Abstract: An apparatus and method for producing a high performance evaporator tube having a subsurface channel formed between adjacent helical fins with the subsurface channels having alternating closed portions and open pores above the subsurface channels. The fins of the tube are rolled-over toward the adjacent fin and then contacted with a notched disc to form the alternating closed portions and open pores.

Abstract: An apparatus and method for producing a high performance evaporator tube having a subsurface channel formed between adjacent helical fins with the subsurface channels having alternating closed portions and open pores above the subsurface channels. The fins of the tube are rolled-over toward the adjacent fin and then contacted with a notched disc to form the alternating closed portions and open pores.

Abstract: A heat transfer surface for effecting boiling of a high pressure refrigerant in contact with the surface. The surface includes a plurality of spaced apart fins which extend from the side in contact with the boiling fluid. Each of the fins has a base portion joined to the base of the surface and a tip portion. The tip portions are bent over towards the next adjacent one of the fins to define a subsurface channel between adjacent fins. The sub-surface channel has alternating closed sections where a length of the tip portion is bent over by an additional amount so that the length of the tip portion contacts an adjacent fin, and, open sections wherein the bent over tip portion is spaced from the adjacent fin. Each of the open sections has a cross sectional area of from 0.000220 square inches to 0.000440 square inches such that the open sections define alternating re-entrant openings of a size to promote optimum boiling of a high pressure refrigerant.

Abstract: A method for manufacturing a heat transfer surface and the surface so manufactured. The porous surface is produced by flame spraying a metal substrate with a mixture of metallic and nonmetallic powder particles. The surface is then heated, causing the nonmetallic powder particles to oxidize into gases which diffuse from the surface, leaving voids where the nonmetallic powder particles were located. The voids provide nucleate boiling sites for a liquid being heated by the surface.

Abstract: A high-performance heat transfer tube for an evaporator of an air-conditioning or refrigeration system is formed on a grooved mandrel that has a sufficient number of grooves, such as 60 to 90 for a 5/8 inch tube, to produce a small-pitch internal rib enhancement. The small pitch ensures that the spaces or grooves between ribs are about two to five times the characteristic film thickness of the refrigerant liquid on the inside of the tube. This construction permits use of a thinner tube wall starting blank without loss of strength. Lands or unworked portions can be left at the tube ends to facilitate flaring into a tube sheet.

Abstract: A high-performance heat transfer tube for an evaporator of an air conditioning or refrigeration system is formed on a grooved mandrel that has a sufficient number of grooves, such as 60 to 90 for a 5/8 inch tube, to produce a small-pitch internal rib enhancement. The small pitch ensures that the spaces or grooves between ribs are about two to five times the characteristic film thickness of the refrigerant liquid on the inside of the tube. This construction permits use of a thinner tube wall starting blank without loss of strength. Lands or unworked portions can be left at the tube ends to facilitate flaring into a tube sheet.

Abstract: A high performance heat transfer tube for use in the condenser for an air conditioning or refrigeration system is formed on a grooved mandrel which has a sufficient number of grooves i.e., thirty six to forty eight, with a suitable helix angle, such as thirty degrees, and a sufficiently small pitch, such as 0.10 inches or less, so that a Moire imprint is avoided in the external fin enhancement. This makes the fin height uniform over the exterior of the tube, which results in an increase in condenser efficiency.

Abstract: An apparatus for measuring the surface pore size in an externally enhanced evaporator tube. Basically, the apparatus includes a pressure housing and gage that are sealingly engagable around a portion of the surface of the enhanced tube, so that fluid pressure flows into the housing and then through the pores and subsurface channels on the tube and then to the outside of the housing. The pressure drop across the pores and subsurface channels of the tube relates to the size of the pores.

Abstract: A porous coated enhanced evaporator tube and a method for producing the tube. The porous coating of the tube is applied by arc spraying two dissimilar metals on a tube and then etching the tube so that only one of the metals is etched out, and a porous surface, having voids where the etched out metal is developed. The voids form subsurface channels which provide nucleate boiling sites.

Abstract: A high performance heat transfer tube for use in the condenser of an air conditioning or refrigeration system is formed on a grooved mandrel which has a sufficient number of grooves i.e., thirty six to forty eight, with a suitable helix angle, such as thirty degrees, and a sufficiently small pitch, such as 0.10 inches or less, so that a Moire imprint is avoided in the external fin enhancement. This makes the fin height uniform over the exterior of the tube, which results in an increase in condenser efficiency.

Abstract: An apparatus for producing a high performance evaporator tube having a subsurface channel formed between adjacent helical fins with the subsurface channels having alternating closed portions and open pores above the subsurface channels. The fins of the tube are rolled-over toward the adjacent fin and then contacted with a notched disc to form the alternating closed portions and open pores.

Abstract: A porous coated enhanced evaporator tube and a method for producing the tube. The porous coating of the tube is applied by arc spraying two dissimilar metals on a tube and then etching the tube so that only one of the metals is etched out, and a porous surface, having voids where the etched out metal is developed. The voids form subsurface channels which provide nucleate boiling sites.

Abstract: A method of determining the average size of a plurality of pores on the external surface of an enhanced tube having subsurface channels connecting adjacent pores. A pressure measurement apparatus is positioned on a portion of the enhanced tube surface and regulated air supply pressure is blown into the pressure measurement apparatus whereby a portion of the air pressure escapes through the pores and subsurface channels. Accordingly, the difference between the supply pressure and the pressure lost across the pores and subsurface channels is a measurement of the pore size which correlates to the boiling heat transfer coefficient of the tube.

Abstract: A low leakage varistor which is resistant to the high temperature, corrosive conditions encountered during assembly of such devices includes a protective layer disposed on the surface of the varistor body between first and second, spaced-apart electrodes. Both, varistors with electrodes on opposing major surfaces and varistors with laterally spaced electrodes on a single surface are described.