Heat exchange – With protector or protective agent
Patent
1989-09-19
1990-05-29
Davis, Jr., Albert W.
Heat exchange
With protector or protective agent
165 71, 16510427, 138 27, 137 59, 137593, 237 80, F28F 1700, E03B 710
Patent
active
049287540
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a heat exchanging apparatus for circulating or conducting heated water through conduits swept by air to be heated. The invention relates particularly to improvements of a heat battery in the form of pipes in a duct leading air from outside to inside of a building, and to improvements of radiators.
Installations of water-air heat exchangers of different kinds, heat batteries in air conditioning equipment, ordinary water radiators etc often have problems with pipe ruptures due to freezing in low air temperatures. Attempts to achieve reliable protection against pipe rupture due to freezing in such installations have not been successful so far. The heavily dimensioned pipes have not been able to withstand the heavy compression forces occurring when ice forms in the piping system. Pipe rupture in heat batteries of the type illustrated in FIG. 1 usually occur at the pipe bends, and for preventing freezing of these portions, they have been further insulated against the cold air flowing through the battery. These measures have been unsuccessful, however, for a reason which will be clearly apparent below.
Attempts have also been made to sense the temperature at the places where pipe rupture usually occurs. When the temperature approaches 0.degree. C. at the sensors, the flow rate is automatically increased by a regulating unit. These attempts have also been unsuccessful for the same reason which will be explained below.
Within the industry, these problems with rupture due to freezing have been regarded for some time as more or less insoluble.
The present invention thus has the object of achieving a heat exchanger of the types mentioned above, that is heat batteries and radiators, which is protected against pipe rupture, should ice formation occur in the piping. The heat exchanger should be reliable, maintenance-free and function without electronic or other sensors. This is achieved by a heat exchanger of the type described in the opening paragraph of claim 1 and having the features set forth in the characterizing clause thereof.
The solution which the present invention signifies is partly based on a discovery completely incompatible with the generally accepted understanding as to how pipe rupture during freezing occurs, and on which all the previous attempts to provide a satisfactory solution have been based. Tests carried out by me under controlled conditions in a research laboratory have namely shown that pipe rupture during freezing does not occur at the ice plug formd, but at a part of the pipe where the water is not yet frozen. The pipe rupture customarily occurs due to the increasing pressure in the still unfrozen water due to a growing ice plug somewhere else in the pipe. This explains why temperature-controlled frost-protection means have not been able to solve the problem. It is not possible to measure the temperature everywhere in the circulation system. The pipe rupture occurs where the water is warmest, and it is here that temperature sensors have been placed. Reliable temperature sensing in the unprotected heat-exchanging parts of the pipes is not possible due to the widely varying temperatures between the pipe fin surfaces, which are subjected to flowing cold air and the interior of the pipe. Furthermore, the sensors have a reaction time which is too long in the rapid freezing process.
This situation, that pipe rupture takes place at a part of the pipe where the water has not yet frozen, has avoided discovery due to another scarcely noted property of water, namely that its freezing point falls with increasing pressure. Growing ice plugs increase the pressure in the as yet unfrozen part, simultaneously as the temperature can fall below 0.degree. C. in the still unfrozen water. When the pipe subsequently bursts, the pressure falls suddenly and the freezing point is instantaneously raised to 0.degree. C. again, the water immediately freezing to ice. In most cases the repairman is confronted with a protruding ice plug at the place of rupture, and draws the conclusion that
REFERENCES:
patent: 1323955 (1919-12-01), Bohannon et al.
patent: 2238952 (1941-04-01), Stacey, Jr.
patent: 2301433 (1942-11-01), McElgin
patent: 2954213 (1960-09-01), Pellegrini
patent: 3319657 (1967-05-01), Nyiri
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