Degree Of Temperature Uniformity Research Articles

Numerical investigation of combustion characteristics for hydrogen mixed fuel in a can-type model of the gas turbine combustor

Numerical simulations are performed to analyze the combustion characteristics of propane fuel mixed with different amounts of hydrogen in a can-type combustor. The volume fraction of the hydrogen fuel varies from 0% to 100% in the fuel mixture. The results indicate that the hydrogen enrichment of the fuel significantly affects the flow structure, mixture fraction, and combustion characteristics. An increase in the volume fraction of hydrogen significantly affects the mean mixture fraction distribution, promotes combustion, and increases the flame temperature and the width of the flammable range within the combustor. Therefore, the degree of temperature uniformity at the outlet of the combustor increases with hydrogen enrichment, corresponding to an increase of 49.64% in the uniformity factor. The hydrogen enriched fuel can also reduce the emissions of CO and CO2, owing to the reduced amount of carbonaceous fuel.

Two-phase lattice Boltzmann simulation of natural convection in a Cu-water nanofluid-filled porous cavity: Effects of thermal boundary conditions on heat transfer and entropy generation

Abstract The present work investigates the effect of four different thermal boundary conditions on natural convection in a fluid-saturated square porous cavity to make a judicious choice of optimal boundary condition on the basis of entropy generation, heat transfer and degree of temperature uniformity. Four different heating conditions- uniform, sinusoidal and two different linear temperature distributions are applied on the left vertical wall of the cavity respectively, while maintaining the right vertical wall uniformly cooled and the horizontal walls thermally insulated. The two-phase thermal lattice Boltzmann (TLBM) model for nanofluid is extended to simulate nanofluid flow through a porous medium by incorporating the Brinkman–Forchheimer-extended Darcy model. The close agreement between present LBM solutions with the existing published results lends validity to the present findings. The current results indicate that the uniform and bottom to top linear heating are found to be efficient heating strategies depending on Rayleigh number (103 ≤ Ra ≤ 105) and Darcy number (10−1 ≤ Da ≤ 10−6). It is observed that the nanofluid improves the energy efficiency by reducing the total entropy generation and enhancing the heat transfer rate although its augmentation depends on the optimal volume fraction of nanoparticles.

Transitional flow regime heat transfer and pressure drop in an annulus with non-uniform wall temperatures

Abstract An experimental investigation was carried out to determine the average heat transfer coefficients and friction factors in the transitional flow regime of a horizontal concentric annular passage. The flow was in the mixed convection flow regime and was both hydrodynamic and thermally developing. The annular diameter ratio was 0.483 with an inner passage wall diameter of 15.90 mm. The test facility, which consisted of a counter-flow heat exchanger having a heat transfer length of 5.08 m, was operated at different degrees of longitudinal wall temperature uniformity on the inner wall of the annular passage. Both heated and cooled flow applications with water as fluid (cold fluid and hot fluid respectively) were investigated using a conventional annular inlet geometry type. It was found that the degree of temperature uniformity on the inner surface of the annular passage had an influence on the transitional Reynolds number span, the heat transfer coefficients, and friction factors. Depending on the wall temperature uniformity it was found that the critical Reynolds number, based on the Nusselt number results, was approximately between 350 and 500 for a cooled annulus and between 430 and 510 for a heated annulus. The critical Reynolds numbers based on the friction factor results were different from those based on the Nusselt number and was found to be approximately 800 for isothermal flow, between 1000 and 1030 for a cooled annulus, and approximately 1000 for a heated annulus. Correlations for the prediction of the transitional regime Nusselt number and friction factor as a function of among others, the wall temperature uniformity are proposed. The Nusselt number correlation predicts all the experimental data within a ±6% error band for the heated and cooled annulus cases. The friction factor correlation also predicts all the data points, within a ±6% error band.

Research on Heat and Mass Transfer of Flat Grooved Heat Pipes

Flat grooved heat pipes, which are especially useful in obtaining a high degree of temperature uniformity on flat surfaces, have been successfully used in the temperature control of electronic systems, however, the mechanisms governing the flow and heat transfer of this kind of heat pipes are still under scrutiny as some reported results cannot be reproduced by others or some assumptions have been proven to be unreasonable or ideal. The theoretical and experimental studies on flat grooved heat pipes and introduce work performed on modeling flat grooved heat pipes are reviewed in this paper.

Effects of Thermal Boundary Conditions on Entropy Generation during Natural Convection

A comprehensive numerical study on entropy generation during natural convection is studied in a square cavity subjected to a wide variety of thermal boundary conditions. Entropy generation terms involving thermal and velocity gradients are evaluated accurately based on the elemental basis set via the Galerkin finite element method. The thermal and fluid irreversibilities during the conduction and convection dominant regimes are analyzed in detail for various fluids (Pr = 0.026,988.24) within Ra = 103–105. Further, the effect of Ra on the total entropy generation and average Bejan number is discussed. It is observed that thermal boundary conditions significantly affect the thermal mixing, temperature uniformity, and the entropy generation in the cavity. A case where the bottom wall is hot isothermal with linearly cooled side walls and adiabatic top wall is found to result in high thermal mixing and a higher degree of temperature uniformity with minimum total entropy generation.

Vacuum radiation furnace with precise control of temperature gradients for crystal growth by sublimation

The furnace was designed for the growth of lead selenide single crystals at 775° C. It provides an inherently high degree of temperature uniformity and, without the use of a servo control system, the gradients can be adjusted and maintained to less than 1/10 deg C/cm and ¼ deg C in 10 cm. A changed gradient can be established in 5 minutes. In heating from cold a steady temperature is attained in 75 minutes, and the furnace can be cooled in a few minutes. This performance is achieved by minimizing the total mass of heated material, and by the use of highly reflecting water-cooled silvered surfaces for the walls. An outline is given of the regulating system for controlling the absolute temperature to 0.1 deg C. Evaporation of the alloy heater element limits the maximum temperature to about 940° C, but this should be raised by the use of other elements.