Hamdy Kandil | The German University in Cairo (original) (raw)

Papers by Hamdy Kandil

Journal of Engineering and Applied Science, 2022

This paper presents a comprehensive review regarding the published work related to the effect of ... more This paper presents a comprehensive review regarding the published work related to the effect of dust on the performance of photovoltaic panels in the Middle East and North Africa region as well as the Far East region. The review thoroughly discusses the problem of dust accumulation on the surface of photovoltaic panels and the severity of the problem. Moreover, a survey of the most advanced cleaning techniques is presented, and their applicability is evaluated. There are plenty of techniques that have been used to remove the dust accumulated on the surface of PV panels, and these include manual and self-cleaning methods. However, it is concluded from the presented review that there is a strong need for developing new cleaning methods especially for the Middle East and North Africa region, which do not consume water and have low capital and operational costs with less human intervention, especially for hot, arid, and dusty regions.

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 2020

The Fresnel system can achieve high electrical energy yield compared to the traditional photovolt... more The Fresnel system can achieve high electrical energy yield compared to the traditional photovoltaic (PV) panel techniques due to the concentration of solar energy. However, this huge energy might cause overheating of the PV panel. The objective of this research is to mathematically model a linear Fresnel system that is cooled by either spraying the PV panel by tap water or chilled water, in order to determine the maximum possible concentration ratio, which is called the critical concentration ratio. Then, the model is further used to study the effect of cooling on the PV panel in real life operating conditions in two cities; the first one is a hot city which is Cairo, Egypt, and the other one is a cold city which is Stuttgart, Germany. The objective is to find out the Critical concentration ratio (Cr) at which the maximum energy output from the system can occur as a function of the operating conditions. The results of this study show that cooling of the PV panels using chilled water system is not feasible. Therefore, in order to improve the feasibility, a low energy cooling system should be adopted. Such system may include spraying tap water on the PV panels, recollecting the water and cooling it naturally underground and finally spraying it again on the panels. The maximum output energy has increased by approximately 75%, compared to the nocooling case, due to water spraying, which indicates the feasibility of water spraying in Fresnel systems.

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 2020

The Fresnel system can achieve high electrical energy yield compared to the traditional photovolt... more The Fresnel system can achieve high electrical energy yield compared to the traditional photovoltaic (PV) panel techniques due to the concentration of solar energy. However, this huge energy might cause overheating of the PV panel. The objective of this research is to mathematically model a linear Fresnel system that is cooled by either spraying the PV panel by tap water or chilled water, in order to determine the maximum possible concentration ratio, which is called the critical concentration ratio. Then, the model is further used to study the effect of cooling on the PV panel in real life operating conditions in two cities; the first one is a hot city which is Cairo, Egypt, and the other one is a cold city which is Stuttgart, Germany. The objective is to find out the Critical concentration ratio (Cr) at which the maximum energy output from the system can occur as a function of the operating conditions. The results of this study show that cooling of the PV panels using chilled water system is not feasible. Therefore, in order to improve the feasibility, a low energy cooling system should be adopted. Such system may include spraying tap water on the PV panels, recollecting the water and cooling it naturally underground and finally spraying it again on the panels. The maximum output energy has increased by approximately 75%, compared to the nocooling case, due to water spraying, which indicates the feasibility of water spraying in Fresnel systems.

The vortex tube is a simple device with no mechanical operation and no moving parts which by inje... more The vortex tube is a simple device with no mechanical operation and no moving parts which by injecting compressed air at room temperature circumferentially into the tube at high velocity this simple device separates the inlet compressed air into outward radial high temperature vortex and inner low temperature one. Temperature separation occurs along the tube from the inner vortex to the outer vortex Vortex tubes are used in applications as cooling cutting tools (lathes and mills) during operation &, electronic component cooling. It has advantages as it is maintenance free, reliable and compact A CFD study and analysis of the RHVT is presented in this book. The performance of the RHVT in this study is investigated at different cold orifice diameter to tube diameter ratios A 3D analysis of the air flow inside the RHVT is carried out to have a better visualization of the air inside the tube and to investigate some of its properties as the inner and outer vortex and the stagnation point. The 3D study showed that two vortices exist inside the tube, that both vortices have the same direction of rotation. The stagnation point existence is investigated in this study.

2021 International Conference on Microelectronics (ICM), 2021

Energy Reports, 2020

Abstract Many types of coatings are available in the market, which prevent the adhesion of dust t... more Abstract Many types of coatings are available in the market, which prevent the adhesion of dust to the surface of PV panels, but do not repel the dust off the surface of the panel. The objective of this research is to experimentally investigate the influence of using a nano-coating for PV panels together with an automated mechanical vibrator on the electrical performance of the panel. The function of the vibrator is to shake the panel twice daily, such that the dust on the panel can fall off by gravity. Three PV panels are examined where the first panel is with no coatings or vibration and is used as a reference for comparison, the second panel is coated with a nano-coating, while the third panel is coated with a nano-coating and shaken using a mechanical vibrator. It has been found that the accumulation of dust on the surface of solar panels is gradual and increases with time, especially in dry and desert regions, such as Egypt. The results show that the average electrical efficiency of the PV panels with coating and mechanical vibrator has decreased by 12.94% during six weeks of operation, whereas the efficiency of the PV panel with coating dropped by 24.46%. However, the reference panel had a drop in efficiency of 33%. Dust mitigation using coatings is an effective technique in cleaning solar panels, and its performance can be improved if a vibration system is applied.

Lake Nasser was created as a result of the construction of the Aswan High Dam in 1968. In 1978 Eg... more Lake Nasser was created as a result of the construction of the Aswan High Dam in 1968. In 1978 Egypt began building the Sadat Canal NW from Lake Nasser through Toshka valley to allow water levels higher than 178 m to be drained off into Toshka depression. In the late 1990s water began flowing through the Canal into the depression. The lakes were first noticed after the easternmost lake growing in November 1998. Starting in year 1999 three additional lakes formed successively westward. Since 2001 the water level in the Nile did not exceed 178 m and no water entered the lakes. About six years of regional drought and rapidly increasing demand for water have resulted in decreasing water levels in the lakes throughout East Africa. The drought impacted the water source of the Nile River, reducing water flow downstream into Lake Nasser which resulted in stopping the water supplication to Toshka lakes and shrinking their areas with time due to the evaporation. The appearance of Toshka lakes...

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

The seasonal temperature inversion over Cairo, Egypt is evaluated during the period, September 20... more The seasonal temperature inversion over Cairo, Egypt is evaluated during the period, September 2004 - September 2005. The area suffers from annually increased concentrations of suspended Particulate Matter (PM) associated with temperature inversion mainly during autumn and spring. The temperature inversion phenomenon was simulated using the 5th generation of the Penn State NCAR mesoscale Model (MM5) improved by using accurate topology model and monthly averaged vegetation index. The results agree with ATOVS data and ground measurements of the PM10. The results conclude that the ground temperature inversion predominantly occurs during winter and spring, whereas the subsidence inversion role is observable in summer and autumn. Results show also that the inversion strength correlates to the PM10 measurements with a correlation coefficient of 0.87 during April and 0.79 during the simulation period. The co-existence of the GTI and STI over Cairo contributes to the observed high concentrations of the PM10 concentrations associated with the dark or black cloud episodes.

2011 IEEE International Geoscience and Remote Sensing Symposium, 2011

The objective of this paper is to evaluate the effects of changing different physics schemes on t... more The objective of this paper is to evaluate the effects of changing different physics schemes on the accuracy of weather simulations at different locations inside Egypt. The model sensitivity to physics options was tested in the four seasons and the results were compared to observations at different locations. Different physics packages were used based on different planetary boundary layer (PBL)

Computers & Fluids, 1993

ABSTRACT Existing numerical simulations and physical aspects of subsonic and supersonic vortex-br... more ABSTRACT Existing numerical simulations and physical aspects of subsonic and supersonic vortex-breakdown modes are reviewed. The solution to the problem of supersonic vortex breakdown is emphasized in this paper and carried out with the full Navier—Stokes equations for compressible flows. Numerical simulations of vortex-breakdown modes are presented in bounded and unbounded domains. The effects of different types of downstream-exit boundary conditions are studied and discussed.

ABSTRACT Air pollution episodes have been recorded in Cairo, during the fall season, since 1999. ... more ABSTRACT Air pollution episodes have been recorded in Cairo, during the fall season, since 1999. The main reason for the smog-like episodes (black clouds) is adverse weather conditions with low and variable winds, high humidity and strong temperature inversions in the few-hundred meters above the ground. The two important types of temperature inversion affecting the air pollution are surface or ground (radiation) inversion and subsidence (elevated) inversion. The surface temperature inversion is associated with a rapid decrease in the ground surface temperature with the simultaneous existence of warm air in the lower troposphere. The inversion develops at dusk and continues until the surface warms again the following day. Pollutants emitted during the night are caught under this "inversion lid." Subsidence inversion forms when warm air masses move over colder air masses. The inversion develops with a stagnating high-pressure system (generally associated with fair weather). Under these conditions, the pressure gradient becomes progressively weaker so that winds become light. These light winds greatly reduce the horizontal transport and dispersion of pollutants. At the same time, the subsidence inversion acts as a barrier to the vertical dispersion of the pollutants. In this study, the Penn State/NCAR Meso-Scale Model (MMS) is used to simulate the temperature inversion phenomenon over Greater Cairo region during the fall season of 2004. Accurate computations of the heat transfer at the surface are needed to capture this phenomenon. This can only be achieved by high-resolution simulations in both horizontal and vertical directions. Hence, for accurate simulation of the temperature inversion over Greater Cairo, four nested domains of resolutions of 27 km, 9 km, 3 km and 1 km, respectively, were used in the horizontal planes. Furthermore, 42 levels were used in the vertical direction to capture the correct surface heat flux and to observe the small changes in the vertical temperature gradient. The results of the numerical model showed that it is possible to capture both types of temperature inversion during the night and early morning hours. This can be observed from the results of the vertical temperature profile and temperature gradient, which indicate that an inversion system was present over Cairo at a layer extending between 300 m and 800 m above the ground.

Computer Physics Communications, 1991

The unsteady, compressible, thin-layer and full Navier-Stokes equations are used to numerically s... more The unsteady, compressible, thin-layer and full Navier-Stokes equations are used to numerically simulate steady and unsteady asymmetric, supersonic, locally conical flows around a 5-deg semiapex angle circular cone. The main computational scheme is the implicit, upwind, flux-difference splitting, finite-volume scheme. Comparison of asymmetric flow solutions using the thin-layer and full Navier-Stokes equations is presented and discussed. The implicit, upwind, flux-vector splitting, finite-volume scheme has also been used to solve for the unsteady asymmetric flow with vortex shedding. The unsteady-flow solution using the flux-vector splitting scheme perfectly agrees with the previously obtained solution using the flux-difference splitting scheme. Passive control of asymmetric flows has been demonstrated and studied using sharp- and round-edged, thick and thin strakes.

Energy Conversion and Management

Abstract Overheating of silicon PV panels due to excessive solar irradiance and high environmenta... more Abstract Overheating of silicon PV panels due to excessive solar irradiance and high environmental temperatures is a major problem especially in the Middle East and North Africa (MENA) region. The temperature of PV panels can easily go up to 75 °C in such regions, which corresponds to a drop in efficiency of about 25%. An innovative solution is presented in this research to minimize overheating of PV panels, and that is based on natural convection. Through holes are drilled in the PV panel to assist the uprising of the hot boundary layer under the panel causing cooling of the panel. Experiments have been performed to proof the idea, and then numerical simulations are performed for further exploration of the influence of the hole size and number of holes. It was found that the temperature of the perforated PV panels is lower than the temperature of the non-perforated panels, and that temperature difference increases with increasing number of holes. However, there is a critical diameter for the hole size, such that before and after that diameter the temperature of the PV panel increases. It can be concluded from the performed research that adding through holes in the PV panel is a passive cooling technique that can minimize overheating of the panel.

OALib

The Ranque-Hilsch vortex tube is a simple device with no moving parts and no mechanical operation... more The Ranque-Hilsch vortex tube is a simple device with no moving parts and no mechanical operations. This tube separates the inlet air into two distinctive regions; an outward high temperature region and an inner low-temperature one. A computational study of the vortex tube is presented in this article using the ANSYS Fluent ® software whose results showed good agreement with the experimental measurements. The effects of different geometrical parameters such as the tube length to diameter ratio and the cold orifice size on the coefficient of performance of the tube were investigated. The results showed that the coefficient of performance (COP) of the tube is highly affected by the tube length to diameter ratio (L D), and this effect varies when operating at different cold mass fractions where the maximum coefficient of performance occur at cold mass fraction of 0.64. The results also showed that the coefficient of performance of the tube is also affected by the cold orifice to tube diameter ratio (c d D) and that the maximum (COP) at any (c d D) ratio occurs also at a cold mass fraction of 0.64.

International Journal of Sustainable Energy

Journal of Photonics for Energy

Renewable Energy, 2016

ABSTRACT Solar tracking systems would probably increase the efficiency of a PV module, but when a... more ABSTRACT Solar tracking systems would probably increase the efficiency of a PV module, but when and where. There are many factors that affect the performance of PV panels, especially crystalline silicon panels, e.g. overheating due to excessive exposure to solar irradiance in a hot climate as in Sunbelt countries. So, it could be the case that a tracking system is not necessary for a Sunbelt country. The objective of this research is to determine mathematically the performance of a PV panel as a function of tracking the sun and the operating conditions. The used mathematical model is validated experimentally and then applied for several environments, i.e. hot as well as cold regions. It has been found that the gain in electrical energy from tracking the sun is about 39% in case of a cold city as Berlin, Germany. While the gain in energy does not exceed 8% in case of a hot city as Aswan, Egypt, due to overheating of the PV panels. However, if the energy needed for running the tracking system, which ranges from 5% to 10% of the energy generated, is included in this analysis then tracking the sun will not be feasible in hot countries.

Journal of Engineering and Applied Science, 2022

This paper presents a comprehensive review regarding the published work related to the effect of ... more This paper presents a comprehensive review regarding the published work related to the effect of dust on the performance of photovoltaic panels in the Middle East and North Africa region as well as the Far East region. The review thoroughly discusses the problem of dust accumulation on the surface of photovoltaic panels and the severity of the problem. Moreover, a survey of the most advanced cleaning techniques is presented, and their applicability is evaluated. There are plenty of techniques that have been used to remove the dust accumulated on the surface of PV panels, and these include manual and self-cleaning methods. However, it is concluded from the presented review that there is a strong need for developing new cleaning methods especially for the Middle East and North Africa region, which do not consume water and have low capital and operational costs with less human intervention, especially for hot, arid, and dusty regions.

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 2020

The Fresnel system can achieve high electrical energy yield compared to the traditional photovolt... more The Fresnel system can achieve high electrical energy yield compared to the traditional photovoltaic (PV) panel techniques due to the concentration of solar energy. However, this huge energy might cause overheating of the PV panel. The objective of this research is to mathematically model a linear Fresnel system that is cooled by either spraying the PV panel by tap water or chilled water, in order to determine the maximum possible concentration ratio, which is called the critical concentration ratio. Then, the model is further used to study the effect of cooling on the PV panel in real life operating conditions in two cities; the first one is a hot city which is Cairo, Egypt, and the other one is a cold city which is Stuttgart, Germany. The objective is to find out the Critical concentration ratio (Cr) at which the maximum energy output from the system can occur as a function of the operating conditions. The results of this study show that cooling of the PV panels using chilled water system is not feasible. Therefore, in order to improve the feasibility, a low energy cooling system should be adopted. Such system may include spraying tap water on the PV panels, recollecting the water and cooling it naturally underground and finally spraying it again on the panels. The maximum output energy has increased by approximately 75%, compared to the nocooling case, due to water spraying, which indicates the feasibility of water spraying in Fresnel systems.

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 2020

The Fresnel system can achieve high electrical energy yield compared to the traditional photovolt... more The Fresnel system can achieve high electrical energy yield compared to the traditional photovoltaic (PV) panel techniques due to the concentration of solar energy. However, this huge energy might cause overheating of the PV panel. The objective of this research is to mathematically model a linear Fresnel system that is cooled by either spraying the PV panel by tap water or chilled water, in order to determine the maximum possible concentration ratio, which is called the critical concentration ratio. Then, the model is further used to study the effect of cooling on the PV panel in real life operating conditions in two cities; the first one is a hot city which is Cairo, Egypt, and the other one is a cold city which is Stuttgart, Germany. The objective is to find out the Critical concentration ratio (Cr) at which the maximum energy output from the system can occur as a function of the operating conditions. The results of this study show that cooling of the PV panels using chilled water system is not feasible. Therefore, in order to improve the feasibility, a low energy cooling system should be adopted. Such system may include spraying tap water on the PV panels, recollecting the water and cooling it naturally underground and finally spraying it again on the panels. The maximum output energy has increased by approximately 75%, compared to the nocooling case, due to water spraying, which indicates the feasibility of water spraying in Fresnel systems.

The vortex tube is a simple device with no mechanical operation and no moving parts which by inje... more The vortex tube is a simple device with no mechanical operation and no moving parts which by injecting compressed air at room temperature circumferentially into the tube at high velocity this simple device separates the inlet compressed air into outward radial high temperature vortex and inner low temperature one. Temperature separation occurs along the tube from the inner vortex to the outer vortex Vortex tubes are used in applications as cooling cutting tools (lathes and mills) during operation &, electronic component cooling. It has advantages as it is maintenance free, reliable and compact A CFD study and analysis of the RHVT is presented in this book. The performance of the RHVT in this study is investigated at different cold orifice diameter to tube diameter ratios A 3D analysis of the air flow inside the RHVT is carried out to have a better visualization of the air inside the tube and to investigate some of its properties as the inner and outer vortex and the stagnation point. The 3D study showed that two vortices exist inside the tube, that both vortices have the same direction of rotation. The stagnation point existence is investigated in this study.

2021 International Conference on Microelectronics (ICM), 2021

Energy Reports, 2020

Abstract Many types of coatings are available in the market, which prevent the adhesion of dust t... more Abstract Many types of coatings are available in the market, which prevent the adhesion of dust to the surface of PV panels, but do not repel the dust off the surface of the panel. The objective of this research is to experimentally investigate the influence of using a nano-coating for PV panels together with an automated mechanical vibrator on the electrical performance of the panel. The function of the vibrator is to shake the panel twice daily, such that the dust on the panel can fall off by gravity. Three PV panels are examined where the first panel is with no coatings or vibration and is used as a reference for comparison, the second panel is coated with a nano-coating, while the third panel is coated with a nano-coating and shaken using a mechanical vibrator. It has been found that the accumulation of dust on the surface of solar panels is gradual and increases with time, especially in dry and desert regions, such as Egypt. The results show that the average electrical efficiency of the PV panels with coating and mechanical vibrator has decreased by 12.94% during six weeks of operation, whereas the efficiency of the PV panel with coating dropped by 24.46%. However, the reference panel had a drop in efficiency of 33%. Dust mitigation using coatings is an effective technique in cleaning solar panels, and its performance can be improved if a vibration system is applied.

Lake Nasser was created as a result of the construction of the Aswan High Dam in 1968. In 1978 Eg... more Lake Nasser was created as a result of the construction of the Aswan High Dam in 1968. In 1978 Egypt began building the Sadat Canal NW from Lake Nasser through Toshka valley to allow water levels higher than 178 m to be drained off into Toshka depression. In the late 1990s water began flowing through the Canal into the depression. The lakes were first noticed after the easternmost lake growing in November 1998. Starting in year 1999 three additional lakes formed successively westward. Since 2001 the water level in the Nile did not exceed 178 m and no water entered the lakes. About six years of regional drought and rapidly increasing demand for water have resulted in decreasing water levels in the lakes throughout East Africa. The drought impacted the water source of the Nile River, reducing water flow downstream into Lake Nasser which resulted in stopping the water supplication to Toshka lakes and shrinking their areas with time due to the evaporation. The appearance of Toshka lakes...

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

The seasonal temperature inversion over Cairo, Egypt is evaluated during the period, September 20... more The seasonal temperature inversion over Cairo, Egypt is evaluated during the period, September 2004 - September 2005. The area suffers from annually increased concentrations of suspended Particulate Matter (PM) associated with temperature inversion mainly during autumn and spring. The temperature inversion phenomenon was simulated using the 5th generation of the Penn State NCAR mesoscale Model (MM5) improved by using accurate topology model and monthly averaged vegetation index. The results agree with ATOVS data and ground measurements of the PM10. The results conclude that the ground temperature inversion predominantly occurs during winter and spring, whereas the subsidence inversion role is observable in summer and autumn. Results show also that the inversion strength correlates to the PM10 measurements with a correlation coefficient of 0.87 during April and 0.79 during the simulation period. The co-existence of the GTI and STI over Cairo contributes to the observed high concentrations of the PM10 concentrations associated with the dark or black cloud episodes.

2011 IEEE International Geoscience and Remote Sensing Symposium, 2011

The objective of this paper is to evaluate the effects of changing different physics schemes on t... more The objective of this paper is to evaluate the effects of changing different physics schemes on the accuracy of weather simulations at different locations inside Egypt. The model sensitivity to physics options was tested in the four seasons and the results were compared to observations at different locations. Different physics packages were used based on different planetary boundary layer (PBL)

Computers & Fluids, 1993

ABSTRACT Existing numerical simulations and physical aspects of subsonic and supersonic vortex-br... more ABSTRACT Existing numerical simulations and physical aspects of subsonic and supersonic vortex-breakdown modes are reviewed. The solution to the problem of supersonic vortex breakdown is emphasized in this paper and carried out with the full Navier—Stokes equations for compressible flows. Numerical simulations of vortex-breakdown modes are presented in bounded and unbounded domains. The effects of different types of downstream-exit boundary conditions are studied and discussed.

ABSTRACT Air pollution episodes have been recorded in Cairo, during the fall season, since 1999. ... more ABSTRACT Air pollution episodes have been recorded in Cairo, during the fall season, since 1999. The main reason for the smog-like episodes (black clouds) is adverse weather conditions with low and variable winds, high humidity and strong temperature inversions in the few-hundred meters above the ground. The two important types of temperature inversion affecting the air pollution are surface or ground (radiation) inversion and subsidence (elevated) inversion. The surface temperature inversion is associated with a rapid decrease in the ground surface temperature with the simultaneous existence of warm air in the lower troposphere. The inversion develops at dusk and continues until the surface warms again the following day. Pollutants emitted during the night are caught under this "inversion lid." Subsidence inversion forms when warm air masses move over colder air masses. The inversion develops with a stagnating high-pressure system (generally associated with fair weather). Under these conditions, the pressure gradient becomes progressively weaker so that winds become light. These light winds greatly reduce the horizontal transport and dispersion of pollutants. At the same time, the subsidence inversion acts as a barrier to the vertical dispersion of the pollutants. In this study, the Penn State/NCAR Meso-Scale Model (MMS) is used to simulate the temperature inversion phenomenon over Greater Cairo region during the fall season of 2004. Accurate computations of the heat transfer at the surface are needed to capture this phenomenon. This can only be achieved by high-resolution simulations in both horizontal and vertical directions. Hence, for accurate simulation of the temperature inversion over Greater Cairo, four nested domains of resolutions of 27 km, 9 km, 3 km and 1 km, respectively, were used in the horizontal planes. Furthermore, 42 levels were used in the vertical direction to capture the correct surface heat flux and to observe the small changes in the vertical temperature gradient. The results of the numerical model showed that it is possible to capture both types of temperature inversion during the night and early morning hours. This can be observed from the results of the vertical temperature profile and temperature gradient, which indicate that an inversion system was present over Cairo at a layer extending between 300 m and 800 m above the ground.

Computer Physics Communications, 1991

The unsteady, compressible, thin-layer and full Navier-Stokes equations are used to numerically s... more The unsteady, compressible, thin-layer and full Navier-Stokes equations are used to numerically simulate steady and unsteady asymmetric, supersonic, locally conical flows around a 5-deg semiapex angle circular cone. The main computational scheme is the implicit, upwind, flux-difference splitting, finite-volume scheme. Comparison of asymmetric flow solutions using the thin-layer and full Navier-Stokes equations is presented and discussed. The implicit, upwind, flux-vector splitting, finite-volume scheme has also been used to solve for the unsteady asymmetric flow with vortex shedding. The unsteady-flow solution using the flux-vector splitting scheme perfectly agrees with the previously obtained solution using the flux-difference splitting scheme. Passive control of asymmetric flows has been demonstrated and studied using sharp- and round-edged, thick and thin strakes.

Energy Conversion and Management

Abstract Overheating of silicon PV panels due to excessive solar irradiance and high environmenta... more Abstract Overheating of silicon PV panels due to excessive solar irradiance and high environmental temperatures is a major problem especially in the Middle East and North Africa (MENA) region. The temperature of PV panels can easily go up to 75 °C in such regions, which corresponds to a drop in efficiency of about 25%. An innovative solution is presented in this research to minimize overheating of PV panels, and that is based on natural convection. Through holes are drilled in the PV panel to assist the uprising of the hot boundary layer under the panel causing cooling of the panel. Experiments have been performed to proof the idea, and then numerical simulations are performed for further exploration of the influence of the hole size and number of holes. It was found that the temperature of the perforated PV panels is lower than the temperature of the non-perforated panels, and that temperature difference increases with increasing number of holes. However, there is a critical diameter for the hole size, such that before and after that diameter the temperature of the PV panel increases. It can be concluded from the performed research that adding through holes in the PV panel is a passive cooling technique that can minimize overheating of the panel.

OALib

The Ranque-Hilsch vortex tube is a simple device with no moving parts and no mechanical operation... more The Ranque-Hilsch vortex tube is a simple device with no moving parts and no mechanical operations. This tube separates the inlet air into two distinctive regions; an outward high temperature region and an inner low-temperature one. A computational study of the vortex tube is presented in this article using the ANSYS Fluent ® software whose results showed good agreement with the experimental measurements. The effects of different geometrical parameters such as the tube length to diameter ratio and the cold orifice size on the coefficient of performance of the tube were investigated. The results showed that the coefficient of performance (COP) of the tube is highly affected by the tube length to diameter ratio (L D), and this effect varies when operating at different cold mass fractions where the maximum coefficient of performance occur at cold mass fraction of 0.64. The results also showed that the coefficient of performance of the tube is also affected by the cold orifice to tube diameter ratio (c d D) and that the maximum (COP) at any (c d D) ratio occurs also at a cold mass fraction of 0.64.

International Journal of Sustainable Energy

Journal of Photonics for Energy

Renewable Energy, 2016

ABSTRACT Solar tracking systems would probably increase the efficiency of a PV module, but when a... more ABSTRACT Solar tracking systems would probably increase the efficiency of a PV module, but when and where. There are many factors that affect the performance of PV panels, especially crystalline silicon panels, e.g. overheating due to excessive exposure to solar irradiance in a hot climate as in Sunbelt countries. So, it could be the case that a tracking system is not necessary for a Sunbelt country. The objective of this research is to determine mathematically the performance of a PV panel as a function of tracking the sun and the operating conditions. The used mathematical model is validated experimentally and then applied for several environments, i.e. hot as well as cold regions. It has been found that the gain in electrical energy from tracking the sun is about 39% in case of a cold city as Berlin, Germany. While the gain in energy does not exceed 8% in case of a hot city as Aswan, Egypt, due to overheating of the PV panels. However, if the energy needed for running the tracking system, which ranges from 5% to 10% of the energy generated, is included in this analysis then tracking the sun will not be feasible in hot countries.