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Phase Change Materials (PCMs) are widely used in thermal energy storage and thermal management systems due to their small volume for a given stored energy and their capability for maintaining nearly constant temperatures. However, their performance is limited by their low thermal conductivity and possible leaks while in the liquid phase. One solution is to imprison the PCM inside a polymer mesh to create a Polymeric Phase Change Material (PPCM). In this work, we have studied the cooling and solidification of five PPCMs with different PCMs and polymer fractions. To understand the heat transfer mechanisms involved, we have carried out micro- and macrorheological measurements in which Brownian motion of tracers embedded in PPCMs has been depicted and viscoelastic moduli have been measured, respectively. Beyond a given polymer concentration, it was shown that the Brownian motion of the tracers is limited by the polymeric chains and that the material exhibits an elastic behavior. This would suggest that heat transfer essentially occurs by conduction, instead of convection. Experiments were conducted to measure temperature variation during cooling of the five samples, and a semi-empirical model based on a phenomenological approach was proposed as a practical tool to choose and size PPCMs. [ABSTRACT FROM AUTHOR]

Abstract: The convective heat transfer of SiO2/water colloidal suspensions (5–34wt.%) is investigated experimentally in a flow loop with a horizontal tube test section whose wall temperature is imposed. Experiments were performed at different inlet temperatures (20, 50, 70°C) in cooling and/or heating conditions at various flow rates (200

This paper summarizes some applications of ultrasonic vibrations regarding heat transfer enhancement techniques. Research literature is reviewed, with special attention to examples for which ultrasonic technology was used alongside a conventional heat transfer process in order to enhance it. In several industrial applications, the use of ultrasound is often a way to increase productivity in the process itself, but also to take advantage of various subsequent phenomena. The relevant example brought forward here concerns heat exchangers, where it was found that ultrasound not only increases heat transfer rates, but might also be a solution to fouling reduction. [ABSTRACT FROM AUTHOR]

This article presents a study of heat transfer during condensation of n-hexane or isopropanol with a noncondensable gas (nitrogen) in a new plate heat exchanger geometry. Three test sections were installed on the test rig devoted to condensation of mixtures, either in reflux or co-current condensation configurations. For both configurations, heat transfer measurements were carried out. In single-phase flow tests, experimental data reduced by a log mean temperature difference were compared with new correlations on the gas side, adapted to the present specific plate geometry. Correlations of the Fanning friction factor were deduced from gas-side pressure drop measurements on the two geometries tested. In two-phase flow tests, the log mean temperature difference method was assumed to be correct to the first-order for the comparison of results in two test sections. The condensation curve method was applied to the present results, and co-current and reflux condensation configurations were then compared in terms of experimental overall heat transfer coefficients. It is shown that for a gas Reynolds number higher than 2,000, heat transfer coefficients in reflux condensation become higher than those for co-current condensation. Flooding phenomena were observed for specific experimental conditions in reflux condensation mode. The flooding experimental data are compared with five existing correlations (i.e., Wallis, modified Wallis, English et al., McQuillan & Whalley, and Zapke & Kröger) to observe fluid property effects for the same ranges of heat duty and mass flow rates in the condenser. The English et al. and Zapke & Kröger correlations show the best agreement with experimental flooding data in the present geometry. [ABSTRACT FROM AUTHOR]

An experimental investigation of the liquid flow friction factor and heat transfer coefficient in small diameter channels is presented. Rectangular and circular mini-channels with hydraulic diameters from 0.77 to 2.01 mm were used. Literature in the 1990s showed scattered experimental results and concluded that new physical phenomena in mini-channels could occur. However, the present experimental results show that three main causes can explain how different results were obtained in mini-channels compared to macro-tubes: uncertainties on the channel dimensions, inlet and outlet singular pressure losses, and longitudinal heat conduction. When these elements are taken into account, good agreement is found with standard correlations or theories. [ABSTRACT FROM AUTHOR]

Abstract: This article presents an experimental study of ascendant forced flow boiling in mini-channels with refrigerant R134a. A flat aluminium multi-port extruded tube composed of 11 parallel rectangular channels (3.28mm×1.47mm) with hydraulic diameter of 2.01mm was used. Mass flux ranged from 90 to 295kg/m2 s and heat flux from 6.0 to 31.6kW/m2. Two working pressures, 405 and 608kPa, were tested. Inlet subcooling varied from 1 to 17K. Heat transfer was found to be greater than that previously reported in the literature for conventional tubes, while dry-out occurred at low qualities. [Copyright &y& Elsevier]

Highlights: [•] Thermal energy storage in building floors with phase change materials was studied. [•] Thermophysical properties of a new polymer–PCM composite material were measured. [•] An alveolar floor filled with the composite was built to study storage capabilities. [•] Temperatures and heat fluxes have been measured under cyclic conditions. [•] Experimental results have been compared with a numerical simulation. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to characterize the thermal behaviour of different materials subjected to an ultrasonic fountain created by an ultrasonic piezoelectric transducer. Tests were conducted with an infrared camera to determine the surface temperature of the material samples. The main conclusion is that the plastics when subjected to the ultrasonic fountain tend to heat up strongly and can reach temperatures up to 200°C in few seconds. The temperature rise depends on the nature of the plastic material and the experimental conditions namely the height of liquid above the transducer and also the distance between the liquid surface and the sample. The comparison with an aluminium plate and a Pyrex plate gives a better understanding of the phenomenon that is related to three characteristics of the experiment: the transmission of the incident wave, the ability of the material to absorb this energy as heat and finally, the thermal and thermodynamic properties. These three parameters determine the behaviour of the plate when it is subjected to the ultrasonic fountain. In order to achieve a performing active control system, the choice of the material that faces an ultrasound fountain is very important to avoid any damage. [Copyright &y& Elsevier]