Experiment research on grain drying process in the heat pump assisted fluidized beds

A heat pump assisted fluidized bed grain drying experimental system wasdeveloped. Based on this system, a serial of experiments was performed under four kinds of air cycleconditions. According to the experimental analysis, an appropriate drying medium-air cycle for theheat pump assisted fluidized bed drying equipment was decided, which is different from the commonlyused heat pump assisted drying system. The experimental results concerning the drying operationperformance of the new system show that the averaged coefficient of performance (COP) can reach morethan 2.5. The economical evaluation was performed and the power consumption for removing a kilogramwater from grains was about 0.485 kW-h/kg (H_2O), which shows its reasonable commercial efficiencyand great application potentiality in future market.

Impacts of different drying strategies on drying characteristics,the retention of bio-active ingredient and colour changes of dried Roselle

The drying kinetics of Roselle （Hibiscus sabdariffa L） of variety Terengganu （UMKL-1） and the quality attribution of Roselle were studied. The experiments were conducted using four different drying methods, including solar greenhouse drying （SD）, solar greenhouse with intermittent heat pump drying （SIHP）, hot air drying （HA） and heat pump drying （HP）. Among the four drying methods, HP achieved the highest drying rate at a range from 0.054 g H20-（g DM）-1. rain-1 to 0.212 g H20-（g DM）-1. rain 1 while SD had the lowest drying rate, measured at 0.042 g H2O. （g DM） 1.min- 1. The analysis on colour kinetics revealed that there is no significant colour loss （p 〉 0.05） observed from HP＇s dried Roselle. Greater amount of flavonoid compounds i.e. protocatechuic acid was found in SD and SIHP dried finished product whereas HP＇s dried Roselle contains higher percentage of catechin as compared to other drying methods.

Photovoltaic-thermal solar-assisted heat pump systems for building applications:Integration and design methods

The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion,com-bining electric and thermal energy production in a single device.Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs.The combination of these two technologies in an integrated“photovoltaic-thermal solar-assisted heat pump”(PVT-SAHP)system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump.The first is cooled down increasing its energy conversion efficiency,while providing low-temperature thermal energy to the second,which benefits from a higher evaporation temperature.The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings,with a particular focus on the integration methodologies,the possible configurations,the use of different sources and the design of sub-system components.These issues are addressed by much scientific research,to improve the reliability and applicability of this technology,as an option for the building decarbonization.This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments.More in detail,the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances.However,the distinction of the two circuits lead to more reliable,flexible and robust systems,especially when combined with a second heat source,being able to cover both heating and cooling needs.The implementation of real-time control strategy,as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology,which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings.

Energy Analysis of Pid Controlled Heat Pump Dryer

In this experimental study, a heat pump dryer was designed and manufactured, in which drying air temperature was controlled PID. Manufactured heat pump dryer was tested in drying kiwi, avocado and banana from among tropical fruits and energy and exergy analyses were made. Drying air temperature changed between 40 oC - 40.2 oC while drying the tropical fruits. Before the drying process in heat pump dryer, initial moisture contents were determined as 4.31 g water / g dry matter for kiwi, 1.51 g water / g dry matter for avocado and 4.71 g water / g dry matter for banana. Then tropical fruits were dried separately in heat pump dryer. Drying air temperature was kept unchanged with the error of +0.2 oC. Drying air velocity changed between 0.3 and 0.4 m/s in a period of 310 min. COPws of the heat pump dryer was calculated as 2.49 for kiwi, 2.47 for banana and 2.41 for avocado during the experiments. EUR changed between 13 % and 28 % for kiwi, 18% and 33% for avocado and 13% and 42% for banana in heat pump dryer.

基于机器视觉的陈皮热泵干燥含水率预测模型研究

为定量预测陈皮热泵干燥过程中含水率的变化,基于机器视觉技术提取陈皮干燥过程中的图像特征,建立含水率预测模型。采集不同干燥时期的陈皮图像,采用图像处理的方法对陈皮图像进行预处理操作,提取陈皮图像的6个颜色特征和6个纹理特征共计12个图像特征,分析特征参数和含水率变化关系,将相关图像特征作为模型的输入,陈皮的含水率作为模型的输出,分别建立基于BP神经网络和支持向量机的陈皮干燥含水率预测模型进行对比分析,得到不同干燥时期含水率最佳预测模型。结果表明,支持向量机的预测效果更好,准确率达到99.01%,均方误差达到0.006 5,模型运行稳定,含水率预测结果准确且快速,能够为陈皮干燥过程中的含水率在线预测提供科学依据。

基于模糊控制的高温热泵果脯干燥系统设计

针对高温热泵干燥技术替代传统蒸汽或热风干燥在果脯烘干中的应用场景,研制高温热泵干燥系统。结合热交换器结构与换热特性,分析果脯干燥工艺特点,将模糊逻辑控制应用于热泵干燥过程;考虑干燥箱的热场分布、温度梯度控制与干燥时间的耦合,对模糊控制器、模糊规则表进行详细设计,采用可编程逻辑控制器(PLC)控制的热泵干燥控制系统进行龙眼干燥实验测试。结果表明,模糊控制具有良好的稳态和瞬态性能,具有温度调节快、误差小、干燥效率高、节能效果好等优势,适用于干燥工艺复杂、温度调节要求高、减少人为干预影响品质的果蔬类农产品深加工。

Optimization of chanterelle mushroom drying kinetics under heat pump dryer using Taguchi design method

The optimum drying conditions with regard to minimum color changes, high rehydration ratio and drying rate for chanterelle mushrooms is inadequately known. To address this problem, drying kinetics for chanterelle mushroom samples with sizes of 20 mm×20 mm×20 mm cube, 20 mm×20 mm×30 mm cuboid, and Ø40 mm×20 mm cylindrical shape were experimented. Drying air temperatures of 40℃, 48℃, and 56℃ at superfluous humidity and velocity of 2.2 m/s were used. Initial color pixels for each sample were determined using Note 8 Pro Xiaomi smartphone camera and image processing tool in Matlab R2019a. Triplicate experimentation was done based on L9 Taguchi orthogonal arrays with drying rate, specific moisture extraction rate, color change, and rehydration ratio being the response parameters. The drying rate increased from 1.1174 g/g∙min to 1.3478 g/g.min as the temperature rose from 40℃ to 56℃. The mushroom cube had the highest drying rate of 1.2860 g/g∙min while the cylindrical shape had the lowest rate of 1.1764 g/g∙min. Similarly, SMER increased from 0.006 326to 0.013 27 g/kWh with the temperature rise. Contrary, SMER decreased from 0.006 92 to 0.013 63 g/kWh in cylinder to cube respectively. Color change was highest at 40℃ (13.49) and lowest at 56℃ (11.94). The mushroom cube had the lowest color change of 9.28 on average when compared to other shapes. Rehydration ratio was highest at 56℃ (3.824) as compared to 48℃ and 40℃. Additionally, the mushroom cube had the highest rehydration ratio of 4.55 on average as compared to other shapes. Temperature variation significantly influenced the drying rate and SMER. However, temperature variation had insignificant differences in color change and rehydration ratio. Mushroom shape variation had a significant difference in all the response variables tested. Conclusively, mushroom cubes at the drying temperature of 56℃ gave optimized drying conditions for chanterelle mushrooms with minimal quality deviations. Thus, chanterelle mushrooms can be sliced into cubes to allow quick drying rate, better SMER, rehydration ratio, and have minimal color change.

Stability of phenolic compounds and drying characteristics of apple peel as affected by three drying treatments

To realize high-value utilization of discarded apple peel,this study investigated the effects of three selected commercial drying methods on drying kinetics,microstructure,color,phenolic stability and antioxidant capacity of apple peel.Apple peel was dehydrated by hot air drying(AD)at 75,65 and 55℃,heat pump drying(HP)at 65,55 and 45℃,and vacuum freeze-drying(FD),respectively.The results showed that HP was superior to AD and FD in terms of drying rate.In addition,HP at 65℃provided high-quality dried apple peel due to less browning and brighter appearance,the highest retention of total phenolics(29.35 mg/g)and the strongest antioxidant activities,with the highest ABTS and FRAP value of 127.15 and 219.57μmol TE/g,respectively.The content of the six major individual phenolics,i.e.caffeic acid,(-)-epicatechin,hyperoside,rutin,phlorizin and quercitrin,were found to be the highest in HP dried samples.Interestingly,the content of rutin was even increased after HP compared to the fresh sample.Considering drying efficiency,organoleptic quality and phenolic stability of the products,HP at 65°C is suggested for drying of apple peel.

Dehydration property of Shrimp(Pandalus borealis)undergoing heat-pump drying process

Peeled,headed or whole shrimp(Pandalus borealis)was dried in a heat-pump dryer at-2-0℃and 20℃,respectively,and desorption isotherms characterizing the dehydration property of each shrimp sample group were determined.Desorption isotherms of shrimp handled differently and dried at different temperatures(-2-0℃or 20℃)could be well described by Oswin’s model(X=a(1-a_(w)/a_(w))).The regression model of peeled,headed or whole shrimp was established,which is reliable for predicting the desorption isotherms of shrimp undergoing heat-pump drying.The handling methods of shrimp exhibit measurable influence on desorption isotherms of shrimp,whereas drying temperature(-2-0℃or 20℃)has little influence on the constants of a and n in Oswin’s model,of whole shrimp,even though it has certain influence on these constants of peeled and headed shrimp.For heat-pump drying,headed shrimp may have a better stability than peeled or whole shrimp due to the best stability.

Degradation kinetics of functional components of honeysuckle flowers during controlled-atmosphere heat pump drying

To investigate the change law of functional components and exterior color of honeysuckle flowers(HF)during controlled-atmosphere heat pump drying,nitrogen was used as drying medium in this study to reduce the oxygen concentration.The influences of drying temperature,HF’s loading amount and oxygen concentration on chlorogenic acid content,cynaroside content and L value(on behalf of browning degree)were explored,and the degradation kinetics models of chlorogenic acid and cynaroside were constructed.The results showed that chlorogenic acid content,cynaroside content and L value decreased with the rise of temperature,HF’s loading amount and oxygen concentration.The degradation kinetics models of chlorogenic acid and cynaroside during the drying process were established through introducing an exponent r related to time t in the first order reaction kinetics equation.The models had good fitting precision and can be used to predict the degradation law of chlorogenic acid and cynaroside.

Effects of heat pump drying temperature and dietary fat on carrot β-carotene bioaccessibility

Dehydration can significantly extend the shelf life of dried carrots and still retain nutrition of provitamin A carotenoids.In vitro digestion model was used in this study to assess the effect of drying temperatures of heat pump and dietary fat on the bioaccessibility ofβ-carotene in carrots.Also,low-speed centrifugation was employed to obtainβ-carotene release rate in supernatant.Microfiltration was applied to obtainβ-carotene micellar rate in micelle phase.These assays were used as indicators to assess the bioaccessibility of theβ-carotene.Despite higher drying temperatures had a negative effect on the retention rate ofβ-carotene in carrots,it showed a positive impact on the micellar rate.In addition,dietary fat significantly increased the release rate and micellar rate ofβ-carotene for both fresh carrots and dried carrot products,with the highest release rate and micellar rate obtained when 10%dietary fat was added.Therefore,the heat pump drying process and dietary fat can significantly improve the bioaccessibility ofβ-carotene in carrots,which may increase theβ-carotene bioavailability to human.

不同高温热泵干燥条件对龙眼干品质的影响

以龙眼为研究对象,考察了不同热泵干燥温度和干燥风速对龙眼干一般理化特性、色泽、质构和活性成分等品质的影响。结果表明:采用高温热泵干燥时,干燥温度越高,龙眼干的总酸含量越高,复水率越低;干燥风速相同时,龙眼干的pH值随着温度的升高而降低;龙眼干燥后总体色泽的变化主要在色泽的变暗及变黄,干燥温度的升高和干燥风速的增加都会导致龙眼色泽变化的增加;总体来说,不同高温热泵干燥条件下,龙眼干的弹性、回复性、硬度以及耐咀性的变化均不显著,干燥风速较低,龙眼干的黏性较大;当干燥温度为60℃时,龙眼干中保留的游离酚含量最高,不同干燥条件下,结合酚含量、多糖含量的差异不显著。

基于电子鼻识别的热泵干燥鲢鱼品质评价模型的建立

为提高干制水产品品质评价的客观性,建立可靠的电子鼻评价模型。运用电子鼻技术根据总挥发性盐基氮(total volatile base nitrogen,TVB-N)值对不同干燥工艺条件下的腌制鲢鱼进行检测,通过主成分分析并结合统计模式识别方法和偏最小二乘(partial least squares,PLS)回归分析方法对输入的鲢鱼TVB-N值进行模式识别。结果表明:电子鼻对同一因素不同水平下干燥白鲢的TVB-N值产生不同的响应;建立的K最近邻分类算法判别模型对训练集和预测集的识别率均在90%以上,能够对样本进行准确的判断;PLS法分析不同条件下干燥的鲢鱼样品训练集(30个样本)和预测集(15个样本)的相关系数分别为0.913 5和0.933,训练集的交互验证均方根误差为3.67,而预测集的预测均方根误差为3.26,达到理想效果。结论:所建立的电子鼻PLS模型能根据TVB-N值实现不同腌干鲢鱼制品的电子鼻区分识别,可用于热泵干燥的白鲢鱼品质预测监督,为干制水产品品质客观的评价提供理论基础和技术指导。

不同护色处理对龙眼干制品品质的影响

以龙眼为原料,结合护色、热泵干燥工艺加工龙眼干制品,研究护色处理过程中护色剂的护色时间、干燥温度及干燥时间等因素对龙眼干制品品质的影响。结果表明:龙眼干制品中总糖含量随着护色时间的延长而上升,随着热泵干燥温度的升高先增加后下降;龙眼干制品的酸度随着干燥时间和温度的增加先升高后降低。以1%偏重亚硫酸钠+0.5%抗坏血酸的复合护色剂对去皮、去核的果肉护色,在此基础上热泵干燥制备龙眼干制品的最佳工艺为护色时间4 min、热泵干燥温度60℃、干燥时间12 h,所制得的龙眼干制品色泽均匀、总糖含量2.55%、酸度25.7%。因此,不同护色和热泵干燥工艺影响龙眼干制品的品质,响应面优化的热泵干燥制备龙眼干制品的最佳工艺较好,所得龙眼干制品品质较佳。

超声波辅助漂烫预处理对太阳能-热泵联合干燥南瓜片品质的影响

研究超声波辅助漂烫预处理方法对太阳能-热泵联合干燥南瓜片品质的影响,以超声波温度、功率、频率和处理时间为单因素,研究其对干燥南瓜片色差、硬度、β-胡萝卜素及抗坏血酸含量的影响。通过正交优化分析获得最优工艺条件,并与传统漂烫预处理进行干燥南瓜品质的对比实验。结果表明,在超声波温度70℃、超声波功率为300 W、超声波频率为35 k Hz、超声波处理时间为3 min条件下,干燥处理对南瓜片的颜色及营养物质含量的影响最小,色差值为9.95,相比于传统热烫的预处理方法减少61.64%;硬度值为36.61 N;抗坏血酸含量为13.00 mg/100 g,较传统热烫提高41.38%。因此,相比于传统热烫的预处理方法优势依然明显。证明超声波这一物理手段可显著减少南瓜热处理时色泽变化及抗坏血酸等营养物质的流失,超声波辅助漂烫预处理手段可用于南瓜片干燥加工中。

Performance Study of a Hybrid Heat Pump Dryer based on Numerical Analysis and Experimental Set-up

Seafood,especially sea cucumbers and oysters are an expensive delicacy in several Asian countries.Traditional sun-drying of these products takes 3 to 4 days and fetches a lower market price.Modern industrial drying machines used for seafood drying are unable to dry sea cucumbers and oysters without texture and color degradation as they are delicate,temperature-sensitive and have longer drying time.An economical drying system that does not cause texture or color degradation is the heat pump drying system and is commonly applied for agriculture and fabric drying.In this study,the heat pump technology is applied to develop two hybrid dryer models(bottom discharge and front discharge)to dry shellfish and sea cucumbers in large scale for storage and transportation.Each model is tested in a laboratory-scale with wet sponges as input material for its dehumidification capacity and the power consumed to attain the target dryness.The front discharge model is found to have rapid drying capability and economy.Computational fluid dynamic tools are used to study the hot air flow behavior and flow uniformity inside the drying chamber.The front discharge model showed smooth uniform flow over the trays with fewer losses in the flow velocity.The front discharge model with higher drying rate,lower power consumption and uniform airflow distribution over the trays is chosen for the industrial-scale design.

风干板栗太阳能-热泵联合干燥特性与数学模型研究

为研究风干板栗太阳能-热泵联合干燥特性,以新鲜板栗为原料,探讨干燥温度、干燥风速、装载量对风干板栗干燥速率和干基含水率的影响,在不同干燥温度、干燥风速、装载量条件下分别对新鲜板栗进行干燥,并比较了6种数学模型在风干板栗太阳能-热泵联合干燥的适用性,同时以Fick第二扩散定律为依据,确定风干板栗不同干燥条件下的有效水分扩散系数。结果表明:风干板栗干燥过程由调整阶段和降速干燥阶段控制,主要表现为降速干燥;干燥温度越高、干燥风速越高以及装载量越小,干燥至目标含水率所用时间越短,干燥速率越大;干燥过程中,有效水分扩散系数随干燥温度及干燥风速的升高、装载量的降低呈现增大的趋势,干燥温度从15℃升高到35℃,其有效水分扩散系数由3.00124×10^-10 m^2/s增大到8.42115×10^-10 m^2/s,干燥风速由1.0 m/s升高到5.0 m/s,其有效水分扩散系数由4.54717×10^-10 m^2/s增大到9.13767×10^-10 m^2/s;装载量从0.6 kg升高至5.4 kg,其有效水分扩散系数由1.14753×10-9 m^2/s降至3.20443×10^-10 m^2/s;通过比较决定系数(R2)、残差平方和及卡方(χ^2)得出,Page模型为描述风干板栗太阳能-热泵联合干燥的最优模型,验证发现试验值与模型预测值拟合度较高,Pearson相关系数为0.998,二者显著相关(P<0.05),说明Page模型能够较好地反映风干板栗干燥过程中水分变化规律。

自控热泵柿饼烘干房及快速干制出霜工艺研究

传统柿饼加工为自然晾晒生产,受天气因素影响,加工周期长,易受灰尘及细菌污染,劳动强度大,正逐步被人工烘干替代。为此进行了一种自控热泵柿饼烘干房研制及干制和出霜工艺研究,介绍了烘干房的系统设计、电气控制、结构设计及生产工艺试验过程。利用该设备和工艺技术,使柿饼烘干周期从自然晾晒的40多天缩短为5-6天,成品柿饼水分控制在30%左右,烘干柿饼色泽优于传统柿饼,口感与传统柿饼相当,而卫生程度与生产效率远高于传统工艺,为柿饼的清洁化工厂化生产奠定了基础。

基于真空冷冻-热泵联合干制鱼片的解吸-吸附等温线及热力学特性

为探讨超声波辅助聚葡萄糖渗透预处理结合真空冷冻-热泵联合干燥罗非鱼片的品质及其后期贮藏稳定性,采用静态称重法测定真空冷冻-热泵联合干制罗非鱼片在25、35、45℃时及水分活度(a_(w))为0.1116~0.8434时的解吸-吸附等温线,选取8种常见的数学模型对解吸-吸附等温线数据进行拟合,通过决定系数(R^(2))和均方误差(E_(MS))确定解吸-吸附等温线的最佳模型,再根据干制罗非鱼片在不同温度下的解吸-吸附等温线数据获取干制罗非鱼片的热力学性质。结果表明:干制罗非鱼片的水分解吸-吸附呈Ⅲ型等温线,Peleg模型是描述真空冷冻-热泵联合干制罗非鱼片解吸-吸附等温线的最佳模型,同时获得25、35、45℃条件下干制罗非鱼片的绝对安全含水率分别为16.30%、13.68%、13.64%,相对安全含水率分别为22.89%、19.21%、19.77%;干制罗非鱼片的净等量吸附热、等量解吸热、微分熵均随平衡含水率上升呈现指数递减,解吸与吸附过程均由焓驱动,且均属于非自发性。研究表明,不同贮藏温度和水分活度对干制罗非鱼片的解吸-吸附等温线及热力学性质有较大影响,该研究结果可为罗非鱼片的干燥工艺优化及贮藏条件的设置提供数据参考。