Prior Art
Cooling systems for automobile engines have long been in use wherein the liquid coolant is delivered by a pump to the cylinder block, and directed forward along the row of cylinders to a thermostat. The thermostat controls the flow of the coolant from the engine block to a radiator, where a heat exchange occurs between the coolant and an air flow created by the combined effect of the forward motion of the vehicle and an engine fan.
Also well known are air conditioning systems for automotive engines, wherein a high pressure refrigerant vapor is discharged from a compressor in a superheated state and directed to a heat exchanger known as a condenser. There the refrigerant vapor is condensed through a heat exchange with a liquid coolant or the surrounding atmosphere. The liquid refrigerant is collected in a receiver in liquid communication with a thermostatic expansion valve. The valve controls the flow of the liquid refrigerant to a heat exchanger known as an evaporator, where a transfer of heat occurs between the refrigerant and the space to be refrigerated. Vaporized refrigerant then is supplied to the suction side of the compressor where the cycle is repeated.
A recurring problem in automotive engines is the overheating of the engine and lubricants, particularly under load conditions including air conditioning and the towing of trailers. To overcome the heating problem, the capacity and number of circulation coils of the engine radiator has been increased, and a bottom tank has been added to the radiator to accommodate an interchange of heat between the coolant and the oil. Under load conditions, however, a further problem has been encountered. The engine or transmission oil may impart excessive heat to the coolant, thereby overheating the engine.
A further improvement of transmission and engine oil cooling systems has been the addition of air cooled heat exchangers. Typical of these are those disclosed in U.S. Pat. No. 2,502,554 to Bonanni; U.S. Pat. No. 3,334,704 to Geherke; and U.S. Pat. No. 2,554,437 to Alexander. The Bonanni patent discloses an oil cooling apparatus including an air cooled heat exchanger and a supplemental fan mounted forward of the engine radiator. The patents to Alexander and Geherke disclose an air cooled heat exchanger for cooling engine oil which is mounted forward of the engine radiator. Each of these systems has alleviated but not satisfactorily elminated the overheating problem.
In each of these systems, the heat exchanger is composed of a plurality of tubes or a single continuous tube through which the fluid is directed. Cooling fins are attached to the outer surface of the tubes and heat conducted from the fluid to the tube is carried into the fin and dissipated to the surrounding atmosphere. To improve this heat dissipation process, rigid cores have been inserted into the tubes to assist in the transfer of heat from the fluid carried in the tube to the tube's surface.
These inserts have generally taken the form of coiled wire or cross plates with the longitudinal edges of the plates engaging the inner wall of the tube. Wire inserts have not been very effective in that the wire is positioned near the wall of the tube and therefore does not assist in the transfer of heat from the fluid moving in the center of the tube to the tube wall. Because of the close tolerances which must be maintained in order to insure continuous contact between the edges of the plate inserts and the inner wall of the tube, heat exchangers incorporating these inserts have not been economical to produce. Where the tolerances required to assure contact have not been maintained, these inserts have not provided the heat exchange properties for which they are intended.