1. Field of the Invention
The present invention relates to a heat exchanger which can be used, for example, in the freezing chamber of a refrigerator and, more particularly, to a heat exchanger having an enhanced cooling power to enable the freezing chamber to serve as a rapid freezing chamber.
In a refrigerator of the type broadly used, e.g., the chilled air circulation type, a cooling chamber is disposed at the innermost portion of a freezing chamber. The cooling chamber accommodates various parts such as a primary cooler, blower and so forth. In operation, air is forcibly supplied by the blower to the primary cooler and the air chilled by the primary cooler is discharged from the chilled air outlet provided at the upper part of the cooling chamber. The chilled air is introduced through a chilled air inlet provided at the lower part of the freezing chamber into the cooling chamber and is blown again from the chilled air outlet. In this type of refrigerator, a considerably long time is required for the cooling because the freezing chamber is cooled solely by the circulation of the chilled air. In fact, it takes about two hours for the water of normal temperature in a freezing pan placed in a refrigeration chamber to be frozen into ice.
Various improvements have been proposed up to now for shortening the cooling time. For instance, Japanese Utility Model Publication No. 52-52684 proposes to provide a heat exchanger, which is referred to as a "secondary cooler", in addition to the primary cooler mentioned above. This secondary cooler consists of a hollow vessel composed of a horizontal portion and a riser portion and filled with a refrigerant. The riser portion is held in contact with the primary cooler while the horizontal portion constitutes the bottom of a rapid freezing chamber. This type of refrigerator, however, can provide only a small heat exchanging efficiency because the area of contact between the refrigerant and the wall of the hollow vessel is limited. In addition, it is difficult to absorb the heat from the cooling object and to discharge the absorbed heat at a high efficiency because the horizontal portion for absorbing the heat and the riser portion for discharging the heat have an identical structure.