Low density polyethylene (LDPE) reactors are used to manufacture polymer products. The reactors are typically of the tubular or autoclave variety. To make the (multi-molecule chain) polymer, a minute amount of initiator is added to a (single-molecule) monomer. Several reaction steps take place in which the monomer is transformed to a polymer product with a range of chain lengths (corresponding to a range of molecular weights). Heat is released in many of the reactions, and one goal of LDPE reactor design is to prevent hot spots that give rise to a condition called thermal runaway, which results in low product quality. Fluent software successfully simulates the complex set of reactions in the reactor, and provides results about temperature, viscosity distribution, and the spread of molecular weights. This information can be used to troubleshoot problem installations and to design new reactors.

A hybrid mesh of 166,000 cells is used for this simulation. The reactor contains both paddle and twisted blade impellers, which are modeled using a sliding mesh. The initiator is pre-mixed with the monomer and injected into the reactor through an annular ring. The RNG k-e model is used to account for the turbulence in the highly swirling flow.

The conversion of monomer increases to about 7% as the material moves through the reactor

Temperature increases from 460K to 540K in the reactor

Contours of the molecular weight distribution are used to assess the range of molecular weights in the product