ME304 Final Project

PresentationFall 2012

The Solar Still

Aaron YuengertAyah Yamani

What is a Solar Still?

Solar stills use heat from incident sunlight to evaporate contaminated water.

A parabolic concentrator would accelerate the process.

The purpose of our solar still is to distill and desalinate water.

Distillation is a method of separating mixtures based on differences in volatility of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction.

Desalination refers to any of several processes that remove some amount of salt and other minerals from saline water. More generally, desalination may also refer to the removal of salts and minerals, as in soil desalination.

More about Parabolic Troughs:

• Parabolic mirrors focus sunlight onto a receiver, usually a tube containing a moving fluid.

• Parabolic troughs were first used to power a steam engine c. 1870.

• They’re currently used for electrical power generation.

• Area of the aperture (reflector) = 1.9 m^2

• The length of focus of the received with respect to the reflector = 0.25 m

The Problem

Lack of clean water sources in Sub-Saharan Africa.

780 million people lack access to an improved water source.

More than 3.4 million people die each year from water, hygiene-related causes.

Why did we decide to make this our project?

Immense interest in the possibilities that Solar energy offers.

Research about the parabolic trough technology which relies on Solar Energy.

So, we decide to create a device that combines these two to solve the problem identified.

The thermodynamic processes considered when a designing Solar Still:

• ConvectionHeat losses and transfers between pipes

• Vaporization

• Condensation

Design:

• Shell-and-tube condenserIncoming liquid absorbs heat from steam as it

condenses.

• Insulated tubingDecreases heat loss between components

• Flow splitterAdjustable valve controls how much of the heated

water goes to the

• BoilerLiquid is vaporized inside the receiver tube of the

parabolic trough.

Materials used:

REFLECTOR: (PARABOLIC TROUGH)

• PVC (Polyvinyl chloride)

• Aluminum Foil (gently applied on reflector and stuck using super glue)

The reflectivity of bright aluminium foil is 88%.

Standard household foil is typically 0.016 millimetres (0.6 mils) thick

• Galvanized tubing painted black

Boiler

• Galvanized tubing insulated with fiberglass

Condenser:

1. Piping: Copper tubing

2. Shell: Carbon Steel

Key calculations made:

Fixed temperature/enthalpy of

• cooling water (112 kJ/kg)

• feedwater (419 kJ/kg)

• condensate (419 kJ/kg)

• steam exiting boiler (2678 kJ/kg)

All others calculated based on heat losses from/between components

Useful heat calculated from

• Thermal efficiency data of a similar trough

• Solar irradiance data from Zambia

Useful heat rate divided by desired enthalpy change inside boiler equals mass flow rate.

Important factors:

Climate & Location.The climate of Zambia is tropical modified by

elevation.Temperature: Ranges from 22.8 – 30.6 degrees CelsiusSo, ambient temp = 26.7 degrees Celsius

Solar Radiance:Ranges between 198 - 970 (Wm^-2)

Estimates & variables:

We estimated and fixed the value for the aperture = 1.9 m^2

Length of tubing to be 1 m

Estimated the Solar Radiance based on data collected in Zambia.

Estimated the thermal efficiency of the aperture from data collected in Tikrit, Iraq.

Thermal efficiency ranges between 45-70%

Difficulties encountered:

Dearth of applicable datao Most publications on parabolic troughs are about costlier models for power plants.

Single-stream designOriginally had the same stream of water flowing

through all components in succession.Could not condense steam completely

How we tackled these difficulties:

•Increase inflowo Only a fraction of the cooling water is

diverted to the boilero Less energy can be recycled than

originally thought

Evaluation:Total estimated cost =<$200NOT VIABLEMaximum flow rate is approximately a liter and a half per

hour.

It is not realistic to try and vaporize an entire flow of water with the available energy from the trough model under consideration.

ALTERNATIVES:

•Use the trough to increase the efficiency of a more

traditional still.

References:Eck, M., Zarza, E., Eickhoff, M., Rheinländer, J., and Valenzuela, L. “Applied Research

Concerning the Direct Steam Generation in Parabolic Troughs”. Solar Energy. 74.4 (2003): 341-351. Electronic.

Holman, J.P. Heat Transfer, fifth ed. New York: McGraw-Hill, 1981. Moran, Michael J., Shapiro, Howard N., Boettner, Daisy D., and Bailey, Margaret M.

Fundamentals of Engineering Thermodynamics, seventh ed. Hoboken, NJ: John Wiley and Sons, 2011.

Nasitwitwi, M., Bailey, W.G., and McArthur, L.J.B. “Global Solar Radiation in a Southern

African Savanna Environment”. Electronic. “Thermal Conductivity of Metals”. The Engineering Toolbox.

http://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html Yassen, Tadahmun Ahmed. “Experimental and Theoretical Study of a Parabolic Trough

Solar Collector”. Anbar Journal of Engineering Sciences. 5.1 (2012): 109-125. Electronic.