This presentation will present a comparison of flow between four possible designs for ceramic high temperature heat exchanger that is used as a sulfuric acid decomposer which may be used for hydrogen production within the sulfur iodine thermo-chemical cycle. The decomposer is manufactured using fused ceramic layers that allow creation of channels with dimensions below one millimetre. The basic design uses parallel straight channels with rectangular cross sections. This design is compared with similar design with varying cross sections or where the input manifolds dimensions have been altered to improve heat transfer within the unit. Measurements have been taken using a pressure mat that has been calibrated to allow for precise measurements of the flow data. Results of this research are used as a basis for investigation optimal design of the decomposer that can provide maximum thermal performance while maintaining stresses within design limits.