Heat transfer is an integral part of centrifugal compressor working process. The heat transfer can be generated by compressed gas (internal heating) or external heat sources (external heating). The heat transfer affects compressor performance directly through two mechanisms: dissipate impeller shaft power to heat to generate thermal losses; add extra thermal energy (enthalpy) to working fluid to distort stage performance value. The impacts of both these mechanisms are inversely proportional to the flow coefficient of the compressor. To optimize the compressor design and to evaluate their performance accurately, the physical mechanisms that control thermal fluid flow and heat transfer inside centrifugal compressors need to be studied.The current work investigates both internal and external heat transfer inside a single stage centrifugal compressor with low design flow coefficient. An integrated conjugate heat transfer (CHT) model of the compressor stage includes both the solid parts (impeller, guide vanes, and stationary walls) and the test gas. The heat transfer processes between the solid and fluid surfaces were quantified using the ANSYS CFX software. The stage studied was tested in a closed loop arrangement with both nitrogen and R134a gases over a range of speeds from choke to surge flow. The gas temperatures and pressures were measured throughout the flow path from inlet flange to discharge. The temperatures of the solid components were obtained for the regions with large temperature gradients. The concept of thermal losses is introduced to characterize the dissipation of the shaft work to heat. The fundamental physical mechanisms of thermal fluid flow inside the compressor are defined and the influence of heat transfer on the centrifugal compressor stage performance is quantified.

This study examines the potential hazard of an individual nanomaterial on the Cu biotoxicity to aquatic organisms. Daphnia magna in the absence or presence of nano-TiO2 was exposed to Cu. Maintaining nano-TiO2 at a safe concentration cannot eliminate its potential hazard. The biomarkers superoxide dismutase, catalase, and Na+/K+-ATPase in D. magna were measured. Cu in the presence of nano-TiO2 induced higher levels of oxidative stress and physiological damage because of the sorption of Cu. Nano-TiO2 also caused Na+/K+-ATPase inhibition possibly by impeding the Na+/K+ transfer channel. The correlations among the biomarkers, mortality, and accumulation further showed that the overloading reactive oxygen species generation caused by nano-TiO2 contributed to deeper oxidative stress and physiological regulation, thereby causing greater toxic injury.

The suction process of a scroll compressor was investigated. The investigation started from the numerical simulation of the entire scroll compressor working process. The simulation included the upper main bearing housing, thrust plate, scrolls, dummy and discharge ports, check valve, plenum, and discharge line. The basic geometric features and physical mechanisms that the scroll compressor performance is associated with were simulated first. The working fluid was Refrigerant 134a. The suction process was studied as a part of the integrated working environment. The fundamental mechanism of the suction process was defined. The interaction of the compressor design features was quantified. The overall parameters were calculated from the field quantities. The relationship between design details, flow physics, and performance characteristics was established. The methodology developed and the data obtained can be applied to the design and optimization of scroll compressors.

The impact of the power frequency on the performance of a scroll compressor was investigated. Two representative frequencies, 50 and 60 Hz, were used to quantify the effects of the power frequency on the scroll compressor performance characteristics for the same design. The major physical mechanisms responsible for the scroll compressor performance were identified. The changes induced by the power frequency on these physical mechanisms were illustrated by numeric simulations and laboratory measurements of the detailed flow physics inside the scroll compressor. The design parameters were obtained by integrating the field quantities over the relevant regions. The link between the design features and flow physics was established. The new design ideals can be generated from the fundamental understanding the physical mechanisms induced by the power frequency change.

A numerical model is developed for the complete oil supply system of a scroll compressor. The system includes oil sump, pickup tube, oil gallery, bearings, and associated oil feed holes, vent, and port. There are two fluids, oil and gas, inside the system. The flow is numerically simulated as a heterogeneous Eulerian-Eulerian turbulent multi-phase flow. The investigation covers the entire working process of the scroll compressor from dry-start to steady state. Two design parameters, initial oil sump depth and viscosity, are studied comparatively. The detailed oil-gas flow inside the oil supply system is characterized by the field quantities. The physical mechanisms controlling oil supply rate are defined. The oil supply rate and the bearing prime time (the time after which oil is flowing through a bearing) are obtained. The results can be used to design and optimize the oil supply system to improve the reliability and efficiency of scroll compressors.

A dummy port plays an important role in the porting process and the improvement of the performance of a scroll compressor. This paper documents an investigation on the working mechanism of the dummy port in a scroll compressor. To characterize the dummy port effects on the different parts of the scroll compressor, two scroll compressors, one with and the other without a dummy port, are studied comparatively. The flow through the dummy port is examined in the background of an integrated compressor working process. The assembly of the compressor under investigation includes the upper bearing housing, scrolls, check valve, and discharge plenum. The Navier–Stokes equations with a k–ɛ turbulence model are solved at the standard operating conditions of a scroll compressor. Refrigerant-22 is used as the working fluid. The thermodynamic and transport properties of the refrigerant gas are modeled by the Martin–Hou equation of state and power laws, respectively. Global flow physics is investigated first to lay a foundation to understand the working mechanisms that control the porting process before averaging techniques are applied. The behavior of the gas pockets in the porting process is characterized in both geometric and dynamic nature. The time-dependent variation of volume, mass, energy, and volume-averaged field quantities inside the gas pockets are studied throughout the porting process. The impact of the dummy port on the compressor performance is defined.

The suction process of a scroll compressor was investigated. The investigation started from the numerical simulation of the entire scroll compressor working process. The simulation included the upper main bearing housing, thrust plate, scrolls, dummy and discharge ports, check valve, and plenum. The basic geometric features and physical mechanisms that the scroll compressor performance is associated with were simulated first. The working fluid was Refrigerant 134a. The suction process was studied as a part of the integrated working environment. The fundamental mechanism of the suction process was defined. The interaction of the compressor design features was quantified. The overall parameters were calculated from the field quantities. The methodology developed and the data obtained can be applied to the design and optimization of scroll compressors.

The three-dimensional time-dependent porting process of a scroll compressor is investigated numerically. In the first part of the investigation, the porting flow is examined in the background of an integrated compressor working process. The compressor studied includes the upper bearing housing, scrolls, check valve, and discharge plenum. The Navier-Stokes equations with a k-ɛ turbulence model are solved at the standard operating condition of the scroll compressor. Refrigerant-22 is used as the working fluid. The thermodynamic and transport properties of the refrigerant gas are modelled by the Martin-Hou equation of state and power laws, respectively. Global flow physics is investigated first to lay a foundation to understand the working mechanisms that control the porting process before averaging techniques are applied. The behaviour of the gas pockets in the porting process is characterized in both geometric and dynamic nature. The time-dependent variation of volume, mass, energy, and volume-averaged field quantities inside the gas pockets is studied throughout the porting process. The performance of the given compressor design during the porting process is defined.

Suction elbow and inlet guide vanes (IGVs) are typical upstream components in front of the first-stage impeller in a centrifugal compressor. As the flow field in the front of the impeller is subsonic, the flow motion induced by the rotating impeller interacts with the elbow and IGVs. These interactions induce turbulent unsteady flows inside compressors. The resulting unsteadiness affects efficiency, vibration, and noise generation of the compressor. To understand the mechanism controlling the interactions between upstream components and to optimize the compressor design for better efficiency and reliability, the turbulent unsteady flow inside the first stage of the compressor was simulated. The model included the suction elbow, IGV housing, and first-stage impeller. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modelled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was numerically simulated. The overall performance parameters were obtained by integrating the field quantities. The force, torque, and the arm of moments acting on the IGVs were then calculated. The results can be used to design IGVs; and their motion control system to achieve higher efficiency and improve reliability.

Since scroll compressors contain gas pockets whose shapes and sizes change continuously, the flow fields inside the compressors are time dependent and three-dimensional. The spatial and temporal variations inside the gas pockets also induce unsteady flows between the gas pockets. This unsteadiness controls the mechanisms responsible for the behavior of the scroll compressor components and their interactions. The dynamic nature inherent in the scroll compressors affects the performance and reliability of the scroll compressors. To improve and optimize the scroll compressor design for better performance and reliability, information is needed to understand the detailed physics of the unsteady flows inside the scroll compressors. To provide the fundamental information needed, the unsteady flows in a scroll compressor are studied numerically. The system simulated includes upper bearing housing, scrolls, check valve, and discharge plenum. Refrigerant-22 is used as the working fluid. The unsteady flows inside and between the gas pockets are characterized by the instantaneous distributions of field quantities and the area- and mass-averaged parameters.

As the flow field experiences drastic changes at the discharge and dummy ports of a scroll compressor, the local geometry and movement, including the sizes, shapes, and movement of the ports and scrolls, have significant impact on the porting process. To assess quantitatively the performance of a given design during porting, the local characteristics of the porting process are studied. The study is conducted both on the field quantity distributions and area-averaged parameters. These field quantities define both temporal and spatial changes of the flow field at the discharge and dummy ports. The investigation on these field quantities, provides a basic understanding of the porting process. The fundamental phenomena controlling the porting process are identified. The area-averaged parameters describe the dynamic features of the porting process. The components involved in the porting process, especially the scrolls, dummy and discharge ports, are studied. The area schedule, mass flowrate, pressure, temperature changes at the dummy and discharge ports are quantified. The impact of the porting process on the compressor efficiency, vibration, and noise generation is analysed.

Combined with the geometric features, the pressure differential and bearing motion define the gas flow through the rolling-element-bearing assembly of a centrifugal compressor. The gas flow field then affects the oil distribution and heat transfer characteristics of the assembly accordingly. Investigations of the refrigerant gas flow through the rolling element bearing assembly of a centrifugal compressor are presented. A series of cases are studied for different operating conditions. The analyses include the geometric details of the assembly, such as the shaft, races, cages, balls, oil feeding system, and surrounding components. Refrigerant R123 is used as the working fluid. Both detailed three-dimensional flow field features and integrated parameters are calculated. The interactions between bearing motion and the surrounding structures are characterized. The flow patterns inside the bearings are defined. These results help us gain an insight into the basic physics that governs the bearing internal mass and heat transfer. The data and techniques developed can be used to design and optimize bearing and oil supply systems for the improvement of lubrication and cooling efficiency.

To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In the current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k−ε turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both the unsteady flow field and the overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both the overall performance data and local flow-field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow-field quantities is defined. The methodology developed and data obtained in these studies can be applied to the centrifugal compressor design and optimization.

Suction elbows and inlet guide vanes (IGVs) are typical upstream components in front of first-stage impellers in centrifugal compressors. The three-dimensional distortion induced by elbows and IGVs affects the flow field behind the IGV housing. Since the flow field in front of the impeller is subsonic, the flow motion induced by the rotating impeller will interact with the elbow and IGVs as well. The flow field resulting from these interactions is three-dimensional. The nature of this flow field defines design requirements of upstream components and impact overall performance of the compressor. To understand the mechanism controlling the interactions of up-steam components and optimize the compressor design for better efficiency and reliability, a numerical simulation of the flow field inside the entire first stage of the compressor was conducted. The stage studied includes suction elbow, IGV housing with vanes, and first-stage impeller. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws respectively. The three-dimensional flow field was simulated with a Navier-Stokes solver using the k-ε turbulence model. The overall performance parameters are obtained by integrating the field quantities. The force, torque, and arm of moment acting on the IGVs were then calculated. The results can be used to improve centrifugal compressor design to achieve higher efficiency and improve reliability. The methodology developed in the current study can be applied to centrifugal compressor design and optimization.

Vaneless and vaned diffusers in a transonic centrifugal compressor with the refrigerant HFC-134a were studied experimentally and numerically. The compressor was tested on a closed-loop stand instrumented to obtain both overall performance data and local flow field quantities. In numerical studies, the thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. To include the interaction of the compressor components in these analyses, a unified three-dimensional numerical model was built for the complete compressor stage. The flow field was calculated with a Navier-Stokes solver using the k-ε turbulent model. The impact of the different diffusers on both local flow field and overall performance is analyzed comparatively for each component. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.

Two index-matched systems of solid particles in liquid have been developed to enable the study of velocity and concentration distributions in the highly concentrated solid–liquid flows. The mixtures have excellent optical transparency up to depths exceeding 80 mm at concentrations up to 50% solids by volume. Highly visible marker particles with nearly the same mechanical properties as the index-matched particles are formed by metal plating or substitution. Good quality images of marker particles are obtained in both stationary and moving two-phase mixtures, and permit accurate tracking of the individual markers.