a water tank 510, flame flue 520, and burner 530. The cross-section of the flame flue 520 is also rectangular with aspect ratio 10: 1. Instead of being straight in its path going upward, the flue 520 is curved. As the flame travels up the flue, it moves along the curved path of the flue which has a longer path than the straight flue, experiencing more surface area to transfer heat to the water. Preferably, the curve of the path will provide a 50% increase of flue length over the straight flue.

A shorter version of the water heater can be converted to a stock pot for cooking liquids for restaurants. The stock pot will be a conventional stock pot with a flame flue through the center. The cross-section of the flame flue is an eccentric ellipse, and the lid of the stock pot will have an opening for the gas to exit though. There will be a set of handles attached to the wall of the pot. FIG 6 is a cookware designed in such a way. A stock pot 600 is built such that there is a flame flue 620 is connected to the base of the pot 610 that extends to over the top rim of the pot 610. The cross-section of the flame flue is an ellipse with the long axis of the ellipse to be 10 times the length of the short axis. As the pot sits on the stovetop a portion of the flame is coming through the flame flue to have heat exchange via wall of the flame flue. The opening area of the flame flue will need to be optimized to maximize the overall heat transfer from the bottom of the pot and the wall of the flame flue. Similarly, the flue of the stock pot can be a rectangular shape. There can be baffles placed inside the flue to increase the interaction of the flame flow with the flue wall.

Similarly to the energy efficient cookware we have designed in US patent 8037602B2, fins or serpentine posts can be used to put on the bottom of the cookware and inside of the flame flue to further increase the surface area.

The flue can be made easily by extrusion, and fins can be formed during the extrusion. The pot is made by deep drawing. A rectangular hole is punched on the bottom of the pot. The flue and the pot can be attached with welding, brazing or other advanced watertight fitting methods.

It will be valued to those skilled in the art that the preceding examples are exemplary and not limiting. It is intended that all permutations, enhancements, equivalents, and

improvements thereto, that are apparent to those skilled in the art, upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present disclosure. It is therefore intended that the following appended claims include all such modifications, permutations and equivalents that fall within the true spirit and scope of present disclosure.