Liquid crystal thermography was used in a water-operated concentric tube-in-tube heat
exchanger to determine local annular heat transfer coefficients at the inlet region. An
annular diameter ratio of 0.54 was considered with the inlet and outlet orientated
perpendicularly to the axial flow direction. Both heated and cooled cases were considered
at annular Reynolds numbers ranging from 1000 to 13 800. Wall temperature distributions
were directly measured by means of a coating of thermo-chromic liquid crystals. Local heat
transfer coefficients at the inlet were higher than those predicted by most correlations, but
good agreement was obtained with some literature.