Numerical heat transfer in annular fins of curved profile formed with the intersection of two equal circles

Purpose The purpose of this paper is to investigate the heat transfer attributes of annular fins with quarter circle profile in terms of the Biot number Bi and the radius ratio rr. The latter corresponds to the internal radius of the tube divided by the length of the fin in question. Design/methodology/approach To this end, the governing two-dimensional (2-D) heat conduction equation in cylindrical coordinates is numerically solved via finite element analysis for different Bi (i.e., 0.1, 1 and 5) and rr (i.e., 0.5, 1 and 2). Findings The obtained results for the mid-plane and surface temperatures show that these profiles, which exhibit nearly rr-independent responses, only present one-dimensional (1-D) radially linear distributions for the case Bi = 1. For Bi = 0.1, the temperature profiles also possess a 1-D character but with a clearly defined concave pattern. Finally, for Bi = 5, a 2-D temperature field in a wide zone from the fin base is achieved with a convex pattern for the mid-plane and surface temperatures. Originality/value Exhaustive assessment of the heat transfer in annular fins with quarter circle profile in terms of different Biot numbers and radius ratios

Response Suppression of FGM Plate Using Piezoelectric Layers Under Parametric Uncertainty Conditions with Markovian Jump Approach

It should be noted that in addition to the geometry, constituent material also affects the strength and rigidity of the cylindrical shell, some factors that determine the transient response are its geometry and the constituent material. The capability of piezoelectric materials to adept their properties in reaction to environmental factors including electricity and loading is one of the major reasons for using in this work. Therefore, in this study, the transient response of a symmetric annular sandwich plate incorporating functionally graded core and piezoelectric layers under external harmonic force and electrical voltage is investigated. The properties of the core material vary along its thickness according to a power law model. The displacement field is represented by the third-order shear deformation theory. With the aid of Hamilton’s principle, the structural equations are obtained in terms of displacement components, then solved using the differential quadrature method. In addition, the time response is evaluated with respect to effective parameters including the internal radius, power law index, core thickness, and external voltage. According to the simulation results, the oscillation amplitude decreases as the internal radius of the plate increases over the desired time interval. Also, a higher index parameter is associated with a wider time response range. Moreover, the stability analysis of a piezoelectric system with [Formula: see text] performance is considered based on the theory of Markovian jump systems. To this end, a Markovian jump state-space model of the piezoelectric system obtained using system identification under the effect of external disturbance is presented. The [Formula: see text] stability index is selected based on a candidate Lyapunov function that leads to a set of linear matrix inequalities for each region. The uncontrolled and controlled transient responses of the coupled system under external disturbance are calculated and compared, indicating the satisfactory controller performance in the presence of external disturbance and jump in the sensor and system dynamics.

Effects of Turning Angle and Turning Internal Radius on Channel Impingement Cooling for a Novel Internal Cooling Structure

Recently, a novel internal cooling structure, namely multi-channel wall, has been put forward to enable higher overall cooling effectiveness with less coolant and pressure loss. Our previous work has proved the advantages of the design relative to conventional impingement cooling and swirl cooling. Channel impingement cooling structure, which is utilized at the turning region of the leading edge, is the critical factor to realize the high cooling performance of the design. Hence, the turning angle and turning internal radius of the cooling channel are two key parameters, and this paper focuses on the effects of these two parameters on the flow and heat transfer characteristics of the channel impingement cooling structure. Nine simplified single-channel models with different turning angles (45°, 60°, and 75°) and radiuses (0.6 mm, 0.9 mm, and 1.2 mm) were adopted to conduct the study, and the jet Reynolds number ranges from 10,000 to 40,000. The results show that the turning angle and turning internal radius affect the jet form significantly for the same mechanism. Small turning angle means large impingement, which leads to stream-wise counter-rotational vortices and high turbulence intensity, but increasing turning internal radius transfers the jet form from impingement jet to laminar layer attaching the target surface with low heat transfer. The turning internal radius has stronger effect than turning angle. With higher jet Reynolds number, both the heat transfer and total pressure loss increase dramatically, and the effects of geometrical parameters are clearer.

Energy Levels in Nanowires and Nanorods with a Finite Potential Well

The energy of electrons and holes in cylindrical quantum wires with a finite potential well was calculated by two methods. An analytical expression is approximately determined that allows one to calculate the energy of electrons and holes at the first discrete level in a cylindrical quantum wire. The electron energy was calculated by two methods for cylindrical layers of different radius. In the calculations, the nonparabolicity of the electron energy spectrum is taken into account. The dependence of the effective masses of electrons and holes on the radius of a quantum wires is determined. An analysis is made of the dependence of the energy of electrons and holes on the internal and external radii, and it is determined that the energy of electrons and holes in cylindrical layers with a constant thickness weakly depends on the internal radius. The results were obtained for the InP/InAs heterostructures.

Effects of Turning Angle and Turning Internal Radius on Channel Impingement Cooling for a Novel Internal Cooling Structure

Leading edge multi-channel double wall design, a novel internal cooling structure, has been put forward recently to enable higher overall cooling effectiveness with less penalty of coolant mass flow and pressure loss. Our previous work has proved the advantages of the design under operating condition relative to conventional internal cooling methods including impingement cooling and swirl cooling. Channel impingement cooling structure, which is utilized at the turning region of the leading edge, is the critical factor to realize the high cooling performance of the design. Hence, the turning angle and turning internal radius of the cooling channel are two key parameters for the novel design, and this paper focuses on the effects of these two parameters on the flow and heat transfer characteristics of the channel impingement cooling structure. Nine simplified single-channel models with different turning angles (45°, 60°, and 75°) and radiuses (0.6 mm, 0.9 mm, and 1.2 mm) were adopted to conduct the study, and the jet Reynolds number ranges from 10,000 to 40,000. The results show that the turning angle and turning internal radius affect the jet form significantly for the same mechanism. Small turning angle means large impingement, which leads to stream-wise counter-rotational vortices and high turbulence intensity, but increasing turning internal radius transfers the jet form from impingement jet to laminar layer attaching the target surface with low heat transfer. The turning internal radius has stronger effect than turning angle. With higher jet Reynolds number, both the heat transfer and total pressure loss increase dramatically, and the effects of geometrical parameters are clearer.

Bearing Capacity of Ring Foundations on Sand Overlying Clay

The vertical bearing capacity of rough ring foundations resting on a sand layer overlying clay soil is computed in this study by using finite element limit analysis (FELA). The sands and clays are assumed as elastoplastic models, obeying Mohr–Coulomb and Tresca failure criteria, respectively. Based on the FELA results, design charts are provided for evaluating the ultimate bearing capacity of ring foundations, which is related to the undrained shear strength of the clay, the thickness, the internal friction angle, the unit weight of the sand layer, and the ratio of the internal radius to the external radius of the footing. A certain thickness, beyond which the clay layer has a negligible effect on the bearing capacity, is determined. The collapse mechanisms are also examined and discussed.

TO A QUESTION OF DETERMINATION OF HYDRAULIC RADIUS OF A BACKFILL FLOW FOR THE EXCENTRATIVE PLACEMENT OF PIPES IN DRILLING BORE

The processes of displacement of drilling clay backfill flow from the intertubular space formed by internal surface of external and external surfaces of inner tubes are considered. In case of eccentric placement of pipes it is proposed in the form of a cross-section of the flow of a backfill to take the area limited from the outside by the Pascal's snail, and from the inside - the outer surface of the inner pipe at the first time. The formulas for determining areas of the cross section of the flow and the stagnant zone, the perimeter and the hydraulic radius of the section ofthe flow for the eccentric placement of the pipes in the bore are proposed. The dimensionless parameter α is introduced as the ratio of the centripetal distance to difference between internal radius of outer pipe and outer radius of inner tube. It was found that with increasing of α cross-sectional area and their hydraulic radii are increasing, and the area of stagnant zones decreases according to parabolic laws.It is established that with the growth of α velocity of the backfill flow decreases according to parabolic laws and their values are in good agreement with the experimental data.