UWE Bristol Engineering showcase 2015

Heat Exchanger Operating Conditions
An Experiment was conducted in order to
determine the optimum placement of the
heat exchanger within the exhaust.
Thermocouples were inserted in both the
exhaust manifold and the stack to measure
the difference in temperature and time taken
to reach steady state conditions.
Cameron Adams
Mechanical Engineering
The Conceptual Design and Development of a Steam Powered Rankine
Cycle for the Energy Recovery of Exhaust Gases
Concept Designs for Heat Exchangers
Two different heat exchanger designs were completed, in order to account for the difference in thermal
and dimensional restrictions imposed at the potential mounting positions. An NTU-Effectiveness
calculation was then undertaken in order to determine the best heat exchanger design for the job, with
the counter flow achieving an effectiveness of 69.5% compared with the 37.6% achieved by the crossflow
.
Design 1 – Counter-Flow
Design 2 – Cross-Flow
Project Supervisor : Dr. Rohitha Weerasinghe
Project summary
The Purpose of this investigation is to analyse the
feasibility of the implementation of a steam powered
Rankine cycle within a standard automobile exhaust.
This report uses existing research accompanied with
experimental and simulation techniques in order to
provide validation of the thermodynamic cycle and its
application within a petrol fuelled exhaust.
Two designs are proposed and evaluated for the
evaporation stage of the cycle; resulting in a final
design being chosen. This design was then developed
by theoretical calculation and simulation, evaluating
the incurred pressure-drop across the component.
System analysis is then completed in order to
optimise the cycle and thermal efficiencies based on
the specified design of the heat exchanger.
Project Objectives
Temperature (°C)
• Provide investigation into optimum working fluid
• Produce the conceptual design and comparison of
multiple methods of heat exchange
• Analyze the system performance based on the
designed heat exchanger
Time (s)
When the most effective heat
exchanger had been determined, a
simulation was created to analyze the
effect of the inlet velocity of the shell
side fluid on the pressure drop across
the component. A full scale model was
created within the ANSYS environment
and used to display pressure contours
over the longitudinal axis.
Log Mean Temperature Calculation
Post simulation, a calculation was undertaken in
order to determine the length of pipe required to
achieve the desired outlet temperature of the heat
exchanger. It was found that using the velocity
previously determined, a minimum length of pipe
required was 2.49m which exceeded the
dimensional restrictions set by the on road
applicability of the system.
System Analysis
After concluding that the outlet temperature
required couldn’t be achieved within the design
specification, alternate suggestions were evaluated.
The graph on the right shows a reheat cycle with a
system efficiency of 55.7% and thermal efficiency
of 46.8%. The downside to this suggestion is that
additional heat exchangers will be required to
achieve the reheat and superheat sections of the
cycle.
Simulation
Using the results of the simulation, an inlet velocity of 0.3
m/s was selected, the pressure drop measured for this
velocity was considered relatively negligible, and therefore
a suggestion for further investigation into the effect of
baffles on the increase of heat transfer has been made.
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Project Conclusion
The double pipe design concept was proven to be
the most effective design considering the thermal
and dimensional restrictions imposed.
Preliminary investigation has proven that water is
the most effective working fluid, due to its inherent
ability to increase the mechanical and thermal
efficiency of the desired cycle. In addition to this the
availability and low environmental impact of this
working fluid further give validation to the selection.
Moreover, experimentation has proven that the
temperature achieved within the exhaust is sufficient
to provide a viable heat source for application of a
Rankine thermodynamic cycle. However considering
the design restrictions imposed on the exhaust by the
on road applicability of the system, the required
temperature for a feasible Rankine cycle cannot be
achieved with a single heat exchanger.
Finally, to mitigate this problem alternate
suggestions have been provided to provide useful
means for the recovery of energy within the system.