Heat exchanger for pressure washer

Abstract

A high pressure washer of this invention comprises a heat exchanger for heating a cleaning fluid, and a dispenser for dispensing heated cleaning fluid under pressure onto a surface to clean it. The heat exchanger comprises a tubular casing and a generally coaxial tubular heat shield inside the casing defining a combustion chamber. A burner is mounted adjacent a first end wall of the casing for discharging flames and hot combustion gases into the combustion chamber. A heating coil inside the casing extends longitudinally with respect to the casing for containing cleaning fluid to be heated. The heating coil comprises a length of unfinned tubing disposed in a gap between the heat shield and a second end wall of the casing, and a length of finned tubing in the annular space between the heat shield and the casing. The burner is operable to emit flame and hot gases of combustion into said combustion chamber in a direction toward the second end wall of the casing. The heat shield serves to protect the finned tubing by directing the hot gases of combustion for contact first with said unfinned tubing, resulting in cooling of the gases, followed by contact with the finned tubing in said annular space, thereby enhancing the heat transfer between the gases and the fluid contained within the heating coil.