S.S. Alam

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.

Circulation rates in thermosiphon reboiler

Abstract An experimental investigation of heat transfer to boiling liquids with natural convective flow has been carried out in a single tube natural circulation reboiler. Three test liquids—water, acetone, and ethylene glycol—were used 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 ID and 1900 mm long. The uniform heat fluxes in the range of 3800–40,000 W/m 2 were employed while inlet liquid subcooling varied from 0.2–45.5°C. The liquid submergence levels were maintained around 100, 75, 50, and 30 percent. All the data were generated at 1 atmospheric pressure. The effect of heat flux and submergence on the variation of circulation rates have been graphically presented and discussed. Circulation rates for all test liquids have been correlated in terms of dimensionless groups.

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.