459742 Head Loss in Gate and Globe Valves on Pumping Thixotropic Polymer Solutions

Monday, November 14, 2016
Market Street (Parc 55 San Francisco)
Daniel Torneiros1, Vitor Rosa2, Marco Cesar Matos3, Maria Elena Taqueda4, José Paiva4 and Deovaldo Moraes Júnior2, (1)Epoxy Resin Plant, Olin Corporation, Guarujá, Brazil, (2)Chemical Engineering, Santa Cecília University, Santos, Brazil, (3)Santa Cecília University, Santos, Brazil, (4)Chemical Engineering, University of São Paulo, São Paulo, Brazil

Pumping is one of the most important unit operations process, being used in chemical as well as petrochemical procedures, such as, transportation of polymeric solutions, paints, resins, hydrocarbons, oils and pastes. The project of a pumping system is based on the determination of the pump motor power, which is expressed as a function of the potential and kinetical energies, taking into consideration head losses for straight sections and accessories (valves and connections). In particular, the determination of head losses in accessories is done through abacus obtained by empiric methods, such as equivalent lengths, K and 2K methods, in the way that the literature is rich in information on the Newtonian fluid’s transportation (e.g. water, hydrocarbons and oils). Nevertheless, around 80% of the fluids that are industrially transported are featured as Non-Newtonian, and, in most cases, thixotropic. The polymeric solutions follow a thixotropic behavior according to their rheology, meaning that their apparent viscosity decrease as time passes and shear stress rises alongside temperature and pressure. The existing literature provides some information on the K method for gate valves and globe valves as they transport pseudoplastic fluids, however, lacks consistent data on the transport of thixotropic fluid’s. This study aimed to determine empirical equations for K coefficient for a gate valve and for a globe valve, with two diameters, during the transport of sodium carboxymethylcellulose of high viscosity at two concentrations based on the modified Reynolds number of Metzner and Reed. The experimental unit consists, basically, on a centrifugal pump with closed impeller and a break horse power equal 0, 75 cv, 2 gate valves (0, 5 in. and 1 in.), 2 globe valves (0, 5 in. and 1 in.), both screwed down and transparent PVC piping of 0, 5 in. and 1 in. diameter. It were used two aqueous solutions of carboxymethylcellulose (CMC) in two different mass concentrations: 0,5% and 1%. The mentioned solutions were analyzed according to their rheology in a Stormer viscometer, varying the shear stress and temperature. The current time of experiments were registered. The rheological behavior was based on the power law, however, the consistency factor and behaviour index were expressed as a function of time and temperature, due to the thixotropic solutions behavior. The experiments were carried measuring head losses through the differences between two piezometer’s heights, being one of them placed downstream the accessory and the other upstream. The head loss varied according to the employed flow in each trial. Tests were performed for each valve in terms of its diameter, and polymer solution concentration. All tests conducted using accessories, were also produced using straight sections of pipe. Deducting the values obtained with the straight sections from the values obtained with the accessories, it was possible to obtain the head loss for each of the valves isolatedly. The modified Reynolds number of Metzner and Reed was calculated according to each volumetric flow rate measured and it was noted that any of the four valves reached the transition flow, so that the entire modeling was performed into laminar flow. The values of the coefficient K were calculated and plotted using two regressions between the values of K and its corresponding Reynolds numbers, one for the gate valve and other for the globe valve. In order to provide a practical model for projects, this article modeled equations for Reynolds, in different ranges, for the two valves studied as a function of CMC concentrations and the pipe diameter (0.5 in. and 1 in.). Based on the K equations depending on the Reynolds number for the pseudoplastic fluids, using gate valves; literature contains a functional relationship for K as follows: K = A / Re, similar for globe valves. The results of this article demonstrated for the gate valve, two expressions depending on the range of the Reynolds number: for values lower than 231, K = 294.36 / Re, with a deviation of 14.2% compared to the experimental data, and for Reynolds between 373 and 2804 (below the transition zone, Reynolds less than 3100), K = 717.73 / Re, with a deviation of 2.9%. Similarly, for the globe valve, with lower Reynolds 176, K = 1163.96 / Re, providing a deviation of 14.2% and for Reynolds between 324 and 872, the value of the K coefficient was almost constant at 18.49. It was concluded that the expressions obtained for the determination of the coefficient K are adjusted to the experimental data, due to the low experimental error, allowing engineers to design more reliable pumping systems for thixotropic polymer solutions.

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See more of this Session: Poster Session: Fluid Mechanics (Area 1J)
See more of this Group/Topical: Engineering Sciences and Fundamentals