基于阻隔性的卷烟内衬材料应用性能研究

为探讨不同阻隔性能卷烟内衬材料的实际应用性能,模拟了卷烟包装条件,采用烘箱法和静态顶空-气质联用法,分别评价了不同存储条件下内衬材料对烟丝含水率和2种外加致香成分含量的影响。结果显示,内衬材料的透氧透湿性能与烟丝含水率及致香成分含量之间没有明显的对应关系,实际应用性能基本不受透湿透氧性能的影响。     

复合软包装材料结构的设计研究

文中提出了一种确定塑料复合薄膜的透湿度/透气度的计算方法,需要使用塑料薄膜透湿度/透气度数据、食品饮料允许的最大吸氧量以及塑料原材料的成本等数据,同时对复合塑料薄膜的试验值和计算值进行比较,说明该计算方法对塑料复合薄膜的设计及加工是一个很好的工具.     

板翅式静止型全热交换器的研制及其热工性能

板翅式静止型全热交换器是一种同时回收空调排风中显热(冷)和潜热(冷)的设备,应用在空调工程中可以明显地节约新风负荷。本文对影响热湿交换效率的因素作了分析,阐明不能用焓交换效率评定板翅式静止型全热交换器的热工特性,而应该用热交换效率和湿交换效率。作为评定指标,对于一定结构的全热交换器,影响后两效率的只是面风速和两股进风的风量比,而与进风参数无关。文章还列出了样机热工特性的实验结果。     

微波处理对塑料薄膜包装材料阻隔性能影响的研究

研究了常用的塑料薄膜包装材料经微波处理不同时间后其透氧率、透湿率的变化规律.研究结果表明,塑料单膜随微波处理时间增加,透氧率明显增大,而复合薄膜透氧率变化较小;透湿率变化正好相反,微波处理相同时间后,复合薄膜透湿率增长明显大于塑料单膜.     

射频磁控溅射SiOx薄膜的制备与阻隔性能研究

利用磁控溅射技术,以SiO2为靶材,Ar为射频源气体,在PET基材上制备SiOx薄膜.研究了不同放电功率、氩气流量、镀膜时间等参数对SiOx薄膜阻隔性能的影响.结果表明:在一定范围内,薄膜的阻隔性能随放电功率的增大而增大,而后逐渐减小;氩气流量对薄膜的阻隔性能也有一定影响;镀膜时间在10min时SiOx薄膜的阻隔性能最好.扫描电镜SEM测试表明,在氩气流量为100cm3/min,镀膜时间10min,1500W放电功率下制备的SiOx薄膜阻隔性能较好、表面较均匀.     

阻燃剂对沥青性能影响的试验研究

隧道中的沥青路面使用过程中,一旦发生交通事故引起路面着火,后果不堪设想。故在长隧道沥青路面表面层铺装过程中,有必要应用阻燃剂来提高基质沥青的氧指数,从而达到隧道路面阻燃的效果。本文从阻燃剂对沥青性能的影响入手,通过对加入阻燃剂后沥青三大指标的试验检测和氧指数试验,研究阻燃沥青的路用性能和阻燃性能。     

食品包装复合材料结构设计研究

本文提出了一种确定塑料复合薄膜的透湿度/透气度的计算方法,需要使用塑料薄膜透湿度/透气度数据、食品饮料允许的最大吸氧量以及塑料原材料的成本等数据,同时对复合塑料薄膜的试验值和计算值进行了比较,说明了该计算方法对塑料复合薄膜的设计及加工是一个很好的工具。     

几种食品包装用塑料膜阻透性能比较

目的研究不同厚度、不同材质的食品包装用塑料膜透氧量、透湿量的变化情况,为食品包装在阻隔性方面的选材提供依据和指导。方法采用压差法和杯式法分别测试塑料膜的透氧量和透湿量。结果单层塑料膜随厚度的增加,透氧量和透湿量均减小,阻隔性能变好。相同厚度的PE,PET,BOPP,PA这4种单层塑料膜中,PA的透氧量最小,PE的透氧量最大,BOPP的透湿量最小,PA的透湿量最大。复合膜厚度增加,其透氧量、透湿量均减小,但减小幅度逐渐变小。塑塑复合膜外层材料厚度不变时,透氧量、透湿量随总厚度变化不太明显,EVOH塑料复合膜的透氧量值和透湿量值较小,通常在5以下,铝箔塑料复合膜的透氧量值和透湿量值均小于1。结论单层塑料膜PA的氧气阻隔性最好,PE的氧气阻隔性最差,BOPP的水蒸气阻隔性最好,PA的水蒸气阻隔性最差。复合膜中,塑塑复合膜的阻隔性主要取决于外层材料,铝塑复合膜的阻隔性最好,含高阻隔材料EVOH的塑料复合膜的阻隔性比普通塑塑复合膜好,其阻隔性可与铝塑复合膜媲美。     

打坑BOPP薄膜的透湿性能研究

打坑薄膜通过对薄膜进行打坑微处理,可提高其透氧性能及透湿性能。打坑BOPP薄膜在食品包装中得到了广泛的应用,但使用过程中其透湿性不好的问题较为突出,包装内易出现结露问题。以透湿性能为试验指标,选用2种不同透氧系数的打坑BOPP薄膜和未打坑BOPP薄膜进行了对比试验。结果表明,透氧系数大的打坑BOPP薄膜的透湿量也相对较大;同时,透氧系数相同的打坑BOPP薄膜的反面透湿量要大于其正面透湿量;对于不同透氧系数规格的薄膜,反面的透湿性增加量要大于正面的。可见,在实际应用中,不仅需要根据透氧系数来选择合适的包装用BOPP薄膜,且在应用时还需调整薄膜正反面的选择。     

新型无孔透湿TPU薄膜的制备及其服用性能研究

采用熔融共混和吹塑成型工艺制备了无孔型热塑性聚氨酯弹性体(TPU)薄膜。以膜厚度、温度和相对湿度为变量对TPU薄膜的透湿和透气性能进行测试分析,并对其表面形貌、成分含量、热稳定性进行了表征。实验结果表明:TPU薄膜的透湿量随着膜厚度的增加而减小,薄膜透湿量随着温湿度的升高而显著增加;按ASTME96BW—2000标准测试,厚度为0.012mm的TPU薄膜透湿量达7093g/(m~2·d)。利用扫描电子显微镜观察到TPU薄膜表面相对平整,未发现微孔结构。气体渗透率测试分析表明,CH_4和N_2基本无法透过TPU薄膜,因此TPU薄膜可以有效地阻隔细菌与病毒入侵。傅里叶变换红外光谱表征结果显示,1000～1300cm~(-1)处出现Si—O伸缩振动吸收峰,证明纳米SiO_2成功掺杂到TPU中。     

翅片管式换热器表面结霜特性的数值分析和实验研究

换热器表面结霜会增加传热热阻和流动阻力,为合理确定融霜周期,必须对其结霜特性作深入的了解。文中采用了数值求解方法预测了平翅翅片管式换热器的结霜量和霜层密度的变化过程。翅片管结霜是一个瞬变问题,为了计算方便,将其简化为准稳态过程,即在时间步长内,认为该过程是稳定的,然后把所得的霜层厚度以及霜层的表面温度作为下一时间步长内传热传质的边界条件。在研究中考虑了霜层阻力引起风量下降这一因素,模型的计算结果与翅片管式换热器结霜的实际工况相符。     

An experimental study of carbon-carbon composite materials

A systematic exploratory development study of the mechanical behaviour of pyrolyzed organic resin matrices reinforced with high performance carbonaceous fibres was performed. Fourteen combinations of fibre and precursor matrices in unidirectional composite form were fabricated and tested. Physical, thermal, and mechanical properties were determined at various process stages. A principal conclusion was that it is the very poor interfacial bond which is typically achieved between fibres and matrix that accounts for the low mechanical properties which are commonly observed. This poor bond was attributed primarily to the mismatch between the transverse thermal expansion coefficient of the graphite fibres and the thermal expansion coefficient of the surrounding matrix. Among the recommendations made is that the carbonization/graphitization conditions be modified to promote better interfacial bonding.Consultant, Philco-Ford Corporation.     

淀粉基绿色建筑材料应用及试验研究

利用可再生资源发展绿色建筑材料已成为趋势之一,为了开发淀粉基绿色建材,首先,总结归纳了淀粉在木材环保胶黏剂、涂料、砂浆、陶瓷生产和混凝土减水剂制备等方面的研究和应用,其次.对改性淀粉拌合生土进行了无侧限抗压强度和直接剪切试验,结果表明改性淀粉可提高生土的强度,研究结果为淀粉基绿色建材的发展提供参考.     

套管管束式换热器换热特性试验研究

清华大学核能与新能源技术研究院对具有特殊结构的套管管束换热器(其传热单元由带螺旋肋片的外套管和带微波浪弯的内套管组成,通过自身结构实现传热管的支撑和定位)的换热特性进行了试验研究.试验结果表明,与一般流道的换热性能相比,不规则环形窄缝流道的换热系数不仅降低,而且随雷诺数的变化趋势也较平缓;外套管管间流道的换热系数降低,但变化趋势与普通流道相同.根据试验数据,采用分离系数法,拟合出了不规则环形窄缝流道和外套管管间流道的换热公式.     

An experimental study of on‐line computer control techniques applied to a double pipe heat exchanger

Abstract

Three different on‐line computer control methods, namely the identification and optimizing control technique, the direct design method and the digital form of P‐I‐D control, are applied to control the response of a double pipe heat exchanger. The relative merits of the methods are studied and discussed.

The experimental work is accomplished by the use of a HP‐1000 model 5L microcomputer. A digital voltmeter; the HP‐3456A, is used for reading and transferring data from the process to the computer. A data acquisition system, the HP‐3497A, contains a thermocouple relay and a D/A converter which can read input data from a thermocouple and also convert digital outputs to 4–20 mA signals required by control elements.

Results indicate that the identification and optimizing control technique gives superior performance in most cases, but requires longer computation time. Digital form of the P‐I‐D control requires the least computation time but yields poor performance and is limited in its potential for application to multivariable systems or to tracking problems.     

Performance comparison between enthalpy recovery wheels and dehumidification wheels

A mathematical model of desiccant wheels is established and validated by experimental results. The different effects of substrate, air mixing, and rotation speed on the performance of enthalpy recovery wheels and dehumidification wheels are analyzed. Substrate with high heat capacity and low heat conductivity is recommended for enthalpy recovery wheels, while substrate with low heat capacity and low heat conductivity is suitable for dehumidification wheels. Air mixing should be considered in evaluating recovery wheels' performance but can be ignored for dehumidification wheels. For recovery wheels without considering air mixing, higher the rotation speed, higher the recovery efficiency; when considering air mixing, the optimal rotation speed is lower than the corresponding rotation speed at a 5% air mixing rate. There also exists an optimal rotation speed to obtain better dehumidification performance for dehumidification wheels. Meanwhile, the reasons behind the discrepancies between recovery wheels and dehumidification wheels are discussed.     

Degradation of heat exchanger materials under biomass co-firing conditions

Abstract

Co-firing biomass in conventional pulverised coal fired power stations offers a means to rapidly introduce renewable and CO₂ neutral biomass fuels into the power generation market. Existing coalfired power stations are both much larger and more efficient than current designs of new biomass combustion systems, so feeding a few percent of biomass feed into an existing large coal fired station will give more biomass derived power than a new dedicated biomass station. Co-firing levels started at ～2% biomass, but this has increased to ～5–10% biomass, with higher levels of biomass co-firing being investigated, although supply of biomass becomes an issue with increasing co-firing levels. The lower levels of biomass co-firing (up to ～5%) can be achieved with relatively minor modifications to existing plants, so avoiding the large capital costs and risks of building new biomass-only fired power systems. However higher levels of co-firing are more difficult to achieve, requiring dedicated biomass supply systems and burners. For existing coal-fired power stations, the co-firing of biomass causes some practical problems, e.g.: the control of co-firing two fuels; changes to bottom/fly ash chemistry; changes to deposition (fouling and slagging) within the boiler; reduced reliability of key high temperature components (e.g. heat exchangers) due to increased corrosion problems relative to those experienced with coal alone.

This paper reports the results of assessments carried out to evaluate the potential operating conditions of heat exchangers in combustion systems with biomass (wood or straw) and coal cofiring, as well as laboratory corrosion tests that have been carried out to give an initial assessment of potential effects of biomass-co-firing.

The corrosion tests have been carried out using the deposit recoat method in controlled atmosphere furnaces. A series of 1000 hour tests have been carried out at typical superheater and evaporator metal temperatures using simulated deposit compositions and gaseous environments (selected on the basis of plant experience and potential fuel compositions). Five materials were exposed in these tests: 1Cr steel, T22 steel, X20CrMoV121, TP347HFG and alloy 625. In order to produce statistically valid data on the actual metal loss from the materials, the performance of the materials in these tests was determined from dimensional metrology before and after exposure. For each material, these data have been used to determine the sensitivity of the corrosion damage to changes in the exposure conditions (e.g. deposit composition, gas composition) thereby producing initial models of the corrosion performance of the materials. The corrosion data and model outputs have been compared with data available from power plants operating on coal, straw or wood fuels.     

Impact of powder composition on processing-relevant properties of pharmaceutical materials: An experimental study

In this work, we studied the influence of powder composition on packing density and other processing-relevant properties of binary mixtures, including powder flowability. Binary mixtures of pharmaceutical powders with different particle size ratios, α and varying fractions of large and small particles were analyzed systematically. Mixtures of three excipients and one API with different composition (2, 5, 10, 30, 50, 70, 90, 95 and 98 wt%) were prepared in a Turbula mixer. Powders with different properties and particle size distribution were chosen, in order to obtain three binary mixtures with different size ratios. Then, macroscopic powder properties including bulk (poured) and tapped density (BD and TD) were measured. A powder rheometer was used to measure the flow function coefficient (ffc), cohesion, compressibility and permeability of the binary mixtures. We considered experimentally three classes of binary mixtures, which are characterized by two critical ratios of particle diameter: the critical size ratio of entrance (α_c) and the critical size ratio of replacement (α_r), where α_c = 0.154 and α_r = 0.741. Below the critical size ratio of entrance (α_c), the particle asymmetry (ratio between large and small particle diameters) is high and small particles can fill the voids between larger ones. Between α_c and the critical size ratio of replacement (α_r), the smaller particles are too large to fit in the voids between larger particles (packing structure changes). Above α_r, the particles are more or less symmetric in size and overall packing structure does not change by mixing the particles. Our experiments show that there is a non-linear and non-monotonic dependence of all relevant properties on composition for powder mixtures that have an α < α_r. This non-linear behavior is even more significant for strongly asymmetric binary mixtures with α < α_c. We argue that this behavior is related to the composition dependence of random packing of particulate systems. Our results have relevance to pharmaceutical particle processing operations where constant powder mixture properties are needed to ensure quality standards are met; such operations include capsule or die filling during tableting, and the continuous feeding of powders via screw feeders. Our results suggest that for pharmaceutical particle processing operations, where constant powder mixture properties are a prerequisite for process robustness, the size ratio of API and excipient particles, α should not be smaller than α_r = 0.741.     

Performance study on air-cooled household refrigerator with cold storage phase change materials

The air-cooled frost-free refrigerator has become the main power consumer among household appliances. This study presents a new air-cooled household refrigerator that uses PCM in the fresh food and freezing chambers. Operational characteristics and performance test results are provided in the conditions of off-peak refrigeration with PCM and conventional refrigeration with/without PCM. Results show that refrigeration off-peak modes resulted in the peak temperature difference between M-packs and maximum temperature increase of M-packs in the freezing chamber. The energy consumption of the refrigerator is relatively increased. The energy consumption of the refrigerator prototype with PCM under the original control mode is reduced by 18.6% and the compressor ON-time ratio is reduced by 13.6% compared with the refrigerator prototype without PCM. Frost-free refrigerator with PCM under original control type exhibits advantages in terms of energy consumption and food quality.     

冷氦换热器低温换热试验研究

为验证采用液氧对冷氦加温的可行性,研究光管、整体翅片管两种形式的换热器在不同流量、压力下的换热性能,开展了冷氦换热器的原理性试验和数值仿真研究.研究结果表明:相同工况下,整体翅片管换热效果比光管好很多,整体翅片管对强化换热效果明显,数值仿真结果与试验结果吻合较好.