CO_2冷凍サイクルにおいて内部熱交換器が成績係数および交換熱量に及ぼす影響  [in Japanese] Effects of an Internal Heat Exchanger in a Refrigerant System with Carbon Dioxide on Its Cooling Coefficient of Performance and Cooling Capacity  [in Japanese]

本論文ではCO2冷凍サイクルを対象として，内部熱交換器が交換熱量および成績係数に及ぼす影響を解析を用いて検討した．はじめに圧縮機の体積効率および断熱効率を算出し，解析精度を検証するため，CO2冷凍サイクルのサイクル試験を行った．次に本解析を用いて，内部熱交換器伝熱面積，環境温度，低圧側圧力および高圧側圧力を変化させて，内部熱交換器が交換熱量および成績係数に及ぼす影響を検討した．実験結果との比較により，本解析は蒸発器での交換熱量を+5.1%，冷房成績係数を+5.2%および冷却器での交換熱量を+3.0%の精度で実験結果を予測可能である．環境温度がより高い条件で，蒸発器の伝熱性能が低く，蒸発器出口の過熱度が小さい運転状態の場合に，内部熱交換器を設置すると，より大きい交換熱量および成績係数の増加が可能であることがわかった．とくに，冷却器出口温度が擬臨界温度近傍の場合，さらに大きな交換熱量および成績係数の増加が可能であることがわかった．

The effects of an internal heat exchanger in a refrigerant system with carbon dioxide on its cooling capacity and cooling coefficient of performance were numerically investigated. First, experiments were carried out for a refrigerant system with carbon dioxide to obtain volumetric and isoentropic efficiency and to verify numerical accuracy. Second, the effects of varying internal heat exchanger area, environmental temperature, lower side pressure and higher side pressure on cooling capacity and cooling coefficient of performance were numerically investigated. By comparing calculated results with experimental ones, our simulation predicts capacity in the evaporator with +5.1% error, cooling coefficient of performance with +5.2% error, and capacity in the gas cooler with +3.0% error. When the environmental temperature is high and superheat is equal to 0 due to low performance of the evaporator, an internal heat exchanger gives a larger cooling capacity and cooling coefficient of performance. In particular, when the gas cooler exit temperature is close to the critical temperature, the internal heat exchanger gives higher performance.