Miniaturization of Freon Compressor: The Bellows Pump

MINIATURIZATION OF THE FREON COMPRESSOR: THE BELLOWS PUMP James L. Kamm University of Toledo Thermal Engineering Company Toledo, Ohio All indicators point to the decade of the 1980's as the years of conservation. Whatever the technological "fix" of the future that will bring endless and sufficient energy supplies, if one exists, it will not be available within this time framework. Conservation is the only immediate answer to maintain energy requirements within increasingly strict guidelines. Conservation comes in two packages. There is the conservation of curtailment1 simply doing without. Turning back the thermostat and reducing the mileage traveled are the two most popular examples. The second packa9e is far more exciting to engineers. It is conservation by innovation; accomplishing the same task but using less energy. Insulatmg and improving EER' s are two well known ex:rmples. Some argue that these initial attempts at efficiency improvement are just the tip of the iceberg. In many cases, total redesign of energy-consuming devices with the ideal goal of zero energy use may in fact create machines that use one-fifth to one-tenth of the power of their predessors. In the domestic appliance sector, the commercially successful example of this redesign is the microwave oven; accomplishing the same goals as the conventional oven but at one-quarter of the power. A household refrigerator that can reduce operating expense up to eightfold has already been projected. Although these future concepts are welcomed, they imply far-reaching consequences for refrigeration component manufacturers. For example, if the present refrigerator is powered by a 1/4 hp compressor and the future model will cut this load by eight times, this implies that a 1/32 hp compressor must be in the offing. Yet the conventional reciprocating compressor does not lend itself to economical miniaturization. This is best evidensed by comparing the present cost of a l/6 hp hermetic compressor with that of a l/12 hp unit. The price is almost the same. Yet who is to say that the reciprocating concept is the best alternative for these microminiature models. The University of Tolerto Climate Control Laboratory is attempting to identify an economical alternative design with the goal of having a 1/32 hp model fit in the palm of your hand and sell at re·tail for less than $20.00. This report documents one such concept. The Bellows Compressor: Very small air compressors often operate on the principle of the bellows. A bellows is a chamber whos volume can be readily increased or decreased. It is made of a synthetic material which expands and contracts causing suction and pressure. Often it is referred to as a vibrating pump. The vibrations are created by the push and pull of an electromagnet. This takes the place of a motor. Pumps of this type are as small as a fish tank aerator, or industrially, can run over ten hp. There adaptability to freon compression systems is documented in the full paper. A survey of the characteristics of commercially available bellows pumps is followed by discussion of the pressure differences achievable by the bellows concept. Suggestions of modifications in design and alterna·tive refrigerants are made to achieve a viable product. The difficult question of whether any hellows material can stand up to the chemical attack of refrigerants for extended periods of time under undesireable temperatures is investigated. Finally, efficiency measurements are made to determine whether the bellows trades off low initial cost for high operating expense.