Flat plate heat exchangers

Claim 1

A flat plate solar energy collector comprising a bottom plate of rigid plastic foam material, said bottom plate having four side walls and multiple flow guides within said side walls, an inlet nozzle on a first of said side walls, a straight flow guide opposite said nozzle and extending from a second side wall whereby fluid from the inlet nozzle is split into two flow channels, the area between said nozzle and said straight flow guide comprising a diffuser means, means comprising two elongated curved discontinuous flow guides to further split said two flow channels into four flow channels, two exit ports in said bottom plate with each exit port lying within the confines of one of said two elongated curved discontinuous flow guides, said exit ports being located near the nozzle side of the solar collector, plural relatively short flow guide means for directing fluid from said second side wall back to said first side wall to be combined with flow from said nozzle, wherein all of said flow guides are formed as a unitary structure with said plastic bottom plate, a transparent plastic top plate secured over said bottom plate to admit sunlight to fluid in the collector.