Proceedings of the Institution of Mechanical Engineers,Part A: Journal of Power and Energy

Large fans for the thermal power industry operate more and more on part load. This paper discusses how the total cost of an investment is increasingly based on the inclusion of the operating costs. Today there is still a high demand for conventional thermal power stations. New ones are under construction and existing ones are in the process of conversion with new desulfurization units; more and more emphasis is being concentrated on:

Operating efficiency

Because these priorities are contradictory, the objective of this paper is to guide the reader to the best choice of fan technology given differing circumstances.

The correct choice is important concerning primary air, forced draft, induced draft and booster fans which can represent a total power consumption of 2–4 per cent in a 350–600 MW power plant depending on the quality of coal used and the boiler type. These fans are generally characterized by a large volume flow and a relatively large pressure and can be of the centrifugal or axial type.

Many solutions are possible for controlling the air flow of these fans. The main ones will be examined by looking at their general principles, their performance and characteristics, and then comparing them from an energy consumption point of view.

In this paper the steady state performance of epitrochoid generated orbital ‘rotary piston machine’ (ROPIMA) type ‘low-speed high-torque’ (LSHT) hydrostatic unit has been studied. The complex variation of the volume of a chamber of such a machine with shaft rotation, along with the various flow and torque losses, demand a structured approach to arrive at its mathematical model. In conventional approaches the system morphology becomes obscured as the mathematical model is approached. Bondgraph provides a structured approach to model engineering systems in a simplified manner. A reduced Bondgraph model of the LSHT Orbital motor is made where the various losses are lumped in suitable resistive elements. The variations of the loss coefficients are identified. The predicted performance of the motor has been experimentally verified.

A contra-rotating Wells turbine as an alternative to a biplane Wells turbine for wave energy conversion is investigated. The aerodynamic analysis and control of such a turbine are presented. It is shown that for a given pressure amplitude a contra-rotating Wells turbine is aerodynamically more efficient and can operate over a wider range of flowrates when compared to a biplane Wells turbine.

Natural gas is an alternative fuel that has potential for low emissions and a high efficiency. This paper presents the experimental results and predictions from a computer simulation of a fast burn high compression ratio (FBHCR) combustion system intended for use in a lean burn natural gas engine. Comparisons are made between the FBHCR combustion system at two compression ratios, predictions made by a two-zone combustion model and measurements from the original combustion system, for the brake efficiency, brake mean effective pressure, maximum cylinder pressure and the brake specific NO_x emissions. Experimental measurements of the unburnt hydrocarbon emissions, the burn duration and the cycle-by-cycle variations in combustion are also discussed from the original and fast burn combustion systems. The results show how the conflicting aims of low emissions and low fuel consumption can be satisfied using a lean burn combustion system. The computer predictions are shown to be reliable, and thus suitable for estimating the performance of other engine builds.

This study presents a simple method for designing the blade geometry of a centrifugal compressor impeller. In this method, instead of giving the mean swirl distribution on the meridional surface, the blade angle distribution is specified and the blade shape is derived, making it easier to perform the design. The quasi-three-dimensional potential flow field inside the impeller is obtained using the streamline curvature method, which solves the Euler equation along arbitrary quasi-orthogonals. The viscous effect is incorporated indirectly into the inverse design of the impeller via the simplified three-dimensional boundary layer calculation and the performance prediction. A three-dimensional centrifugal impeller was designed using this inviscid-viscous method and eventually manufactured. The newly designed impeller (B) and another impeller (A) designed previously were tested on a standard apparatus for model impellers. With the aid of three-hole probes and thermocouples, the flow parameters downstream of the exit of the impellers were measured along the axial direction of the impellers. A viscous loss model related to the boundary parameters is developed and used for the performance predictions of the impellers together with other loss models. From both the boundary layer analysis and the performance prediction, it is concluded that impeller B is superior to impeller A, which is in close accordance with the measurements.

A numerical study has been conducted to assess the viability of a new sealing mechanism for gas and steam turbines. This new static-to-rotating sealing mechanism is mounted on flexible legs which permit radial movement and is designed to take advantage of the hydro-dynamic pressure forces, which result from fluid leaking around the seal, to maintain an ideally small and constant clearance. Relatively simple seal geometries have been numerically tested to find an optimal shape. These results indicate that a substantial sealing improvement (between two and four times less leakage) relative to a labyrinth seal is possible. Although these results show that a brush seal is more effective than the present seal, the present seal is designed to operate in high-speed and high-temperature environments in which the brush seal would degrade.