Pool Boiling of Liquids & their Mixtures on Enhanced Surfaces at Sub-atmospheric Pressures M. Siraj Alam 1 and V. K. Agarwal 2 1 Chemical Engineering, MED, MNNIT Allahabad – 211004, Uttar Pradesh, INDIA Email: msalam@mnnit.ac.in , Phone: +91-0532-2271504, Fax: +91-532-24455101 2 Chemical Engineering Department, IIT Roorkee – 247667, Uttarakhand, INDIA Email: vijayfch@iitr.ernet.in , Phone: +91-1332-285718 Fax: +91-1332-276535 This paper is an attempt to measure heat transfer coefficient (HTC) for the nucleate pool boiling of liquids and their binary mixtures on a plain as well as copper coated stainless steel tubes at atmospheric and subatmospheric pressures. Basically, it deals with the effect of heat flux, pressure and composition of mixture on HTC for the boiling of methanol, distilled water, and their mixtures on a plain as well as copper coated stainless steel heating tube surfaces. An experimental setup has been designed and fabricated for the study. Experimental results obtained shows that HTC of binary liquid mixtures have different features as compared with that of pure liquids depending upon their vapor-liquid equilibria behaviors at the prevailing system pressure. 1. Introduction It has been known from the plenty of experimental investigations on nucleate pool boiling of liquids binary mixtures that the boiling HTC of binary mixtures is significantly lower than those of pure liquids. This trend was observed by almost all the researchers for various types of liquid mixtures at different pressures. The explanations of this behavior of mixtures have been summarized by Thome (1983, 1984). Nucleate pool boiling of binary mixtures is a complex phenomena and variation in system pressure other than atmospheric may also increase its complexity. Many authors have studied effects of system pressure on binary HTC but most of the literature available is either at atmospheric or at super atmospheric pressures. In fact, data available at atmospheric or higher pressures can not be used with confidence to predict the HTC at sub-atmospheric pressures. Though, few recent works Alam et al. (2008) and Prasad et al. (2007) for boiling of pure liquids are available in literature under sub- atmospheric conditions but measured data are scarce for the boiling of liquid mixtures at lower pressures. Keeping these in view, the present work was aimed to generate experimental data for the boiling of methanol, distilled water and their binary mixtures on plain as well as copper coated stainless steel surface at various pressures.