Ibrahim M. Ismail

Cooling of water flowing through a night sky radiator

Experimental and theoretical studies of nocturnal cooling of water flowing through a night sky radiator unit were carried out. The system used for this study is two parallel plates night sky radiator with the top one (radiator) being a painted black aluminum plate. The radiator plate was covered by a polyethylene windscreen cover. The experimental study was conducted for a gravity flow open loop system. The parameters studied include the effect of average water mass flow rate, uncovered from the ambient versus covered supply warm water tank, and windscreen cover thickness on the performance. A new definition of the performance was expressed by an overall efficiency. A comparison between nocturnal cooling of stagnant and flowing water was also done. In the theoretical study a thorough radiation model was developed which calculates the radiation heat losses from both the cover and the radiator plate considering multiple reflections and absorptions between cover and plate. Energy balance was then applied on the cover, the radiator plate and the water. The cover and insulation were considered one lump each, while each of the radiator plate and the water were divided into discrete number of lumps. Energy storage in the radiator frame and insulation, and water elements was considered. Experimental results were used for verification of the theoretical model.

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.

Upgrading of heat through absorption heat transformers

Abstract In this paper, we study the performance of absorption heat transformers for upgrading low-level heat. A mathematical model was developed utilizing the equation of state to calculate the properties of ammonia-water mixture. The performance of the heat transformer is defined by COP and circulation ratio. The parameters that affect the performance are level of waste heat, condenser temperature, and effectiveness of heat exchangers. This study leads to identification of the field of the operating conditions.

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.