ZEMCH 2019 International Conference Proceedings April.2020 | Page 137
Since most of the favorable characteristics are found in paraffin waxes, a commercial grade of
paraffin wax (RT‐31, Rubitherm, 2016) proposed due to its favorable features such as its availability,
lower cost, lower corrosion rates, chemical stability and human friendliness compared with other PCM
such as salt hydrates. The material is also recommended for its congruent melting with no supercooling
effect.
2.3. System Designing
The typical AC duct cooling system consist of supply and return air transfer systems. The supply
system is designed to distribute the conditioned air to the selected space. The proposed pre‐cooling
unit will be placed in the duct system as shown in Fig 3.
Figure 3. The schematic design of the PCM enclosures embedded in air duct.
The hot air will be supplied to the test chamber with specified velocity while the PCM containers
will be placed facing the hot air. The hot air will be bumped through the surfaces of the PCM containers
allowing the heat to transmit to the PCMs. The PCM will work as latent heat storage units cooling the
surrounding air.
2.3.1. Experimental Setup
The experiments conducted in Falaj Hazza Campus, UAE University Al Ain – UAE. The ambient
temperature of in summer day in Al‐Ain is considered as an input to the test chamber. The experiment
run for three consecutive days.
A chamber with dimensions of 45 cm × 90 cm × 20 cm, to mimic the air conditioning duct system
installed in building. The air duct system was tested subjected to variant air velocities supplied by air
pump. A 4‐mm thick sheet of aluminum alloy (1050A) was used to fabricate the metallic PCM
containers. Four PCM enclosures (5*300*20 cm3) filled with the solid PCM were embedded vertically
inside the duct with a gap of 5‐cm between the containers.
Multiple calibrated T‐type copper‐constantan thermocouples were placed at different positions
across the air duct system and inside the PCM. The sensors were connected to a data logger (National
Instruments‐NI, Compact‐Rio) to store and retrieve the data. The PCM was filled as liquid in the
containers and subsequently cooled until it was completely solidified. The solidified PCM left a 7‐cm
free space on top of the container which was intended to accommodate volume expansion during the
PCM melting. The experiments are running in Falaj Hazza Campus, UAE University Al Ain – UAE,
and the results are under preparation.
2.3.2. Numerical Model
A two‐dimensional, finite‐volume, heat transfer model of four PCM enclosures embedded in air
duct is developed. The PCM is treated as incompressible fluid since no pressure induced volume
changes are expected in the computational domain with melt flow. The model ignores marginal effects
such as the volume changes in PCM after phase transition, natural convection within melted PCM and
floating/sinking of solid dendrites within melted PCM caused by buoyancy.
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