1. The Design of an Evaporating Unit for Continuous Boiler Blow-down Water Purification Richard R Libardi MANE-6980

2. The need for boiler blow- down Boiler operation leads to scale buildup on heat transfer surfaces. Scale layers can be reduced by replacing some of the water in the boiler: The blow-down water is typically thrown away as waste however. Recycling some of this water may be possible.

3. How to evaporate the water? An evaporator/condenser system was proposed for the design. The evaporator would create a 50% quality vapor. The vapor would be condensed and saved as make-up water for the boiler.

4. Annular Flow regime of boiling Chens correlation for convective boiling assumes that the flow inside the pipe is undergoing boiling in the annular flow regime. This coats the internal surface of the tube with a film of water and provides a steam core internal to the flow.

5. The calculation process: Corrected Forster-Zuber correlation for Nucleate boiling Corrected Dittus-Boelter correlation for convection

6. Microscopic heat transfer coefficient The value of the Suppression factor is a function of the two phase Reynolds number. This value corrects the Forster-Zuber correlation for nucleate boiling. Increased values of the two phase Reynolds number indicate that nucleation sites at the surface of the pipe where convective boiling is occurring are suppressed. Thus the nucleate boiling term becomes less significant with increasing Reynolds numbers.

7. Macroscopic heat transfer coefficient Dittus –Boelter correlation corrected for the two phase flow:

8. Results of the analysis Heat exchanger of 2 tubes with a.02 m diameter at 1.28 m length.

9. Initial attempts Attempted using an annulus heat exchanger in the design. This was discovered to not be applicable based upon Chen’s findings. Chen’s findings required calculation of local heat transfer coefficients and not the average or mean value of heat transfer coefficients. Heat source ended up being in the ships main condenser where a constant wall superheat was capable of being maintained.

10. Final Results The results of the analysis indicate that the proposed system is possible The cost required to add the system to a ship’s design would have to be evaluated. It was discovered that the nucleate boiling term was the most significant term in the convective boiling heat transfer coefficient.

11. References for this presentation Correlation For Boiling Heat Transfer To Saturated Fluids In Convective Flow. Brookhaven National Laboratory, Upton, N.Y. (July, 1966) Liquid-Vapor Phase-Change Phenomena. Van P. Carey. Taylor and Francis Group. (New York, New York) 2008 Principles of Heat Transfer-fifth edition. Krank Kreith, Mark S. Bohn. Boston, MA: PWS Publishing Company, 1997.