Search

Solar energy was used to boost the drying process of Habanero chilli. The drying of habanero chilli is a significant seasonal commodity for Mexican producers; however, this process is costly and wasteful of energy. To determine the market trend and the optimal drying conditions for redesigning the Habanero chilli drying process using a hybrid solar-electric energy system, a feasibility study was developed. There will be two stages to the new drying process: (a) an open solar dryer was used; (b) an existing pilot fluidized bed dryer was adapted with a low temperature solar collector for air heating. Habanero chili was dehydrated from 90% to 5% moisture in 10.3 h, with good quality product, available for commercialization. With an energy savings of 0.52 kg of natural gas per kg of fresh Habanero chilli, a 50% reduction in average drying time was achieved, as well as a % reduction in energy consumption in the fluidized bed dryer.In order to expand the market for Habanero chilli, an innovative sustainable efficient drying process was created, which will save % on energy when compared to conventional equipment.

Intermittent drying is a common technique for food conservation. The objective of this work is to evaluate the effect of non-isothermal drying and the wave periods using the effective diffusivity (Deff), the glass transition temperature (Tg), their relationship to moisture content and the temperature of the product, as parameters for controlling quality deterioration. The heating–cooling profile was developed as a trapezoidal wave form using three different wave periods (τ:60, 120 and 160 min), with a midpoint temperature (Tm) of 50 °C and ∆T = 10 °C. The ascending (AC) heating–cooling treatment began at 40 °C, and the descending (DC) heating–cooling treatment began at 60 °C. The drying temperature (Ta), the surface temperature of the garlic (Ts), the internal temperature of the garlic (Ti), and the weight of the garlic slices were measured and recorded in real time. The Deff was calculated using the slope method. A higher drying rate was observed in the AC drying treatment. The Tg variations were associated with the Ti and moisture content of the garlic. The drying time (ts) for the AC and the DC heating–cooling profiles was found to be between 180 to 238 min.

Chilli is a vegetable that is produced and consumed in various parts of the world, not only for its culinary qualities but also for its nutritional content and potential industrialization. Mexico has the highest genetic diversity of chilli, with more than 40 varieties. A dried chilli has different properties of flavour, colour and pungency and a high added value; however, information about its dehydration is scarce. In this work, the dehydration of a red chilli, the “costeno” ( Capsicum annuum L.), which is highly appreciated for its organoleptic properties and used in the food industry, was carried out. The experimental study was performed at the Instituto of Energias Renovables (IER) of the Universidad Nacional Autonoma de Mexico (UNAM) in Temixco, Morelos, Mexico, located at 18°51′NL and 99°14′WL. The drying process was carried out at controlled temperatures of 45 °C, 55 °C and 65 °C, using a laboratory oven and an indirect tunnel-type solar dryer. The drying kinetics between 55 °C and 65 °C are similar, with drying times of 2.75 h and 3.0 h, respectively, while at 45 °C, the drying time was 6.25 h. Wang and Sing’s model gave a better fit for the drying kinetics at 45 °C, and the Page model was better for 55 °C and 65 °C. In the solar drying processes, two ranges of air velocity were established; high velocity was between 1.4 and 2.6 m/s, and low velocity was between 0.7 and 1.48 m/s. In both cases, a temperature between 31 °C and 45 °C was obtained. For the first range, the total drying time was 16 h, reaching a final moisture content between 0.057 kg of water/kg dry matter and 0.90 kg water/kg dry matter. For the second range, the time was 21 h, with a moisture content of 0.0611 kg of water/kg dry matter and 0.109 kg of water/kg dry matter.

The distribution of turbulent kinetic energy (TKE), temperature, and velocity of humid air inside the greenhouse solar dryer (GHSD) was numerically investigated using 3D CFD ANSYS FLUENT code. The effect of solar radiation was coupled with the energy equations using the discrete ordinate model. Numerical simulations were based on two geometric models: Real model and model with reduced height, the solution was in good agreement with experimental data of temperature. The results of the real model showed that the TKE is ranged between 1.27 m2/s2 and 6 m2/s2 with an average of about 1.6 m2/s2 for the entire greenhouse dryer (GHD) volume. The greatest TKE magnitude is in the paths of the diffusers, which caused a temperature drop of about 2 K in the areas near the walls. Consequently, almost homogeneous temperature distribution was obtained in the entire volume of the GHD, although the average temperature was 315 K, and a gradient with respect to ambient temperature was of 14 K, that is, suitable for drying. Also, the average air velocity at 1 m height was 0.71 m/s, which is a value near the lowest limit (0.6 m/s) of forced convection drying. The improvement in the GHD by 36.5% volume reduction allowed an increase in the average TKE of 3.8 m2/s2 (2.4 times more than the previous one) located in the middle of the greenhouse; the average temperature reached 316.5 K with a gradient of 15.5 K, which represents an increase of 1.5 K (11%) compared to the real geometric model. The air velocity at 1 m height increased to 0.9 m/s in the improved geometric model (a growth of 35.7% compared with the previous geometry). More than 95% of the improved GHD volume has a uniform temperature, which is very suitable for a good quality drying process with higher speed.

In this article, the effect of direct solar drying, indirect solar drying, and freeze drying on the phenolic compound contents and antioxidant capacities of blackberry fruits was investigated. The solar drying kinetics were determined and fitted to six thin layer different mathematical models. The total phenolic, anthocyanin, and flavonoid contents as well as the antioxidant capacity based on ABTS, DPPH, and OH• assays were determined for the dried blackberry samples. The results show that the Midilli–Kucuk model provides the best fit to the experimental data of solar drying in both methods tested. Greater antioxidant capacities were observed in the samples dried by using direct solar drying method in all experiments, that is, the ABTS, DPPH, and OH• activities were 36,757 ± 1.27; 21.120 ± 1.33, and 47 ± 7.31 μmol TEAC/g dm, respectively. The creation of compounds during food dehydration at moderately high temperatures can enhance the antioxidant capacities and phenolic contents. PRACTICAL APPLICATIONS: Rubus fruticosus is a berry with nutraceutical potential by the presence of bioactive compounds. The removal of water from a fruit extends the conservation time of the product during storage and transportation, facilitating the access to such foods when required. One of the most economical and sustainable ways to do the drying is to use solar dryers. Direct and indirect solar drying are technologies that have effects that must be taken into account according to the food that is to be dried and the final characteristics that are desired to obtain. However, the phenolic compounds present in the fruit are sensitive to the thermal process. Thus, it is important to know its consequences phenolic compounds and antioxidant activity for better use of the fruit.

The mortino fruit (Vaccinium meridionale Swartz) has been recognized as an excellent source of antioxidants, phenolic compounds, and anthocyanins. Drying conditions, particularly temperature, often lead to food quality degradation. The present study investigated the influence of drying temperature (40, 50, and 60°C) on antioxidant activity, anthocyanin, and phenol content of mortino. Four different thin layer drying models of drying kinetics (Modified page, Newton, Henderson & Pabis and, two-terms) were fitted to the experimental data. For antioxidant capacity determination, oxygen radical absorbance capacity and ferric ion reducing antioxidant power assays were used. The results showed that antioxidant capacity, and phenolic and anthocyanin content all decreased with increasing temperature and drying time. It was observed that phenols and anthocyanins were conserved in greater amounts at 60°C with 34% (5.85 mg gallic acid/g dm) and 32% (2.36 mg Cyanidin-3-glucoside/g dm) preservation of initial c...

This paper presents the thermal and energy analysis of a Solar-LP gas hybrid drying plant built in Zacatecas, Mexico. It is focused on the dehydration of agricultural products. The drying system is a forced convection hot air type with a drying chamber. For the air heating required in the drying process, there are two solar thermal systems: a direct air heating system (48 solar air heaters with an area of 111.1 m2) and an indirect air heating system (40 solar water collectors with an area of 92.4 m2 and 6000 L of thermal storage). Also, there is a backup system of conventional energy (LP gas burner). Two hybrid tests were carried out to dry Nopal (Opuntia ficus-indica) initially operating with the direct system, after that with the indirect system and complementing the energy demand of drying with the conventional system. The effective drying time was 14.3 and 11.7 h, removing a total of 179 and 183 kg of water, respectively. The air temperature at the entrance of the drying chamber was around 59 °C. The solar fraction obtained for this hybrid mode of operation was around 80%. The thermal analysis of the direct and indirect air heating system, together with the conventional system, are presented and discussed. The performance of the solar systems is finally compared with a conventional LP gas drying system via a cost and return on investment analysis.

The goal of reducing energy consumption (EC), losses and waste (FL) in the food processing is a challenges in the worldwide. The use of active solar greenhouse dryers (GHD) for EC and FL reductions has increased due to its capacity, and low operating costs. In this work the effective diffusivity (Deff) and the moisture content modeling were analized for basil (Ocimum basilicum) and blackberry pulp (Rubus rosoideae) dried in a conventional stove (CD) and an GHD coupled to an additional air solar heating system (SCHa). The loss of water and the drying rate in food materials dehydrated in the GHD is consistent with the increment or decrement of temperature during the solar day. The Deff values for basil and blackberry pulp was ranged between -1.1044x10-7 and -3.9167x10-9. The solar energy obtained in the GHD supplied the heating requirements. In general, the Page’s model was the best fit for the drying kinetics for basil and blackberry pulp. Keywords: Solar Collector for air heating, solar energy, variable conditions

Technical performance of two solar drying technologies was evaluated: Solar Greenhouse Drying (SGD) with auxiliary heating system, and Direct Solar Drying (DSD) in order to evaluate its effect on antioxidant activity (AA) and total flavonoids of blackberry (rubus spp) waste destined. The SDG and DSD results were compared with those of the dehydrated samples in an electric stove (ES). The fresh and dried fruits were evaluated; the blackberry seedless pulp was used. The AA and flavonoids showed degradation of 70% and 20% compared to the fresh sample. For both compounds, SGD is the one that offers the greatest conservation.Keywords: solar drying; antioxidant capacity; flavonoids; blackberry pulp (rubus spp); solar energy

Considering the important demand of fresh water and its scarce availability, water desalination is an interesting technology, producing about 44 Mm3/year worldwide, but, in general the most common desalination techniques are highly energy demanding. Freezing-Melting (F/M) desalination uses just up to 70% less thermal energy, but is the least used process mainly, due to the difficulty of the salt separation. This study proposes a model able to analyses the thermodynamic potential that allows the salt diffusion during the F/M process, using an aqueous solution of sodium chloride. This should allow to obtain a sensitive analysis of the process to promote the separation between the high concentration brine and the ice with liquid separation by physical process. The unidimensional model is based on the evolution of both processes: thermal and mass diffusions, depending on temperature and saline gradients, predicting whether the salt will remain inside the ice or not. Thus, the thermal potential is adjusted to frozen only when the salt has been "pushed" towards the brine. Mostly models have base their results on the assumption of a “certain value of saline concentration of the liquid fraction”, value in which there is great disagreement. In this paper the calculations are based on the concentration in the solid-liquid interface, which has been extensively studied and there is a coincidence in those results, being the main advantage of the proposed model.

The fresh water production in single and double slope solar stills (DSSS) depends on the rates of simultaneous processes of evaporation and condensation, where optical material properties, solar irradiance, temperature, velocity and air direction and the operating mode, natural or forced convection, are involved. Scarce experimental studies of the behavior of air velocity on water production on DSSS have been published, but mostly, the applied methodology is not clear. We analyzed the effect of the air velocity on the water production, temperature distributions and efficiency in a modified double slope solar still and compared the results with another with the same characteristics operating at natural convection. The influence of the other climatic parameters was minimized, placing a transparent wind tunnel on the solar still external cover. We tested the solar still at different average air velocities; 2.5, 3.5, 5.5 and 6.9 m/s. During the test period, the climatic parameters such as daily average solar irradiance (750–850 W m −2 ), and the maximal ambient temperature (33–37 °C), had small variations. We experimentally demonstrated that the thermal efficiency and production increment when the air velocity increases up to the value limit around 5.5 m/s and it then decreases at higher velocities and the velocity of 3.5 m/s is considered to be the optimum. The experimental uncertainty and error analysis was also presented. These results can be applied to any type of solar still; single or double slope, operating at natural or forced convection and improve both efficiency and production within the domain of the tested air velocities.

El tomate verde (Pysalis Ixocarpa Brot), conocido también con los nombres de tomatillo, tomate de cáscara, miltomate, etc., es muy apreciado en la gastronomía de muchos países como Guatemala, Colombia, Chile, Brasil, España, Polonia, Estados Unidos, Israel Sudáfrica, India, Australia y principalmente en México, en donde ocupa el 4º lugar como la verdura más consumida en el país. A nivel nacional se producen 8 tipos: Silvestre, Milpero, Arandas, Tamazula, Manzano, Rendidora, Salamanca y Puebla. Además de sus propiedades culinarias, tiene propiedades nutrimentales con un alto contenido de vitaminas, principalmente A, C, y de Potasio y otros minerales. Se le atribuyen propiedades medicinales. En este trabajo se realizó un estudio experimental conducente a conocer el potencial de este producto en estado deshidratado, a través de un análisis de las cinéticas de secado en un dominio de temperaturas de 40, 50 y 60 ºC, bajo condiciones controladas, así como las cinéticas de deshidratación utilizando un secado solar tipo directo (directo) con funcionamiento pasivo (convección natural) y activo (convección forzada). Se analizó la influencia de la temperatura sobre la cinética de secado con velocidad de aire establecida de 2 m/s. Los experimentos se realizaron en el Laboratorio de Secado Solar del Instituto de Energías Renovables de la Universidad Nacional Autónoma de México, localizado en la Ciudad de Temixco ubicado a 18º 51´ de L.N. y 99º 14´ L.O. a 1280 msnm. Durante el período de pruebas, la irradiancia solar varío entre 526 y 1083 W/m2. Con la tecnología de secado solar tipo directo se obtuvieron humedades finales entre el 7 y el 8.5% para convección natural y 9 y el 13% para convección forzada. Los tiempos de secado de entre 13 y 13.5 horas y entre 13 y 14 horas con convección natural convección forzada respectivamente.Palabras clave: deshidratación de tomate verde tomate verde con cascara, secado solar.

In recent years, interest toward berries has increased (e.g., Myrciaria cauliflora or jaboticaba) because of their high phenolic content (phenolic acids, flavonoids, and anthocyanins) that has been associated with positive effects on consumer health and which play an important role in the antioxidant properties of food. This study analyzed the sorption isotherms, thermodynamic properties of sorption (isosteric heat and Gibbs free energy), and the evolution of the antioxidant capacity during the drying process. The effects of drying temperatures of 40°, 50°C, and 60°C on the antioxidant capacity and thermodynamic properties of sorption were evaluated. The gravimetric static method for sorption isotherm determination over a range of relative humidity levels from 0.10 to 0.90 was used. The sorption isotherms exhibited a Type II behavior, typical for many foods. The Guggenheim, Anderson, and Boer (GAB); Oswin; Peleg; and Lewicki models were used to fit the experimental data, and it was determined that the GAB...