Heat transfer

About: Heat transfer is a research topic. Over the lifetime, 181795 publications have been published within this topic receiving 2923586 citations. The topic is also known as: heat exchange.

Mechanism of heat transfer to fluidized beds

Abstract: In order to determine the nature of the resistance controlling heat transfer between fluidized beds and surfaces in contact with them, heat transfer measurements were made on the same solid constituents with several different fluidizing gases. The heat transfer coefficients obtained with fluidized beds are found to be proportional to the square root of the thermal conductivity of the quiescent beds. This result indicates that the process controlling fluidized heat transfer may be considered to be an unsteady-state diffusion of heat into mobile elements of quiescent bed material. This picture is analyzed mathematically to yield an equation for the heat transfer coefficient h = h wherein the effects of the bed thermal properties are separated from the effects of the stirring factor S, which accounts for bed motion and geometry. The mass transfer analogue is also derived and shown to correlate existing mass and heat transfer data reasonably well. It is concluded that the proposed mechanism yields a satisfactory picture of the fluidized heat transfer process and may provide the beginnings of a rational approach to the correlation and prediction of fluidized heat transfer in engineering work.

Thermal Properties and Temperature-Related Behavior of Rock/Fluid Systems

Abstract: I. Thermal Processes and Terms. Applications requiring thermal data. Definition of terms. II. Heat Capacities of Rocks. Experimental measurements. Calculated heat capacities. Heat capacities of fluid saturated rocks. Generalized calculations of heat capacities. Heat capacity of shales. III. Thermal Reactions in Rocks. Experimental methods. Results of measurements. IV. Thermal Expansion of Rocks. Thermal expansion of dry sandstones. Thermal expansion of fluid saturated rocks under stress. Conclusions on thermal expansion. V. Thermal Conductivities of Rock/Fluid Systems. Methods of measuring thermal conductivities. Effects of rock/fluid properties on thermal conductivity. Effects of temperature on thermal conductivity. Effects of stress on thermal conductivity. Summary. VI. Thermal Conductivity Models. Mixing law models. Empirical models. Theoretical models. Summary. VII. Thermal Diffusivities of Rocks. Experimental methods of measurement. Measured diffusivities of rocks. Calculated thermal diffusivities of rocks. VIII. Heat Transfer with Flowing Fluids. Natural convection in porous media. Fluid phase changes in porous media ( VCC effect ). Convective heat transfer with flowing fluids. IX. Thermal Alterations of Rocks. High temperature alterations. Role of fluxing agents in high temperature alterations. Reduction in fracture pressures by intensive borehole heating. Effects of steaming on rock properties. X. Effects of Temperature on Rock Properties. Bulk and pore compressibilities. Elastic wave velocities. Permeability. Formation resistivity factor. Summary and conclusions. XI. Low Temperature Behavior of Rock/Fluid Systems. P- and S-wave velocities and elastic moduli. Electrical properties. Thermal conductivity. Other low-temperature effects. XII. Wellbore Applications. Thermal data from well logs. Thermal gradients in wells. Heat losses in wells due to VCC effect. Summary and conclusions. Appendix A. Thermal Units Conversion Factors. Appendix B. Thermal Properties Data for Various Rocks. Appendix C. Thermal Properties of Subsurface Reservoir Fluids. References. Author Index. Subject Index.

Hybrid nanofluids preparation, thermal properties, heat transfer and friction factor – A review

Abstract: In the past decade, research on nanofluids has been increased rapidly and reports reveal that nanofluids are beneficial heat transfer fluids for engineering applications. The heat transfer enhancement of nanofluids is primarily dependent on thermal conductivity of nanoparticles, particle volume concentrations and mass flow rates. Under constant particle volume concentrations and flow rates, the heat transfer enhancement only depends on the thermal conductivity of the nanoparticles. The thermal conductivity of nanoparticles may be altered or changed by preparing hybrid (composite) nanoparticles. Hybrid nanoparticles are defined as nanoparticles composed by two or more different materials of nanometer size. The fluids prepared with hybrid nanoparticles are known as hybrid nanofluids. The motivation for the preparation of hybrid nanofluids is to obtain further heat transfer enhancement with augmented thermal conductivity of these nanofluids. This review covers the synthesis of hybrid nanoparticles, preparation of hybrid nanofluids, thermal properties, heat transfer, friction factor and the available Nusselt number and friction factor correlations. The review also demonstrates that hybrid nanofluids are more effective heat transfer fluids than single nanoparticles based nanofluids or conventional fluids. Notwithstanding, full understanding of the mechanisms associated with heat transfer enhancement of hybrid nanofluids is still lacking and, consequently it is required a considerable research effort in this area.