Heat exchange – With timer – programmer – time delay – or condition responsive... – Temperature responsive or control
Reexamination Certificate
1998-10-05
2001-02-20
Lazarus, Ira S. (Department: 3743)
Heat exchange
With timer, programmer, time delay, or condition responsive...
Temperature responsive or control
C165S098000, C165S096000, C165S299000
Reexamination Certificate
active
06189608
ABSTRACT:
TECHNICAL FIELD
The invention relates to a cooling apparatus comprising an air-cooled heat exchanger, a plurality of louvres to control a cooling air flow passing the heat exchanger, a mechanism for operating the louvres and means for actuating the operating mechanism according to temperature of the heat exchanger.
BACKGROUND ART
In the industry and at power stations, cooling apparatuses, in which the medium to be cooled can be of a liquid or vaporous phase, are well known.
The known cooling apparatuses primarily used in large-size cooling systems of power stations comprise an air-cooled heat exchanger having a plurality of finned tubes connected in parallel, a plurality of air-side louvres, a mechanism for operating the louvres and means for actuating the operating mechanism according to temperature of the heat exchanger.
According to the current practice, the purpose of louvres used in cooling apparatuses is to control heat dissipation and to provide frost protection of heat exchangers. In the case of power station cooling apparatuses, controlling of heat dissipation is a secondary function, proven by the fact that louvres are generally not applied under climatic conditions where no frost risk prevails.
However, frost protection is extremely important because the finned tubes represent extremely large air side heat transfer surface, and heat dissipation is significant under air flow conditions. Thus, if the medium flowing in the finned tubes is overcooled or its flow stops, the medium could freeze within 1 to 2 minutes, leading to serious damage of the heat exchanger. By closing the louvres, the flow of cooling air can be reduced or totally stopped, thereby freezing can be avoided.
The number and size of louvres used in power station practice vary in an extremely wide range. As an example, in the case of a cooling tower associated with a 200 MW steam turbine, approximately 120 heat exchanger units, each having 60 louvres of 2.5×0.25 m size are required. The louvres are rotatably mounted adjacent to each other on frames in front of the heat exchangers in the direction of the cooling air flow.
In the current practice, these louvres are actuated by an electric motor or by hydraulic or pneumatic systems. The actuator is linked to the louvres by an operating mechanism, preferably a linkage of bars. In order to ensure a reliable protection of high value heat exchangers, a large number of temperature sensors, an associated transmitter and cable system as well as electric or electronic control equipment have to be used.
For ensuring a reliable protection complicated and costly detector and control system is required because it is difficult to identify unambiguously the temperature of medium flowing in heat exchangers. This depends on the location of the relevant finned tube in relation to the air flow direction, on the uniformity of the distribution of the medium to be cooled and also on other factors. Since the purpose of louvres is to ensure frost protection of heat exchangers, within a given group of finned tubes always the lowest temperature is to be determined for the medium, and the louvres are to be operated accordingly.
Another drawback of the known solutions is that it is difficult to ensure that the power required for operating the louvres is safely available, because the most critical condition from the aspect of frost risk could arise exactly at the time of operational disturbances and power breakdowns.
DISCLOSURE OF INVENTION
The object of the invention is to create a cooling apparatus having a simple and cost efficient louvre actuating, which also ensures safe operation on critical conditions.
The basic principle of the louvre actuating of the cooling apparatus according to the invention is that the actuating is carried out by a properly designed mechanism operated or controlled by the thermal expansion of the finned tubes of the heat exchanger and that of the frame. Thereby, the safety of operation does not depend on an external power supply.
In the case of aluminium finned tubes, because the aluminium's thermal expansion coefficient is high and because long finned tubes of 15 to 25 m length are involved, thermal expansion could even reach 10 to 20 mm under normal operating conditions. By means of the mechanism to be described later, it can be ensured that if the medium approaches a dangerously low temperature from the aspect of freezing, e.g. +10° C., the louvres are closed as a result of the contraction of the finned tubes, and when reaching the operating temperature, e.g. +45 to +50° C., the finned tubes expand and the louvres are fully open.
Thus, the invention is a cooling apparatus comprising an air-cooled heat exchanger, a plurality of louvres to control a cooling air flow passing the heat exchanger, a mechanism for operating the louvres and means for actuating the operating mechanism according to temperature of the heat exchanger, wherein the actuating means comprise a bar having a first end and a second end and being of a material having a considerably lower thermal expansion coefficient than that of the heat exchanger, said bar being attached by its first end substantially at a first end of the heat exchanger, and means for controlling the position of the operating mechanism in dependence on a difference in displacements of the second end of the bar and a second end of the heat exchanger due to the thermal expansion of the bar and that of the heat exchanger.
In this way a simple and cost efficient louvre actuating is achieved, which can be fitted on each heat exchanger of a cooling tower, and thereby the heat exchangers close or open the associated louvres independently of each other as a function of the temperature of the medium flowing in them. Thus, regardless of wind direction and a non-uniform distribution of the medium flowing in the heat exchangers, each heat exchanger of a cooling tower can safely be protected from freezing.
The heat exchanger preferably comprises upward finned tubes, said first end of the heat exchanger is at bottom ends of the finned tubes and the bar is arranged substantially parallel to the finned tubes.
In a preferred embodiment the heat exchanger is made of aluminium and the bar is made of invar alloy having practically zero thermal expansion coefficient. In this way the displacement difference will be relatively high.
The louvres are preferably rotatably mounted adjacent to each other on a frame placed in front of the heat exchanger in the direction of the air flow and the operating mechanism is a linkage of bars comprising an operating bar and rotating arms connected to the louvres.
Preferably, the linkage of bars further comprises a linkage head hinged to the operating bar, said linkage head comprising a slot for a bolt connecting the controlling means and the linkage of bars, said slot allowing further displacement of the bolt in a direction corresponding to a closing of the louvres after the louvres have reached their closed end position.
In another preferred embodiment the frame comprises a limit stop for the linkage of bars to stop an opening of the louvres at an opened end position, and in the linkage head there is a spring support for the bolt for allowing further displacement thereof in a direction corresponding to the opening of the louvres after the louvres have reached their opened end position.
The controlling means are preferably a two-armed controlling lever rotatably fixed by a bolt in a support attached to the second end of the heat exchanger, the controlling lever being hinged with its first arm to the second end of the bar and with its second arm to the operating mechanism.
The cooling apparatus preferably further comprises means for adjusting the control of the operating mechanism according to ambient temperature conditions. In this preferred embodiment the frame is fixed substantially at the first end of the heat exchanger, the controlling means are a two-armed controlling lever supported by a roller on a support attached to the second end of the heat exchanger, the adjusting mea
Bodas Janos
Guba Janos
Duong Tho
Energiagazdalkodasi Resvenytarsasag
Lazarus Ira S.
Wright PLLC Dickinson
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