Experimental and Numerical Analysis of a PCM-Supported ...

9 Summary and conclusions
9.1 Summary
This work discusses the results of experimental and numerical studies on a
humidification-dehumidification (HDH) system utilizing conductive packing media in
the evaporator and condenser. The objective of using conductive packing is to
achieve multiple-effects of heating/humidification (MEHH) and
cooling/dehumidification (MECD) while air passing through the successive packing
layers in the evaporator and condenser respectively. The major objective of this
study is to examine the innovative approach for locally creating MEHH and MECD
and to determine the technical and economic feasibility of applying conductive
packing media in the evaporator and condenser and PCM thermal storage in HDH
solar desalination plants under both steady state operation conditions.
A mixed micro-macro balance transient simulation model has been established and
validated against experimental measurements using COMSOL Multiphysics and
MATLAB for solving fluid flow and heat and mass transfer phenomena in one spatial
dimension for different components in such a loop. At the macroscale, the wetting
phase is described in terms of its average properties within a small volume by using
the interpenetration continua and volume averaging technique. Thus, at each point,
a macroscale phase is characterized as occupying a fraction of the available volume
and to have a certain interface per unit volume with other phases. Each phase in the
system is described in a similar way. Precise definition of the interface shape is
neither required nor possible to obtain at the macroscale. On the macro level, the
continuous solid approach for modeling phase change regenerators (PCR) is applied
using the apparent heat capacity formulation. All sensible and latent heat rates are
defined at the common interfaces based on the local temperatures of all phases,
which are coupled together and updated as a function of space and time. Thus, the
MEHH and MECC can be captured at successive points along the packing height.
Using the simulation tools, a detailed heat and mass transfer analysis for the
dynamic performance of a PCM-supported HDH system over a wide range of
operation conditions has been undertaken. Experiments, not only on laboratory scale
but also as a prototype, were designed and performed to measure fundamental time
dependent variables and critical parameters affecting the system performance. A
system parameters analysis for the main single components as well as for the whole
HDH plant with its supporting solar collector field and PCM thermal energy storage
has been performed under varying weather conditions over one year for Al-Arish City
on the eastern north coast of Egypt. The analysis focuses on the optimum coupling
and operation conditions of the HDH system with the solar collector field and the
external thermal buffer. Special attention has been paid to the effect of thermophysical
properties of the packing media and heat recovery enhancement.
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