Generation, Use, Conversion and Exchange of Thermal Energy

Dear Colleagues,

Heat is either the final product of the energy conversion chain or an energy vector, and its management is a crucial issue in many aspects of everyday life. The first case regards all the ambient conditioning systems, including refrigeration, and many industrial processes that require controlled temperatures. The second category is mostly related to electricity generation, such as all combustion systems, nuclear energy, solar thermal and geothermal power systems, in which the energy is in the form of heat at the source or in an intermediate step of the conversion process.

The current crises related to the containment of emissions and energy resources further the need to increase the efficiency of energy utilization in all sectors. All the processes related to the utilization of thermal energy – including production, conversion, storage and distribution – play a crucial role on the path to reducing emissions and the consumption of primary sources. Official estimates state that there is a huge amount of heat at different temperature levels that is not valorized.

This Special Issue aims to collect research and review articles on the topic of thermal energy utilization in a broader sense. Analyses of technologies and systems involved in the production, conversion and transfer of thermal energy are specifically suitable. Concepts such as cogeneration, tri-generation and waste heat recovery are included. Studies on cooling and refrigeration technologies are welcome. Thermal energy storage techniques, including Carnot batteries, are also suitable topics.

In brief, topics of interest for publication include, but are not limited to, the following:

• Waste-Heat Recovery applications;
• Thermal energy storage;
• Combined heat and power generation;
• Carnot batteries;
• Renewable heat and low-enthalpy applications;
• Cooling and refrigeration;
• Heat exchangers technologies;
• Modelling and design of heat exchangers;
• Organic Rankine cycles for waste heat recovery.

Dr. Saverio Ottaviano
Dr. Lisa Branchini
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• heat valorization
• heat storage
• waste heat recovery
• heat sources
• heat transfer

Title: Review of supercritical CO2-based thermal energy flow and transport mechanisms inside porous media
Authors: Mengshuai Chen; Karim Ragui; Jiaxin Liu; Atsuki Komiya; Lin Chen
Affiliation: Institute of Engineering Thermophysics, Chinese Academy of Sciences, China;

Title: Effect of Nanoparticle Size and Corresponding Deposition Layer on Aluminum Surface in Spray Cooling
Authors: Yunus Tansu Aksoy; Farid Enayati; Pınar Eneren; Maria Rosaria Vetrano
Affiliation: KU Leuven, Department of Mechanical Engineering, Division of Applied Mechanics and Energy Conversion (TME), B-3001 Leuven, Belgium
Abstract: Spray cooling is one of the most effective methods, yet technological advancements are driving the demand for improved thermal management systems. Although nanofluids have shown great potential as coolants due to their unique properties, their undiscovered mechanisms limit their heat transfer applications. In this study, we experimentally investigate the impact of nanoparticle deposition layer thickness on the spray cooling performance of a preheated aluminum block. Specifically, we measure the temporal temperature decrease of the block from 190 to 65 °C, employing TiO2 nanoparticles with size ranges of 5-30 nm and 30-50 nm. We then systematically evaluated their cooling performances on clean and nanoparticle-coated surfaces to distinguish the effect of nanofluids and their corresponding coatings. Our results show that optimal nanoparticle size, concentration, and coating thickness can double the heat transfer performance despite their lower bulk thermal conductivity with respect to the aluminum block. Surface modification by nanoparticle deposition significantly enhances the cooling rate during the initial phases of spray, i.e., in the boiling regime by introducing extra nucleation sites. However, this increase could not be achieved by water spray on nanoparticle-coated surfaces. We conclude that nanofluids improve heat transfer not only through surface coating but also by maintaining it through continuous nanoparticle deposition.