A thermal power plant for the East African Rift countries is under study for combined energy and freshwater generation using geothermal water, available at above 500 kPa pressure and temperature exceeding 150°C. This article presents the computational fluid dynamics (CFD) model and analysis of the two-phase turbine used for power generation in this total flow thermal plant. Flash boiling was implemented using a two-fluid multiphase model with the thermal phase-change criteria for heat, mass, and momentum transfer in the CFD solver ANSYS CFX. Initially, flashing flow in a converging–diverging nozzle was validated. This stationary nozzle model was then extended to a curved rotating nozzle reaction turbine and the results of flow and power were evaluated against available test data at 400 kPa feed water pressure under subcooled condition of 117°C and a very low backpressure of 6 kPa. Flow through this turbine was predicted within 8% deviation. An overestimate in thermodynamic power by 30–50% was predicted at speeds below 4000 rpm, while at the design speed of 4623 rpm the deviation was less than 5%. Rotor torque and hence power estimate was found to be dependent on the bubble size, bubble number density, and heat transfer parameters prescribed in the CFD model. The vapour dryness fraction at turbine exit was close to an isentropic expansion vapour quality. The isentropic efficiency was 7.5–17% for the analysed speed range.

中文翻译：

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两相地热透平设计中闪蒸流的CFD分析

正在研究东非大裂谷国家的火力发电厂，利用地热水将能源和淡水联合发电，压力在500 kPa以上，温度超过150°C。本文介绍了该总流热电厂用于发电的两相涡轮机的计算流体动力学（CFD）模型和分析。使用CFD求解器ANSYS CFX中具有热，质量和动量传递的热相变准则的双流体多相模型实现了闪蒸。最初，对渐缩式喷嘴中的溢流进行了验证。然后将此固定喷嘴模型扩展到弯曲的旋转喷嘴反应涡轮机，并在117°C过冷条件和6 kPa的极低背压下，根据400 kPa给水压力下的可用测试数据评估流量和功率的结果。预计流经该涡轮的流量偏差在8％以内。在低于4000 rpm的速度下，预计热力学功率高估30-50％，而在4623 rpm的设计速度下，偏差小于5％。发现转子转矩以及因此的功率估计值取决于CFD模型中规定的气泡大小，气泡数密度和传热参数。涡轮出口处的蒸汽干燥分数接近等熵膨胀蒸汽质量。在所分析的速度范围内，等熵效率为7.5–17％。预计流经该涡轮的流量偏差在8％以内。在低于4000 rpm的速度下，预计热力学功率高估30-50％，而在4623 rpm的设计速度下，偏差小于5％。发现转子转矩以及因此的功率估计值取决于CFD模型中规定的气泡大小，气泡数密度和传热参数。涡轮出口处的蒸汽干燥分数接近等熵膨胀蒸汽质量。在所分析的速度范围内，等熵效率为7.5–17％。预计流经该涡轮的流量偏差在8％以内。在低于4000 rpm的速度下，预计热力学功率高估30-50％，而在4623 rpm的设计速度下，偏差小于5％。发现转子转矩以及因此的功率估计值取决于CFD模型中规定的气泡大小，气泡数密度和传热参数。涡轮出口处的蒸汽干燥分数接近等熵膨胀蒸汽质量。在所分析的速度范围内，等熵效率为7.5–17％。气泡数密度和CFD模型中规定的传热参数。涡轮出口处的蒸汽干燥分数接近等熵膨胀蒸汽质量。在所分析的速度范围内，等熵效率为7.5–17％。气泡数密度和CFD模型中规定的传热参数。涡轮出口处的蒸汽干燥分数接近等熵膨胀蒸汽质量。在所分析的速度范围内，等熵效率为7.5–17％。