Dehumidifier and Regenerator Parametric Analysis

Section 3.4 has validated, to an acceptable level, the dehumidifier and regenerator models, operating with a LiCl solution. This section presents a parametric analysis for the desiccant dehumidifier and regenerator, operating with a CHKO2 solution.

The modelling work in this thesis does not aim to progress the state of the art, but to facilitate a better understanding of the process and performance of such systems and thus draw relevant conclusions that are pertinent to the integration of liquid desiccant air conditioning technology with a SOFC in a novel tri-generation system set-up. The parametric analysis will investigate both the dehumidification and regeneration processes, focusing on the impact inlet environmental and operating conditions have on performance.

The geometric specification and operating values for the dehumidifier and regenerator parametric analysis are presented in Table 3.9. The dimensions of the modelled heat and mass exchanger are based upon the experimental dehumidifier and regenerator (SDCS) presented in Chap. 6. The desiccant solution mass flow rate selected is based on a value that provides acceptable wetting of the membrane in the experimental system, without creating superfluous desiccant flow into the supply airstream. Often, theoretical investigations do not consider the practical implications of the operating values used. In liquid desiccant air conditioning systems high liquid desiccant flow rates result in unwanted desiccant solution carryover to the supply airstream. Furthermore, high volumetric air flow rates are not achievable due to pressure drops in the exchanger core.

In the parametric investigations, a high humidity scenario has been selected to demonstrate the capability of liquid desiccant dehumidification systems in reducing air moisture content. Next, Sect. 3.5.1 presents the dehumidifier parametric analysis.

Table 3.9 Dehumidifier and regenerator geometrical specification and operating values

Parameter

Value

Length of exchanger (mm)

410

Height of exchanger (mm)

210

Width of air channel (mm)

10

Wall thickness (mm)

1

Inlet air temperature (°C)

30

Inlet air relative humidity (%)

85

Inlet air absolute humidity (kgvap0ur/kgdryair)

0.02297

Desiccant solution volumetric flow (L min-1)

3.2

Desiccant solution mass flow rate per channel

(kg s-1)

0.00192

Table 3.10 Dehumidifier base simulation conditions

Parameter

Value

Inlet air velocity (m s-1)

1.2

Inlet air volumetric flow (m3 h-1)

191

Desiccant solution mass concentration (-)

0.7

Desiccant solution temperature (°C)

24

Convective heat transfer coefficient (W m-2 K)

11.4

Convective mass transfer coefficient (kg m-2 s)

0.0082

 
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