Nusselt Number

Natural convection effects of the numerical solution for unsteady, laminar, free convection flow over an incompressible viscous fluid past a no n-isothermal vertical cone with surface temperature T ' w(x) = T ' ∞ + ax n varying as power function of distance from the apex (x = 0) is presented here. The dimensionless governing equations of the flow that

A series of experiments was conducted to study the effect of twisted-tape width on the heat transfer and pressure drop with laminar flow in tubes. Data for three twisted-tape wavelengths, each with five different widths, have been collected with constant wall temperature boundary condition. Correlations for the friction factor and Nusselt number are also available. The correlations predict the experimental data to within 10 to 15 percent for the heat transfer and friction factor, respectively. The presence of the twisted tape has caused the friction factor to increase by a factor of 3 to 7 depending on Reynolds number and the twisted-tape geometry. Heat transfer results have shown an increase of 1.5 to 3 times that of plain tubes depending on the flow conditions and the twisted-tape geometry. The width shows no effect on friction factor and heat transfer in the low range of Reynolds number but has a more pronounced effect on heat transfer at the higher range of Reynolds number. It i...

A 3D numerical study was carried out to analyze flow, heat and mass transfer first in a single half-cell cathode channel of proton exchange membrane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells in a stack. Hence, the above study on a single half-cell is extended to a stack of channels. Due to stacking, the assumption of uniform flow distribution would no longer hold true. Therefore, the channel flow-maldistribution is considered. The water formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the gas flow duct. The higher gas velocities in the duct result in faster water vapour removal which leads to a lower value of water vapour into the duct and hence a lower Nusselt number.

A numerical simulation has been carried out to investigate the buoyancy induced flow and heat transfer characteristics inside a wavy walled enclosure. The enclosure consists of two parallel wavy and two straight walls. The top and the bottom walls are wavy and kept isothermal. Two straight-vertical sidewalls are considered adiabatic. Governing equations are discretized using the control volume based Finite-Volume method with collocated variable arrangement. Simulation was carried out for a range of surface waviness ratios, =0.00-0.25; aspect ratios, A=0.25-0.5; and Rayleigh numbers Ra=100-107 for a fluid having Prandtl number equal to 1.0. Results are presented in the form of local and global Nusselt number distributions, streamlines, and isothermal lines for different values of surface waviness and aspect ratios. For a special case of =0 and A=1.0, the average Nusselt number distribution is compared with available reference. The results suggest that natural convection heat transfer is changed considerably when surface waviness changes and also depends on the aspect ratio of the domain. In addition to the heat transfer results, the heat transfer irreversibility (HTI) in terms of Bejan number (Be) was measured. For a set of selected values of the parameters (, A, and Ra), a contour of the Bejan number is presented at the end of this paper.

A numerical investigation of the airside performance of a plain fin-and-tube heat exchanger having 4 row configurations has been presented in this study. Fluid flow is steady, incompressible and three dimensional. Laminar (400<Re H <1200) and transitional (1300<Re H <2000) flow conditions are considered for both in-line and staggered tube arrangements. For transitional flow calculations, the k-ω turbulence model is used. Uniform flow with constant velocity and temperature are considered at inlet and no-slip boundary condition and constant wall temperature is assumed at fin and tube surfaces. In this study the geometrical parameters such as fin pitches, longitudinal pitches and transverse pitches of tube spacing are studied. The results are compared with previous experimental data of Wang et al. [1]. Results are presented in the form of friction factor (f) and Colburn factor (j). For both laminar and transitional flow conditions heat transfer and friction factor decrease ...

The purpose of this study is to investigate the influence of indentations on the parameters of fluid flow and heat of water-silver nanofluid in a rectangular two-dimensional micro channel. It includes heat transfer water silver nano fluid in an indented micro channel under the constant temperature. The system is numerically modeled, by Finite Volume Method. After solving the governing equations for U, V and θ, other useful quantities such as Nusselt number and friction factor can be determined. The hot fluid inlet exits after cooling by the cold walls of the micro channel. Calculations are done for the two ranges of Reynolds number (Re). It was observed that at times the fluid has more indentations; it has a greater temperature drop that is at the output cross section of the micro channel. With increasing Reynolds number (Re), number of the indentations and the increasing volume fraction of the nanoparticles, greater temperature drop occurs. The presence of indentation in the micro channel increases the speed and the dimensionless temperature at the center line. Finally, the results are provided in the form of the contour of flow and isothermal lines, the coefficient of friction, Nusselt number, temperature and velocity profiles in different micro channel sections. The results of the numerical simulation indicate that the heat transfer rate is significantly affected by the solid volume fraction and Reynolds number.

Numerical simulation of an air and water two-phase flow in a micro tube is carried out. The focus is laid upon bubbly and slug flows with dry-out. An axisymmetric two-dimensional flow is assumed. The Phase-Field method is adopted to capture the interface, as well as to resolve the singularities arising at the rupture of liquid film and the consequent contact

The rates of heat transfer for flow through a periodic array of wavy passages are studied with an accurate numerical scheme. The flow was observed to be steady until Re around 180 after which self-sustained oscillatory flow was observed. The self-sustained oscillations lead to the destabilization of laminar thermal boundary layers, replenish the near-wall fluid with the fluid in the core region, and thus provide a natural mechanism of heat and mass transfer enhancement. In the steady-flow regime, the average Nusselt numbers for the wavy wall channel were only slightly larger than those for a parallel-plate channel. On the other hand, in the transitional-flow regime, the enhancement of heat transfer was about a factor of 2.5. Friction factors for the wavy channel were about twice those for the parallel-plate channel in the steady-flow region, and remained almost constant in the transitional regime.