Russian Journal of Applied Chemistry, 2011, Vol. 83, No. 3, pp. 550−558.
Pleiades Publishing, Ltd., 2011.
Original Russian Text
I.O. Mikulionok, L.B. Rodchenko, 2010, published in Khimicheskaya Promyshlennost’, 2010, Vol. 87, No. 8, pp. 379−388.
Heat Exchange in Granulating Thermoplastics
I. O. Mikulionok and L. B. Rodchenko
Ukrainian Technical University “Kyiv Polytechnical Institute”, Kiev, Ukraine
Received November 27, 2010
Abstract—Cooling of polymer granules and strands in air and water was examined. The greatest effect of
a turbulence of air ﬂ ow on the cooling rate of granules was revealed in the starting period. An analysis of the
cooling of granules in water demonstrated that the rate of heat transfer from a volume of thermoplastic material
to its surface was a rate-limiting step and, thus, an effect of turbulization of a water ﬂ ow on the cooling was
negligible. We showed that it would be appropriate to install partitions destroying a heated boundary layer of
water for intensifying process in a cooling bath since an actual cooling of the strands in the water bath longer
corresponds to the case when water moves together with strand.
A permanent growth in a polymer application,
the world manufacturing of which in 2008 achieved
245 million tons necessitates disposal of the waste .
One of the most appropriate ways is regranulation of the
thermoplastic polymers and using the produced granules
in manufacturing of various products [1–4].
Hot and cold granulations are the main methods
of the thermoplastics granulation. In the ﬁ rst case the
strands being formed by an extrusion head are cut into
granules directly close to the head and then they being
hot are entrained by air or water ﬂ ow in which are
simultaneously cooled. In cold granulation the formed
strands at ﬁ rst are cooled in a water bath and pass
through a pulling device and only then they are cut into
In the case of incomplete cooling granules can stick
together during packing forming agglomerates unsuit-
able to further use in polymer treating equipment, e.g.,
in extrusion apparatuses. This effect occurs due to tem-
perature equalization along a radius of a granule (as
a result of cooling the inner and heating the outer layers
of the granules) under conditions when heat exchange of
the granules with surrounding air is poor due to mutual
contact of a large amount of granules of thermoplastics
with low thermal conductivity.
Thus, a relative low temperature of a surface of the
strands in the course of their granulation is necessary but
insufﬁ cient condition to yield the high-quality granular
In addition in treatment of crystal polymer the
material structure in obtained granules is formed upon
cooling strands of granules and depends on a cooling
mode. The structure of granules deﬁ nes also a structure
of products from them and therefore an examination of
cooling is of great importance in designing technological
and auxiliary equipment [2– 5].
The cooling processes of granules or strands are
simulated by the equation of unsteady heat conduction.
For its solution commonly used boundary conditions of
the ﬁ rst  or the third kind ; i.e., it is assumed that
is is known either the surface temperature of granule or
strand taken as the temperature of the cooling medium or
heat transfer coefﬁ cient to the cooling medium. However
in the ﬁ rst case since there is the boundary layer of the
cooling medium near the polymer surface, it is almost
impossible to ensure a constancy of its temperature (in
this case it should be ensure large cooling water ﬂ ow
), therewith in the second case determination of the
heat transfer coefﬁ cient is quiet difﬁ cult in respect to
experimental studies. In addition, known theoretical