1.  Field of the Invention
This invention relates to household refrigerators of the type in which an above-freezing and a below-freezing storage compartment are cooled by an evaporator positioned outside the compartments and more particularly with the arrangement for linking the evaporator conductively as well as convectively to the below-freezing and fresh food compartment. 
2.  Description of the Prior Art
Many present day household refrigerators include a compartment maintained at a below-freezing temperature for the storage of frozen foods and a second compartment maintained at an above-freezing temperature for storage of fresh foods.  In many such refrigerators, an evaporator for providing cooling for both the frozen food compartment and the fresh food compartment is positioned outside both compartments and air is circulated over the evaporator and then through the compartments to provide for cooling thereof.  The evaporator itself is maintained at a temperature substantially below freezing.  In order to maintain the greatly differing temperatures required in the two compartments, a substantially greater portion of the air flowing over the evaporator is directed to the frozen compartment than to the fresh food compartment.  For example, approximately 90% of the air may be directed to the frozen food compartment. 
Much more frequent access is usually required to the fresh food compartment than to the frozen food compartment.  Particularly, in warm and humid weather, such frequent door opening causes entry into the fresh food compartment of air having a substantial amount of moisture therein.  When this air is circulated over the evaporator, which may be at a temperature of -5.degree.  F., for example, the moisture in the air is deposited as frost on the evaporator.  This deposition of frost on the evaporator has two adverse effects on the efficient operation of the refrigerating system.  First, the frost, by providing an insulating coating over the evaporator, reduces the heat transfer thereby decreasing the cooling effectiveness of the evaporator.  Secondly, in a refrigerator of the type here under consideration, when the evaporator is positioned in a confined passage and air is circulated over the evaporator and then to the storage compartments, the build-up of frost progressively restricts the space for flow of air through the passage and thereby further decreases the effectiveness of the refrigerating system. 
A number of arrangements have been proposed in the prior art for reducing the rate of accumulation of frost on the evaporator employed in refrigerators of this type in an effort to reduce or solve the above problems.  In several of these arrangements, an auxiliary evaporator is provided upstream of the evaporator so that the moist circulating air first comes in contact with the auxiliary evaporator and deposits moisture thereon, thereby reducing the amount of frost accumulation on the main evaporator.  In some such arrangements, the frost on the auxiliary evaporator may be removed without at the same time defrosting the main evaporator. 
In other prior art arrangements, a single evaporator is employed but formed in two sections, the first of which has spaced fins spaced relatively widely and the second of which has fins spaced more closely together.  In such arrangements, the air returning from the fresh food compartment is first caused to flow over the first section and then over the second section of the evaporator.  Since the air first strikes the first section, the frost tends to deposit more heavily thereon and since the spacing between the fins is greater, the frost has a lesser effect in blocking flow of circulating air over the evaporator. 
In another prior art arrangement, air returning from the fresh food and frozen food compartments is caused to flow through two adjacent passages arranged in heat exchange relationship.  This causes a reduction in the temperature of the air returning from the fresh food compartment and causes the moisture therein to be deposited in one of the passages before reaching the evaporator, thereby reducing the amount of frost forming on the evaporator.  The frost depositing in this passage is later removed by defrosting. 
In still another prior art arrangement, the evaporator is mounted in heat exchange relationship to a plate.  The evaporator and plate are arranged in one passage.  A second passage is arranged adjacent the opposite side of the plate.  Moist air returning from the fresh food compartment is caused to circulate through the second passage in contact with the plate so that moisture in this air deposits on the plate as frost before the air reaches the first passage and the cooling element. 
In accordance with the present invention, a construction is provided which reduces the amount of frost forming on the evaporator, and which accomplishes this result in a simpler and more effective manner and with advantages not present in the prior art type arrangement discussed above. 
Accordingly, it is an object of this invention to provide a two-temperature, two-compartment refrigerator including an improved arrangement for air circulation. 
It is another object of this invention to provide in a refrigerator of this type an improved air circulation and frost deposition arrangement which significantly reduces the amount of frost deposited on the evaporator and materially reduces interference with the circulation of air. 
It is an object of this invention to provide an arrangement whereby the evaporator is linked conductively, as well as convectively, to the fresh food compartment.