ON THE STUDY OF TIME-VARYING TEMPERATURE DRYING—EFFECT ON DRYING KINETICS AND PRODUCT QUALITY

ABSTRACT

The ability of heat pump dryer to produce controlled transient drying conditions, in terms of temperature, humidity and air velocity, has given it an edge over other drying systems. Exploiting this characteristic, we studied and compared the effect of different temperature-time profiles on the quality of agricultural products in a tunnel heat pump dryer capable of providing up to 14.6 kW of cooling capacity. The product quality refers to the color change of the products. Samples of banana and guava were dried in batches in a two-stage heat pump dryer. The effects of the starting temperature of a selected profile and the cycle time on both drying kinetics and product quality were studied. It was observed that by employing a step change in drying air temperature with the appropriate starting temperature and cycle time, it was possible to reduce significantly the drying time to reach the desired moisture content with improved product color.     

ON THE STUDY OF TIME-VARYING TEMPERATURE DRYING—EFFECT ON DRYING KINETICS AND PRODUCT QUALITY

The ability of heat pump dryer to produce controlled transient drying conditions, in terms of temperature, humidity and air velocity, has given it an edge over other drying systems. Exploiting this characteristic, we studied and compared the effect of different temperature-time profiles on the quality of agricultural products in a tunnel heat pump dryer capable of providing up to 14.6 kW of cooling capacity. The product quality refers to the color change of the products. Samples of banana and guava were dried in batches in a two-stage heat pump dryer. The effects of the starting temperature of a selected profile and the cycle time on both drying kinetics and product quality were studied. It was observed that by employing a step change in drying air temperature with the appropriate starting temperature and cycle time, it was possible to reduce significantly the drying time to reach the desired moisture content with improved product color.     

MODELING AND OPTIMIZATION FOR DESIGN UNDER PRODUCTION PLANNING CRITERIA IN MULTIPRODUCT DEHYDRATION PLANTS

ABSTRACT

The design problem of a multiproduct dehydration plant involving continuous conveyor-belt dryers utilised for the dehvdration of agricultural products over a fmite tim horizon, is presented. The peculiarities of the problem under demand-varying market patterns and time-variable market prices of raw materials are underlined. Limitations imposed by storage capacity, custormer orders, and constraints dictated by the process itself, are also taken into consideration. The overall problem is cast into a MINLP formulation involving the total annual cost of the plant as its objective function. This was infered by deducing the mathematical model of conveyor-belt dryers. Repeated evaluation of the total annual cost for various structures and operating points, allowed the determination of overall performance characteristic operational and structural curves. approximated by suitable mathematical expressions. A test case is presented in order to demonstrate the effectiveness of the proposed approach.     

Study of hybrid dryer prototype and its application in pregerminated rough rice drying

In this study, a hybrid dyer, combining heat pump drying (HPD) with fluidized bed drying (FBD) concepts were designed and fabricated. The pregerminated rough rice (pre-GRR) was dried in multistage using this hybrid dryer to compare with the single-stage drying by hot air dryer. The objectives were to test the application of this hybrid dryer and determine the suitable drying condition for pre-GRR. The result indicated that the punched plate distributor was the most suitable distributor. The pre-GRR should be dried by the three-stage drying method using either FBD or HPD at 45°C in the last stage to obtain higher head rice yield, lower fissure grain, and better color values than their counterparts. The scanning electron micrographs proved that starch gelatinization occurred when applying FBD at temperatures between 100 and 140°C causing the adhesive connections inside the kernels and subsequent decrease in fissures.     

两段节流蒸发两段压缩热泵干燥装置模拟分析

为提高干燥后期干燥速率、降低能耗,提出了两段节流蒸发两段压缩热泵干燥装置的构想。模拟分析了以R134a为热泵工质、采用卧式流化床干燥机时,蒸发器1中工质蒸发温度te1、蒸发器2中工质蒸发温度te2、冷凝温度tc、两股空气质量流量比r(q1/q2)对制热系数COPH、除湿能耗比SMER的影响规律。结果表明:r=1,tc1=75℃,te2=15℃时,te1由15℃提高到25℃,COPH值由2.40提高到2.75,SMER由1.46 kg/(kW·h)提高到1.82 kg/(kW·h);tc1=75℃,te1=25℃,te2=15℃时,r由0.5提高到3.0时,COPH值由2.44提高到2.62,SMER由1.26 kg/(kW·h)提高到1.96 kg/(kW·h);在模拟条件范围内的COPH为2.40-3.01,SMER为0.89~1.96 kg/(kW·h)。     

Effects of Component Arrangement and Ambient and Drying Conditions on the Performance of Heat Pump Dryers

Performances of five heat pump dryer (HPD) configurations were studied by computer simulation. The component arrangement covers the fully open, the partially open, and the fully closed systems with external condenser or external cooler. The HPD performance was investigated for high and low drying rate and within the ambient temperature range of 20°C to 40°C. The best operating mode of the HPD depends on both drying rate and ambient condition. For the case of tropical climate and high drying rate, the partially open system is the optimum operating mode in general, except at some particular conditions where the fully open and fully closed systems are recommended. However, the operation for the low drying rate is more complicated, as the optimum configuration is sensitive to the change of ambient temperature.     

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.     

新型节能圆盘干燥器的开发与应用

干燥作业是耗能大户。热传导式多层圆盘干燥(冷却)器在节能方面具有显著优势。介绍了该干燥(冷却)器的设计、功能及其应用,并进行了经济性评价。     

Experimental analysis and CFD simulation of infrared apricot dryer with heat recovery

Drying is one of the easily accessible and the most widespread processing technologies that have been used since ancient times for preserving fruits. Drying is an energy-intensive and time-consuming process, so reducing energy demand is important. The main aim of this paper is to analyze the heat and mass transfer characteristics of product in the drying chamber and in addition to this, three-dimensional (3-D) computational fluid dynamic (CFD) simulation was performed. The analyses of heat and mass transfer were investigated theoretically and experimentally in infrared dryer (IRD). The dryer consists of air to air heat recovery unit and proportional temperature controller. Experiments were performed at 0.5 and 0.25?m/s air velocities and at 60 and 65°C apricot surface temperatures which were controlled by three thermocouples contacted on top side of the product. In order to use energy more effectively and improve the drying characteristics of apricot, analyses were performed under different drying conditions. Since the heat recovery unit has a key role in this system, the performance of this unit was investigated and recovered energy ratio was between 58 and 62%. The calculated moisture diffusivity values varied from 1.7?×?10^?10 to 1.15?×?10^?9 for apricot, and the highest value of average energy efficiency was obtained as 16.43% at 65°C temperature and 0.25?m/s air velocity. Theoretical and experimental results are in line with each other.     

落叶松太阳能热泵干燥特性研究

本文介绍了一种木材太阳能热泵干燥装置及其三种不同的运行方式,并以落叶松为试材,通过两组对比实验,分析干燥介质与干燥箱内的温度变化以及木材含水率变化之间的关系。结果表明太阳能水源热泵联合干燥的优化比传统干燥节能约76．7％,太阳能水源热泵联合干燥比传统干燥节能约66．2％,优化模式比只用太阳能水源热泵联合干燥木材时耗能更低,且干燥质量更好。     

Can Drying Be an Alternative Tissue Preservation Method in Cancer Research Biobanking?

The currently available methods for conservation of biobank material are mainly based on formalin fixation or the use of different freezing techniques. For molecular biological analysis, it is common to use quick freezing and low-temperature storage of the tissue materiel. This is a very energy-intensive and expensive method that requires advanced infrastructure, including monitoring and control procedures. The purpose of this work has been to study drying as an alternative process to cryogenic storage of undried biobank material, especially for use in cancer research groups.

Fast freezing has been shown to be suitable to preserve the integrity of RNAs, while traditional formalin fixation preserves proteins and thus morphology in a good way. Various fresh-harvested murine tissues, such as lung, heart, skeletal muscle, liver, and kidney, were quickly frozen in liquid nitrogen and then subsequently dried at +5°C and ?10°C, respectively, in a heat pump dryer. After drying, the RNA integrity was measured. The dried material was then stored for five months at +4°C and ?20°C in commercial refrigerators, with subsequent measurement of RNA integrity. Dried materials were also evaluated with light microscopy and by electron microscopy with respect to tissue and cell structure. The same pattern was found for all five murine tissues. We conclude that drying at temperatures below 0°C is most careful to preserve the RNA integrity, with approximately the same RIN score of dried and non-dried samples for all five tissues. What characterized the general pattern of stored samples is that drying leads to a preservation of RNA integrity. Moreover, architecture in tissue resembled normal sections prepared from fresh tissue. In some places in the rim of the tissue sample, the lung tissue revealed alveolar-like morphology. In the electron microscope, few organelles other than the nuclei could be identified. Drying of biological material is a promising and cost-effective method for biobanks that store tissue, compared to cryogenic storage of undried material. Degradation of RNA, measured by the RIN number, is a critical factor in storing biobank tissue. In low-temperature dried material, the RIN factor is at the same level as storage of undried material at cryogenic temperatures, which is the common way of storing biobank material today. In this study, a heat pump dryer was used successfully to establish drying temperatures below and above the freezing point of the material. Further work has to be done in order to study different drying methods, drying conditions, and drying costs.     

Influence of Kiln Venting on Brown Stain in Pinus Radiata Sapwood

This study assesses the influence of a closed drying environment on kiln brown stain in Pinus radiata sapwood. Three sets of matched timber samples (N = 50) were dried at low temperature (50°C), one without and two with kiln venting. Statistical analysis showed that the closed drying environment produced no significant change in the lightness (L*) of kiln brown stain. Relative to the samples dried in the vented process, there was a small but statistically significant increase in the green color (Δa* ≈ - 1.7) for both the stained area and the unstained early-wood of the samples dried in the non-vented kiln.     

EFFECT OF BLOW BOXES ON EVAPORATION DURING CYLINDER CONTACT IN A PAPER MACHINE DRYER SECTION

ABSTRACT

In this paper an inexpensive configuration for a cylinder blow box (CBB) and its effect on the evaporation rate are described. The objective of this work was to determine the effect of the blow boxes on drying intensity on a paper machine. The pilot machine trials were simulated with a computer program. Based on these results two cases were simulated for a commercial paper machine with and without blow boxes on single cylinders. The results revealed that when using the blow boxes on single cylinders, the drying rate can be increased by up to 15%. The potential for using this kind of configuration is biggest at the beginning of a dryer section. A simple construction of blow boxes makes this technique useful especially in boosting the drying performance of older paper and board machines. The exhaust air from the boxes can be utilized in ventilation of dryer pockets.     

热泵干燥箱的干燥过程

通过对热泵干燥箱的热力学分析和对热泵干燥箱干燥过程的试验研究，认为热泵干燥箱干燥物料具有高效节能、干燥温度低和对周围环境无污染等优点。试验结果表明热泵干燥箱在干燥过程中干燥室内的各点温度和相对湿度在干燥０１～２．５ｈ之间相差最大，最大温差为１３．５℃，这时热泵干燥箱的除水量也最大为６．１ｋｇ水／ｈ。     

Energy Analysis on Use of Air and Superheated Steam as Drying Media

ABSTRACT

The physical properties of air and superheated steam were analysed in a range of temperature applied in paper and paperboard drying processes. On the basis of tests carried out on a pilot stand the values of energy indices for air and steam drying processes are compared. With the drying media temperature as T_m = 300°C, nozzle velocity v= 60m/s and using the Huang and Mujumdar model as well as relationships given by Chance a compartive analysis of the results has been carried out Variation of several indices in the range of temperatures 100-600°C and various nozzle velocities was studied.     

蒸汽列管回转脱硫石膏干燥机的数值模拟

根据初步的实验和蒸汽列管回转干燥机传热机理的分析研究,对干燥机内固体颗粒运动轨迹、固体浓度场、速度场、温度场等采用多相流与粒子传热模型来描述,并以CFD软件为平台,将实际工程情况进行简化后对间接换热蒸汽列管回转石膏干燥机进行了数值模拟。与实验结果对比表明,该模型具有较高的模拟精度,可为间接换热蒸汽列管回转石膏干燥煅烧机的工程设计及结构优化提供参考。