Track: Renewable Energy

Abstract

In this work, the role of Phase Change Material (PCM) submerged in water tank in controlling its temperature is
investigated both theoretically and experimentally. In the experimental part, an organic PCM (Tricosane) is used
inside vertical tubes submerged in the water tank to absorb heat when heat is provided to the tank at constant
rate and then release it to the water when the source of heat is turned off. The effect of the amount of PCM on the
water temperature is studied. The amount of PCM is represented by a parameter (R) defined as mass of PCM
mass of water
. The
effect of using PCM is demonstrated by measuring the change in the water temperature. The presence of PCM in
the water resulted in the appearance of two zones in which the temperature remains constant due to melting and
solidification of the PCM. In the melting zone the heat provided to the PCM is absorbed hence maintaining its
temperature constant. The second zone appears after the heating is stopped where heat losses is subsidized by
the heat of fusion of the PCM. The experimental results showed that as the value of R increases, both zones
become longer specially the second zone. Accordingly, the time for the temperature to drop to a certain value say
45 °C (a temperature that one can use the water comfortably) is longer as the value of R increases. In fact, the
time it took the water to drop to 45 °C is doubled when R=0.95 compared to the case when no PCM is present in
the system.
The change in water temperature was theoretically calculated by performing heat balance on the system in
the different zones (heating and cooling zones). It is assumed that the temperature of the components of the
system (water, PCM, glass tubes, tank) is the same. The results verified those observed experimentally. The effect
of the overall heat transfer coefficient (U), type of PCM expressed by its latent heat (λ), was investigated. It was
found that the time it took the temperature of the system to drop to a given temperature increases as U decreases
and λ increases. Moreover, the zones at which the temperature remains constant become longer when U decreases,
λ and R increase. This suggests that the system temperature can be controlled by insulating the system
and using proper values of R and λ. The developed model was validated using the experimental results of this
work. The outcome showed an excellent agreement between the experimental results and the model.