A mechanistic model of heat transfer for gas–liquid flow in vertical wellbore annuli

The most prominent aspect of multiphase flow is the variation in the physical distribution of the phases in the flow conduit known as the flow pattern. Several different flow patterns can exist under different flow conditions which have significant effects on liquid holdup, pressure gradient and heat transfer. Gas-liquid two-phase flow in an annulus can be found in a variety of practical situations. In high rate oil and gas production, it may be beneficial to flow fluids vertically through the annulus configuration between well tubing and casing. The flow patterns in annuli are different from pipe flow. There are both casing and tubing liquid films in slug flow and annular flow in the annulus. Multiphase heat transfer depends on the hydrodynamic behavior of the flow. There are very limited research results that can be found in the open literature for multiphase heat transfer in wellbore annuli. A mechanistic model of multiphase heat transfer is developed for different flow patterns of upward gas-liquid flow in vertical annuli. The required local flow parameters are predicted by use of the hydraulic model of steady-state multiphase flow in wellbore annuli recently developed by Yin et al. The modified heat-transfer model for single gas or liquid flow is verified by comparison with Manabe＇s experimental results. For different flow patterns, it is compared with modified unified Zhang et al. model based on representative diameters.

3-D transient numerical simulation on the process of laser cladding by powder feeding

A 3-D transient mathematical model for laser cladding by powder feeding wasdeveloped to examine the macroscopic heat and momentum transport during the process, based on whicha novel method for determining the configuration and thickness of cladding layer was presented. Byusing Lambert-Beer theorem and Mie's theory, the interaction between powder stream and laser beamwas treated to evoke their subtle effects on heat transfer and fluid flow in laser molten pool. Thenumerical study was performed in a co-ordinate system moving with the laser at a constant scanningspeed. A fixed grid enthalpy-porosity approach was used, which predicted the evolutionarydevelopment of the laser molten pool. The commercial software PHOENICS, to which several moduleswere appended, was used to accomplish the simulation. The results obtained by the simulation werecoincident with those measured in experiment basically.

Approximate solution of the nonlinear heat transfer equation of a fin with the power-law temperature-dependent thermal conductivity and heat transfer coefficient

In this paper,differential transform method(DTM)is used to solve the nonlinear heat transfer equation of a fin with the power-law temperature-dependent both thermal conductivity and heat transfer coefficient.Using DTM,the differential equation and the related boundary conditions transformed into a recurrence set of equations and finally,the coefficients of power series are obtained based on the solution of this set of equations.DTM overcame on nonlinearity without using restrictive assumptions or linearization.Results are presented for the dimensionless temperature distribution and fin efficiency for different values of the problem parameters.DTM results are compared with special case of the problem that has an exact closed-form solution,and an excellent accuracy is observed.