M. Kamil

Heat transfer studies during natural convection boiling in an internally heated annulus

Abstract Heat transfer study has been carried out during natural convection boiling in an internally heated vertical annulus. The test section consists of a stainless steel tube, enclosed in a corning glass tube, forming an annular space through which the working fluid (water) flows. The S.S. tube is electrically heated. The experimental measurements have been made of wall temperatures along the length of the stainless steel tube and the inlet–outlet temperatures of the working fluid at the test-section, separator and condenser. Temperatures and mass flow rates of the cooling water entering and leaving the condenser, have also been recorded. The experiment was carried out for different heat fluxes impressed over the steel tube and repeated for two submergence levels of the liquid in the down flow pipe. Local and average heat transfer coefficients of the water film on the stainless steel tube surface, have been determined. Subsequently, the non dimensional parameters governing heat transfer and buoyancy induced flow processes, have been calculated and exhibited graphically. Correlations between the various parameters have also been developed.

Heat transfer to boiling liquids in a single vertical tube thermosiphon reboiler

Abstract An experimental investigation of heat transfer to boiling liquids has been carried out on a single tube natural circulation reboiler. Experiments were performed with distilled water, methanol, benzene, toluene, and ethylene glycol to cover a wide range of boiling points and thermophysical properties. The heat transfer section consisted of an electrically heated stainless steel tube 25.56 mm I.D. and 1900 mm long. Uniform heat flux values were used in the range of 4.1 to 43.0 kW/m 2 while inlet liquid subcooling was varied from 0.5 to 11.6°C. Liquid submergence levels were maintained around 100, 75, 50, and 30%. All the data were generated with increasing heat flux at atmospheric pressure. The effect of heat flux and liquid submergence on the variation of wall and liquid temperatures have been graphically presented and discussed. The heat transfer coefficients in the nonboiling and boiling regions for all the test liquids have been correlated by two separate correlations in terms of dimensionless groups. The experimental results are compared with different correlations given in the literature.

Isoflavones from Garcinia nervosa

Abstract A new isoflavone, 5,7,4′-trihydroxy-2′,3′,6′-trimethoxyisoflavone, nervosin, along with two known isoflavones, irigenin (5,7,3′-trihydroxy-6,4′,5′-trimethoxyisoflavone) and 7-methyltectorigenin(5,4′-dihydroxy-6,7-di-methoxyisoflavone) have been isolated from the leaves of Garcinia nervosa . Their structures have been elucidated on the basis of chemical and spectral evidence.

Polymer-Surfactant Interactions and the Effect of Tail Size Variation on Micellization Process of Cationic ATAB Surfactants in Aqueous Medium

The interactions between oppositely charged surfactant-polymer systems have been studied using surface tension and conductivity measurements and the dependence of aggregation phenomenon over the polyelectrolyte concentration and chain length of cationic ATAB surfactants, cetyltrimethyl ammonium bromide (CTAB), tetradecyltrimethyl ammonium bromide (TTAB), and dodecyltrimethyl ammonium bromide (DTAB) have been investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolyte at critical aggregation concentration (cac). The cac values of ATAB surfactants in the presence of anionic polyelectrolyte, sodium carboxy methyl cellulose (NaCMC), are considerably lower than their critical micelle concentration (cmc). After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in polyelectrolyte aqueous solution than in pure water. Among the cationic surfactants (i.e., CTAB, TTAB, and DTAB), DTAB was found to have least interaction with NaCMC. Surfactants with longer tail size strongly favor the interaction, indicating the dependence of aggregation phenomenon on the structure, morphology, and tail length of the surfactant.

Sorbifolin 6-galactoside from Garcinia andamanica

Abstract A new flavone glycoside, sorbifolin 6-galactoside, has been isolated from the leaves of Garcinia andamanica along with the known scutellarein 7-diglucoside. Their structures were established using spectroscopic and chemical evidence.

Experimental study of heat transfer to boiling binaries in a reboiler tube

Abstract An experimental investigation of heat transfer to boiling binaries under natural convective flow through a reboiler tube has been carried out to study the effect of composition on heat transfer coefficient. The heat transfer section consisted of an electrically heated stainless steel tube of 25.56 mm i.d. and 1900 mm long. Three binary systems: methanol-water, benzene toluene and water-ethylene glycol were used for a variety of concentrations. The heat flux values ranged from about 4.1 to 33.0 kW m −2 . The liquid submergence levels were maintained around 100, 75, 50 and 30%. A significant reduction in the heat transfer coefficient is observed for binary mixtures attributable to the effect of mass diffusion on heat transfer. The heat transfer coefficients in the non-boiling and boiling regions for all the binary mixtures have been correlated by two separate correlations in terms of dimensionless groups.

Effect of Bubble Turbulence and Submergence on Onset of Boiling in Natural Circulation Loop

Analysis of incipience boiling was developed for five different types of organic liquids including water covering wide range of physical properties. Incipience in liquid films is influenced by turbulent eddies and liquid submergence. This approach utilizes physical parameters of commonly accepted incipience models and provides a means of correcting these models for the effect of turbulent eddies and submergence. The results predicted from the theoretical analysis are consistent with the experimental data, having average absolute relative error of 13.61 percent.Copyright