生物制品贮藏新技术——过冷技术

多年来,人们一直在寻找一项有效技术用于提高生物制品和细胞培养物贮藏时的稳定性。随着生物技术产业的发展,对这项技术的需求越来越迫切。特别对于那些对冷冻特别敏感的不稳定产品,高度纯化的化合物和工程细胞系。到目前为止,常规使用的技术包括冷冻(-80℃)和冷冻干燥。而对于蛋白质,常采用盐析制成稳定的晶体后再低温贮藏。尽管这些技术在特定的运用中确有其优点。

低温推进剂过冷技术研究

综述了低温推进剂3种过冷方式(换热过冷、抽空减压过冷和冷氦气鼓泡过冷)的过冷机理,并对比分析了其利弊,在地面全过程过冷加注时推荐采用抽空减压过冷对低温推进剂进行冷却.基于热力学理论推导了低温推进剂抽空减压过冷时耗液量、制冷量、抽空时间和泵最低抽速的表达式.研究得出低温推进剂耗液量主要用于自身温降,抵消外部漏热和贮罐材料比热容所占比例很小,如液氢自身过冷、材料比热容和外部漏热所占的相对耗液量分别为10.94%,0.38%,0.098%.推荐采用变物性算法来精确计算低温推进剂耗液量,可降低运载火箭发射成本,提高低温推进剂利用率,与现有公式对比,其相对误差为18%.

高密度脉冲电流对Fe-B共晶合金熔体过冷度的影响

采用熔融玻璃净化加循环过热相结合的深过冷技术及高密度脉冲电流作用于金属熔体的方法,研究了Fe-B共晶合金深过冷条件下及脉冲电流作用下的凝固组织。通过DSC方法分析了高密度脉冲电流对Fe-B共晶合金熔体过冷度的影响。结果表明,高密度脉冲电流作用下的凝固组织与深过冷条件下的凝固组织形貌类似,且两种实验条件下获得的过冷度基本相同,证明了脉冲电流可以对金属熔体实现深过冷。

The Shandong Shidao Bay 200 MW_e High-Temperature Gas-Cooled Reactor Pebble-Bed Module(HTR-PM) Demonstration Power Plant: An Engineering and Technological Innovation

In 2005, the US passed the Energy Policy Act of 2005 mandating the construction and operation of a high-temperature gas reactor （HTGR） by 2021. This law was passed after a multiyear study by national experts on what future nuclear technologies should be developed. As a result of the Act, the US Congress chose to develop the so-called Next-Generation Nuclear Plant, which was to be an HTGR designed to produce process heat for hydrogen production. Despite high hopes and expectations, the current status is that high temperature reactors have been relegated to completing research programs on advanced fuels, graphite and materials with no plans to build a demonstration plant as required by the US Con- gress in 2005. There are many reasons behind this diminution of HTGR development, including but not limited to insufficient government funding requirements for research, unrealistically high temperature requirements for the reactor, the delay in the need for a ＂hydrogen＂ economy, competition from light water small modular light water reactors, little utility interest in new technologies, very low natural gas prices in the US, and a challenging licensing process in the US for non-water reactors.

A Review of Heat Transfer Enhancement through Flow Disruption in a Microchannel

In this paper a comprehensive review of heat transfer enhancement through microchannels has been presented. Over the past few years due to multifunetion, shrinking package size and high power dissipation, the heat flux per unit area has increased significantly. Microchannels, with their large heat transfer surface to volume ratio and their small volumes, have shown a good thermal performance. Microchannels have been proven to be a high per- formaace cooling technique which is able to dissipate heat flux effectively from localized hot spots over small surface area. A good amount of heat transfer augmentation techniques have been reported on flow disruption through microchannel. These techniques promote free stream separation at the leading edge which results in boundary layer development and enhanced mixing leading to increased heat transfer. Flow disruption can be achieved through passive surface modifications, such as, shape of channel, dimple surfaces, ribs, cavities, groove structures, porous medium, etc. Combined effects of these geometrical configurations in heat transfer augmenta- tion are also reported in the literature. In this paper recent developments in experimental and numerical simula- tions of single-phase liquid cooled microchannel have been discussed to analyze the pressure drop, friction and heat transfer characteristics due to different flow conditions, roughness structure and passive surface modifica- tions. It has been observed that the flow disruption techniques are effective for heat transfer enhancement with lower penalties of increased pressure drop. The review concludes with suggestions for future research in this area.

Numerical simulation of heat transfer process in cement grate cooler based on dynamic mesh technique

A grate cooler is key equipment in quenching clinker and recovering heat in cement production. A two-dimensional numerical model based on a 5000 t/d cement plant is proposed to for a study on the gas-solid coupled heat transfer process between the cooling air and clinker in a grate cooler. In this study, we use the Fluent dynamic mesh technique and porous media model through which the transient temperature distribution with the clinker motion process and steady temperature and pressure distribution are obtained. We validate the numerical model with the operating data of the cooling air outlet temperature. Then, we discuss the amount of mid-temperature air outlet and average diameter of clinker particles, which affect the heat effective utilization and cooling air pressure drop in clinker layer. We found that after adding one more mid-temperature air outlet, the average temperature of the air flowing into the heat recovery boiler increases by 29.04℃ and the ratio of heat effective utilization increases by 5.3%. This means heat recovery is more effective on adding one more mid-temperature air outlet. Further, the smaller the clinker particles, the more is the pressure drop in clinker layer; thus more power consumption is needed by the cooling fan.

Solidified morphology and mechanism of bulk nanocrystalline Fe_(80)P_(13)C_7 alloy at isothermal undercooling

The molten Fe80P13C7 alloys can achieve a large undercooling up to 320 K by fluxing technique. With the help of fluxing technique, the molten Fe80P13C7 alloys can be solidified at different undercooling （△T） through isothermal undercooling experiment It is indicated that the microstructure of the solidified Fe80P133C7 alloy specimens is refined significantly with the increasing undercooling and the grain size is about 20 μm, 10 μm, 200 nm and 70 nm for △T=50 K, 150 K, 250 K and 320 K, respectively The solidification morphologies of the solidified Fe80P13C7 alloy specimens under different undercooling are quite different. When △T=50 K, it presents a traditional solidification microstructure under a undercooling condition, composed of the primary dendrite and anomalous eutectic within the dendrites. When △T=150 K, a cell-like solidification morphology can be found, which can be proposed to be formed based on the nucleation and growth of spinodal decomposition mechanism. When △T=250 K, there is a strong direction of the solidification under an optical micrograph, two zones can be divided, and the microstructure of each zone presents a network which results from a liquid spinodal decomposition. When △T=320 K, the microstructure presents a random network completely. Microhardness test shows that the hardness of the solidified specimens increases with the undercooling.

Temperature Measurement of Supercooled Droplet in Icing Phenomenon by means of Dual-luminescent Imaging

The collision of a supercooled water droplet with a surface result an object creates ice accretion on the surface. The icing problem in any cold environments leads to severe damages on aircrafts, and a lot of studies on prevention and prediction techniques for icing have been conducted so far. Therefore, it is very important to know the detail of freezing mechanism of supercooled water droplets to improve the anti-and de-icing devices and icing simulation codes. The icing mechanism of a single supercooled water droplet impacting on an object surface would give us great insights for the purpose. In the present study, we develop a dual-luminescent imaging technique to measure the time-resolved temperature of a supercooled water droplet impacting on the surface under different temperature conditions. We apply this technique to measure the exact temperature of a water droplet, and to discuss the detail of the freezing process.

Morphology and structure evolution of metallic nanowire arrays prepared by die nanoimprinting

Metallic nanowire arrays （NWAs） possess wide application prospects due to their unique property, and the tailoring of NWAs＇ structure and morphology is of importance since it would significantly influence the per- formance of NWAs. In the present work, the morphology and structure evolution of the NWAs prepared by the newly developed die nanoimprinting technique has been investigated in detail. It was found that increasing pro- cessing temperature, time and pressure could increase the length of the nanowires and change the NWAs＇ morphol- ogy from monodispersed form to aggregated form. Increasing processing time and temperature within the supercooled liquid region would promote crystallization, while increasing processing pressure could suppress the crystallization. This work provided important insights into the structure and morphology evolution, and therefore, the tailoring of metallic NWAs prepared by die nanoimprinting through adjusting the process parameters.