Abstract: A method of making and the resulting heat exchanger in which there is provided a header plate having a tube receiving opening closely embracing the tube in the opening with a sheet of solder on at least one of the tube and plate adjacent to the opening together with a retainer wettable by the molten solder attached to the tube and plate and bearing against the solder to retain it in position. The assembly of tube, plate, retainer and solder is heated to a melting temperature for the solder with the result that the molten solder flows over the wettable retainer and into the space between the plate and tube by capillary attraction after which the solder is cooled to a solidifying temperature to form a solder joint uniting the tube and header.

Abstract: A heat exchange device comprising a liquid flow tube with an inner cylinder located interiorly of the tube and a turbulator arranged generally helically around the cylinder with edgewise adjacent fins in the form of separate tongues in which each fin is at an angle of about 100.degree.-110.degree. from the inner cylinder on which the turbulator is located. This angle is measured from the cylinder in the direction of flow of the liquid flowing through the tube. Adjacent edges of adjacent fins describe a divergent V from the cylinder toward the tube and thereby describe channels between adjacent fins for directing the liquid outwardly toward the tube.

Abstract: A recuperator structure for recovering heat values from a hot gas stream comprising exhaust gases from a combustion burner supplied with combustion air for burning a fuel in which a heat exchanger is used for exchanging heat between the hot exhaust gases and the combustion air for preheating the combustion air and including a variable temperature control for selectively restricting the volumetric flow of either the air or the exhaust gases or both through the heat exchanger in order to control the temperature in the heat exchanger.One of the features of this invention is to provide a recuperator structure for recovering heat values by extracting heat in a heat exchanger from the hot exhaust gases from a combustion burner and using this heat in the exchanger to preheat the combustion air to the burner and including means for controlling the temperature in the heat exchanger by controlling the volumetric flow of either the combustion air or the exhaust gases or both through the heat exchanger.