טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMerksamer Itzhak
SubjectAn Investigation of the Mutual Interaction between the
"Energy Tower" and its Surroundings
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Samuel Hassid
Dr. Rami Guetta
Full Thesis textFull thesis text - English Version


Abstract

"Energy Towers" is a method of electricity production from hot and dry air by evaporating tiny droplets at relatively high rate. The cooling process results in the heavier  flowing downwards and then through an array of turbines which generate electricity.

In this work the mutual interaction between “Energy Towers” and their immediate environment is investigated. Temperature, humidity, wind velocity, stratification and topography have an influence on the power generated, while the emission of cold and humid air together with the remains of the brine droplets which spread into the environment may constitute sources of pollution. The research is based both analytical and computational tools, including CFD (computational fluid dynamics) computations using FLUENT, adapted for geophysical environmental flows.

The analysis shows that turbine power increases with the increasing outside temperature (and decreasing outside humidity) and lapse rate (the temperature at the spraying height remaining the same). The Coriolis force due to Earth rotation  is shown to have almost no influence on turbine power or on the flow pattern, although a rotational flow just above the Tower top can cause a reduction in power due to enhanced friction at the tower walls and between the droplets and air.

The cold and humid air may be accumulated under several topographic conditions (such as mountains surrounding the Tower) and thus harm the Tower's operation. For flat ground, the air tends to sink and mix with the surroundings.  

The major environmental problem are the tiny salted droplets which leave the diffusers and may fly for long distances resulting in unacceptable airborne salt particle concentrations in the air and salt deposition in the ground. It is shown that this salt concentration and deposition rates cannot be correctly estimated without accounting for coalescence between droplets of different sizes, resulting in larger droplets with a  higher terminal velocity. Thus the largest part of the water that has not evaporated is deposited in the bottom of the tower and in the diffuser and the salt concentration in the air and deposition rate at the immediate surroundings (up to 2 kms from the exit of the diffusers) is within the requirements of the respirable particles standard. For axisymmetric configurations, these results are confirmed  by  CFD computations using FLUENT and by a simplified one-dimensional approximate model. For the case of external wind, the one dimensional model shows that the salt particles may reach somehow higher distances before the standard is satisfied.