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Methylene blue 319112 (empirical formula: C18H18ClN3S) 0.05 wt. % in H2O and light absorbance peak at λ = 665 nm was purchased from SIGMA ALDRICH. Its extinction coefficient varies by concentration (70,000 mol-1_•cm-1 _{at 2.5 ppm in DI water) and hence} forth a calibration curve of its concentration versus VIS light absorbance was experimentally determined prior to using it in the experiments.

Different concentrations of MB dye were prepared and its absorbance was recorded at λ

= 665 nm using a VRAIAN CARY® _{UV-VIS-NIR spectrophotometer. One, 1 cm thick}

Pyrex plastic container was used to contain the solution of MB dye, which was placed in the spectrophotometer for absorbance measurements. The catalyst dosage mixed with MB dye solution in the system was initially measured in a high precision weighing scale (resolution of 0.1 mg). This mixture was poured into the system shown in Figure 3-1.To attain the concentrations at the inlet and outlet during the experiments, a 15 mL suction syringe was inserted at these locations to extract a sample of the mixture to measure the MB dye concentrations. Since this solution contained catalyst, the separation of the TiO2 P90 catalyst from these mixture samples was performed .The separation was done by

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centrifuging the sample at 8000 rpm for 60 minutes in 15 mL centrifuge tubes. The dye solution with no catalyst particles was then read for its absorbance value in the spectrophotometer. The absorbance was converted to concentration using a calibration curve. The calibration curve was created by making various known concentrations of MB dye solution and measuring the absorbance from the spectrophotometer. The curve was almost linear in nature. This curve was used to attain all the concentrations reported in the present study. Absorbance of the MB dye at λ = 665 nm is not reported.

With these methods, the initial concentration and the final concentration of MB dye were acquired. These were respectively, at the inlet and outlet port in Figure 3-1. The outlet concentration read decreased from the influence of adsorption of MB dye on the catalyst, photosensitization and from photocatalysis. All three were measured in this study.

Experiments using MB dye in de-ionized water with various dosages of TiO2 P90 were performed in the dark to attain the amount of dye adsorbed on this catalyst. These experiments were performed using a beaker of solution of MB dye with de-ionized water

with various dosages of TiO2 P90 suspended in it. The beaker was covered with opaque

material which simulated dark conditions. Significant agitation of the mixture was provided. Concentrations of MB dye were measured at different times until the amount of concentration decrease remained steady.

To understand the amount of photosensitization, an experiment was performed using MB dye solution in the collector system without catalyst. This experiment consisted of pouring a homogenous solution of MB dye in the collector system in Figure 3-1 and turning the halogen lights on. The solution was allowed to circulate in the system by the thermosyphon effect. The concentrations at the inlet and outlet were compared over time for this experiment and the results from photosensitization were recorded. After these two experiments, MB dye in water was used against various concentrations of TiO2 P90 to attain the photodecomposition results.

The front surface/front glass temperature of the collector during these experiments was measured from non-invasive infra-red temperature on 50 locations. These provide the analytically determined front surface heat loss from natural convection and radiation,

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assumed to be occurring in this setup with relevance to the stagnant wind conditions. The surface temperatures of the side walls of the collector were measured and compared to ambient temperature in-order to assume they were adiabatic. The total heat gain by the mixture is attained by analytical methods which require the temperatures inside the collector and at the inlet and outlet.

Temperatures inside the collector constituted of acquiring the inner glass temperature, fluid (air and water) and the absorber temperature using four temperature sensors in each chamber (J-type thermocouples, accuracy ± 0.1°C), as shown in Figure 3-3. These are customized in a 3.2 mm diameter aluminum probe (1/8” probe specified by McmasterCarr, the supplier), so that they may withstand the water pressure and temperature and bend adequately to ensure their tips are in contact with the hot surfaces. Over all, there are 24 locations in the device that are measured for temperature. The placements of these thermocouples are shown in Figure 3-3. They are placed at a distance from the leading edge of the collector, which is at x = 0 m in Figure 3-3. The locations are x = 0.025 m, x = 0.123 m, x = 213 m and x = 0.247 m at the air chamber. No thermocouples are present at the partitioning wall. The mixture chamber has thermocouples at x = 0.273 m, x= 0.298 m, x = 0.369 m and x = 0.495 m. In order to determine the temperature gain of the mixture the inlet and outlet temperatures of the collector are measured using two K-type thermocouples. These are placed at the center of the insulated tubes spaced 25 cm from the port wall. The inlet temperature of the mixture was controlled using packet ice in the insulated cold reservoir tank. The mass flow rate was not measured in this setup and is analytically determined in this thesis work.

All of the temperatures are read over time till steady state. Different days are chosen for each experimental runs. The flow movement via thermosyphoning was monitored prior to conducting water cleaning experiments. This was done with clear water in the system and injecting dye at the inlet port. The results show that the direction of the flow in the system is as demonstrated in Figure 3-3. There are no claims about the type of flow in the mixture chamber in the present study. It is simply flowing through the chamber and to and from the cold reservoir. It is also crucial to mention that the mass flow rates were not measured in this system as those in previous works on solar collectors.

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Figure 3-3: Experimental setup layout and placement of temperature sensors inside the collector and the system

Flow direction DAQ Fluid centerline Temperature Sensor input x =0 y x z PC

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