It is common practice (o recover waste heat from an oil-or gas-fired furnace by using the exhaust gases to preheatthe combustion air. A device commonly used for thispurpose consists of a concentric pipe arrangement forwhich the exhaust gases are passed through the innerpipe, while the cooler combustion air flows through anannular passage around the pipe.
Consider conditions for which there b a uniformheattransferrateperunitlength,
(a) Ifairentersat
(b) If the airflow b fully developed throughout theannular region, what b the temperature of the innerpipe at the Inlet
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