Abstract: An oil cooler 11 comprises oil channel members 2A arranged one above another in parallel at a spacing and each composed of a pair of plates 20A, each of the plates 20A having a hole 21 at each of opposite ends thereof and a channel portion 22 between the end holes 21, the pair of plates 20A being joined with recessed surfaces of their channel portions 22 opposed to each other to form the oil channel member 2A; and annular header members 4A each interposed between each pair of adjacent oil channel members 2A at each of opposite lateral ends of the cooler.

Abstract: A solar water heater comprising at least one casing having housed therein a heat collector of the heat pipe type having a condenser portion and a heat receiving tank for receiving heat from the condenser portion of the collector, and a hot water tank disposed outside the casing. The heat receiving tank is in communication with the hot water tank by a supply pipe and a return pipe to heat water in the hot water tank with the heat of a liquid within the heat receiving tank.

Abstract: A solar water heater comprises a platelike heat pipe having a working fluid enclosed therein. The heat pipe includes a heat collector having parallel tubular portions and a radiator having hollow portions in communication with the tubular portion. A hot water tank has a metal bottom plate and is placed on the radiator of the heat pipe. The heat pipe has a collector to radiator surface area ratio of from 3/2 to 9/1. The collector tubular portions are 10 to 500 mm in pitch. Each of the tubular portions is 5 to 150 mm.sup.2 in cross sectional area. The head pipe may have a sacrificial protective layer and heat blocking holes. The main body of the hot water tank is jointed with a groove of the metal bottom plate using a sealant.