The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform
Eiji Hihara - One of the best experts on this subject based on the ideXlab platform.
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experimental study on condensation heat transfer and Pressure Drop of low gwp refrigerant hfo1234yf in a horizontal tube
International Journal of Refrigeration-revue Internationale Du Froid, 2012Co-Authors: Linlin Wang, Chaobin Dang, Eiji HiharaAbstract:Abstract Condensation heat transfer of low GWP refrigerant HFO1234yf was Measured in a horizontal tube (inner diameter: 4 mm) at a mass flux range of 100–400 kg m −2 s −1 and different saturation temperatures (40, 45, and 50 °C), and the results were compared with that of R134a and R32. Effects of mass flux, vapor quality, saturation temperature, and thermophysical properties on the heat transfer coefficient were analyzed. Mass flux and vapor quality were presented to primarily affect the heat transfer coefficient in shear-force dominated flow regimes, whereas the thermal conductivity and density ratio are the primary parameters as thermophysical properties influencing the heat transfer coefficient. Observed annular flow regimes agreed with Tandon’s flow pattern map. The Measured Pressure Drop compared with that predicted by the Lockhart–Matinelli correlation, Huang correlation and Haraguchi correlation. And, when comparing the experimental heat transfer coefficient with four heat transfer coefficient correlations, the Haraguchi correlation fairly agreed with the experimental data, with a 10.8% mean deviation.
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boiling heat transfer of hfo 1234yf flowing in a smooth small diameter horizontal tube
International Journal of Refrigeration-revue Internationale Du Froid, 2011Co-Authors: Shizuo Saitoh, Chaobin Dang, Yoshitaka Nakamura, Eiji HiharaAbstract:The flow boiling heat transfer coefficient of the low-GWP (global warming potential) refrigerant HFO-1234yf inside a smooth small-diameter horizontal tube (inner diameter: 2 mm) was experimentally investigated. The local heat transfer coefficient was Measured at heat fluxes of 6–24 kW m -2 , mass fluxes of 100–400 kg m -2 s -1 , evaporating temperature of 288.15 K, and inlet vapor quality of 0–0.25. The results show that the effect of heat flux on the heat transfer was large at low vapor quality, while the effect of mass flux was large at high vapor quality. The heat transfer coefficient of HFO-1234yf was almost the same as that of R-134a. The heat transfer coefficients calculated based on correlations with Saitoh et al. agreed well with the Measured values compared to other correlations. The Measured Pressure Drop agreed well with that predicted by the Lockhart-Martinelli correlation.
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effect of tube diameter on boiling heat transfer of r 134a in horizontal small diameter tubes
International Journal of Heat and Mass Transfer, 2005Co-Authors: Shizuo Saitoh, Hirofumi Daiguji, Eiji HiharaAbstract:Abstract The boiling heat transfer of refrigerant R-134a flow in horizontal small-diameter tubes with inner diameter of 0.51, 1.12, and 3.1 mm was experimentally investigated. Local heat transfer coefficient and Pressure Drop were Measured for a heat flux ranging from 5 to 39 kW/m 2 , mass flux from 150 to 450 kg/m 2 s, evaporating temperature from 278.15 to 288.15 K, and inlet vapor quality from 0 to 0.2. Flow patterns were observed by using a high-speed video camera through a sight glass at the entrance of an evaporator. Results showed that with decreasing tube diameter, the local heat transfer coefficient starts decreasing at lower vapor quality. Although the effect of mass flux on the local heat transfer coefficient decreased with decreasing tube diameter, the effect of heat flux was strong in all three tubes. The Measured Pressure Drop for the 3.1-mm-ID tube agreed well with that predicted by the Lockhart–Martinelli correlation, but when the inner tube diameter was 0.51 mm, the Measured Pressure Drop agreed well with that predicted by the homogenous Pressure Drop model. With decreasing tube diameter, the flow inside a tube approached homogeneous flow. The contribution of forced convective evaporation to the boiling heat transfer decreases with decreasing the inner tube diameter.
R V A Oliemans - One of the best experts on this subject based on the ideXlab platform.
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oil water liquid flow rate determined from Measured Pressure Drop and water hold up in horizontal pipes
Journal of The Brazilian Society of Mechanical Sciences and Engineering, 2011Co-Authors: R V A OliemansAbstract:Stimulated by rapid progress in down-hole measuring techniques production engineers wonder whether in the near-future monitoring of oil/water production rates for horizontal wells can become possible on the basis of Measured oil/water Pressure losses and water hold-ups. A complicating issue is that these Measured data depend on the oil and water flow patterns. The question then is if we use a flow-pattern-dependent model for Pressure Drop and water hold-up in an inverse mode, what then will be the accuracy by which production rates can be determined? In this review the progress with the inverse modeling will be investigated.
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parametric study of a model for determining the liquid flow rates from the Pressure Drop and water hold up in oil water flows
International Journal of Multiphase Flow, 2007Co-Authors: M Hadžiabdic, R V A OliemansAbstract:Abstract A flow-pattern-dependent model, traditionally used for calculation of Pressure Drop and water hold-up, is accustomed for calculation of the liquid production rates in oil–water horizontal flow, based on the known Pressure Drop and water hold-up. The area-averaged steady-state one-dimensional two-fluid model is used for stratified flow, while the homogeneous model is employed for dispersed flow. The prediction errors appear to be larger when the production rates are calculated instead of Pressure Drop and water hold-up. The difference in the calculation accuracies between the direct and inverse calculation is most probably caused by the different uncertainties in the Measured values of the input variables and a high sensitivity of the calculated phase flow-rates on even small change of the water hold-up for certain flow regimes. In order to locate the source of error in the standard two-fluid model formulation, several parametric studies are performed. In the first parametric study, we investigate under which conditions the momentum equations are satisfied when the Measured Pressure Drop and water hold-up are imposed. The second and third parametric studies address the influence of the interfacial waves and Drop entrainment on the model accuracy, respectively. These studies show that both interfacial waves and Drop entrainment can be responsible for the augmentation of the wall-shear stress in oil–water flow. In addition, consideration of the interfacial waves offers an explanation for some important phenomena of the oil–water flow, such as the wall-shear stress reduction.
Rean-der Chien - One of the best experts on this subject based on the ideXlab platform.
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rheological behavior of ps polymer melt under ultra high speed injection molding
Polymer Testing, 2012Co-Authors: Shiachung Chen, Wonhsion Liao, Jungpeng Yeh, Rean-der ChienAbstract:Abstract Determination of the rheological behavior of a polymer melt under high shear rate is generally considered to be crucial for accurate simulation modeling of ultra high speed injection molding, a process that has been attracting more attention from researchers. In this study, a melt viscosity measurement system under high shear rate was established using an instrumented injection molding machine combined with a slit die. Polystyrene melt was studied. From Measured Pressure Drop and volumetric flow rate, the slit flow model was used for the calculation of viscosity at wall shear strain rates up to 105 s−1. Good agreement in shear viscosity was found between results from conventional capillary rheometry and in-line measurement made using an injection molding machine for strain rates of 7 × 103 to 104 s−1. Measured shear viscosity in the test range was found to follow shear thinning power law behavior at shear rates below 7 × 104 s−1. However, the Measured viscosity values are significantly lower (28%–46%) than the database obtained from the Moldflow package software (Cross-WLF model) at melt temperatures of 200, 215, and 230 °C. Further, the reduction in the viscosity value increases as the injection speed increases. It seems that the wall-slip effect plays a dominant role, becoming more significant as the melt temperature increases. Alternatively, as shear strain rates approached or exceeded 7 × 104 s−1, shear viscosity deviations from shear thinning behavior were observed and reached a rate-independent plateau. The behavior is thought to be influenced by Pressure effects on viscosity. In the present study we emphasize that the Measured results are significant for the design and simulation of ultra high speed injection processes such as micromolding and thin-walled injection molding.
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rheological behavior of pom polymer melt flowing through micro channels
European Polymer Journal, 2008Co-Authors: Chunsheng Chen, Weilianq Liaw, Rean-der ChienAbstract:Abstract Determination of the rheological behavior of the polymer melt within micro-structured geometry is vital for accurate simulation modeling of micro-molding. The lack of commercial equipment is one of main hurdles in the investigation of micro-melt rheology. In this study, a melt viscosity measurement system for POM melt flowing through micro-channels was established. For Measured Pressure Drop and volumetric flow rate, both capillary and slit flow models were used for the calculation of viscosity. The calculated results were also compared with those of PS resin to discuss the effect of morphology structure on the viscosity characteristics of polymer within micro-channels. It was found that the Measured POM viscosity values in the test ranges are significantly lower (about 29–35% for a channel size of 150 μm) than those obtained with a traditional capillary rheometer. Meanwhile, the percentage reduction in the viscosity value and the ratio of slip velocity relative to mean velocity all increase with decreasing micro-channel size, but less significantly when compared with PS resin. In the present study we emphasize that the rheological behavior of the POM resin in microscopic scale is also different from that of macroscopic scale as PS resin but displays a less significant lower. It also revealed that the wall slip occurs more easily for the PS resin within micro-channels than POM resin due to enlarge the effect of molecular weight.
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study on rheological behavior of polymer melt flowing through micro channels considering the wall slip effect
Journal of Micromechanics and Microengineering, 2005Co-Authors: Rean-der Chien, Wenren JongAbstract:Micro molding is attracting more attention nowadays and determination of the rheological behavior of the polymer melt within micro structured geometry is considered to be very important for the accurate simulation modeling of micro molding. The lack of commercial equipment is one of the main hurdles in the investigation of micro melt rheology. In this study, the melt viscosity measurement system for PS (polystyrene) melt flowing through a micro-channel was established using a micro-channel mold operated at a mold temperature as high as the melt temperature. From Measured Pressure Drop and volumetric flow rate both the capillary flow model and the slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the Measured viscosity values in the test ranges are significantly lower (decreased by a factor of about 1.4–4.1) than those obtained from the traditional capillary rheometer at a melt temperature of 200 °C using both the capillary flow model and the slit flow model. As the micro-channel size decreases, the reduction in the viscosity value increases when compared with data obtained from the traditional capillary rheometer. The ratio of slip velocity relative to mean velocity was also found to increase with decreasing size of micro-channels. It seems that wall slip plays a dominant role when melt flows through micro-channels and would result in a greater percentage in apparent viscosity reduction when the size of the micro-channel decreases. In addition, the wall-slip effect becomes more significant as the melt temperature increases. In the present study we emphasize that the rheological behavior of the melt in the microscopic scale is different from that of the macroscopic scale and that current simulation packages are not suitable for micro molding simulation without considering this difference.
R P Vedula - One of the best experts on this subject based on the ideXlab platform.
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heat transfer and Pressure Drop measurements in a square cross section converging channel with v and w rib turbulators
Experimental Thermal and Fluid Science, 2016Co-Authors: Satyanand Abraham, R P VedulaAbstract:Abstract Ribs on the opposite walls of internal cooling passages of gas turbine blades are often used for heat transfer enhancement. These passages can be straight, converging or diverging. In the present study, experimental data for local heat transfer coefficients are presented for a converging channel with rib roughening elements with the cross-section being maintained square from inlet to exit. The local heat transfer coefficient distribution shows the same qualitative behavior observed for the straight channel. The overall averaged heat transfer coefficient along with the Measured Pressure Drop across the test channel is used to calculate thermal performance based on constant pumping power and constant heat transfer area criterion. Data are presented for straight ribs normal to the flow, V ribs with included apex angle of 45° and with apex pointing in the upstream and downstream directions, W ribs with all included angles of 45° and with central apex pointing in the upstream and downstream directions. The inlet Reynolds number ( Re in ) was varied from 5000 to 35,000. The rib height ( e ) was maintained constant throughout the length of the channel. The rib height to mean duct hydraulic diameter ratio ( e / D h,m ) was kept constant at 0.08. Data for three pitch to height ratios ( P / e ) equal to 6, 10 and 17.5 are reported for straight and V ribs. The optimum P / e ratio based on constant pumping power thermal performance criterion was observed to be equal to 10 and this was the only configuration studied for W ribs. The difference in thermal performance between the V and W ribs was within uncertainty limits. However, the local variation in heat transfer coefficient in the cross stream direction on the ribbed wall was noticed to be very high for the V ribs compared to that for the W ribs making the W ribs a better choice as enhancement device.
David A. Dicarlo - One of the best experts on this subject based on the ideXlab platform.
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measurements of co2 brine relative permeability in berea sandstone using Pressure taps and a long core
Greenhouse Gases-Science and Technology, 2017Co-Authors: Xiongyu Chen, Amir Kianinejad, David A. DicarloAbstract:We Measured CO 2 ‐brine relative permeability by performing five steady‐state primary drainage experiments in a 116 mD Berea sandstone core at 20°C and 10.34 MPa. We used a long (60.8 cm) core and four Pressure taps to study and minimize end effects that can plague CO 2 ‐brine relative permeability measurements, and we obtained in situ saturation profiles using a medical X‐ray Computed Tomography (CT) scanner. We found that entrance and exit effects propagated ∼5 cm into the core, but the center sections of the core had uniform saturation. From the saturations and Pressure Drops, we obtained both CO 2 and brine relative permeability in the center sections. We also obtained CO 2 relative permeability at the entrance section where the brine saturation was lower and not uniform. The 15‐cm long exit section of the core had non‐uniform saturation and a Measured Pressure Drop that was on the order of the capillary Pressure and hence was unreliable for calculating relative permeability. We found that the CO 2 and brine relative permeabilities determined in five experiments were consistent with each other and followed two simple Corey‐type models that are similar to those seen in oil‐brine relative permeability measurements. We discuss why end effects are much greater in the CO 2 ‐brine system than in oil‐brine systems, and how this is a possible explanation of the low CO 2 relative permeabilities recently reported for the CO 2 ‐brine systems. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.