Taking the phase change heat transfer process in an evaporator of organic Rankine cycle system(ORCs)as the object

the criterion of whether the flow exergy loss caused by viscous fluid can be neglected or not(namely the non-dimensional exergy variation number NΔE)was put forward

from the viewpoints of exergy recovery and exergy loss

on the basis of the first and second laws of thermodynamics.Moreover

the external finned tube and smooth tube were taken as examples to discuss the effects of geometric parameters of the finned tube

internal Reynolds number and evaporating temperature on the criterion.The results show that

when investigating the effect of flow exergy loss on the evaporator performance from different aspects

whether the flow exergy loss can be neglected will affect the performance evaluation results.Selection of the evaluation aspect is related to engineering application of the evaporator.For the evaporators applied for waste heat recovery

evaluating their performance from the recovery exergy aspect is appropriate

considering the benefit;while for the conventional evaporators

evaluating their performance form the exergy loss aspect will be reasonable

considering the cost.