Responses of plastic shading nets to global and diffuse PAR transfer: Optical properties and evaluation

AbstractTo cover agricultural structures for protecting plants from high solar radiation in hot and sunny regions different types of shading nets are used. In summer, the amount of photosynthetically active radiation (PAR) transmitted through these nets usually fulfils plant growth requirements. However, their applicability in winter is still unknown. So far, the choice of nets has mostly been empirical, because technical data such as the radiometric properties that are used to characterize the different types of nets are not available. This paper presents a simple method for measuring the radiometric properties related to global and diffuse PAR of seven types of shading nets including nets with colours and shading rates that are commonly used in hot regions. A shading system was developed to simulate the diffuse PAR under cloudy conditions. The results show that under clear sunny and cloudy conditions the radiometric properties depended on both net porosity and colour. Net reflectance strongly depended on net colour. Net transmittance and absorptance depended primarily on colour and secondarily on porosity. The radiometric properties of nets under global and diffuse PAR conditions tended to be similar to those of translucent materials so that a plastic net can be considered as translucent material when investigating the equivalent optical parameters (refractive index and absorption coefficient). This can help to predict the radiometric properties of the net without the need of measurements. Under the sunny conditions of winter seasons, the structures covered with the tested nets are suitable for growing crops that can grow at PAR less than 150Wm−2. However, under cloudy conditions very few plants will grow that can grow at PAR less than 30Wm−2

Numerical and experimental studies on a Building integrated Semi-transparent Photovoltaic Thermal (BiSPVT) system: Model validation with a prototype test setup

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Modified plastic net-houses as alternative agricultural structures for saving energy and water in hot and sunny regions.

The transmitted radiation into the conventional net-houses is very low in the early morning and late afternoon that may not fulfill the crop growth requirements. To solve this problem, two types of nethouse models (polygon and curved-arch net-houses) were newly designed, each having seven surfaces made up of different net types. The spectral radiative properties of 32 nets were examined and three nets were selected to cover the surfaces of each model. The two designs showed high transmittance in the morning and afternoon, and low at around noon (U shape). The polygon style was scaledup and an experiential net-house was constructed with a floor area of 28 m2. An evaporatively-cooled greenhouse with a floor area of 28 m2 was used for comparison; each floor was planted with 500 potted Chrysanthemum plant. The results showed that the PAR and microclimate in the net-house and cooled greenhouse were similar. The net-house reduced water consumption by 13 kg m-2 day-1 in summer and by 0.94 kg m-2 day-1 in winter; and reduced electric energy consumption by 0.26 kwh m-2 day-1 in summer and by 0.18 kw-h m-2 day-1 in winter compared to the greenhouse

Neural network based correlations for estimating temperature elevation for seawater in MSF desalination process

NoModelling played an important role in simulation, optimisation, and control of multi-stage flash (MSF) desalination processes. Top brine temperature (TBT) is one of the many important parameters that affect optimal design and operation of MSF processes. Within the MSF process model, calculation of TBT is therefore important. For a given pressure, TBT is a function of boiling point temperature (BPT) at zero salinity and temperature elevation (TE) due to salinity. In this work, we develop several neural network (NN) based correlations for predicting TE. It is found that the NN based correlations can predict the experimental TE very closely. Also predictions by the NN based correlations were good when TE values, obtained using existing correlations from the literature are compared. Due to advancement of the microcomputer, plant automation becomes reliable means of plant maintenance. NN based correlations (models) can be updated in terms of new sets of weights and biases for the same architecture or for a new architecture reliably with new plant data

Optimisation of design and operation of MSF desalination process using MINLP technique in gPROMS

NoOptimal design and operation of MSF desalination process is considered here using MINLP technique within gPROMS model builder 2.3.4. gPROMS provides an easy and flexible platform to build a process flowsheet graphically and the corresponding master model connecting automatically individual unit model equations during simulation and optimisation. For different freshwater demand throughout the year and with seasonal variation of seawater temperature, the total annualised cost of desalination is minimised. It is found that seasonal variation in seawater temperature results in significant variation in design and some of the operating parameters but with minimum variation in of process temperatures. The results also reveal the possibility of designing stand-alone flash stages which would offer flexible scheduling in terms of the connection of various units (to build up the process) and efficient maintenance of the units throughout the year as the weather condition changes. In addition, operation at low temperatures throughout the year will reduce design and operating costs in terms of low temperature materials of construction and reduced amount of anti-scaling and anti-corrosion agents

Nano-ZnO film photocatalysts in bench-scale continuous-flow mineralization of olive mill waste contaminants in water

Olive oil milling, widely practiced in Mediterranean countries, including Palestine, yields the so-called olive mill waste water (OMWW) or Zebar (Zibar). The waste contains minerals and organic materials (including phenols and polyphenols) which undergo continuous oxidation and cause environmental hazards if not well managed. This work basically aims at purifying surface waters, intentionally pre-contaminated with OMWW organic contaminants. Fate of other mineral ions present in the contaminated water is also investigated. ZnO nanoparticles, deposited as films onto glass reactor bottom (165 cm2 area), are described as catalyst for photodegradation of the organic contaminants, in a continuous flow reaction mode (gravity fed, typically at flow rate 3.5 mL/min). Two types of ZnO materials, namely commercial ZnO onto glass (C–ZnO/Glass) and synthetic ZnO supported onto clay and deposited on glass (Syn–ZnO/Clay/Glass), have been examined. The Syn–ZnO/Clay/Glass catalyst is slightly more efficient in removing organic contaminants (~ 43%), compared to the C–ZnO/Glass (41%) in 30 h. Different reaction parameters have been investigated, such as waste dilution factor, exposure duration, pH and catalyst recovery and reuse

Lights Out, Let's Move About: Locomotory Activity Patterns of Wagner's Gerbil from the Desert of Saudi Arabia

We investigated the circadian activity rhythm in the little-studied Wagner's gerbil (Gerbillus dasyurus) from the Raydah Protected Area, southwestern Saudi Arabia. In order to assess whether these animals possess an endogenous rhythm of locomotor activity that entrains to the light:dark cycle, they were subjected to three distinct light cycles: an LD cycle (12 h light/12 h dark), a DD cycle (constant darkness) and a DL light cycle (an inverse of the LD light cycle). All eight individuals studied exhibited entrainment of their activity to the light cycles. Under LD, the total percentage of activity during the dark phase was 93.7 ± 1.8%. Activity was distributed throughout the night (mean peak activity 22:46 ± 0:14). All eight animals expressed distinct endogenous free-running rhythms of locomotor activity (mean í = 23:55 ± 0:36). During constant darkness, animals still displayed more activity during the subjective night (75.6 ± 0.4%). Under the DL light cycle, the total percentage of activity was 92.7 ± 1.8% during the dark phase. In conclusion, the daily locomotor activity rhythm of Wagner's gerbil is strongly entrained by the light:dark cycle with the most activity concentrated during the night and consequently this desert-dwelling mammal may thus be considered truly nocturnal.We extend our appreciation to the Deanship of Scientific Research at the King Saud University for funding the work through the research group project No. RGP_VPP_020. We thank HH Prince Bandar Bin Mohammed Bin Saud, Secretary General, Saudi Wildlife Authority, for permission to trap the animals in the Raydah Protected Area in southwestern Saudi Arabia. NCB gratefully acknowledges support from the Visiting Professors Programme of King Saud University to undertake research in Saudi Arabia.http://africanzoology.journals.ac.za/am2013ab201