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New Challenges in Heat Transfer Enhancement

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J1: Heat and Mass Transfer".

Deadline for manuscript submissions: closed (31 January 2024) | Viewed by 5342

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Prof. Dr. Paolo Coppa

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Department of Industrial Engineering, University of Rome “Tor Vergata”, 00133 Rome, Italy
Interests: renewable energy sources; energy communities; energy exchange modelling; environment protection through RECs; social Impact of RECs
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Dear Colleagues,

Heat transfer pervades every moment of our lives: the heating and cooling of ambientes, foods, metallic, ceramic and polymeric materials are operations that humanity has performed since the beginning of civilization. However, at present, more sophisticated techniques and materials have been developed, so it is fundamental that we study these new subjects and the devices developed to exploit them. The scientific and technological research in this field is developing quickly, and collecting diverse contributions on the subject can help to establish the advancement of the state of the art.

Considering that heat transfer must be either incremented or inhibited, scientific research seeks to develop more and more efficient systems to enhance heat transfer, with new highly conductive materials (e.g., two-dimensional materials such as graphene) or devices as heat pipes. Or, on the other side, disabling heat transfer can help to reduce energy consumption in building heating and cooling, and so reduces the inauspicious effects of human activities, with well-known consequences taking place in front of our very eyes.

This are the reasons why we are presenting this Special Issue, with the goal of supplying all interested people working in this field with a helpful resource which could contribute to deepening our understanding of heat transfer issues.

The following topics are particularly suitable to this Special Issue:

Heat transfer in special materials:
- Anisotropic materials: single crystals, fiber composites, two-dimensional materials such as graphene.
- Biological materials: animal and human tissues, foods, plants and other systems from the nature.
- Soils and building construction materials.
New types of insulating materials.
Devices to increment the heat transfer:
- Heat pipes.
- Engine assisted fluid circulation.
Devices or systems to insulate:
- New insulating materials, eventually directional.
- Passive solar systems such as Trombe–Michel wall or Barra–Costantini wall.
- Convection reduction or abolition through insertion of screens and interlayers.

Prof. Dr. Paolo Coppa
Guest Editor

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Keywords

heat transfer in composites
heat transfer in soils
heat transfer during human therapy (hyperthermia, cryotherapy)
new insulation systems
progress in the heat pipes construction and application
analytic and/or numerical modelling of heat transfer in special systems
heat transfer in magneto fluid dynamic systems
thermal ablation
combined heat and mass transfer
heat transfer with phase change
exploitation of solar irradiation (thermal and photovoltaic panels)
relevance of heat transfer in energy systems
modelling and measuring thermophysical properties

Related Special Issue

Energy, Environment, and Social Effects Obtainable through the Renewable Energy Community Institution in Energies

Published Papers (6 papers)

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Research

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32 pages, 8588 KiB

Open AccessArticle

Heat Convection in a Channel-Opened Cavity with Two Heated Sources and Baffle

by Farhan Lafta Rashid, Asseel M. Rasheed Al-Gaheeshi, Hayder I. Mohammed and Arman Ameen

Energies 2024, 17(5), 1209; https://doi.org/10.3390/en17051209 - 03 Mar 2024

Cited by 1 | Viewed by 505

Abstract

This study employs COMSOL software v 5.6 to investigate a novel approach to heat transfer via mixed convection in an open hollow structure with an unheated 90° baffle elbow. Two 20 W heat sources are strategically positioned on the cavity’s bottom and right-angled wall for this research. Notably, the orientation of the baffle perpendicular to the airflow is used to direct external, unrestricted flow into the square cavity. The research investigates a range of air velocities (0.1, 0.5, 1.0, and 1.5 m/s) and the intricate interaction between input air velocity, dual heated sources, and the presence of a right-angle baffle on critical thermodynamic variables, such as temperature distribution, isotherms, pressure variation, velocity profile, air density, and both local and mean Nusselt numbers. Validation of the applicable computational method is achieved by comparing it to two previous studies. Significant findings from numerical simulations indicate that the highest velocity profile is in the centre of the channel (2.3–2.68 m/s at an inflow velocity of 1.5 m/s), while the lowest profile is observed along the channel wall, with a notable disruption near the inlet caused by increased shear forces. The cavity neck temperature ranges from 380 to 640 K, with inflow air velocities varying from 0.1 to 1.5 m/s (Re is 812 to 12,182), respectively. In addition, the pressure fluctuates at the channel-cavity junction, decreasing steadily along the channel length and reaching a maximum at the intake, where the cavity neck pressure varies from 0.01 to 2.5 Pa with inflow air velocities changing from 0.1 to 1.5 m/s, respectively. The mean Nusselt number exhibits an upward trend as air velocity upon entry increases. The mean Nusselt number reaches up to 1500 when the entry air velocity reaches 1.5 m/s. Due to recirculation patterns, the presence of the 90° unheated baffle produces a remarkable cooling effect. The study establishes a direct correlation between input air velocity and internal temperature distribution, indicating that as air velocity increases, heat dissipation improves. This research advances our understanding of convective heat transfer phenomena in complex geometries and provides insights for optimising thermal management strategies for a variety of engineering applications. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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17 pages, 5708 KiB

Open AccessArticle

Steady- and Transient-State CFD Simulations of a Modified Barra–Costantini Solar System in Comparison with a Traditional Trombe–Michel Wall

by Sandra Corasaniti, Luca Manni, Ivano Petracci and Michele Potenza

Energies 2024, 17(2), 295; https://doi.org/10.3390/en17020295 - 07 Jan 2024

Viewed by 587

Abstract

Passive solar systems are one of most important strategies to reduce the heating loads of buildings. The Trombe–Michel (TM) wall and its variants are some of the better-known structures in the field of solar systems. An alternative to the TM wall is the Barra–Costantini (BC) system. In the present paper, CFD numerical simulations, both in steady and transient states, of modified BC and TM walls were carried out in the winter season. Different interspace thicknesses were simulated in order to evaluate their effects on the temperature field and air velocity, and the numerical results were compared among them. It was found that the BC system offers greater hot air flow compared with the TM wall; the mass flow rate increased up to 43% in the BC system and up 28% in the TM system when the interlayer thickness was increased by 500%. The transient simulations (100 h simulated) demonstrated that the dynamic response of the BC wall was shorter than that of the TM wall, even when the TM wall was simulated with initial thermal conditions that were more advantageous than those for the BC wall. The BC system reached a periodic stabilized regime within 24 h, whereas the TM system failed to stabilize in 100 h. The results show that for both TM and BC structures, the interlayer thickness scarcely influenced the temperature of the environment reached (the temperature peak increased up to 3–4% as the interlayer thickness was increased by 500%), while larger air speed changes were observed in the BC system in the transient state compared with the TM system. Thus, in the TM system, the outlet air velocity was practically constant as the interlayer thickness was increased; in contrast, the outlet velocity peak increased up to 50% in the BC system. Moreover, the BC wall presented a quicker response to satisfy the ambient thermal loads. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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15 pages, 5546 KiB

Open AccessArticle

Experimental Tests of Conduction/Convection Heat Transfer in Very High Porosity Foams with Lattice Structures, Immersed in Different Fluids

by Gianluigi Bovesecchi, Paolo Coppa, Sandra Corasaniti, Girolamo Costanza, Michele Potenza and Maria Elisa Tata

Energies 2023, 16(16), 5959; https://doi.org/10.3390/en16165959 - 12 Aug 2023

Cited by 1 | Viewed by 804

Abstract

This experimental work presents the results of measurements of thermal conductivity λ and convection heat transfer coefficient h on regular structure PLA and aluminium foams with low density ratio (~0.15), carried out with a TCP (thermal conductivity probe), built by the authors’ laboratory. Measurements were performed with two fluids, water and air: pure fluids, and samples with the PLA and aluminium foams immersed in both fluids have been tested. Four temperatures (10, 20, 30, 40 °C) and various temperature differences during the tests ΔT (between 0.35 and 9 °C) were applied. Also, tests in water mixed with 0.5% of a gel (agar agar) have been run in order to increase the water viscosity and to avoid convection starting. For these tests, at the end of the heating, the temperature of the probe reaches steady-state values, when all the thermal power supplied by the probe is transferred to the cooled cell wall; thermal conductivity was also evaluated through the guarded hot ring (GHR) method. A difference was found between the results of λ in steady-state and transient regimes, likely due to the difference of the sample volume interested by heating during the tests. Also, the effect of the temperature difference ΔT on the behaviour of the pure fluid and foams was outlined. The mutual effect of thermal conductivity and free convection heat transfer results in being extremely important to describe the behaviour of such kinds of composites when they are used to increase or to reduce the heat transfer, as heat conductors or insulators. Very few works are present in the literature about this subject, above all, ones regarding low-density regular structures. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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17 pages, 4592 KiB

Open AccessArticle

Heat Transfer Intensification in a Heat Exchanger by Means of Twisted Tapes in Rib and Sawtooth Forms

by Pasu Poonpakdee, Boonsong Samutpraphut, Chinaruk Thianpong, Suriya Chokphoemphun, Smith Eiamsa-ard, Naoki Maruyama and Masafumi Hirota

Energies 2022, 15(23), 8855; https://doi.org/10.3390/en15238855 - 23 Nov 2022

Cited by 2 | Viewed by 1021

Abstract

This experimental study aimed to intensify the aerothermal performance index (API) in a round tube heat exchanger employing twisted tapes in rib and sawtooth forms (TTRSs) as swirl/vortex flow generators. The TTRSs have a constant twist ratio of 3.0, a constant rib pitch ratio (p/e) of 1.0, and six different sawtooth angles (α = 20°, 30°, 40°, 50°, 60°, and 70°). Experiments were carried out in an open flow using air as the working fluid for Reynolds numbers between 6000 and 20,000 in the current study, which was conducted in a heated tube under conditions of uniform wall heat flux. A typical twisted tape (TT) was also tested for comparison. The experimental results suggest that TTRSs yield Nusselt numbers ranging from 1.42 to 2.10 times of those of a plain tube. TTRSs with larger sawtooth angles (α) offer superior heat transfer. The TTRSs with α = 20°, 30°, 40°, 50°, 60°, and 70° respectively, enhance average Nusselt numbers by 158%, 162%, 166%, 172%, 180%, and 187% with average friction factors of 3.51, 3.55, 3.60, 3.67, 3.75 and 3.82 times higher than a plain tube. Additionally, TTRSs with sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° offer APIs in the ranges of 0.99 to 1.19, 1.01 to 1.21, 1.03 to 1.26, 1.05 to 1.31, 1.07 to 1.42, and 1.09 to 1.48, respectively, which are higher than those of the typical twisted tape (TT) by around 5%, 7%, 11%, 16%, 25%, and 31%, respectively. This demonstrates that twisted tapes in rib and sawtooth form (TTRSs), with appropriate geometries, give a promising trade-off between enhanced heat transfer and an increased friction loss penalty. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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19 pages, 5458 KiB

Open AccessArticle

Thermal Visualization and Performance Analysis in a Channel Installing Transverse Baffles with Square Wings

by Smith Eiamsa-Ard, Arnut Phila, Khwanchit Wongcharee, Varesa Chuwattanakul, Monsak Pimsarn, Naoki Maruyama and Masafumi Hirota

Energies 2022, 15(22), 8736; https://doi.org/10.3390/en15228736 - 20 Nov 2022

Viewed by 1225

Abstract

The experimental examination of local heat transfer, thermal intensification, friction factors, and thermal performance factors (TPF) in a rectangular channel with square-winged transverse baffles (SW-TB) are presented in this paper. The purpose of this study is to modify the typical transverse baffles (TB) into square-winged transverse baffles (SW-TB) in order to improve the thermal performance and heat transfer rate of the channel. The effects of SW-TBs with various wing attack angles and Reynolds numbers on the heat transfer performance characteristics were examined using a thermochromic liquid crystal sheet. In the experiments, the SW-TBs were attached to the bottom wall of the channel, which had an aspect ratio (W:H) of 3.75:1. The SW-TBs had a width (w) of 150 mm, a square perforated cross-sectional area (a × b) of 8 × 8 mm², and attack angles (θ) of 0° (solid transverse-baffle), 22.5°, 45°, 67.5°, and 90°. The bottom wall of the channel was evenly heated, while the other walls were insulated. The temperature contours on the heated surface were plotted using temperatures obtained through using the thermochromic liquid crystal (TLC) image-processing method. Experimental results revealed that the SW-TBs created multiple impinging jets, apart from the recirculation. At the proper attack angles (θ = 22.5° and 45°), the SW-TBs offered greater heat transfer rates and caused lower friction losses, resulting in higher TPFs than the solid transverse baffles. In the current work, channels where the SW-TBs display a θ = 45° presented the greatest TPF, as high as 1.26. The multiple impinging jets issuing by the SW-TBs suppressed the size of the recirculation flow and allowed better contact between the fluid flow and channel wall. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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Review

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19 pages, 16728 KiB

Open AccessReview

A Brief Review of the Latest Advancements of Massive Solar Thermal Collectors

by Alessia Aquilanti, Ignacio Peralta, Eduardus A. B. Koenders and Giovanni Di Nicola

Energies 2023, 16(16), 5953; https://doi.org/10.3390/en16165953 - 12 Aug 2023

Viewed by 766

Abstract

Technologies that can contribute to the reduction of greenhouse gases are mandatory, and those based on solar energy are good candidates to achieve this. In this sense, massive solar thermal collectors are suitable technologies for supplying the primary energy demand of buildings. To design these devices, it is necessary to fully understand the physics of the problem before proposing any new optimized solution. This review aims to briefly summarize significant aspects regarding the current state of development of these solar technologies. Attention is paid to works devoted to experimental studies to analyze the behavior of these systems, as well as numerical models to predict the physics of the problem. Furthermore, the future directions and prospects in the field of massive collectors are briefly described. The main novelty of this review is to provide a comprehensive overview that summarizes the works done so far in the field over the past 30 years, which allows the reader to delve deeper into the topic. According to the reviewed works, it can be concluded that these technologies can contribute to the reduction of greenhouse gases while at the same time being excellent examples of the integration of solar energy devices with buildings. Full article

(This article belongs to the Special Issue New Challenges in Heat Transfer Enhancement)

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