Essam E. Khalil

The Calculation of Two-Dimensional Turbulent Recirculating Flows

Numerical predictions are presented for seven different two-dimensional turbulent “elliptic” flows. The solution procedure, which is embodied in the TEACH computer program, is described and numerical tests reported. The calculated properties of the seven flows are compared with experimental results and demonstrate that the procedure, with a two-equation turbulence model, provides adequate precision for many engineering applications. The two-equation model is shown, however, to be deficient in detail.

Calculation of radiative heat transfer in a large gas fired furnace

Abstract The heat transfer and local flow properties in a large gas fuelled process heater are predicted using a calculation method based on a finite-difference numerical solution of the time-averaged equations governing the conservation of mass, momentum, chemical species and energy. Special attention is given to the modelling of radiant heat transfer. The accuracy of the predictions is assessed by comparison with experimental data. The comparison suggests that the calculation method can be used to obtain realistic predictions in practical gas fired furnaces.

Measurements of three velocity components in a model furnace with and without combustion

Measured values of three components of mean velocity and the corresponding normal stresses are reported in the flow within an enclosure which is representative of a small-scale furnace with an axi-symmetric, swirling flow configuration. The measurements were obtained in isothermal air flow and in a combusting mixture of air and natural gas, exit swirl numbers of zero and 0.52 were investigated for both the isothermal and combusting cases. A laser anemometer was used to obtain the measurements and comprised an argon-ion laser, a rotating diffraction grating as beam spiltter and frequency shifter, transmission and collection optical components, a photomultiplier and a filter-bank signal processor. The grating provided a frequency shift of ±0.54 MHz and allowed measurements in regions of high turbulence intensity and negative mean velocity. The filter bank consisted of 50 filters spanning the range from 0.6 to 6 MHz which, with the frequency shift indicated above and the optical arrangement employed, corresponded to a measurable velocity range of −2 m/sec to 23 m/sec. Measured values of mean axial velocity and the corresponding normal stress are presented for the four flow conditions of zero and finite swirl, with and without combustion. The turbulent-kinetic energy is presented for the isothermal cases and the regions of near-isotropic turbulence identified, only the axial and tangential normal stresses were measured for the combusting cases. The measurements were designed to be used for the evaluation of turbulent-flow prediction procedures. They demonstrate, for example, that the regions of recirculation are substantially different for the combusting measurements and that the turbulence is far from isotropic over most of the flow fields; similarly, the velocity-probability-density distributions indicate that Gaussian turbulence exists in only negligible regions of the flows.

Energy Efficiency, Air Quality, and Comfort in Air-Conditioned Spaces

To design an optimum HVAC airside system that provides comfort and air quality in the air-conditioned spaces with efficient energy consumption is a great challenge. This paper evaluates recent progresses of HVAC airside design for the airconditioned spaces. The present evaluation study defines the current status, future requirements, and expectations. It has been found that, the experimental investigations should be considered in the new trend of studies, not to validate the numerical tools only, but also to provide a complete database of the airflow characteristics in the air-conditioned spaces. Based on this analysis and the vast progress of computers and associated software, the artificial intelligent technique will be a competitor candidate to the experimental and numerical techniques. Finally, the researches that relate between the different designs of the HVAC systems and energy consumption should concern with the optimization of airside design as the expected target to enhance the indoor environment.Copyright

Potable water technology development in Egypt

Abstract The availability of fresh water and energy is the key factor in the development of many countries, particularly those of large, overpopulated, arid areas. Potable water supply shortage and recent technological development have led to wider application of conventional, yet advanced saline/brackish water desalination plants. The growing potable water demand in Red Sea and Sinai resorts led to an organized national plan for implementation of desalination technologies [1]. The present work analyzes water demand in Egypt and reviews the current research activities to establish the appropriate technology for adaptation, local manufacturing experiences, unit size, process and economics. Water demand in a vastly growing and developing Egyptian community is characterized by a rising standard of living, expanded industrialization in the mining and petroleum sectors and the vast expansion of tourism development [2]. With the limited resources to support the infrastructure, the problem is acute. Khalil [3] have emphasized the importance of establishing a water master plan, a technoeconomic assessment of the desalting process. The present work reviews water demand, availability, and new developments in small- and medium-sized locally manufactured units. The advantages and limitations, based on technoeconomic concepts of the application of different desalting process in Egypt, are outlined and discussed.

Geometrical Optimization of Thermoacoustic Heat Engines

Thermoacoustics is concerned with the interaction of thermodynamics and acoustics. This interaction can bring numerous innovative applications in power generation and refrigeration. Thermoacoustic phenomenon can be classified into two main categories: the first one where the thermal energy (heat) is transformed into acoustic energy (sound) is called thermoacoustic engine; the second type, where the acoustic energy is transformed into thermal energy, is called thermoacoustic refrigerator or heat pump (1). The main objective of this work is to inspect the effect of the main geometrical parameters of the thermoacoustic heat engine on the performance, in order to increase the thermal efficiency. In this work, the thermoacoustic heat engine is modeled using the DeltaEC software (2). The results show that the efficiency of the thermoacoustic engine can be increased from 9.6 % to 16 % by changing the mean pressure, stack spacing, stack mid-position and stack length. The physics behind these changes and the suggested design guidelines are presented.

THERMAL MANAGEMENT IN HOSPITALS: COMFORT, AIR QUALITY, AND ENERGY UTILIZATION

The balance between thermal comfort and air quality in healthcare facilities to optimize the Indoor Air Quality (IAQ) is the main aim of this paper. The present paper will present this balance from the viewpoint of the air conditioning design. It was found that the design of the HVAC airside systems plays an important role for achieving the optimum air quality beside the optimum comfort level. This paper highlights the importance of the proper airside design on the IAQ. The present paper introduces some recommendations for airside designs to facilitate the development of optimum HVAC systems. This paper also stresses on the factors that improve the thermal comfort and air quality for the already existed systems (for maintenance procedure). To design an optimum HVAC airside system that provides comfort and air quality in the air-conditioned spaces with efficient energy consumption is a great challenge. The present paper defines the current status, future requirements, and expectations. Based on this analysis and the vast progress of computers and associated software, the artificial intelligent technique will be a competitor candidate to the experimental and numerical techniques. Finally, the researches that relate between the different designs of the HVAC systems and energy consumption should concern with the optimization of airside design as the expected target to enhance the indoor environment. The present paper reviews the results of recent investigations in the world that are concerned with the HVAC design engineering in the healthcare applications.

On the modelling of turbulent reacting flows in furnaces and combustion chambers

Abstract A general computer programme was developed to calculate the local flow properties in turbulent reactive and non reactive flows with recirculation; these calculations were obtained by solving the appropriate conservation equations in finite difference form with the corresponding boundary conditions. The calculation procedure employs a two equation turbulence model, and embodies various combustion models appropriate to diffusion, premixed and arbitrary fuelled flames. The phenomenon of unmixedness caused by turbulent fluctuations, which lead to a situation where the instantaneous value of fuel and/or oxidant concentrations and, therefore, their corresponding chemical reaction rates vanish, is investigated. The combustion models considered here are characterized by, for instance, instant reaction with clipped Gaussian probability distribution of concentration, which corresponds to random variation of fuel concentration with time, finite reaction rate with an eddy break up formulation, and finite reaction rate with a second order closure which accounts for temperature and concentration fluctuations. The radiative heat flux, which appears in the energy conservation equation, is obtained using a coupled four flux representation and integrating the radiation intensity distribution over a solid angle of 2π. The validity of the computational procedure incorporating the proposed turbulence, combustion and radiation models was assessed by comparisons with the experimental data in reacting and non reacting flows, and indicated satisfactory agreement. The obtained agreement assesses the validity of the physical assumptions of the models and supports the use of such procedure for furnace design purposes.

Numerical analysis and optimization of different ventilation systems for commercial aircraft cabins

The ventilation systems in commercial aircraft cabins are important for providing a healthy and comfortable environment for the passengers and crew. The high density and close proximity of passengers in the modern aircraft cabin exposes them to the risk of contracting airborne diseases such as flu, severe acute respiratory syndrome (SARS), and tuberculosis. Current aircraft personalized ventilation (PV) systems still cannot ensure a constant circulation of fresh humidified air around each passengers breathing zone to shield them from airborne contaminants. It is proposed to investigate the use of PV systems in aircraft cabins using computational fluid dynamics (CFD) techniques. This would lead to better understanding and an improved microclimate around the breathing zone of each passenger. A comprehensive analysis framework based on the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) thermal comfort assessment models has been developed. The components of the framework consists of the age of air, predicted mean vote (PMV), predicted percentile dissatisfied (PPD), draught risk (PD), a contaminant aerosol transport model and a humidity model. The objective of this paper is to compare and analyze the simulated cabin environment with mixing, under-floor displacement, and personalized ventilation systems to improve air quality in the aircraft cabin of the economy section of a Boeing 767 airplane during cruise and to reach the optimum design to protect passengers fromair pollution inside the cabin. CFD modelling techniques using the ANSYS FLUENT 15.0 package solved the continuity, momentum, energy, and species transport equations in addition to k-e model equations for turbulence closure. The SIMPLEC algorithm was used for the pressure-velocity coupling and a second order upwind scheme was used for discretization of the governing equations. Mesh sizes used in the present work exceeded 6,000,000 mesh volumes in one case.

Potable water technology transfer and assessment in Egypt

Abstract Egypt as well as many other countries, faces the problem of accute potable water supply shortage in many areas that are remote from fresh water supplies. The lack of water that struck some twenty African countries for four consecutive years and resulted in death of several thousands of people and loss of animals and properties will always remind us of the vital importance of potable and soft waters. The overpopulation and its uneven distribution contributed greatly to intensify the problem. The present work is devoted to analyse the present water demand in Egypt and the prevailing constraints. The feasibility of local manufacture of small desalination units, typically 50 and 500 cubic metre per day is demonstrated with the economic evaluation of these plants for small and medium sized communities.