Heat exchange – Regenerator – Checker brick structure
Patent
1982-09-29
1986-06-10
Richter, Sheldon J.
Heat exchange
Regenerator
Checker brick structure
165 34, 165 38, 165 39, 165 40, 165 41, 165 51, 165101, 165102, F28F 1306
Patent
active
045937494
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention pertains to a process for increasing the heat flow density of heat exchangers employing at least one high-velocity gaseous medium, and to a heat exchanger apparatus for undertaking the process.
Because of the decreasing importance of air-cooled automobile engines, there has in recent years been a great decrease in the use of exhaust gas heat for heating the interiors of such vehicles. In vehicles using water-cooled engines, it is simple for the radiator water to be used as a source of energy for interior heating. However, in view of steps being taken for increasing mileage in automobile engineering, there has come to be less and less waste heat from the cooling system of the engine which can be used for this purpose. In view of this, especially in the case of high efficiency engines, it is frequently no longer possible for all the interior and other heating needs of a vehicle to be covered without the use of back-up heating system.
In order to increase the amount of heat transferred by the engine to the engine coolant, a pressure build-up in the exhaust gases has been used. As a result, however, the mileage is decreased, and the temperature of the exhaust gases and the emission of noxious substances is increased. The only source of waste heat which may still be realistically used as a source of energy for such interior heating needs, is the heat of the exhaust gases. If the exhaust gas heat is recovered by a gas-water heat exchanger and thus made part of the heating and cooling system of the vehicle, the mileage and the emission of exhaust gases can be improved because of the increase in the temperature level of the engine.
Some of the earlier shortcomings experienced with exhaust gas heat exchangers, such as cracks caused by thermal stresses and decomposition of the anti-freeze liquid or other engine coolant, have been overcome by providing the exhaust gas-water heat exchanger in a bypass of the exhaust gas system, with the heat exchanger being exposed to exhaust gas only when necessary to get the desired heating effect, and with the water or coolant constantly running through the heat exchanger to keep it at a more or less constant temperature.
The main shortcoming of such heat exchangers has, however, been the dependency of the usable waste heat of the exhaust gas on the engine power output, such power output varying over a wide power ratio of about 200 to 1 in the case of diesel and gasoline engines, for example. Because the amount of usuable heat of the engine coolant is dependent on the engine power output as well, the need for a stepped-up heating effect is highest in those cases in which there is the least usable waste heat of the exhaust gas, thus necessitating large-area and heavy heat exchangers that take up much space. This tendency goes against current attempts to down-size and reduce the weight of a vehicle and the decrease, going hand in hand therewith, in the space on hand. Therefore, since the amount and temperature of the exhaust gas is relatively low at low engine output, it is desirable to increase the exhaust gas heat flow density by other measures.
One way of increasing the exhaust gas heat flow density is to increase the velocity of the exhaust gas contacting the heat exchanger surface. By increasing the velocity of the exhaust gas flow, the heat transmission coefficient (k-value) is increased, which especially in the case of gases is a function of the flow velocity. Also, the price, overall size, and weight of the heat exchanger are greatly dependent on the heat transmission coefficient.
However, there are economic limits to the degree to which the exhaust gas velocity may be increased because such increases in velocity generally mean that the flow cross-sections are decreased. In order to obtain the higher pressure difference necessary for the higher flow velocity, it is necessary for gas blowers and blower drives to be made larger and more complex. Furthermore, the operating costs are greatly increased by the higher use of ene
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