污泥热泵干燥速率及能耗的实验研究

利用小型热泵干燥试验台，对污泥干燥过程含水率、空气参数（温度、相对湿度）及热泵参数（制冷工质参数、排水量、能耗等）的变化进行了试验测试，并着重对干燥速率、能量回收率及影响因素进行了分析。试验显示，依靠外热源预热后，污泥干燥过程仅依靠热泵回收的排气余热供热，干燥箱内平均温度可达63℃，最高迭71℃。干燥箱内温度的高低取决于受制冷工况影响的热泵供风温度。污泥干燥速率随空气温度升高和相对湿度的降低而增大，湿基含水率从42．6％到18．74％的平均干燥速率为0．123％／（m·min）。热泵干燥回收排气余热的节能效果显著，并随热泵排水量的增加而增大。平均能量回收率为39．1％，最大值为48．9％和最小值为23．6％，分别发生在热泵排水量最大和最小的阶段。     

褐煤热风-红外联合干燥方式优化与物性分析

褐煤干燥脱水是实现其高效利用、节能减排的重要技术措施。基于不同热风温度(60℃,80℃,100℃)和煤样粒度(小于2 mm, 2 mm～5 mm, 5 mm～7 mm, 7 mm～10 mm, 10 mm～13 mm)对高西沟低阶褐煤单一热风干燥特性进行探讨,依次采用单一热风干燥、热风-红外串联和热风-红外并联联合干燥方式,通过实验分析了干燥过程褐煤水分比和干燥速率的变化特征,应用比能耗(Q_SEC)和能效(η_e)对比了三种干燥方式的能耗,采用SEM和FTIR分别分析了煤样表观形貌和官能团。结果表明：单一热风干燥温度越高,煤样与空气温差越大,煤样获得的热量越高,干燥速率越快;煤样粒度越小,煤样水分比下降越快,结束时的水分比越低;热风-红外串联联合干燥转换时间节点越早,所需干燥时间越短,在热风与红外干燥阶段干燥速率各出现一次最大值;并联干燥中褐煤水分比呈指数下降,并以降速期为主要阶段;三种干燥方式按比能耗由大到小依次为单一热风干燥(334.54 MJ/kg)、热风-红外并联干燥(273.89 MJ/kg)、热风-红外串联干燥(121.18 MJ/...     

热风与真空冷冻联合干燥毛竹笋的试验研究

对毛竹笋进行了热风与真空冷冻联合干燥(AFD)的研究，应用热风与真空冷冻(AD FD)和真空冷冻与热风(FD AD)两种方式做不同转换点试验，将得到的产品分别与完全的热风干燥和冷冻干燥的产品比较其能量消耗和物化特性，并对它们的产品进行理化分析，确定了AFD联合干燥的方式和最佳转换点，得出了真空冷冻与热风(FD AD)联合干燥的产品接近完全真空冷冻干燥(FD)产品的结论，AFD联合干燥对于提高脱水笋干的质量、节省能量消耗是有效的。     

开放式热风穿流干燥蔬菜降低能耗的研究进展

开放式热风干燥（AD）工艺以其设备成本低、操作和维修简单等特点，在国内大批量脱水蔬菜生产中仍占有较高的比例。但开放式AD蔬菜的能耗高，故对其进行节能技术研究是项急需而有意义的。我们可以从AD工艺前处理、AD和其它干燥方法联合、干燥系统改进、余热回收以及工艺参数再优化等5个方面来降低AD蔬菜生产中的能耗。     

太阳能与热泵联合干燥木材特性的实验研究

介绍了国内外利用太阳能干燥木材的概况、太阳能与热泵联合干燥系统的组成与工作原理、太阳能与热泵联合干燥木材的特性和干燥木材的工艺实验。实验结果显示。太阳能与热泵联合供热可以弥补太阳能或热泵单独供热的缺点。太阳能比联合干燥节能3．8％,而联合干燥比热泵干燥节能11．8％;联合干燥比太阳能干燥时间缩短了14．9％。从能耗及生产效率综合考虑。太阳能与热泵联合干燥是值得推荐的一种干燥方法。     

哈密瓜片充氮低氧热泵干燥工艺研究

本文以哈密瓜为试验材料,以氮气为干燥介质置换空气降低设备中氧体积分数,研究了温度、切片厚度、氧体积分数和风速对哈密瓜热泵干燥速率、L值、Vc和总酚含量等指标的影响,正交试验结果表明最佳干燥工艺参数为：干燥温度50℃,切片厚度5mm,氧体积分数5％,干燥后哈密瓜片水分含量为7．42％,L值为71．28,Vc含量为21．06mg／100g,总酚含量为8．46mg／100g。     

粘胶短纤维的热风干燥特性研究

利用自行研制的热风干燥实验装置研究了热风温度、纤维层厚度、热风速度、纤维层含水率等对粘胶短纤维干燥特性的影响规律。结果表明:粘胶短纤维的热风干燥过程可依次分为4个阶段,即蒸发预热段、表面自由水分干燥段、纤维内部自由水分干燥段和纤维内部结合水分干燥段;热风温度对纤维第2阶段干燥速率的影响很大,100~140℃的含水率相差37.3%,对后面阶段的干燥速率影响较小,最佳热风温度为120℃;纤维层厚度对粘胶短纤维的第3阶段干燥速率略有影响,纤维层厚度以12 cm为宜;热风速度对短纤维干燥速率的影响很大,热风速度以2.0 m/s为宜,纤维层含水率对第2和第3阶段的干燥速率影响较大,应尽量减少纤维层的表面含水率。     

热泵干燥怀山药片的工艺研究

以提高怀山药干燥效率和产品品质为目标,本文利用热泵干燥方法,研究了热泵温度,风速,怀山药切片厚度对干燥曲线,L值,以及干制品复水率的影响。试验表明,热泵温度,风速及切片厚度都对怀山药片的干燥速率有显著影响。怀山药片热泵干燥的最佳工艺参数为：热泵温度40℃,风速1．0m/s,切片厚度5mm,干燥后怀山药片的L值和复水率分别为82．07和85．08％。     

香蕉片热泵干燥过程动力学模型研究

利用自制的热泵干燥设备,选择加热温度为45℃、风速为1．0m／s、物料厚度为3mm条件下的热泵干燥香蕉切片试验数据作为实测值样本。基于Matlab软件,利用高斯一牛顿算法,对传统干燥模型进行非线性最小二乘数据拟合求解,确定干燥系数。通过决定系数（R＇）、卡方差（x^2）、平均相对偏差（MBE）和均方根误差（RMSE）等拟合优度评价指标对7种干燥模型进行评价。结果表明,HendersonandPabiS模型的理论值和实测值吻合良好,能够很好地预测和控制香蕉切片热泵干燥过程的水分比变化规律。     

豆腐渣制取膳食纤维脱水脱腥工艺研究

豆腐渣制取膳食纤维时,因其水分,腥味而影响膳食纤维的风味和品质,所以对豆腐渣进行脱水、除腥前处理很有必要。文章分别用热风干燥、真空干燥、真空冷冻干燥对豆腐渣进行脱水干燥处理,结合干燥产品的持水性、溶胀性、结合脂肪能力,确定豆腐渣的摄佳脱水干燥方法,用豆腐渣粉进行NaOH浓度、脱腥时间、脱腥温度的单因素与正交实验,确定最佳的脱腥工艺条件。结果表明：热风千燥最好;最佳脱腥工艺条件为NaOH浓度0．9％,脱腥时间80min,水浴温度90℃。     

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

Abstract

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

Low-Temperature Drying Using a Versatile Heat Pump Dehumidifier

A drying system incorporating a commercial 2.3 kW heat pump dehumidifier was designed and constructed. The HPD was equipped with an external water-cooled condenser that rejected excess heat out of the system. The design of the system allowed for conducting drying with recirculation of air as well as use of electrical heaters. In an open mode, the drying could be carried out simultaneously with room dehumidification and water heating in the secondary condenser. Drying experiments were conducted with apple and comparisons were made between HPD assisted drying (partial and complete) and hot air drying (at 45 and 65°C). The HPD dried fruit exhibited better rehydration properties than the hot air dried samples. Water activity of the HPD dried samples was noticeably lower than that of the hot air dried samples at the same water content, indicating that the residual moisture was probably held under higher tension in the former. In terms of energy consumption, the process of HPD assisted drying is more expensive as much of the energy input is rejected at the secondary condenser as excess heat.     

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.     

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)。     

HEAT PUMP DRYING OF AGRICULTURAL MATERIALS

Heat pump-assisted drying is an energy-efficient process because the heat is recoverable. However, the economic feasibility of the heat pump dryer (HPD) is debatable because high grade energy (electricity) is used. In this study, sawn rubber wood and bananas were dried in an experimental HPD. The moisture extraction rates (MER) and the specific moisture extraction rates (SMER) of wood drying and banana drying decreased rapidly with the drying time but the compressor power was relatively constant. If the final moisture content of wood is less than 10%, the maximum average MER and SMER were 2.854 kg/h and 0.572 kg/kWh, respectively. Banana drying yielded the highest average MER of 2.710 kg/h when the drying load was highest. The corresponding SMER was 0.540 kg/kWh. Economic analyses among the HPD, an electrically-heated hot air dryer and a direct-fired dryer revealed that the HPD had the lowest operating cost.     

The Effects of Predrying Treatments and Different Drying Methods on Phytochemical Compound Retention and Drying Characteristics of Moringa Leaves (Moringa oleifera Lam.)

The most appropriate maturity stage of Moringa oleifera leaves was selected for drying based on phytochemical content, including quercetin and kaempferol. Desorption isotherms were developed and were best fit by the modified Henderson model. Prior to drying, samples were left untreated, blanched in boiling water, and blanched in NaHCO₃/MgO. The leaves were dried by hot air tray drying (TD) and heat pump–dehumidified drying air (HPD) at air temperatures of 40, 50, and 60°C. Alternatively, leaves were subject to microwave drying (MWD) at 150, 450, and 900 W and to freeze drying (FD). The moisture versus time data were fitted to five drying models. In general, a three-parameter model gave the best fit. The drying constant was related to the drying temperature or microwave power using an Arrhenius model. Effective moisture diffusivity (D _eff) increased with higher drying temperature, higher microwave power, or blanching treatments. Structural changes in the leaves after drying and upon rehydration were observed by scanning electron microscopy (SEM). Leaves blanched and dried using HPD at 50°C and fresh and dried using FD showed a partial breakdown of the tissue structure upon rehydration. HPD and blanching reduced the drying time by 8.3% and increased quercetin and kaempferol levels by 42.1 and 51.4%, respectively, compared to TD at 50°C. MWD provided the quickest drying followed by HPD and TD, respectively. HPD drying of M. oleifera after blanching resulted in relatively greater quality compared to TD and MWD.     

Effects of different drying methods on the physical characteristics and flavor of dried hawthorns (Crataegus spp.)

ABSTRACT

The objective of this study was to compare the physical characteristics and flavor of dried hawthorns obtained by freeze-drying (FD), microwave freeze-drying (MFD), atmospheric freeze-drying (AFD), and heat pump drying (HPD). The parameters including moisture content, product temperature, rehydration ratio, chroma, hue angle, yellowness index, total color difference, and energy consumption were investigated. The use of fuzzy reasoning for the sensory evaluation of hawthorn quality was also performed. As expected, AFD, FD, and MFD produced better accepted dried hawthorn products than did HPD. Nevertheless, FD consumed the highest energy and had a long drying time, but its product was the best; AFD had a similar energy cost as HPD, but its drying time was the longest; and MFD had a higher energy cost and longer drying time than HPD, but its product quality was similar to that of FD products. As a result, MFD and AFD had potential to replace FD to yield dried hawthorns with high product quality and relatively low cost.     

一种衣物空气低温烘干循环系统的设计及分析

基于机械热泵除湿原理,同时结合洗衣机衣物烘干温度的要求,设计出一种衣物空气低温烘干循环系统。借助EES软件对该系统建立系统模型,通过理论模拟分析研究其热力学性能,并对影响其热力性能的关键操作参量影响进行分析。研究结果表明,在保证冷凝量均为1.02 kg/h的情况下,该设计系统的单位能耗除湿速率（moisture extraction rate,MER）为0.5018 kW?h/kg,较常规电加热热风烘干系统降低了16.5%;COP为0.79,较常规烘干系统提高了16.5%。此外,相比较常规电加热热风烘干系统方案烘干温度90 ℃,该方案设计的滚筒操作温度仅为57.68 ℃,有效地拓展了可烘干衣物的范围。     

榴莲蜜变温间歇干燥

新鲜的榴莲蜜舍糖量高,水分多,是一种很容易腐烂的水果。为了能够延长贮存时间必须降低含水量。由于舍糖量高,当用传统的热风干燥进行干燥时,榴莲蜜表面会出现焦糖化。为了克服这个问题,在干燥的开始阶段应用间歇热泵干燥机,在干燥中期应用低温的除湿空气。结果表明：利用循环温度和递升温度干燥的样品湿含量可降低到0．081—0．110（g水／g干物质k此研究中用有限差分法来估算有效扩散系数值,较好地模拟了干燥动力学数据。就产品质量而雷,在循环温度干燥中减少热风干燥时间可生产柔软的干燥产品。而且,低温除湿空气的缓苏作用能减少干燥样品的总体颜色变化。