Embodiments of a heat transfer apparatus, and related methods, involve a first flow path through at least one neck portion defined by at least one boundary wall, a first heat source external to and in thermal communication with the at least one boundary wall, an inflow portion in fluid communication with the first flow path, an outflow portion in fluid communication with the first flow path, and a drive system for driving a first fluid through the first flow path, whereby heat is transferred from the first heat source to the first fluid as it flows through the first flow path.