Thermal DEM study of heat transfer and flow patterns of fine cohesive particles under vertical vibration

Heat transfer characteristic of R-600a during flow boiling inside horizontal plain tube

Heat transfer and flow patterns in a minichannel with various acoustic standing wave configurations and thermal boundary conditions

Experimental study and CFD simulation of wall effects on heat transfer of an extrudate multi-lobe particle

In this study, the heat transfer pattern and flow bifurcation in the fluid is observed by the application of low intensity magnetic field in the gradually constricted cavity. The natural convection flow solver with Lorentz force and Boussinesq approximation as a source term is developed in the open-source CFD platform OpenFOAM. The Lorentz force in the flow is altered by varying the Hartmann number of Ha = 0 – 100, however the buoyancy force is kept constant in the flow at fixed Rayleigh number of Ra = 106. The orientation of magnetic field is exposed to be in the y-direction (By). The significance of using the By magnetic field with its various intensity in the constricted enclosure on the heat transfer and flow pattern is reported. It is perceived that the transverse magnetic field (By) and its varying intensity regulates the heat transfer with multiple convection rings. The detail study on the isotherms, streamlines, and the time average Nusselt number is reported.

In the present study, the characteristics of heat transfer and flow pattern are investigated experimentally for evaporation of pure refrigerant HFC134a in capillary tubes of 2.0 and 0.84mm I. D. The test section consists of a heating stainless steel tube section and a glass-tube section, which is located at the right after the outlet of the heating section. The experiments were carried out in the ranges of mass velocity of 100∼600kg/m2s and heat flux of 1.16∼46.8kW / m2 at a constant inlet pressure of about 920kPa. Experimental results of local heat transfer coefficient, pressure drop and flow pattern were compared with previous studies.

Boiling heat transfer, pressure drop, and flow pattern in a horizontal square minichannel

A numerical study is conducted to understand the effect of rotation on the axisymmetric flow driven by buoyancy in an annular cavity formed by two concentric vertical cylinders which rotate about their axis with different angular velocities. The inner and outer side walls are maintained isothermally at temperature θ c and θ h , respectively, while the horizontal top and bottom walls are adiabatic. The vorticity-stream function form of the Navier-Stokes equations and the energy equation have been solved by modified Alternating Direction Implicit method and Successive Line Over Relaxation method. Numerical results are obtained for a wide range of the Grashof number, Gr, nondimensional rotational speeds Ω i , Ω o of inner and outer cylinders and for different values of the Prandtl number Pr. The effects of the aspect ratio,A, on the heat transfer and flow patterns are obtained forA=1 and 2. The numerical results show that when the outer cylinder alone is rotating and the Grashof number is moderate, the outward bound flow is confined to a thin region along the bottom surface while the return flow covers a major portion of the cavity. For a given inner or outer cylinder rotation the temperature field is almost independent of the flow in the annulus for fluids with low Prandtl number, while it depends strongly for high Prandtl number fluids. At a high Grashof number, with moderate rotational speeds, the dominant flow in the annulus is driven by thermal convection, and hence an increase in the heat transfer rate occurs. In the case of unit aspect ratio, the flow pattern is unicellular for the rotation of the cylinders in the same direction, and when they rotate in the opposite direction two or more counter rotating cells separated by a stagnation surface are formed. The rate of heat transfer at the hot cylinder is suppressed when its speed of rotation is higher than that of the cooler cylinder. The computed heat transfer and flow patterns are compared with the available results of a nonrotating cylindrical annulus, and good agreement is found.

The heat transfer, pressure drop and flow patterns during flow boiling of R407C in a horizontal microfin tube have been investigated. The microfin tube is made of copper with a total fin number of 55 and a helix angle of 15°. The fin height is 0.24 mm and the inner tube diameter at fin root is 8.95 mm. The test tube is 1 m long. It is heated electrically. The experiments have been performed at saturation temperatures between −30°C and +10°C. The mass flux was varied between 25 and 300 kg/m2/s, the heat flux from 20,000 W/m2 down to 1,000 W/m2. The vapour quality was kept constant at 0.1, 0.3, 0.5, 0.7 at the inlet and 0.8, 1.0 at the outlet, respectively. The measured heat transfer coefficient is compared with the correlations of Cavallini et al., Shah as well as Zhang et al. Cavallini’s correlation contains seven experimental constants. After fitting these constants to our measured values, the correlation achieves good agreement. The measured pressure drop is compared to the correlations of Pierre, Kuo and Wang as well as Muller-Steinhagen and Heck. The best agreement is achieved with the correlation of Kuo and Wang. Almost all values are calculated within an accuracy of ±30%. The flow regimes were observed. It is shown, that changes in the flow regime affect the heat transfer coefficient significantly.

Numerical and experimental investigations have been conducted to study the flow and heat transfer characteristics for the buoyancy-induced flow inside an inclined arc-shape enclosure. Mathematical model in form of a stream function-vorticity formulation representing the laws of conservation in mass, momentum, and energy is expressed in a curvilinear coordinate frame and solved by a finite-volume discretization method. Heat transfer and flow pattern are predicted at various Grashof numbers and inclination angles. Meanwhile, an experimental system is developed and a flow-visualization technique using smoke is employed to observe the flow pattern. Results show that when the Grashof number is higher than 105, the increase in natural convection heat transfer becomes appreciable. The vortex strength and pattern are found to be greatly dependent on the inclination angle. The range of the Grashof number considered in this study is up to 107 and the inclination angle is varied from 0 to π.

This research numerically investigates the heat transfer and flow patterns of supercritical carbon dioxide (sCO2) in a six‐start spirally fluted tube. The research focuses on the geometrical optimization of the tube based on three key parameters: the groove depth (e1), the gap between the main tube and the outer sleeve (e2), and the thread pitch (p). The influence of these parameters on the heat transfer coefficient (h) and friction factor (f) was also investigated and analyzed. Furthermore, the study examined the overall impact of the gravity inclination angle (δ) on the thermal performance and flow velocity of the spirally fluted tube. The results indicated that the optimal geometrical parameters are as follows: e1/D = 0.33, e2/D = 0.04, and p/D = 8.33, yielding the highest values of h/h8/(f/f8) in the spirally fluted tub. The change in e2 has a more significant effect on turbulent kinetic energy (TKE) and thermal performance than the change in e1. The p value showed a more substantial effect on the f value compared with the h value. Furthermore, the h value was positively correlated with the gravity inclination angle δ in the region where Tb < Tpc. In the region where Tb > Tpc, increasing the gravity inclination angle δ led to a reduction in h value. When δ < 0°, the h value experienced a slight increase. However, the h value showed a substantial variation when δ > 0°, and the near‐wall fluid experienced a reduced flow velocity because of the combined effects of gravity and buoyancy, leading to a decrease in heat transfer. Larger gravity inclination angles led to a more pronounced deterioration in heat transfer. This study is anticipated to provide a theoretical basis for the optimized design of heat exchangers and the enhancement of energy conversion efficiency.

Book review

CFD simulation and experimental validation for wall effects on heat transfer of finite cylindrical catalyst

Characteristic patterns of heat flow are observed across present-day convergent and constructional margins. At active oceanic subduction margins heat flow varies systematically from normal oceanic values to low values, over the cold subducting slab, to high values over the zone of volcanism associated with slab melting, to normal continental values. A similar pattern is observed over active continent-continent collision zones. In both, hydrothermal circulation cells associated with the high heat-flow zone lead to ore deposition. In old continent-continent collision terrains the heat-flow pattern is broadly similar to that over active collision zones, although for quite different reasons. Low heat flow occurs over volcanic belts associated with subduction, because of their low radiogenic heat production. Higher heat flow occurs over plutons injected during subduction, because they have higher heat generation than normal crust. A zone of low heat flow may occur over middle-lower crustal terrains, now exposed by deep erosion, because of their low heat generation. The variation of heat flow can be used to indicate the direction of the ancient subduction.At active spreading ridges heat flow decreases systematically away from the axis of magma injection. The heat flow pattern across old continental rift systems is quite different, with bands of higher-than-usual heat flow delineating the edges of the rift, the result of thermal refraction at the boundary between low thermal conductivity rift-fill material and higher conductivity felsic crust. If the rift contains substantial volumes of low heat generation volcanic rocks, heat flow over the rift may be lower than that outside.Examples are taken from the Canadian Shield. Heat flow and heat-generation patterns across the boundary between the western Superior Province and Churchill Province imply subduction of Churchill crust under Superior, contrary to some previous models. Heat flow patterns across the Mid-Continent Rift in eastern Lake Superior contradict recent interpretations of seismic reflection data and suggest it is an asymmetrical rift containing a relatively small volume of volcanic rocks.KeywordsHeat FlowHigh Heat FlowCanadian ShieldSuperior ProvinceIdaho BatholithThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Numerical modelling and simulation of heat transfer for micro-sized spherical Al-4.5 wt% Cu alloy particles

Flow boiling in micro- and mini-channels has attracted much attention in recent years. But the phenomena is such confined channels have not been fully understood and explained. Some conclusions reached by different authors are even contradictory. The present research is trying to study some aspects of flow boiling in mini- and micro-channels. In the present paper boiling heat transfer and two-phase flow patterns in rectangular narrow channels were studied. The gap size of the channel was varied as 2, 1, 0.5 and 0.2 mm with the channel width and length being kept at 20 mm and 100 mm, respectively. In the present mini- and micro-channels, four flow patterns were identified; bubbly, intermittent, wavy and annular flow. They can be also divided into several sub-flow patterns. Flow patterns showed strong channel gap size dependence. Smaller gap size deleted bubbly flow, thus induced simpler flow patterns to shift the annular flow at lower vapor quality. The channels can be divided into two groups depending on the gap size; the larger gap group of 2 and 1 mm, and the smaller gap group of 0.5 and 0.2 mm. The larger gap group showed similar heat transfer behavior as conventional size of tubes. The smaller gap group indicated some peculiar phenomena. Heat transfer coefficient in the smaller gap group was relatively high in the low quality region. Then heat transfer coefficient decreased monotonously with increasing vapor quality. This behavior was considered attributable to the micro-bubble generation in the channel corners and an early partial dryout of thin liquid film. Thus the relationship between heat transfer coefficient and flow pattern should be carefully pursued in micro- and mini-channels to develop heat transfer correlations based on flow patterns.