Portal de Periódicos da CAPES

Distributed steady and dynamic modelling of dry-expansion evaporators

1999; Elsevier BV; Volume: 22; Issue: 2 Linguagem: Francês

10.1016/s0140-7007(98)00043-7

1879-2081

Xiaoxu Jia, C.P. Tso, Pascal Jolly, Y.W. Wong,

Heat Transfer and Optimization

A general distributed parameter model is presented to describe both steady and dynamic behaviors of dry-expansion evaporators. The homogeneous and three different non-homogeneous two-phase flow models are used to evaluate the impact of different flow models on the accuracy of the simulation. The experimental work was carried out on a full-scale refrigeration system with R-134a as the working fluid and without frost formation at the evaporator. Comparison between the modelling and experimental measurements shows that the drift flux flow models give satisfactory predictions. The simulation results indicate that an even air temperature distribution off the evaporator may be obtained by controlling liquid dry-out point at the two ends of the coil. The study also indicates that the counterflow configuration provides a higher heat exchange efficiency with a slower transient response compared with the cocurrent-flow configuration. A general distributed parameter model is presented to describe both steady and dynamic behaviors of dry-expansion evaporators. The homogeneous and three different non-homogeneous two-phase flow models are used to evaluate the impact of different flow models on the accuracy of the simulation. The experimental work was carried out on a full-scale refrigeration system with R-134a as the working fluid and without frost formation at the evaporator. Comparison between the modelling and experimental measurements shows that the drift flux flow models give satisfactory predictions. The simulation results indicate that an even air temperature distribution off the evaporator may be obtained by controlling liquid dry-out point at the two ends of the coil. The study also indicates that the counterflow configuration provides a higher heat exchange efficiency with a slower transient response compared with the cocurrent-flow configuration. Un modèle générale des paramètres de distribution est présenté afin de décrire le comportement des évaporateurs à détente sèche à régime stable et à régime transitoire. Le modèle homogène et les trois modèles non homogènes de flux biphasiques ont été utilisés pour évaluer l'impact des différents modèles de flux sur la précision de la simulation. L'étude expérimentale a été effectuée utilisant un système frigorifique taille nature utilisant du R134a comme fluide actif et sans formation de givre sur l'évaporateur. La comparaison des valeurs de la simulation et les mesures expérimentales montre qu'on peut obtenir une distribution régulière de la température de l'air au-dessus de l'évaporateur en maitrisant le désechement aux deux extremités du serpentin. L'étude montre ausii que la configuration à contre-courant donne un rendement plus élevé de l'echange de chaleur et une réponse transitoire plus lente que celle obtenue avec la configuration à écoulements parallèles.