Water n' Spice

Project undertaken in course year 2018-2019 with Precourt Institute for Energy

Project Goal

Recapture water vapor from drying chilies and turn it into clean drinking water

This project provided by Stanford Precourt Institute for Energy

Project Motivation

Provide supplemental drinking water to rural Indian communities without reliable access to clean water

Background

Existing solar chili dryers being developed in the Karnataka region are estimated to echaust 300-400L of water vapor per day

Karnataka land is drought-prone, resulting in overdrawn water tables and contaminated ground water, making clean drinking water scarce

High Priority Requirements

Safe water with less than 10 µg of Arsenic per liter
Minimal electical energy input below 0.014 kWh per 1-liter cycle
Cost under $230, produce water for less than $0.27/liter

Ethical Considerations

Cost related to access
Sanitation during transportation
Use of Labor

Solution

We created GEN Z, a water-condensing surface made of two aluminum plates sandwiched together with a gasket into which water flows from a cool water tank. The chilled water flows between the surfaces, cooling the aluminum collecting surfaces to below the dew point temperature to allow for condensation. Gen Z produces 266 mL of water per hour under chili dryer-like conditions.

A scale-up model of the full system to be implemented in India involves the potential use of solar panels. Our full scale model is projected to cost $3500 and produce 150 L of drinking water each day. At this upfront cost, our solution can generate filtered water at a cost comparable to filtered water in the region while recovering the initial capital cost in about three years. After that payback period, the cost of filtered water drops to $0.0024 / L all while running on fully renewable solar energy.

Existing Dryer

The dryer, scaled up to 500 kg capacity in India

Inside the Dryer

The current racks are stacked, shown in red, in the drying portion of the dryer

Prototype test setup

This setup enables creation and control of both humidity and temperature

First prototype (Waves)

This system is intended to circulate cold water through the pipes to cool the copper plate. Maintaining that temperature below the dew point of the internal temperature of the dryer will result in condensation on the copper plate

Second prototype (Sando)

This system used a coolant pumped between two copper plates to create uniform chilling over both surfaces

Third prototype (GenZ)

This prototype pumped water into the bottom of the chamber, and then the water exits out the top. This ensures warm water is flushed out getting better mixing than in SanDO

Test Results

Testing was first conducted with SanDO and Waves prototypes in a shower to identify relative performance difference. Waves performed better, though SanDO was seen to not mix water well
Testing conducted in the test chamber with better control over RH and Temp showed a single GenZ system could result in 266 mL water per hour
To implement in a full-size 2000-kg capacity chili dryer would then require 24 plates, holding tanks for water, chilling equipment, and solar power system to run the chilling equipment

Student team

Future Work

Filtration - incorporate water filter with water generation device
Cost - explore minimizing cost of GenZ without sacrificing performance / further testing
Scale - scale up our design according to cost model, minimize cost per liter produced

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