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[en] Energy from microalgae is one of the growing alternatives for traditional energy sources. However, the economic viability of processing microalgae for energy has been a major concern thus far. Microalgae slurry, typically with 85-95% initial moisture content, is perishable and must be processed immediately after harvest but drying alone will be responsible for 25-30% of the total production cost. Utilizing a solar dryer would improve the yield of the production. The study investigates the solar radiation heat transfer inside the microalgae solar dryer and determines available heat to the microalgae in the drying chamber as well as describes the airflow profile of air inside the solar dryer using the ANSYS CFD software. ANSYS CFX package was utilized to mesh and solve for the numerical solution. The drying chamber design based from Forson et al (2007) is coupled to a single-pass flat plate air heater to drive the air flow through natural convection. The simulation of the drying process of the microalgae involves heat transfer inside the solar dryer and employs the Monte Carlo thermal radiation model in a steady-state solution. Air domain temperature is set to 30°C, based on the average ambient temperature in Manila. Based on the material selected, the walls of the solar chamber are set to allow thermal radiation with a heat transfer coefficient of 50 W/m2 K. The floor of the chamber was assigned to be an adiabatic wall. Also, a constant velocity of 1 m/s at the air outlet was set to account for the density gradient at the chimney and to eliminate stagnation points inside the dryer for the initial run. The numerical results gave a maximum and minimum velocity of 1.11 m/s and 0.28 m/s. The achieved temperature range inside the drying chamber was comparable to the data published by Prakash et al. (1997). The resulting profile showed that the geometry causes air from the main flow to partially re-circulate. This is significant since residence time of air inside the drying chamber could prove to be a noteworthy factor to consider in future studies. (author)
[en] The African Energy Programme (AEP) was established by the Commonwealth Science Council (CSC) to strengthen Africa's scientific and technical capabilities to develop and utilise the continent's enormous renewable energy resources to assist its socio-economic development. The AEP was conceived at a regional workshop held at Arusha, Tanzania in 1979, at which African researchers met to share their experiences of and explored the feasibility of establishing a collaborative regional R and D programme to develop and adapt technologies appropriate to the specific needs of the participating countries. The AEP researchers accorded the highest priority to seeking solutions to the energy problems of Africa's predominantly rural populations and identified eight project areas as the nodes for regional collaborative research and development: 1. Biogas for rural development; 2. Wood/Charcoal production and utilisation; 3. Solar crop drying; 4. Solar thermal heating and cooling; 5. Wind electricity generation; 6. Wind water pumping; 7. Resources Assessments; 8. Energy policy and planning. The primary goal of the AEP activities were to develop indigenous national capabilities to enable the examination and application of technological solutions appropriate to the unique problems and socio-cultural environments of each country. However, the severe limitations on expertise and the broad similarity of many of the critical problems favoured regional R and D cooperation around common techniques and methodologies in each project area. This work has made a significant contribution to Science and Technology. Prior to this work there was no detailed information in natural convection solar dryers. This work has exposed a number of critical design factors which must be considered in order to design an efficient dryer. Buoyancy-induced pressure inside the dryer, problems of multiple radiative heat exchange in the heater and cooling effects of wind have been studied in detail. The final dryer design also has succeeded in solving the identified problems associated with the tradition sun drying techniques. One would therefore expect the demand for these dryers to be high. The actual situation is different. Farmers are not willing to spend money to acquire the dryers. Perhaps this is attributed to the fact that there is still high level of underemployment (or unemployment) of rural population and the fact that traditional drying method does not cost anything. Moreover the land area required for spreading the crops is still abundant in the rural areas. The farmers therefore appear not to appreciate the advantages of the solar dryer. Due to seasonal maize shortages which occasionally occur in Kenya, the government is now emphasizing the need to preserve cereal grains through proper drying and storage facilities. Expensive large oil-fired dryers have been imported and the government, through National Cereals and Produce Board, spends a lot of money to run these dryers. If small scale solar crop dryers were used at the farm level so that all cereal grains reaching the National Cereals and Produce Board were dry to the required moisture content for- long term storage, the government would save on the imported oil needed to operate the large industrial dryers. The individual farmer does not realize this and it is high time the government adopted a firm policy on the promotion of renewable energy devices. The policy should aim at assisting not only in educating the farmers but also in supporting researchers to disseminate knowledge about these devices. Relevant government ministries e.g. Ministry of Energy and Regional Development, Ministry of Agriculture and Ministry of Environment and Natural Resources should actively be involved in the dissemination process through Newspapers, Radio and T.V. Perhaps the Kenya National Council for Science and Technology should play a coordinating role
[en] This research paper deals with the design development and testing of a forced convection solar dryer, for drying and converting to flour of high moisture content vegetables like potatoes. The angle of solar collector was made adjustable for the absorption of maximum solar radiation by the absorber plate. The air flow rate was controlled by adjustable gate valve to find the optimum flow rate for dehydration of the product. The penetration of solar radiation raised the temperature of the absorber plate of the dryer to 110 deg. C during the operation under stagnation or no load conditions. The maximum air temperature attained in the solar air heater, under this condition was 80 deg. C. The dryer was loaded with 12 Kg of blanched potato chips having an initial moisture content of 89.75%, and the final desired moisture content of 6.95% was achieved within five hours without losing the color of potato chips, while the moisture contents reduction was from 89.75% to 33.75% for five hours in open sun drying under shade. The drying cost for 1 Kg of potatoes was calculated as Rs. 245 and it was Rs. 329 in the case of an electric dryer. The life span of the solar dryer was assumed to be 20 years. The cumulative present worth of annual savings over the life of the solar dryer was calculated for blanched potato chips drying, and it turned out be Rs.163177.67/- which was much higher than the capital cost of the dryer (Rs. 25000). The payback period was calculated as 0.89 years, which was also very small considering the life of the system (20 years). (author)
[en] Six types of solar installations for drying various agricultural products are presented: the solar drying platform, the solar dryer for granular products, the hotbed dryer, solar dryer with natural draught, radiation-convection solar dryer and solar dryer for cotton. Relative simplicity, cheapness and opportunity of use near to a place of these products cultivation are the general characteristics of these installations. The numerous long tests which have been carried out in the Scientific-Industrial Corporation [Sun] of Turkmenistan Academy of Sciences have proved their efficiency and convenience in operation
[en] A solar tunnel drier was used to dry red hot pepper under the tropical weather conditions of Bangladesh in order to investigate its performance and the quality of the drier product. The drier comprises a plastic sheet-covered flat plate collector and a drying tunnel. The drier is arranged to supply hot air to the drying tunnel using two small fans powered by a 40 watt PV module. Fresh red pepper was water blanched before drying. In each drying batch in the solar tunnel drier, 20 kg of dried red pepper with 4 to 6% moisture content (wb) was obtained from 80 kg of fresh red pepper with initial moisture content of 73 to 75% (wb) in 20 to 22 hours of drying while it took 32 to 34 hours to bring down the moisture content of similar sample to 8 to 10% (wb) in sun drying methods. The pepper dried in the solar tunnel drier was completely protected from dust, dirt, rain, insects, birds, rodents and microorganisms and it was a quality-dried product in term of colour and pungency. The solar tunnel drier is recommended for drying of pepper as well as vegetables and fruits in developing countries especially in Bangladesh
[en] The access to energy by the populations remains a primary preoccupation for the Government of Upper Volta (currently Burkina Faso). Due to this reason, a seminar on the utilization of renewable energy in rural area has been organized under the sponsorship of the Economic Community of West Africa (CEAO), the Canadian Agency of International Expansion and the Scout Movement. The goal of this seminar was to teach participants of several countries on how to put into practice the use of new sources of energy such as the cooker with closed fire, biological gas, the solar water-heater and the solar drier. The adoption of these new sources of energy by the populations would help mitigate problems of desertification caused by the intensive deforestation in the country. All the participants in this meeting are thus sensitized so that they will be able to positively contribute, along with their community, for a better conservation of the available natural resources. This can be done through the erection of closed fire cookers which can help get two sources of energy. This type of cooker is of easy construction and can be usable only three days after its construction. It helps avoid the loss of energy which has characterized the traditional way of cooking (around 95% of energy loss); this comes to rhyme with consuming less wood while ensuring an output of about 60 to 70%. It was question for the participants in this seminar to be initiated to the installation of gas by following Chinese and Indian models. They have been thus initiated to the realization of technologies of biological gas production throughout mastering the general diagram of the process of discontinuous fermentation. In the same way, they have acquired the know-how on the techniques of installation of the solar-fired heater by solar furnace and the solar drier. These tools help not only save energy but also the solar drier is a conservation tool which allows a bigger storage capacity of dry products and a volume of transport much more reduced. Mastering these new technologies will help fight efficiently against desertification, and fruits and vegetables rotting
[fr]L'acces a l'energie par toutes les populations reste une des preoccupations du Gouvernement de Haute Volta (Burkina Faso). C'est ainsi que sous l'egide de la Communaute Economique de l Afrique de l'Ouest (CEAO), de l'Agence Canadienne de Developpement International et du Mouvement Scout, un seminaire sur l'utilisation des energies renouvelables en zone rurale y a ete organise. Il s'agit pour les participants venus de plusieurs pays, d'apprendre a mettre en pratique, l'utilisation des energies nouvelles telles la cuisiniere a feu ferme, le gaz biologique, le chauffe- eau solaire et le sechoir solaire. L'adoption de ces nouvelles sources d'energie par les populations permettrait de pallier les problemes de desertification lies au deboisement intensif dans le pays. Tous les participants a cette rencontre sont donc sensibilises pour qu'ils apportent leur contribution et celle des populations de leurs terroirs respectifs pour une meilleure conservation des ressources naturelles disponibles. Cela passe aussi par la construction de cuisinieres a feu ferme qui permettent d'avoir deux sources d'energie. Ce type de foyer est d'une construction facile et utilisable seulement trois jours apres. Il permet d'eviter la perte d'energie qui caracterisait le foyer traditionnel (pres de 95% de perte d'energie) ; ce qui revient a consommer moins de bois tout en assurant un rendement de l'ordre de 60 a 70%. Il s'est agi pour les participants aux travaux de s'initier a l'installation de gaz suivant des modeles chinois et indien . Ils ont donc ete inities a la realisation des technologies de production de gaz biologique a travers la maitrise du schema de principe du procede de fermentation discontinue. De meme, ils ont acquis le savoir- faire sur les techniques de mise en place du chauffe- eau solaire par insolateur et du sechoir solaire. Ces outils permettent non seulement une economie d'energie, mais le sechoir solaire est un outil de conservation permettant une plus grande capacite de stockage des produits seches et un volume de transport plus reduit. La maitrise de ces nouvelles technologies va permettre de lutter efficacement contre la desertification et le pourrissement des fruits et legumes
[en] Drying is a very sophisticated process which consumes a large amount of energy. Solar energy can be used as an alternative or supplementary energy source to fossil fuels. Solar dryers are common ways for saving fossil fuel consumption during agricultural products drying. In this study, the performance of an active solar dryer equipped with an energy recovery system was investigated at three levels of drying air temperature. The results showed that the energy recovery system was able to increase inlet air temperature by 16.8, 18.5 and 18.9 ° C at drying temperatures of 55, 65 and 75 ℃, respectively. Meanwhile 47.8, 42.9 and 40.9 percents of the dryer exhaust air energy were recovered respectively at these conditions which subsequently led to a reduction of 30.7, 19.2 and 14.7 percents in electrical heater energy consumption.
[en] The efficient performance of a solar dryer is mainly depending on the good distribution of the thermal and flow field inside the dryer body. This paper presents simulation results of a solar dryer with a biomass burner as backup heater. The flow and thermal fields were simulated by CFD tools under different operational modes. GAMBIT software was used for the model and grid generation while FLUENT software was used to simulate the velocity and temperature distribution inside the dryer body. The CFD simulation procedure was validated by comparing the simulation results with experimental measurement. The simulation results show acceptable agreement with the experimental measurements. The simulations have shown high temperature spot with very low velocity underneath the solar absorber and this is an indication for the poor design. Many other observations have been visualized from the temperature and flow distribution which cannot be captured by experimental measurements.
[en] Drying algal biomass with the use of solar radiation is an economical and environmentally compatible option. The aim of this work was to design an indirect solar dryer with natural air circulation for seaweeds drying. The equipment supports discrete quantities of wet biomass and is protected from environmental situations that may damage the product; it does not need electricity to operate and the construction and operating costs are low. This comprises a collector made of copper plates for air circulation, heated by solar radiation, a glass cover and drying trays with a wooden structure. The dryer was designed to obtain 0, 3 kg / day of dry biomass. The methodology allows construction and operation of a flexible solar dryer in different operating conditions for research on seaweeds. Correspondingly with environmental and operating conditions the design included estimation of drying time, the determination of drying area, number of trays, air flow from the collector to the trays, collector sizing; heat transfer area, temperature reached by air and collector efficiency. (author)
[en] Highlights: ► Mushrooms (Paris variety) were dehydrated in a hybrid solar dryer. ► Effective diffusivity was estimated by the Constant Diffusivity Model. ► Drying kinetics were adjusted by a semi-theoretical and the empirical Page model. ► Temperature, thickness and air recycle significantly affected critical moisture. ► The input of solar energy resulted in 3.5–12.5% electrical energy saving. - Abstract: Mushrooms (Paris variety) were dehydrated in a hybrid solar dryer (HSD) provided with a 3 m2 solar panel and electric resistances. Mushrooms were cut in 8 mm or 4 mm thickness slices. At the outlet of the tray dryer 80–90% air was recycled and the air temperature was adjusted to the pre-defined levels (50 or 60 °C). At the outlet of the solar panel the air temperature raised between 2 and 20 °C above the ambient temperature, depending mainly of solar radiation level. Temperature, slices thickness and air recycle level had statistically significant effects on critical moisture content (Xc), as well as on the time necessary to reach a moisture content of 0.1 (wb). The color parameters of dehydrated mushroom indicate a notorious darkening, in all runs. Rehydration assays at 35 °C showed that in less than 30 min rehydrated mushrooms reached a moisture content of 0.8 (wb). Effective diffusivity (Deff) was estimated by the Simplified Constant Diffusivity Model (SCDM), and it ranged between 6E−10 and 40E−10 m2/s, with R2 higher than 0.98, agreeing with literature. The adjustment of experimental drying kinetics with the empirical Page’s model resulted in R2 higher than 0.997. Finally, the input of solar energy resulted in 3.5–12.5% energy saving. These values could even be improved by increasing the agro-product load in the HSD