Brahim Benhamou

Buoyancy effects on upward and downward laminar mixed convection heat and mass transfer in a vertical channel

Purpose – The objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a vertical parallel‐plates channel. The plates are wetted by a thin liquid water film and maintained at a constant temperature lower than that of the air entering the channel.Design/methodology/approach – The solution of the elliptical PDE modeling the flow field is based on the finite volume method.Findings – Results show that buoyancy forces have an important effect on heat and mass transfers. Cases with evaporation and condensation have been investigated for both UF and DF. It has been established that the heat transfer associated with these phase changes (i.e. latent heat transfer) may be more or less important compared with sensible heat transfer. The importance of these transfers depends on the temperature and humidity conditions. On the other hand, flow reversal has been predicted for an UF with a relatively high temperature ...

ANALYSIS FOR THERMAL BEHAVIOR AND ENERGY SAVINGS OF A SEMI-DETACHED HOUSE WITH DIFFERENT INSULATION STRATEGIES IN A HOT SEMI-ARID CLIMATE

ABSTRACT The purpose of this research is to assess thermal performance and energy saving of a residential building in the hot semi-arid climate of Marrakech (Morocco). The studied house is built as usual in Marrakech without any thermal insulation except for its external walls, facing East and West, which are double walls with a 5 cm air gap in between (“cavity wall” technique). The cavity wall effective thermal conductivity was carefully calculated taking into account both radiation and convection heat transfers. Experimental results, obtained from winter and summer monitoring of the house, show well dampening of air temperature, thanks to its thermal inertia. However, this temperature remained outside the standard thermal comfort zone leading to large cooling/heating load. Simulation results indicate that the cavity wall contributes to an overall reduction of 13% and 5% of the house heating and cooling loads respectively. Moreover, the addition of XPS roof thermal insulation significantly enhances the h...

Effect of thermal insulation and ground coupling on thermal load of a modern house in Marrakech

The objective of this work is to improve the energy performance of a residential building in Marrakech. A study of the effect of thermal insulation of the envelope and the thermal inertia of the ground and furniture on heating/cooling loads was done. The building is a two floors house, built on-ground with an east-west orientation. North and south walls are affixed to the neighboring houses of the same type. The energy performance of the building are determined through a numerical study; which is achieved by dynamic multizone modeling of several configurations of the house using the TRNSYS software. The simulations were performed over a year through TMY weather file. To validate the simulation results, a monitoring for each area of the house was realized. The simulation results show that the roof insulation can reduce the heating/cooling loads by 11% and 53% respectively. In addition, the external walls insulation by an air gap allows us to reduce the heating and cooling loads by 27.4% and 16.7% respectively. Moreover, coupling the building with the ground reduces the average temperature of the ground floor by about 4 °C in summer, and increases it by approximately 1°C in winter. On the other hand, the thermal inertia of furniture has a negligible effect on the heating and cooling loads. It reduces the cooling load by almost 1.2%, while it reduces the thermal load during the winter season by 1.1%.

Energy efficiency in buildings: Thermophysical characterization of building materials

In Morocco, the construction sector is the largest consumer of energy. Reducing the energy consumption in buildings represents a major economic and ecological issue. The building sector has the highest potential for improving energy efficiency which concerns, among other the choice of appropriate materials and improvement of their thermal characteristics. The present work deals with measurement methods and characterization of thermophysical proprieties of building materials. Primary results of measurement of thermal proprieties of extruded polystyrene, expanded polystyrene, soil, gypsum and marble are presented. The measurements were carried out using two devices available at the National Centre for Studies and Researches on Water and Energy (CNEREE) at Marrakech. The two devices EI700 and FP2C use respectively the boxes method and the method of the hot plan and hot wire.

RafriBAT: A project to introduce energy efficiency in buildings in Marrakech area by means of passive and low exergy air-conditioning systems

RafriBAT is a project funded by the Hassan II Academy of Sciences and Technology for the period 2012-2015. It aims to study the use of passive and hybrid systems in buildings for natural air refreshment and heating. The project also focuses on the building envelope in order to point out the synergy between an adapted envelope and the use of the passive/hybrid systems for cooling/heating. Specifically, some existing buildings with passive and hybrid systems for cooling/heating will be monitored and modeled. In the second part of the project, the passive and hybrid systems for cooling/heating will be tested individually in Outdoor Test-Cells. The dynamic response of these systems will be also calculated by means of TRNSYS software. The comparison of the monitoring results and the dynamic modeling will produce an efficient and well-validated simulation tool. This tool may be used for the design of energetically efficient buildings in an arid climate such as that of Marrakech. The final target, of this project is to accompany the elaboration of the building energy efficiency code in the frame of the national energy efficiency strategy.

Mixed Convection Heat and Mass Transfer with Phase Change and Flow Reversal in Channels

Due to its widespread applications, heat and mass transfer in an air stream with liquid film evaporation or condensation in open channels has received considerable attention in the literature. This kind of flows is present in many natural and engineering processes, such as human transpiration, desalination, film cooling, liquid film evaporator, cooling of microelectronic equipments and air conditioning. Since the original theory for flow of a mixture of vapour and a non-condensable gas by Nusselt (1916) and its extension by Minkowycz & Sparrow (1966), many theoretical and experimental studies have been published in the literature. These studies deal with different geometric configurations such as a flat plate, parallel-plate channel and rectangular or circular-section ducts. Heat and mass transfer convection over a flat plate wetted by a liquid film has been investigated by Vachon (1979). He performed an analytical and experimental study of the evaporation of a liquid film streaming along a porous flat plate into a naturally driven airflow. This author established correlations for Nusselt and Sherwood numbers in connection with a combined Grashof number. Ben Nasrallah & Arnaud (1985) investigated theoretically film evaporation in buoyancy driven airflow over a vertical plate heated with a variable heat flux. The solutions of the governing equation have been obtained by means of semi-analytical and finite difference methods. The authors present their results in term of expressions of the wall temperature and mass fraction as well as the local Nusselt and Sherwood numbers. A numerical and experimental analysis has been carried out by Tsay et al. (1990) to explore the detailed heat transfer characteristics for a falling liquid film along a vertical insulated flat plate. Free stream air temperature was set at 30°C and inlet liquid film temperature was taken equal to 30°C or 35°C. The results show that latent heat transfer connected with vaporization is the main cause for cooling of the liquid film. The authors affirm that when the inlet liquid temperature is equal to the ambient one, latent heat transfer due to the film vaporization initiates heat transfer in the film and gas flow. Aguanoun et al (1994; 1998) studied numerically the evaporation of a falling film on an inclined plate heated

Thermal comfort analysis of a house retrofitted according to the Moroccan building energy code

The research presented in this paper aims to identify the impact of the Moroccan Thermal Regulation for Construction (RTCM) on thermal performance of a typical house located in the climate zone 5 (Marrakech). To broaden this study, we did the same inspection as if the house is located in the climate zone 1 (Casablanca). The study is based mainly on two aspects: experimental validation of the computer code and numerical analysis. The experimental study consists of two measurement campaigns during winter and summer. The numerical study is conducted through the house model implemented in the TRNSYS software environment which was calibrated by comparison to the experimental measurements. The results show that thermal insulation material thicknesses of 20 mm to 40 mm of EPS for the walls, 40 mm of XPS for the roof and 20 mm of XPS for the slab-on-grade floor satisfy the requirements of the RTCM for both studied climates zones. Furthermore, the application of the RTCM leads to a reduction of the annual thermal load of the studied building by 35% in Marrakech, while this reduction does not exceed 17% in Casablanca. On the other hand, the soil thermal inertia has a beneficial effect on the house in Marrakech (climate zone 5). Indeed, if the slab-on-grade floor of the house is thermally insulated, as required by the RTCM, its annual thermal load increases at least by 7%. In contrast, the insulation of the slab-on-grade floor of the house located in Casablanca (climate zone 1), which is not statutory, is recommended, as it reduces the house annual heating load by at least 17%.

Thermophysical investigation of a TiO2 embedded phase change material

TiO2 nanoparticles were dispersed into a stearic acid to enhance the low thermal conductivity of this phase change material. The transient hot wire measurement technique showed an improvement of thermal conductivity by 43% in liquid state and 21% in solid state only by adding 0.3% of TiO2 mass concentration. Prediction models of nanofluids thermal conductivity are found to be - unevenly - under predicting the obtained results. The rheological behavior of the prepared nanofluid is studied in a temperature range of 65°C-85°C. It is a shear thining nanofluid which becomes more viscous by adding nanoparticles or reducing temperature. The theoretical models gave good viscosity estimate. The Differential Scanning Calorimetry (DSC) shows an insignificant instability of the latent heat capacity in the case of 0.3% nanofluid mass concentration.

Dynamic modeling of thermal behavior of a solar floor heating system for a HAMMAM in Marrakech

This paper deals with the energy performances and thermal behavior of a solar system for space heating of a Turkish bathroom (Hammam) through a heated floor, in Marrakech. Two configurations with or without thermal storage were compared. Moreover, an optimization study has been made for the collector area, the inclination of the solar collectors, storage tank, pipes material and pumps flow rates. Dynamic simulation of the Hammam coupled with the floor heating system was conducted using TRNSYS software. The Hammam was monitored via air temperature and humidity measurements during four days of the 2015 winter season. Simulations and monitoring results are compared using in-situ measured weather data, while the parametric study was performed along a typical meteorological data (TMY). Comparison between simulation and experimental results showed good accordance with a maximum deviation of 1.5 °C and a maximum relative difference less than 4%. Simulation results show that the system without thermal storage allows the Hammam operative temperature to reach the desired one, since it ranges between 36 °C and 39 °C for a sunny day in winter; while the system with thermal storage leads to at least 10 °C operative temperature lower compared to system without thermal storage. In addition, the former allows having quasi-constant floor temperature that depends on the storage volume, so it avoids day/night temperature large fluctuations thanks to thermal storage inertia. Nevertheless, the configuration of the floor heating system with a storage tank does not achieve the desired temperature for the floor of the Hammam. Furthermore, results of simulations show that the use of serpentine of PEX tubes, 4 m2 water solar collectors with 80 kg.h-1 flow rate works properly for the configuration without thermal storage, since the Hammam air temperature has to be maintained at around 37 °C.

Effects of three passive techniques on thermal performance of a building in Marrakech region

This study deals with dynamic simulation of a villa type house located in Marrakech region (Morocco) which was designed as a green house with several passive systems, techniques and local materials. Three of these techniques were examined: hemp insulation, hollow core slab and high inertia. Simulations were carried out during one year using TRNSYS software with the multi-zone model. The effects of integrating these passive systems and materials on air temperature in the building were analyzed for two configurations: real house and standard one. The latter refers to materials commonly used in Marrakech region. The results indicate that combining all of these passive techniques lowered the cooling load by 76% and the heating load by 62%.