Electronic expansion valves(EEVs) in air conditioner systems may induce serious flow noise when the refrigerant flows into them with unstable two-phase flow patterns. The addition of a flow pattern regulator in the flow path of an EEV is expected to stabilize the refrigerant flow pattern, thereby reducing flow noise. Therefore, determining the influence of flow pattern regulators on the flow noise of EEVs is essential for optimizing their structural parameters. In this study, a method for flow pattern simulation was verified through experiments. Then, the influence of the structural parameters of the flow pattern regulator, including the hole interval, thickness, and hole diameter, on the flow noise of the EEV under the typical unstable slug flow pattern was determined. Finally, the structure of the flow pattern regulator was optimized by reasonably combining the parameters to minimize the flow noise of the EEV. The results showed that the flow noise increased as the hole interval increased, whereas it initially decreased and subsequently increased as the thickness or hole diameter increased. The hole diameter is the most important factor affecting flow pattern regulation, and flow noise can be significantly reduced by appropriately designing the hole diameter. Under the working conditions of this study, noise was reduced by 6.88 dB.

The electronic expansion valve (EEV) used in multisplit heat pump air conditioners has the structural characteristics of import and export tubes perpendicular to each other, such that the refrigerant has two forms of flow into the EEV, that is, in the direction perpendicular to the valve needle axis and the direction parallel to the valve needle axis. The sound pressure level of the throttling noise exhibits evident differences in these two directions, and it is necessary to clarify the impact of the flow direction on the throttling noise. The purpose of this study is to design and build an experimental rig that can regulate the refrigerant state flowing into and out of the valve, observe the refrigerant flow pattern, and measure the sound pressure level of the throttling noise, thus obtaining the effects of the refrigerant flow directions on the throttling noise under different refrigerant flow rates and vapor qualities. The results show that when the refrigerant flows from the inlet pipe perpendicular to the direction of the valve needle axis, the throttling noise is mainly the collapse noise of vapor bubbles generated by the refrigerant throttling cavitation, and the overall noise sound pressure level is low. When the refrigerant flows from the inlet pipe parallel to the direction of the valve needle axis, the throttling noise is a combination of the noise due to bubble collapse and the noise due to vibrations of the valve needle, and the overall noise sound pressure level is high. In this experiment, the sound pressure levels of the throttling noise in these two flow directions range from 47.1 dB to 57.1 dB and 61.9 dB to 67.7 dB, respectively. The throttling noise in the air-conditioning system can be effectively reduced by optimizing the design of the refrigerant flow direction of the air-conditioning system and ensuring that the refrigerant always flows into the EEV from the inlet pipe parallel to the direction of the valve needle axis.

The two-phase flow pattern of hydrocarbon working fluids on the shell side of a helically baffled heat exchanger for liquefied natural gas determines its heat transfer performance. This study tested the two-phase flow patterns of propane and ethane/propane mixtures on the shell side of a helically baffled heat exchanger using a visualization experimental method. The test results demonstrated that with the increase in vapor quality, the experimental observations sequentially included stratified flow, stratified-spray flow, and spray flow; as the mass flux of propane increased from 20 kg/(m²·s) to 40 kg/(m²·s), the transition vapor quality from stratified flow to stratified-spray flow decreased from 0.7 to 0.3, while the transition vapor quality from stratified-spray flow to spray flow decreased from approximately 1 to 0.7; when the proportion of ethane increased from 0 to 50%, the transition vapor quality from stratified flow to stratified-spray flow increased from 0.30-0.45 to 0.43-0.55, while the transition vapor quality from stratified-spray flow to spray flow increased from 0.69-0.85 to 0.83-close to 1. The existing flow pattern map for water-air mixtures was inadequate for predicting the flow patterns of hydrocarbon working fluids. A new set of flow pattern transition criteria was established with prediction deviations of approximately 6.5%, 5.5%, and 4.2% for the experimental stratified flow, stratified-spray flow, and spray flow, respectively.

Circulating water is used as the working medium in water-based chillers. Salt ions, such as calcium in circulating water, may precipitate during long-term operation, resulting in the attenuation of heat transfer performance. The application of small-diameter tubes in heat exchangers may lead to more prominent fouling problems. This study developed an accelerated fouling method to evaluate water fouling risk. The most typical operating conditions for water-based chillers were selected as the experimental conditions. The test samples included small diameter (5 mm) smooth tubes, with 7 mm smooth tubes selected for the control experiment. The experimental conditions include a circulating water inlet temperature of 60 ℃, a flow rate of 1 m/s, a foulant mass concentration of 800 mg/L, and a test time of 0-400 h. The results revealed that the total fouling mass was 39.5% higher and required fouling time was 17.6% shorter when comparing the 5 mm and 7 mm smooth tubes; the small diameter tubes had a larger total fouling mass and higher fouling rate. The heat transfer coefficients of the 5 mm and 7 mm tubes after fouling decreased by 12.5% and 9.7%, respectively, and the pressure drops increased by 50.6% and 10.4%, respectively, demonstrating a more severe heat transfer performance deterioration of small diameter tubes after fouling. The microscopic observation results of the fouling layer morphology demonstrated that the fouling layer in 5 mm tubes is a form of compact lamellar scaling, which is more difficult to remove compared with the 7 mm tube; therefore, the fouling risk should be considered when promoting the application of small diameter tubes in chillers.

To simulate and optimize an enhanced vapor-injection system, it is necessary to develop a vapor-injection scroll compressor model with fast calculation speed, high accuracy, good extrapolation accuracy, and few parameters for computation. However, existing models cannot meet these demands simultaneously. In this study, a physics-based explicit form semi-empirical model of a scroll compressor with vapor injection was developed to predict its mass flow rate, input power, and discharge temperature. In this model, the suction mass flow rate was derived by correcting the pressure ratio using the specific heat ratio and multiplying it by the quadratic function of frequency. The injection mass flow rate was based on the assumption of an isochoric mixing process and obtained by expanding the coefficients. The discharge flow rate was the sum of the suction and injection mass flow rates. The input power was based on the assumption of isentropic compression and corrected by pressure, and the discharge temperature model was based on the heat leakage factor. The model was validated based on experimental data, and the results showed that the model had a calculation speed of milliseconds, and was able to accurately predict the performance of the compressor, with the average deviations of the suction mass flow rate and discharge mass flow rate both within 2%, and the average deviations of the injection mass flow rate, input power, and discharge temperature within 5%, 3%, and 3 ℃, respectively. The model can provide reasonable results outside the range of fitted conditions, and the amount of data required for model fitting has been reduced by more than 50% compared to that of existing models.