A. Jamil

Asymptotic Behavior of a Storage Unit Undergoing Cyclic Melting and Solidification Processes

In this paper, the asymptotic behavior of a thermal latent-energy storage system undergoing periodic charge/ discharge cycles is numerically investigated. The system consists of a cylindrical tank, which is randomly packed with spheres having uniform sizes and encapsulating paraffin as phase change material. The working fluid flowing through the bed is pure air. In the main part of this study, the entrance air temperature is supposed to vary in a sinusoidal way with a one-day period. The related governing equations are solved by a control-volume-based finite difference method. First- and second-law-based efficiency indicators are used to characterize the performances of the system. The effects of the phase change material melting point temperature on the energy efficiency and the irreversibility of the system are investigated. It is shown that in all situations, an asymptotic regime of charge/ discharge cycles is reached. For a zero-cycle-average Stefan number, the bed proves to behave like a quasi-perfect reject band filter (i.e., it yields a quasi-constant outlet temperature signal). In such a case, the energy efficiency reaches its maximum value, which also corresponds to a maximum of irreversibility. Thus, this indicates that because of such opposite trends, the design of practical systems should be based on a sound compromise, on a case-by-case basis, and between energy and exergy efficiencies on one side and utilization requirements on the other side. Finally, the predictive capability of such a model is assessed in the situation in which a realistic inlet temperature of the working fluid is considered. The predicted time evolution of the outlet temperature of the working fluid proves to be in good agreement with that reported in the selected reference

5.1 Energy Auditing

This chapter presents the fundamentals of energy auditing as one of the most important approaches for reducing energy losses and minimizing the damaging effects of climate change and global warming. It classifies energy audits according to their type and level and describes their general methodology and tools. A case study of an energy audit carried out in the cement industry is presented as an illustrative example.

Modeling and CFD study of heat transfer within the circulation pipes of solar water heating systems

The main objective of this work is to study numerically the thermal behavior of solar collectors. In particularly, we performed a detailed design and parametric study of the circulation pipe of an evacuated tube collector. Indeed, we altered the geometry of the anodes by adopting three configurations: circular, rectangular and triangular. In each configuration, we changed the inlet position of cold water and the outlet of hot water: either at the top, middle or bottom. The obtained results show that rectangular shape is most optimal due to the large exchange area. On the other hand, the water inlet must be positioned at the bottom and the outlet at the top in order to take profit of the stratification of the hot water and subsequently obtain high efficiency.

Parametric study on the influence of geometrical characteristics of horizontal wavy surface on nusselt number: Solar applications

In this paper a steady-state natural convection was numerically simulated in horizontal rectangular cavity with a sinusoidal bottom wavy wall. This new type of surface rarely studied and investigated. The vertical walls are insulated while the bottom surface maintained to higher temperature than the top surface. In this numerical simulation that based on our elaborated code. the investigated parameters are Rayleigh number that is fixed to Ra=106, the wave length λ varied from 1 to 6 and the amplitude of the wave A is changing from 0.10 to 0.20 with a step of 0.05 were chosen in order to analyze the effect of these parameters on the heat transfer and the flow fields in two dimensional (2-D) enclosure filled with air. It is found that the geometrical parameters has a significant influence on the heat transfer inside the cavity, and also the importance of this study occur in the different applications where this kind of phenomena is present such as cooling, drying systems and solar captors.

CSP plants optimization in Morocco: Best practices and real challenges

Against the background of an increasing energy demand and growing environmental problems in Morocco due to the strong foreign dependence (Import over 95% of the countrys energy needs), renewable energy resources offer interesting opportunities for Morocco. This paper suggests the simulation and perform the analysis of CSP using a Parabolic Trough Collector PTC as a technology. Therefore, the code developed not only used for the optimization of CSP plants implemented in Morocco but also for performance prediction under variable weather conditions of Moroccan zones. On this way, a detailed model on the Ouarzazate CSP project is given taking into account actual data and all technical constraints. Then, a comparison between potentials sites is performed. The analysis shows the competitive viability of CSP plants in Morocco.

Simulation of a thermoelectric heating system for small-size office buildings in cold climates

This paper suggests the analysis and the simulation of a thermoelectric heat pump for heating a small-size office building in Ifrane (Morocco). Meteorological data of the site are imported from the METEONORM Database and used by the TRNSYS buildings simulator in order to estimate the heating loads of the office building. The thermoelectric heat pump coupled to the building was mathematically modeled and the set of equations were solved in MATLAB to evaluate the systems performance. The number of modules maximizing the coefficient of performance and the optimal electric current were determined for extreme operating conditions.

Analysis of the electrical energy consumption and energy audit of interior lighting for an industrial site in Morocco

This paper is an energy audit performed for an industrial site based in FEZ (Morocco), specialized in producing and commercializing cattle feed It evaluates the economic gains related to an optimized management of the electrical energy use and focuses on the improvement of energy efficiency for the interior lighting.

Effect of inclined wavy surface on heat transfer inside a rectangular cavity: Solar applications

In this present work a steady-state natural convection was numerically simulated in an inclined rectangular cavity with a sinusoidal bottom wavy wall. The vertical walls are insulated while the bottom surface maintained to higher temperature than the top surface. In this numerical simulation, Rayleigh number (103, 106 and 6×106) and inclination angle (30°, 60° and 90°) were chosen in order to analyze the effect of these parameters on the heat transfer and the flow fields in two dimensional(2-D) enclosure filled in air (Pr=0.71). It is found that the same Rayleigh number, the heat transfer is influenced by the inclination angle. In other words the increase of inclination angle leads to an increase in the heat transfer inside the rectangular cavity.

Heat transfer inside cavities heated by discrete sources: Solar systems

In this paper, we studied numerically laminar natural convection in two types of configurations: the first a square enclosure with four types of discrete sources (Plane, Circular, Square and Triangular) with partial heating of the bottom wall while the rest is maintained constantly adiabatic. The second configuration a rectangular enclosure in which we increased the number of discrete sources for each geometric shape. This study simulates the case of heat generation in a storage tank of hot water or in an electronic component mounting enclosure. The light source is considered to be located in the lower wall with a heated fixed width. This heating will be introduced either as an isothermal or uniform flow. For the purposes of this analysis, the length of the source is set at 20% of the total length of the lower wall. The upper wall, the unheated portion of the bottom wall, the right and left walls will be considered adiabatic. For all configurations the Rayleigh number was fixed at 106. The streamlines and isotherms are presented for various combinations of forms of the heated zone. The results will also be presented in a number of local Nusselt on heated wall.

Solar absorption air-conditioning systems: An energy and economy approach

This paper suggests the analysis and the simulation of a complete solar absorption cooling installation. The building reference is a three floors office located in Fez (Morocco). Energy and economy analysis were investigated based on different performance indicators. It was put in evidence that the adoption of solar air conditioning systems depends strongly on the thermal energy market status.