Solar Thermal Ice Production Adam Gage, Peter Shoaf, Jeromie Webster, Logan Olsen Dr. Alex Yokochi*, Justin Pommerenck, Peter Kreider Chemical Engineering 2013 Senior Project Oregon State University, Corvallis, OR Abstract Theoretical Background Adsorption is the accumulation of molecules of a gas (adsorbate) to adhere to the surface of a solid (adsorbent). Adsorption refrigeration consists of the evaporation and condensation of a working fluid to draw heat from the system. It does not use any mechanical energy decreasing maintenance for continued operation. Figure 1 shows a Clapeyron diagram illustrating an adsorption refrigeration cycle. Bill of Materials Acknowledgements References Thanks to Dr. Alex Yokochi, Justin Pommerenck, Peter Kreider, Andy Brickman, & Dr. Philip Harding. The project objective is to complete a set of plans, instructions, and bill of materials for a low cost solar thermal ice production system purposed for vaccine storage without electricity. The design will produce 2 kg ice/day to keep a 2 L refrigerant space between 2 and 8 ˚C for vaccine storage. Experiments were performed for each of the four thermodynamic saturation steps: desorption, condensation, evaporation, and adsorption. An adsorbance ratio was determined to be 358 g methanol/kg and 253 g ethanol/kg. A 95 % confidence interval of 46 g methaonl/kg biochar and 52 g ethanol/kg biochar was determined respectively. A 36 cm air cooled 5 mm diameter copper tube condenser was calculated to be sufficient to condense methanol vapor. Evaporative cooling experiments were performed by utilizing two methods: forced convection and a vacuum assembly. The vacuum assembly was able to cool water to 7 ˚C at a rate of 2.4 W while the forced convection method cooled water to 0 ˚C at a rate of 32 W without ice forming. Ice Production Biochar (adsorbent) • Charcoal created by pyrolysis of biomass • Supplied by Pacific Northwest Biochar • Widely available in developing countries • No chemical additives which can interact in the system Methanol (adsorbate) • Produced from the fermentation of biomass • Also known as “wood alcohol” • Heat of Vaporization: 1200 kJ/kg • Boiling Temperature: 64.7 ˚C Adsorbate Path • BC: desorption of adsorbate from adsorbent due to solar radiation • CD: condensation of desorbed adsorbate • DA: evaporation of adsorbate from evaporator • AB: readsorption of adsorbate by adsorbent Forced convection was employed to increase the evaporative cooling rate of water. 250 mL of water was cooled at a rate of -1.9 ˚C/min, which corresponds to a heat removal rate of 32 W. At 10 minutes, 0 ˚C was achieved and sustained for 20 minutes where 115 g of ice was expected to have formed. A vacuum was implemented to create a pressure driving force. The cooling rate was determined to be -8.3 ˚C/hr for methanol and -9.6 ˚C/hr for ethanol. Further cooling was not attained due to evaporated alcohol mixing with the water. Project Objective Material Cost Plywood (21"x 20"x1/4") $ 1.25 7 feet of 2x4 $ 2.25 Spray Paint $ 4.00 Caulking $ 2.00 Valves (2) $ 7.00 ABS tubing $ 3.00 Copper coil $ 9.00 Biochar Free Methanol $ 5.00 Styrofoam Cooler $ 5.00 Total Cost $ 38.50 Develop a low cost solar thermal ice production system to refrigerate vaccines in developing countries utilizing adsorption/desorption cycles. Figure 3: Vacuum driven evaporative cooling Figure 2; Forced convection evaporative cooling Figure 4: Attempted system Integration results Methanol T = -8.3t + 18.0 R² = 0.9643 Ethanol T = -9.6t + 16.3 R² = 0.897 0 5 10 15 20 0 1 2 3 4 5 6 7 8 Temperature ( o C) Time (hr) Methanol Temp Ethanol Temp Figure 1: Adsorption refrigeration cycle [1] Dieng, A. O., & Wang, R. Z., 2001. Litterature review on solar adsorption technologies for ice- making and air-conditioning purposes and recent developments in solar technology. Renewable and Sustainable Energy Reviews, Vol 5, page 331. [2] M. Li, et. al. 2004 Development of no valve solar ice maker, Applied Thermal Engineering, Vol 24, Issues 5–6, Pages 865-872. [3] Vasta, S., et al. 2008. An Adsorptive Solar Ice-maker Dynamic Simulation for North Mediterranean Climate. Energy Conservation and Management, Vol 49, Pages 3025-3035. [4] Sumathy, K., Zhongfu, Li., 1999. Experiments With Solar-Powered Adsorption Ice-maker. Renewable Energy, Vol 16, Pages 704-707. The cost of construction of one ice-production unit is as follows: Adsorption/Desorption Three adsorbance tests were run to determine an adsorbance. Methanol and ethanol was boiled and passed through a biochar-packed column. The adsorbance ratio was determined to be 358 g methanol/kg and 253 g ethanol/kg. A 95 % confidence interval of 46 g methaonl/kg biochar and 52 g ethanol/kg biochar was determined respectively. Table 1: Methanol/biochar adsorbance results At 30 minutes, 100 mL of methanol was added in an attempt to completely crystalize the water. No ice was visible. Ambient heating was believed to have overcome the evaporative cooling, melting the ice. “Sandbox” Collector • 2.25 x 2.25 m wood frame with acrylic cover • 23 kg biochar • 900 mL methanol Vaccine Storage • 2 L stainless steel Evaporator • 28 qt Styrofoam cooler • 2 L copper evaporator Condenser • 36 cm air cooled 5 mm diameter copper tube Overall System biochar methanol , = ℎ∆ ℎ = = 0.52 0.25 , = 4 ∆ , = 2 (∆ ,20 + ,2 ∆) Thermocouple 1 T = -1.87t + 19.5 R² = 0.9502 Thermocouple 2 T = -1.84t + 19.4 R² = 0.9899 -5 0 5 10 15 20 0 10 20 30 40 50 60 Temperature ( o C) Time (min) Thermocouple 1 Thermocouple 2 The water and air temperature of the sealed vacuum container during the evaporative cooling experiment is shown in Figure 4. 0.5 kg of biochar was used to adsorb the evaporated methanol. The goal of the experiment was for the biochar to adsorb the evaporated methanol and inhibit the alcohol mixing with the water. Additionally, the successful adsorption would be the first step in system integration. Ethanol Adsorption (g/biochar kg) Average 253 Error +/- (95% CI) 52 Methanol Adsorption (g/biochar kg) Average 358 Error +/- (95% CI) 46