UWE Bristol Engineering showcase 2015

Harry Carmichael
Meng Mechanical Engineering
Project Supervisor
Dr Aruna Palipana
Design and Viability Analysis of a Diffuser Augmented Hydrokinetic Power
Generation System
Introduction
As the search for alternative renewable energy sources continues amidst
dwindling fossil fuel resources, hydropower has seen a strong increase in interest
and development over the last few decades. However, a subsidiary of
hydropower- hydrokinetic power, has only come into the spotlight in recent years,
namely to generate electricity from the tides. Unfortunately this method of
power production is expensive and thus economically unfeasible for countries in
the developing world. It stands to reason that similar, although on a smaller scale,
hydrokinetic power systems could be applied to other fast flowing water
resources such as rivers that could be economically viable in poverty stricken
regions. An investigation was performed into the optimal design of a diffuser and
the economical feasibility of hydrokinetic power generation system in a rural area
of South Africa
The aim of this thesis is to explore the development of a diffuser augmented
hydrokinetic turbine to relieve electricity poverty in rural areas. This system is
then compared against other power generation systems to find which option is
the most viable.
Finally a discussion took place on how assumptions and errors may have affected
results. It was found that the CFD results have a 6% over prediction in results
compared to the theoretical results.
System Hydrokinetic Solar Wind Diesel
Generator
Capital cost (£) 42,408 28,969 65,200 22,110
Operating cost
(£/year)
Total cost over life
time (£)
Cost of energy
(£/kWh)
Carbon dioxide
emission
(kg/year)
1,062 1,564 1,304 Including the
cost of diesel
fuel: 4,897
132,315 155,070 190,338 174,657
0.076 0.089 0.109 0.099
0 0 0 27,919
Computational Fluid Dynamics
Due to the complex and large number of equations involved in calculating
numerical solutions of fluid flow, computational fluid dynamics software
packages are used to perform the analysis in as short a time as possible. An
image of the outcome of one of the simulations is shown below to the left
The power coefficient, also thought of as the efficiency, was also compared
between the diffuser augmented turbine and the bare turbine. As can be seen
from the graph, the power coefficient is highest for the diffuser augmented
turbine. This led to a power increase of 75% compared to the un-ducted
turbine .
Economical Viability
An economical analyses was performed on the hydrokinetic turbine compared
to other power generation methods. From the table shown below, the
hydrokinetic power system was shown to be the best long term investment
option despite having a higher capital cost than solar power.
From the data collected and the results gained, it can be said with a strong
amount of confidence that the diffuser caused a positive power augmentation.
The percentage increase in power production is considerable, and is a much
more attractive solution than deploying a turbine without a diffuser.
0.8
0.7
0.6
0.5
POWER COEFICIENT
0.4
0.3
0.2
0.1
0
Velocity against the Power
Cp no diffuser Coefficient
Cp with diffuser
0 0.5 1 1.5 2 2.5 3 3.5 4
VELOCITY (M/S)
Project summary
An investigation has been performed to study the
viability of a diffuser augmented hydrokinetic power
generation system for deployment in rural or poverty
stricken regions without access to electricity.
A variety of computational fluid dynamic models were
designed and tested to find an optimal diffuser design.
This was followed by an economical viability study for
the hydrokinetic power generation system compared to
other power generation methods such as solar, wind
and a diesel generator.
The optimal diffuser design had a diffusion angle of 16
degrees and a length of 0.6m. The cost per kWh for this
system was £0.0701 per kWh
Project Objectives
• Investigate the study site for river parameters.
• Develop and analyse the diffuser concept using
software simulations to find an optimal diffuser
design
• Compare the economic feasibility of this concept
compared to other power generation methods.
• Examine how assumptions made during the design
of the concept and analysis could have affected
results.
Project Conclusion
It can be confidently concluded that an optimal diffuser
design was found as the system produced an increase in
power equal to 175% of the turbine without a diffuser
installed.
The economical analyses also found the hydrokinetic
system to be the best long term investment. Despite
not having the lowest capital investment cost.