Stoves and furnaces – Stoves – Cooking
Patent
1991-10-08
1994-03-22
Dority, Carroll B.
Stoves and furnaces
Stoves
Cooking
126 39J, 126 39K, 126 39R, F24C 300
Patent
active
052954765
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a gas hob. An appliance with such a hob is used for delivering heat to the base of cooking utensils and is known variously as a "hob unit", "boiling top", "hot plate", or "boiling table", being used either domestically or in commercial catering food preparation.
Recent developments of electrically heated hob units have led to the extensive use of ceramic glass cover plates, of a type known as "Ceran", a Trade Mark of SCHOTT GLASSWERKE, OF MAINZ, WEST GERMANY, over the various types of heating elements in use and with the heat being transferred to the pan through the glass by radiation and also by conduction from the glass directly to the base of the pan.
Attempts to utilize gas heating for similar ceramic glass top hobs have been less successful because whilst the advantages of easy cleaning etc, as for instance described in U.K. patent no. 1,419,499, can be achieved, the speed of heating, ease of control and thermal efficiency, when compared to an open flame gas burner used in a traditional type gas hob, are quite inferior.
It has been shown when utilizing tests commonly used to compare gas hobs, as for instance detailed in British Standard 5386 part 3, that thermal efficiencies of only 32% can be obtained with ceramic glass tops, compared to open flame cookers which easily exceed 50%. Similarly when heating speeds were compared, although the ceramic glass gas heated top achieved roughly similar times to electrically heated hobs, it was at best 25% slower than would be accepted for a conventional gas heated hob.
One of the most important functional aspects of a gas hob is its ability to be adjusted quickly and easily to vary the heat input to a wide range of cooking requirements, and this has in the past been seen as a significant advantage for the open flame hob over all others. The amount of heat being supplied can be easily judged by the appearance of the flames.
It is widely known that radiant heating burners will not operate well at gas inputs much less than their optimum, due to flame instability. A minimum heat input no less than 60% of the maximum is the least that can commonly be achieved. It is also widely known that the radiant output of such burners reduces rapidly when their gas input and operating temperature is reduced only slightly. This is due to the reduction in primary aeration when gas pressure is reduced and has led to such partial solutions as multiple injector jets (British patent application GB 2201 506A).
Because of these factors, and because a cooker hob burner must have a very wide range of outputs so that small pans can also be controlled at a low temperature, it has been common practise to use a pulsed on/off system whereby the ratio of burner time on (at full rate) to burner time off sets the heat input.
Since cooker hob burners are usually adjusted to below their maximum heat outputs for most cooking demands, it follows that they are nearly always operating at a much reduced efficiency and that the lower they are set, the lower the efficiency becomes.
When comparing the controllability of various types of hob units, it is found that the ability rapidly to `lose` heat input to the pan is quite as important as the ability to increase heat input quickly. In this respect, since the ceramic glass hob has considerable thermal mass when particularly compared with open flame burners, it is at some disadvantage, although the performance is similar to electronic heated ceramic hobs, which in turn have somewhat poorer performance than conventional tubular element electric heated hobs.
The amount of heat that is transmitted from one body to another is greatly affected by the distance between them. However, with gas burners in closed hobs this minimum is set by the space above the burner necessary for the gaseous products of combustion to escape and also for any secondary combustion air to reach the burner flames. This factor also limits the maximum area burner which can be used.
An object of the present invention is to provide a gas hob burner system which over
REFERENCES:
patent: 2870829 (1959-01-01), Williams
patent: 3606612 (1971-09-01), Reid
patent: 3785364 (1974-01-01), Reid, Jr. et al.
patent: 3843313 (1974-10-01), Helgeson
patent: 3968785 (1976-07-01), Perl
Blue Circle Domestic Appliances Limited
Dority Carroll B.
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