Page 280 - Mechanical Engineers' Handbook (Volume 4)

11 Waste Heat Recovery Systems 269

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Figure 45 Stack-type recuperator. (Courtesy Morgan Engineering Company.)

high velocity by gas radiation and convection, or by solid-state radiation from inner to outer
cylinders and convection. The radiation recuperator has the advantage of acting as a portion
of an exhaust stack, usually with flue gas and air counterflow. Disadvantages are distortion
and resulting uneven distribution of air flow, resulting from differential thermal expan-
sion of the inner tube, and the liability of damage from secondary combustion in the inner
chamber.
Figure 46: cross-flow tubular type. By passing air through a series of parallel passes, as
in a tube assembly, with flue gas flowing across tubes, relatively high heat-transfer rates can
be achieved. It will ordinarily be more practical to use higher velocities on the air side, and
use an open structure on the flue gas side to take some advantage of gas radiation. Figure