STUDY OF THE EFFECT OF ADDITIVES OF ORGANIC SUBSTANCES ON HEAT TRANSFER AND HYDRAULIC RESISTANCE IN FLOW

I. P. CHASHCHIN, A. G. PYANKOV, V. P. IGNATOV

(Presented by the scientific seminar of the Department of Processes, Apparatuses, and Cybernetics of Chemical Production)

Not a single branch of modern industry can do without the transport of liquids through pipelines and channels. In this connection, questions associated with reducing the power expended in overcoming the hydraulic resistance of friction during the motion of a liquid flow through pipelines are of great importance.

In recent years, scientists have become interested in reducing the hydraulic resistance of a liquid flow by introducing organic additives into it [1—3].

We have carried out laboratory experimental studies on the effect of the molecular weight of a polymer additive, the limits of the thermal stability of the polymer, and the effect of the pH of the medium on the effectiveness of polymer additives in reducing hydraulic resistance. Also used as organic additives were certain alcohols (propyl, decyl, glycerin), for which their effect on heat transfer and hydraulic resistance in the flow was determined.

The studies were conducted on a heat exchanger with electric heating. Distilled water with an addition of polymer (alcohol) circulated through the heat exchanger; circulation was provided by a centrifugal pump of the “Kama-3M” type. In order to reduce the influence of the inlet conditions of the flow into the heat exchanger (copper tube \(d = 18 \times 2\)), its entire length was conventionally divided into sections, and a stabilized section of the tube was selected, on which measurements of the pressure drop and temperatures were carried out and for which \(l/d_{\text{eq}} > 50\). The static pressure drop was measured with a V-shaped two-liquid manometer; the flow rate of the working liquid was measured by the volumetric method. The temperatures of the tube wall and of the flow were measured with chromel–copel thermocouples connected to an M 193/3 millivolt microammeter. The experiments were carried out with various additives and differed from one another in flow rate, \(Re = (1 \div 3) \cdot 10^4\), and additive concentration.

Of the polymers considered, polyethylene oxide (PEO) and polyacrylamide (PAA) proved to be the most effective in reducing hydraulic resistance (50–60%). Studies were also conducted on the effect of the pH of the medium on the effectiveness of polymer additives. The pH of the medium in the experiments varied from 3 to 13. The results showed that, with an increase in the pH of the medium from 7 to 10, the effectiveness of PAA increased sharply.

decreases, and at pH = 12 it is equal to zero. In alkaline media the effectiveness remains maximal. For PEO the opposite dependence is observed.

Experiments were carried out to determine the optimal concentrations of PAA and PEO additives for reducing the hydraulic resistance due to friction and heat transfer. The dependence obtained is of an extremal character. The presence of an extremal point (optimal concentration) is evidently explained by the fact that, at concentrations of the polymer additive \(C > C_{\text{opt}}\), polymer macromolecules are in an aggregated state owing to intermolecular cohesion forces; and the higher the degree of aggregation, the more they differ from linear structures. At high dilution, when \(C < C_{\text{opt}}\), the molecules are in a linear state, and the probability of damping turbulent pulsations decreases for purely quantitative reasons. It was also established that, with an increase in the molecular weight of the polymer additive, its effectiveness in reducing hydraulic resistance and heat transfer increases.

Studies were carried out on the influence of the temperature stability of PEO and PAA additives. The experiments showed that the PEO additive loses its ability to reduce hydraulic resistance already at \(80^\circ\text{C}\), whereas the PAA additive changes little in its properties with respect to its influence on flow turbulence up to a temperature of \(200^\circ\text{C}\).

Studies were also carried out on heat transfer and hydraulic resistance in a flow with additions of alcohols: normal propyl, normal decyl, and glycerin. The concentration of alcohol in the solution was varied within the range from 0.1 to 1% by weight. The experimental results showed that, at \(Re = (1\text{–}3)\cdot 10^4\), adding a small amount of alcohol to the flow substantially (by a factor of 2) increases the intensity of heat transfer and slightly reduces hydraulic resistance. For each alcohol, within the indicated limits, optimal concentrations were established at which the greatest effect on the intensification of heat transfer was observed. It was noted that, as the number of carbon atoms in the alcohol increases, the optimal concentration decreases. The results obtained also show that an increase in the number of hydroxyl groups in the alcohol molecule has a positive effect on the intensification of heat transfer.

REFERENCES

1. I. G. Barenblat et al., PMTF, No. 5, 1965.
2. I. G. Il’perin, B. M. Smol’skii. IFZh, Vol. 10, No. 2, 1966.
3. F. Yu. Ivanyuta, L. A. Chekalova. IFZh, Vol. 18, No. 6, 1970.