热泵干燥装置的特性方程及其应用分析

以应用最广泛的封闭式热泵干燥装置为例,建立了其SMER计算方程。在此基础上,对SMER随干燥器进口空气温度、干燥器出口空气温度和蒸发器出口空气温度而变化的规律进行了计算和分析。结果表明,其他两个参数一定时,SMER随干燥器出口空气温度上升而降低,随蒸发器出口空气温度上升而增加,但当干燥器进口空气温度取适宜值时,SMER存在最大值。     

热泵干燥装置操作参数的分析

分析了热泵干燥装置的独立操作参数,给出了热泵的蒸发温度、冷凝温度、干燥器进口空气的速度、干燥器出口空气的温度及相对湿度与热泵干燥装置除湿能耗比之间的关系式,计算了除湿能耗比随独立操作参数的变化规律,相关结论为热泵干燥装置测控系统的开发提供了较好的参考。     

内加热式热泵干燥装置的设计

内加热式热泵干燥装置通过导热加热方式提供物料中水分气化所需热能,可获得较高的能源效率和除湿能耗比。在介绍内加热式热泵干燥装置基本结构和工作过程的基础上,给出了其物料衡算、能量衡算和主要部件选型参数的计算公式,为内加热式热泵干燥装置的设计提供了较好的参考。     

复叠式热泵高温段实验研究

热泵高温化可以有效拓展其应用范围,复叠式热泵是实现高温热泵的有效方法之一。以R123为高温工质,以喷水模拟干燥脱水过程,实验研究了用于干燥系统的复叠式热泵的高温段。结果表明:热泵的冷凝温度可达到95℃;蒸发温度60℃冷凝温度90℃时,热泵COP达到最大为5.78;在整个蒸发、冷凝温度范围内COP维持在2.2以上,SMER达到4~5 kg/(kW·h),单位干燥介质除水量为0.006~0.012 kg水/kg干空气。     

欧洲的热泵干燥

这里介绍一种较现代化的干燥方式“热泵”系统。从陶瓷到木材许多制品都可以用热泵系统进行干燥。热泵的主要机械部分是热泵脱湿器。在对流干燥中,制品是由通过其表面的预热空气干燥的,其干燥速度与空气流速、温度和湿度成正比。在传统的干燥器中,加热空气进入干燥带,将制品中的水分吸收后,热空气不是被消耗掉,就是被排到     

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)。     

热泵干燥装置循环空气的参数优化研究

热泵干燥具有节能、低温干燥及环境友好等特点,热泵干燥装置中循环空气的参数对其性能指标具有重要影响。为优化循环空气参数,提出了蒸发器冷量有效利用率的概念,对蒸发器冷量有效利用率、循环空气参数、装置性能指标SM ER三者之间的关系进行了计算分析,以此为指导,提供了四种可实现热泵干燥装置循环空气参数优化的技术方案。     

利用焦炉热烟道气对不同粒径炼焦煤均匀干燥的调湿装置

正本发明涉及煤调湿干燥技术领域,特别涉及一种利用焦炉热烟道气对不同粒径炼焦煤均匀干燥的调湿装置,包括干燥器壳体、焦炉热烟道气入口、烟道气出口、未调湿焦煤入口、干燥后煤出口,在干燥器壳体内设有物料分散装置,在干燥器壳体内壁上设有多个向下倾斜的挡板一,干燥器壳体内壁上还设有挡板二,挡板     

利用热泵干燥污泥技术的试验研究

为了对热泵干燥污泥的方法进行研究,采用自行设计的污泥热泵干燥装置对含水率为55%-60%的污泥进行干燥试验研究。分析了风量、空气参数、冷凝温度和蒸发温度等对干燥效果的影响。试验表明,风量、空气参数、冷凝温度和蒸发温度对干燥效果有较大的影响,随着风量的增大,出水量逐渐增多,在风量达到800-1000m3/s,达到一个最佳的干燥效果,此时能耗比为0.73。     

热泵干燥装置中干燥介质的物性及其应用分析

在热泵干燥装置中,干燥介质对干燥过程的传热传质速率、物料干燥质量和装置的能源效率均具有重要影响。给出了空气、氮气、二氧化碳、氩气、氢气、氦气六种干燥介质的热物性数据及其计算方程,并分析了其适宜的应用场合,为热泵干燥装置中选择适宜的干燥介质提供了较好的参考。     

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.     

Heat Pump Drying of Green Sweet Pepper

Thin-layer drying experiments under controlled conditions were conducted for green sweet pepper in heat pump dryer at 30, 35, and 40°C and hot air dryer at 45°C with relative humidities ranging from 19 to 55%. The moisture content of sweet pepper slices reduced exponentially with drying time. As the temperature increased, the drying curve exhibited a steeper slope, thus exhibiting an increase in drying rate. Drying of green sweet pepper took place mainly under the falling-rate period. The Page equation was found to be better than the Lewis equation to describe the thin-layer drying of green sweet pepper with higher coefficient of determination and lower root mean square error. Drying in heat pump dryer at 40°C took less time with higher drying rate and specific moisture extraction rate as compared to hot air drying at 45°C due to lower relative humidity of the drying air in a heat pump dryer though the drying air temperature was less. The retention of total chlorophyll content and ascorbic acid content was observed to be more in heat pump–dried samples with higher rehydration ratios and sensory scores. The quality parameters showed a declining trend with increase in drying air temperature from 30 to 45°C. Keeping in view the energy consumption and quality attributes of dehydrated products, it is proposed to dry green sweet pepper at 35°C in heat pump dryer.     

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.     

Transcritical CO2 Heat Pump Dryer: Part 2. Validation and Simulation Results

The simulation model of a transcritical CO₂ heat pump dryer presented in Part 1 has been first validated with available experimental data in this part and then used to simulate the heat pump dryer to study the variation of performance parameters such as heating COP, moisture extraction rate, and specific moisture extraction rate. The validation with experimental data shows that the model slightly over predicts the system performance. The possible reasons for the difference between experimental and numerical results are explained. Simulation results show the effect of key operating parameters such as bypass air ratio, re-circulation air ratio, dryer efficiency, ambient condition (temperature and relative humidity), and air mass flow rate. Results show that unlike bypass air ratio and ambient relative humidity, the effect of dryer efficiency, recirculation air ratio, ambient temperature, and air mass flow rate are very significant as far as the system performance is concerned.     

Effect of ambient conditions on drying of herbs in solar greenhouse dryer with integrated heat pump

An even span solar greenhouse dryer was built and applied to dry Java tea (Orthosiphon aristatus) and Sabah snake grass (Clinacanthus nutans Lindau). Findings showed that the solar greenhouse dryer performs satisfactorily during clear weather except at nighttime and rainy day due to product rehydration which is heavily influenced by high relative humidity from ambient air. Integrating of heat pump into the solar greenhouse dryer has successfully reduced the room relative humidity by 10–15%. Also, heat pump has mitigated the product rehydration issue by maintaining room relative humidity at maximum of 65% throughout the drying period. The drying rate of Java tea was improved three to fourfold, i.e., from 0.004–0.008 to 0.018–0.025?g H₂O/g DM min, whereas 10% of drying time was saved for both Java tea leaf and Sabah snake grass leaf with the assistance of heat pump system. Meanwhile, the supply of dry air from the heat pump system with a magnitude of 0.25–0.50?m/s helps in enhancing the drying rate of the herbs as well as minimizing the nonuniformity of drying temperature and relative humidity inside the solar greenhouse 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.     

Exergoeconomic Analysis of a Heat Pump Tumbler Dryer

In this study, exergy and exergoeconomic analyses of a heat pump tumbler dryer are carried out by using actual thermodynamic and cost data. The wet cotton fabric is used as the test drying material. The results show that the specific moisture extraction rate (SMER) and evaporation rate of dryer are equal to 1.08 kg/kWh and 0.018 kg/s, respectively. Also, the respective exergetic efficiencies of the heat pump and overall system are equal to 0.07 and 0.11. A parametric study is then conducted in order to investigate the system performance and costs of the components, depending on the operating temperature and mass flow rate of air.     

Drying of Soybean Seeds in a Concurrent Moving Bed: Heat and Mass Transfer and Quality Analysis

The purpose of the present work is to study the simultaneous heat and mass transfer between air and soybean seeds in a concurrent moving bed dryer, based on the application of a two-phase model to the drying process. The numerical solution of the model is obtained by using a computational code based on BDF methods (Backwards Differentials Formulas). The experimental data of air humidity and temperature and of seed moisture content and temperature at the dryer outlet are compared to the simulated values, showing a good agreement. This work also analyzes the effect of the main process variables (drying air temperature, air relative humidity, air velocity and solids flow rate) on the soybean seeds quality during drying. Empirical equations fitted to the experimental data are proposed for predicting the soybean seed quality (germination, vigor and fissures) as a function of the investigated variables.