Because magnesium alloy tube has good formability at elevated temperature, uniaxial tensile tests were employed to evaluate the warm properties of AZ31 magnesium alloy. After that, this paper has designed and manufactured a hydraulic bulge warm forming machine which can be used to experiment with fixed tube length. Using this testing machine, the experiments of hydraulic bulge forming of AZ31 magnesium alloy and 6061 aluminum alloy tube at elevated temperatures were carried out. According to experimental results, the hydraulic bulge forming properties of tubes at different temperatures are discussed.

Research and development department of the industry are generally depend on the experience rule to design products. But the designing process may be very time consuming. The experience, which the former designer accumulates, is probably unable to pass on to new personnel. This will makes new engineer have to use the traditional way to seek the solution slowly. This paper will study the socket, which test the integrated circuit, with forced convection. To discuss the difference of the inlet and outlet positions and geometry when the high-pressure air flow into the socket. And the fluid distribution may have the influence on heat dissipation result. This study uses Taguchi method with CFD software FLUENT, with different design parameters, to do the numerical simulation on the fluid field. To reach the design parameter of the optimization, Fluent uses the grid adaptive technique; it adjusts and optimizes the grid according to a result of calculation, and then made the result of calculation more accurate to offer more reliable design considerations to the designer.

No description available.

No description available.

Abstract The experiment was performed to measure the flow-induced vibration of tubes in cross flow and to study the effect of different experimental parameters, natural frequency, tube patterns and positions of the missing tube, on the tube vibration. The vibration mode of structures was investigated by root-mean-square values of tube displacements, dominant response frequencies, power spectral densities and orbits. The vibration signals in various velocities were used to analyze the mode and mechanism of the tube vibration by examining the interrelations between power spectral densities and orbits of the tube vibration. It was found that the stability thresholds were higher at the higher natural frequencies of the tubes and approach angles of the flow. Missing tube would affect the stability of local flow field, so that the surrounding tubes became more unstable. For each array pattern, the dominant response frequency of tube was changed with the flow velocity. It should be associated with the flow field, the mode and mechanism of vibration. As the tube frequency jumped, it should be the change of vibrating mode and mechanism. From the spectra and orbits of the tube vibrations, it can be found that the dominant frequencies are more complex at the high flow velocity.

Flow induced vibration of flow around a flexible tube array in cross flow are investigated experimentally. The different parameter including velocity, turbulent intensity, and nature frequency of tube. The flow structure and stability between flow and tube are analyzed by flow visualization and flow measurement. Further more, missing tube to find the change of the flow and the influenced of nearby tube, to get the way decreasing the vibration of tube.

Abstract Pool boiling process is frequently encountered in a number of engineering applications. However, it is difficult to exactly predict the heat transfer coefficient. This is because the nucleate pool boiling phenomenon is rather complex and influenced by many factors, such as surface roughness, areas of heater, material, geometry, arrangement of heated rods, and refrigerants, etc. The key boiling parameters (bubble dynamics data) such as bubble departure frequency, diameter and active nucleation site density will be varied in such different heated surface resulting in the different effect of heat transfer. This study was performed experimentally. R-134a was used as refrigerants, and the present study is aim at providing the pool boiling data for smooth and plasma coating enhanced tube bundles. It is expected that the surface condition, amount of test tubes, geometric of bundles and different heat flux can affect the nucleate boiling heat transfer in certain degree. In addition were calculated and developed that heat transfer coefficients and relevant corrections. Furthermore, more fundamental of the physical phenomenon can be obtained. According to the results of experiments, Boiling curves and calculations of the bundle factors and geometry factors were subsequently secured. The enhanced heat transfer coefficients with coated tube bundles are 1.1-2.0 times higher than smooth tube bundles. The 1.5-2.3 and 1.1-3.8 bundle factors obtained from the smooth tube bundles and coated tube bundles respectively. The geometry factors were about 1 for all arrangements studied herein. Thermal design data of a flooded type evaporator of high performance as well as more and further physical insight of the above-stated nucleate boiling heat transfer can be acquired. The results will hopefully be helpful not only for the academia but for the industry.

A mathematical model considering ellipsoidal surface for the forming tube is proposed in this work to examine the plastic deformation behavior of a thin-walled tube during tube bulge hydroforming process in an open die. In the formulation of this mathematical model, nonuniform thinning in the free bulged region and sticking and sliding friction modes between the tube and die are considered. In the sticking friction mode, the elements in contact with the die do not move or slide after contact with the die. Whereas, in the sliding friction mode, the elements in contact with the die will continue to deform plastically in the subsequent forming process. The relationship between the internal pressure and the bulge height of the tube is examined. The effects of various forming parameters such as the die entry radius, the initial thickness, the length/diameter ratio, material property, etc., upon the forming pressure and the thickness distribution of products were discussed systematically.

ABSTRACT The flow-induced vibrations of tubes in a rotated triangular array subject to cross flow are investigated numerically and experimentally. The parameters are inlet velocity of cross flow, number of tube, and tube natural frequency. In the study, the instantaneous fluid forces on tube surfaces are computed numerically, the instantaneous displacement of the tubes due to the fluid forces is calculated, and thus the motions of the tubes in cross flow are described. Experiments are also conducted to compare the numerical results. The tube vibrations in a water tunnel are measured by two accelerometers. The amplitudes, spectra, and trace of tube motion are presented. The critical velocities of tube vibrations are then determined. Experimental results show that some tubes vibrate seriously when the flow velocity increases up to a critical value, and hysteresis of the tube vibrations is observed. In case of the seven-tube array, the tubes in the fourth row exhibit the most serious vibration. When the flow velocity is above the critical value, only one dominant frequency of the tube vibrations is detected, comparing to multiple dominant frequencies in subcritical condition. Furthermore, the tube in supercritical condition behaves like a limit cycle, especially when the natural frequency is equal to or near the vortex shedding frequency from the upstream tubes. It is also shown that the critical velocity decreases with more surrounding tubes in the upstream and does not change as more adjacent tubes are added in the downstream. However, the tube number seems to have no effect on the critical velocity when the tube natural frequency is far from the vortex shedding frequency.

Switchgrass (Panicum virgatum L.) is a warm-season perennial bunchgrass native to North America. In addition to its importance as a forage grass, it has promise as a biofuel crop. However, its use is limited because the grass is difficult to establish. Improving seedling vigor is one approach for improving establishment. The objectives of this study were to: 1) select for increased seedling mass through half-sib family selection; 2) calculate an estimate of heritability for seedling mass; and 3) determine the mode of pollination of switchgrass. One cycle of selection was completed using a half-sib methodology. Seedling mass was determined in a series of growth chamber studies. The seed was produced in different space planted field nurseries in the College Station, TX area. Mean seedling weight of the base population (C0) was 0.014 gm seedling-1, while the mean seedling weight from the C1 cycle of selection was 0.029 gm seedling-1. Unfortunately, bulked seed from the base population was old and did not germinate well. Therefore, a new base population was recreated, and the C0 seedlings from this population were heavier than the C1 seedlings, 0.020 and 0.016 gm seedling-1, respectively. The calculated heritability estimate was H2 = 0.6. Since the C0 and C1 nurseries were not grown on the same soil type, the lack of a positive response for seedling weight may be due to the different soil types. However, it may require another cycle of selection to determine if seedling mass can be positively impacted via half-sib selection. The mode of pollination of the species was determined by 1) observing pollen germination and tube growth in the pistils using fluorescent microscopy and 2) determining seed set with selfed plants. When self-pollinated, the pollen tubes never grew into the ovaries but when cross-pollinated the tubes readily grew to the micropyle. Also, when switchgrass plants were self-pollinated, viable seed were not produced. These findings indicate that switchgrass is highly self-sterile because a self-incompatibility mechanism prevents the pollen tubes from growing into the ovary of the same genotype.