A solar assisted heat pump drying system for grain in-store drying

For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COP_S) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.     

Solar desiccant systems for grain drying

The mathematical model for the Kathabar Spray-Cel System developed by the authors in a previous work was used to predict the temperature and humidity ratio of the air at the drying bin inlet. The unsteady grain cooling model developed by Huzayyin (Ph.D. dissertation, Kansas State Univ. at Manhattan (1972); Ref. [1]) is modified and coupled with the liquid desiccant system model to study the feasibility of using the system desiccated air in drying applications. The model shows the infeasibility of using desiccated air for grain drying. The liquid desiccant system was modified to simulate adiabatic operation and coupled to the drying model. The new system gave much better results, but its use for grain drying is still predicted to be economically unfeasible.     

Optimization of a solar-assisted drying system for drying bananas

This paper presents a mathematical model for optimal design of a solar-assisted drying system for drying bananas. The optimization model consists of a simulation model of a solar-assisted drying system combined with an economic model. The simulation model is composed of two systems of differential equations: one for the collector and other for the drying cabinet. These systems of the differential equation were solved using the finite difference method. Values of the model parameters were determined experimentally. A computer program in FORTRAN was developed to simulate the performance of the drying system. The model was validated by comparing the simulation results with the experimental results and they were in good agreement. This simulation model was used for the optimization of the solar-assisted drying system. An economic model was formulated to calculate the annual drying cost. The optimization problem was defined as the optimization of the geometry and operational parameters of the drying system so as to minimize the drying cost per unit of dried product. Currently used collector area and the air recycle factor were considered as the parameters for basic mode of operation of the drying system. The adaptive pattern search technique was adopted to find the optimum values of the solar collector area and the recycle factor. The optimum values of the collector area and the recycle factor were found to be 26 m² and 90%, respectively. The computer program developed in this study can be used to optimize similar drying systems.     

The drying of grain with heat pumps in South Africa: A techno-economic analysis

The economic viability of air heating for grain drying with the aid of heat pumps and the viability of replacing existing heating methods (i.e. direct electrical heaters and diesel burners) with heat pumps are investigated. The energy costs of different types of heating apparatus to dry grain are calculated and, taking the different capital costs into account, the life cycle costs of the heating methods can be predicted. On comparing the life cycle costs of the different heating methods, it is concluded that heat pumps are more economical than other methods of heating provided that the apparatus is used for more than a minimum period per year. Drying of grain is usually done for periods shorter than this minimum; the result is that the use of heat pumps cannot be economically justified for the drying of grain only.     

A review of solar dryers developed for grape drying

This paper attempts to review various solar dryers developed exclusively for grape drying on a normal scale. Many popular varieties of solar dryers, certain typical models as well as traditional methods practiced for drying grapes are presented in this paper. Technical and economical results have proved that solar drying of grapes is quite feasible. Commercialization of solar drying of grapes has not gained momentum as expected, may be due to high initial investment and low capacity of the dryers. Even, the farmer’s acceptance of solar dryers developed is not encouraging. Exhaustive research and development work has to be carried out in order to make solar drying of grapes economical and user friendly. There has been a remarkable achievement in solar drying of grapes due to sustained research and development associated with the adoption of advanced technologies. A review of various solar drying models for grapes is thus necessitated.     

Solar drying vs. open sun drying: A framework for financial evaluation

Initiatives towards large-scale dissemination of solar dryers for drying of agri-produce face severe competition from the largely prevalent practice of open sun drying in most of the developing countries. Therefore, solar drying systems must offer exceptionally attractive financial gains to enhance their acceptance among the potential users. A modest attempt to develop a simple framework to facilitate a comparison of the financial feasibility of solar drying as against open sun drying has been made in the present work. Results of some exemplifying calculations are presented and briefly discussed.     

Technical feasibility assessment of a solar chimney for food drying

Solar dryers use free and renewable energy sources, reduce drying losses (as compared to sun drying) and show lower operational costs than the artificial drying, thus presenting an interesting alternative to conventional dryers. This work proposes to study the feasibility of a solar chimney to dry agricultural products. To assess the technical feasibility of this drying device, a prototype solar chimney, in which the air velocity, temperature and humidity parameters were monitored as a function of the solar incident radiation, was built. Drying tests of food, based on theoretical and experimental studies, assure the technical feasibility of solar chimneys used as solar dryers for agricultural products. The constructed chimney generates a hot airflow with a yearly average rise in temperature (compared to the ambient air temperature) of 13 ± 1 °C. In the prototype, the yearly average mass flow was found to be 1.40 ± 0.08 kg/s, which allowed a drying capacity of approximately 440 kg.     

Thin layer solar drying and mathematical modeling of mulberry

In this study, drying parameters of mulberry grown in Elaz?? were investigated as experimental and theoretical using solar dryer system. The drying experiments were conducted at seven different drying mass flow rates varied between 0.0015 and 0.036 kg s^?1. As results of the drying experiments were conducted at different drying mass flow rates, it was shown that the drying time was decreased with the drying mass flow rate. This paper also presents a new mathematical modeling of thin layer solar drying of mulberry samples. In order to estimate the suitable form of solar drying curves, 10 different mathematical models to be in the literature and new model were applied to the experimental data and compared according to their correlation coefficients (R) and chi‐squared (χ²), which were predicted by non‐linear regression analysis using the Statistica Computer Program. It was concluded that the Midilli model and the newly developed model represent drying characteristics better than the other models. The effective moisture diffusivity values were in the range 3.47×10^?12–1.46×10^?9 m² s^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

Design and development of a simple solar dehydrator for crop drying

In this paper, a simple solar collector cum crop drying system is described. The categorical objectives of this paper are (1) to identify a suitable medium capacity solar drying system and (2) to study analytically and experimentally the performance characteristics of this newly fabricated solar drying system. The drying ratio, rehydration ratio, culinary and organoleptic characteristics, of Methi and Bhendi crops were studied and presented in this paper.     

锂电池极片干燥系统耗能分析

介绍了锂电池极片干燥系统的组成及工作原理。根据热力学第一定律,建立了干燥系统的能量平衡分析模型。该模型描述了极片基材和涂层的升温耗能、溶剂蒸发相变耗能、干燥介质加热耗能、系统通风耗能的计算方法及其与系统总投入能之间的平衡关系。以水溶剂负极涂层的典型工况干燥过程为例进行了实际分析计算。结果表明：系统的主要耗能用于干燥介质升温,占系统总耗能的93.30%;干燥介质的能量中,用于基材、干涂层升温部分甚微,分别占0.14%和0.21%,另有6.74%用于溶剂耗能;而系统通风耗能主要用于克服干燥系统的阻力和输送干燥介质,且其在总能耗中所占比例不高,为6.70%。分析了供风量变化、极片走带速度变化等变工况与系统各项耗能的关系。为实际干燥过程中合理选择加热器功率和风机选型提供了参考依据。     

A solar assisted heat pump drying system for grain in-store drying

For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COPS) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.     

Solar—drier—desiccator system evaluation

This paper discusses the design of solar drying systems which include a desiccator as part of the cycle. The influence of the desiccator investigated and the performance of a counter flow unit is discussed.     

Design of a new solar dryer system with swirling flow for drying seeded grape

In this study solar energy supported, swirling flow new drying system is designed and artificial drying of grapes grown around Elazığ/Turkey is investigated. With the developed swirling flow dryer with airy solar collector it is examined that drying occurs homogenously and lower moisture values are obtained in when compared with classical drying system. Also it is found that with an increase in the drying air velocity decreases drying time. When air directing elements are placed inside drying chamber and rotating element to the entrance, it is examined that drying time gets shorter compared to that of natural drying. Thus, drying time which is 200 h in natural conditions decrease to 80 h with an air velocity of 1.5 m/s with the developed solar energy supported swirling flow dryer.     

A mathematical model of thermal performance of a solar air heater with slats

A mathematical model for computing the thermal performance of a single pass flat-plate solar air collector is presented. Air channels were formed by providing metal slats running along the circulated air passage linking the absorber plate by the bottom one in an endeavor to enhance the thermal efficiency of the solar air collector. A mathematical model, therefore, is developed by which the influence of the addition of the metal slats on the efficiency of the solar collector is studied. A computer code that employs an iterative solution procedure is constructed to solve for the governing energy equations to estimate the mean temperatures of the collector. The effect of volume airflow rate, collector length, and spacing between the absorber and bottom plates on the thermal performance of the present solar air heater was investigated. Furthermore, a numerical comparison of the present design with the most common type of solar air heaters is conducted. The results of the comparison have indicated that better thermal performance was obtained by the modified system.     

中密度纤维板纤维干燥系统热能应用分析

综述了当前中密度纤维板(MDF)生产过程中纤维干燥工序热能供应的工况参数,重点分析了基于热能中心能源供应模式下纤维干燥工序热能的优化应用,提出了MDF生产工艺进一步节能的设计思路.     

A study of the drying effect on lemon slices using a closed-type solar dryer

An experimental closed-type dryer associated with a photovoltaic system (PV) was developed. The transparent drying cabinet was designed with high transmittance glass to decrease the reflection of direct sunlight and to offer extra direct solar heating on the raw material during drying. Parallel wiring with a local electrical grid was necessary for switching purposes if there is insufficient battery backup during peak operation. Lemon slices were dried using the closed-type solar dryer and results were compared with hot air drying at 60 °C. The results indicate that the dried lemon slices using a closed-type solar dryer has better general levels of quality in terms of sensory parameters.     

上海市竹园污泥干化焚烧系统的能量平衡分析

结合上海市竹园污泥处理工程,根据竹园污泥干化焚烧工程的设计方案,研究了污泥干化焚烧系统的能量平衡模型。根据所建立模型的计算结果,上海竹园污泥处理工程焚烧系统可产生47×106kJ的能量,而干化机所需的能量约为57.2×106kJ,焚烧系统产生的能量不足以提供污泥干化系统所需的全部能量。     

Solar crop drying in A low humidity environment

Comprehensive field performance data are reported for solar cabinet dryers, with and without crop load, under the low humidity conditions of the local harmattan season. The field data collected provide a frame of reference for similar data on dryer performance gathered under the normal local conditions of high relative humidity. The relative humidity, it is found, plays a most decisive role in the entire drying process.