Ahmed Hamza H. Ali

Experimental study on laminar flow forced-convection in a channel with upper V-corrugated plate heated by radiation

Experimental study of the effects of the operating parameters on laminar flow forced-convection heat transfer for air flowing in a channel having a V-corrugated upper plate heated by radiation heat flux while the other walls are thermally insulated has been carried out. The parameters studied and their ranges were as follows: flow Reynolds number (Re) ranging from 750 to 2050, incident radiation fluxes (qinc) of 400, 700, and 1000 W/m2, inlet air bulk temperatures (Tb,in) ranging from 12.4 to 59.4 °C and tilting angles of the channel (β) of 0°, 15°, 30°, 45°, and 60°. The results show that, the effect of Re on local Nusselt number (Nux) are clear and more significant at the channel entrance region. While, changing β from 0° to 60° leads to an increase in Nux by a ratio ranging from 33% to 67.3% depending on Re values and other operating parameters. Increasing the qinc values by 175% and 250% leads to an increase in Nux values by 26% and 50%, respectively. In addition, the results indicate that there are significant increases in Nux in the channel entrance region due to the increase in inlet air bulk temperature and this influence diminishes downstream.

Evaporator Air-Side Fouling: Effect on Performance of Room Air Conditioners and Impact on Indoor Air Quality

This study investigated experimentally the effects of real fouling material at the air side of the evaporators heat exchanger coil on the performance of room air-conditioner units as well as the impact of some fouling material compositions on indoor air quality. At the end of the experiments, examination of the biological contents of the fouling material on the coil was performed; it was found that the coil frontal face had heavy colonies of Aspergillus fungi of different species. This result is important to fill in the knowledge gaps between biological deposition, colonization, and occupant problems of staying in an environment with a fouled evaporator coil. The results of the effect of such fouling materials on the unit performance show that the unit coefficient of performance at the standard air face velocity of 1.53 m/s for a clean evaporator coil was 2.82. It decreased to 1.89 (67%) after injection of 100 g of fouling materials, dropped to 1.79 (63.4%) after injection of 200 g of fouling materials, and fell to 1.23 (43.6%) after injection of 300 g of fouling materials. However, these results demonstrate that the predominant effect of fouling is to cause significant degradation in a room air conditioners coefficient of performance.

A One-Dimensional Model of Viscous Liquid Jets Breakup

The breakup process of a low speed capillary liquid jet is computationally investigated for different Ohnesorge numbers (Z), wave numbers (K), and disturbance amplitudes (ζo ). An implicit finite difference scheme has been developed to solve the governing equations of a viscous liquid jet. The results predict the evolution and breakup of the liquid jet, the growth rate of disturbance, the breakup time and location, and the main and satellite drop sizes. It is found that the predicted growth rate of disturbance, the breakup time, and the main and satellite drop sizes depend mainly on the wave numbers and the Ohnesorge numbers. The results are compared with those available, experimental data and analytical analysis. The comparisons indicate that good agreements can be obtained with the less complex one-dimensional model.

Effect of aging, thickness and color on both the radiative properties of polyethylene films and performance of the nocturnal cooling unit

This study presents the effects of the changing in color due to aging, thickness and the new color of polyethylene films on the radiative properties. Also, the influences of the radiative properties on the performance of the nocturnal cooling unit used to cool flowing water were studied. The measured data of the transmittance of the polyethylene films having a thickness of 50 μm and having changes in its color by 5, 30 and 100 days aging and also new film data were used to study its effects on the performance of the cooling unit theoretically. Also, two films of thickness 25 and 50 μm and two films having a thickness of 25 μm, with colors of light blue and colorless, were used to examine their effects on the performance of the cooling unit experimentally. The results showed that aging of the polyethylene films leads to substantial degradation in its transmissivity from average values of 0.72, 0.69, 0.57 and 0.42 corresponding to a new one, 5, 30 and 100 days aging in the wavelength range of 8–13 μm. Also, neither thickness of the films nor their new colors have significant effects on the transmittance. It has been found that the effects of aging of the polyethylene film by 100 days led to the reduction in performance of night cooling by 33.3%. The decrease in thickness of the polyethylene films from 50 to 25 μm leads to an increase in its radiative properties (transmittance) and the performance of the night sky radiation unit by 8.6%, approximately.

A Theoretical Model for the Formation of Functional Micro- and Nano-Particles from Combustion of Emulsion Droplets

In this paper a theoretical model is developed to simulate the process of vaporization and burning of emulsion droplets of a fuel and the evolution and formation of micro- and nano-particles. This process is usually known as the Emulsion Combustion Method (ECM). In the ECM, a proper salt solution is mixed with a fuel to form an emulsion of micro-solution droplets. The emulsion is then sprayed into micron-sized emulsion droplets; spray droplets burn in a spray flame to form final micro- or nano-particles. A mathematical model for the entire process from the droplet interior to the gas phase processes is proposed. Model equations are solved numerically. It is found that particle characteristics are dependent on the operating and processing conditions, such as the initial size and concentration of the suspended micro solution droplets in emulsion droplets and the fuel type and fraction of the emulsion droplets. Although a quantitative evaluation of the model performance is not yet possible due to the lack of sufficient experimental data, the developed model may be used to design an ECM process to produce particles with tailored properties. The main novelty of the model is that in an ECM process it can predict whether mono-dispersed single particles will be formed or agglomerated larger particles.

Effect of dust deposition on performance of thin film photovoltaic module in harsh humid climate

This study investigated experimentally the effect of air born suspend matters deposition on PV module located in harsh climate close to the sea. The experimental measurements are carried out under outdoor conditions in Alexandria, Egypt to identify the module performance degradation as a function of time as well as the time schedule for module surface cleaning. However, as the sea is nearby its a source for nocturnal condensate on module surface. The experiments were conducted during period from 13 March to 17 April, 2013. The results indicated that the dust accumulation on the module surface has a significant impact on PV module output power. As the dust deposition density increased from 0 to 0.36 mg cm-2, the corresponding reduction of PV output efficiency as well as short circuit current Isc are degraded by 17.71%. Conversely, the reduction of open circuit voltage was insignificant where the maximum reduction of Voc from 100% to 97.86 of the clean module value. The average degradation of power and efficiency during the entire period of work (30 days) is 9.86%. Also the results show that the dust effect on thin film PV modules becomes most significant in cloudy weather day rather than clear day and the degradation in performance reaches about 16.01% in cloudy day.

Numerical study on laminar flow forced‐convection heat transfer for air in a channel with offset plates heated by radiation heat flux

A two‐dimensional numerical study was carried out to investigate laminar forced‐convection heat transfer characteristics of air flow in a two parallel plate channel with offset plates and heated by a radiation heat flux. The SIMPLE method was used for the numerical prediction of the flow and thermal fields. The flow field temperature boundary conditions were obtained by applying the energy balance equation to boundary elements. The ray tracing technique was used to obtain the net absorbed radiation fractions in the boundary elements. The numerical results were validated with measured temperature values and experimentally calculated values of local Nusselt number (Nux), and a reasonable agreement was shown. Then the numerical simulation was used to study effects of design parameters on the convective heat transfer coefficient. It was found that in Re numbers from 650 to 2,550, the optimum spacing of offset plates relative to the nearest channel wall was around one third of the channel height. Also, the optimum offset plates’ numbers can be calculated based on one offset plate length being equal to one and a half times the channel hydraulic diameter. A correlation of average Nusselt number between the flowing air and the offset plates was obtained as follows; —Nu = 1.81 Re 0.352Pr1/3(Dh/l)1/2.

Experimental study of laminar flow forced-convection heat transfer in air flowing through offset plates heated by radiation heat flux

An experimental study of the steady state laminar flow forced-convection heat transfer of air flowing through offset plates located between two parallel plates and heated by radiation heat flux was carried out. The ranges of parameters tested were incident radiation heat fluxes of 500, 700, and 1000 W/m2 . With Re ranging from 650 to 2560. the inlet air bulk temperatures changed from 18.2 to 70 °C and the tilting angel of the unit with the horizontal ranged from 0 to 90° respectively. The results show that the rate of the increase in the local Nusselt number was observed to be proportional with Re up to 1900, while it became less sensitive over Re range of 1900–2500. Also. in this range of Re, with the inlet air temperature of 20 °C, the angel of inclination of the unit has no effect on the local Nusselt number. Increasing the incident radiation heat flux in the case of higher values of Re leads to a slight decrease in the value of the local Nusselt number. The effect of the inlet air bulk temperature on the forced-convection heat transfer coefficient shows. in the case of the horizontal position. an increase in the inlet air bulk temperature leads to slight decreases in the value of the average Nusselt number. while it leads to a significant decreases in the value of the average Nusselt number as the tilting angle increases up to the vertical position. This effect is clearer in the case of Re = 650 rather than Re = 2550.

A fundamental study of combined free and forced convective heat transfer from a vertical plate followed by a backward step

Combined forced and free laminar convective heat transfer on a vertical plate with a backward‐facing step has been studied numerically and experimentally, considering the effects of the interaction between the buoyancy and inertia forces which play a significant role in this phenomenon with the step‐geometry factor of d/L. The convective heat transfer behavior in connection with the reattachment and recirculation flows appearing in the step region has been investigated based on the numerical calculations and Mach‐Zehnder interferometer measurement under the wide range of the thermal condition. The behaviors of local Nusselt number NuL, velocity and temperature boundary layers and streamline fields in the recirculating region have been discussed for the various parameters of Grashof number GrL, Reynolds number ReL and the geometry factor d/L. The characteristic behavior of this convection heat transfer, including the vortex flow mode in the recirculating region and the unstable fluctuating mode near the re...

Performance of a small-scale solar-powered adsorption cooling system

ABSTRACT In this study, an experimental investigation on the performance of a small-scale residential-size solar-driven adsorption (silica gel-water) cooling system that was constructed at Assiut University campus, Egypt is carried out. As Assiut area is considered as hot, arid climate, field tests for performance assessment of the system operation during the summer season are performed under different environmental operating conditions. The system consists of an evacuated tube with a reflective concentration parabolic surface solar-collector field with a total area of 36 m2, a silica gel-water adsorption chiller of 8 kW nominal cooling capacity, and hot and cold water thermal storage tanks of 1.8 and 1.2 m3 in volume, respectively. The results of summer season field test show that under daily solar insolation varying from 21 to 27 MJ/m2, the solar collectors employed in the system had high and almost constant thermal efficiency. The daily solar-collector efficiency during the period of system operation ranged from about 50% to 78%. The adsorption chiller performance shows that the chiller average daily coefficient of performance (COP) was 0.41 with the average cooling capacity of 4.4 kW when the cooling-water and chilled-water temperatures were about 31°C and 19°C, respectively. As the chiller cooling water is cooled by the cooling tower in the hot arid area, the cooling water is at a higher temperature than the design point of the chiller. Therefore, an experiment was carried out using the city water for cooling. The results show that an enhancement in the chiller COP by 40% and the chilling power by 17% has been achieved when the city water was 27.7°C.