热泵干燥节能技术研究与经济评价

本文提供了一套热泵干燥实验装置及流程,并在整个干燥周期内对其动态性能进行了全面考察。对装置的适宜操作范围进行实验,运用正交实验法找到一组使得热泵干燥单位能耗最小的最优操作条件。以陶瓷粘土、木材、棉布为干燥物料,进行热泵干燥与电加热干燥节能对比实验表明,热泵干燥的节能效果为50～57％。本文还对热泵干燥、电加热干燥、蒸汽加热干燥的一次能源消耗和能源费用进行了比较和经济评价。     

浅析热风干燥技术中的节能途径

阐述了我国碳排放现状及节能减排的紧迫感。以传统的热风炉粮食干燥的和传统的木材蒸汽干燥为例,分析了传统干燥热效率不高的主要因素,指出排气余热回收是传统干燥作业节能减排的主要途径之一,采用普通换热器、热泵及热管换热器回收排气余热,均有明显的节能效果。采用普通换热器平均节能12.4%,采用热泵平均节能40%左右,采用热管换热器居二者之间。介绍了太阳能干燥、太阳能与热泵组合干燥、热风与真空微波组合干燥、超声波与热风干燥组合等各种低碳干燥技术。建议逐渐推广用生物质能源作为干燥的热源,有利于实现低碳干燥。     

污泥热干燥技术的研究现状与进展

热干燥技术是污泥处理并资源化利用的有效方法,本文介绍了常见污泥的干燥特性及几种主要的干燥方法,包括热泵热风干燥、过热蒸汽干燥、太阳能干燥和微波干燥等方法,并对这几种技术的研究现状和发展趋势进行分析,为污泥热干燥技术的进步提供理论支撑,推动我国环保事业快速发展。     

蒸汽与热泵联合干燥木材的匹配分析

对单独的常规蒸汽干燥、热泵(除湿)干燥以及二者联合干燥三种工况进行了能耗分析，结果以联合干燥能耗最低，热泵(除湿)干燥次之，常规蒸汽干燥能耗最高。文中还就相应干燥条件下蒸汽-热泵(除湿)联合干燥的匹配条件作了研究。     

木材干燥的国内外现状与发展趋势

阐述了常规蒸汽（热风）干燥、除湿（热泵）干燥、真空干燥、微波与高频干燥等各种木材干燥技术的国内外现状以及我国木材干燥技术与国际水平的差距；介绍了国内外木材干燥的理论研究动态；指出了今后木材干燥技术的发展趋势。     

双孢白蘑菇干燥前微波与高温瞬时蒸汽联合漂烫预处理对酶活和品质影响的研究

试验研究了双孢白蘑菇干燥前微波与高温瞬时蒸汽对多酚氧化酶(PPO)活性以及Vc的影响。通过微波强度(w/g)、微波处理时间(t1)、蒸汽强度(Pa/g)、蒸汽处理时间(t2)的单因素试验,设计正交试验,对PPO、Vc进行综合评价分析,得出最佳的试验条件:微波强度为5.656w/g、微波处理时间(t1)为120s、蒸汽强度为2.69Pa/g、蒸汽处理时间(t2)为80s,综合评分值最高。并对微波与高温蒸汽联合漂烫最优结果与热水漂烫处理、纯微波、纯高温蒸汽漂烫进行了比较,体现了微波与高温蒸汽联合漂烫的优势。     

拉瓦尔喷嘴应用于蒸汽喷射式热泵性能分析

将拉瓦尔喷管的结构特性与传统全收敛型喷嘴结构性能进行对比,分析了拉瓦尔喷管型喷嘴在蒸汽喷射式热泵中的使用性能。通过对拉瓦尔喷嘴应用于蒸汽喷射式热泵的实际样机进行测试,得出了以实测数据为依据的性能分析结论,为提升传统蒸汽喷射式热泵性能提供了理论及数据参考。     

基于加热均匀性的微波干燥研究进展

微波干燥通过电磁场辐射物体而在其内部产生热量,促进物体内部水分向外部迁移,是一种先进的干燥技术。但是,微波干燥存在加热不均匀的问题。本文针对该问题,分析了导致微波加热/干燥不均匀的影响因素,综述了通过提高微波干燥室内电磁场分布均匀性及改变被处理物料位置,以改进微波加热均匀性的可行措施,最后指出进一步实现微波均匀干燥的研究发展趋势。     

微波干燥卫生陶瓷的研究与设备开发

本文利用微波干燥法进行卫生陶瓷坯体干燥试验,探究微波可以实现对卫生陶瓷快速干燥的原因。在此基础上,对围绕着微波设备大型化、连续化中面临的关键技术及微波干燥电耗相对较高等技术进行攻关,开发了卫生陶瓷微波干燥辊道窑,并在实际工厂使用。结果表明:微波干燥过程实现了沿坯体纵向与沿坯体局部区域横向的均匀干燥及微波干燥能显著提高干燥的内扩散速率,最终实现对卫生陶瓷的快速干燥;采用微波、热风耦合加热技术能显著降低微波干燥电耗;开发的卫生陶瓷微波干燥辊道窑,可极大缩短干燥周期,降低场地占地面积,提高干燥合格率。     

热泵蒸发对节约蒸汽的作用

在蒸发操作过程中,一般采用具有一定压强的加热蒸汽来加热水溶液而使之蒸腾。蒸发所产生的二次蒸汽,其压强与温度虽较原加热蒸汽为低,但所含的热量却仍相当高,通常都被送到冷凝器中加以凝缩而排去。这样,蒸汽的潜热即完全被废弃,而且耗费水量也大,很不经济。倘若能设法将此二次蒸汽重新加以利用,则可大大减少加热蒸汽的消耗,从而节约大量煤炭。目前工业生产上常采用的方法大致有两种,即热泵蒸发与多效蒸发。热泵蒸发的原理系将蒸发器所产生的二次蒸汽通过压缩机的绝热压缩,提高其压强及饱和温度,再送回蒸发器的加热室中用作加热蒸汽(见图1甲及图1乙),     

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.     

Calculation Steps for the Design of Different Components of Heat Pump Dryers Under Constant Drying Rate Condition

Heat pump–assisted dryers are an alternative method for drying heat-sensitive food products at low temperature and less relative humidity with lower energy consumption. The mathematical models of a heat pump dryer consist of three submodels; namely, drying models, heat pump models, and performance models. Heat and mass balance of both refrigerant and air circuits in all components of the system are used for development of mathematical models. The models are used for design of different components of heat pump dryers operating under constant drying rate condition. A simple stepwise design procedure for batch-type, closed-loop heat pump dryer is also presented.     

MATHEMATICAL MODEL DEVELOPMENT AND SIMULATION OF HEAT PUMP FRUIT DRYER

ABSTRACT

A mathematical model of a heat pump fruit dryer was developed to study the performance of heat pump dryers. Using the moisture content of papaya glace' drying, the refrigerant temperature at the evaporator and condenser and the performance, was verified. It was found that the simulated results using closed loop heat pump dryer were close to the experimental results. The criteria for evaluating the performance were specific moisture extraction rate and drying rate. The results showed that ambient conditions affected significantly on the performance of the open loop dryer and the partially closed loop dryer. Also, the fraction of evaporator bypass air affected markedly on the performance of all heat pump dryers. In addition, it was found that specific air flow rate and drying air temperature affected significantly the performance of all heat pump dryers.     

Condenser Coil Optimization and Component Matching of Heat Pump Dryer

The heat pump dryer is an energy-efficient piece of drying equipment, but due to its complicated system of the two interactive working fluids (refrigerant and drying air), the optimum design remains the question. A heat exchanger is the major component influencing the heat pump dryer (HPD) performance. This article reports a study to optimize the condenser coil of the HPD and the component matching in order to obtain optimum performance. The study was carried out by a mathematical model for system simulation and followed by experimental verification. Five HPD configurations were studied, including different designs in air and refrigerant flow paths. It was found that the closed-loop HPD with air bypassing over the evaporator is the most appropriate configuration. The proper coil design is 2-row, 2-circuit configuration with optimum refrigerant mass flow rate of 16-20 g/s/circuit. The optimum air flow rate was found to be in the range of 0.6-0.8 kg/s. The corresponding number of coil modules is 8.     

Condenser Coil Optimization and Component Matching of Heat Pump Dryer

The heat pump dryer is an energy-efficient piece of drying equipment, but due to its complicated system of the two interactive working fluids (refrigerant and drying air), the optimum design remains the question. A heat exchanger is the major component influencing the heat pump dryer (HPD) performance. This article reports a study to optimize the condenser coil of the HPD and the component matching in order to obtain optimum performance. The study was carried out by a mathematical model for system simulation and followed by experimental verification. Five HPD configurations were studied, including different designs in air and refrigerant flow paths. It was found that the closed-loop HPD with air bypassing over the evaporator is the most appropriate configuration. The proper coil design is 2-row, 2-circuit configuration with optimum refrigerant mass flow rate of 16–20 g/s/circuit. The optimum air flow rate was found to be in the range of 0.6–0.8 kg/s. The corresponding number of coil modules is 8.     

A Simulation Model for Heat Pump Dryer Plants for Fruits and Roots.

Dryer design requires food properties, drying rate and mass-heat transfer coefficients. These values change continuously during drying due to changes in food fractions, particularly the water fraction. The high energy demand and costs allied to inefficient devices, creates a great need for new processing equipment. Along these guide-lines, several heat pump drying research projects were established at the Norwegian University of Science and Technology. The heat pump dryer provides high quality final product as its drying conditions can be controlled. Its efficiency and non-polluting operation come from closed air-refrigerant circuits and from its ability to fully recover the latent heat of moist air as it exits the drying chamber. Most of the above features are quite the opposite of the conventional dryer characteristics. Several experiments were made on heat pump drying of fruits and roots at temperatures from -22.5 to 40°C to obtain data and correlations on thermophysical properties, specific enthalpy and rehydration. Also, tests were done on drying rate, moisture content, drying constant, effective mass diffusivity and heat and mass transfer equations. The next important phase is the development of a simulation model to predict the performance and characteristics of the heat pump dryer plant. The objectives of the present work are to develop and lo test a heat pump dryer simulation model. The simulation provides results on the characteristics of both plant and components which are integrated by heat and mass transfer equations. The program has menus with click-on icons, input and output pop-up dialogue boxes. The usual commands such as, file-open, file-save, edit-delete are available in this program simply called Hpdryer. The model contains moist air psychrometric. natural and conventional refrigerant property libraries. Ammonia is a time-tested, self-alarming and natural refrigerant. It has been used extensively in the past, and it has better thermodynamic and transport properties than halocarbons. Safety is easily attained by design and its restrictive standards have helped increase its use in several countries. There are 36 ammonia installations in Norway and in the United Kingdom, including a drying plant. Ammonia has zero Odp, zero Gwp and the recent R&D has led to viable small-sale heat pump plants. Ammonia and dichlarodifluoromethane refrigerants were used in the test cases simulated by Hpdryer madel.     

A Simulation Model for Heat Pump Dryer Plants for Fruits and Roots.

ABSTRACT

Dryer design requires food properties, drying rate and mass-heat transfer coefficients. These values change continuously during drying due to changes in food fractions, particularly the water fraction. The high energy demand and costs allied to inefficient devices, creates a great need for new processing equipment. Along these guide-lines, several heat pump drying research projects were established at the Norwegian University of Science and Technology. The heat pump dryer provides high quality final product as its drying conditions can be controlled. Its efficiency and non-polluting operation come from closed air-refrigerant circuits and from its ability to fully recover the latent heat of moist air as it exits the drying chamber. Most of the above features are quite the opposite of the conventional dryer characteristics. Several experiments were made on heat pump drying of fruits and roots at temperatures from -22.5 to 40°C to obtain data and correlations on thermophysical properties, specific enthalpy and rehydration. Also, tests were done on drying rate, moisture content, drying constant, effective mass diffusivity and heat and mass transfer equations. The next important phase is the development of a simulation model to predict the performance and characteristics of the heat pump dryer plant. The objectives of the present work are to develop and lo test a heat pump dryer simulation model. The simulation provides results on the characteristics of both plant and components which are integrated by heat and mass transfer equations. The program has menus with click-on icons, input and output pop-up dialogue boxes. The usual commands such as, file-open, file-save, edit-delete are available in this program simply called Hpdryer. The model contains moist air psychrometric. natural and conventional refrigerant property libraries. Ammonia is a time-tested, self-alarming and natural refrigerant. It has been used extensively in the past, and it has better thermodynamic and transport properties than halocarbons. Safety is easily attained by design and its restrictive standards have helped increase its use in several countries. There are 36 ammonia installations in Norway and in the United Kingdom, including a drying plant. Ammonia has zero Odp, zero Gwp and the recent R&D has led to viable small-sale heat pump plants. Ammonia and dichlarodifluoromethane refrigerants were used in the test cases simulated by Hpdryer madel.     

Saffron Drying with a Heat Pump–Assisted Hybrid Photovoltaic–Thermal Solar Dryer

Saffron is the most expensive spice and Iran is the largest producer of this crop in the world. Saffron quality is profoundly affected by the drying method. Recent research has shown that hybrid photovoltaic–thermal solar power systems are more efficient in comparison with individual photovoltaic and thermal systems. In addition, heat pump dryers are highly energy efficient. Furthermore, they are suitable for heat-sensitive crops such as saffron. Therefore, in the present study, the performance of a hybrid photovoltaic–thermal solar dryer equipped with a heat pump system was considered for saffron drying, in order to obtain a high-quality product and reduce fossil fuel consumption. The effect of air mass flow rate at three levels (0.008, 0.012, and 0.016 kg/s), drying air temperature at three levels (40, 50, and 60°C), and two different dryer modes (with and without the heat pump unit) on the operating parameters of the dryer was investigated. The results of the investigation showed that total drying time and energy consumption decreased as air flow rate and drying air temperature increased. Applying a heat pump with the dryer led to a reduction in the drying time and energy consumption and an increase in electrical efficiency of the solar collector. The average total energy consumption was reduced by 33% when the dryer was equipped with a heat pump. Maximum values for electrical and thermal efficiency of the solar collector were found to be 10.8 and 28%, respectively. A maximum dryer efficiency of 72% and maximum specific moisture extraction rate (SMER) of 1.16 were obtained at an air flow rate of 0.016 kg/s and air temperature of 60°C when using the heat pump.     

Drying Kinetics and Antioxidant Phytochemicals Retention of Salak Fruit under Different Drying and Pretreatment Conditions

Kinetics of hot air drying and heat pump drying were studied by performing various drying trials on salak slices. Isothermal drying trials were conducted in hot air drying and heat pump drying at a temperature range of 40–90°C and 26–37°C, respectively. Intermittent drying trials were carried out in heat pump drying with two different modes: periodic heat air flow supply and step-up air temperature. It was observed that the effects of relative humidity and air velocity on drying rate were significant when moisture content in salak slices was high, whereas the effects of temperature prevailed when the moisture content was low. As such, it was proposed that drying conditions should be manipulated according to the moisture transport mechanisms at different stages of drying in order to optimize the intermittent drying and improve the product quality. Generally, loss of ascorbic acid during drying was attributed to thermal degradation and enzymatic oxidation, whereas the loss of phenolic compounds was mainly due to thermal degradation. Experimental results showed that heat pump drying with low-temperature dehumidified air not only enhanced the drying kinetics but produced a stable final product. Heat pump–dried samples retained a high concentration of ascorbic acid and total phenolic compounds when an appropriate drying mode was selected.     

Convective Drying with Time-Varying Heat Input: Simulation Results

Intermittent drying aims to match the heat input rate to the drying kinetics of the material so as to avoid thermal degradation of heat-sensitive products in particular. This paper presents results of a liquid diffusion model to examine the effect of varying the rates of heat input by convection heat transfer. This is accomplished by varying the drying air velocity, varying the air temperature as well as its relative humidity over different periods of time in a sequential manner. One of the outcomes of this work is guidelines for use of a heat pump to dehumidify the drying air. While most heat pump dryers are designed to operate continuously, our results show that it is not necessary to use heat pump continuously over the entire drying period. This option saves running costs by reducing use of electrical power in the drying cycle. Furthermore, it is possible to save capital costs by utilizing a smaller heat pump for a given dry product output. Alternatively, a given heat pump system can be used to service two or more drying chambers that may dry the same or different products by simply switching the dehumidified and heated air from one chamber to the other sequentially. When the heat pump air is switched off, unsaturated ambient air maybe used to accomplish rest of the drying. It is shown that using heat pump air over only a part of the drying cycle does not increase the drying time appreciably.