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Papers by Ahmed El-sebaii

Using phase change material (PCM) as an energy storage medium is one of the most efficient ways o... more Using phase change material (PCM) as an energy storage medium is one of the most efficient ways of storing thermal energy. The latent heat storage provides much higher storage density than sensible heat storage, with a smaller temperature difference between storing and releasing heat. In addition, phase change materials provide constant and moderate temperature which is needed for drying most agriculture crops sufficiently. This paper reviews the previous work on solar drying systems which implemented the phase change material as an energy storage medium. It is concluded that the solar dryer with a PCM reduces the heat losses and improves the efficiency of the system. Furthermore, this review paper summarizes the previous methods that have been used for improving the thermal conductivity of the used phase change material particularly paraffin wax since it is commonly used as a storage medium in solar drying systems. It is inferred that carbon fibers, expanded graphite, graphite foam and high thermal conductive particles may improve the thermal efficiency of solar energy devices employing paraffin waxes as thermal energy storage media.

a b s t r a c t Solar air heaters (SAHs) form the foremost component of solar energy utilization ... more a b s t r a c t Solar air heaters (SAHs) form the foremost component of solar energy utilization system. These air heaters absorb the irradiance and convert it into thermal energy at the absorbing surface and then transfer this energy to a fluid flowing through the collector. SAHs are inexpensive and most used collection devices because of their inherent simplicity. SAHs are found in several solar energy applications, especially for space heating, timber seasoning and agriculture drying. It has been observed by studying the previous literature that all the elements of a solar air heater such as; an absorber tray, the ducts, glazing, insulation, extended surfaces, as well as the tilt angle, have a significant effect on the thermal performance of the system. This review article focus on the developments that has followed round the globe in various aspects of solar air heating systems since 1877 up to now, with a glimpse of some novel patents of SAHs. The various methods that are used to improve the thermal performance of SAHs such as; optimizing the dimensions of the air heater construction elements, use of extended surfaces with different shapes and dimensions, use of sensible or latent storage media, use of concentrators to augment the available solar radiation, integrating photovoltaic elements with the heaters, etc, are also reported. Besides this, some benefits by using the SAHs has been discussed.

a b s t r a c t Transient mathematical models are presented for a single slope-single basin solar... more a b s t r a c t Transient mathematical models are presented for a single slope-single basin solar still with and without phase change material (PCM) under the basin liner of the still. Analytical expressions for temperatures of the still elements and the PCM have been obtained. The still performance has been investigated by computer simulation. Numerical calculations have been carried out, using stearic acid as a PCM, on typical summer and winter days in Jeddah (lat. 21°42 0 N, long. 39°11 0 E), Saudi Arabia. Effect of mass of the PCM (m pcm ) on the daylight P dl , overnight P on and daily productivity P d and efficiency g d of the still for different masses of basin water m w has been investigated. It is found that P dl decreases as m pcm increases; but P on and P d increase significantly with an increase of m pcm due to the increased amount of the heat stored within the PCM. During discharging of the PCM, the convective heat transfer coefficient from the basin liner to basin water is doubled; thus, the evaporative heat transfer coefficient is increased by 27% on using 3.3 cm of stearic acid beneath the basin liner. Therefore, on a summer day, a value of P d of 9.005 (kg/m 2 day) with a daily efficiency of 85.3% has been obtained compared to 4.998 (kg/m 2 day) when the still is used without the PCM. The PCM is more effective for lower masses of basin water on winter season.

The performance of a FBLS was investigated experimentally and theoretically.

Desalination and Water Treatment, 2011

ABSTRACT A transient mathematical model was presented for a single basin solar still with and wit... more ABSTRACT A transient mathematical model was presented for a single basin solar still with and without an external reflector. The model was based on an analytical solution of the energy balance equations for various elements of the still. The performance of the still with and without the external mirror was investigated by computer simulation using the climatic conditions of Jeddah (lat. 21° 42' N, long. 39° 11' E), Saudi Arabia. Effects of solar radiation intensity and mass of basin water on the daily productivity Pd and efficiency ηd of the still were studied. On typical summer (17/7/06) and winter (17/1/06) d, values of Pd of 10.563 and 6.650 (kg/md) with daily efficiencies of 56.78 and 52.04% were obtained with mirror compared to 4.605 and 2.260 (kg/md) with daily efficiencies of 50.69 and 44.76% when the still is used without mirror. To validate the proposed mathematical model, the simulated results were compared with the measurements that had been performed for the still under Tanta, lat. 30° 47' N (Egypt), weather conditions. It was found that the proposed model is able to predict the daily productivity and efficiency of the still with a reasonable accuracy. Furthermore, the proposed model was used to predict the annual performance of the still with and without mirror. The annual average of Pd with mirror is found to be 52.75% higher than that when the still is used without mirror.

Using phase change material (PCM) as an energy storage medium is one of the most efficient ways o... more Using phase change material (PCM) as an energy storage medium is one of the most efficient ways of storing thermal energy. The latent heat storage provides much higher storage density than sensible heat storage, with a smaller temperature difference between storing and releasing heat. In addition, phase change materials provide constant and moderate temperature which is needed for drying most agriculture crops sufficiently. This paper reviews the previous work on solar drying systems which implemented the phase change material as an energy storage medium. It is concluded that the solar dryer with a PCM reduces the heat losses and improves the efficiency of the system. Furthermore, this review paper summarizes the previous methods that have been used for improving the thermal conductivity of the used phase change material particularly paraffin wax since it is commonly used as a storage medium in solar drying systems. It is inferred that carbon fibers, expanded graphite, graphite foam and high thermal conductive particles may improve the thermal efficiency of solar energy devices employing paraffin waxes as thermal energy storage media.

a b s t r a c t Solar air heaters (SAHs) form the foremost component of solar energy utilization ... more a b s t r a c t Solar air heaters (SAHs) form the foremost component of solar energy utilization system. These air heaters absorb the irradiance and convert it into thermal energy at the absorbing surface and then transfer this energy to a fluid flowing through the collector. SAHs are inexpensive and most used collection devices because of their inherent simplicity. SAHs are found in several solar energy applications, especially for space heating, timber seasoning and agriculture drying. It has been observed by studying the previous literature that all the elements of a solar air heater such as; an absorber tray, the ducts, glazing, insulation, extended surfaces, as well as the tilt angle, have a significant effect on the thermal performance of the system. This review article focus on the developments that has followed round the globe in various aspects of solar air heating systems since 1877 up to now, with a glimpse of some novel patents of SAHs. The various methods that are used to improve the thermal performance of SAHs such as; optimizing the dimensions of the air heater construction elements, use of extended surfaces with different shapes and dimensions, use of sensible or latent storage media, use of concentrators to augment the available solar radiation, integrating photovoltaic elements with the heaters, etc, are also reported. Besides this, some benefits by using the SAHs has been discussed.

a b s t r a c t Transient mathematical models are presented for a single slope-single basin solar... more a b s t r a c t Transient mathematical models are presented for a single slope-single basin solar still with and without phase change material (PCM) under the basin liner of the still. Analytical expressions for temperatures of the still elements and the PCM have been obtained. The still performance has been investigated by computer simulation. Numerical calculations have been carried out, using stearic acid as a PCM, on typical summer and winter days in Jeddah (lat. 21°42 0 N, long. 39°11 0 E), Saudi Arabia. Effect of mass of the PCM (m pcm ) on the daylight P dl , overnight P on and daily productivity P d and efficiency g d of the still for different masses of basin water m w has been investigated. It is found that P dl decreases as m pcm increases; but P on and P d increase significantly with an increase of m pcm due to the increased amount of the heat stored within the PCM. During discharging of the PCM, the convective heat transfer coefficient from the basin liner to basin water is doubled; thus, the evaporative heat transfer coefficient is increased by 27% on using 3.3 cm of stearic acid beneath the basin liner. Therefore, on a summer day, a value of P d of 9.005 (kg/m 2 day) with a daily efficiency of 85.3% has been obtained compared to 4.998 (kg/m 2 day) when the still is used without the PCM. The PCM is more effective for lower masses of basin water on winter season.

The performance of a FBLS was investigated experimentally and theoretically.

Desalination and Water Treatment, 2011

ABSTRACT A transient mathematical model was presented for a single basin solar still with and wit... more ABSTRACT A transient mathematical model was presented for a single basin solar still with and without an external reflector. The model was based on an analytical solution of the energy balance equations for various elements of the still. The performance of the still with and without the external mirror was investigated by computer simulation using the climatic conditions of Jeddah (lat. 21° 42' N, long. 39° 11' E), Saudi Arabia. Effects of solar radiation intensity and mass of basin water on the daily productivity Pd and efficiency ηd of the still were studied. On typical summer (17/7/06) and winter (17/1/06) d, values of Pd of 10.563 and 6.650 (kg/md) with daily efficiencies of 56.78 and 52.04% were obtained with mirror compared to 4.605 and 2.260 (kg/md) with daily efficiencies of 50.69 and 44.76% when the still is used without mirror. To validate the proposed mathematical model, the simulated results were compared with the measurements that had been performed for the still under Tanta, lat. 30° 47' N (Egypt), weather conditions. It was found that the proposed model is able to predict the daily productivity and efficiency of the still with a reasonable accuracy. Furthermore, the proposed model was used to predict the annual performance of the still with and without mirror. The annual average of Pd with mirror is found to be 52.75% higher than that when the still is used without mirror.