SDCS Experimental Set-up
This section provides a detailed description of the experimental set-up, instrumentation and experimental method used in the testing of the SDCS.
As previously discussed in Sect. 5.4, operational issues with the IDCS means it is not suitable for tri-generation system integration. Therefore a SDCS has been developed. As with the IDCS, the SDCS uses a semi-permeable micro porous membrane based cross flow contactor, operating with a low cost, environmentally friendly, non-corrosive potassium formate desiccant solution. Figure 6.1 shows a schematic diagram of the complete SDCS with labelled components.
The SDCS consists of three separate cores; dehumidifier (D/C), regenerator (R/C) and evaporative cooler (E/C). In the dehumidifier and regenerator, each HMX is 410 mm in length, 210 mm in height and 230 mm in width. The cores consist of 21 channels that allow air and desiccant solution to flow in a cross flow manner (air through the core, desiccant downwards through the core), separated by a fibre membrane. The solution channels consist of a polyethylene sheet, with fibre membranes attached on either side. The gap between the two solution channels provide the space for the air to flow. The semi permeable micro-porous fibre membrane allows the diffusion of water vapour, but prevents liquid desiccant solution migrating across it, thus overcoming the issue of liquid desiccant entrainment in the air stream. The evaporative cooler core is also 410 mm in length, 210 mm in height and 230 mm in width, with 21 air channels. There is no inclusion of a membrane, only a fibre material to create the air channels and provide a wetted surface for the water to flow down. Air and water come into contact in a cross flow manner. All three cores are housed in a polyethylene box as shown in Fig. 6.2.
The dehumidification system consists of a 15 L polyethylene tank and a 15 W single phase centrifugal magnetically driven pump (0-10 L min-1), which delivers strong desiccant solution to the top of the dehumidifier membrane HMX through a spray nozzle. Prior to the desiccant solution entering the dehumidifier membrane
Fig. 6.1 SDCS schematic with labelled components
Fig. 6.2 SDCS HMX cores
HMX, a plate heat exchanger (PX1) is used to pre-cool the desiccant solution using cooling water from the evaporative cooler. This serves to increase the dehumidification potential of the solution and provide sensible cooling to the supply air. The strong cool desiccant solution flows downwards, due to gravity, through the dehumidifier membrane HMX. Humid air is passed across one side of the membrane via a 400 m3 h-1 (nominal) 23 W 24 V DC axial fan. The supply air is dehumidified by absorption of moisture into the desiccant solution, and depending on the solution temperature the air is sensibly cooled. The weak warm desiccant solution flows out of the bottom of the dehumidifier membrane HMX and back into the dehumidifier tank.
The regenerator consists of a 15 L polyethylene tank and a 15 W single phase centrifugal magnetically driven pump (0-10 L min-1), which delivers weak desiccant solution to the top of the regenerator membrane HMX through a spray nozzle. Prior to the desiccant solution entering the regenerator membrane HMX, a plate heat exchanger (PX2) is used to enable the transfer of heat from the heat source to the desiccant solution to facilitate solution regeneration. The experimental work presented in this chapter uses a vented 120 L hot water cylinder with a 3 kW electrical immersion heater as the regenerator heat source. However, the electrical immersion heater could be replaced with any heat source that can provide hot water at the desired temperature and flow rate. In Chap. 7 this is the SOFC CHP system. A Wilo-Smart A-rated 230 V AC pump has been employed to circulate the hot water in the heating circuit. A Honeywell L641A cylinder thermostat has been used to maintain the flow temperature from the tank at a constant temperature. Following PX2 the heated weak desiccant solution flows downwards, due to gravity, through the regenerator membrane HMX. Air is passed across one side of the membrane via a 400 m3 h-1 (nominal) 23 W 24 V DC axial fan. Moisture is vaporised from the desiccant solution and is absorbed by the air, resulting in re-concentration of the desiccant solution. The strong hot desiccant solution flows out of the bottom of the regenerator membrane HMX and back into the tank. The dehumidifier and regenerator tanks are connected via a 15 mm balance pipe to allow the transfer of weak and strong desiccant solution respectively. The potassium formate is provided from the supplier at a solution mass concentration of around 0.74. However, during operation, the solution mass concentration is measured at 0.65-0.7. At the start of testing around ten litres of desiccant solution is loaded into the dehumidifier and regenerator tanks respectively.
The evaporative cooler system consists of a 15 L polyethylene tank and a 15 W single phase centrifugal magnetically driven pump (0-10 L min-1), which delivers water to the top of the evaporative cooler exchanger through a spray nozzle. Air is passed through the exchanger via a 320 m3 h-1 (nominal) 18 W 24 V DC axial fan. Direct evaporative cooling takes place as moisture is absorbed by the air and directly cools the supply water. A plate heat exchanger (PX1) is used to transfer this coolth to the desiccant solution. Figure 6.3 provides a labelled photograph of the complete SDCS.
Next, Sect. 6.2.1 describes the instrumentation used in the experimental testing of the SDCS.