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.

Thermometry and Thermal Transport in Micro/Nanoscale Solid-State Devices and Structures

Abstract: We review recent advances in experimental methods for high spatial-resolution and high time-resolution thermometry, and the application of these and related methods for measurements of thermal transport in low-dimensional structures. Scanning thermal microscopy (SThM) achieves lateral resolutions of 50 nm and a measurement bandwidth of 100 kHz: SThM has been used to characterize differences in energy dissipation in single-wall and multi-wall carbon nanotubes. Picosecond thermoreflectance enables ultrahigh time-resolution in thermal diffusion experiments and characterization of heat flow across interfaces between materials; the thermal conductance G of interfaces between dissimilar materials spans a relatively small range, 20

Predicted Efficiency of a Low-Temperature Nanofluid-Based Direct Absorption Solar Collector

Abstract: Due to its renewable and nonpolluting nature, solar energy is often used in applications such as electricity generation, thermal heating, and chemical processing. The most cost-effective solar heaters are of the "flat-plate" type, but these suffer from relatively low efficiency and outlet temperatures. The present study theoretically investigates the feasibility of using a nonconcentrating direct absorption solar collector (DAC) and compares its performance with that of a typical flat-plate collector. Here a nanofluid-a mixture of water and aluminum nanoparticles—is used as the absorbing medium. A two-dimensional heat transfer analysis was developed in which direct sunlight was incident on a thin flowing film of nanofluid. The effects of absorption and scattering within the nanofluid were accounted for. In order to evaluate the temperature profile and intensity distribution within the nanofluid, the energy balance equation and heat transport equation were solved numerically. It was observed that the presence of nanoparticles increases the absorption of incident radiation by more than nine times over that of pure water. According to the results obtained from this study, under similar operating conditions, the efficiency of a DA C using nanofluid as the working fluid is found to be up to 10% higher (on an absolute basis) than that of a flat-plate collector. Generally a DAC using nanofluids as the working fluid performs better than a flat-plate collector, however, much better designed flat-plate collectors might be able to match or outperform a nanofluids based DAC under certain conditions.

A four-layer model for the heat budget of homogeneous land surfaces

Abstract: The present model envisions the heat balance of a homogeneous land surface in terms of available energy, a set of driving potentials, and parameters for the physical state of the soil and vegetation. Two unique features of the model are: (1) the expression of the interaction of evaporation from the soil and from foliage by changes in the value of the saturation vapor pressure deficit of air in the canopy (the conclusions of this interaction being consistent with field observations); and (2) the treatment of sensible and latent heat exchange between the atmosphere and a soil consisting of two discrete layers.

Liquid Vapor Phase Change Phenomena : An Introduction to the Thermophysics of Vaporization and Condensation Processes in Heat Transfer Equipment

Abstract: Part 1:Thermodynamic and Mechanical Aspects of Interfacial Phenomena and Phase Transitions 1.Introductory Concepts 2.Interfacial Tension 3.Wetting Phenomena and Contact Angles 4.Transport Effects and Dynamic Behavior of Interfaces 5.Phase Stability Part 2:Boiling and Condensation Near Immersed Bodies 6.Heterogenous Nucleation and Bubble Growth in Liquids 7.Pool Boiling 8.Other Aspects of Boiling and Evaporation in an Extensive Ambient 9.External Condensation Part 3:Internal Flow Convective Boiling and Condensation 10.Introduction to Two-Phase Flow 11.Internal Convective Condensation 12.Cnvective Boiling in Tubes and Channels Part 4:Special Topics 13.Special Topics and Applications Appendix I:Basic Elements of the Kinetic Theory of Gases Appendix II:Saturation Properties of Selected Fluids Index

Onset of Thermohaline Convection in a Porous Medium

Abstract: The problem of the onset of convection, induced by buoyancy effects resulting from vertical thermal and solute concentration gradients, in a horizontal layer of a saturated porous medium, is treated by linear perturbation analysis. It is shown that oscillatory instability may be possible when a strongly stabilizing solute gradient is opposed by a destabilizing thermal gradient, but attention is concentrated on monotonic instability. The eigenvalue equation, which involves a thermal Rayleigh number R and an analogous solute Rayleigh number S, is obtained, by a Fourier series method, for a general set of boundary conditions. Numerical solutions are found for some special limiting cases, extending existing results for the thermal problem. When the thermal and solute boundary conditions are formally identical, the net destabilizing effect is expressed by the sum of R and S.