• Proceedings of the Korean Society of Rheology Conference
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• 2001.09a
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• pp.154.4-154
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• 2001

(No abstract, see full-text)

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.1032-1043
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• 1989

The heat transfer characteristics of the drag reducing polymer solutions are investigated experimentally in the thermal entrance region of circular tube flows. Fluids used in experiments are the aqueous solutions of high molecular polymer, polyacrylamide Separan AP-273 and the range of polymer concentrations is from 20 to 1000 wppm. Two stainless steel tubes with inside diameter 8.5mm(L/D=712) and 10.3mm(L/D=1160) are used for the heat transfer flow loops. The flow loop is set up to measure friction factors and heat transfer coefficients of test sections in two different modes; the recirculating flow system and once-through flow system. The test tubes are heated directly by electricity to apply the constant heat flux boundary conditions to the wall. Three different types of adaptors are used to observe the effects of the upstream flow conditions of the heat transfer test sections. The viscosity and characteristic relaxation time of the test fluids circulating in the flow system are measured by the capillary tube viscometer and falling ball viscometer at regular time intervals. The installed adaptors exhibit slight effect on the entrance heat transfer of Newtonian fluid. However, no noticeable effects are observed for the entrance heat transfer of the drag reducing fluids. The order of magnitude of the thermal entrance lengths of the drag reducing fluids which follow the minimum friction asymptote is much longer than that of Newtonian fluids in turbulent flows. A new dimensionless parameter, the viscoelastic Graetz number, is defined and all the experimental data are recasted in terms of the viscoelastic Graetz number. The local Nusselt number of the viscoelastic fluids is represented as a function of flow behavior index n and the viscoelastic Graetz number. As degradation continues the viscosity and the characteristic relaxation time of the testing fluids decrease. Weissenberg number defined by the relaxation time and D/V appears to be a proper dimensionless parameter in describing degradation effects on heat transfer of the viscoelastic fluids.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.825-828
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• 2005

Experimental and numerical study was done to confirm the effect of the flexible tube in pipeline on transient flow oscillation. Experiment was made for a pipeline with and without deformable flexible tube using a single pumping system of main stainless pipe. The wave speeds of main pipe and flexible tube were calculated from the pipe material properties, structures, and boundary conditions. Time dependent pressure fluctuations were calculated for the pipeline using the simple and the Kelvin-Voigt viscoelastic models for the deformation of main pipe and flexible tube. Pressure calculated by the Kelvin-Voigt viscoelastic model showed better agreement with measured one than pressure by the simple model. Experimental and numerical results show that the maximum pressure as well as amplitude of pressure oscillation was decreased by inserting short flexible tube in pipeline. Hence, inserted short flexible tube to pipeline was found to be effective for the suppression of strong pressure oscillation. Moreover, the wave speed in pipe was discussed based on numerical and experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1189-1196
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• 1988

Thermal entrance lengths of turbulent tube flow for viscoelastic polymer solutions are investigated experimentally in the recirculating flow system with tubes of inside diameters 8.5mm(L/D=710) and 10.3mm(L/D=1158), respectively. In the present system, the hydrodynamic and thermal boundary layers develop simultaneously from the beginning of the test section. To provide the boundary condition of constant heat flux at the wall, the test tubes are heated directly by electricity. The polymer solution used in the current study is 1000 wppm aqueous solution of polyacrylamide(Separan AP-273). The apparent viscosity of the polymer solutions circulating in the flow system are measured by the capillary tube viscometer at regular time intervals. Thermal entrance lengths vary due to the rate of degradation. The entrance lengths of degraded polymer solutions are about 500~600 times the diameter. However, the entrance lengths of fresh polymer solutions are greater than the lengths of the test tubes used in this study suggesting that thermal entrance lengths for viscoelastic polymer solutions are greater than 1100 tube times the diameters. Friction factor is almost insensitive to the degradation, but the heat transfer $j_{H}$-factor is affected seriously by degradation. Based on the present experimental data of fresh solutions a correlation for the heat transfer $j_{H}$-factor is presented.ted.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.465-470
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• 2006

An experimental investigation is carried out to study 2-phase vertically upward hydraulic transport of solid particles by water and non-Newtonian fluids in a slim hole concentric annulus with rotation of the inner cylinder. Rheology of particulate suspensions in viscoelastic fluids is of importance in many applications such as particle removal from surfaces, transport of proppants in fractured reservoir and cleaning of drilling holes, etc. In this study a clear acrylic pipe was used in order to observe the movement of solid particles. Annular fluid velocities varied from 0.2 m/s to 3.0 m/s. Pressure drops and average flow rate and particle rising velocity are measured. For both water and 0.2% CMC solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become.

• Proceedings of the Korean Society of Rheology Conference
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• 2001.09a
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• pp.158.4-158
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• 2001

• Transactions of The Korea Fluid Power Systems Society
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• v.3 no.2
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• pp.21-26
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• 2006

With the increasing concerns on noise and vibration in hydraulic fluid power systems, it is important to find better way to reduce noise and vibration. In this study, the authors survey former researches on hose(viscoelastic tube) modeling in advance. And a summary of several existing methods for measuring the speed of sound in the fluid in pipes is presented. Their basic principles, advantages and limitations are compared. And The authors suggest a far simple identification procedure to obtain wave speed in hose by just using an experimental pressure data for the object tube with hose. In the new procedure, flow in hose is basically modeled by transfer matrix method, and wave speed in hose is obtained as data in frequency series. The wave speed in hose as data in frequency series will be used to compute the pressure pulsation attenuation in hydraulic pipe systems. The computed results are compared with the experimental ones, and the validity of the new procedure to obtain wave speed in hose is confirmed

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.1
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• pp.37-48
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• 1990

The drag and heat transfer reduction phenomena and degradation effects of drag reducing polymer solutions which are known as the viscoelastic fluids are investigated experimentally for the turbulent circular tube flows. Two stainless steel tubes are used for the experimental flow loops. Aqueous solutions of Polyacrylamide Separan AP-273 with concentrations from 300 to 1000 wppm are used as working fluids. Flow loops are set up to measure the friction factors and heat transfer coefficients of test tubes in the once-through system and the recirculating flow system. Test tubes are heated by power supply directly to apply constant heat flux boundary conditions on the wall. Capillary tube viscometer and falling ball viscometer are used to measure the viscous characteristics of fluids and the characteristic relaxation time of a fluid is determined by the Powell-Eyring model. The order of magnidude of the thermal entrance length of a drag reducing polymer solution is close to the order of magnitude of the laminar entrance length of Newtonian fluids. Dimensionless heat transfer coefficients of the viscoelastic non-Newtonian fluids may be represented as a function of flow behavior index n and newly defined viscoelastic Graetz number. As degradation continues viscosity and the characteristic relaxation time of the testing fluids decrease and heat transfer coefficients increase. The characteristic relaxation time is used to define the Weissenberg number and variations of friction factors and heat transfer coefficients due to degradation are presented in terms of the Weissenberg number.

• The Korean Journal of Rheology
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• v.2 no.1
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• pp.33-45
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• 1990

This study analyzes the planar 4:1 contraction flow of viscoelastic fluids with retardation time using finite volume method. To consider separately the elasticity effect of the viscoelastic fluid without shear thinn-ing effect, Oldroyd B liquid model is adopted for the numerical simulation. Instead of the stream function-vorticity formulation, SIMPLER algorithm with staggered grid system which incorporates primitive variable has been introduced in discretizing the momentum equations. An upwind corrected scheme has been used in discetizing the constitutive equations for the non-Newtonian part of the stress. The size of the corner vortex is shown to be slightly influenced by the Weissenberg number. However as the Weissenberg number is increased the chang-ing of the vortex shape agrees qualitatively well with some experimental studies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.3 no.4
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• pp.251-256
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• 2002

The average diffusion time of a polyacrylamide solution was determined by measuring the terminal velocities of the falling balls. The diffusion time increased as the polyacrylamide concentration increased. The PIV (Particle Image Velocimetry) system was employed to visualize the flow phenomena around balls. For a time interval of 30 seconds in the 2000 wppm, velocity vectors were larger than in case of 0 seconds, 40 seconds and 50 seconds in the falling ball. However, in the Newtonian fluid, flow vsualization around balls were performed at both upstream and downstream of the falling ball.