Optimization Analysis Of Supercritical Carbon Dioxide Microchannel Heat Exchanger

Because of its compact structure and high heat transfer efficiency,the supercritical carbon dioxide Brayton cycle has a wide application prospect in the field of new generation nuclear power.In the supercritical carbon dioxide Brayton cycle,microchannel heat exchangers are generally used as regenerators,and its heat transfer performance has a great influence in the overall cycle efficiency.For the optimization of heat exchangers and the improvement of overall cycle heat efficiency,it is of great significance to study the flow and heat transfer performance of supercritical carbon dioxide in microchannel heat exchangers.In this paper,supercritical carbon dioxide is used as the flow medium.Firstly,the numerical simulation of airfoil microchannel heat exchanger with different fin arrangement is presented.The effects of mass flow rate and fins spacing on the flow and heat transfer performance of heat exchanger are studied.The results show that the pressure drop and heat transfer performance increase with the increase of mass flow at the inlet.In addition,within the range of spacing calculated in this paper,the heat transfer performance and pressure drop loss of the heat exchanger will decrease with the increase of the fin spacing.Under the same condition of pressure drop loss,the heat transfer performance of the heat exchanger with larger spacing will be better.In the process of comparing airfoil microchannel heat exchanger with Z-shaped microchannel heat exchanger,it is found that under the same calculation conditions and the same Reynolds,the pressure drop loss of airfoil microchannel heat exchanger is only 54%of Z-shaped microchannel heat exchanger,and its heat transfer performance is improved by 25%.In this paper,a novel design of microchannel heat exchanger model is introduced,and the effects of mass flow rate and operation pressure on its flow and heat transfer performance are studied by numerical simulation.The results show that the pressure drop loss of the newly designed microchannel heat exchanger is reduced and the heat transfer performance is enhanced when the horizontal spacing increases from 10 mm to 12 mm.and this phenomenon is more obvious with the increase of flow velocity.It indicates that the over-dense fin design is not suitable for the heat transfer places with higher flow velocity.Compared with airfoil microchannel heat exchanger,it is found that the novel design is more suitable for high Reynolds number,its heat transfer performance is relatively low at low Reynolds number.In this paper,different operation pressures have a few influence on the heat transfer performance and f friction factor of the heat exchanger,but the pressure change will lead to changes in the density of supercritical carbon dioxide,and affect its flow speed,thus the pressure drop will be affected.With the increase of working pressure,the pressure drop loss in the flow passage decreases.