<p>The demand for heat pumping technologies is expected to see
tremendous growth over the next century. Traditional vapor compression cycles
are approaching practical limits of efficiency and running out of possibilities
for environmentally friendly and safe refrigerants. As a result, there is an increasing interest
in pursuing non-vapor compression technologies that can achieve higher
efficiencies with alternative working fluids. The chemical looping heat pump
(CLHP) investigated here utilizes a chemical reaction to alternate a working
fluid between more and less volatiles states. This allows the main compression
to take place in the liquid phase and enables the utilization of a range of
different working fluids that would not be appropriate for vapor compression
technology. </p>
<p> </p>
<p>Thermodynamic models were developed to assess the potential
performance of a chemical looping heat pump driven by electrochemical cells. A
number of potential working fluids were identified and used to model the
system. The thermodynamic models indicated that the chemical looping heat pump
has the potential to provide 20% higher COPs than conventional vapor
compression systems. </p>
<p> </p>
<p>An experimental test stand was developed to
investigate the efficiency with which the electrochemical reactions could be
performed. The working fluids selected were isopropanol and acetone for reasons
of performance and availability. The test stand was designed to measure not
only the power consumed to perform the conversion reaction but also the
concentration of products formed after the reaction. The experimental tests
showed that it was possible to perform the reactions at the voltages required
for an efficient chemical looping heat pump. However, the tests also showed
that the reactions proceed much slower than expected. To increase the rates of
the reactions, an optimization effort on the membrane and catalyst selections
was performed. </p>
<p> </p>
<p>Traditional catalyst materials used by solid
polymer electrochemical cells, like those used in the testing, perform best in
hydrated environments. The fluids isopropanol and acetone tend to displace
water in the membranes, reducing the system conductivity. Multiple membrane types
were explored for anhydrous operation. Reinforced sPEEK membranes were found to
be the most suitable choice for compatibility with the CLHP working fluids.
Multiple catalyst mixtures were also tested in the experimental setup. Density
functional theory was used to develop a computational framework to develop
activity maps which could predict the performance of catalyst materials based
on calculated parameters. </p>
<p> </p>
<p>A detailed model of the CLHP electrochemical cell
was developed. Built on open-source tools, the model was designed to determine
the charge, mass, and heat transfers within the cell. The conversion of
reactants along the channel of the cell as well as overall power consumption
are predicted by the model. The model was validated against measurements and
used to determine parameters for a CLHP cell that would have improved
conversion performance and energy efficiency compared with the tested cell. </p>
<p> </p>
<p>The cell model was integrated into an overall
system model which incorporates the effect of concentration changes throughout
the entire cycle. Compared to the early-stage thermodynamic modeling,
consideration of incomplete reactions provided more accurate predictions of the
potential performance of CLHP systems. Different cell and system architectures
were investigated to boost system performance. The model predictions
demonstrated that the CLHP has the potential to provide high heat pumping
efficiencies, but more work is still needed to improve the energy density of
the system. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/7473842 |
| Date | 10 May 2019 |
| Creators | Nelson A. James (5929826) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Investigation_of_Chemical_Looping_for_High_Efficiency_Heat_Pumping/7473842 |
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