AggiE-Challenge

High Efficiency, Low Cost Water Purification: Solar Powered Membrane Distillation

By: Maria Gracia, Matthew Martinez, Troy Menendez, Matt Moerbe, Kori Mondin, Cody Wainscott

Faculty Sponsors: Dr. Devesh Ranjan, Dr. Arun Srinivasa

Need Statement:

Create a low cost, simplistic, efficient, and reliable

system to improve water quality utilizing a non-grid

energy source.

0.2

0.4

0.6

0.8

1

0

0.02

0.04

0.06

0.08

0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Membrane Pore Size (um)Dirty Water Salt Concentration (M)

Mem

bra

ne M

ass F

lux (

kg/m

2/h

r)

Molarity (M) F Ratio Pore Size (mm) F Ratio Pore Size (mm) F Ratio

0.001 0.170 0.2 1.54 0.2 0.052

0.01 2.29 0.45 1.46 0.45 0.854

0.1 1.48 1 4.51 1 0.343

Varying Molarity 2nd SetVarying Molarity 1st SetVarying Pore Size

Membrane Distillation Unit Solar Collector

0

100

200

300

400

500

600

700

800

900

1000

0 2000 4000 6000 8000 10000 12000 14000

So

lar

Ra

dia

tio

n D

en

sity

(W

/m

2)

Time (s)

IR

Start Time: 9:36:35am 4/13/13 End Time: 1:16:00pm 4/13/13

0

10

20

30

40

50

60

70

80

0 2000 4000 6000 8000 10000 12000 14000

Te

mp

era

ture

( C

)

Time (s)

Temperature Differential

T1

T2

T2-T1

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2000 4000 6000 8000 10000 12000 14000

Flo

w R

ate

(m

L/s)

Time (s)

Flow Rate

System Decomposition

In order to gain an understanding of the factors affecting each

component of the system, the system was decomposed into three

main sub-blocks:

Membrane Distillation Unit

Solar Collector

Pump

Since the pump will be a standard pump powered by

thermoelectrics it was not considered in the testing conducted

this semester. The membrane distillation unit and solar collector

were constructed and tested separately. The data collected from

them was then used to develop a design for a 2nd generation

system which integrates all of the components.

System Operating Principles

The design uses solar radiation and a hydrophobic membrane to

purify water. The dirty water is heated by a solar radiation

collector to create a temperature gradient between the hot and

cold sides of the system. This temperature gradient creates a

vapor pressure differential which causes water vapor to pass

through a hydrophobic membrane and condense on the other side.

The pure water is then collected to be used for drinking and

sanitation purposes.

System Schematic

Testing Results

Conclusions and Recommendations

Testing Results

Conclusions and Recommendations

Using a 90% confidence interval with 2

degrees of freedom in the numerator and 9

degrees of freedom in denominator, an F

ratio of 3.006 is required for statistical

significance. Due to the extra trials

conducted with the 0.01M dirty water, the

0.01M varying pore size F ratio requires a

different value for statistical significance.

For this case 2 degrees of freedom were

used in the numerator and 21 degrees of freedom were used in the denominator,

requiring an F ratio of 2.575 for statistical significance at a 90% confidence interval. As

can be seen from the table, only the 1mm pore size while varying molarity on the 1st set

resulted in statistical significance using the 90% confidence interval. It is felt,

however, that the statistical significance shown by the 1mm pore size while varying

molarity on the 1st

set is an erroneous result and can be ignored.

Membrane pore size and the dirty water salt concentration have no

effect on the mass flux through a hydrophobic PTFE membrane

within the ranges tested

As long as fresh water is used specific salt concentrations in the

water do not need to be determined as they will not affect system

performance

A corser (and therefore cheaper) membrane can be used just as

effectively in the system as a more expensive and finer membrane