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The present study deals with the effects of wall geometry on the fluid flow and heat transfer in a channel with a wavy wall heated with constant heat dissipation. The waviness is characterized by wave amplitude and period. A detailed parametric numerical investigation of the effect of waviness on the local heat transfer parameters is performed for different turbulent flow conditions and compared with the literature. The effect of flow and geometry parameters is assessed quantitatively. Generalization is done based on the Reynolds number, ReA, which uses doubled wave amplitude, or height, A = 2a, as the characteristic length, and on the geometry parameter, A/λ, which essentially is the amplitude-to-wavelength ratio. A dimensionless location of the hottest spot on the wavy wall is shown to be dependent on these two dimensionless parameters. A correlation which encompasses the hottest spot locations for all the cases studied in the work is suggested. In order to obtain generalization for the hottest spot temperature, the Nusselt number is introduced based on the constant (uniform) heat flux and variable temperature difference, with wave amplitude as the characteristic length. It is shown that, for all cases studied herein, the hottest temperature is represented as NuA,min(ReA, A/λ). Accordingly, a correlation for the minimum Nusselt number is suggested. A further generalization for the hottest spot temperature is attempted for the conjugate problem with a conducting wall. It includes wall-to-fluid thermal conductivity ratio, ks/kl, as the additional dimensionless parameter which determines the Nusselt number.

Melting of a phase change material (PCM) is studied in a heat sink with vertical internal fins and a horizontal base to which a constant heat flux is applied. The phase change material is stored between the fins. A detailed parametric investigation explores various fin height and thickness, PCM layer thickness, and applied heat flux. Transient numerical simulations are performed using the Fluent 6 software. The results show how the transient phase change process depends on the heat flux from the base, heat capacity of the PCM, and fin dimensions. Dimensional analysis of the results is performed, and the generalized results are presented in terms of the melt fractions and Nusselt numbers vs. the Fourier, Stefan and Rayleigh numbers.

This study deals with natural-convection heat transfer from a vertical electrically heated plate, which is symmetrically placed in a chimney of variable height. The heated plate serves as a thermal pump for ventilation of a symmetrical enclosure beneath the chimney. In order to provide a comprehensive picture of the phenomena, three main approaches are used in parallel: temperature and velocity measurements, flow visualization, and numerical simulation. Temperature measurements are done by thermocouples distributed inside the plate and through the chimney. Velocity measurements are performed by means of a precise anemometer. Visualization is performed using smoke of incense sticks, with video recording and consequent image processing. Computer simulations of unsteady flow and temperature fields are performed in 3D and compared with measurements and visualization, with special attention paid to velocity fluctuations. Analysis is presented on the dependence of the temperature distribution on the flow field. The air flow rate on the heating plate in the chimney increases with the chimney height and is adequately predicted by the numerical simulation of the system.

Experimental investigation of a heat sink for cooling of electronic devices is performed. The objective is to keep the operating temperature at a relatively low level of about 323–333 K, using a dielectric liquid that boils at a lower temperature, while reducing the undesired temperature variation in the both streamwise and transverse directions. The experimental study is based on systematic measurements of temperature, flow and pressure, infrared radiometry and high-speed digital video imaging. The heat sink has parallel triangular microchannels with a base of 250 lm. Experiments on flow boiling of Vertrel XF in the microchannel heat sink are performed to study the effect of mass velocity and vapor quality on the heat transfer, as well as to compare the two-phase results to a heat sink cooled by single-phase water flow. 2002 Elsevier Science Ltd. All rights reserved.

The present paper addresses the issue of mixed convection from a small heated sphere in assisting and opposing flow configurations. The sphere is suspended in an electrodynamic chamber (EDC), where it is heated by a focused laser beam up to several hundred degrees above room temperature. As a result, free convection is induced from the sphere, with the Grashof number smaller than 0.02. A vertical forced flow is then applied and gradually increased in a quasi-static manner. The forced flow velocities are in the range 0–0.1 m/s, providing very low particle Reynolds numbers, usually less than 0.5. The effects of the free convection on the drag force experienced by the particle, and of the forced flow on the free convection are assessed quantitatively, measuring continuously the vertical forces experienced by the sphere. A similarity law developed in the previous study is successfully applied to determine the behavior of the drag force at various particle heating levels.

The present paper addresses the issue of mixed convection from a small heated sphere in cross-flow configuration. The sphere is suspended in an electrodynamic chamber (EDC), where it is heated by a focused laser beam up to several hundred degrees above room temperature. As a result, there is free convection from the sphere, with the Grashof number smaller than 0.01. Then, a horizontal forced flow is applied and gradually increased in a quasi-static manner. Horizontal flow velocities are in the range 0–0.1 m/s, providing very low particle Reynolds numbers, usually less than 0.5. The effects of the free convection on the drag force, and of the forced flow on the free convection, are assessed measuring continuously the horizontal and vertical forces experienced by the sphere. It is shown quantitatively how the forced flow suppresses the free convection. A similarity law is suggested for the behavior of horizontal and vertical forces at various particle temperatures.

The present paper deals with heat transfer inside a ventilated enclosure. The enclosure is heated by a horizontal downward-facing constant-temperature hot plate. In order to provide a comprehensive picture of the problem, three main approaches are used in parallel: temperature measurement, flow visualization, and numerical simulation. The measurements are done by thermocouples distributed uniformly at the vertical mid-plane of the enclosure. The visualization is performed using the smoke of incense sticks, with video recording and consequent image processing. The computer simulations of the flow and temperature fields are performed both for steady and transient ventilation and compared with the results of the measurements and visualization. Applicability to ventilation is discussed.