Numerical Study on Influences of Drag Reducing Additive in Supercritical Flow of Kerosene in a Millichannel

To improve the performance of a high-pressure refueling liquid oxy-kerosene engine, the influence of drag-reducing additive on the heat transfer characteristics in the supercritical flow of kerosene in a microchannel for regenerative cooling is explored. The finite-volume CFD numerical simulation method is applied using the RNG k-ε turbulence model and enhanced wall function. The current work faithfully represents the effect of the drag-reducing additive in kerosene through numerical calculations by combining a 10-component model for the physical properties of the kerosene and the Carreau non-Newtonian fluid constitutive model from rheological measurements. Results suggest that the 10-component kerosene surrogate can describe the supercritical physical properties of kerosene. The inlet temperature, inlet velocity, and the heat flux on the channel wall are driving factors for the supercritical kerosene flow and heat transfer characteristics. The pressure influence on the heat transfer is negligible. With polymer additives, the loss in pressure drop and heat transfer performance of supercritical kerosene flow decrease 46.8% and 37.5% respectively. The enhancement of engine thrust caused by reduction in pressure drop is an attractive improvement of concern.

Scaling and forecast of drag reducing additive mechanical degradation along the pipeline

Введение. Целесообразным является применение стендовых и численных экспериментов с целью определения интегральной гидравлической эффективности присадки при малой добавке высокомолекулярного полимера в трубопроводы большого диаметра. Однако проблема прогнозирования в промышленных условиях неразрывно связана с необходимостью учета деградации присадки. Цель статьи - построение такой математической модели путевой деградации присадки, чтобы ее свободные параметры могли быть идентифицированы на основе как опытно-промышленных, так и стендовых испытаний. Методы. На основе положений теории распространения примесей и тепла в осевых турбулентных потоках сформулирован одномерный вариант математической модели неизотермического течения раствора. С использованием аналогии уравнений распространения тепла и примесей и аналогии в граничных и начальных условиях записано решение для распределения концентрации активной части присадки в виде аналога формулы Шухова для тепловых задач. Результаты. Предложена расчетная процедура для прогнозирования распределения гидравлической эффективности присадки на основе «диффузионного» аналога формулы Шухова с учетом механической деградации. С этой целью разработан алгоритм идентификации входящих параметров. Обсуждение. Определена система соотношений для расчета локальной и интегральной гидравлической эффективности присадки по длине трубопровода. Замыкающие соотношения могут быть получены путем обработки данных опытно-промышленных либо стендовых гидравлических экспериментов. Сформулированы некоторые требования к процедурам проведения и обработки данных экспериментов. Выводы. Прогнозирование гидравлической эффективности присадки целесообразно проводить путем предварительного расчета распределения концентрации активной части полимерной добавки с использованием «диффузионного» аналога формулы Шухова и известных зависимостей гидравлической эффективности от концентрации и других параметров. Introduction. To go before the field tests of drag reducing agents (DRA) in the trunk lines they do laboratory experiments and numerical simulations. A forecasting effort in DRA behavior includes taking account of their degradation. That is why a mathematical model of running degradation where free variables can be determined both in laboratory or full-scale experiment is an actual problem. Methods. One-dimension mathematical model of non-isothermal flow was formulated on the base of corresponding heat and ingredients transfer in the axial turbulent flow. According to correspondence equations as well as boundary conditions of DRA concentration distribution we’ve got a solution in a form of Shukhov’s equation for heat transfer. Results. Forecasting of DRA effectiveness distribution was suggested on the base of “diffusive” analogue of Shukhov’s equation for heat transfer including the degradation effect. Characteristics’ identification procedure was made up. Discussion. Set of correlations was derived for local and cumulative DRA effectiveness along the pipeline while closing relations were evaluated both from laboratory and full-scale experiments. The way of data handling is also suggested. Conclusion. Drag reducing effectiveness forecast should be based on concentration distribution estimation according to “diffusive” analogue of Shukhov’s equation for heat transfer with taking in account of concentration dependence of drag reduction.

An Experimental Study of the Effect of Drag Reducing Additive on the Structure of Turbulence in Concentric Annular Pipe Flow Using Particle Image Velocimetry Technique

The effect of drag reducing additive on the structure of turbulence in concentric annular pipe flow was investigated using Particle Image Velocimetry (PIV) technique. Experiments were conducted using a 9m long horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The drag reducing additive was a commercially available partially hydrolyzed polyacrylamide (PHPA). The experiments were conducted using 0.1% V/V polymer concentration, giving a drag reduction of 26% at a solvent Reynolds number equal to 56400. Near wall local fluctuating velocity values were determined by analysing the PIV data. The root mean square (RMS) values of radial velocity fluctuations showed a significant decrease with the use of drag reducing additive. The RMS values of axial velocity fluctuations near the wall (Y+<10) were similar for both water and polymer fluid flow; though, higher peaks were obtained during the polymer fluid flow. As compared to water flow, a strong reduction in vorticity was observed during polymer fluid flow. The degree of vorticity reduction on the inner wall was higher than that of the outer wall. Results of the viscous dissipation and the shear production terms in the kinetic energy budget showed that less energy was produced and dissipated by the route of turbulence when using polymer fluid.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.