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

For liquid-gas phase change problems, the gas phase is assumed to be saturated at
its local temperature, since the air circulates in a closed loop. This implies that the
water vapor concentration (or vapor pressure) at the liquid-gas interface and in the
bulk gas phase can be calculated as a function of the interface and gas
temperatures respectively. Hence the driving forces for heat and mass transfer are
coupled together through equations (4.36) to (4.39). The bulk gas concentration is
calculated according to Dalton’s law and equation of state for ideal gas mixture,
assuming saturation conditions and the total pressure of the water vapor-air mixture
equals to the atmospheric pressure. It can also be calculated using equation (2.11).
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, heating/cooling the gas and liquid phases by the
solid phase at a certain point or packing height, is directly influencing their local
temperatures and mass transfer rates at the next point of the numerical calculations
scheme.
Those overall characteristics of the MEHH and MECD phenomena on both micro
and macro scale levels could be captured through the implementation strategy
adopted (as will be proved and validated against experimental measurements in
chapter 6) while the computational efforts and cost are incomparably much better
than a detailed micro scale analysis using for instance a CFD simulation platform.
For simulation of the natural flow system, the model couples the momentum balance
to energy and mass balances through a bouyant force term, dependant on
temperature and concentration gradients (i.e. equation 4.31). The bouyant forces are
directly introduced into the source term for the momentum balance.
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