Monthly Archives: August 2023

Symmetry boundaries are set at the middle of the length and width of the room

Furthermore, employment of light emitting diodes as light sources can initiate and sustain photosynthesis reactions and the optical wavelength, light intensity, and radiation intervals can further enhance growth quality. Recently, many studies have been carried out to investigate how environmental parameters, such as closed-loop control, ultrasound, and electro-degradation, affect hydroponic cultivation of leafy vegetables in these systems. One of the most influential factors affecting growth in IVFS is to maintain a uniform air flow at an optimal air current speed over plants canopy surfaces. Poor flow uniformity or variation in air velocity over culture beds destabilizes crop production rates. It has been found that inducing a horizontal air speed of 0.3–0.5 m s−1 boosts photosynthesis through more efficiently exchanging species between the stomatal cavities in plants and the flow of air. Lee et al. studied the effects of air temperature and flow rate on the occurrence of lettuce leaf tip burn in a closed plant factory system. Furthermore, it was observed that the relative humidity of the air flow can significantly influence calcium transportation in lisian thus cultivars . According to Vanhassel et al., higher levels of relative humidity can significantly decrease the occurrence of tip burn. Therefore, it is vital to maintain relative humidity in the desired range to ensure even distribution of calcium in lettuce leaves. Over the past few years, researchers have been trying to develop techniques for improving uniformity over cultivation zones. Regardless of the recent progress, the control and automation systems of IVFS bring additional costs,seedling grow rack which makes systematic experimental investigation and optimization a challenge. Computational fluid dynamics has been utilized as a reliable tool to numerically simulate complex physical phenomena. Markatos et al. developed a CFD procedure to study velocity and temperature distribution in enclosures using buoyancy-induced physics. Stavrakakis et al. investigated the capability of three Reynolds Averaged Navier-Stokes models to simulate natural ventilation in buildings.

Papakonstantinou et al. presented a mathematical model for turbulent flow and accordingly developed a 3- D numerical code to compute velocity and temperature fields in buildings. A novel gas-liquid mass transfer CFD model was developed by Li et al. to simulate the absorption of CO2 in a micro-porous micro-channel reactor. Yuan et al. visualized the air paths and thermal leakages near a complex geometry using a transient thermal model with buoyancy-driven convection, conduction and thermal radiation heat transfer and flow field near a vehicle structure. In the context of agriculture, researchers have extensively employed CFD analysis for study of ventilation, air flow, and microclimate in indoor systems. Zhang et al. developed a CFD simulation to assess single-phase turbulent air stream in an indoor plant factory system and achieved the highest level of flow uniformity with two perforated tubes. Karadimou and Markatos developed a transient two-phase model to study particle distribution in the indoor environment using Large Eddy Simulation method . Baek et al. used CFD analysis to study various combinations of air conditioners and fans to improve growth rate in a plant factory. More recently, Niam et al. performed numerical investigation and determined the optimum position of air conditioners in a small vertical plant factory is over the top. In addition, a variety of mathematical techniques are proposed to provide sub-model for investigating photosynthesis. According to Boulard et al., tall canopies can induce a stronger cooling of the interior air by using a CFD model to study the water vapor, temperature, and CO2 distribution in a Venlo-type semi-closed glass greenhouse. Despite the fact that photosynthesis plays an integral role in distribution of species and uniformity along cultivation trays, this issue has not been well addressed. Although numerous research works have been done to investigate the turbulent flow in enclosures and buildings, this study is the first to numerically investigate the transport phenomena considering the product generation and reactant consumption through photosynthesis and plants transpiration with CFD simulations for IVFS-based studies.

Furthermore, a newly proposed objective uniformity parameter is defined to quantify velocity uniformity for individual cultivation trays. Moreover, numerical simulations are performed to simulate and optimize fluid flow and heat transfer in an IVFS for eight distinct placements of flow inlets and outlets in this study. Accordingly, the effects of each case on uniformity, relative humidity, temperature, and carbon dioxide concentration are discussed in detail. Finally, an overall efficiency parameter is defined to provide a holistic comparison of all parameters and their uniformity of each case.In this study, three-dimensional modeling of conjugated fluid flow and heat transfer is performed to simulate the turbulent flow inside a culture room having four towers for hydroponic lettuce growth. Assuming that the four towers are symmetric, a quarter of the room with four cultivation trays is selected as the computational domain, as illustrated in Fig. 1a.The effect of LED lights on heat transfer is considered through constant heat flux boundary conditions at the bottom surface of each tray as shown in Fig. 1b. Lastly, the species transfer due to photosynthesis are occurring only in the exchange zone, which is illustrated in Fig. 1c. To study the impact of air inlet/exit locations on characteristics of air flow, four square areas, denoted as A, B, C, and D in Fig. 1a, are considered to be inlet, exit, or wall. To perform a systematic study, Table 1 presents the location of inlet and exit for all eight cases studied. With the aim of comparing all of the proposed designs, case AB is selected to be the baseline.In our model, a tetrahedral grid type is used to discretize the entire computational domain. To ensure that the numerical results are independent of grid dimensions, five grid numbers ranging from 196,951 to 1,164,624 are used to study the baseline Case AB at a mass flow rate of 1 kg s−1. Fig. 2 summarizes the average temperature and pressure difference for the five grid numbers. Balancing between the accuracy of the simulation results and computational cost, the grid number of 697,537 is employed throughout the rest of the study.

The simulation domain consists of rectangular prisms as cultivation tray, the exchange zone in which the photosynthesis processes occur, and the rest of the open volume. To validate our numerical code, we performed simulation of conjugated heat transfer and turbulent flow passing over one rectangular prism in a duct. The exact dimensions and input conditions of this test case can be found in the study of Nakagawa et al.. The induced flow involves periodic vortex shedding that can be problematic for numerical analysis. The results of the numerical simulations are compared with the experimental measurements done by Lyn et al., Franke and Rodi , and Durao et al. [46]. Fig. 3 shows the average axial velocity distribution and our simulation results agree well with the experimental data both before and after the rectangular prisms. To further validate the reliability of heat transfer calculation, the simulated local Nusselt number along the upper wall of the square prism are compared with the experimental data measured by Nakagawa et al. in Fig. 4. When x/H is between 1and 2, the wake flow is extremely unsteady and adverse flow can be observed in Fig. 3. Therefore, it is extremely difficult to accurately predict the convective heat transfer in this region. Nevertheless,indoor growing racks the simulation results show good agreement with the experimental data, especially in the wake region . Further, the calculation of species transport in this work is simulated using species exchange sub-model, which has been validated extensively in the literature.In this study, three dimensional simulations of conjugated turbulent flow and heat transfer are carried out to study the concept of the IVFS. The exchange zone above each tray is designed to represent the volume where the photosynthesis reaction takes place including carbon dioxide consumption along with water transpiration and oxygen production. In addition, the room is assumed to be insulated by wooden walls with known thickness and thermal properties for modeling heat exchange with the outdoor ambient air. In this study, we analyze the effect of eight distinctive inlet outlet placements on flow uniformity over the lettuce canopy, temperature and relative humidity distribution in the room, and the power required for air circulation.One of the most critical factors affecting crop growth rate is the air flow velocity over plants. A fluid stream with horizontal speed ranging from 0.3 to 0.5 m s−1 can escalate the species exchange between the flow and plant leaves resulting in enhancement of photosynthesis. In indoor farming systems, the flow velocity can be controlled well using ventilation fans for more efficient plant growth. However, heterogeneous distribution of feeding air over plant trays can cause undesirable non-uniformity in crop production, which should be avoided.

Therefore, it is important to study the effect of inlet-outlet location and flow rate on the flow patterns throughout the culture room. Herein, the most favorable condition is defined as the condition at which the flow velocity above all trays is equal to the optimum speed Uo, which is set to be 0.4 m s−1. The objective uniformity, OU, defined in Eq. is used to assess the overall flow conditions. The OU for all eight cases as a function of mass flow rate are summarized in Fig. 5. Since the inlet/exit area and air density remain the same, the mass flow rate is directly proportional to flow velocity. In addition, the target flow velocity over the plants is set to be 0.4 m s−1. Therefore, a general trend of OU first increases and then decreases when increasing the overall mass flow rate. Depending on the design, the peak of OU occurs at different mass flow rate for each case. Another general trend can be observed that the peak of OU occurs at a lower mass flow rate if the inlet is located at the top due to buoyancy force. This can be clearly demonstrated by cases AB and BA or AD and DA . Therefore, there exists a different optimal inlet/exit design for each mass flow rate condition. As can be seen from Fig. 5, the maximum OU at flow rates of 0.2, 0.3, 0.4 and 0.5 kg s−1 is observed for configurations AD, BC, BA, and DA, respectively. Therefore, this simulation model can identify optimal flow configuration at a specific mass flow rate condition. Since OU quantifies the deviation of average velocity of each tray from the designed velocity, a higher OU value indicates that the crops will have better and more uniform photosynthesis. It can be observed from Fig. 5 that the maximum OU obtained for all conditions is case BC at a flow rate of 0.3 kg s−1. To develop a better understanding, the two-dimensional velocity and vorticity distributions in the x-y plane along the middle of the z-direction for all eight cases at a mass flow rate of 0.3 kg s−1 are plotted in Figs. 6 and 7. As can be observed from Figs. 6 to 7, the OU is highest for case BC due to its uniform velocity and vorticity distributions between trays. This can be attributed to the position of inlet/exit location with respect to the tray orientation. For case BC, the inlet flow is parallel to the longitudinal direction of the tray and the exit is along the transverse direction . This design allows the flow to travel through the long side of the tray uninterrupted and then form a helical flow orientation near the end of the tray. This spiral formation of flow induces a more uniform and regular flow in the room. This also explains why case AD has very high OU. Similar spiral formation can also be observed when the inlet flow is parallel to the transverse direction of the tray and the exit is along the longitudinal direction , like case DA. However, since the inlet flow is along the short side of the tray, the benefit is not as great and requires much higher inlet mass flow rate. On the other hand, for cases where the inlet and exit are located on the same wall, such as AB or CD, the air flow only has strong mixing effect along the inlet/exit direction which, in turn, reduces the overall flow uniformity.

The information from this study can help to inform future malaria control planning

Part of the reason might be that important windows for atopic sensitization such as prenatal exposures were not captured in the study. The number of cases of allergic sensitization to dogs, cats, and ragweed were small among the study children , resulting in compromised statistical power. The low number of dog and cat allergies might have been due to the high dog ownership and medium cat ownership in the study population : living in proximity to animals is associated with lower sensitization to allergens among children. No significant differences in allergic sensitization or symptoms were found between children in group 1 and group 2, among whom chimney stoves were installed around birth and around 18 months old, respectively. This might have been due to the gradual deterioration of chimney stoves during the 2-year gap between the RESPIRE and CRECER studies, during which group 1 might have been exposed to higher HAP than group 2 because of the older stoves. Another reason might be insufficient exposure reduction, which was also found in a previous analysis of the RESPIRE study: a larger reduction in mean CO exposure was associated with reduction in pneumonia risks, but the moderate difference in group mean CO levels between groups 1 and 2 was not enough to yield a statistically significant difference in pneumonia risk between the groups. The high percentages of reported allergic symptoms and high prevalence of cockroach sensitization among the children in this study is contrary to the “hygiene hypothesis” or “microbial deprivation hypothesis” that early life exposure to microorganisms shapes the Th1 , Th2, and regulatory T cell responses and alters immune response patterns.

For instance,grow rack greenhouse children exposed to enteric pathogens have higher resistance to allergic sensitization compared to those living in pathogen-free environments. While the study population was exposed to abundant microorganisms, it is possible that exposure to HAP prenatally, in early life, or even in reduced amounts after the stove upgrade intervention, could promote a shift toward Th2 responses and thus increase risk for atopy. Previous studies have demonstrated that exposure to PM2.5 may increase the risk of asthma via airway inflammation, increase in oxidative stress, changes in immune signaling, and subsequent disruptions of airway epithelial cells and mucosal barrier function. Studies on rhesus monkeys have also found that co-exposure to a pollutant that causes oxidative stress, ozone, and allergen altered airway structural development and increased risk of an asthma-like phenotype. Another consideration is that the increased wheezing and rhinitis symptoms reported by their mothers among children exposed to higher HAP could also be due to the direct irritating effects of biomass smoke to the upper and lower airway epithelium rather than an underlying allergic mechanism. During study design, we hypothesized that group 3 index study children would have the highest cumulative biomass smoke exposure because they were provided the upgraded chimney stoves the latest, thus were exposed to higher levels of biomass smoke for the longest period of time. We also expected groups 2 and 3 to have comparable levels of biomass smoke exposure during the RESPIRE study period because both groups did not have upgraded chimney stoves at this time. While assessing cumulative CO exposure for the index study children, we used the group 3 proxy infant siblings’ personal CO exposure during CRECER as a proxy for group 3 index study children’s personal CO exposure during the RESPIRE study period when the personal CO exposures of groups 1 and 2 were measured. This allowed us to account for the missing early life personal CO information due to the late recruitment of the group 3 households.

This approximation assumes that newborn children raised in the same household by the same parent will have similar activity patterns and thus similar levels of CO exposure. However, several sources of uncertainty may compromise the accuracy of this proxy measure. Firstly, secular differences between RESPIRE and CRECER , such as different biomass fuels used, different CO diffusion tube batches, as well as the potential changes in household cooking conditions and ventilation, were not accounted for. Secondly, group 3 proxy infant siblings’ CO exposures were measured less frequently , compared to groups 1 and 2 index study children’s early life CO exposures , resulting in potential differential exposure mis-classification. These uncertainties might be the reasons that the estimated CO exposure during the RESPIRE study period is much lower for group 3 compared to group 2 , and the subsequent lower cumulative CO exposure for group 3 compared to group 2 , which was different from our original hypothesis. If group 3 CO exposures were indeed underestimated, it would have caused a downward bias of our secondary analysis results because of the high number of cases in group 3, and the true associations would be higher than reported. This is the first cohort study that looked at SPT prevalence in a rural population of a low-income country. The strengths of this study include the quality of the SPTs, which was supported by positive and negative controls and multiple rounds of field worker training, and use of extensive questionnaires on household information, building structure, animal allergen exposures and SES to allow adequate control of potential confounding variables. The partial randomized controlled trial design between groups 1 and 2 further reduced the possibility of residual confounding. The estimation of cumulative CO exposure was based on repeated personal measurements, which was of higher accuracy than commonly used ambient or static household air pollution monitors.

An important limitation of the study was the self-reporting of allergic symptoms. Since the stove upgrade intervention could not be blinded, the mothers’ responses to questionnaires may have been subject to an upward response bias. In addition, the missing exposure information and stove deterioration during the 2-year gap between the RESPIRE and CRECER studies may have led to exposure mis-classifications. The cumulative CO exposure estimation was also less accurate for group 3 because of the use of infant siblings as proxy for the early life exposure of the older children in this group, as well as the less frequent exposure monitoring during CRECER compared to RESPIRE, potentially resulting in differential exposure mis-classification in the secondary analysis.Historically, malaria in the western Kenya highlands has existed. Since the late 1980s, epidemic to hyperendemic malaria has evolved in the western Kenya highlands because of severe public health problems associated with high morbidity and mortality. Prior to the 1990s, malaria was managed by chemotherapy. However, following the resistance of Plasmodium falciparum to chloroquine and sulfadoxine-pyrimethamine, the country shifted to the use of artemisinin-based combination therapy. Insecticide-treated bed nets and other vector control strategies gained favour based on large-scale randomized control trials. Initial trials with ITNs indicated promising protection and a reduction in morbidity and mortality. However, the affected populations could not afford the ITNs in early 2000. The Kenya Government policy on subsidized ITNs and targeting vulnerable populations increased the number of people who had ITNs in their households but the overall effect on malaria transmission was low. By 2011, the government rolled out the universal bed net programme where every two persons in a household were provided with a free ITN. It was expected that ownership and usage of 80% of ITNs would have a high epidemiological impact on malaria transmission. This programme has faced numerous challenges, among them insecticide resistance, non-compliant human behaviour,grow rack systems changes in biting habits of the vector, changes in species composition, and vector density. It has been shown that Anopheles gambiae has developed resistance to pyrethroids in western Kenya. Biting behaviour has seen a small but significant increase in early biting of malaria vectors in the western Kenya lowlands. The proportion of Anopheles arabienis has progressively increased in the western Kenya highlands. Although high ownership of ITNs has been reported in western Kenya, the usage has not been as high. Consequently, this has led to high transmission of the malaria parasite in the population with low usage. This study was carried out to determine the impact of ITNs on indoor vector densities and biting behaviour in western Kenya.This study was carried out to assess the impact of ITNs on indoor vector densities and biting behaviour in western Kenya as the use of ITNs has been shown to be effective in reducing mortality and malaria transmission in the past.

Before the mass distribution of ITNs in 2011, bed net ownership in western Kenya was reported to be below 80% and parasite resurgence had been seen in areas of western Kenya. This was attributed to vector resistance to pyrethroids and the inefficacy of bed nets because of the low ownership. Afterwards, the Roll Back Malaria Partnership raised coverage of ITNs to ≥80% through the free mass distribution of long-lasting insecticidal nets /ITN campaigns, which were carried out in various parts of Africa. The current policy for vector control in Kenya includes the use of LLINs and limited use of IRS where the government-marketed, subsidized bed nets in 2002, 2006 to vulnerable groups until 2011 when there was a universal distribution policy was implemented with every two persons in a household receiving a free bed net. In this study, high bed net ownership of >80% in all six sites was confirmed. The high bed net ownership has a community effect where people without nets are protected by the area-wide effects of ITNs nearby. Anopheles gambiae indoor resting densities over the last decade have decreased tenfold in Iguhu, sixfold in Marani and fourfold in Kombewa, while densities of An. funestus have decreased threefold in Iguhu and sixfold in Kombewa.

However in Marani, over the decade densities of An. funestus have increased threefold compared to a study by Ndenga et al.. Likewise, sporozoite rates of An. gambiae have declined fourfold in Iguhu and Kombewa while they have increased fourfold in Marani. Anopheles funestus sporozite rates remained constant in Kombewa, while in the other sites there were no confirmed infectious An. funestus. Anopheles funestus is seen as one of the most abundant vectors in Kombewa, which has been reported previously. The species is re-emerging in Marani where it was the most abundant species, as shown in the results. Anopheles funestus breeds in permanent habitats towards the end of the wet season and is known to require vegetation and shade and the larval habitats are found mainly in swamps and pastures. Anopheles funestus takes 3 weeks to mature, which is longer than An. gambiae maturation period. Other studies conducted in western Kenya lowland region have reported that An. funestus is re-emerging, which is suspected to be as a result of pyrethroid resistance after a long-term implementation of ITNs. Previous studies in the sugar-belt region of Miwani reported the ratio of An. arabiensis to be higher than that of An. gambiae s.s., especially during the dry season. The use of ITNs has had a great impact on densities, species and sporozoite rates. The proportion of An. arabiensis is increasing in the highlands, a factor that could have malaria transmission implications as An. arabiensis is a less efficient vector than An. gambiae, as An. arabiensis is zoophilic. Githeko et al. found that malaria vectors fed during the late part of the night with peaks at 05.00 h. In this study, An. gambiae caught after midnight was blood fed, while fed An. funestus were caught throughout the night both indoors and outdoors. It is likely that blood-fed An. funestus may have been avoiding resting. This observation supports exophilic behaviour in An. funestus, a phenomenon that requires further investigation. In regard to human and mosquito activity, data from this study suggests that there is a risk of transmission at dusk and at dawn. Data collected during the study did not support continuous outdoor transmission since the majority of humans were indoors between 21.00 and 05.00 h. The use of LLINs has been reported to change the feeding and resting behaviour of mosquitoes. The study reports similar findings that there was high host seeking activity of the vectors at around 18.00 and 20.00 that led to earlier feeding in An. gambiae populations. This could be as a result of the use of ITNs. Anopheles funestus showed no change in feeding habits as the results show that they bite throughout the night both indoors and outdoors. This poses a great risk of malaria transmission throughout the night despite high bed net coverage.