A general method for calculation of flow boiling and flow condensation heat transfer coefficients in minichannels

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Flow boiling and flow condensation are often regarded as two opposite or symmetrical phenomena, however their description with a single correlation has yet to be suggested. In the case of flow boiling in minichannels there is mostly encountered the annular flow structure, where bubble generation is not present. Similar picture holds for inside tube condensation, where annular flow structure predominates. In such case the heat transfer coefficient is primarily dependent on the convective mechanism. In the paper a method developed earlier by D. Mikielewicz et al. (2007) is applied to calculations of heat transfer coefficient for inside tube condensation. Satisfactory consistency with well established correlations for condensation has been found

Heat transfer enhancement, flow visualization and friction characteristics in rib-roughened channels

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.In the last two decades thermochromic liquid crystal (TLS), true-color digital image processing and laser anemometry (PIV) have been successfully used in non-intrusive, technical and heat and mass transfer studies and applications. The aim of the paper is to asses the state of the art in the exploration of heat transfer control by transverse vortex generators. They are able to increase heat transfer by several hundred percent. Prior to the use of vortices to influence heat transfer it must be known how different vortices are generated and controlled and how they interact with the original or base flow and temperature field. Liquid crystals were used to determinate the distribution of surface temperature and then evaluation of heat transfer coefficient or the Nusselt number. The flow pattern produced by transverse vortex generators (rib-roughened passages) was visualized using a planar beam of double-impulse laser tailored by a cylindrical lens and oil particles. Sequential images of particles in the cross sectional plane taken with CCD video camera from the downstream side the flow were stored on a personal computer to obtain distributions of velocity vectors by means of the PIV method. Local and average Nusselt numbers, friction factors and velocity fields are presented for rectangular channels with an aspect ratio of 6.35 and five types of transverse vortex generators which were brought to required temperatures by hot film method. The pitch-to-height-ratio of the ribs was 11.mp201

Liquid crystal thermography and image processing in heat and fluid flow experiments

Liquid crystal techniques, combined with sophisticated software in increasingly powerful personal computers, are now permitting fairly comprehensive full-field studies of velocity, temperature and heat transfer coefficent-distributions, with their accompanying automatic analysis. Liquid crystals and true-colour image processing have opened some new approaches for heat transfer research and offer satisfactory accuracy and resolution. New and more incisive experiments are being designed for conventional situations, and other problems can now be studied which were previously not practical to consider. The history of these techniques is reviewed and the principal methods are described using illustrative examples from the literature and work of the author. A new liquid crystal thermometry method is described to determine quantitatively two-dimensional temperature distributions on a surface and in a fluid, from colour records obtained using a thermosensitive chiral-nematic material combined with image processing. Application type experiments have been carried out both to visualise the complex distribution of temperature and local heat transfer coefficient over a cooled surface disturbed by different solid obstacles, and also to investigate temperature and flow patterns in a rectangular cavity for natural convection. A new experimental method (optical and non-invasive) has been established to measure simultaneously both flow and thermal fields - this method may be described as particle image velocimetry and thermometry (PIVT). Some of the experimental results presented are applied to an important Industrial improvement in heat exchanger design and could result in substantial reductions in energy costs

Comparative isoschizomer profiling of cytosine methylation:the HELP assay

The distribution of cytosine methylation in 6.2 Mb of the mouse genome was tested using cohybridization of genomic representations from a methylation-sensitive restriction enzyme and its methylation-insensitive isoschizomer. This assay, termed HELP (HpaII tiny fragment Enrichment by Ligation-mediated PCR), allows both intragenomic profiling and intergenomic comparisons of cytosine methylation. The intragenomic profile shows most of the genome to be contiguous methylated sequence with occasional clusters of hypomethylated loci, usually but not exclusively at promoters and CpG islands. Intergenomic comparison found marked differences in cytosine methylation between spermatogenic and brain cells, identifying 223 new candidate tissue-specific differentially methylated regions (T-DMRs). Bisulfite pyrosequencing confirmed the four candidates tested to be T-DMRs, while quantitative RT-PCR for two genes with T-DMRs located at their promoters showed the HELP data to be correlated with gene activity at these loci. The HELP assay is robust, quantitative, and accurate and is providing new insights into the distribution and dynamic nature of cytosine methylation in the genome. ©2006 by Cold Spring Harbor Laboratory Press

Challenges with high temperature air combustion

Combustion behavior is significantly affected by temperature of the reactants, amount of gas recirculation and temperature of the flue gases. High temperature air combustion technology has significant impact on the design and development of advanced industrial furnaces for energy savings and materials conservation. In this technology the combustion air is preheated to very high temperatures using regenerative burners. Experimental and theoretical studies are underway for determining the structure of flames using high temperature combustion air. Specifically information on ignition and flame stability, chemical kinetics, flame spectral characteristics, turbulence, flame chemistry, heat flux distribution from the flame is being obtained. The objectives of this paper is to provide fundamental understanding on the physical and chemical processes and optimal utilization of the technology for some specific application.

Liquid crystal thermography and image processing in heat and fluid flow experiments

SIGLEAvailable from British Library Document Supply Centre- DSC:DX187865 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Improved Liquid Crystal Thermography by Using True-Colour Image Processing Technology

No abstract availabl