A Comprehensive Review of Design and Technological Advancements across Various Types of Solar Dryers

This analysis investigates the widespread use of solar drying methods and designs in developing countries,particularly for agricultural products like fruits,vegetables,and bee pollen.Traditional techniques like hot air oven drying and open sun drying have drawbacks,including nutrient loss and exposure to harmful particles.Solar and thermal drying are viewed as sustainable solutions because they rely on renewable resources.The article highlights the advantages of solar drying,including waste reduction,increased productivity,and improved pricing.It is also cost-effective and energy-efficient.The review study provides an overview of different solar drying systems and technologies used in poor nations,aiming to identify the most effective and efficient designs.The focus is on comparing current models of solar dryers for optimal performance.The review underscores the importance of solar drying as a long-term,eco-friendly approach to drying food in developing countries.This review aims to evaluate how using solar-powered drying techniques can enhance food preservation,minimize waste,and enhance the quality and marketability of agricultural goods.The paper will specifically focus on examining the efficacy of these methods for drying bee pollen and pinpointing where enhancements can be made in their advancement.

Review:Resuspension of wall deposits in spray dryers

Wall deposition occurs in spray dryers when dried or partially dried particles contact and adhere to the walls during operation, thus reducing the yield of product collected. Wall deposits also present a product contamination risk and a fire or explosion risk when spray drying products that oxidize exothermically, such as milk powder. Re-entrainment is the resuspension of spray dryer wall deposits into the main gas stream for collection as product. Literature suggests that the process for re-entrainment of particles from spray dryer wall deposits is strongly dependent on particle size and gas velocity.

Optimizing Solar Drying: A Critical Review of Shapes, Orientation, and Future Prospects for Hybrid Solar Dryers

This comprehensive review focuses on the performance of solar dryers, with a specific emphasis on their structural shape and orientation. Researchers have extensively examined these design parameters, often employing Computational Fluid Dynamics (CFD) to assess thermal attributes and predict temperature distribution, airflow patterns, and temperature profiles within the structures. Geographical location significantly influences solar dryer shape preferences, with the parabolic shape finding favor in tropical regions for its superior solar radiation capture and storm resistance, while even-span and Quonset shapes are popular elsewhere. Solar dryer orientation is another crucial factor, with east-west alignment consistently proving optimal due to its ability to maximize year-round solar radiation absorption and, consequently, enhance drying efficiency. Economic considerations, however, fall beyond the scope of this review, which predominantly focuses on thermal aspects. This investigation reveals diverse global preferences for solar dryer shapes and orientation, highlighting the necessity of considering geographical factors in design choices. While CFD and shape/orientation dynamics have provided valuable insights, there remains room for future research to expand into transient state simulations under various conditions, contributing to a more comprehensive understanding of solar dryer performance. Such insights promise to promote sustainable and efficient drying processes, benefitting agricultural and drying applications across the globe.

Industrial and Small-Scale Biomass Dryers:An Overview

The quality of the drying process depends mainly on the efficient use of thermal energy.Sustainable systems based on solar energy takes a leading role in the drying of agro-products because of low operating cost.However,they are limited in use during off–sun periods.Biomass dryer is one of the simplest ways of drying because of its potential to dry products regardless of time and climate conditions.The other benefit is that crop residues could be used as fuel in these systems.However,the major limitation of the dryer is unequal drying because of poor airflow distribution in the drying medium,which can be improved by integrating some design changes in the dryer.This review analyses the two types of biomass dryers:industrial biomass dryers and small biomass dryers for food product,along with their efficiency.Further,studies on technical,sustainability and economic aspects are expected to provide a greater understanding of biomass drying.

Drying of Fish Sardines in Oman Using Solar Tunnel Dryers

This paper deals with the design, construction and performance evaluation procedure of a solar tunnel dryer in drying fish. A 12 meter long and 2 meter width half-circled tunnel was designed and constructed to dry about 50-100 kg of freshly harvested fishes per batch. The half of the tunnel base was used as the flat plate air heating solar collector and the remaining half as a dryer. The drying air was forced from the collector region （north side） to the drying region （south side） of the half circled tunnel where the product is to be dried. The drying temperature could be easily raised by some 5-30 ℃ above the ambient temperature inside the tunnel at an air velocity of approximately 0.2 m/sec. The test was conducted with 51.5 kg freshly harvested sardines （hall-load） with initial moisture content of 66.5% （wet-basis） to analyze the performance of the dryer. The fishes were dried to a final average moisture content of 15.5% （wet-basis） within three days （30 hours）. It was possible to reach the moisture content level for safe storage within less than three days （30 hrs） with solar tunnel dryer and 7 days in open air natural sun drying. The improvement in the quality of fishes in terms of color, brightness, flavor, and taste and food value was distinctly recognized.

Research on Cassava Drying, Application and Promotion of the Reversible Airflow Flatbed Dryers for Sliced Cassava

The study was conducted by researchers of the Research Center for Agricultural Energy and Machinery （CAEM） of the Ho Chi Minh City Nong Lam University （NLU） with the objectives of researching on drying ways for cassava and of evaluating the adaptability of the reversible-airflow dryers in drying of cassava. The results obtained were as follows： done with thin-layer drying experiments, deep-layer drying experiments in the lab, and conducted drying experiments at the cassava dryer in actual production scale with two capacity sizes of 8 tons/batch and 16 tons/batch, that operates based on principle of reversible-airflow drying （SRA dryers）. By the means of drying experiments, the performance of the SRA dryers such as optimal drying temperature, drying time, drying airflow reversal timing, moisture content uniformity of the sliced cassava mass after finishing drying process, drying cost, etc. was defined, the optimal drying temperature was 70 ~C, the total actual drying time for finishing one batch was 25-28 hours, applicable time for drying airflow reversal was after drying 16 hours since startup, the deviation in moisture content of the cassava mass after drying was just 2%-3%, the drying costs （per one kg of dried cassava） calculated were in turns VND407/kg at the SRA-8 dryer （8 tons/batch）, and VND351/kg at the SRA-16 dryer （16 tons/batch）. Obviously, comparing with the sale price of dry cassava at present, these levels of drying cost are accounting for 7%-10%, which are suitable and acceptable. Thus, investment of the dryers for sliced cassava would be effective and contribute to bring more income for Vietnamese cassava farmers and dryer end-users.

Recent trends on energy-efficient solar dryers for food and agricultural products drying:a review

The energy efficiency enhancement of solar dryers has attracted the attention of researchers worldwide because of the need for energy storage in solar drying applications,which arises primarily from the irregular nature of solar energy that leads to improper drying which will reduce the quality of the products being dried.This work comprehensively reviews the state-of-the-art research carried out on solar dryers for energy efficiency enhancement using various alternative strategies,including hybrid solar dryers that use auxiliary heating sources,such as electric heaters or biomass heaters,solar-assisted heat pump dryer,use of desiccant materials,and heat storage systems that use both sensible and latent heat storage.The advent of phase change materials(PCM),such as thermally and chemically stable PCMs,for long-term storage,bio-degradable and bio-compatible PCM materials to alleviate the negative environmental impact of conventional PCMs is also presented.The performance parameters considered for evaluating dryers include the maximum temperature attained inside the drying chamber,drying time and efficiency,specific moisture extraction rate(SMER),energy and exergy efficiency and CO_(2) mitigation effect.The factors considered to analyze the PCMs application in solar dryers include cost and sustainability of PCMs,and both energy and exergy analyses of dryers using PCMs.The gaps in current knowledge and future scope for further improvement of solar dryers are also elucidated.

Sustainability assessment of solar drying systems:a comparative life-cycle analysis of phase-change material-based vs.cylindrical solar dryers

Solar drying systems are becoming a popular alternative to traditional energy-based drying systems for agricultural products due to their effectiveness and reduced fuel consumption.Although the efficiency of solar drying systems has been thoroughly investigated,their sustainability has not been studied enough.This study aims to fill that gap by conducting a life-cycle assessment of two new solar drying systems built in Udaipur,Rajasthan,India.The environmental implications of an innovative cylindrical solar-assisted drying system and a phase-change material-based solar drying system were evaluated using cradle-to-gate life-cycle analysis.The study uses the ReCiPe 2016 endpoints(H)technique to calculate various aspects such as midpoint,endpoint,single score,normalization result,and network diagram for phase-change material-based solar drying and cylindrical solar-assisted drying.Results show that phase-change material-based solar drying has an average of 40%more impact on the environment than cylindrical solar-assisted drying,with a high impact found in human non-carcinogenic toxicity,mainly due to the production of phase-change materials.However,cylindrical solar-assisted drying system crossover phase-change material based solar drying in terms of its impact on human carcinogenic toxicity and fossil resource scarcity.The contribution to global warming of phase-change material-based solar drying is 13.7%more than that of cylindrical solar-assisted drying.The endpoint characterization indicates that phase-change material-based solar drying exceeds in terms of human health(40%)and ecosystem(37.04%),whereas cylindrical solar-assisted drying surpasses phase-change material-based solar drying in terms of impacts on resources,at 14%.The early drying in phase-change material-based solar drying makes up for its higher impact than that in cylindrical solar-assisted drying,which takes 3 hours longer to dry.This study offers guidance and methods for making the best choice of solar-powered dryers.

Analysis and survey of the application of solar dryers in eastern Nigeria

A survey on the use of solar dryers for drying purposes was carried out in some communities in eastern Nigeria.The objective of the study was to ascertain the extent uses of solar dryers by local farmers and the rural populace.The survey method included oral interview and questionnaire administration.The results of the study revealed that the practical use of solar dryers is absent domestically and industrially.However,great enthusiasm was shown by the farmers in the use of solar crop dryers if their performance is satisfactory with respect to quality and quantity of products dried at a given time interval.Most farmers rejected the idea of establishing communally maintained and operated systems but preferred commercialized systems where payments are made per unit quantity of products dried.The study therefore recommends the development of affordable solar crop dryers with auxiliary heat sources to mitigate the effects of daily and seasonal fluctuation in solar radiation in order to cope with the demands of a profit oriented commercial drying system.Such a system holds a lot of promises for entrepreneurs.

Some construction parameters of unglazed perforated solar dryers for medicinal plants

Erecting solar dryers for medicinal plants require the best design option to suit such plants.Investigations were carried out on some design parameters of the unglazed perforated solar dryers under the prevailing weather conditions of Ismailia,Egypt.Effects of different parameters on the heat exchange effectiveness were investigated.Parameters considered in this study including hole(perforation)diameters,dimensions apart,material being used and its thickness all were investigated to reveal the effects of suitable suction velocity,prevailing wind speed and its direction under the simulated incident solar radiation of the investigation site.Based on the obtained results for heat exchange effectiveness under controllable conditions,solar drier was built and investigated outdoors under the prevailing weather conditions of the investigation site.Holes diameter of 3 mm for all the investigated plates and under the different conditions resulted the highest obtained heat exchange effectiveness.Diamond shape for Holes distribution with dimensions of 29 mm×29 mm apart gave higher heat exchange effectiveness above the commonly used distribution(square shape).Temperature increase above ambient per unit of incident radiation was found as(0.0162±0.0007)℃m^(2)/W,when the best designed performance was investigated in the open environment.Using that perforated surface as an absorber in constructed dryer to dry Rosemary(Rosmarinus officinalis L.),reduced the moisture content from 65%(wet basis)to 38.1%on eight hours on the first drying day of the 18th April,2010 while the reduction in moisture content of the sample dried in the shade area was from 65%(wet basis)to 42.2%under the same prevailing weather conditions at the same time.

Feasibility Study of R134a/R404a Cascade Heat Pump Cycle in Heat Pump Dryers with Electrical Heaters at Low Temperatures

Heat pump cycles have been widely applied to dryers for their high efficiency. However, low–efficiency electrical heaters are often used during early drying stage for frozen foods or winter since a standard heat pump cycle cannot operate at low temperature. This study introduced cascade heat pumps replacing electrical heaters to improve dryer performance at low temperatures. Experiments were performed to examine changes in performance of the cascade heat pump dryers in relation to ambient temperature, low-stage cycle mass flow rate, and high-stage cycle mass flow rate. The results showed a significant improvement in low-temperature dryer performance with the introduction of cascade heat pump cycles.

Drying rates of some fruits and vegetables with passive solar dryers

Two passive solar dryers were designed and constructed with available local materials.The passive solar dryers which were direct and indirect types were tested with pepper(Capsicum annum L.),okro(Abelmoschus esculentus L.)and vegetables(Amaranthus hybridus L.)in order to evaluate the drying rate of these produces.The moisture content of 78.9%(w.b.)for 180 g freshly harvested peppers was reduced to 24.0%(w.b.).The drying rate in the direct passive solar dryer was found to be higher than the indirect passive solar dryer.The initial moisture content of 92%(w.b.)for 1000 g okro was reduced to 20%(w.b.).The drying rate in the direct passive solar dryer was also found to be higher than in the indirect passive solar dryer.The initial moisture content of 90%(w.b.)for 400 g vegetable was reduced to 20%(w.b.).The drying rate with the direct passive solar dryer was found to be higher than that with indirect passive solar dryer.During the course of drying,after each crop was kept inside the drying system,the temperature of the drying was monitored at an-hour interval;the moisture content was also monitored at a three-hour interval until there was no more change in the weight of the crop.The crops dried faster with the direct passive solar dryer than with the indirect passive solar dryer.As a result of the highest temperature attained in the direct passive solar dryer,the rate of moisture removal was the highest in this dryer.

Mathematical Modelling and Design of Helical Coil Heat Exchanger for Production of Hot Air for Fluidized Bed Dryer

In global industrialization, efforts have been made to increase the rate of heat transfer in heat exchanger, minimizing the size of heat exchanger to reduce cost as well as increasing the effectiveness. Helical coil heat exchanger (HCHE) has been proven to be effective in improving heat transfer due to its large surface area. In this study, HCHE was designed to provide hot air needed for fluidized bed drying processes. The HCHE design model was fabricated and evaluated to study the efficiency of the hot air output for a laboratory fluidized bed dryer. The mathematical model for estimation of the final (output) temperature of air, Taf, passing through the HCHE was developed and validated experimentally. The drying of bitter kola particulates was carried out with a drying temperature of 50C 3C and a bed height-to-bed diameter ratio (H/D) of 1.5. The time taken to dry bitter kola particulates to 0.4% moisture content was 1 hour 45 minutes. Hence, HCHE is recommended for use in the production of hot for laboratory-scale fluidized bed dryers.

Experimental Study and Thermal Modelling of Cocoa Shell Convective Drying in an Indirect Solar Dryer

The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.

Heat and Mass Transfer for a Nanofluid Flow in Fluidized Bed Dryer in Presence of Induced Magnetic Field

This research entails the study of heat and mass transfer of nanofluid flow in a fluidized bed dryer used in tea drying processes in presence of induced magnetic field. A mathematical model describing the fluid flow in a Fluidized bed dryer was developed using the nonlinear partial differential equations. Due to their non-linearity, the equations were solved numerically by use of the finite difference method. The effects of physical flow parameters on velocity, temperature, concentration and magnetic induction profiles were studied and results were presented graphically. From the mathematical analysis, it was deduced that addition of silver nanoparticles into the fluid flow enhanced velocity and temperature profiles. This led to improved heat transfer in the fluidized bed dryer, hence amplifying the tea drying process. Furthermore, it was noted that induced magnetic field tends to decrease the fluid velocity, which results in uniform distribution of heat leading to efficient heat transfer between the tea particles and the fluid, thus improving the drying process. The research findings provide information to industries on ways to optimize thermal performance of fluidized bed dryers.

Design and Development of a Parabolic Trough Solar Air Heater for a Greenhouse Dryer

Design and Development of a Parabolic Trough Solar Air Heater (PTSAH) for a Greenhouse Dryer (GD) was done to improve the dryer’s performance. The materials used for the fabrication of the PTSAH included galvanized sheets covered with aluminium foil, an absorber tube made of GI pipe painted matt black to increase heat absorbance at the focal line, mild steel square tubes, shutter plywood, and an axial fan to push air through the absorber tube. Key geometrical parameters used for the design of the PTSAH were a rim angle of 98 degrees, focal length of 0.2608 m, height of 0.3451 m, length of 2 m, and an aperture width of 1.2 m. The PTSAH’s total aperture surface area was 2.4 m2, while its absorber tube surface area was 0.1587 m2. The PTSAH was experimentally tested to establish its thermal performance. It was found that the ambient air recorded an average value of 31.1˚C and that the air heater could increase the air temperature by 45.6˚C above ambient with a thermal efficiency of 5.3%. It can, therefore, be concluded that the PTSAH can significantly improve the performance of a GD by supplying the GD with air at a higher temperature than ambient.

Development and Experiment of Multi- functional Wood Dehumidification Dryer

A multi functional wood dehumidification dryer has been developed recently. The dryer can carry out air dehumidification by using only one refrigeration system, in which heat supplying and moisture air are exhausted by changing the position of several air dampers. In this paper, the work principles and characteristics of the dehumidification dryer are introduced, and the testing results about the thermal engineering performance of the dehumidification dryer, as well as the experiment results of drying several species of lumbers are expounded.

Hydrodynamics of Continuous Spiral Dryer with Rotatory Conical Sleeves: Experiments versus CFD Simulations

In this study, a continuous and airtight twin-spiral dryer was developed in accordance with the characteristics and challenges in the process of disposing polysilicon slurry. Computational fluid dynamics (CFD) simulations were used to investigate the flow field in the rotating twin-spiral continuous dryer and an original discrete phase model was also elaborated to compare with the cold-modeling experimental results. The corresponding flow field was obtained using the available inlet velocity of 0.05–0.3 m/s and the rotational speed of the inner cone of 12–44 r/min, the residence time distribution, and tracked particles trajectory. Results showed that the residence time of the tracer particles in the cone cylinder was about 15.8–25.4% of the time spent out of it, and the particle’s residence time was much shorter in contrast to the rotational speed and inlet velocity. The external ribbon had a larger influence on the fluid, thereby leading to a larger velocity in the region outside the cone compared to that in the region inside the cone. In addition, the appearance of the vortex and boundary layer separation at the back of the ribbon and the spoke bar had secondary diversion effects on the fluid. Furthermore, the inlet velocity had little influence on the flow field while the rotational speed of the cone greatly affected the flow field. Hence, the CFD simulations showed good agreement with the experimental results. © 2017 Tianjin University and Springer-Verlag GmbH Germany

Evaluating Low Cost and Sustainable High Quality Cassava Drying Technologies among Small and Medium Processors in Uganda

Cassava regarded as a white gold of Africa is driving the agricultural commercialization and industrialization with small to medium technologies in Uganda. There is an over-whelming demand for high quality cassava flour （HQCF） by Bakeries, beverage industry, paper board and composite end markets. The end market for HQCF dictates on its quality attributes and rewards for its quality in terms of price offered within their minimum standards. However, obtaining sustainable amounts of HQCF for these markets calls for devoted efforts. Limited types of HQCF processing technologies exist and if they exist, their efficiency, costs and sustainability are not well understood. We evaluated high quality cassava drying technologies in Northern and Eastern Uganda in two years using naturally ventilated wooden screen solar drying structures and open air sun drying structures. Naturally ventilated wooden screen solar dryers produced clean dry high quality cassava chips free off insect and bird contamination and caused faster drying to less than 14.3% MC in 1.5 hours than open outside drying conditions. We recommend naturally ventilated wooden screen solar dryers for small and medium cassava processors during dry and rainy season. Halftone to one tone cassava chips dryers per day drying unit can cost one 2,258-4,338 USD to make it functional. Also open outside raised metallic racks with black surface can give good results on a good sunny day especially for starters on small scale basis. A small durable unit of 150 kilograms per day can be made with 500 USD.

Iodine Determination by Microwave Plasma Torch Atomic Emission Spectrometer Coupled with Online Preconcentration Vapor Generation Technique

This article focuses on iodine determination by microwave plasma torch atomic emission spectrometry （MPT-AES） coupled with online preconcentration vapor generation method. A new desolvation device, multistrand Nafion dryer, was used as the substitute for condenser desolvation system. Some experimental conditions, such as preconcentration time, acidity of sample solution, rinsing solution acidity and dynamic linear range were investigated and optimized. The new desolvation system eliminates the problem of decreasing emission intensity of I（I） 206.238 nm line with the increase of working time on a conventional condenser desolvation system, thus greatly improving the reproducibility.