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Regeneration Validation

During the regeneration process water vapour contained within the desiccant solution is desorbed to a scavenger air stream, usually by heating the desiccant solution such that it has a higher vapour pressure than that of the inlet air stream. Table 3.7 shows the inlet conditions for thirteen regenerator tests (R1-R13) carried out by Ge et al. (2014). These conditions were used as the inlet boundary conditions for the regenerator model during validation.

The performance indicators used for the regenerator validation are outlet desiccant temperature, outlet desiccant solution mass concentration and latent and enthalpy effectiveness, as shown in Figs. 3.12 and 3.13 respectively. In terms of regenerator performance and its impact on the performance of the whole desiccant air conditioning system, the outlet conditions of the scavenger air stream are not critical. However, the outlet condition of the desiccant solution is, as this is what then flows back to the dehumidifier. As a result, the desiccant outlet condition is what has been focused on in the regenerator validation work.

Table 3.7 Inlet experimental conditions for LiCl regenerator tests Ge et al. (2014)

Test

ma (kg s ')

Ta (°C)

^a (kgvap/kgdryair)

mSol (kg s ')

o

о

n

Xsol (-)

R1

0.001479444

30

0.0146

0.002237778

55.1

0.3216

R2

0.001017778

30

0.0137

0.001523889

55

0.3229

R3

0.000748611

30

0.0144

0.001113889

55

0.3229

R4

0.001505278

25

0.0142

0.0022775

55

0.3232

R5

0.001455278

35

0.0135

0.002198611

55

0.3232

R6

0.0014675

30

0.0199

0.002243889

55.1

0.3202

R7

0.001486667

30.1

0.0084

0.002206944

55

0.322

R8

0.001481667

29.9

0.0134

0.001123889

55

0.32

R9

0.001481389

30

0.0138

0.003326111

55

0.32

R10

0.001483611

29.9

0.0139

0.002241111

50.1

0.3204

R11

0.001483889

30

0.0142

0.002245833

45

0.3204

R12

0.001482778

30.1

0.0144

0.002265556

55.1

0.37

R13

0.00148

30

0.0143

0.0021375

55

0.27

a Regenerator outlet desiccant temperature and b regenerator outlet solution mass concentration

Fig. 3.12 a Regenerator outlet desiccant temperature and b regenerator outlet solution mass concentration

a Regenerator latent effectiveness and b regenerator enthalpy effectiveness

Fig. 3.13 a Regenerator latent effectiveness and b regenerator enthalpy effectiveness

Table 3.8 Average percentage difference results over the thirteen regenerator tests

Parameter

Average relative difference (%)

Tsol,out

6.6

-Xsol,out

0.28

nL

22.14

nL,th

18.08

nh

16.22

Figure 3.12a, b show that the simulated solution outlet temperature and desiccant solution mass concentration respectively, fit within the 10 % margin for all thirteen experimental tests. However, Fig. 3.13a, b show that the latent and enthalpy effectiveness do not fit the experimental data so well. Ge et al. (2014) explains that during regeneration, crystallisation of the desiccant solution at certain concentrations and temperature could pose a barrier to heat and mass transfer across the membrane, evident in the lower experimental latent and enthalpy effectiveness values compared to the simulation results. The average difference with the theoretical latent effectiveness values is lower.

Table 3.8 shows the average relative percentage difference between the paper’s experimental work and the simulations, for all regenerator performance parameters. The average difference for outlet solution temperature and mass concentration is acceptable i.e. <10 %; however for the latent and enthalpy effectiveness the values show larger discrepancy. As highlighted by Ge et al. (2014), this difference can be attributed to the issue of solution crystallisation.

Next, Sect. 3.4.3 provides a validation summary.

 
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