THERMOPHYSICAL CHARACTERISTICS OF

MEDIA AND GRANULATES

V. I. Gorodnichev, G. N. Borisov,

and V. I. Egorova

M E D I C I N A L

UDC 615.012 : 66.047].073 : 536.1

Thermophys ica l c h a r a c t e r i s t i c s of medic inal media and granula tes such as heat capaci ty , heat con- ductance, and t h e r m a l conductivity m u s t be known for the calculat ion and ana lys i s of drying p r o c e s s e s in the pha rmaceu t i ca l c h e m i s t r y industry . The knowledge of the rmophys ica l c h a r a c t e r i s t i c s makes it pos - sible to c lass i fy a l a rge va r i e t y of medic ina l media and granula tes into s epa ra t e groups. This p e r m i t s the choice of ra t ional methods and opt imal r e g i m e s of drying p r o c e s s e s for a l a rge group of products s i m - i l a r in their characteristics.

The regular-regime method, the impulse method, and the method of a horizontal heat source [1-4] are used at the present time to determine thermophysical characteristics of free-flowing materials. How- ever, the indicated methods are complex in instrumental formulation and require a long time to carry out

the experiment.

We used the method of two temperature-time intervals, developed at the Lensovet Leningrad Institute of Chemical Technology [3]. The thermophysical characteristics of medicinal media and granulates were

investigated using the apparatus depicted in Fig. i.

The initial material at a set humidity in an amount of 10-15 g is poured onto measuring ring I of de-

tachable container 2. Then the heat receiver 3 prepared from organic glass, joined on the thread with de- tachable container 2 in such a way that the assembled level of the junction of the copper-constantanthermo- couple 4 with the surface of heat receiver 3 touches the poured material, the thickness of which is mea- sured using a deformation indicator. Circulating water enters cylinder 5 having a perforated lid 6 to cool heat receiver 3. Excess water is carried away as drainage through the perforations in lid 6. A junction

of a copper- constantan thermoeouple 7 serves to measure

3 9

r - - - ~ I

I V / ' "

Fig. 1. Appara tus scheme for d e t e r m i - nation of t he rmophys ica l c h a r a c t e r i s t i c s . Explanation in text .

the wa te r t e m p e r a t u r e . Since the wa te r t e m p e r a t u r e is dif- f e ren t f r o m the t e m p e r a t u r e of the ma te r i a l , the light spot of ga lvanomete r 8 (M-~95 m i c r o a m m e t e r ) will show the di - v is ion cor responding to this t e m p e r a t u r e d i f ference . Using rheos t a t 9 switched into the d i f fe ren t ia l - the rmocouple c i r - cuit, the light spot of the ga lvanomete r is adjusted to the m a x i m u m division of the sca le of the N0-100 appara tus . The heat r e c e i v e r 3 with s c r ewed-on cell 2 is placed on the p e r - fo ra ted lid 6 of cyl inder 5. The ga lvanomete r readings be - gin to dec rea se with t ime as a r e su l t of cooling of the in- ves t iga ted m a t e r i a l .

T imes ~'1 and ~'2, in which the light beam of the ga l - v a n o m e t e r pa s se s sect ions of the appara tus sca le f r o m di- v is ions N1-95 to N2-90 and f r o m divisions N2-90 to N3-75 , a r e m e a s u r e d in the exper iment . All des i red t h e r m o p h y s - ical c h a r a c t e r i s t i c s can be found f r o m values of I- 1 and ~-2-

Leningrad Inst i tute of P h a r m a c e u t i c a l Chemis t ry . Trans la ted f r o m K h i m i k o - F a r m a t s e v t i c h e s k i i Zhurnal , Vol. 5, No. 11, pp. 57-59, November , 1971. Original a r t i c le submit ted Sep tember 18, 1970.

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TABLE 1. Thermophysica l Charac te r i s t i c s of Certain Medicinal Media and Granulates (moisture content W=0%, t empera tu re 23- 24~

Name

iTher$nal I conauc - tivity I - -

Q. 10 '

(mZ/sec)

Heat Volume- conduc- tric laeat tance capacity

(W/m" c~,. 10 -6 deg) (J/m 8. deg)

Medicinal media: hexamidine amidopyrine methionine aspirin ptienaeetin

Granulates: citramon calcium gluconate ethoxyel, cu d~medrol diethyl asphene

5,00 5,50 5,35 3,24 3,98

5,80 11,90 6,55 1,85 4,20 4,95 3,63

0,061 1,22 0,070 1,27 0,059 1,10 0,063 1,94 0,070 1,76

0,075 0,695 0,065 0,198 0,135 0,129 0,058

1,29 5,85 0,99 1,06 3,22 2,60 1,61

thermal conductivity coefficient:

a = m m2mo 4 p ' r 1 '

heat conductance coefficient:

~ , = K E ] / a , W/m- deg

volumetr ic heat capacity of the mater ia l :

cv = + , I/m s �9 deg

where H is the layer thickness of the poured mater ia l , m; K is a constant of the apparatus charac ter iz ing the r - mal proper t ies of the heat rece iver ; and E and P are dimensionless pa rame te r s , the values of which are given in the tables of [5] compiled for No=100 and def in i teval - ues: N1, N2, and N 3.

Thermophysieal cha rac te r i s t i c s for medicinal media and granulates (average values calculated f rom resul ts of three measurements) are presented in Table 1. The relat ive e r r o r of the measurements did not exceed 5%.

values of thermophysica l cha rac te r i s t i c s , which we determined The obtained data agree with calculated by the method of a regula r reg ime.

Calculation of thermophysical cha rac te r i s t i c s on the example of calc ium gluconate granulates were ca r r i ed out in the following order .

Readings of the t imer s at a layer thickness of calcium gluconate granulate H=3.57 mm gave c o r - respondingly T i = Ii.2 sec and i- 2 = 71.8 sec. Then T2/~- 1 = 71.8/11.2 = 6.44.

At N0=I00 , N I =95, N 2 =90, and N3=75 , from the tables of [5] we find: E =0.383, p=2.39. From this,

the thermal conductivity coefficient:

H 8 3,57 ~. 10-6 a = 4pxi -- 4.2,39.1 l, 2 = 11,9.10 -8 mZ/sec.

and the constant K of the apparatus prepared f rom organic g lass :

~n 0.173 K= V ~ n -- V]-:]-.~_7 512W secls

where Xn=0.173 W / m . d e g is the heat conductance of organic glass , and a n = l . 1 �9 10 .7 m2/sec is the thermal conductivity of organic glass (polymethyl methacryla te) .

We then derive the coefficient of heat conductance:

~, = KE ]/a = 512.0,383 ~ 10 -s = 0,695 W/m .deg.

and the volumetr ic heat capacity of the mater ia l :

~. o. 695 c v - a - 11.9-10 -s=5"85"106 J/m3"deg"

The specific heat capacity C of the mater ia l can be determined as a quotient by division of volumetr ic heat capacity by density of the mater ia l .

Thermophysieal cha rac te r i s t i c s of medicinal granulates depend on mois ture , t empera ture , and many other factors~

Applied to the drying p rocess of medicinal granulates , the heat capacity of mois t granules can be ca l - culated [4] as the weighted mean value between the heat capacity of the mater ia l Cc and heat capacity of

mois ture C w"

Cw-- Cc C = Ce + 1--T-~-v-.W,

where W is the mois ture content of the mater ia l (kg of mois ture per 1 kg of dry material) .

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In the calculat ion of the drying p roces s the dependence of value C on tempera ture , as a rule, is ig- nored.

When necessa ry , the method used gives the possibil i ty of studying thermophysical cha rac te r i s t i c s of medicinal media and granulates as a function of mois ture , g ranulometr ic composition, and t empera tu re .

The analysis c a r r i e d out by us of exist ing methods of determining thermophysical cha rac t e r i s t i c s of medicinal media and granulates shows that the most rapid and re l iable method is the method of two t em- p e r a t u r e - t i m e in tervals . This method can be recommended for use in l abora tor ies of fac tor ies of the phar - maceut ica l chemis t ry industry.

LITERATURE CITED

1. G . M . Kondrat 'ev , Heat Measurements [in Russian], Moscow-Leningrad (1957). 2. A . F . Chudnovskii, Thermophys ica l P ro p e r t i e s of Disperse Mater ia ls [in Russian], Moscow (1962). 3. A . V . Lykov (editor), Invest igat ion of Thermal Conductivity [in Russian], Minsk (1967). 4. I . L . Lyuboshi ts , L. S. Slobodkin, and I. F. Pukus, Drying of Disperse Heat-Sensit ive Mater ia ls [in

Russian], Minsk (1969).

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