145. Studies on vacuum condensation point (V.C.P.) in sublimatography

The tradition of fruit dehydration in Serbia has been long and anviable. It seems that Serbian machine-building in the area of fruit processing technology has given its greatest contribution in this field. It has been one 100 years since the smoking house of Mr Stokovic, PhD was announced to be the best and the most promising plum dehydrator at the open competition organized in Topcider by the Ministry of Agriculture. It was the first real almost continual fruit dehydrator where plums were moved at certain intervals closer and closer to the source of heat. Such a concept of plum dehydration from lower to higher temperatures was held on even later in perhaps our most famous dehydrator CER. Even the smoky smell was retained but liquid fuel was used for technical purposes. For a long time, it has been a well- known fact that vacuum dehydration has many advantages. In our country there have been many attempts to make fruit dehydrator of greater capacities in which vacuum would be used. Of course, there have been many problems, both technical and technological, but today a hundred years after accepting Stojkovic?s smokehouse, it is our great honor to present to you the results of plum dehydration in a home-made vacuum condensation dehydrator. We hope that now path is widely open to high quality dehydration, and not only for that plum, but for fruit susceptible to oxidation which is the reason our food industry has not produced it so far. This is probably a farewell to the most dangerous, but for the product quality, the most necessary operation - sulphuration.

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Microstructural Design by Controlled Crystallization of Metallic Glasses

MRS Proceedings ◽

10.1557/proc-806-mm1.2 ◽

2003 ◽

Vol 806 ◽

Cited By ~ 1

Author(s):

Uwe Köster ◽

Rainer Janlewing

Keyword(s):

Glass Transition ◽

Metallic Glasses ◽

Nanocrystalline Materials ◽

Nanocrystalline Alloy ◽

High Energy ◽

Fine Grained ◽

Annealing Conditions ◽

Diffusion Controlled ◽

Microstructural Design ◽

Vacuum Condensation

ABSTRACTNanocrystalline materials can be produced e.g. by high energy ball milling or vacuum condensation; these methods require powder compaction as a final step. In another route - the nano-crystallization - metallic glasses are used as precursors for nanocrystalline materials without any porosity. The conditions for achieving an ultra-fine grained material by crystallization are small growth, but large nucleation rates. Whereas in Fe-Ni-B glasses the finest microstructure is produced at annealing temperatures above the glass transition close to the maximum of the nucleation rate, in Zr-based metallic glasses nanocrystallization was found to proceed only at relatively low temperatures below the glass transition. The aim of this contribution is to study systematically the micromechanisms involved in the microstructural design.Crystallization was studied in detail in Fe-Ni-B and Zr-based metallic glasses by means of TEM, X-ray diffraction and DSC. Nucleation and growth rates were estimated from crystallization statistics. By modeling the obtained time-dependent nucleation rates in the framework of diffusion controlled classical nucleation all relevant crystallization parameter could be derived. Using these data TTT-diagrams could be drawn and annealing conditions deducted, e.g. for the formation of a nanocrystalline alloy.Isothermal DSC plots for polymorphic crystallization can only be explained with a very significant decrease in the growth rate at later stages. Such a decrease is assumed to result from stresses building up during crystallization beyond the percolation limit for the crystalline phase; under this condition stresses resulting from the volume change during crystallization cannot be compensated by viscous flow as in the case of isolated crystals in an amorphous matrix.

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Shellside Vacuum Condensation With a Noncondensable Gas

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2016-67417 ◽

2016 ◽

Author(s):

Susan N. Ritchey

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Atmospheric Pressure ◽

High Speed ◽

Process Conditions ◽

Transfer Data ◽

Noncondensable Gas ◽

Overall Heat Transfer Coefficient ◽

Vacuum Condensation

Shell-and-tube vacuum condensers are present in many industrial applications such as chemical manufacturing, distillation, and power production [1–3]. They are often used because operating a condenser under vacuum pressures can increase the efficiency of energy conversion, which increases the overall plant efficiency and saves money. Typical operating pressures in the petrochemical industry span a wide range of values, from one atmosphere (101.3 kPa) down to a medium vacuum (1 kPa). The current shellside condensation methods used to predict heat transfer coefficients are based on data collected near or above atmospheric pressure, and the available literature on shellside vacuum condensation generally lacks experimental data. The accuracy of these methods in vacuum conditions well below atmospheric pressure has yet to be validated. Recently, HTRI designed and constructed the Low Pressure Condensation Unit (LPCU) with a rectangular shellside test condenser. To date, heat transfer data have been collected in the LPCU for shellside condensation of a pure hydrocarbon and of a hydrocarbon with noncondensable gas at vacuum pressures ranging from 2.8 to 45 kPa (21 to 338 Torr). Traditional condensation literature methods underpredict the overall heat transfer coefficient by 20.8% ± 20.4% for the pure condensing fluid; whereas they overpredict heat transfer by 36.8% ± 40.0% with the addition of the noncondensable gas. Over or under predicting the overall heat transfer coefficient in the presence of noncondensable gases leads to inefficient condenser designs and the inability to achieve desired process conditions. With the addition of the noncondensable gas, the measured heat exchanger duty was significantly reduced compared to the pure fluid, even at inlet mole fractions below 5%. In one case, a noncondensable inlet mole fraction of 0.63% was estimated to reduce the duty by approximately 10%. Analysis of the acquired high-speed videos shows that the film thickness changes significantly from the top row to the bottom. The videos also display condensate drainage patterns and droplet interactions. The ripples and splashing of the condensate observed in the videos indicates that the Nusselt idealized model is not appropriate for analysis of a real condenser. This article presents the collected heat transfer data and high-speed images of shellside vacuum condensation flow patterns.

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