Twin-screw compressors are often used for generating compressed fluids useful for various industrial applications, thereby necessitating the need for evolving energy efficient designs. In the past few decades, several experimental studies were conducted to understand the phenomenon inside the twin-screw compressor, thereby leading to performance improvement and design optimization. The present study summarizes the various experimental investigations on screw compressors which include analysis related to various parameters such as leakages, pulsations, noise, liquid injection, capacity control, pressure losses, optimization of rotor, indicator diagrams, etc. In order to improve the understanding of thermo-fluid-solid interaction phenomenon in twin-screw compressor, further investigations using visualization techniques such as LDV/PIV are suggested. As the leakages within the screw compressor are complex phenomenon, it is suggested to explore simplified experimental and numerical studies by simulating the leakages using equivalent nozzles and developing appropriate leakage models.

The phenomenon of leakages through various clearances in the twin-screw compressor and its accurate prediction affect its design and performance. The blowhole leakage within the twin-screw compressor is estimated by previous researchers using the convergent nozzle equation, which has certain idealized assumptions and hence has a scope of improvement considering the actual phenomena taking place within the screw compressor. The mathematical model presented in this study takes into account, the shape of a gap and its geometric dimensions, the parameters before and after the gap, the gas friction and the local resistance at entry and exit. An iterative model is used to calculate the leakage rate through the blowhole cross-sections at different pressure differences. The analytical results for the leakage using the mathematical models are verified experimentally by simulating the leakages through the circular cross section convergent nozzles of different sizes at different pressure differences. The experimental study along with analytical deduction suggests suitable multiplier to estimate the blowhole leakages within ±7.2%. This methodology may be extended to estimate the other types of leakages occurring dynamically within the screw compressor and fluid flow systems.

The adiabatic and volumetric efficiencies are key performance parameters of any positive displacement machines including twin screw compressors. These efficiencies are affected by clearances and leakages in these machines. The leakage happen because of clearance gap and pressure difference between two pressurized chambers the compression module. In this work, findings from all the numerical and mathematical models are presented for different leakages in the twin-screw compressor. Authors proposed an iterative method to estimate the leakages by taking in account the geometry of the clearance, friction and local resistances. An experimental set up to collaborate the leakage model is presented, which can be used for further investigation of these leakages.

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The clearance gaps in positive displacement machines such as compressors, pumps, expanders, and turbines are critical for their performance and reliability. The leakage flow through these clearances influences the volumetric and adiabatic efficiencies of the machines. The extent of the leakage flow depends on the size and shape of clearance paths and pressure differences across these paths. Usually, the mass flow through the gaps is estimated using the isentropic nozzle equation with the flow coefficients applied to correct for the real flow conditions. However, the flow coefficients applied generally do not take into account the shape and size of these leakage paths. For that reason, a proper understanding of the relationship between flow coefficients and shape parameters is crucial for an accurate prediction of leakage flows. The present study investigates the influence of the various dimensionless parameters such as Reynolds number, Mach number, and pressure ratio on the flow coefficients for circular and rectangular clearance shapes. The flow coefficients are determined by comparing the experimental values obtained in an experimental test rig and the flow rates obtained from the isentropic nozzle equation. It is observed that in the case of circular clearances, the mean deviation of the experimental leakage results (in comparison to the analytical results using isotropic nozzle equations) is +9.1%, which is significantly lower than the mean deviation (+20.5%) in the case of rectangular clearance leakages. The study indicates that the isentropic nozzle equation method is more suitable for predicting the leakages through the circular clearances and needs modifications for consideration of the rectangular clearances. Using regression analysis, empirical correlations are developed to predict the flow coefficient in terms of Reynolds number, Mach number, pressure ratio, aspect ratio, and β ratio, which are found to match within ±6.4 percent of the numerical results for the rectangular clearance and within the range of -3.6 percent to +5.1 percent of the numerical result for the circular clearance. The empirical relationships presented in this study can be extended to evaluate the flow coefficients in a positive displacement machine.