The thermal behavior of the inside air of a closed Venlo glasshouse without plants was analysed under semi-arid climate conditions. The aim of the study was to investigate to what extent the characteristics of the greenhouse design and outside climatic conditions influence airflow and temperature patterns inside the greenhouse. For the purpose of the present work, a CFD modeling approach was combined with field surveys. The study focuses on the effects of (i) the thermal inertia of the soil, (ii) the movement of the interior air, and (iii) the distribution of the temperature inside the greenhouse. Two contrasted days were considered: a windy overcast day and clear day. From the results, it is concluded that when the greenhouse is fully closed with bare soil, the heat absorbed and stored by the ground during daytime represents a significant heat source which enhances buoyancy forces, the main driving forces of the movement of the air, especially during the night. The temperature of the roof was relatively low and the air temperature distribution inside the greenhouse disclosed a vertical gradient from the roof towards the ground surface due to the movement of the air above the surface of the ground absorbing thermal energy (solar energy). Maximum air velocities inside the greenhouse were observed near the ground surface, while they reached their minimum values in the middle of the greenhouse. Similar results were obtained for the windy overcast day and for the clear day.

Semi-arid regions are frequently subject to major temperature changes during a 24 h period, which may drastically affect greenhouse indoor climates. In order to improve energy management of these buildings, numerical tools have been developed to predict the evolution of the inside climatic conditions. However, most of the available models neither take account of the transmittivity variation through the day nor of differences between wall temperatures. In the present paper, a model for predicting the thermal and water behaviour inside an unheated agricultural green-house is presented. The energy balance method is applied to each element: cover, indoor air and soil surface. Specific modules have been developed to calculate heat transfer coefficients for the cover of the greenhouse as well as heat transfer through the subsoil. These modules have been integrated in the TRNSYS environment. Radiative transfers and view factors were also calculated. The simulations predict two main parameters under transient conditions: the indoor air temperature and the indoor humidity in response to the outside conditions. These parameters were validated with fair agreement from experiments conducted in a monospan greenhouse located in Batna (6.11° E, 35.33° N). Based upon the results of the simulations and the measurements it was also concluded that firstly, the transmittivity was not constant in time and varied with surface orientation; and secondly, vertical surface temperatures were different during the daytime while the temperature difference between roof surfaces remained insignificant. The evolution of humidity was not correctly reproduced by the model, probably because the effects of condensation and variation of soil water content were not properly included in the equations.

Crop cultivation in greenhouses under semi-arid climatic conditions is subject to various stresses, in particular during the winter season at night, when the interior air is poorly controlled, leading to prolonged periods of low temperature. The aim is then to evaluate and control the heat exchanges of the enclosure in order to prevent low indoor air temperatures and reduce the thermal load of the greenhouse. The objectives of this study are to investigate the convective and radiative heat exchanges at the cover in order to establish new correlations for the convective heat transfer coefficients in semi arid regions. The climatic parameters were measured inside and outside a closed empty glasshouse without crop, for three different nights during the winter season in the semi-arid land of Algeria. A physical model for analysing the convective heat transfers was implemented, and new correlations were established, parameterised, calibrated and validated thoroughly. A significant difference was observed between the correlations obtained by this study and the models obtained for other greenhouse designs under different climatic conditions. Results show that the convection mode along the inside wall of the cover is free turbulent. Conversely, the convection mode along the outside greenhouse cover remains forced turbulent. A consistent performance of the correlations was observed, both in the calibration and validation stages.

Heat transfer by convection occurs in various domains such as atmospheric flows, exchangers, passive air conditioning, etc.…For example, in passiveair conditioning, theheat transfer rateat alateral wallof an enclosure can be enhanced if the surface is not flat. Indeed, it is well known that a rough surface allows increasing the heat transfer. Such rough surface can be obtained with the use of protuberances on walls. The purpose of this study is to investigate, numerically in 2D, the effect of rough surfaces at the vertical walls on heat and mass transfers in an enclosure. As boundary conditions, the vertical walls of this enclosure are subject to a uniform heat flux and horizontal walls are supposed to be adiabatic. The numerical modeling, used by us, is briefly described below. The rough surfaces are described as sinusoidal profiles which are transformed, using a homotopic transformation, into a flat plate. Governing equations are discredited using the finite volume method and the resolution is obtained by the THOMAS algorithm. The coupling of the velocity and pressure fields is achieved using the SIMPLE algorithm. The effect ofthe formofprotuberances, and the imposed heat flux at a vertical wall, on streamlines and temperature fields has been considered. The first obtained results are in agreement with previous experimental and numerical results, showing thus that our modeling is accurate. The first results are a validation of code are in agreement with previous experimental, numerical, and software Fluent showingthat our model is accurate

The aim of this work is to analyze the thermal performance of a greenhouse exposed to semi-arid conditions by investigating experimentally the heat transfers occurring through the walls and ground. A closed unheated Venlo greenhouse without crop in the area of Batna (southern Mediterranean basin) was considered. The study focuses on the effects of (i) the thermal inertia of the soil, (ii) the radiative losses through the cover, and (iii) the convection mode and flow regime on the heat transfer coefficients. Experiments were conducted from January to March 2008 under clear or cloudy skies, and low or high wind velocities. From the results, it is concluded that the heat stored in the ground of the greenhouse represents a significant heat source which can compensate the energy losses through the walls, especially during a night preceded by a high diurnal insulation. This process can maintain an average inside - outside temperature difference during the night within the range [1.59-2.81] K. Results also show that the radiation losses are the main component of the energy losses of the greenhouse, mainly through the outside wall surface of the cover. Conversely, the radiative heat exchange along the inner wall represents the main heat supply to this wall. The convection mode inside the greenhouse induced by the air movement seems to play a significant role on the convective exchange coefficient inside the greenhouse. These coefficients both inside and outside the greenhouse were estimated and analyzed, and a good agreement with the models reported in the literature was found. This study could help growers define and adapt their heating strategy to avoid undesired low temperatures which may damage their crops at night.

The sensitivity of many biological and chemical sensors is critically dependent on the stability of the potential of the reference electrode being used. The stability of a reference electrode's potential is highly influenced by the properties of its surface. In this paper, for the first time, the formation of nanosheets of silver chloride on silver wire is observed and controlled using high anodic constant potential (>0.5 V) and pulsed electrodeposition. The resulting nanostructured morphology substantially improves the electrode's potential stability in comparison with the conventional globular surface structure. The increased stability is attributed to the increase in the surface area of the silver chloride produced by the nanosheet formation.

    Up to now, few studies were devoted to the description of the energy balance components of a greenhouse located in the semi arid region of the southern Mediterranean basin, and no attention was paid to the prediction of the inside air temperature. In this study, experiments were undertaken to investigate the response of a greenhouse to the outside climate conditions considering a naturally ventilated Venlo glasshouse with a tomato crop. The measurements show that the difference between inside and outside air temperature is strongly linked to the incoming solar radiation as well as to the wind speed. From these results a simplified model was established to predict the greenhouse air temperature, knowing the greenhouse characteristics and the outside climate variables. The model is based on the energy balance of the greenhouse. Using a parameter identification technique, the model was calibrated against the experimental results. A sensivity analysis was conducted to assess the impact of several physical parameters such as solar radiation, wind speed and cover transmission on the evolution of the inside air temperature. This model appears to be suitable for predicting the greenhouse air temperature satisfactorily, at least during night

    In regions with warm and hot climates as is the case of several countries of the Mediterranean basin, it is interesting to study the energy balance inside a greenhouse and to quantify the heat transfers along the building components (roof, walls and ground) in winter and during night time. The present experimental work was conducted in an unheated glasshouse without crop in the region of Batna, Algeria. Three types of measurements were done from January to March: the first one is at a cloudy night; the second one at a windy night and the third one at a cloudless night. The results indicate that the greenhouse ground is considered as a significant heat source which can compensate the energy losses through the walls especially during a night preceded by a significant diurnal insulation. In addition, the convection heat transfer coefficients inside and outside the greenhouse were estimated and analysed. A good agreement with the models reported in the literature was found.