Heat Transfer in Saline Water Evaporative Cooling

ABSTRACT

The present paper provides an overview and review on heat and mass transfer involved in evaporation of single saline water droplets as well as pure and saline water sprays for cooling purposes. The aim is to demonstrate the advances that have been made toward the deployment of Natural Draft Dry Cooling Tower operating with saline water. A new theoretical model for evaporation of single solid containing droplet is reviewed, and the corresponding advantages are discussed. Moreover, a comparison between pure and saline water sprays is reported and performance correlations are compared. The new approaches to implement saline water injections in numerical simulation and nozzle arrangement in a cooling tower reported in this work provides valuable tools for designing an efficient cooling tower. This work shows that in addition to fresh water preservation and cost savings due to water purification, using saline water can also lead to enhance cooling efficiency by up to 8% and build more compact cooling towers. Overall it has been shown that the use of saline water is a viable and promising concept that requires further exploration.

Nomenclature

ASTRI	=	Australian Solar Thermal Research Initiative
c	=	mass concentration
CGS	=	coal seam gas
CST	=	concentrated solar thermal
D	=	diameter, m
H	=	height of droplet fall, m
k	=	thermal conductivity, W/m.K
Lwet	=	wet length, m
m	=	mass, kg
$\dot{m}$	=	mass flow rate, kg/s
Nu	=	Nusselt number
Pr	=	Prandtl number
R	=	radius
Re	=	Reynolds number, Re = uD/v
RH	=	relative humidity
St	=	Stanton number
t	=	time, s
T	=	temperature, K
u	=	velocity, m/s

Greek Symbols
ηCooling	=	cooling efficiency, %
ρ	=	density, kg/m3
v	=	kinematic viscosity, m2/s

Subscripts
0	=	initial condition
c	=	cold
d	=	droplet
g	=	gas
h	=	hot
w	=	water
wb	=	wet bulb

Acknowledgments

This research was performed as part of the ASTRI, a project supported by the Australian Government, through the Australian Renewable Energy Agency.

Additional information

Notes on contributors

Hosein Sadafi

Hosein Sadafi received his Ph.D. in Mechanical Engineering from The University of Queensland, Australia in 2016. In his Ph.D. dissertation, he investigated the evaporation of solutions and the usage of saline water for spray cooling. He used novel theoretical, numerical, and experimental methods to address this topic. In the outcomes of his research, it was shown that using saline water for spray cooling not only preserves drinking water sources and leads to budget saving, but also may improve the cooling performance of a cooling system. His postdoctoral research is on evaporation from multiphase fluids. He is focusing on heat and mass transfer of complex fluids.

Ingo Jahn

Ingo Jahn joined University of Queensland (UQ) in 2012 as a lecturer in Mechanical Engineering within the School of Mechanical and Mining Engineering. He obtained a Master of Engineering Degree from the University of Oxford, UK in 2003, which was followed by a D.Phil at the Turbomachinery laboratory at the University of Oxford. Between 2007 and 2012, he was working for Rolls-Royce plc in the United Kingdom as a Specialist in Advanced Seals and as Research Technology Leader for Oil Systems. Since 2014, he has been leading turbomachinery research at UQ with the aim of delivering sCO2 turbine technology for the ASTRI. His research to deliver a small and efficient power conversion concept is integral to delivering environmentally friendly and low-cost electricity to rural communities.

Kamel Hooman

Kamel Hooman completed his Ph.D. at University of Queensland, for which he received a Dean's Award for Research Higher Degree Excellence and an Emerald Engineering Award (Outstanding Doctoral Research). He is a T&R academic staff within the School of Mechanical and Mining Engineering. His research interests are in Thermofluids and Energy. He is the QGECE Director (Queensland Geothermal Energy Centre of Excellence) and has a strong research record in the field of heat transfer and energy. He is recognized worldwide for his work on heat exchangers, which are essential technology for power generation and energy management. He has pioneered the use of metal foams in fuel cells, supercritical heat exchangers for geo/solar thermal power plants, and scaling of natural draft dry cooling towers.