Heat exchanger with bypass seal allowing differential thermal expansion

The present invention is embodied in a heat exchanger, which allows differential thermal expansion of its elements while providing a bypass seal. In at least one embodiment, the heat exchanger includes, a shell for containing a first gas, a core positioned within the shell, and a seal positioned between the core and the shell. The seal allows at least some differential expansion between the shell and the core while restricting the flow of the first gas past the seal. This allows a space for expansion of the core to exist between the core and the shell, while preventing the first gas from bypassing the core by traveling through the expansion space. As such, the seal forces the first gas to pass through the core, greatly increasing heat transfer from the first gas to the core. Preferably, the seal is mounted to the core at a position at least adjacent to the free (moveable) end or ends of the core. The seal can be folded into several layers such that the folds abut both the core and the shell. When the core expands or contracts the seal is draw apart (unfolded) or compacted (further folded), as the case may be. In another embodiment, the seal is a single layer of material with sufficient slack between the core and the shell to allow the core to expand and contract separately from the shell.