Parametric studies on hermetic reciprocating compressors

An advanced numerical simulation model for the thermal and fluid dynamic optimization of hermetic reciprocating compressors has been developed. The quality of the numerical solution has been verified by means of a critical analysis of the different sources of errors, and validated through an extensive experimental comparison. This work is focused on presenting different parametric studies of hermetic reciprocating compressors, based on the numerical simulation model developed. Results presented show the influence of different aspects (geometry, motor, valves, working conditions, etc.) on the basis of the meaningful non-dimensional parameters, which describe the compressor behaviour (volumetric and isentropic efficiency, coefficient of performance, etc.). The idea of this paper is to show the possibilities offered by the simulation model and its final objective, a better understanding of the thermal and fluid dynamic compressor behaviour to improve the design of these equipments.     

微波消解电感耦合等离子体发射光谱(ICP-AES)测定黑木耳中5种微量元素

本法选用硝酸和过氧化氢的混合消解液对黑木耳进行封闭微波消解,用电感耦合等离子体发射光谱仪(ICP-AES)同时测定黑木耳中微量铁、钙、镁、钾、钠、磷的含量.该方法检出限低,方法回收率98.4%~100.6%,相对标准偏差(RSD)0.82%~2.24%,该方法具有良好的准确度和精密度,操作流程短,基体干扰少,并且溶样过程无污染,方法简便、快速,适用于植物样品的批量分析.     

Vacuum Hermetic Fumigation: A review

Methyl Bromide and Phosphine are the most widely used chemical fumigants for insect control in stored grains. Ozone depletion, insect resistance, and residues on grain surface are the problems with the use of chemical fumigants. Zero tolerance for chemical residues under the international trade agreements require alternative solutions for safe and durable storage. Controlled atmosphere (CA)/modified atmosphere storage (MAS), temperature manipulation, hermetic storage, pressure manipulation (hyperbaric and hypobaric), safe fumigants of botanical derivatives and combination of these technologies have been practiced. Each method had certain merits and limitations restricting direct replacement for the existing chemical methods. This review explores chemical disinfection and physical methods with special emphasis on vacuum hermetic fumigation (VH-F). Modern hermetic storage systems utilize ultra-low oxygen and water permeability materials for storage of grains. Depletion of oxygen in the storage systems naturally or through the application of negative pressure (50–100 mm Hg) causes slower metabolic rate and finally cessation of basic metabolism and death of insects in a few days (up to 7 days). The efficacy of VH-F on the lethality of insects depends on vacuum level, stage and type of insects, temperature, CO₂ level and exposure time. Suitability of vacuum hermetic storage systems for various agricultural produces as an alternative to chemical fumigation and the future scope of vacuum hermetic fumigation system are discussed.     

Effectiveness of grain storage facilities and protectants in controlling stored-maize insect pests in a climate-risk prone area of Shire Valley,Southern Malawi

Shire Valley is one of Malawi's most vulnerable areas to climate change (CC). In addition to other impacts, CC is expected to affect storage insect pest status, and the efficacy of grain storage facilities and protectants. On-farm grain storage trials were therefore conducted in Shire Valley to assess the performance of storage facilities and grain protectants against storage insect pests. Eight smallholder farmers hosted the trials in Thyolo and Chikwawa districts. Seven grain storage treatments were evaluated for 32 weeks during two storage seasons: Neem leaf powder (NM), Actellic Super dust (ASD), ZeroFly^® bag (ZFB), Purdue Improved Crop Storage bag (PICS), Super Grain Bag (SGB), hermetic metal silo (MS) and untreated grain in a polypropylene bag (PP). Insect pest populations and grain damage increased with storage duration and differed significantly between treatments (p < 0.05). Grain stored in hermetic bags (PICS, SGB) sustained significantly lower (p < 0.05) insect damage and weight loss compared to other treatments across sites and seasons. The hermetic bags also outperformed the other treatments in suppressing insect numbers. However, germination rates of undamaged grains stored in the hermetic storage facilities (MS, PICS, SGB) for 40 weeks were extremely low (<15%) compared to that of undamaged grains from NM treatment (53–58%) and the other treatments (>75%) at both sites. The hermetic MS, ZFB bags, ASD and NM treatments did not effectively protect grain from insect damage. High in-store mean temperature (35.6 °C) and high initial grain moisture content (13.7%) may have negatively affected efficacy of some treatments and seed germination. Tribolium castaneum survival in the MS requires further investigation. The hermetic storage bags (PICS, SGB) can be recommended for long-term maize grain storage (≥32 weeks) by smallholder farmers in Shire Valley and other similar climate change-prone areas in sub-Saharan Africa.     

Triple bagging hermetic technology for post-harvest preservation of paddy rice Oryza sativa L. in the Sahel of West Africa

Trials of the Purdue Improved Crop Storage (PICS) bag technology for the storage of paddy rice, Oryza sativa L., were conducted in Burkina Faso, Ghana and Niger. Paddy rice naturally infested with insects, the most abundant species being Tribolium spp. and Rhizopertha dominica, was sealed in triple layer PICS bags, or in conventional woven polypropylene sacks. At the end of 7–18 months of storage in PICS bags the number of insects did not increase, the weight of 100 seeds did not change, and the proportion of damaged seeds was not different from that present when the paddy was first put into the bags. By contrast, paddy stored in the conventional way in woven polypropylene bags exhibited weight losses ranging from 3 to 8.7%. In Bolgatanga, Ghana, where paddy was stored for 18 months, germination of paddy kept in the PICS bags was comparable to that present at the beginning of the experiment. PICS bags can be used for the safe, low-cost, insecticide free storage of paddy rice.     

Pest control treatments with phosphine and controlled atmospheres in silo bags with different airtightness conditions

The silo bag technology has been extensively used in Argentina for storing grains (e.g. wheat, corn, barley, sunflower and soybean among others) since the mid-1990s. Silo bag are widely considered a hermetic storage system in which PH₃ fumigation is frequently implemented for pest control. However, there is insufficient information regarding the potential airtightness of silo bags and how it could affect the performance of fumigation and controlled atmosphere treatments. In this study, a pressure decay test (PDT) was implemented to characterize airtightness level of silo bags set up following various procedures. PH₃ fumigation treatments with different dosages and hermeticity levels were conducted, and fumigant concentration was monitored. Controlled atmosphere treatments with carbon dioxide were also implemented in silo bags with different hermeticity levels. Results showed that less than half of the bags tested in the field had a PDT indicated for fumigation (90 s), and that when a bag without thermo sealing was used for fumigation, this treatment failed. However, it was demonstrated that with simple and inexpensive practices silo bags can achieve high enough airtightness conditions to implement successful PH₃ fumigation (5 days above 200 ppm with a dosage of 1 g of PH₃/m³) and even controlled atmosphere treatments (more than 18 days with CO₂ concentration above 70%). This study shows that silo bags could be used as a cost competitive hermetic storage technology for performing controlled atmosphere treatments.     

The effect of small leaks,grain bulk,and the patching of leaks on the performance of hermetic storage

Hermetic storage containers are often used by farmers to protect their harvested grain from insect damage and ultimately stop insect population development. Sometimes holes in a storage container are created by insects or by accident; such holes may reduce the effectiveness of the hermetic storage unit. Using cowpea grain and the cowpea bruchid, Callosobruchus maculatus (F), we investigated the degree to which holes in a hermetic storage container wall affect the level of grain damage. When there were low numbers of holes, seed damage increased markedly with each additional hole. The grain itself contributed a barrier to oxygen diffusion through the grain mass. If holes in the container wall were patched with a single layer of HDPE film, grain damage was indistinguishable from that seen under full hermetic conditions. We provide evidence that a single layer of woven polypropylene contributes a small but measurable barrier to oxygen penetration into the container.     

Performance analysis of a series of hermetic reciprocating compressors working with R290 (propane) and R407C

In this paper, a series of compressors with different capacities and geometries working with propane as refrigerant are analyzed in terms of the compressor model developed by [E. Navarro, E. Granryd, J.F. Urchueguía, J.M. Corberán, A phenomenological model for analyzing reciprocating compressors, International Journal of Refrigeration, in this issue, doi:10.1016/j.irefrig.2007.02.006]. The relative influence of the diverse compressor losses is estimated as a function of the operating conditions.In addition, a comparison study between propane and R407C was carried out for one compressor and the observed differences were analyzed in terms of the compressor model. This study was also useful to verify the model's goodness with the aim of predicting the compressor performance with an untested refrigerant.     

一种氨制冷封闭式压缩机密封方法的研究

提出了一种压缩机的压力平衡式密封结构,实现了对电动机定子的无压差静密封,可靠地保证了定子防止氨腐蚀,使得制造氨制冷封闭式压缩机成为可能,为研制制冷设备提供了新思路。     

谐振梁压力传感器的气密封装技术

文章介绍了谐振粱压力传感器的气密封装技术，全面分析了影响气密封装的各种因素，提出了相应的解决方法。