Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e., water-Al₂O₃ and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth copper and stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed test heater. The experiments have been performed to establish the influence of nanofluids concentration as well as tube surface material on heat transfer characteristics at atmospheric pressure. The results indicate that independent of concentration nanoparticle material (Al₂O₃ and Cu) has almost no influence on heat transfer coefficient while boiling of water-Al₂O₃ or water-Cu nanofluids on smooth copper tube. It seems that heater material did not affect the boiling heat transfer in 0.1 wt.% water-Cu nanofluid, nevertheless independent of concentration, distinctly higher heat transfer coefficient was recorded for stainless steel tube than for copper tube for the same heat flux density.

The paper presents a survey of the experimental and numerical studies of shell-and-tube systems in which phase change material (PCM) is used. Due to the multitude of design solutions for shell-and-tube systems, the emphasis is placed on double-tube (DT), triplex-tube (TT), and multi-tube (MT) units. Additionally, only single-pass systems are considered. Particular attention is paid to the method of heat transfer intensification. The analysis of the research results begins with the classification of each of the three mentioned systems. The systems are divided according to the angle of inclination, the method of heat transfer enhancement (HTE), the flow direction of heat transfer fluid (HTF), and the arrangement of tubes in the bundle. Moreover, the simplified schemes of the particular research cases are proposed. Then, the works on each of the mentioned systems, i.e., DT, TT, and MT, are discussed chronologically. Finally, in the corresponding tables, details of the discussed cases are presented, such as geometric dimensions, and the type of PCM or HTF used. A novelty in the present work is the precise classification of PCM TESUs as DT, TTH, and MTH. In the literature, there is a lot of discretion in this regard. Second, the methods of heat transfer intensification in the presented PCM TESUs are listed and discussed. Third, unified schemes of design solutions for the discussed PCM TESUs are proposed. The review shows that development directions for shell-and-tube TESUs include systems with high conductivity fins of different shapes, heights, and spacing, several PCMs, and modified shells.

Because of their superb thermal conductivity, nanofluids are seen as new generation of cooling mediums in many engineering applications. It is well established that even a small amount of nanoparticles mixed with a base fluid may result in distinct thermal conductivity enhancement. On the other hand, addition of nanoparticles to the base fluid results in its substantial viscosity increase. Therefore, it is very difficult to evaluate the relative importance of viscosity and thermal conductivity of the nanofluid on convective heat transfer performance. In order to estimate such resultant impact properly, it is necessary to develop reliable correlation equations for predictions of these two thermophysical properties of nanofluids. In this paper, the thermal conductivity and dynamic viscosity of five fluids, i.e., pure water, ethylene glycol (EG) and three mixtures of water and EG with volume ratio of 40:60, 50:50 and 60:40 have been experimentally determined. The aforementioned fluids served as base fluids in nanofluids with Al₂O₃ nanoparticles at the concentration of 0.01%, 0.1% and 1% by weight. A set of 20 correlations for prediction of thermal conductivity and dynamic viscosity of base fluids and corresponding nanofluids has been developed. Moreover, present results have been confronted with literature data and predictions made by use of carefully selected recognized literature correlations.

The results of experimental investigation of free convection heat transfer in a rectangular container are presented. The ability of the commonly accepted correlation equations to reproduce present experimental data was tested as well. It was assumed that the examined geometry fulfils the requirement of no-interaction between heated cylinder and bounded surfaces. In order to check this assumption recently published correlation equations that jointly describe the dependence of the average Nusselt number on Rayleigh number and confinement ratios were examined. As a heat source served electrically heated horizontal tube immersed in an ambient fluid. Experiments were performed with pure ethylene glycol (EG), distilled water (W), and a mixture of EG and water at 50%/50% by volume. A set of empirical correlation equations for the prediction of Nu numbers for Rayleigh number range 3.6 × 10⁴ < Ra < 9.2 × 10⁵ or 3.6 × 10⁵ < Ra_q < 14.8 × 10⁶ and Pr number range 4.5 ≤ Pr ≤ 160 has been developed. The proposed correlation equations are based on two characteristic lengths, i.e., cylinder diameter and boundary layer length.

In this study the results of simultaneous measurements of dynamic viscosity, thermal conductivity, electrical conductivity and pH of two nanofluids, i.e., thermal oil/Al₂O₃ and thermal oil/TiO₂ are presented. Thermal oil is selected as a base liquid because of possible application in ORC systems as an intermediate heating agent. Nanoparticles were tested at the concentration of 0.1%, 1%, and 5% by weight within temperature range from 20 °C to 60 °C. Measurement devices were carefully calibrated by comparison obtained results for pure base liquid (thermal oil) with manufacturer’s data. The results obtained for tested nanofluids were compared with predictions made by use of existing models for liquid/solid particles mixtures.