Development of model based sensors for the supervision of a solar dryer

Solar dryers are increasingly used in developing countries as an alternative to drying in open air, however the inherent variability of the drying conditions during day and along year drive the need for achieving low cost sensors that would enable to characterize the drying process and to react accordingly. This paper provides three different and complementary approaches for model based sensors that make use of the psychrometric properties of the air inside the drying chamber and the temperature oscillations of the wood along day. The simplest smart sensor, Smart-1, using only two Sensirion sensors, allows to estimate the accumulated water extracted from wood along a complete drying cycle with a correlation coefficient of 0.97. Smart-2 is a model based sensor that relays on the diffusion kinetics by means of assesing temperature and relative humidity of the air inside the kiln. Smart-2 model allows to determine the diffusivity, being the average value of D for the drying cycle studied equal to 5.14 × 10−10 m2 s−1 and equal to 5.12 × 10−10 m2 s−1 for two experiments respectively. The multidistributed supervision of the dryer shows up the lack of uniformity in drying conditions supported by the wood planks located in the inner or center of the drying chamber where constant drying rate kinetics predominate. Finally, Smart-3 indicates a decreasing efficiency along the drying process from 0.9 to 0.

Solar Dryers for Tropical Food Preservation: Thermophysics of Crops, Systems and Components

Drying reduces the moisture content of harvested crops thus slowing decay processes to enable longerterm storage. Solar dryers contain the crop being dried, to enhance solar energy collection incurring lower crop losses than are associated with open-sun drying and recurrent costs than are inherent to uses of fossil-fuels for drying. The influences of key environmental, operational and design parameters for solar dryers are discussed including: (i) psychrometry of drying processes and ambient conditions, (ii) how initial crop properties are converted to final desired product attributes, (iii) feasibility of using powered components such as fans and (iv) air-heating solar collector selection

Design, simulation and optimisation of a chimney-dependent direct-mode solar crop dryer (CDSCD).

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Characteristics of Different Systems for the Solar Drying of Crops

Solar dryers are used to enable the preservation of agricultural crops, food processing industries for dehydration of fruits and vegetables, fish and meat drying, dairy industries for production of milk powder, seasoning of wood and timber, textile industries for drying of textile materials. The fundamental concepts and contexts of their use to dry crops is discussed in the chapter. It is shown that solar drying is the outcome of complex interactions particular between the intensity and duration of solar energy, the prevailing ambient relative humidity and temperature, the characteristics of the particular crop and its pre-preparation and the design and operation of the solar dryer

Mass Transfer in Multiphase Systems and its Applications

This book covers a number of developing topics in mass transfer processes in multiphase systems for a variety of applications. The book effectively blends theoretical, numerical, modeling and experimental aspects of mass transfer in multiphase systems that are usually encountered in many research areas such as chemical, reactor, environmental and petroleum engineering. From biological and chemical reactors to paper and wood industry and all the way to thin film, the 31 chapters of this book serve as an important reference for any researcher or engineer working in the field of mass transfer and related topics

Drying of faecal sludge from ventilated-improved pit latrines( VIP latrines) using solar thermal energy.

Masters Degree. University of KwaZulu-Natal, Durban.Ventilated improved pit (VIP) latrines are a basic form of sanitation in South Africa. The main challenge facing the application of VIP latrines is the gradual fill up of the pit due to usage. A sustainable way of treating FS remains from sanitation systems is by using solar energy. This project is focused on the characterisation of solar drying for FS treatment. A solar thermobalance was designed and constructed to investigate the solar and open-air sun drying of FS. Mass variations, temperature, humidity and solar irradiance properties were monitored during the drying process. The drying experiments for solar drying were conducted with the following variables: weather conditions; air temperature; airflow velocity; sample thickness and surface area. The experiments were carried out in October and November 2017. The drying kinetics were observed to be influenced by the weather conditions, air temperature and air flow rate, but the sample thickness and surface area of the sample did not have any significant effect on the drying rate, under the explored conditions. Solar drying recorded drying rates which averaged 0.892 kg/h.m2 across the investigated parameters and were comprised between 0.622 to 1.135 kg/h.m2, whereas open-air drying averaged a drying rate of 0.479 kg/h.m2, varying in the range 0.686 - 0.078 kg/h.m2. The faecal sludge was found to dry best under sunny conditions, 30 oC air temperature and 0.5 m/s air flowrate. Qualitative and quantitative analysis was also conducted to characterise the influence of solar and open-air sun drying on the physico-chemical characteristics of faecal sludge. Density, shrinkage, thermal conductivity and heat capacity showed great dependence on the final moisture content which depended on the employed drying conditions. Crusting and cracking of the samples were observed to occur, and their intensity depended on the investigated conditions and were suspected to affect the drying rate in specific experimental conditions. This is shown in the lower drying rates for 1.0 m/s air flow rate and 60 oC air temperature. Odour strength increased with lower final moisture content. In summary, the application of solar energy for drying proved to be a feasible option for the treatment of FS. Drying in a solar thermal system with controlled conditions of air properties will consist in an improvement on the current sludge dehydration practices, such as the drying beds (open-air drying)

Testing and Modeling of the Indirect Solar Drying of Thin Film Mangos

In Haiti, 80% of rural people live in dire poverty living on less than a dollar a day. Cultivated and wild grown foods such as mangos and breadfruit could be used to reduce the economic and nutritional disparity for rural communities. Unfortunately in these areas there is a high amount of spoilage due to short harvesting seasons with high yields and lack of preservation options. 80% of breadfruit and 60% of mangoes are lost annually according to a local farmer’s co-op in Borgne, Haiti [1]. Based on a 2018 three-week collaborative design session with Rochester Institute of Technology (RIT) and the local women’s group SEE FANM (women for health, education, and economy), we identified mangos as a potential option for “transfòmayson fwi” - food transformation. Our team proposed drying mangos and then selling them as a juice powder in the off-season. Food preservation by solar drying has become a widespread practice in developing countries. Dryers use solar energy and other supplementary energy sources to heat air entering a drying chamber. Drying is a complex heat and mass transfer process that can take hours or days depending on the properties of the food such as ripeness and temperature and humidity of the drying air. Many studies have attempted to model the transport of moisture within fruits to predict drying performance while others have experimented with different styles of solar dryer designs. These systems are mostly tested outside in variable ambient conditions where the local temperature, relative humidity, and solar flux constantly fluctuate introducing a significant amount of noise . This “noise” is a product of these varying external conditions which affects the quality of the drying air and the performance of solar-thermal systems. Testing thermal systems in cold climates such as Rochester makes it impossible to predict performance in tropical regions like Haiti. This work focuses on eliminating many of these external factors in order to remove noise to provide faster and more repeatable testing. A testing system was designed and built to simulate the output of a solar collector in a tropical environment to explore the impact of the collector size and dryer volumetric flowrate on drying performance in a highly consistent and controlled manner. Testing demonstrated the importance of external conditions during the falling drying rate regime, where internal diffusion typically dominates drying performance. The results of these tests are used to empirically fit a bulk drying model for a shrinking fruit film that exemplifies the impact of external conditions. This model allows for the prediction of drying performance for the first 85% of moisture removed from a fruit film. A system model is also proposed that seeks to capture the deep layer effect associated with drying multiple stacks of fruit. By fitting the thin layer and system model to experimental data, a predictive model is proposed and used to explore design choices for the unglazed transpired solar collector and horizontal drying chamber used in this study. Personal experience with prototyping in Haiti led to the coupling of a simple preliminary economic model with the thin layer model to provide the predicted output per capital spent for this solar dryer design

DEVELOPMENT OF A MODULAR MOBILE SOLAR HEATER FOR APPLICATIONS IN LOW-TEMPERATURE GRAIN DRYING

Crop drying is an energy intensive process and a major cost incurred in productio