1. Evaporative Cooling – A Mechanism Enhanced by Mass Transport Jesse Hamilton ME547

2. How Hot Is Hot? Have you ever been to Phoenix? How about New Orleans? Both are hot, but you experience two different types of hot depending on where you are!

3. Where would you expect to encounter this?

4. Where would you traditionally experience this type of heat?

5. Contrast your experiences in a humid climate (New Orleans) vs. an arid climate (Phoenix).

6. Closer to Home Average Conditions in August Portland: 81 F, 65% Humidity Electricity costs (KWh): $0.1072 Phoenix: 104 F, 36% Humidity Electricity costs (KWh): $0.1196

7. Pause and ask – what is an Engineer’s purpose? Solve problems and answer questions. The questions I present. – 1. How can I stay cool? – 2. How much will it cost? – Assumptions: For energy calculations, 20 hours of operation per day to maintain a comfortable temperature and average temperature/humidity numbers for 31 days (August).

8. Door #1: The A/C 5 ton unit operating at 14 SEER would cost: $317.80 in Phoenix $284.85 in Portland

9. Door #2: The EAC 5000 CFM unit operating would cost: $85.27 in Phoenix $76.43 in Portland

10. Decision Made? That's it... I'm done... I've got my solution that saves $$$... but wait, why are we talking about A/C and EAC?

11. Well, not so fast... A/C and EAC work differently A/C is a closed system with a compressor EAC is an open system that uses water to cool the air

12. What's the rub? A/C is a closed system – As such, its effectiveness is not subject to the variation of atmospheric conditions – A/C works in most any climate

13. On the Other Hand EAC works by cooling air with water. Specifically, the vaporization of water is a phase change and requires significantly more energy (than conductive heat transfer alone). – Specific Heat of water = 4.186 kJ/kg – Energy of Vaporization = 2,257 kJ/kg By nature, this is dependent up the atmospheric conditions... especially humidity.

14. Analytical Solutions Things get complex very quickly It's spherical... take a look.

15. An Interesting Fact One Gallon of Water – Water at 50  F and poured on a sidewalk at 90  F generates 9000 BTU of cooling – Water at 90  Fpoured on a side walk at 90  F generates 8700 BTU of cooling Clearly, there's more going on here...

16. Mass Transfer Impacts To accurately describe this system, it requires the equations of motion, energy, and continuity for species to describe the impact of convection and mass transfer on the energy change.

17. Equations of Motion, Energy, and Species

18. Simplified Model (A. Fouda, Z. Melikyan)

19. Solution? Yeah Right Function... Companion of the Error Function and Gamma Function (I made this up... ) Not really, but the likelihood of producing an analytical solution is remote with 3 complex PDEs

20. Other Options There is significant experimental data A popular presentation of experimental data is graphical Enter the Pyschrometric Chart...

22. What I've Learned and Observed EAC is functional in hot and dry climates like Phoenix. – Phoenix... 104 F and 36% humidity. EAC is not functional in more humid climates like Portland. – Portland... 81 F and 65% humidity.

23. What To Choose? When temperatures are lower, humidity needs to be lower for an EAC to be effective. For example, to be effective at average Portland temperatures, the humidity would need to be below 20%.

24. EAC Viability Temperatures are high (around 95  F) Humidity low (around 30%) Electrical operation costs are less than 27% an A/C. With lower temperatures ( 40%), comfort is consistently produce only with an A/C.

25. Questions???