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In this paper, a numerical model describing the heat transfer and air flow inside and outside the casing of the permanent magnet brushless direct current (PM BLDC) motor is presented. In the model, a conjugate heat transfer including the heat conduction with heat sources in windings, magnets, bearings, natural and forced convection and radiation phenomena within internal and external air domain were analysed. The complex geometrical model included windings, a magnet circuit, a rotor with neodymium magnets, a PCB electronic plate, plastic covers, internal air between solid parts as well as a portion of the external air. The validation process of the developed model was realised on the basis of the velocity and temperature fields. The experimental data were recorded by 7 constant temperature anemometers at 4 levels above the motor housing, Laser Doppler Anemometry sensors in two axes inside the rear portion of the motor and 25 thermocouples fixed inside and outside the motor. The experimental and numerical tests were performed for 4 motor loadings and 3 rotational speeds. The average temperature error for the internal point was of 9 K, while that of the external points was of 2 K. The velocity field was very well predicted close to the housing wall in terms of horizontal and vertical components. A slightly worse agreement was found for the vertical component, especially in the vicinity of the shaft. The results were consistent for all the considered motor loadings and rotational speeds. [ABSTRACT FROM AUTHOR]

The project reported in this paper used CFD as a tool to investigate the effect of multi-pass on the shell side heat transfer of a heat exchanger system. The heat exchanger system is equipped with six vertical thermosyphons transferring thermal energy from a heat source (air) to a heat sink (water). The CFD model has been experimentally validated. The two-phase change processes inside the thermosyphons were not modelled during the simulation. Instead, the thermosyphons were treated as solid rods with a constant thermal conductivity, which was calculated theoretically by applying the thermal resistance analogy with the aid of convection, boiling and condensation correlations found in the literature. The heat source consists of multiple air passes on the evaporator section of the thermosyphons and two water passes on the condenser section. Three different arrangements on the evaporator section were investigated with one, two or three shell passes and the thermal performance compared for the three configurations. The investigation was performed at various inlet conditions: a range of air inlet temperatures (100, 150, 200 and 250 °C) and mass flow rates (0.05, 0.08, 0.11 and 0.14 kg/s). The water inlet conditions were kept constant (a temperature of 15 °C and a mass flow rate of 0.08 kg/s). The overall rate of heat transfer was obtained by both CFD and a theoretical model, and the results lay within 15% of the experimental data. The numerical predictions demonstrated that the k − ε Realizable turbulence model is a reliable tool for predicting heat transfer and fluid flow in such heat exchangers. [ABSTRACT FROM AUTHOR]

High temperature heat pipes offer an efficient way of heat removal in nuclear reactors under both normal operation and postulated accidental scenarios. Heat pipes with sodium as a working fluid has been proposed to be used in Compact High Temperature Reactor (CHTR), 233 U-Thorium fuelled reactor being designed to operate at 1000 °C. High temperature heat pipes can also be used for decay heat removal from dump tanks of molten salt breeder reactor and heat removal from first wall of fusion reactors. High temperature heat pipes of special construction can also be used for heat removal from core without use of coolant. Thus, reliable and long term operation of heat pipes is essential for the safe working of the reactor. In this respect, computer codes have been developed for design and simulation of high temperature heat pipes. To assist in the design stages, codes have been developed, which incorporate performance limits based on correlations and having a user friendly GUI. For system level studies, simplified heat transfer model is developed using a FEM model. For a detailed study of the heat pipe, the vapour flow behavior and interface evaporation condensation phenomena using a full CFD analysis is essential. This has been done by using a commercial CFD code by incorporating user defined functions (UDFs) which address the saturated nature of the vapour phase and the vapour wick interface conditions. A three dimensional transient numerical model has been developed to predict the vapour core, wall temperatures, vapour pressure, and vapour velocity in the screen mesh wick of sodium heat pipe. The results have been compared using a sodium heat pipe developed in-house. This paper will give an outline of all the developed models and compared the predicted results against the experimental data. [ABSTRACT FROM AUTHOR]

Nanofluids have gained significant attention in recent years due their great potential for heat transfer enhancement . The heat transfer of nanofluids can be numerically studied using a single-phase or two-phase approaches. The first assumes that the fluid phase and nanoparticles are in thermal equilibrium and move with the same velocity, while the second requires more computational effort but provides the possibility of understanding the behavior of both fluid phase and solid particles in the heat transfer mechanism. This paper reviews various computational approaches to predict fluid flow and heat transfer characteristics of nanofluids. The characteristics of single-phase and two-phase (volume of fluid, mixture, Eulerian–Lagrangian and Eulerian–Eulerian) approaches have been analyzed and discussed systematically. Latest development and recent researches related to the computational nanofluids are also given. [ABSTRACT FROM AUTHOR]

The mathematical model has been developed to describe the hydrodynamics of supercritical fluid flow in the reactor, heat, and mass transfer during drying processes for aerogels production. The model is based on the provisions of continuum mechanics, and Ansys Fluent is used for its calculation. In this research, the medium inside the reactor is considered as homogeneous two-component compressible viscous fluid, which is described by Peng–Robinson equation of state. In this paper we consider the model of supercritical drying process. A considerable part of the mathematical model is description of the fluid flow inside the porous body (aerogel), where only diffusive transport of substance occurs. The model is used to scale-up the supercritical drying process; the reactor geometry and process parameters optimization in order to intensify the production process, achieve desired properties of aerogels. The geometry of 5 l reactor is proposed and studied using the developed model. [ABSTRACT FROM AUTHOR]