Pool boiling performance of oxide nanofluid on a downward-facing heating surface

In this study, the pool boiling performance of oxide nanofluid was investigated, the heating surface is a 5 × 30 mm stainless steel heating surface. Three kinds of nanofluids were selected to explore their critical heat flux (CHF) and heat transfer coefficient (HTC), which were TiO2, SiO2, Al2O3. We observed that these nanofluids enhanced CHF compared to R·O water, and Al2O3 case has the most significant enhancement (up to 66.7%), furthermore, the HTC was also enhanced. The number of bubbles in nanofluid case was relatively less than that in R·O water case, but the bubbles were much larger. The heating surface was characterized and it was found that there were nano-particles deposited, and surface roughness decreased. The wettability also decreased with the increase in CHF.

Optimizing the shape of PCM container to enhance the melting process

The shape of container influences natural convection inside a latent heat storage with a phase change material (PCM). Often the geometrical design of a PCM container is based on empirical observations. To enhance convection and melting of the PCM, authors propose here new design guidelines for an improved container. Using the so-called Co-factor method as the optimized basis, which is defined as the vector product of the velocity and temperature gradient, the new design method strives to raise the velocity of natural convection in liquid PCM, increase the amount of PCM in the direction of the convective flow, and reduce the amount of PCM far from the heating surface. Following these guidelines and Co factor, an optimized PCM container with an elongated and curved shape is proposed and compared to a rectangular container. Numerical simulations indicated that the total melting time of the PCM in the optimized container could be reduced by more than 20% compared to the rectangular one. The higher natural convection velocity and the better use of it to melt the PCM in the optimized container space attributed to the better performance than that in rectangular container. The results can be used to design more effective PCM storage systems.

A Spatial AMH Copula-Based Dissimilarity Measure to Cluster Variables in Panel Data

Investigating thermal energy demand is crucial for the development of sustainable cities and efficient use of renewable sources. Despite the advances made in this field, the analysis of energy data provided by smart grids is currently a demanding challenge. In this paper, we develop a clustering methodology based on a novel dissimilarity measure to analyze a high temporal resolution panel data for district heating demand in the Italian city Bozen-Bolzano. Starting from the characteristics of this data, we explore the usefulness of the Ali-Mikhail-Haq copula in defining a new dissimilarity measure to cluster variables in a hierarchical framework. We show that our proposal is particularly sensitive to small dissimilarities based on tiny differences in the dependence level. Therefore, the proposed measure is able to better distinguish between objects with low dissimilarity than classic rank-based dissimilarity measures. Moreover, our proposal is defined in a spatial version that is able to take into account the spatial location of the compared objects. We investigate the proposed measure through Monte Carlo studies and compare it with the corresponding spatial Kendall's correlation-based dissimilarity measure. Finally, the application to real data makes it possible to find clusters of buildings homogeneous with respect to their main characteristics, such as energy efficiency and heating surface, to support the design, expansion and management of district heating systems.

Capture of Pollutants from Exhaust Gases by Low-Temperature Heating Surfaces

One of the most effective methods towards improving the environmental safety of combustion engines is the application of specially prepared water-fuel emulsions (WFE). The application of WFE makes it possible to reduce primary sulfur fuel consumption and reveals the possibility of capturing the pollutants from exhaust gases by applying condensing low-temperature heating surfaces (LTHS). In order to realize such a double effect, it is necessary to investigate the pollution processes on condensing LTHS of exhaust gas boilers (EGB), especially the process of low-temperature condensing a sulfuric acid vapor from exhaust gases to investigate the influence of condensing LTHS on the intensity of pollutants captured from the exhaust gases. The aim of this research is to assess the influence of the intensity of pollutants captured from exhaust gases by condensing LTHS in dependence of water content in WFE combustion. Investigations were carried out at a special experimental setup. The processing of the results of the experimental studies was carried out using the computer universal statistical graphic system Statgraphics. Results have shown that in the presence of a condensing heating surface, the degree of capture (purification) of pollutants from the exhaust gas flow is up to 0.5–0.6.

Research and Application of Double-Reheat Boiler in China

The ultra-supercritical (USC) double-reheat technology is an immediate area of research focus in China, since the thermal efficiency of USC double-reheat unit is higher than the USC single-reheat unit. The parameters and capacity of USC double-reheat unit in China have made major breakthroughs, and the thermal efficiency of the units are as high as 47–48%, which is the highest in the world. USC double-reheat boiler is one of the most important devices for USC double-reheat unit, and the design concept and precision have a vital effect on the operation of boiler and power station. The most difficult and important factors in the design of double-reheat boiler are the layout of heating surface and the steam temperature regulation method. Therefore, this work summarizes the arrangement of heating surface and temperature regulation method of existing double-reheat boiler in China. It is hoped that the work will set a benchmark for the development of double-reheat boiler and the future 700 °C power generation unit in the world.

Efficient Thermal Energy Management of Hollow Pin Fin Heat Sinks with and without Phase Change Material

Electronic devices need to be cooled efficiently. Phase change material (PCM) could be incorporated into a conventional fin heat sink (FHS) for such a purpose. This paper reports experimental results obtained on the thermal performances of four FHSs fabricated with different arrays and numbers of hollow aluminium pin fins with various lengths and diameters. Tests were conducted with and without filling them with PCM. Heat input was kept on for 2 hours and varied from 1W, 5W and 10W. Transient heating surface temperatures were recorded on a data logger and plotted every 5 minutes. The results showed that the PCM-filled FHS resulted in faster cooling rates and lower heating surface temperatures. Long and large diameter pins performed better than small and short pins. Efficient fin heat sinks for electronic cooling are essential in view of the weight and size of the component. Hence the findings of this paper would be beneficial for electronic cooling and useful to the electronic industry for efficient thermal energy management.