الفهرس 
THEORETICAL ANALYSISOnly 14 pages are availabe for public view
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Abstract
Solar desalination using humidification-dehumidification processes has
proven to be an efficient technique of utilizing solar energy for obtaining fresh
water from saline water. This technique presents several advantages such as
simplicity, flexibility in capacity, moderate installation and operating costs, and
possibility of using low temperature energy sources.
A theoretical and experimental investigation of humidificationdehumidification
solar desalination system is presented. The system is based on
an open cycle for water and a closed cycle for the air stream. The air is circulated
either by natural draft or by forced circulation using a fan. Saline water is heated
using an electric heater that simulates a solar flat-plate collector. The latent heat
of condensation is recovered in the condenser to preheat the saline feed water.
The system modeling is based on various heat and mass balance equations and
their numerical solution. The effect of changing design and operation parameters
on the system characteristics has been investigated. Results are offered for
system sizing, design, and water yield predictions. An experimental test set up
has been designed, fabricated and assembled. The set up has been equipped with
appropriate measuring and controlling devices. Detailed experiments have been
carried out at various operating conditions and using several packing materials.
The necessary heat and mass transfer coefficients have been obtained
experimentally and fitted in forms of empirical correlations. Three different
packing materials have been used in the investigation in order to select the proper
material which achieves the highest productivity at the lowest cost, namely:
gunny bag cloth, slates of ply wood and PVC material used in cooling towers.
The rate of distilled water in natural and forced air circulation is measured for the
three materials used in the humidifier.
The results of the investigation have shown that the system productivity
increases with the increase in condenser area and the mass flow rate of water
through the unit. Water temperature at condenser exit increases linearly with
water temperature at humidifier inlet and it decreases as water flow rate
A study of heat and mass transfer in humidification dehumidification desalination unit
ii
increases. The air temperature and humidity ratio of the air at condenser inlet
increase with both water temperature at humidifier inlet and water mass flow
rate. The higher water temperature at humidifier inlet or water flow rate, the
higher is the air temperature and humidity ratio at condenser exit. The maximum
productivity of the unit has been obtained using wooden slates packing and with
forced air circulation. The maximum productivity obtained by the unit is about
5.8 liter/hr at water mass flow rate of 2.8 kg/min and water temperature at
humidifier inlet 85 ºC. No significant improvement in the performance of the
desalination unit has been achieved by forced circulation of air at high
temperatures while a larger effect was noticed at lower temperatures. The
theoretical predictions have been compared with actual measurements. The
average relative deviation of predictions from measurements are (-0.9%) in the
air temperature at condenser inlet, (3.8%) in the humidity ratio at condenser exit
and (-1%) in the water temperature at condenser exit. It has been recommended
that the water temperature at humidifier inlet should not exceed a maximum of
75 oC in order to achieve higher productivity and at the same time to avoid the
crystallization of salts in the humidifier.