The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

Greenhouse cultivation has evolved from simple covered rows of open-fields crops to highly sophisticated controlled environment agriculture (CEA) facilities that projected the image of plant factories for urban agriculture The advances and improvements in CEA have promoted the scientific solutions for the efficient production of plants in populated cities and multi-story buildings Successful deployment of CEA for urban agriculture requires many components and subsystems, as well as the understanding of the external influencing factors that should be systematically considered and integrated This review is an attempt to highlight some of the most recent advances in greenhouse technology and CEA in order to raise the awareness for technology transfer and adaptation, which is necessary for a successful transition to urban agriculture This study reviewed several aspects of a high-tech CEA system including improvements in the frame and covering materials, environment perception and data sharing, and advanced microclimate control and energy optimization models This research highlighted urban agriculture and its derivatives, including vertical farming, rooftop greenhouses and plant factories which are the extensions of CEA and have emerged as a response to the growing population, environmental degradation, and urbanization that are threatening food security Finally, several opportunities and challenges have been identified in implementing the integrated CEA and vertical farming for urban agriculture
Keywords: smart agriculture, greenhouse modelling, urban agriculture, vertical farming, automation, internet of things (IoT), wireless sensor network, plant factories
DOI: 1025165/jijabe201811013210

Citation: Shamshiri R R, Kalantari F, Ting K C, Thorp K R, Hameed I A, Weltzien C, et al Advances in greenhouse automation and controlled environment agriculture: A transition to plant factories and urban agriculture Int J Agric & Biol Eng, 2018; 11(1): 1–22

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Advances in greenhouse automation and controlled environment agriculture: A transition to plant factories and urban agriculture

High-resolution laser-Doppler anemometer measurements were acquired in a two-dimensional turbulent boundary layer over a ramp. The goals were to provide a detailed data set for an adverse pressure gradient boundary layer far from separation and to examine near-wall behaviour of the Reynolds stresses as compared to flat-plate boundary layers. The flow develops over a flat plate, reaching a momentum thickness Reynolds number of 3350 at an upstream reference location. The boundary layer is then subjected to a varying pressure gradient along the length of the ramp and partially redevelops on a downstream flat plate. Mean velocity measurements show a log law region in all velocity profiles, but the outer layer does not collapse in deficit coordinates indicating that the boundary layer is not in equilibrium. Measurements of non-dimensional stress ratios and quadrant analysis of the two-component data indicate relatively small changes to the turbulence structure. However, the streamwise normal stress has an extended outer layer plateau, and the shear stress and wall-normal stress have outer layer peaks. Near the wall, the streamwise normal stress and shear stress collapse with flat-plate data using standard scaling, but the wall normal stress is substantially larger than flat-plate cases.

Turbulence development in a non-equilibrium turbulent boundary layer with mild adverse pressure gradient

Thermoeconomic and environmental feasibility of waste heat recovery of a data center using air source heat pump

Fully developed, statistically steady turbulent flow in straight and curved pipes at moderate Reynolds numbers is studied in detail using direct numerical simulations (DNS) based on a spectral elem ...

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Evolution of turbulence characteristics from straight to curved pipes

This paper investigates the effects of co-flow jet on the aerodynamic performance of some symmetric blade sections of wind turbines. The Reynolds number of 1.3 × 105, angles of attack between 0° an...

Effects of CFJ flow control on aerodynamic performance of symmetric NACA airfoils

Experimental study of the effective parameters on the offshore wind turbine's airfoil in pitching case

In the present study, entropy generation analysis of turbulent boundary layer was carried out to examine the effects of the wall curvature and adverse pressure gradient (APG) on air distribution ducts in HVAC systems considering both individual and simultaneous effects of these parameters and using the empirical data. Six walls, including straight wall (A), convex curved wall (B1), concave curved wall (B2), straight wall with APG (D), convex curved wall with APG (C1), and concave curved wall with APG (C2) were investigated. The air distribution ducts can be divided into various geometries, including straight duct (A*), curved duct (B*), straight diffuser (D*), and curved diffuser (C*). Furthermore, for walls with APG (D, C1, and C2), the divergence angle was chosen in such a way that no flow separation occurred in the range under consideration. The findings showed that the entropy generation resulted from turbulence dissipation was highly important in the regions near the boundary layer edge, so that the ratio of the entropy generation rate due to the turbulence dissipation to the total entropy generation rate in the regions near the boundary layer edge approximates 0.9. In fact, in these regions, a large portion of the total entropy generation rate was related to turbulence dissipation. Consequently, the turbulence dissipation in these regions was too large to be ignored. Thus, in order to achieve a more precise criterion of the dissipation of air distribution ducts in HVAC systems, the turbulence dissipation should be taken into account.

The effects of wall curvature and adverse pressure gradient on air ducts in HVAC systems using turbulent entropy generation analysis

Since the ducts are important parts of the engineering facilities and entropy generation decreases the performance of such facilities, it is necessary to study the amount of entropy generation in these geometries in order to reach to maximum efficiency. In addition, the study of turbulent boundary layer flow in curved diffuser has significant importance. Therefore, the current work investigates the effects of curvature and adverse pressure gradient parameter on efficiency and entropy generation due to turbulent and viscosity dissipations in three curved diffusers with curvature ratios of 0.0113, 0.0161 and 0.023 for different adverse pressure gradient parameters of 0.48, 0.56, 0.62, 0.86 and 0.994. Results show that in order to design the curved diffusers to reach the maximum efficiency and minimum total entropy generation in air-conditioning systems, the lowest value of adverse pressure gradient parameter and the highest value of curvature radius should be considered, respectively. The total entropy generation on concave and convex walls decreases with increasing the adverse pressure gradient parameter, while by increasing the curvature radius, it decreases on convex wall and increases on concave wall. Moreover, the rate of increasing the total entropy on convex wall is more than concave wall at constant adverse pressure gradient parameter. Finally, it was found that with decreasing the adverse pressure gradient parameter and increasing the curvature radius, the efficiency increases.

Entropy generation analysis of turbulent boundary layer flow in different curved diffusers in air-conditioning systems

Renewable energies (especially solar energy) are globally suitable alternatives for fossil fuels. On the other hand, greenhouses, as a main part of agriculture industry, use a significant amount of fossil fuels annually to provide the required heat for the under-cultivation crops in the greenhouse. Currently this heat demand is provided by a heater which burns gas oil as its main fuel. The main problem with these heaters is fuel hyper-consumption. That is why feasibility of utilizing a solar energy storage system in greenhouses is studied here. As the low temperature heat is required for preheating the air in the greenhouse, a solar collector array is proposed to be utilized in order to displace heating demand of the heater and to reduce amount of fuel consumption. To evaluate the proposed system effectiveness, an economic survey has been done on the proposed system based on Net Present Value (NPV) method. The optimum capital cost for the project is found based on economic methods. The economic analysis showed that 85 flat plate collector modules and an 8.5 cubic meters of storage tank are optimum selection of the project. The results showed that, by employing the proposed system, 7 735 USD benefit as well as 11 050 litres of fuel providence is obtainable annually. Economic evaluation based on NPV method resulted in the payback period of ten years. 
Keywords: solar energy, greenhouse, storage tank, stratification, NPV
DOI: 10.3965/j.ijabe.20130604.008 

Citation: Farzaneh-Gord M, Arabkoohsar A, Bayaz M D D, Khoshnevis A B. New method for applying solar energy in greenhouses to reduce fuel consumption. Int J Agric & Biol Eng, 2013; 6(4): 64－75.

Abdolamir Bak Khoshnevis

Papers

Effects of CFJ flow control on aerodynamic performance of symmetric NACA airfoils

Experimental study of the effective parameters on the offshore wind turbine's airfoil in pitching case

The effects of wall curvature and adverse pressure gradient on air ducts in HVAC systems using turbulent entropy generation analysis

Entropy generation analysis of turbulent boundary layer flow in different curved diffusers in air-conditioning systems

New method for applying solar energy in greenhouses to reduce fuel consumption