Isobutane flows through electronic expansion valves with hydraulic diameters smaller than 0.19 mm are analyzed in this paper. First, three similar valves but with different orifice sizes were tested with nitrogen to establish the operational envelope in terms of volumetric flow rate and opening ratio. Two valves suitable for household refrigeration were then selected and tested with isobutane under conditions typically observed in practice. To this end, a purpose-built set-up capable of operating with condensation and evaporation temperatures between 25 and 45°C and −28 and −10°C, respectively, was constructed. In order to check for choked flow, performance curves for the mass flow rate were obtained for several opening ratios by varying the backpressure up to values closer to the condensation pressure. The nitrogen results revealed that the largest orifice valve can behave similarly as 3 m long capillary tubes with inner diameters between 0.40 and 0.85 mm. Concerning the isobutane tests, it was found that the valves are nearly insensible to the inlet sub-cooling and that the flow is likely to be choked for household refrigeration conditions. It was observed that the choking pressure ratio is not affected by the inlet pressure, being a function basically of the valve opening. Finally, a π-type correlation was proposed for the flow coefficient, putting forward a model for predicting the valve mass flow rate. An agreement between experiments and model predictions was achieved with 94% of the 138 points within 15% error bounds.

本文分析了异丁烷流经水力直径小于0.19 mm的电子膨胀阀的情况。首先，用氮气测试了三个相似但口径不同的阀门，以建立关于体积流量和开度的操作范围。然后选择两个适用于家庭制冷的阀门，并在实践中通常观察到的条件下用异丁烷进行测试。为此，专门设计的装置能够在25至45的冷凝和蒸发温度下运行°C和-28和-10分别构建了℃。为了检查阻塞流量，通过将背压更改为更接近冷凝压力的值，获得了几种开度比率的质量流量性能曲线。氮气结果表明，最大的孔板阀的行为与内径在0.40至0.85 mm之间的3 m长的毛细管相似。关于异丁烷测试，发现阀门对入口过冷几乎不敏感，在家用制冷条件下，流量可能会阻塞。观察到，节流压力比不受入口压力的影响，入口压力基本上是阀开度的函数。最后，提出了流量系数的π型相关性，提出了一种阀门质量流量的预测模型。