There has been renewed significance for innovative energy conversion
technologies, particularly the heat recovery-to-power technologies for
sustainable power generation from renewable energies and waste heat. This is
due to the increasing concern over high demand for electricity, energy shortage,
global warming and thermal pollution. Among the innovative heat recovery-to-
power technologies, the proposed trilateral flash cycle (TFC) is a promising
option, which presents a great potential for development. Unlike the Rankine
cycles, the TFC starts the working fluid expansion from the saturated liquid
condition rather than the saturated, superheated or supercritical vapour phase,
bypassing the isothermal boiling phase. The challenges associated with the
need to establish system design basis and facilitate system configuration
design-supporting analysis from proof-of-concept towards a market-ready TFC
technology are significant. Thus, there is a great need for research to improve
the understanding of its operation, behaviour and performance. The objective of
this study is to develop and establish simulation tools of the TFCs for improving
the understanding of their operation, physics of performance metrics and to
evaluate novel system configurations for low-grade heat recovery-to-power
generation. This study examined modelling and process simulation of the TFC
engines in order to evaluate their performance metrics, predictions for guiding
system design and parameters estimations. A detailed thermodynamic analysis,
performance optimization and parametric analysis of the cycles were
conducted, and their optimized performance metrics compared. These were
aimed at evaluating the effects of the key parameters on system performances
and to improve the understanding of the performance behaviour. Four distinct
system configurations of the TFC, comprising the simple TFC, TFC with IHE,
reheat TFC and TFC with feed fluid-heating (or regenerative TFC) were
examined. Steady-state steady-flow models of the TFC power plants,
corresponding to their thermodynamic processes were thermodynamically
modelled and implemented using engineering equation solver (ESS). These
models were used to determine the optimum synthesis/ design parameters of the cycles and to evaluate their performance metrics, at the subcritical operating
conditions and design criteria. Thus, they can be valuable tools in the
preliminary prototype system design of the power plants. The results depict that
the thermal efficiencies of the simple TFC, TFC with IHE, reheat TFC and
regenerative TFC employing n-pentane are 11.85 - 21.97%, 12.32 - 23.91%,
11.86 - 22.07% and 12.01 - 22.9% respectively over the cycle high temperature
limit of 393 - 473 K. These suggest that the integration of an IHE, fluid-feed
heating and reheating in optimized design of the TFC engine enhanced the heat
exchange efficiencies and system performances. The effects of varying the
expander inlet pressure at the cycle high temperature and expander isentropic
efficiency on performance metrics of the cycles were significant. They have
assisted in selecting the optimum-operating limits for the maximum performance
metrics. The thermal efficiencies of all the cycles increased as the inlet
pressures increased from 2 - 3 MPa and increased as the expander isentropic
efficiencies increased from 50 - 100%, while their exergy efficiencies increased.
This is due to increased net work outputs that suggest optimal value of pressure
ratios between the expander inlets and their outlets. A comprehensive
evaluation depicted that the TFC with IHE attained the best performance
metrics among the cycles. This is followed by the regenerative TFC whereas
the simple TFC and reheat TFC have the lowest at the same subcritical
operating conditions. The results presented show that the performance metrics
of the cycles depend on the system configuration, and the operating conditions
of the cycles, heat source and heat sink. The results also illustrate how system
configuration design and sizing might be altered for improved performance and
experimental measurements for preliminary prototype development.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/9202 |
| Date | 10 1900 |
| Creators | Ajimotokan, Habeeb A. |
| Contributors | Sher, I., Yeung, Hoi |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Doctoral, PhD |
| Rights | © Cranfield University 2014. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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