Author Identifiers

Farshid Fathinia
ORCID: 0000-0002-7324-3447

Date of Award

2020

Degree Type

Thesis

Degree Name

Doctor of Philosophy

First Advisor

Associate Professor Mehdi Khiadani

Second Advisor

Associate Professor Yasir Al-abdeli

Abstract

Low temperature flash evaporation desalination is a separation system that isolates liquids from other materials when seawater or any fluid undergoes evaporation. Extreme flash evaporation occurs when a low heated liquid is injected into the vacuum area, where the pressure is far below the saturated pressure of the liquid entering the area. This approach of flash evaporation is a key part of this type of system. It has a great potential to develop and improve the implementation of low thermal desalination plants but requires more specific study. Further analysis shows that previous investigations have not given a comprehensive insight into the atomization of sprays or jets in seawater flashing spray desalination. Alternatively, most of the earlier research focused at the macro scale whereby the general process of flashing and its performance was studied. Little or no information is available on the droplet characteristics in spray and jet flash evaporation due to the difficulty of experimental exploration.

In this research study, the effect of operating conditions such as initial temperature, inlet flow rate, superheat degree, nozzle diameter, and salinity of the saltwater on the temperature distribution and evaporation rate of flashing spray is explored and comparisons are made between the results of the present experiments and previous studies. In order to simplify the design of the flash chamber and estimating the evaporation rate, spray angle and droplet size (two important characteristics of spray nozzles) have been analysed using a high-speed camera. These experimental measurements are also compared with mathematical calculation of droplet sizes. In addition, some other experiments have been done to improve the performance of system by utilizing a multi-nozzle head in various arrangements. Investigation of difference between the jet and spray nozzles having single and multiple arrangements is also performed under various operational conditions

The result concluded that flow rate has a different effect on the evaporation rate depending on whether spray or jet flash evaporation is taking place. Increasing the flow rate in sprays leads to higher flash evaporation but lowers the evaporation rate in jets. The spray angle as one of the most important characteristics of the spray is also largely affected by the superheat degree regardless of nozzle type and empirical equation is suggested to correlate this parameter with inlet pressure, saturation pressure. Furthermore, placing nozzles in the farthest distance of each other on the multi-nozzle head leads to maximum 28% performance improvement compared to the conventional single nozzle. At the end of research, it is found that the evaporation rate and gain output ratio of the system using spray nozzle in both single and multiple nozzles are higher than the jet nozzle. This research will contribute to better understanding and development of thermally driven desalination plants.

Available for download on Wednesday, September 08, 2021

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