In thermal recycling plants high performance fans are needed to transport gas through the process. For this application, the fans have to fulfill very special requirements. The pyrolysis and gasification processes transform different kinds of waste, e. g. biomass and municipal scrap waste, electronic or industrial waste, into highly clean efficient synthetic gas, i.e. usable energy. Therefore, the thermal operating range of these fans lies between ambient temperatures of about 20°C and 530°C. Due to the requirements and design space of the recycling facility, new radial fans were developed according to these particular specifications. Two different impellers were designed with an extended analytical method, as described in Epple et al. [1] and [2]. The first one was designed with a parallel flat shroud and the second one with a conical shroud. In order to fulfill the manufacturer requirements of ease of manufacturing, the impellers were designed with circular arc blades. With these two impellers and at a temperature of 530 °C, as it is needed in the recycling plants, a first Bommes spiral casing was optimized adjusting the spiral casing opening angle and the Bommes parameter, i.e. the ratio of the spiral casing width to the impeller exit width, BSC/b2 (Epple et al. [3]). The results show that the predictions of Bommes work well with impellers with conical shrouds, but for impellers with parallel shrouds the Bommes prediction does not work properly.

Fans in industrial plants can be exposed to a strong erosion load due to particle flows. In the present work, the erosion behavior for large radial fans with spiral casings is investigated using the Finnie erosion model, see [1] [2]. Theoretical approaches concerning particle velocity and particle impact angle are validated by numerical methods. For this purpose, a baseline impeller and a parameterized baseline spiral casing have been designed and simulated using computational fluid dynamics. Than different geometrical variations of the spiral casing shape and the blade shapes of the impellers have been designed and simulated in order to determine their respective influence on the erosion behavior as well as on the performance characteristics. Finally, recommendations for an optimal design are presented and explained in detail.

The use of low speed radial impellers is very common for industrial fans and blowers. Some of the applications include fans designed for the transport of biogas in biogas plants. The design process of fans is almost always direct, based on existing impeller series and available experimental data as stated recently in [1]. This paper presents the design results and optimization of low speed/high pressure radial impellers with spiraled casings used for such an application through a combined inverse approach. The aim was to design high efficiency impeller-casing systems for a specified operating point or a specified operating flow range, as well as to adjust the slope of the pressure-flow rate characteristic of the system for the desired high pressure specifications. The design point, and hence the maximum efficiency of these blowers has been set by the manufacturer at very small flow rates implying an iterative design approach of both impeller and casings. Here will be presented how the geometrical design parameters are influencing the performances of such fans. Several casings configurations with and without vaneless diffusers, different tongue radii, design flow rates or casing-impeller height ratios were investigated. They were numerically simulated with a commercial Navier-Stokes CFD solver (ANSYS CFX V11.0) and by evaluating their results an understanding of the inside flow physics could be achieved. To properly filter and analyze the investigated design results of the casings, a new performance parameter was successfully implemented and validated. This performance parameter will be called the casing (or volute) efficiency, and will be explained later in this paper. Results are showing the influences of several geometrical and construction parameters of casings and some backward (reversed) conclusions on impeller design suited to operate in such systems. Finally conclusions are presented, analyzing the suited casing geometries for reaching the desired performances as well as the advantages of this combined analytical and numerical method suited to perform a coupled design of high efficiency spiral casings for radial impellers.

Efficient processes with organic fluids are becoming increasingly important. The high tech fluid Novec™ is such an organic fluid and is used, for example, as a coolant for highperformance electronics, low-temperature heat transfer applications, cooling of automotive batteries, just to mention a few. Thus, efficient designed fans for the transport of organic fluids are becoming more and more important in the process engineering. CFD-simulations are nowadays integral part of the design and optimization process of fans. For air at the most usual application conditions, i.e. no extreme temperatures or pressures, the ideal gas model is in good agreement with the real gas approach. In the present study, this real gas approach for organic fluids have been investigated with CFD methods and, the deviation from the ideal gas model has been analyzed. For this purpose, a simulation model of a centrifugal fan with volute has been designed as a test case. First, the ideal gas model approach has been compared with the real gas approach model of Peng-Robinson for air using the commercial solver ANSYS CFX. Thereafter, the same comparison has been performed using the organic fluid Novec™. After a detailed grid study, the entire fan characteristics, i.e. the design point and the off-design points, have been simulated and evaluated for each fluid (air and Novec™) and gas model (ideal gas and Peng-Robinson real gas). The steady state simulations of the centrifugal fan have been performed using the Frozen Rotor model. The simulation results have been compared, discussed and presented in detail.

High pressure fans for thermal power generation stations, especially biogas plants, usually operate in a spiral casing at high pressures of about p = 12.000–15.000 Pa and low flow rates of around Q = 100–600 m3/s. The motor drive has a constant speed of 3.000 l/min. This corresponds to specific speeds of nq = 3–6 min−1, which is already beyond the conventional range of single stage radial machines. Nowadays these fans for biogas plants usually operate at higher flow rates than specified or are multiple stage radial fans. Therefore a new class of radial impellers has been developed. These single stage impellers have a unique high pressure at a low flow rate operating point. In this work several impellers of this new class have been designed and validated with a commercial Navier-Stokes solver (ANSYS CFX). The design process is described in detail. It is based on a new extended analytical and numerical design method. It is shown that the prescribed unusual operating point can be achieved with single stage radial impellers. An in detail flow analysis is given showing the fundamental flow physics of these impellers.