Profiles of directly measured quantities

The adiabatic test of the heat and mass transfer performance of the polymer scroll tube insert at a nominal flow rate of 10 l/min and a cycle time of 20 min is taken as a base case for the following presentation of the cyclic test data, where the characteristic trends are clearly visible. It should be noted, however, that not all the measurements produced results as consistent as the base case presented here. Especially at cases with a high flow rate of 20 l/min and active water-cooling the experimentally determined data is compromised by a number of factors, as will be discussed later.

0 5 10 15 20 30 50 70 90 tcyc [min] T [ ◦ C] 0 5 10 15 20 0 20 40 60 80 100 tcyc [min] φ [% ] v,si ch,pi ch,ri v,po v,ro

Figure 9.6: Sensor profiles of adiabatic polymer test

The profiles of thermocouple and relative humidity sensor readings for the base case are plotted in figure 9.6. The first 10 min in the plot refer to the adsorption, while the latter correspond to the desorption half-cycle. This half-cycle order will be maintained for all the time-dependent plots in the following. The curve colours correspond to the colour coded measurement locations in schematics 9.2 and 9.5.

From the plot on the left hand side of figure 9.6 it can be seen, that the grey denoted supply inlet temperature measured upstream of the process inlet valve stays at a constant level for both half-cycles.

During the adsorption half-cycle, the blue curve corresponds to the process inlet air. After having been exposed to the regeneration outlet air in the previous half-cycle, the temperature sensor reading decreases from the regeneration outlet temperature level to the constant level of the supply inlet air feeding the process. The amount of time it takes for the inlet air to reach a constant level is a measure of the thermal mass of the inlet channel. It can be seen, that despite the efforts made to minimise the thermal mass of the system by reducing path lengths and insulation volume, the thermal inertia is still noticeable and it takes about 2.5min for the inlet air to equilibriate.

The temperature of the air leaving the test object during the adsorption half- cycle is shown in red in the plot. It can be seen, that without water-cooling, the generated heat of adsorption and the thermal mass of the insert lead to a gradual decrease in temperature that reaches a level approximately 12◦C above the inlet temperature level at the end of the 10min half-cycle. During the second half-cycle the roles of the channel sensors are reversed, i.e. the red curve now corresponds to

the inlet air stream, while the blue slope represents the regeneration outlet air. A thermal mass effect similar to the one observed for the adsorption inlet air can be noted during the regeneration half-cycle, where the red line gradually approaches a steady regeneration inlet temperature level at approximately 85◦C.

It is apparent, that the amplitude of temperature fluctuations the sensor at the channel regeneration inlet position is exposed to is significantly larger than at the channel process inlet position. At the same time, the sorptive heat dissipated to and from the fluid affects the shape of the outlet temperature read by the blue sensor during the second half-cycle more profoundly than during the first half-cycle, where the outlet air is measured by the red sensor.

The yellow and purple curves correspond to the valve process and regenera- tion outlet measurements. A comparison of yellow to the red coloured curve during the adsorption half-cycle and the the purple to the blue line during the desorption phase shows, that the switch valves do indeed act as effective thermal buffers greatly reducing the temperature fluctuations of the respective outlet sensors.

The plot on the right hand side of figure 9.6 shows that the relative humidity readings are noisier than the thermocouple readings, but exhibit clear trends. Due to the different temperature levels corresponding to the relative humidity levels, little information about the dehumidification performance of the system can be derived from those measurements directly. It is, however, worth noting the different regimes the sensors operate in, although at times corresponding to the same absolute humidity level. The channel regeneration inlet sensor operates in the lowest relative humidity regime between 5 and 20% RH, while the channel process inlet sensor, valve supply inlet sensor, and valve process outlet sensor operate at an intermediate relative humidity level between 20 and 60% RH. The valve outlet sensor operates at the highest relative humidity level during the measuring the second half-cycle, where it is exposed to the same air stream as the sensor denoted in blue in the plot, but at a significantly lower temperature level. The variation in the channel process inlet sensor signal of ∆RH _≈ 40% is approximately twice as high as that of the other sensors.

Similar to the temperature sensors, the purple and curves correspond to the measurements of the bypass outlet air during adsorption and desorption half-cycle, respectively.