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.

Pilot Scale Test to Treat High Concentration Gasification Wastewater Using Catalytic Oxidation and Aerobic Biological Fluid-Bed Combination Process

The gasification wastewater is a kind of typical organic industrial wastewater with high chemical oxygen demand （COD） and ammonia nitrogen, which could not be completely degraded by the traditional physical, chemical and biological method. So it is very important to find an effective treatment process. A combination process of catalytic oxidation with noble metal catalysts and aerobic biological fluid-bed packed with the new ultrastructure biological carriers, which was developed by ourselves, was investigated to treat the gasification wastewater. The pilot scale test with 0.5 m^3/h influent flow was carried out to investigate the performance of this new combination process. The results showed that the effluent COD was 84.02 mg/L, ammonia nitrogen was 14.15 mg/L, and total phenol was 0.20 mg/L, which could completely meet the Grade I of Wastewater Discharge Standard （GB8978-1996）, when the influent average COD was 5 564 mg/L, ammonia nitrogen was 237 mg/L, and total phenol was 1 100 mg/L. The two catalytic reactors could evidently improve the wastewater biodegradability, and the value of BOD5/COD （B/C） increased from 0.23 to 0.413 in the one-stage catalytic reactor and from 0. 273 to 0.421 in two-stage catalytic reactor. The further experiment results showed that the effluent quality of this new combination process could still meet the discharge standard, when the COD loading was 8.65 kg / （m^3· d）. Most of aromatic and heterocyclic compounds were degraded effectively in this combination process.

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.

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.

Quantifying the effect of persistent dryer climates on forest productivity and implications for forest planning:a case study in northern Germany

Background: Forest management decisions are based on expectations of future developments. For sound decisions it is essential to accurately predict the expected values in future developments and to account for their inherent uncertainty,for example the impact of climate change on forests. Changing climatic conditions affect forest productivity and alter the risk profile of forests and forest enterprises. Intensifying drought stress is seen as one major risk factor threatening forest management in the north German lowlands. Drought stress reduces tree growth and vitality and might even trigger mortality. But so far, it is not possible to quantify effects of a persistent dryer climate on forest productivity at a level suitable for forest management.Methods: We apply a well-established single-tree forest growth simulator to quantify the effect of persistent dryer climates on future forest productivity. We analyse the growth of Scots pine(Pinus sylvestris L.), European beech(Fagus sylvatico L.) and oak(Quercus robur L. and Quercus petraea(Matt.) Liebl.) in two forest regions in the north German lowlands for a time interval of 60 years until 2070. The growth response under three different climate projections is compared to a baseline scenario.Results: The results show clear differences in volume increment to persistent dryer climates between tree species. The findings exhibit regional differences and temporal trends. While mean annual increment at biological rotation age of Scots pine and oak predominantly benefits from the projected climate conditions until 2070, beech might suffer losses of up to 3 m^3·ha^(-1)yr^(-1) depending on climate scenario and region. However, in the projection period2051 to 2070 the uncertainty ranges comprise positive as well as negative climatic effects for all species.Conclusions: The projected changes in forest growth serve as quantitative contributions to provide decision support in the evaluation of, for example, species future site suitability and timber supply assessments. The analysis of productivity changes under persistent dryer climate complements the drought vulnerability assessment which is applied in practical forestry in northwestern Germany today. The projected species' productivity has strong implications for forest management and the inherent uncertainty needs to be accounted for.

Prediction of wall deposition behaviour in a pilot-scale spray dryer using deposition correlations for pipe flows

The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of a pilot-scale spray dryer was predicted using simple correlations for particle depositions in pipes. The predicted particle deposition fluxes of these materials were then compared with the measured deposition fluxes. The predicted particle deposition regimes of the spray dryer were expected to be in the diffusional and mixed (diffusional and inertial) regimes, but the experimental results suggested that the particle deposition was mainly in the inertial regime. Therefore, using the pipe correlations for predicting deposition in a pilot-scale spray dryer suggests that they do not sufficiently represent the actual deposition behaviour. This outcome indicates that a further study of particle flow patterns needs to be carried out using numerical simulations (computational fluid dynamics, CFD) in view of the additional geometrical complexity of the spray dryer.

Development and Quality Analysis of a Direct Solar Dryer for Fish

The study investigates drying characteristics of common species of fish in the tropics, catfish (Clarias gariepinus) and tilapia fish (Oreochromis niloticus) using a direct solar dryer. The drying process was carried out during the dry and wet season under natural (0 m/s) and forced convective drying (1.5 m/s, 2.5 m/s, 3.5 m/s fan speed). Results obtained showed that the drying air attained by the dryer was satisfactory and the maximum temperature difference between the dryer and the ambient temperatures was 35°C. The moisture content of the dried samples was 13.97% for catfish and 13.35% for tilapia fish during dry season and during the wet season it was 15.68% for catfish and 14.9% for tilapia fish while for the open sun dried samples it was 21.7% for catfish and 17.0% for tilapia fish. Maximum drying efficiency of 74.3% was recorded for the dryer during dry season and the dried samples at 3.5 m/s fan speed were better in drying rates. The proximate compositions of the fish before and after drying were determined. There was significant difference in proximate composition before and after drying (P < 0.05) and no significant difference in proximate composition at fan speeds considered for both fish species (P < 0.05).

Performance Analysis and Drying Kinetics of Maize in an AflaSTOP Dryer

The performance of an AflaSTOP dryer which utilises biomass energy for drying maize was investigated. The drying behaviour of maize grains in the dryer was also investigated using ten (10) thin-layer mathematical models. The models were compared based on coefficient of determination (R2) and Root Mean Square Error (RMSE) values between experimental and predicted moisture ratios. At an average drying air temperature of 50°C and drying air velocity of 2.5 m/s, maize at average moisture content (MC) of 17.5% (wb) was dried to an average MC of 11.5% (wb) in three (3) hours. The drying and thermal efficiency were calculated as 81.1% and 29.6% respectively. Overall, drying took place in the falling rate period. The Logistics model was best to describe the thin-layer drying kinetics of maize in the dryer with R2 value of 0.9902 and RMSE value of 0.04908.

Drying Temperature Effect on Kernel Damage and Viability of Maize Dried in a Solar Biomass Hybrid Dryer

Though several maize varieties have been developed and introduced over the years in Ghana, farmers still face challenges of access to quality seed maize. Among the major constraint is lack of proper drying systems to guarantee quality of seed produced. As in most parts of Africa, drying of maize in the open, on bare ground along shoulders of roads is still a common practice in Ghana. In this study, a 5-tonne capacity hybrid solar biomass dryer was developed for drying maize for seed and food/feed in Ghana. Effect of air temperature in the dryer on the physiological quality and germination of maize kernels was investigated. Maize grains were dried in the open sun simulating farmers practice and using the dryer at 4 varying levels (L1, L2, L3 and L4) with corresponding heights (0.6 m, 1.2 m, 1.8 m and 2.4 m, respectively) from the ground. Harvested maize at 22.8% moisture content was dried at the varying levels until reaching the final desired moisture content of 12.8% ± 0.2% (wb). Results showed that, air temperatures in the dryer increased in accordance with height with lowest mean temperature of 44.4&degC ± 4.6&degC recorded at L1 and mean maximum of 52.8&degC ± 5.4&degC at L4. Drying temperatures recorded at L1 - L3 and ambient had no significant effect (p < 0.05) on kernel damage and viability. Drying conditions at L1-L3 were considered optimum (<50&degC) for kernel drying compared to the topmost tray, L4. Kernel stress crack index (multiple and checked) was therefore reduced on average by 14% while kernel germination increased by 33%. This satisfies the dryer’s potential to be used for commercial drying of maize grains for seed production for smallholder farmers in Ghana.

ON A NEW DRYER FOR SLAG OR FLY-ASH

Granulated blastfurnace slag or fly-ash , as admixture of slag cement or pozzolana cement, has to be dried before it is ground with clinker, for it contains water. Here, a new dryer for drying slag or fly-ash is recommended, which is called suspension dryer.

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

Cyclone as a Sugar Cane Bagasse Dryer

Drying of sugar cane bagasse was theoretically and experimentally studied ina cyclone. The experiments were carried out using hot air as drying agent. The influence of thecyclone conical part was studied. It was shown that the conical part has a great influence on theparticle residence time and, consequently, on moisture reduction. Experimental results were alikeindustrial ones. CFX 4.4 from AEA Technology was used to simulate some experiments. Simulated andexperimental results were close and showed that the presented model leads to a good prediction.