In the present work, a Ranque-Hilsch vortex tube (RHVT) is modified by suggesting a novel vortex chamber at inlet. The performance of the modified vortex tube is studied experimentally. Suggested lengths for the vortex chamber are 10, 15, and 20 mm and the vortex chamber diameters are 12, 16, and 20 mm. All vortex chambers with different lengths and diameters are tested experimentally at variable inlet conditions. It's found that the vortex chamber diameter has a dominant effect on the performance compared with the vortex chamber length. The results are compared with that obtained by a conventional vortex tube. The results show that the vortex chamber gives an enhancement in the isentropic efficiency reach to 15.9 %. The results for a vortex chamber of 15 mm length and 20 mm diameter has the best performance.

Solar greenhouses can be considered as efficient places for biological CO2 capture and utilization if CO2 enrichment becomes a common practice there. As CO2 enrichment is applied only when greenhouses are closed, ventilated greenhouses - which represent a large percentage of greenhouses all over the world - cannot be considered for this practice, consequently cannot be available for CO2 capture and utilization. The aim this paper is to show-through modeling and simulation-that these ventilated greenhouses can be activated for serving as efficient CO2 capture and utilization places if they are kept closed (to apply CO2 enrichment) and used microclimate control methods alternative to ventilation. The paper introduces a realistic mathematical model in which all the processes and phenomena associated with the biological CO2 capture and utilization by photosynthesis inside greenhouses are considered. The model considers solar radiation attenuation through the atmosphere and absorption by the greenhouse components. It also accounts for the estimation of radiative heat exchange between the various surfaces inside the greenhouse. The realistic photosynthesis sub model selected in the present work is a mechanistic one applicable to the commonly planted C3 species. The model also provides a strategy for CO2 enrichment and microclimate control. In these strategies, the CO2 injection specific rate for enriching the greenhouse air to a specific concentration, and the cooling and dehumidification specific rates required to be keep the microclimate temperature and relative humidity within the favorable limits, are estimated. The model validity and accuracy were ensured through the good agreement of its numerical predictions with the available experimental results in the literature. The effect of different environmental conditions and planting conditions on the CO2 capturing process (the photosynthesis process) is investigated. Finally, a case study was chosen to investigate the effects of the cooling method, cooling temperature, planting conditions, and CO2 concentration level on the cumulative amount of captured CO2 considered to represent the greenhouse capturing performance. The results show that the capturing performance of greenhouse can be enhanced from value as low as 1.0 g CO2/m 2.day for ventilated greenhouses to value as high as 52 g CO2/m 2.day when alternative microclimate control methods and CO2 enrichment are used. In addition, the greenhouse has extended ability to capture as high as 140 g CO2/m2.day within its growing period considering the appropriate plant type. Furthermore, additional benefits besides CO2 capture are reported for the possible increase of the plant productivity and possible lowering of water consumption by plants.

Solar greenhouses can be considered as efficient places for biological CO2 capture and utilization if CO2 enrichment becomes a common practice there. As CO2 enrichment is applied only when greenhouses are closed, ventilated greenhouses - which represent a large percentage of greenhouses all over the world - cannot be considered for this practice, consequently cannot be available for CO2 capture and utilization. The aim this paper is to show-through modeling and simulation-that these ventilated greenhouses can be activated for serving as efficient CO2 capture and utilization places if they are kept closed (to apply CO2 enrichment) and used microclimate control methods alternative to ventilation. The paper introduces a realistic mathematical model in which all the processes and phenomena associated with the biological CO2 capture and utilization by photosynthesis inside greenhouses are considered. The model considers solar radiation attenuation through the atmosphere and absorption by the greenhouse components. It also accounts for the estimation of radiative heat exchange between the various surfaces inside the greenhouse. The realistic photosynthesis sub model selected in the present work is a mechanistic one applicable to the commonly planted C3 species. The model also provides a strategy for CO2 enrichment and microclimate control. In these strategies, the CO2 injection specific rate for enriching the greenhouse air to a specific concentration, and the cooling and dehumidification specific rates required to be keep the microclimate temperature and relative humidity within the favorable limits, are estimated. The model validity and accuracy were ensured through the good agreement of its numerical predictions with the available experimental results in the literature. The effect of different environmental conditions and planting conditions on the CO2 capturing process (the photosynthesis process) is investigated. Finally, a case study was chosen to investigate the effects of the cooling method, cooling temperature, planting conditions, and CO2 concentration level on the cumulative amount of captured CO2 considered to represent the greenhouse capturing performance. The results show that the capturing performance of greenhouse can be enhanced from value as low as 1.0 g CO2/m 2.day for ventilated greenhouses to value as high as 52 g CO2/m 2.day when alternative microclimate control methods and CO2 enrichment are used. In addition, the greenhouse has extended ability to capture as high as 140 g CO2/m2.day within its growing period considering the appropriate plant type. Furthermore, additional benefits besides CO2 capture are reported for the possible increase of the plant productivity and possible lowering of water consumption by plants.

Solar greenhouses can be considered as efficient places for biological CO2 capture and utilization if CO2 enrichment becomes a common practice there. As CO2 enrichment is applied only when greenhouses are closed, ventilated greenhouses - which represent a large percentage of greenhouses all over the world - cannot be considered for this practice, consequently cannot be available for CO2 capture and utilization. The aim this paper is to show-through modeling and simulation-that these ventilated greenhouses can be activated for serving as efficient CO2 capture and utilization places if they are kept closed (to apply CO2 enrichment) and used microclimate control methods alternative to ventilation. The paper introduces a realistic mathematical model in which all the processes and phenomena associated with the biological CO2 capture and utilization by photosynthesis inside greenhouses are considered. The model considers solar radiation attenuation through the atmosphere and absorption by the greenhouse components. It also accounts for the estimation of radiative heat exchange between the various surfaces inside the greenhouse. The realistic photosynthesis sub model selected in the present work is a mechanistic one applicable to the commonly planted C3 species. The model also provides a strategy for CO2 enrichment and microclimate control. In these strategies, the CO2 injection specific rate for enriching the greenhouse air to a specific concentration, and the cooling and dehumidification specific rates required to be keep the microclimate temperature and relative humidity within the favorable limits, are estimated. The model validity and accuracy were ensured through the good agreement of its numerical predictions with the available experimental results in the literature. The effect of different environmental conditions and planting conditions on the CO2 capturing process (the photosynthesis process) is investigated. Finally, a case study was chosen to investigate the effects of the cooling method, cooling temperature, planting conditions, and CO2 concentration level on the cumulative amount of captured CO2 considered to represent the greenhouse capturing performance. The results show that the capturing performance of greenhouse can be enhanced from value as low as 1.0 g CO2/m 2.day for ventilated greenhouses to value as high as 52 g CO2/m 2.day when alternative microclimate control methods and CO2 enrichment are used. In addition, the greenhouse has extended ability to capture as high as 140 g CO2/m2.day within its growing period considering the appropriate plant type. Furthermore, additional benefits besides CO2 capture are reported for the possible increase of the plant productivity and possible lowering of water consumption by plants.

This paper introduces the photosynthesis-stomatal conductance coupled model, well known and frequently used in the studies of vegetation-atmosphere interaction, to be incorporated into the studies of modeling greenhouses’ microclimate. The use of this model, unlike many of other models in the literature, allows accurate modeling of stomatal conductance for many plant types and under several environmental conditions. It also guarantees the modeling of the photosynthesis process ,which is important for microclimate and CO2 enrichment purposes, due to the direct coupling between photosynthesis and stomatal conductance in this model. Although the many advantages of this model, the many details associated with it may be the reason behind not being used in greenhouse microclimate modeling studies. Thus, this paper comes with an aim of facilitating the use of this model and encouraging modelers of greenhouses’ microclimate to use this powerful model by providing them the necessary background for the treatment of the model in a well organized form that contains all the necessary and required information they may need in their use of the model. In this paper, the photosynthesis-stomatal conductance coupled model is introduced by first illustrating briefly the biochemical background of the photosynthesis process and then introducing the accurate biochemical model that represents it. Then the photosynthesis-stomatal conductance coupled model is presented with its analytical solution methodology that gives accurate estimation of the photosynthesis rate and the stomatal conductance. Finally, validation of the model results with available experimental data is performed for a representative crop type under different environmental conditions. This validation proves the accuracy of the model in predicting the photosynthesis rate and in turn the stomatal conductance.

This paper introduces the photosynthesis-stomatal conductance coupled model, well known and frequently used in the studies of vegetation-atmosphere interaction, to be incorporated into the studies of modeling greenhouses’ microclimate. The use of this model, unlike many of other models in the literature, allows accurate modeling of stomatal conductance for many plant types and under several environmental conditions. It also guarantees the modeling of the photosynthesis process ,which is important for microclimate and CO2 enrichment purposes, due to the direct coupling between photosynthesis and stomatal conductance in this model. Although the many advantages of this model, the many details associated with it may be the reason behind not being used in greenhouse microclimate modeling studies. Thus, this paper comes with an aim of facilitating the use of this model and encouraging modelers of greenhouses’ microclimate to use this powerful model by providing them the necessary background for the treatment of the model in a well organized form that contains all the necessary and required information they may need in their use of the model. In this paper, the photosynthesis-stomatal conductance coupled model is introduced by first illustrating briefly the biochemical background of the photosynthesis process and then introducing the accurate biochemical model that represents it. Then the photosynthesis-stomatal conductance coupled model is presented with its analytical solution methodology that gives accurate estimation of the photosynthesis rate and the stomatal conductance. Finally, validation of the model results with available experimental data is performed for a representative crop type under different environmental conditions. This validation proves the accuracy of the model in predicting the photosynthesis rate and in turn the stomatal conductance.