Stagnation Zone Near a Corner in Viscoplastic Fluid Flow

The shape, size and location of the stagnation zone between flat non-parallel walls that make up the corner of a tube with non-circular cross-section through which a phase change material of the Bingham plastic type flows is investigated. We show that the stagnant area is bounded by a convex meniscus whose size depends on the degree of plasticity and the vertex angle. The maximum and minimum energy dissipation occurs at the wall and at the bisectrix, respectively. The stagnant zone can be altogether avoided by modifying the shape of the wall in the corner area. A new design of the cross-section of the tube that allows reducing or eliminating this area to optimize the mass transport is developed. Two optimal solutions a vertex with a straight cut and a concavely curved vertex are proposed.

MoS2 Nanoparticle Effects on 80 °C Thermally Stable Water-Based Drilling Fluid

Bentonite-based drilling fluids are used for drilling, where inhibitive fluids are not required. The rheological and the density properties of the drilling fluids are highly affected by high temperature and pressure. Due to high temperature, the clay particles stick together, and the fluid system becomes more flocculated. Poorly designed drilling fluid may cause undesired operational issues such as poor hole cleaning, drill strings sticking, high torque and drag. In this study, the 80 °C thermally stable Herschel Bulkley’s and Bingham plastic yield stresses drilling fluids were formulated based on lignosulfonate-treated bentonite drilling fluid. Further, the impact of a MoS2 nanoparticle solution on the properties of the thermally stable base fluid was characterized. Results at room temperature and pressure showed that the blending of 0.26 wt.% MoS2 increased the lubricity of thermally stable base fluid by 27% and enhanced the thermal and electrical conductivities by 7.2% and 8.8%, respectively.

Model development and simulation of vehicle suspension system with magneto-rheological damper

A vehicle suspension system is designed to maintain directional control (road holding) during manoeuvring or braking while supporting the vehicle’s weight and provide stability (handling). The structure of a suspension system consists of parts connecting the axle to wheel assembly and the chassis of an automobile, thus supporting engine, transmission system and vehicle load. Suspension system components consist of dampening devices, springs, steering knuckles, ball joints and spindles or axles. It could be designed according to a passive, semi-active or active mode of working. For evaluation, this assembly could be modelled as a spring-mass-damper system. The semi-active suspension system has been modelled with a magneto-rheological damper following the Bingham plastic theory. In this paper, the performance of a passive and a semi-active suspension of a quarter car model are compared by MATLAB simulation. Thus, a better suspension system is found out by simulating with different road conditions.

Magnetorheological damper modeling based on a refined constitutive model for MR fluids

A systematic modeling study is conducted to predict the dynamic response of magnetorheological (MR) damper based on a refined constitutive model for MR fluids. A particle-level simulation method is first employed to probe the microstructured behavior and rheological properties of MR fluids, based on which the refined constitutive model is developed. The constitutive model is further validated by comparing the predicted results with the data obtained from microscopic simulations and existing experiments. It is revealed that the proposed constitutive model has comparable accuracy and good applicability in representing MR fluids. Subsequently, a computational fluid dynamics (CFD) model is established to explore MR damper’s behavior by using the proposed constitutive model to describe the fluid rheology. For better capturing the dynamic hysteretic behavior of MR damper, a modified parametric model is developed by combing the Bingham plastic model and the proposed constitutive model. The modified model for MR damper shows its validity and superiority over the existing Bingham plastic models.

Laminar Free Convection From a Heated Square Cylinder in Bingham Plastic Fluids

The free convection phenomenon from a heated square cylinder submerged in Bingham Plastic fluids is numerically investigated. The governing equations are solved for a wide range of physical dimensionless parameters, such as Rayleigh number (10^2 ≤ Ra ≤ 10^5), Prandtl number (10 ≤ Pr ≤ 100) and Bingham number (0 ≤ Bn ≤ 10^7). The heat transfer characteristics are investigated in terms of local Nusselt number distribution over the surface of the cylinder surface average Nusselt number. Streamlines, isothermal contours, yielded and unyielded regions are visualized in detail.

Improving drilling hydraulics estimations-a case study

Accurate pressure drop estimation is important for drill string and bit nozzles design and optimized fluid circulations as well as identifying the drilling problems such as bit nozzle(s) washout or plugging. In this study, the Bingham Plastic model has been modified by applying a coefficient to its turbulent pressure loss calculations. This coefficient encompasses the effects of the drill pipe tool joints and other effects in estimation of pressure losses. The range of the coefficient was determined in field applications for different hole sizes and mud types. The results showed that applying a correction coefficient of 1.08–1.12 to turbulent pressure loss equations (depending on borehole size and mud type) improves the pressure loss estimation. By applying this coefficient, the estimated pressure losses are increased to compensate the under-estimation of the Bingham Plastic model. This is considered a significant contribution to accurate calculation of borehole hydraulics and in-time detection and identification of borehole problems and reduction of invisible lost time. The findings also showed that this enhanced effect is independent of the mud type. The use of this coefficient removes the necessity of using rather complex mud rheological models such as the Herschel–Bulkley model.

Effect of Sinusoidally Varying Flow of Yield Stress Fluid On Heat Transfer From a Cylinder

The effect of pulsating laminar flow of a Bingham plastic fluid on heat transfer from a constant temperaturre cylinder is studied numerically over wide ranges of conditions as: Reynolds number (0.1 = Re = 40) and Bingham number (0.01 = Bn = 50) based the on mean velocity, Prandtl number (10 = Pr = 100), pulsation frequency (0 = w* = Pi) and amplitude (0 = A = 0.8). Results are visualized in terms of instantaneous streamlines, isotherms, apparent yield surfaces at different instants of time during a pulsation cycle. The overall behavior is discussed in terms of the instantaneous and time averaged values of the drag coefficient and Nusselt number. The size of the yielded zone is nearly in phase with the pulsating velocity whereas the phase shift has been observed in both drag coefficient and Nusselt number. The maximum augmentation ( ~30 %) in Nusselt number occurs at Bn = 1, Re = 40, Pr = 100, w* = Pi and A = 0.8 with respect to that for uniform flow. However, the increasing yield stress tends to suppress the potential for heat transfer enhancement. Conversely, this technique of process intensification is best suited for Newtonian fluids in the limit of Bn ~ 0. Finally, a simple expression consolidates the numerical values of the time-average of the Nusselt number as a function of the pertinent dimensionless parameters which is consistent with the widely accepted scaling of the Nusselt number with ~Pe1/3 under these conditions.

Performance of rubber seed oil as an alternative to diesel in oilbased drilling mud formulation

The formulation of an oil-based mud was made possible with the oil extracted from rubber seeds using the famous soxhlet extraction method. The mud was formulated using the API standard of 25 g of bentonite to 350 mL base fluid. The choice of Rubber oil comes as a result of its flash point and aniline point which lies in the range of base oils used for mud formulation. The rheological properties of the rubber OBM were beyond the scope of the viscometer and hence thinner was added to reduce its viscosity and its suitability to compete favorably with diesel OBM was checked. The 10-sec and 10-min gel strength of the Rubber OBM was recorded as 68 lb/100 ft2 and 69 lb/100 ft2 respectively while that of Diesel was 65 lb/100 ft2 and 67 LB/100 ft2 . The plastic viscosity of Rubber OBM was 12 cp while that of Diesel was 17 cp. They both exhibited Bingham Plastic behavior and a similar yield point of 146 lb/100 ft2 . The formulated mud samples were subjected to temperatures of 60 oC and 75 oC and it was discovered that Rubber OBM was likely to retain its rheological property than diesel OBM. Comparison with other rheological properties of diesel OBM showed that the formulated mud could be used alternatively for diesel in drilling operations.