Compressors are widely used across the all technical fields and current pressure on ecology increases the demand for more effective compressor with economical operation costs. The reasons for inefficiencies must be identified during the development process of a new compressor, where simulation tools might become very useful. There are many different tools for compressor analysis and choosing the right one is mostly dependent on the level of detail that must be analyzed. Models based on energy balance seem to be appropriate when the global parameters of a compressor are demanded. These models offer quick results with reasonable degree of accuracy in terms of basic compressor characteristics. The goal of this thesis is to develop such a simulation tool for a reciprocating compressor. The tool can predict compressor behavior based on compressor dimensions and valve properties. The processes inside the cylinder and heat transfer between the components of a compressor are analyzed using energy balance equation. Simulation tools were verified and experimentally validated using two different types of compressors, therefore they might be used for any reciprocating compressor under some conditions. Mathematical solution was developed in Matlab and therefore it is possible to add new sub-models or to couple the actual model with other simulation tools. This work also contains an analysis of heat transfer models used to predict heat transfer coefficient inside the cylinder and comparison with complex numerical approach. Impact of heat transfer on the compressor efficiency was evaluated too.

Master thesis is focused on design of ground heat pump with direct evaporation. First part is dedicated to description of heat pump technology, cooling circulation and sources of low-potential heat. Heat pump ground-water, its main components, classification of refridgerant and systems of direct evaporation are all described in the second part. The last part consists of design of each individual component of heat pump and solution of ground heat exchanger for direct evaporation of refridgerant.

This diploma thesis deals with the design of thermodynamic heat pump, used to utilize thermal energy of flue gases arised from the combustion of natural gas in a heat exchanger. The flow rates of the compader compressor, bypass compressor and turbine are calculated. Part of this thesis is simplified design of gearbox and economical evaluation of heat pump installation. The appendix of the thesis contains technical documentation.

The CFD simulation of cooling piston compressor Stream, manufactured by Emerson company, is the topic of this diploma thesis. Analysis of moving parts (piston, valves) and refrigerant or physical settings for simulation were based on experimental data provided by Emerson. The goal of the thesis is to test opportunities of Star-CCM+ in simulating the flow inside the compressor. In the end there will be a comparison of experimental data and results from the simulation. The thesis also contains a theoretical background of piston compressors and phenomenon following the operating compressor.

<p>The primary objective of this research was to shed light on the changes in performance observed in a high-speed, centrifugal compressor that occur during the transition from subsonic to transonic operating conditions, using experimental data collected on a research compressor developed by Honeywell Aerospace, as well as results from a numerical model of the compressor.</p> <p> An understanding of the flow behavior in transonic centrifugal compressors is critical as the drive for higher stage pressure ratios while maintaining a compact size results in higher rotational speeds and increased aspect ratios in the inducer of the impeller. Both of these design trends result in higher relative Mach numbers near the impeller leading edge, resulting in the formation of shocks and an increasingly complex flow field. Since it is necessary to maintain high efficiency and adequate surge margin at these conditions—to ensure the compressor is stable across the full operating range—it is important to understand the effects of the transition from subsonic to supersonic flow on performance and stability. Due to the limited availability of research in the open literature regarding transonic centrifugal impellers, especially experimental studies, these behaviors are still not fully understood.</p> <p>Experimental data collected during steady state operation as well as during speed transients, showed a sudden decrease in the variance of the unsteady pressure field throughout the compressor, but most dramatically in the inducer shroud. Analysis of the performance also showed a significant increase in impeller efficiency of approximately 2 points as speed was increased from 80% to 90% of the design speed. Temperature measurements upstream of the impeller leading edge indicated a dramatic reduction in the degree of flow recirculation in the same speed range, indicating the increase in performance is related to a decrease in the blockage near the impeller leading edge. A low pressure region was also observed in the inducer passage, which disappeared upon transition to the transonic operating regime, this coupled with decreased inducer static pressure rise and relative diffusion at lower speeds, strongly indicates that increased loss in the inducer at lower speeds is responsible for the observed performance deficiency during subsonic operation.</p> <p>Analysis of the numerical results revealed that the low pressure region in the inducer may be attributable to the interaction between the inlet shroud boundary layer and the low momentum tip leakage flow in the impeller passage, which at lower speeds, results in the tip leakage flow forming a large recirculation region in the inducer passage. It was also determined that the step change in instability coincides with the inducer shock extending to the shroud and reducing the strength of the interaction between the low momentum regions in the inlet and impeller passage, thereby allowing the tip leakage flow to form into a vortex and preventing the development of the recirculation region in the inducer. </p> <p>This research provides a possible explanation for the observed instability in the compressor, which may allow for further testing of techniques to mitigate the instability caused by the blockage in the inducer, such as casing treatment, bleed, or flow injection into the inducer shroud.</p>

The stable operating range of axial compressors is limited by the onset of rotating stall and surge. Mass injection upstream of the tip of an axial compressor rotor is a stability enhancement approach which can be effective in suppressing stall in tip-critical rotors, and thus increasing the operating range of compressors. In this article, investigations on active flow control related to the rotor tip gap sensitivity are discussed. The experiments were performed in a 1.5-stage low-speed research compressor. Measurements at part speed (80 per cent) and full speed (100 per cent) with varying injection rates are discussed. These tests were performed for two rotor tip clearances of 1.3 per cent and 4.3 per cent of rotor blade tip chord. Results on the compressor map, the flow field as well as transient measurements to identify the stall inception are discussed. Supplementary, the numerical results are compared to the experiments based on the configuration with the greatest benefit in operating range enhancement.

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The implementation of a ported shroud casing treatment is often used to extend the operating range of a centrifugal compressor. This work utilizes the STAR-CCM+ CFD package to analyze steady-state, single-passage simulations of a centrifugal compressor with and without a ported shroud to better understand how a ported shroud affects compressor flow physics. Verification and validation of simulations were conducted by comparison of results with a time-accurate full-annulus simulation and experimental data. Four different ported shroud revisions were considered and modeled along the full range of their stable operation, with emphasis placed on the flow limits of choke and stall. A ported shroud is found to improve the choked mass flow limit by increasing the aerodynamic area of the compressor. Near-stall operation is improved through flow recirculation through the ported shroud. This flow, which is induced with a large component of tangential velocity from having passed the impeller blades' leading edge once, reduces the impeller incidence. The influence of a strut is found to restrict both limits of operation by reducing the aerodynamic area and obstruction of tangential velocity. The revisions considered demonstrate that facilitation of flow entering the ported shroud under either near-stall or choked conditions causes a noteworthy improvement in performance. Such alterations, in this application, demonstrate a 3.3% improvement in choked mass flow rate under choked conditions and an 1.3 degree reduction in impeller incidence under near-stall conditions, as compared to the initial ported shroud design. Understanding the effect that a ported shroud casing treatment has on compressor flow physics, especially near its limits of operation, suggests methods for improving centrifugal compressor design to increase its stable operating range.

Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the work reported is to develop acoustic models for these resonators where relevant effects such as the effect of realistic mean flow on losses and possibly 3D effects are considered. An experimental campaign has been undertaken where the two-port matrices and transmission loss of four sample resonators has been measured without flow and for two different mean flow speeds (M=0.05 &amp; M=0.1) using two source location technique. Models for the four resonators have been developed using a 1D linear acoustic code (SIDLAB) and a FEM code (COMSOL Multi-physics). Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been discussed. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The measured acoustic properties compared well with the simulated model for almost all the cases.

Performance of vacuum cleaners are affected by factors such static pressure, airflow rate and efficiency. In this thesis work, attempt has been made to design a fan to meet the requirements of suction static pressure and air flow rate and in the process understand the fan design parameters that affect these performance parameters. Parametric study has been conducted for the same, by choosing six fan design parameters. Additionally, ways to increase the fan efficiency has been investigated during the parametric study. Computational Fluid Dynamics is used to visualize the flow inside the fan casing and further to simulate fan performance at an operational point. Steady state RANS and moving reference frames was used to model the turbulence in the fluid flow and rotation of the fan, respectively. Performance curve showing the relation between static suction pressure and mass flow rate is plotted for the base model is in proximity to the required performance. Parametric study was conducted on the six fan design parameters: Fan diameter, number of impeller blades, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan, diffuser exit length and splitter blade length. The range for each parameter analysis was restricted so that static pressure values are around the required performance. Greater performance variation was found with design parameters: fan diameter, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan and diffuser exit length. This variation at low mass flow rate can be majorly attributed to the randomness in the flow captured by entropy contours. At high mass flow rate, blockage in the flow visualized by pressure contours reasoned for the performance variation. Greater performance variation was not when design parameters such as number of blades and splitter blade length were varied. Larger variation of these parameters is required to see better variation.