Turbulent friction and heat transfer behaviors of dispersed fluids (i.e., uttrafine metallic oxide particles suspended in water) in a circular pipe were investigated experimentally. Viscosity measurements were also conducted using a Brookfield rotating viscometer. Two different metallic oxide particles, γ-alumina (Al2O3) and titanium dioxide (TiO2), with mean diameters of 13 and 27 nm, respectively, were used as suspended particles. The Reynolds and Prandtl numbers varied in the ranges l04-I05 and 6.5-12.3, respectively. The viscosities of the dispersed fluids with γ-Al2O3 and TiO2 particles at a 10% volume concentration were approximately 200 and 3 times greater than that of water, respectively. These viscosity results were significantly larger than the predictions from the classical theory of suspension rheology. Darcy friction factors for the dispersed fluids of the volume concentration ranging from 1% to 3% coincided well with Kays' correlation for turbulent flow of a single-phase fluid. The Nusselt n...

Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles

http://wrap.warwick.ac.uk/44841/1/WRAP_Tian_Review%20on%20thermal%20energy%20storage%20with%20phase%20change.pdf

Review on thermal energy storage with phase change materials (PCMs) in building applications

Energy storage components improve the energy efficiency of systems by reducing the mismatch between supply and demand. For this purpose, phase-change materials are particularly attractive since they provide a high-energy storage density at a constant temperature which corresponds to the phase transition temperature of the material. Nevertheless, the incorporation of phase-change materials (PCMs) in a particular application calls for an analysis that will enable the researcher to optimize performances of systems. Due to the non-linear nature of the problem, numerical analysis is generally required to obtain appropriate solutions for the thermal behavior of systems. Therefore, a large amount of research has been carried out on PCMs behavior predictions. The review will present models based on the first law and on the second law of thermodynamics. It shows selected results for several configurations, from numerous authors so as to enable one to start his/her research with an exhaustive overview of the subject. This overview stresses the need to match experimental investigations with recent numerical analyses since in recent years, models mostly rely on other models in their validation stages.

A review on phase-change materials: Mathematical modeling and simulations

Numerical simulation of natural convection of nanofluid in a square enclosure: Effects due to uncertainties of viscosity and thermal conductivity

This paper presents a detailed review of effect of phase change material (PCM) encapsulation on the performance of a thermal energy storage system (TESS). The key encapsulation parameters, namely, encapsulation size, shell thickness, shell material and encapsulation geometry have been investigated thoroughly. It was observed that the core-to-coating ratio plays an important role in deciding the thermal and structural stability of the encapsulated PCM. An increased core-to-coating ratio results in a weak encapsulation, whereas, the amount of PCM and hence the heat storage capacity decreases with a decreased core-to-coating ratio. Thermal conductivity of shell material found to have a significant influence on the heat exchange between the PCM and heat transfer fluid (HTF). This paper also reviews the solidification and melting characteristics of the PCM and the effect of various encapsulation parameters on the phase change behavior. It was observed that a higher thermal conductivity of shell material, a lower shell size and high temperature of HTF results in rapid melting of the encapsulated PCM. Conduction and natural convection found to be dominant during solidification and melt processes, respectively. A significant enhancement in heat transfer was observed with microencapsulated phase change slurry (MPCS) due to direct surface contact between the encapsulated PCM and the HTF. It was reported that the pressure drop and viscosity increases substantially with increase in volumetric concentration of the microcapsules.

A review on effect of phase change material encapsulation on the thermal performance of a system

Forced convection heat transfer in microencapsulated phase change material slurries: flow in circular ducts

A slurry of micro-encapsulated phase change materials is provided in accordance with the present invention as a heat sink for, for example, the thermal management of electronic components. The slurry of micro-encapsulated phase change material may be provided within an open container and the electronic component immersed therein. In the alternative, the slurry of micro-encapsulated phase change material can be provided within a container of either flexible bag-like design or a relatively rigid preformed structure to be mounted adjacent the article to be thermally controlled.

Microencapsulated phase change material slurry heat sinks

In this note, an analysis of the problem assuming a constant wall temperature and a higher solid density, covering the entire melting process, is presented. The method used is an extension of Bareiss and Beer's analysis of the melting process in cylindrical enclosures, but unlike their study no simplifying assumption for the film thickness has been made. In fact, an earlier analysis by this investigator using such a relation gave results which failed to agree with experimental data.

The melting process within spherical enclosures

Gravity-assisted melting in a spherical enclosure: Effects of natural convection

This paper reports on results of an experimental investigation where the emphasis was placed on obtaining empirical correlations for the frost thickness–time history and the heat transfer coefficient–time history for a cylinder in humid air cross-flow. The facility employed for the investigation consisted of a low-velocity wind tunnel comprised of a rectangular test section, a transition section and a honeycomb placed at the tunnel entrance. An external refrigerator was used to cool an antifreeze solution having a mixture of 90% methanol and 10% ethylene glycol. Measured parameters included, among other things, the heat transfer coefficient as well as the frost thickness. © 1998 John Wiley & Sons, Ltd.

Subrata Sengupta

Papers

Forced convection heat transfer in microencapsulated phase change material slurries: flow in circular ducts

Microencapsulated phase change material slurry heat sinks

The melting process within spherical enclosures

Gravity-assisted melting in a spherical enclosure: Effects of natural convection

Empirical heat transfer and frost thickness correlations during frost deposition on a cylinder in cross-flow in the transient regime