Regenerator Parametric Analysis

The regenerator parametric analysis has a different perspective to that presented in the dehumidifier analysis. For the dehumidifier, the outlet condition of both the

Table 3.11 Regenerator base simulation conditions

air and desiccant solution are of importance. However, in the regenerator the air outlet condition is not critical but the outlet condition of the desiccant solution is, as this is what then flows back to the dehumidifier and governs whether the system is balanced. As a result, the desiccant outlet condition is what has been focused on in the regenerator parametric analysis. The regenerator parametric analysis will investigate the impact: inlet air relative humidity, inlet air temperature, desiccant solution mass flow, desiccant solution temperature and desiccant solution mass concentration have on the overall performance of the regenerator. These variables have been selected due to their influence on regenerator performance.

The regenerator parametric analysis uses the same geometrical specification and operating values used in dehumidifier analysis; these are listed in Table 3.9. Specific regenerator boundary conditions are provided in Table 3.11.

To facilitate continuous operation of a desiccant air conditioning system, the weak desiccant solution leaving the dehumidifier must be regenerated i.e. remove the moisture absorbed in the dehumidifier, and thus restore its dehumidification potential. The regenerator has been simulated in order to allow the continuous operation of the dehumidifier presented in Sect. 3.5.1. In Sect. 3.5.1, it was shown that the desiccant solution leaving the dehumidifier has a mass concentration of 0.6948 and temperature of 25.3 °C. The regenerator model shows that the desiccant solution must be heated to 58.5 °C to regenerate the desiccant solution back to a mass concentration of 0.7. Thus, in the regenerator parametric analysis, the inlet desiccant solution mass concentration and temperature have been set to 0.6948 and 58.5 °C respectively.

Figure 3.20 demonstrates the regeneration process on a psychrometric chart. Based on the regenerator conditions selected, the outlet regenerator air stream is heated to 48.61 °C with a 44.2 % RH. This equates to an increase in the air streams absolute humidity of 0.00994 kg_vapour/kg_dryair. At the regenerator outlet the desiccant solution temperature is 52.43 °C, with a mass concentration of 0.7. The latent effectiveness of this process is 34.44 %.

Following regeneration the desiccant solution needs to be sensibly cooled prior to entering the dehumidifier; this could be achieved in two stages (1) in a desiccant to desiccant plate heat exchanger, exchanging heat with the desiccant flowing to the regenerator, and (2) using cooling water from an evaporative cooling process.

Fig. 3.20 The regeneration process shown on a psychrometric chart