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

The power industry is one that is currently undergoing great change—a trend likely to continue in the future. As it does so, I believe the role of the manager and the engineer within it will change significantly, providing a challenge to those who are schooled in the old ways and with implications for new engineers emerging from universities and training programmes. I would like to share my thoughts on this with you, starting with discussing a little of the background of how the industry has developed and moving on to how it might look in the future and what that would mean for engineers working within it.

A graphical method of calculating the performance of gas turbine cycles, developed by Hawthorne and Davis (1), is adapted to determine the pressure ratio of a combined cycle gas turbine (CCGT) plant which will give maximum overall efficiency. The results of this approximate analysis show that the optimum pressure ratio is less than that for maximum efficiency in the higher level (gas turbine) cycle but greater than that for maximum specific work in that cycle.

Introduction of reheat into the higher cycle increases the pressure ratio required for maximum overall efficiency.

This paper describes a method used to compute the transient performances of assisted circulation heat recovery steam generators. These heat recovery steam generators are composed of several heat exchangers, each of which is a bundle of tubes. The method presented here treats each heat exchanger in a similar way, replacing the bundle of tubes with an ‘equivalent’ linear heat exchanger.

This equivalent linear heat exchanger is then discretized in as many slices as required by the accuracy. The mass and enthalpy equations on each of these control volumes are solved by a fully explicit numerical method, adapted for the special conditions encountered in this kind of problem, allowing a considerable reduction of the computation time compared to other methods.

Some emphasis is put on the modifications required to solve the equations for the evaporators because they are two-phase heat exchangers. A model for the steam drums is also presented together with simple models for the main control loops used in such systems. An example is presented in which an existing dual pressure level heat recovery steam generator is started from a cold state. The numerical predictions are in good agreement with measurements.

In this paper a system of names and symbols for exergy analysis is put forward for further discussion. The concept of exergy is shown to be dependent on that of the environment. The conceptual environment provides a natural reference state for calculating absolute values of exergy. For calculating loss of exergy, or process irreversibility, an exergy balance or the Gouy–Stodola relation can be used. The concept of chemical exergy can facilitate the computational work involved in exergy analysis. The paper offers a glossary of terms used in exergy analysis and shows the proposed symbols in the context of expressions in which they might be used.

BRAKINE is a component-matching thermodynamic analysis computer program designed to simulate both the design point and off-design steady state performance of arbitrary BRAyton or RanKINE cycle plants, or of combined cycles and cogeneration processes. Plant performance can be appraised by simulating either all fluid streams or only those streams that completely describe the working cycle. A power plant is assumed to be constructed in modular form with each component handling a specific thermodynamic process. As a result, flexibility of operation is provided by the use of ‘codewords’, which allow the user to simulate any plant type by stacking in the appropriate sequence the various modules that describe the performances of the components that make up the plant. This paper describes the mechanics of operation of BRAKINE and concludes that the program is a useful tool for power plant performance simulation.

The objective of this study was to derive the thermodynamic formulae for ideal combined driving and cooling cycles when the objective of the overall cycle is to produce cooling by using a high-temperature heat source. For this it has been necessary to investigate absorption cooling thermodynamics and to focus on the analysis of one-, two- and three-stage cycles and multi-stage cycles in general. This paper has investigated the absorption thermodynamic principles involved to obtain simple formulae, in a similar way to the Carnot cycle. The first driving cycle considered has a high-temperature source such as a combustion process. From this driving cycle the heat dissipated at the lower temperature is used to drive the next consecutive driving and/or absorption cooling cycles. All the work produced in the driving cycles is used for the cooling cycles with mechanical compressors, whereas the dissipated heat of the last driving cycle is used to drive the absorption cycles. A simple universal law for driving and cooling cycles has been derived, which is applicable to combined heat and power (cogeneration) systems.

A previous study using a cycle simulation program had identified the possibility that highly rated diesel engines might benefit from a variable valve timing (VVT) system. In particular, the study had shown that, by delaying the start of inlet valve opening at part load, it should be possible to eliminate the reverse flow that can lead to inlet port fouling. The work reported here encompasses the design and implementation of a variable valve timing system on a highly rated high-speed marine diesel engine. The principal topics addressed are the selection and design of a mechanism, a comparison between the predictions and results from mechanism testing on a single-cylinder valve-train rig and the engine performance predictions and results obtained when the mechanism was tested on the engine.

The results from the single-cylinder test rig demonstrated that the mechanism performed satisfactorily, and this led to a design suitable for retro-fitting to the engine. The engine was comprehensively instrumented and the experimental results were in good agreement with the cycle simulation predictions.

Automatic hydraulic ram pumps are environmentally friendly devices using a renewable energy resource to pump water for domestic or agricultural use. Since being superseded by pumps using electrical or fossil fuel energy nearly a century ago, they are now coming back into favour in many parts of the developing world.

In the past, hydraulic ram pumps have been designed by rules-of-thumb having limited scientific basis. On-site adjustment has been used in the hope of rectifying the inevitable shortcomings of this process and ideal performance is rarely achieved. The present proposal for optimum design allows relevant system parameters (including the beat frequency) to be selected prior to installation.

The paper shows how a ram pump system may be designed using two simple equations containing empirical factors dependent upon ram size, delivery head, material and wall thickness of the drive pipe and the configuration of the impulse valve. The design method is illustrated with reference to a number of existing tests. New experimental results for a 53 mm ram with five different impulse valve strokes are also presented.