A study of local heat transfer coefficients in plate fin-tube heat exchangers using the steady state and transient liquid crystal techniques

Optical methods for measuring local heat transfer coefficients using thermochromic liquid crystals are discussed. Two techniques using radiative steady state and transient heating have been used to measure local heat transfer on the fin of a plate fin-tube heat exchanger. The transient method does not give results consistent with the steady state method when the heat transfer coefficients are based on fluid inlet temperature. It is suggested that the steady state method is preferable since it yields numerical values that are closer to those based on local temperature and hence easier to interpret when observing the effects of changing the local surface geometry