The low pressure (LP) exhaust system presents a promising avenue for improving the performance of large steam turbines. For this reason, LP exhaust systems have attracted the attention of the research community for decades. Nevertheless, we still lack understanding of the flow physics and loss mechanisms in the exhaust system, especially at part-load conditions. It is also unclear how the exhaust system should be designed when its required operating range widens. This thesis provides solutions to these aerodynamic issues through experimental and numerical investigations, and provides tools that could contribute to better designs of LP exhaust systems. Firstly, the Computational Fluid Dynamics (CFD) solver ANSYS CFX was validated against experiments performed on a scaled test rig under representative part-load flow conditions. This validation exposed the weakness of Reynolds-averaged Navier-Stokes (RANS) CFD when there is a highly swirling flow and large separation regions in the exhaust diffuser. To facilitate the numerical studies, a series of tools were also developed. A design suite, ExhaustGen, was used to automate the pre- and post-processing of CFD calculations. The exhaust diffuser was parametrised using "Minimum Energy Curves", which reduce the dimension of parameter space. Further, a suitable stage-hood interface treatment (Multiple Mixing Planes) was chosen to predict the circumferentially non-uniform flow in the exhaust hood at low computational cost. Numerical investigation of the baseline geometry provided insights into the key flow features and loss mechanisms in the exhaust system, over a wide range of operating conditions. In particular, the bearing cone separation was identified as a key source of loss at part-load conditions. The effect of stage-hood interaction on the performance and design of the exhaust system was studied by varying the rotor blade design, which can positively influence system performance. Finally, a global sensitivity study was performed to identify the most influential design parameters of the exhaust hood. These findings allow, for the first time, LP exhaust hood performance maps to be constructed, so that the benefits of choosing a suitable hood geometry and blade design can be revealed. The thesis also offers contribution towards formulating LP exhaust system design guidance for a wide operating range.

A subsonic wind tunnel facility was built and tested as part of a base line test investigating flow within a diffuser-collector. Facility controls allowed the quarter scale model to match both Reynolds number and Mach number. Mass averaged conditions at the diffuser inlet during testing were determined as 1.939 ? 106 for Reynolds number based upon diffuser inlet hydraulic diameter, and 0.418 for Mach number. A flow conditioning section prior to test section contained several interchangeable sections. Flow conditioning components were used to create flow characteristic of that leaving the last stage of a land-based gas turbine. The diffuser-collector subsystem was evaluated through the use of wall static pressure measurements, a variety of probe traverse measurements, and Stereo-PIV. Flow within the collector and diffuser were determined to be heavily dependent upon the collector geometry. PIV measurements showed the development of two large counter rotating vortices within the collector. Each symmetric vortex grew and shifted according to the collector geometry while creating complex regions of flow. Pressure recovery within the diffuser was in range of 0.47 to 0.78, and would drop to 0.52 at the collector exit. The drop in pressure recovery was presumed to be a combination of inefficient diffusion in the collector and losses due to the vortices. The baseline test was found to be successful in terms of facility design, and determining the critical flow phenomena. Further testing and experimentation are necessary to evaluate specific details of the collector geometry's effect upon the pressure recovery and flow development. / Master of Science

Takmonterade avluftshuvar kan ha ett krav att kastlängden av luftflödet ska överstiga en minimal höjd över takytan. Moderna ventilationssystem av typen VAV (Variable Air Volume) kan anpassa luftflödet till olika rum beroende på antalet personer och mätvärden på luftkvalitet i rummen, vilket kan leda till ett lägre luftflöde under nätter och helger. Det lägre luftflödet kan leda till att kastlängden på statiskt konstruerade avluftshuvar minskar, vilket i sin tur kan leda till att utkastad luft återcirkuleras in i närliggande inloppskomponenter. För att undvika detta kan ventilationssystemet behöva driva ett onödigt högt luftflöde.  I detta arbete utvecklas en mekanism som kan anpassa geometrin på avluftshuven för att behålla en konstant kastlängd med minskat luftflöde. Mekanismen väljs från ett antal koncept som utvecklas med en systematisk process och modelleras med CAD (Computer Aided Design). Funktionen av varje koncept utvärderas med CFD (Computational Fluid Dynamics) simuleringar.  Den resulterande mekanismen beräknas kunna behålla en konstant kastlängd ner till 39% av det högsta specificerade luftflödet för den valda referensmodellen. / Roof-mounted outflow hoods may have a requirement that the throw of the airflow exceeds a minimum level above the roof surface. Modern ventilation systems are often of the Variable Air Volume (VAV) type which adjusts airflow depending on room occupancy and air quality readings, which may lead to a lower total airflow during nights and weekends. The lower airflow may cause the throw of statically constructed outflow roof-hoods to decrease which in turn may cause exhausted air to be recirculated into nearby inflow components. To avoid this, ventilation systems may need to drive a unnecessarily high airflow to maintian the throw. In this work, a mechanism concept is developed that can adjust the geometry of a outflow roofhood to maintain a constant throw even with adecrease in airflow. The mechanism concept is chosen from a number of concept ideas developed using a systematic process and modeled with CAD (Computer Aided Design). The performance of each concept idea is evaluated with the help of Computer Fluid Dynamics (CFD) simulations. The resulting mechanism is estimated to be able to maintain a constant throw down to 39% of the maximum airflow for the reference hood.

Many production technologies generate a variety of gas pollutants, which are unhealthy. The aim is therefore to minimize the content of such gas pollutants in the work environment. The highest capture efficiency of gas pollutants offers the local exhausting. Its disadvantage is the necessity to surround the source of pollutants, or to be as close as possible which is usually not technically or technologically possible. A possible alternative is to use a reinforced exhaust system that achieves greater capture distances. In the initial stage of the solution of the dissertation, a review of reinforced exhaust systems was carried out. Further, an existing measurement system was modified for measurements with the partition above the exhaust slot and the measurement system was partially automated. In order to investigate the case with pollutants having a lower density than the air, the workbench - the partition was moved above the exhaust slot. Based on of the literature review, a modification of the reinforced slot exhaust system was proposed. The modification consisted in the adjustment of the air inlet adjustment where a set of holes and a tube assembly were used instead of the slot. Such setup allowed for higher flow turbulence and thus for an increased exhaust efficiency. Subsequently, the inlet streams from the slot, holes and tubes were visualized by the smoke method. Further measurements were carried out by the tracer gas method for the determination of the exhaust efficiency. Measurements of velocity fields in front of the proposed configurations of the reinforced slot exhaust hood were also carried out. In conclusion, an energy performance assessment was carried out by means of the measurement of the electric power input to the fans with the determination of the electric loss power.

The master’s thesis deals with design of heat recovery and dehumification for the hotel´s kitchen. The design is made to fullfill functional, hygienic and operational ruqirements for the internal microclimate. The main task of air-conditioning systems is to drain away heat gains and intake of requirement minimum of fresh air. The theoretical part is about analysis of internal microclimate.

The present thesis explores the reinforced exhaust slot system above work table. Its objective was to measure the capture efficiency in front of the suction extension in various elevation levels of the workbench, taking into consideration four mobility ratios, while in the first case we performed traditional suction. The thesis also presents the results of capture efficiency measurements recorded in figures and tables of measured values. The conclusion analyzes the uncertainty in performed measurements.