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[en] Two-dimensional hydromagnetic flow and heat transfer of Walters-B fluid towards a stagnation point region over a stretching cylinder is discussed. Constitutive equations are transformed into dimensionless form by means of suitable similarity transformations. Spectral quasi-linearization method is employed to obtain the solution of similarity equations. Comparison of computed results with existing results in the limiting case of a flat sheet is also provided. Analysis of obtained results is performed through graphs to discuss the influence of emerging parameters on the velocity and temperature profiles. The flow and heat transfer characteristics are analyzed through parameters representing curvature of cylinder, velocity ratio parameter, magnetic parameter, and Weissenberg number. The curvature of the cylinder has significant impact on the velocity and temperature. A magnetic field applied externally suppresses the bulk motion and alters the momentum boundary layer thickness. The drag and heat transfer rate on the surface of the cylinder are examined through skin friction and heat transfer coefficients. Furthermore, streamlines are drawn to see the flow pattern. (author)
[en] Several low-dimensional systems show a crossover from diffusive to ballistic heat transport when system size is decreased. Although there is some phenomenological understanding of this crossover phenomenon at the coarse-grained level, a microscopic picture that consistently describes both the ballistic and the diffusive transport regimes has been lacking. In this work we derive a scaling form for the thermal current in a class of one dimensional systems attached to heat baths at boundaries and rigorously show that the crossover occurs when the characteristic length scale of the system competes with the system size. (paper)
[en] Performance of PFP system is verified by the properly performed experiments so engineers usually apply PFP based on its performance test results. However, in some cases, PFP cannot be applied as its initial design due to the constraints of space, workability, cost and other complicated reasons. In cases of low utilization against in-place load and very limited fire exposure, partially or thinly applied PFP could be acceptable if response under fire is fully assessed to ensure the integrity of the structure. To perform the fire redundancy analysis, temperature field of structural members should be determined at first and finite element tools are utilized for this purpose. In this paper, FAHTS (Heat transfer analysis module of USFOS) and LS-dyna are adopted for simulations. Considering the characteristics and functional limitations of each tool, heat transfer analysis with and without PFP are carried out. By comparing the results with analytical solution, proper modeling techniques to simulate the heat transfer analysis for each software are confirmed. In this paper, case studies for heat transfer analysis with and without PFP are performed using commercial FE tools and characteristics are compared.
[en] The effect of wall geometry on the flow and heat transfer in a channel with one lower furrowed and an upper flat wall kept at a uniform temperature is investigated by large eddy simulation. Three channels, one with sinusoidal wavy surface having the ratio (amplitude to wavelength) α/λ=0.05 and the other two with furrowed surface derived from the sinusoidal curve, are considered. The numerical results show that the streamwise vortices center is located near the lower wall and vary along the streamwise on various furrow surfaces. The furrow geometry increases the pressure drag and decreases the friction drag of the furrowed surface compared with that of the smooth surface; consequently, the total drag is increased for the augment of pressure drag. As expected, the heat transfer performance has been improved. Finally, a thermal performance factor is defined to evaluate the performance of the furrowed wall.
[en] This paper introduces two methods for solving two bottlelike problems regarding the shape memory alloy (SMA) application as actuators. These methods are ‘rotating output,’ which aims to solve the problem of the low working frequency caused by the demand for cool time, and ‘accumulated shifting,’ which solves the problem of difficult-to-obtain output displacements in a large scale. We also introduce a hybrid linear actuator that applies the two methods and achieves both a strong force and an accurate large output displacement while working at a high frequency based on the SMA wires and DC motors. A prototype of this actuator was fabricated and tested to verify the two methods. This hybrid actuator system dynamic model, which was composed of the constitutive model of the SMA, the electrical and heat transfer behavior of the SMA wires and the dynamics of the linear actuation system, was established and discussed. Our study aims to illuminate the application of an SMA in actuators with the proposed methods with regard to its two main problems. An actuator with a high power-weight ratio and the capability to work at a high frequency, as well as accurate linear step displacements in a large scale, is also presented. (paper)
[en] A three-dimensional numerical model for heat transfer tube vibration induced by cross flow is proposed with two ways coupled approach. The characteristics of flow field are investigated based on the numerical model. The results show that, when U_r ≤ 2, lift force coefficient increases as U_r increases, while drag force coefficient decreases first and then increases. When 2 < U_r < 9, the Locked In phenomenon occurs and drag force reaches the peak value prior to that of lift force. As U_r ≥ 9, lift force is tending to zero. The drag force of flexible tube is about 2-2.5 times of that of the fixed tube, and the lift force is 6 times. Vibration makes the pressure distribution and wake vortex mode change. The transverse space between vortexes is amplified obviously compared to the case of fixed tube. There is only 2S mode existing in the present study. (authors)
[en] This paper presents an alternative to cubic spline regularization and its weighted form applied in solving inverse thermal problems. The inverse heat transfer problems are classified as ill-posed, that is, the solution may become unstable, mainly because they are sensitive to random errors deriving from the input data, necessitating a regularization method to soften these effects. The smoothing technique proposed by cubic spline regularization ensures that the global data tend to be more stable, with fewer data oscillations and dependent on a single arbitrary parameter input. It also shows that the weighted cubic spline is able to enhance filter action. The methods have been implemented in order for the search engine to optimize the choice of parameters and weight and, thus, the smoothing gains more flexibility and accuracy. The simulated and experimental tests confirm that the techniques are effective in reducing the amplified noise by inverse thermal problem presented.
[en] One method of increasing the heat-transfer rate is to increase the heat-transfer area. In this study, we test a wide louver fin-and-tube heat exchanger with = 1.03, and we compare the results with those of a louver fin-and tube heat exchanger with = 0.6. The results obtained show that the heat-transfer capacities of the wide louver samples are larger (16% in one row, 29% in two rows, and 38% in three row samples) than those of the louver samples. Considering the area ratio of 2.17, the increase in the heat-transfer capacity is somewhat small. The reason for this may be due to the smaller heat-transfer coefficient and fin efficiency of the wide louver sample. The effect of the fin pitch on the j and f factors are not profounded. The j and f factors decreased as the number of tube rows increased. We compare the data obtained with existing correlations
[en] Floating LNG bunkering offshore terminal (FLBT) has been adopted as a floating unit by the marine industry equipped with the natural gas liquefaction plant on the ship's deck with the practical interest in controlling the plume emission discharged from the ship. The downwash of emitted plumes has adverse consequences on the ship’s engine intake and ventilation system followed by the interference of the smoke with helicopter operations. Owing to this fact, understanding of the plume behavior is considered to be so significant in the aspect of ship design and thereby, flow visualization techniques assist to study the plume path ensuring the safety of the personnel and functioning system. The unignited flare gas emitted from the tower invites heat transfer due to the temperature difference between the atmospheric wind and the ship’s exhaust, which follows the examination of mixing enhancement of fluid mediums as well as the mitigation of plume concentration depending upon wind speeds. The parametric study is intended to investigate the plume dispersion pattern around a ship based on the flare motion and bending angle for light and strong wind speeds. It is observed that the plume gas rises higher and disperses over the larger area with wider streamline separation due to the effect of buoyancy for light wind speeds. On the other hand, the motion of flare gas is found to be narrow for strong winds restricting vertical movements due to dominant inertial forces than gravity pull. Thus, the current numerical investigation facilitates in understanding the configuration and plume distribution by the variation in streamline behavior with contours plots. In this work, the calculated results are analyzed systematically in pretty realistic conditions and simple measures are obtained, which will be applied to the preliminary design of plume stack depending on the ship’s deck arrangement.