In this study a semi-passive pulse thermal loop (PTL) was designed and experimentally
validated. It provides improved heat transfer over passive systems such as the loop heat pipe in
the moderate to high heat flux range and can be a sustainable alternative to active systems as it
does not require an electric pump. This work details the components of the engineering
prototype and characterizes their performance through the application of compressible and two-phase
flow theory. A custom LabVIEW application was utilized for data acquisition and
control. During operation with refrigerant R-134a the system was shown to be robust under a
range of heat loads from 100 W to 800 W. Operation was achieved with driving pressure
differentials ranging from 3 bar to 12 bar and pulse frequencies ranging from 0.42 Hz to
0.08 Hz. A smaller pressure differential and an increased pulse frequency results in improved
heat transfer at the boilers.
An evolution of the PTL is proposed that incorporates a novel, ejector-based pump-free
refrigeration system. The design of the pulse refrigeration system (PRS) features valves at the
outlet of two PTL-like boilers that are alternately actuated to direct pulses of refrigerant through
an ejector. This is intended to entrain and raise the pressure of a secondary stream of refrigerant
from the cooling loop, thereby replacing the compressor in a conventional vapor-compression
cycle. The PRS is therefore characterized by transient flow through the ejector. An experimental
prototype has been constructed which is able to operate as a conventional PTL when the cooling
section is bypassed, although full operation of the refrigeration loop remains to be
demonstrated. The design of the ejector is carried out using a one-dimensional model
implemented in MATLAB that accounts for compressibility effects with NIST REFPROP vapor
data sub-routines. The model enables the analysis of ejector performance in response to a
transient pressure wave at the primary inlet.
The high driving pressures provided by the PTL permit operation in a micro-gravity
environment with minimal power consumption. Like the PTL, the proposed PRS is therefore
well suited to terrestrial and aerospace applications where it could be driven by waste heat from
electronics or solar thermal energy. As a novel semi-passive thermal management system, it will
require complex control of the valves. Further analysis of the transient thermodynamic cycle is
necessary in order to characterize and effect successful operation of the PRS. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2013.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9124 |
| Date | January 2013 |
| Creators | Du Clou, Sven. |
| Contributors | Brooks, Michael J., Roberts, Lance W. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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