摘要:

A numerical approach is developed to study the thermal transport in polymer melts flowing through narrow channels with contraction. Attention is focused on the flow and heat transfer of practical polymer melts used in plastic industries, such as low-density polyethylene (LDPE), which cannot be regarded as Newtonian in their behavior. The rheological model used in this study is based on a power law variation of viscosity with shear rate, along with temperature and pressure dependent viscosity. The flow and heat transfer, which are strongly coupled through the temperature dependence of the viscosity, are solved by using a finite volume method with a nonuniform staggered grid system. The results are presented for axisymmetric tubes, which characterize the nozzle for an injection molding machine or the die in plastic extrusion. The effect of heat generation by viscous dissipation is included. The effects of varying the channel contraction ratio and other dimensions, as well as of the mass flow rate, are explored for channels with isothermal walls. The heat transfer rate, the pressure drop, and the temperature and shear stress distributions are determined. The results show that viscous dissipation significantly affects the temperature field and thus the heat transfer and shear stress in the narrowing region. The maximum temperature is observed near but not at the wall of the constricted portion of the channel. The influence of pressure on viscosity is usually neglected for low-pressure situations. However, this effect is not negligible when the magnitude of pressure is very large, as is the case for many practical problems, and is included in the investigation.

ISSN:1040-7782    

DOI:10.1080/10407789608913831

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Increase in the heat transfer rate during melting and freezing of a phase change material (PCM) with a low thermal conductivity is demonstrated by inserting a high-porosity metal matrix into the PCM. A vertical annulus space (r1⩽r⩽r0,0⩽z⩽h)homogeneously fitted with water and an aluminum matrix, is selected for this study. The Navier-Stokes equations are modified to account for Darcy's effect. For both the melting and freezing cases, the density inversion phenomenon of water is considered. The irregularity and time-varying nature of the solid and the liquid regions are accounted for by a geometric coordinate transformation. The numerical results are presented in the form of solid-liquid interface movements, isotherms, streamlines, and heat transfer rates for some representative cases. The heat transfer rates for enhanced cases show an order-of-magnitude increase over the base case, where no metal matrix is inserted.

ISSN:1040-7782    

DOI:10.1080/10407789608913832

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical model is presented to analyze a two-dimensional, time-dependent heat transfer and flow process in a melting, heterogeneous snow cover with the underlying soil layer that is permeable and initially frozen. The model considers flow fingering phenomena due to variation of permeability in layered snow. A unit block ofsnowpack is modeled and divided into a heterogeneous domain with specified number of snow layers and a water-fingering domain with initially uniform properties, in addition to coupling with a formulation of infiltration in the frozen soil. Typical results of snow depth, wetting front location, snow water equivalent, basal ice thickness, and soil infiltration show good agreement with experimental data under field conditions. A parametric study is performed to investigate the sensitivity of several properties and parameters in boundary conditions.

ISSN:1040-7782    

DOI:10.1080/10407789608913833

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A three-dimensional Navier-Stokes code has been used to study the effect ofspanwise pitch of shower-head holes and coolant to mainstream mass flow ratio on the adiabatic effectiveness and heat transfer coefficient on a film-cooled turbine vane. The mainstream is akin to that under real engine conditions with stagnation temperature 1900 K and stagnation pressure 3 MPa. It is found that with the ratio of coolant to mainstream mass flow being fixed, reducing the spanwise pitch for shower-head holes (P) from 7.5d to 3.0d, where d is the hole diameter, increases the average effectiveness considerably over the blade surface. However, when P / d = 7.5, increasing the coolant mass flow increases the effectiveness on the pressure surface but reduces it on the suction surface owing to coolant jet lift-off. For P / d = 4.5 or 3.0, such an anomaly does not occur within the range of coolant-to-mainstream-mass-flow ratios analyzed. In all cases, adiabatic effectiveness and heat transfer coefficient are highly three-dimensional,

ISSN:1040-7782    

DOI:10.1080/10407789608913834

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical investigation of laminar forced convective heat transfer was performed in a three-dimensional channel with baffles in which a uniform heat flux was applied to the top and bottom walls, and the sidewalk were considered adiabatic. The trade-off between heat transfer enhancement and pressure drop produced by the baffles was studied for periodically fully developed flow (PDF). The numerical analysis was performed using a finite volume approach. The computer code was validated against the experimental results of Goldstein and Kreid [1] and Beavers et al. [2] for a three-dimensional channel without baffles. Parametric runs were made for Reynolds numbers of 150, 250, 350, and 450 for baffle height to channel width ratios (H/Dy) of 0.5, 0.6, 0.7, and 0.8. Heat transfer behavior was studied for Prandtl numbers of 0.7 and 7.0, and for wall thermal conductivity to fluid thermal conductivity ratios (K) of 1, 10, 100, and 1000.

ISSN:1040-7782    

DOI:10.1080/10407789608913835

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical study is presented for natural convection flow and heat transfer in a rectangular enclosure cooled from above with five discrete protruding heaters mounted on one vertical wall. The governing equations for natural convection and conjugate conduction within protruding heaters were solved using a finite volume method over a range of Rayleigh numbers from 5.0 × 105to 1.0 × 107. Results showed the flow pattern and temperature profile within the entire enclosure for various power inputs, the correction of local Nusselt number versus modified Rayleigh number was presented. Comparison of the numerical results with experimental data showed good agreement.

ISSN:1040-7782    

DOI:10.1080/10407789608913836

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor