P07401: Solar Water Pasteurizer with Integral Heat Exchanger (SPIHX) Dr. R. StevensTeam Guide Sang LeeProject Manager Elaine AikenDesign Engineer Kellen BucherDesign Engineer Drazen HadzialicTest Engineer Nathan La CroixTest Engineer Alexander KinlockMaterials & Fabrication Analysis Sulen GoncMaterials & Life Cycle Analysis Sponsor: Environmental Protection Agency MSDII - Project ReviewMay 18, 2007 KGCOE Multidisciplinary Sr. Design at R·I · T

Agenda Project description Selected concept Performance review Future improvements

Background Scary facts about unclean water:  According to WHO, over 1 billion people worldwide do NOT have access to clean water  This results in 5 million deaths from waterborne diseases.  Most susceptible to disease: children Most of the countries with least amount of treated water are close to equator  High rates of poverty  High levels of solar radiation

Project Scope To develop a solar pasteurizer to treat water in third-world countries:  Project end-user: families in Venezuela  Future end-user: Global community Courtesy of WHO/Unicef “Water for Life: Making it Happen” (2005).

Customer Needs Low cost Easy to manufacture Ability to fabricate locally Carbon neutral during usage Safe inaction of dangerous pathogens Efficiently treat enough water for daily usage Minimal end-user monitoring required Durable to external forces and over time Courtesy of World Water

Pasteurization Method used to clean water Exposing food or a beverage to a temperature below boiling point for a certain amount of time in order to kill harmful microorganisms Safety Zone Required to Pasteurize Hepatitis A Virus Safety Zone must be reached to ensure pasteurization. This is a function of temperature and time. (i.e. water must be held at 68 degrees C for 15 minutes for pasteurization.)

Overall System

How it functions Untreated water in Treated water out Glass Plate Treated water Untreated water  Flow Diagram

Integral Heat Exchanger IHX provides a large portion of heat energy used for pasteurization. Very basic device used to transfer heat from one medium to another. Considered integral because it is incorporated in the pasteurizer, and not an independent part. Figure 5: Schematic of solar pasteurizer with integral heat exchanger (SPIHX) assembly. Water enters the pasteurizer and heats up from the sun’s radiation. Once it passes underneath the middle plate it begins exchanging heat with the cold water entering.

VALVE HOUSING Auto thermostat valves, most commonly found in car radiators, open when a certain temperature is reached. Most have a hole that allows for a small flow, even when completely closed. If used in the pasteurizer design, this would allow un-pasteurized, contaminated water to enter the output bucket. The valve housing was designed and machined to encapsulate the auto thermostat valve, effectively eliminating any flow when the valve is closed. Created using round aluminum stock and a heat resistant gasket.

Concept Evolution Dimpled Surface Initial Concept Issues Inconsistencies with the dimples lining up between the top and bottom plates Spot welding was difficult due to lack of compromise between resistance and structural integrity Iteration #1 The plates are formed under a rolling process to substitute for the structural purpose of dimples The heat exchanger is made up of 3 plates where the top and bottom plates have dimples and the middle plate that contains the air and the temperature valves is flat The system incorporates glass surface on top The top plate contains a selective coating With the required welding, warping was observed Could not prevent bulging under pressure Welding is costly Issues

Concept Evolution (2) Iteration #2 Large flat plates were welded on the sides with ½ cm thick channels Issues Welding costs Ballooning, had to be held down using metal holders at multiple locations Final Iteration Small flat plates were held together with bolts, nuts and washers Channel thickness was reduced to 1 mm Advantages Welding costs were avoided Efficiency was increased due to thinner channels Utilization of bolts, nuts and washers prevented warping and bulging More dimensionally rigid and sealable

Modeling the Mass Flow Rate (Steady-State) Excel was used to model the flow rate of the system so that key parameters could be adjust to achieve the desired flow. Calculations were done with a series of complex solar calculations m. m.

Some Key Parameters Width Collector0.25m Length Collector1m Thickness of Channel0.005m Area Collector0.25m2m2 collector efficiency factor, F'0.95 valve open temperature, T past 75°C thickness of collector0.0010m thickness of glass m thickness of air between plate and glass0.08m thickness of heat exchanger0.0010m thickness of insulation0.03m thermal conductivity of insulation, k ins W/m- K emissivity of collector plate,  p 0.49 emissivity of glass,  g tilt angle of collector, s10° Latitude8°N index of refraction for glass, n extinction coefficient, K32m -1 solar absorptance value of collector,  0.88  of plate 7854kg/m 3 C p of plate434 J/kg- K

Transient (Warm-up Period) Where: The system has a warm-up time each morning before pasteurization will begin

Example of Warm-up Time Average time to reach pasteurization temperature is about 5 hours after sunrise

Average Daily Output -For Each Month- (L/day) JanFebMarchAprMayJun JulAugSeptOctNovDec

Testing Testing from April-May, during mostly sunny conditions Data Collected:  Temperature: Valve Water Inlet and Outlet Along the top and bottom channels  Solar Radiation (W/m 2 )  Pressure change of the outlet tank Flow Rate

Performance Review MetricUnitsMarginal ValueObtained ValueSpec Met Cost per unit to manufacture$ no Local fabrication possible% of component type80100yes Total coliform reductionlog498% reduction undetermined Reached Safety Zoney/nynno Leak proofy/nyyyes Average daily potable output for typical Venezuelan climate L/day2023yes Usability of setup1-7 rating4.25.4yes

Flow Rate Critical to prove the model is similar to the experimental flow rate. Enables predictions for future use. Test data is similar to model data, after averaging out fluctuations. Fluctuations in test data resulted from the thermostat valve closing and opening in a cyclic manner.

Safety Zone

Coliform Reduction Drinking water: <4 cells/100 ml Scottsville Road creek:  Initial Reading 500 cells/100 ml  After Pasteurization 4 cells/100 ml  More than 99% coliform reduction Perkins Road stream:  Initial Reading 80 cells/100 ml  After Pasteurization <2 cells/100 ml  More than 98% coliform reduction More precise testing needed for log scale reduction data

Strengths/Weaknesses Strengths  Effective use of a heat exchanger  Ease of fabrication in developing countries  Fast warm-up time Weaknesses  Temperature and flow control  Valve cycling  No assurance that safety zone was met  Brass air valve

Future Improvements More compact valve housing Better precision for testing pathogen reduction Better flow regulation Ensure that safety zone is reached at all times

Concluding Remarks Successfully developed working prototype Obtained flow rates > 20 L/day  Sufficient for a family of 5 Easy to mass produce Easy to integrate in third world regions