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Relationship Between Molecular Structure And Drag Reduction Performance

Polymeric drag reducing agents have attracted widespread attention in the chemical industry since the research of B 1A 1T oms began. In the past 50 years, a large number of experimental and theoretical studies have been carried out at domestic and abroad, and a large amount of data on the structure of polymers and drag reduction performance have been accumulated in theory. Level is of great significance.

1. molecular weight

The molecular weight (M) of a polymer is one of the basic structural parameters that affect drag reduction performance. The high molecular weight polymer must exceed a certain molecular weight M C (referred to as the initial molecular weight) before it can have drag reduction effect. Its drag reduction efficiency (DR) increases rapidly with molecular weight at the beginning and then reaches equilibrium.

Many researchers have tried to use mathematical analysis expressions to describe the relationship between DR and M. Hunston proposed the characteristic drag reduction rate (DR) defined by the Virk 2Little relationship, and the relationship between the characteristic concentration (C) and M is [DR] / [C] = K (M -MC) where K is a constant, MC is the initial molecular weight mentioned above, and [DR] / [C] is the drag reduction rate that characterizes the unit concentration of the drag reducer when it is infinitely dilute. A measure of the level of resistance.

Dai Jialin et al. Systematically studied the drag reduction performance of polyhexyl methacrylate in kerosene and kerosene acetone. From the data processing, a new DR 2M mathematical correlation was obtained.

DR = A+M / (M + B) -D

A, B, and D in the formula are constants under a certain flow condition.

2. molecular weight distribution

Most polymer samples have a certain molecular weight distribution (MWD). Under certain conditions, not all molecules have drag reducing effects, and the drag reducing properties of polymers have a great relationship with molecular weight distribution. Strictly speaking, it is not strict to study the relationship between molecular weight and drag reduction performance without a clear molecular weight distribution. So far, there are two different interpretations of the molecular weight distribution, one is that DR is related to the average molecular weight of the polymer; the other is that DR is related to the high molecular weight portion of the sample. The author believes that the latter is more reasonable.

3. polymer main chain structure

The chemical composition of polymer chains and the type of bond are not the only factors that determine the efficiency of drag reduction. The geometry and flexibility of the chain have a great effect on drag reduction efficiency. Currently found that effective polymer drag reducers are mostly flexible polymers with linear or spiral structure. Gramain et al. Studied the drag reduction efficiency of linear, star, and comb PS in toluene solution, and the experimental results showed that the branching of the molecular chain greatly reduced the drag reduction efficiency of the polymer.