Đạt được hiệu quả chưng cất cao hơn khi sử dụng Máy cô quay chân không Buchi – Impact of thickness of flask
ĐẠI DIỆN ĐỘC QUYỀN HÃNG BUCHI TẠI VIỆT NAM
Summary
The evaporation rate is
noticeably greater if the evaporating flask’s glass walls are thinner. The
simple reason is that thinner glass allows better heat transmission from the
heating bath through the glass of the evaporating flask to the solvent.
Generally speaking, the glass wall thickness should be selected to be as thin
as possible, while still being robust enough to prevent breakages of the
evaporating flask even at very low pressures. Concerning both these issues, the
optimum thickness for a 1 L evaporating flask is between 1.5 and 2.0 mm.
Introduction
Formerly, the glass walls of
evaporating flasks were generally thicker. Thanks to years of research, modern
technology and automated manufacturing processes, the design of the evaporating
flask is now optimized to maximize efficiency. The demands and requirements are
high as the glass has to be resistant to breakages and withstand conditions
such as high temperatures as well as rapid temperature changes at very low
pressure. It is therefore of great importance to be aware of the optimum glass
thickness and of the safety issues when choosing an evaporating flask.
The evaporation efficiency
depends primarily on the amount of heat energy which reaches the solvent inside
the evaporating flask. It is obvious that a thicker (glass) barrier hinders heat
transfer.
Experiment
The aim of the following
experiment was to analyze the influence of the evaporating flask glass
thickness on the evaporation rate of a solvent single-stage distillation. The
experiment was executed with a BUCHI
Rotavapor®. (Máy cô quay chân không Buchi)
For the realization of the
experiment, the evaporation process was first performed with acetone, using
five 1 L evaporating flasks differing in the glass wall thickness (from 1.6 to
2.7 mm) and then with water, using three different flasks (from 1.5 to 2.6 mm
thickness respectively).
Results
As illustrated in the above
graphic, the thinner the evaporating flask’ glass walls, the higher the
evaporation output. The disparity was especially obvious in the experiment
using acetone. For example, the evaporating flask, with a thickness of 1.6 mm,
achieved 54 % higher evaporation output compared to the flask with 2.7 mm glass
wall thickness.
Interpretation
This experiment shows that glass
wall thickness has a significant impact on the evaporation output. With thinner
glass walls, the heat transfer from the heating bath medium to the solvent
inside the evaporating flask is improved, speeding up the evaporation. On the
other hand, the thicker the glass, the more prolonged the heat transfer
becomes, thus reducing the evaporation output significantely.
Recommendation
There is a fine line between
glass that is too thin and glass that is too thick. For instance, using thinner
glass might put the glass at higher risk of breaking. On the other hand,
thicker glass slows down the evaporating output. Generally speaking, the
evaporating flask should be as thin as possible, but still withstand very low
pressure and other exposures as high temperature and rapid temperature changes.
The BUCHI evaporating flasks are designed for high evaporation output
and to fulfill highest safety requirements. The standardized 1 L evaporating
flask has a glass wall thickness around 1.8 mm. According to customer feedback
and internal tests, this condition provides the optimum ratio of high heat
transfer efficiency along with high safety.
The high-quality glass consists
of inert industrial glass, borosilicate glass 3.3, resistant to chemicals high
temperatures and rapid temperature changes. The quality and precision of BUCHI glassware also guards from
breakages. In addition, if there are special requirements from customers, BUCHI modifies glass components in any
ways or develops complex new designs for individual needs.
ĐẠI DIỆN ĐỘC QUYỀN HÃNG BUCHI TẠI VIỆT NAM
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