Conjugate Heat Transfer In Flow Research Articles

Conjugate Heat Transfer in Thermal Inkjet Printheads

The mass of individual droplets ejected from a thermal inkjet printhead increases with increasing local temperature near the ejector nozzles. The amount of ink deposited on the page and so the printed image density depends on the droplet mass. Thus, printhead temperature nonuniformity results in printed image density variations that can be unacceptable to the end users of the printed output. Such temperature variations arise from a combination of the ink fluid flow and the heat transfer in both the ink and the solid components in the printhead. Conjugate heat transfer (CHT) in thermal inkjet printheads is investigated here using validated numerical simulations. A typical thermal inkjet printhead is considered here for the first time, with cold ink drawn through the solid structural components by the ejector nozzle refill. The effect of the width of the feedhole above the printhead chip on the temperature field within the chip is analyzed. Validation of the simulation model required the derivation of novel analytical solutions for the relatively simple problems of fully developed forced convection in a differentially heated planar channel and conduction against convection in plug flow. The results from numerical simulations of these two problems are found to compare well with the newly derived analytical solutions. CHT in flow over a backward-facing step with a heated downstream wall was also simulated as part of the validation process, and good agreement was observed with earlier numerical studies. For the main part of the study, it was found that increasing the width of the feedhole reduces the gradients in temperature on the surface of the printhead chip, thus reducing temperature-related printing defects.

Conjugate heat transfer analysis of liquid-vapor two phase flow in a microtube: A numerical investigation

Flow boiling in microchannel is a promising way of high heat flux removal. In account of this, numerous experimental and numerical studies have been performed on flow boiling in conventional as well as in microchannels focusing on heat transfer, bubble dynamics and flow pattern while studies on conjugate heat transfer in flow boiling are yet to be explored. This work presents a systematic three-dimensional numerical study of conjugate effect of heat transfer in two-phase flow in a microtube subjected to constant wall heat flux. Volume of fluid (VOF) model along with phase change model are used to capture bubble shape and flow pattern. Water enters the microtube at a temperature of 300 K. The effect of (i) wall to fluid conductivity ratio (ksf), (ii) wall thickness to inner radius ratio (δsf), and (iii) inlet mass flux (G) in unsteady flow boiling condition are explored. Transformation of nucleating bubbles into elongated bubbles are characterised in terms of wall thickness (δsf) and its material conductivity (ksf). The results indicate that bubble length increases with increasing wall material conductivity but decreases with increasing wall thickness as well as mass flux. Growth and motion of vapor bubbles due to phase change are also explored. Comparison between single and two-phase flow under conjugate heat transfer scenario is also discussed.

Hydrodynamics and heat transfer prior to onset of nucleate boiling in a rectangular microchannel heat sink

The conjugate heat transfer of flow boiling in a rectangular microchannel heat sink (MCHS) was modelled numerically to investigate the hydrodynamics and thermal responses of flow prior to the onset of nucleate boiling (ONB). Local hydrodynamics and thermal conditions leading to ONB are analysed numerically for different heat flux. The flow patterns of different modes of microconvection and mixed convective flows including the circulating flow, wavy flow and seeping flow were demonstrated and discussed. The numerical study proposes the mechanism leading to the first bubble nucleation which cover the initiation of fluid instability until the ONB. This work provides better understanding of the superheat induced flow instability and the progressive fluid convection under transient heating.

Studies of finite element procedures—the use of ADIANA-F in fluid flow analyses

We present in this paper some experiences obtained with the program ADINA-F in fluid flow analyses. The theory and numerical methods used in the program for laminar and turbulent flow, and flow with heat transfer, are summarized and then the solutions of various problems are presented. These problem solutions comprise the analyses of turbulent flow in a pipe and natural convection in a porous medium, the prediction of flow around a cylinder, the conjugate heat transfer in flow through a pipe and in the cooling of electronic equipment, and the 3D analysis of natural convection in a cavity.