Solar Drying of Peeled Longan Using a Side Loading Type Solar Tunnel Dryer: Experimental and Simulated Performance

This article presents experimental and simulated results of drying of peeled longan in a side-loading solar tunnel dryer. This new type of solar tunnel dryer consists of a flat-plate solar air heater and a drying unit with a provision for loading and unloading from windows at one side of the dryer. These are connected in series and covered with glass plates. A DC fan driven by a 15-W solar cell module supplies hot air in the drying system. To investigate the experimental performance, five full-scale experimental runs were conducted and 100 kg of peeled longan was dried in each experimental run. The drying air temperature varied from 32 to 76°C. The drying time in the solar tunnel dryer was 16 h to dry peeled longan from an initial moisture content of 84% (w.b.) to a final moisture content of 12% (w.b.), whereas it required 16 h of natural sun drying under similar conditions to reach a moisture content of 40% (w.b.). The quality of solar-dried product was also good in comparison to the high-quality product in markets in terms of color, taste, and flavor. A system of partial differential equations describing heat and moisture transfer during drying of peeled longan in this solar tunnel dryer was developed and this system of nonlinear partial differential equations was solved numerically by the finite difference method. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5. The simulated results agreed well with the experimental data for solar drying. This model can be used to provide the design data and it is essential for optimal design of the dryer.     

Investigation on Drying Performance and Energy Savings of the Batch-Type Heat Pump Dryer

Simulation of the heat pump cycle and the drying process has been carried out to obtain the design parameters of the dryer. The analysis indicates that a specific moisture extraction rate (SMER) greater than 3.4 kg/kWh can be obtained. A box-type heat pump dryer has been developed and investigated for the performance of drying of shredded radish. Heat pump drying took 1.0–1.5 times longer than hot air drying. However, the heat pump dryer showed considerable improvement in energy savings. The SMER of the heat pump dryer was about three times higher than that of the hot air dryer.     

Research on Modeling and Simulation of Mixed Flow Grain Dryer

Mathematical modeling and computer simulation of grain drying are the major emphasis of grain drying research in CAU (China Agricultural University). Since 1988, research on simulation of concurrent flow, counterflow, cross-flow, and mixed-flow grain dryers has been accomplished. The developed mixed-flow grain drying software has been used in analysis of dryer performance, design, and optimization of new grain dryers and management of existing ones. Effect of size, shape, number of rows, and arrangement of air duct on the performance of a mixed-flow grain dryer has been studied.     

Numerical Investigation of the Effect of Using CO2 as the Refrigerant in a Heat Pump Tumble Dryer System

CO₂ appears to be a suitable refrigerant for dryer operation conditions due to its thermophysical and environmentally friendly properties. In this study, a heat pump tumble dryer system using CO₂ as the refrigerant was theoretically investigated, and a computer model was developed using MATLAB software. The changes in the energy consumption and drying time, depending on the inlet CO₂ pressure into the gas cooler, inlet CO₂ temperature into the evaporator, air mass flow rate, and dryer efficiency, are presented. The results show that the optimum operating parameters are extremely effective in reducing the drying time and energy consumed.     

Development and Thermal Modeling of a New Construction Biomass Dryer

A new dryer construction has been developed for drying biomass basic materials for energy purposes (straw, sawdust, and other light granular materials). As a result of its simple design, the machine is perfectly suitable for reducing moisture by heat transfer. Compared to the machine types applied thus far, this new construction provides a better ratio of dryer floor space and drying distance and, as a result, a longer drying time. A differential equation system for convection drying was applied for the thermal modeling of the equipment; the mathematical model produced on the basis there of is suitable for examining the heat and mass transfer processes within the dryer. In the course of experimental measurements performed in an industrial size apparatus, the temperature and moisture content of the drying gas were recorded with the initial and final moisture content and surface temperature of the product. The measured values were compared to the results of calculations using the mathematical model.     

An Experimental Study on the Influence of Using a Draft Tube in a Continuous Spouted Bed Dryer

Further increasing the production of processed biofuel also increases the demands on drying capacity. With the aim of increasing the heat capacity flow, experimental tests have been performed on the process of drying sawdust in a continuous spouted bed dryer with nine different draft tube designs. The results showed that a draft tube with an increased length and an increased disengagement height decreased the dry substances’ flow rate throughout the dryer. The results also showed that the mass of the material in the dryer was approximately the same in all the tests. This means that the draft tubes, no matter their size, do not influence the amount of material in the dryer.     

Experimental Research on Parallel Conversion Control of Drying Temperature in a Closed-Loop Heat Pump Dryer

The paper proposes a method to handle the challenge of temperature control in a closed-loop heat pump dryer that can operate both in heating cycle and refrigeration cycle. It is hard to avoid the violent fluctuations of drying temperature as the operation mode changes. Hence, the parallel conversion control is introduced to realize the accurate control of drying temperature. The main idea of the controller design lies in the use of different membership functions and fuzzy control rules for the two operation modes. Experimental results show that the temperature fluctuations are reduced when using parallel conversion control with fast and stable response as compared to the fixed-frequency and PID control system. One of the parameters, R _f , representing the value of undershoot ratio is 0.4, 0.48, and 0.64 when drying temperature is fixed at 30, 35, and 38°C, respectively, with a parallel conversion controller. In order to study the application prospects of the parallel conversion control system, a comparison experiment with different compressor frequency ranges was also conducted.     

Investigation of Particle and Air Flows in a Mixed-Flow Dryer

Even though the mixed-flow dryer is well established on the commercial market for the drying of grain, maize, and rice, there further potential as well as a need to optimize the dryer apparatus and to improve product quality. Unfavorable designs can cause uneven mass flow and air flow distributions, resulting in locally different drying conditions and, hence, uneven grain drying. The aim of the present article is to evaluate traditional designs of mixed-flow dryers by numerical and experimental investigation of particle and air flows and to discover design deficits. For this purpose, the dryer geometry and different air duct arrangements (horizontal and diagonal) were studied using the discrete element method (DEM) and computational fluid dynamics (CFD). Drying experiments were performed to evaluate the grain moisture and temperature distributions. With regard to particle flow, a typical core flow was detected as in silos with a retarded particle flow at the dryer walls and a fast flow region in the center of the dryer. This was caused by the wall friction effect and the half air ducts fixed at the side walls. With regard to the air flow, dead zones were discovered for the diagonal air duct arrangement. Based on the design deficits identified for the traditional geometry, a new geometry for the mixed-flow dryer that is still under development is discussed.     

The Effect of Resonant Acoustic Oscillations on Heat and Mass Transfer Rates in a Convection Air Dryer

There has been much debate in recent years as to the effectiveness of enhancing heat and mass transfer rates with resonant acoustic oscillations in industrial equipment such as boilers, dryers, calciners, gasifiers, and others. This article will briefly discuss the theoretical background of acoustic drying, the setup of the experimental apparatus used to investigate the feasibility of acoustically enhanced drying, the results of these experiments, and, finally, some conclusions drawn from this work. The theoretical discussion focuses on the use of the quasi-steady assumption to estimate the potential for enhancing the heat and mass transfer rate to and from the material using acoustic oscillations. The experimental work reported focuses on the successful application of acoustical oscillations to drying a cellulose sponge, which is a material that readily transports moisture to its surface where it can be effectively dried. Also reported is the unsuccessful application of acoustic oscillations to the drying of polyethylene terephthalate, which is a saturated, thermoplastic, polyester resin made by condensing ethylene glycol and terephthalic acid and is commonly used in the manufacture of plastic food and drink containers. Reasons for success and failure in each case are discussed along with the implications of these to the successful application of acoustic oscillations to future drying applications.     

The Effect of Resonant Acoustic Oscillations on Heat and Mass Transfer Rates in a Convection Air Dryer

There has been much debate in recent years as to the effectiveness of enhancing heat and mass transfer rates with resonant acoustic oscillations in industrial equipment such as boilers, dryers, calciners, gasifiers, and others. This article will briefly discuss the theoretical background of acoustic drying, the setup of the experimental apparatus used to investigate the feasibility of acoustically enhanced drying, the results of these experiments, and, finally, some conclusions drawn from this work. The theoretical discussion focuses on the use of the quasi-steady assumption to estimate the potential for enhancing the heat and mass transfer rate to and from the material using acoustic oscillations. The experimental work reported focuses on the successful application of acoustical oscillations to drying a cellulose sponge, which is a material that readily transports moisture to its surface where it can be effectively dried. Also reported is the unsuccessful application of acoustic oscillations to the drying of polyethylene terephthalate, which is a saturated, thermoplastic, polyester resin made by condensing ethylene glycol and terephthalic acid and is commonly used in the manufacture of plastic food and drink containers. Reasons for success and failure in each case are discussed along with the implications of these to the successful application of acoustic oscillations to future drying applications.     

Comparison of Drying Kinetics of Paddy Using a Pneumatic Conveying Dryer with and without a Cyclone

The objective of the present work is to find the possibility of reducing the high initial moisture content of wet paddy using a small-scale, low-cost pneumatic conveying dryer that can be provided for each farming household. The dryer without a cyclone equipped at the exit of the dryer is studied and the data obtained from this system is compared with those obtained previously from the dryer with a cyclone. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, and drying air temperature from 35 to 70°C. From the experimental results it is found that the drying process with and without a cyclone are able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. For the same experimental conditions, the cyclone-equipped dryer gives around 1% higher decrease of moisture content, 2°C higher average surface temperature of paddy, 3-4% higher average percentage of head rice yield, and 2 kg/h higher average evaporation rate. However, the energy consumption per evaporated mass of water is 20-30% lower than the non-cyclone-equipped dryer.     

Comparison of Drying Kinetics of Paddy Using a Pneumatic Conveying Dryer with and without a Cyclone

The objective of the present work is to find the possibility of reducing the high initial moisture content of wet paddy using a small-scale, low-cost pneumatic conveying dryer that can be provided for each farming household. The dryer without a cyclone equipped at the exit of the dryer is studied and the data obtained from this system is compared with those obtained previously from the dryer with a cyclone. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, and drying air temperature from 35 to 70°C. From the experimental results it is found that the drying process with and without a cyclone are able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. For the same experimental conditions, the cyclone-equipped dryer gives around 1% higher decrease of moisture content, 2°C higher average surface temperature of paddy, 3–4% higher average percentage of head rice yield, and 2 kg/h higher average evaporation rate. However, the energy consumption per evaporated mass of water is 20–30% lower than the non-cyclone-equipped dryer.     

Experimental Study and CFD Modeling of Wall Deposition in a Spray Dryer

The wall deposition phenomenon in a pilot-scale spray dryer was investigated based on mathematical modeling and experimental trials. For this purpose, the governing equations were obtained and solved numerically by applying a mathematical modeling technique and an open-source computational fluid dynamics (CFD) software. The wall deposition, velocity distribution of the existing phases, and droplet trajectory in the drying chamber were determined. The effect of the operating parameters including the feed flow rate, inlet concentration of dissolved solid, and initial droplet diameter on the air flow pattern, droplet trajectory, and wall deposition was investigated. Through the experiments, the wall deposition of powder product in different positions of the drying chamber was measured. In modeling part of this study, we attempted to determine the effect of particle diameter on the percentage of wall deposition and the position where it occurred.

The model results obtained for wall deposition were compared with collected experimental data and good agreement was observed.     

Subcritical Water Reaction Behavior of D‐Glucose as a Model Compound for Biomass Using Two Different Continuous‐Flow Reactor Configurations

Recently, cellulosic materials have been considered as a useful resource for the recovery of valuable chemicals and liquid fuels, etc. Cellulose is a homopolymer of D ‐glucose, which is often used as a model compound for biomass. Reactions of D ‐glucose in subcritical water as the reaction solvent were conducted using a single‐flow‐type reactor ( S1 ) and an admixture‐type reactor with feed and preheated‐water flow ( S2 ) at temperatures from 200 to 240 °C, pressures from 15 to 20 MPa, residence times from 40 to 120 s, and initial feed concentrations of 1.5–10 wt %. D ‐Glucose was converted into aldehydes, organic acids and furans, with mainly organic acids obtained at 240 °C. D ‐Glucose decomposition using reactors S1 and S2 revealed that the conversion rate of D ‐glucose was promoted more using S2 than by S1 . The yield of furans with S1 was higher than with S2 , while the yield of organic acids from S1 was lower than that from S2 .     

Performance Study of a Closed-Type Heat Pump Tumble Dryer Using a Simulation Model and an Experimental Set-Up

In the interests of competitiveness, manufactures of tumble dryers are seeking to reduce both their electricity use and the drying time. This study examines how the cylinder volume of the compressor and the total heat transfer of the condenser influence the drying time and electricity use in a heat pump tumble dryer. A transient simulation model was developed and compared to an experimental set-up with good similarity. The simulations show that increasing the cylinder volume of the compressor by 50% decreases the drying time by 14% without using more electricity.     

Numerical Simulation of Monolithic Catalysts with a Heterogeneous Model and Comparison with Experimental Results from a Wood‐fired Domestic Boiler

An increased utilization of biomass for heat and power production contributes to reduced emission of the greenhouse gas CO₂. However, when combusted in small‐scale units, such as domestic stoves and boilers, the emissions of unburned gases, i.e. CO and light and heavy hydrocarbons, tend to be high. An attractive solution to reduce these emissions is the integration of oxidation catalysts. In this paper the development of a multidimensional heterogeneous mathematical model for the simulation of one channel in a monolithic catalyst is presented. The results of the simulation are compared with experimental data from a wood fired domestic boiler in which a monolithic catalyst has been integrated. The results show that the mass transfer inside the channels limits the conversion and that segmentation of the monolithic catalyst may therefore significantly increase the conversion. A good agreement between the simulation and the experimental data was achieved, for both the segmented and the unsegmented catalyst, and the model was proven to be a valuable tool for the optimization of the catalyst design.     

Simulation Model for the Model-Based Control of a Biofuel Dryer at an Industrial Combined Heat and Power Plant

The primary aim of this article is to present a simulation model for a bark dryer integrated into a combined heat and power plant. The same model can be used for the model-based control of the dryer. The secondary aim is to evaluate how useful the control is from an economic point of view. Results show that the final fuel moisture content can be stabilised by controlling the drying temperature(s). On the other hand, the deviation in final bark moisture decreases even when the dryer has no control at all. Net incomes resulting from drying increase in most cases compared to dryers without control. The need for control cannot be justified on economic grounds.     

Simulation Model for the Model-Based Control of a Biofuel Dryer at an Industrial Combined Heat and Power Plant

The primary aim of this article is to present a simulation model for a bark dryer integrated into a combined heat and power plant. The same model can be used for the model-based control of the dryer. The secondary aim is to evaluate how useful the control is from an economic point of view. Results show that the final fuel moisture content can be stabilised by controlling the drying temperature(s). On the other hand, the deviation in final bark moisture decreases even when the dryer has no control at all. Net incomes resulting from drying increase in most cases compared to dryers without control. The need for control cannot be justified on economic grounds.     

An Experimental Study of Wheat Drying in Thin Layer and Mathematical Simulation of a Fixed-Bed Convective Dryer

Drying of wheat (Algerian cultivar: Hadba03) in thin layers was studied and mass flux phenomenon was used to characterize the thin-layer drying process. Thin-layer drying of wheat was determined for drying air temperature range of 40–60°C, relative humidity of drying air from 10 to 30%, air velocity of 0.7 m/s, and initial grain moisture from 26 to 31% (dry basis). Equilibrium moisture content of wheat was determined using desorption isotherms obtained from the thin-layer drying data. An equilibrium model for a stationary deep bed with drying air moving vertically upward was developed using mass and energy balance between grain and drying air in the bed and drying air characteristics obtained from thin-layer drying experiments. The developed model was validated by drying wheat in a laboratory dryer using different drying air temperatures and initial moisture contents.     

Fluid Dynamics in Concurrent Rotary Dryers and Comparison of their Performance with a Modified Dryer

The present work analyzed aspects of the fluid dynamics of the conventional concurrent dryer equipped with lifting flights and their influence on the performance of a rotary dryer. The drying of granulated fertilizers (GTSP) in a conventional concurrent rotary dryer was experimentally investigated and compared with a modified configuration known as the roto‐aerated dryer. The main feature of this new dryer is the presence of an aerated system consisting of a central pipe (encased in the drum) from which a series of mini‐pipes lead hot air directly to the particle bed, flowing at the bottom (without flights). The results obtained confirm the superior performance of the roto‐aerated dryer due to its more effective gas‐particle contact.