Patent ID: 6793015
Filing Date: 2004-09-21
Classification: F23C,F24H,F28D,F28F

Abstract:
A furnace heat exchanger for exchanging energy between heated gases flowing internally and comfort air flowing eternally thereover, comprising:a series of interconnected flow passages for conducting flue gases between an inlet and an outlet of said series; wherein, in at least one flow passage the cross-sectional shape thereof transitions from an unenhanced form to an enhanced form in a gradual manner so as to reduce the occurrence of stress therein, the length of said transition being defined by the following relationship: 1.7wherein, L/Dha=The ration of transition length (L) to the average hydraulic diameter (Dha) over the entire transition length, and wherein, the hydraulic diameter Dh is defined as: Dh=4A/P, where A is the cross-sectional area of the flow passage is the â€œwettedâ€  perimeter.