Liquid heaters and vaporizers – Fluid fuel – Explosion
Patent
1986-03-28
1988-06-14
Favors, Edward G.
Liquid heaters and vaporizers
Fluid fuel
Explosion
122 19, 122161, 236 20R, 236 21R, 236 21B, 431 1, F22B 3100
Patent
active
047504528
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a water heater suitable for use in a domestic hot water supply.
More particularly, the invention relates to an "instantaneous" hot water heater, that is to say a heater of the type which does not have a storage reservoir for heated water but rather is provided with a relatively powerful burner system in order to heat water at a high rate, for instance of the order of say 20 liters per minute which is typical for a domestic hot water supply.
The object of the present invention is to provide a novel form of water heater which is compact and of relatively simple and inexpensive construction. A further object of the invention is to provide a new method of control for the heater.
According to the present invention there is provided a fuel fired water heater comprising a hollow elongated heat exchanger having a water conduit which has a cold water inlet and a hot water outlet, fuel supply means for supplying fuel and air to the interior of said heat exchanger, and means for causing rapidly repetitive ignitions of said fuel within the interior of said heat exchanger.
Preferably, the fuel comprises gas.
In a heat exchanger of the invention, the gas burns or explodes in pulses within the heat exchanger. This mode of combustion ensures that the conditions within the heat exchanger are highly turbulent, thereby avoiding formation of boundary layers adjacent to the surface of the heat exchanger and thus very efficient heat exchange occurs. With the high efficiency of heat exchange, the heat exchanger may be comparatively small and thus the size of the overall water heater can be made correspondingly small.
The invention also provides a method of controlling an instantaneous hot water heater having a heat exchanger and a fuel burner comprising the steps of maintaining the temperature of the heat exchanger at a first predetermined level when there is no flow of water therethrough, sensing the temperature of the heat exchanger, and activating the fuel burner when the temperature sensed falls below a predetermined level consequent upon flow of relatively cold water into the heat exchanger.
Preferably the method includes the steps of generating a control signal related to the difference in temperatures between temperature A and temperature B, where temperature A is the temperature of the water admitted to the cold water inlet and temperature B is the temperature of the water leaving the hot water outlet or the temperature at a point in the water conduit intermediate of the cold water inlet and the hot water outlet, and controlling flow of fuel to the burner in accordance with said control signal.
Preferably, said control signal (hereinafater called the first control signal), is used for initiating flow of gas to a pilot flame and the method includes the step of generating a second control signal related to the difference in temperatures between temperatures A and temperature C where temperature C is the temperature of water leaving the hot water outlet, temperature B being sensed relatively close to said cold water inlet and controlling the main flow of fuel to the burner after ignition of said pilot flame in accordance with said second control signal.
In practice, temperature B is chosen at a point a predetermined distance along the heat exchanger from the cold water inlet, say one quarter of the total length of the heat exchanger whereby said temperature difference will be approximately the same fraction of the temperature differential of the water at the hot water outlet. By sensing the temperature B at a fraction of the distance along the heat exchanger, faster response times are available for controlling flow of gas to the burner compared to the situation where sensing takes place at the hot water outlet.
The invention will now be further described with reference to the accompanying drawings, in which:
FIG. 1 is a schematic cross sectional view through an embodiment of the invention;
FIG. 2 is a cross sectional view taken along the line 2--2;
FIG. 3 is a fragmentary view of part of the heater
REFERENCES:
patent: 2465697 (1949-03-01), Peet
patent: 3469929 (1969-09-01), Haag
patent: 4241723 (1980-12-01), Kitchen
patent: 4465025 (1984-08-01), Schroder
patent: 4488865 (1984-12-01), Davis
patent: 4501261 (1985-02-01), Tsutsui et al.
Favors Edward G.
Vulcan Australia Limited
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