Advancements in Heat Transfer and Fluid Mechanics (Fundamentals and Applications)

1. Introduction

Thermo-fluid science is a foundational discipline for numerous mechanical systems, particularly in energy production and building equipment, where thermal and mechanical energy transfer play critical roles. Advancements in heat transfer and fluid mechanics have significantly enhanced these systems, driving progress in associated market sectors. For instance, evaporator and condenser coils are essential for optimizing vapor compression cycles in building equipment [1]. Heat pumps used for space and water heating constitute a major share of building systems, with microchannel heat exchanger technology at the forefront of these innovations. It is worth mentioning that advancements in heat transfer and fluid mechanics significantly alleviate the challenge of designing energy-efficient building equipment. The development of research techniques has contributed significantly to the advancement of science; for example, in the experimental field, non-intrusive measurement techniques such as Particle Image Velocimetry (PIV) are now capable of resolving flow behavior in a 3D format for different length and time scales.

Microchannel heat exchangers represent a significant advancement in HVAC technology by offering enhanced heat transfer performance through their compact, efficient design [2]. These heat exchangers utilize multiple parallel channels with hydraulic diameters typically ranging from 0.1 to 1.0 mm, dramatically increasing the surface-area-to-volume ratio compared to conventional tube-and-fin heat exchangers [3]. In the HVAC industry, their adoption has led to several key benefits, including reduced refrigerant charge (typically 30–50% less than traditional coils) and improved heat transfer coefficients due to their larger surface area density and decreased overall system size and weight [4,5,6]. These advantages have made microchannel heat exchangers particularly valuable in modern air conditioning systems, where they have enabled manufacturers to meet stricter energy efficiency standards while reducing material costs and environmental impact [7]. Additionally, their all-aluminum construction often provides better corrosion resistance compared to traditional copper–aluminum designs, potentially extending system lifespan and reducing maintenance requirements, though airside fouling effects must be taken into consideration due to the reduced airside flow area associated with microchannel heat exchangers [8]. These advancements underscore the crucial role of thermo-fluid science in improving the energy performance of building systems.

This Editorial is intended to highlight recent developments in heat transfer and fluid flow through the articles published in this Special Issue, which examines different research techniques in a variety of applications. The industrial applications covered in this Issue include fluidized beds, chemical reactions, propulsion, ice-storage air conditioning, and high-pressure methanol steam reformers. These advancements in heat transfer and fluid mechanics are essential for higher system efficiency and lower energy consumption. The published papers utilize important analytical, experimental, and numerical research techniques in thermo-fluid science.

2. Advancements in Heat Transfer and Fluid Flow

Advancements in research have greatly enhanced the study of how mass transport is affected by non-coaxial rotation. Computational methods, such as high-resolution numerical solvers, allow for the precise modeling of coupled partial differential equations, providing insights into the interactions between rotational dynamics, diffusion, and chemical kinetics [9,10]. Additionally, experimental techniques like advanced imaging and laser diagnostics enable accurate visualization and validation of theoretical models [11]. These innovations have improved our understanding of rotational effects in fields such as environmental science, industrial mixing, and astrophysics, leading to more efficient designs and applications [12,13].

A particular priority is hydrogen production for energy applications. High-pressure methanol steam reforming with integrated water vapor condensation represents an innovative approach to hydrogen production and energy efficiency optimization [14]. The process leverages the significant enthalpy of condensation from water vapor, which provides additional thermal energy to support the endothermic reforming reaction [15]. Operating at elevated pressures of 20–50 bar enhances the system’s efficiency by facilitating better heat integration and improving reaction kinetics [16]. The integration of condensation heat recovery can increase overall system efficiency by 15–20% compared to conventional reforming processes [17]. This approach is particularly advantageous in applications requiring high-pressure hydrogen output, as it eliminates the need for subsequent compression stages and reduces the overall energy requirement of the system [18]. Furthermore, the incorporation of heat pipe technology for efficient heat transfer between the condensation and reforming zones has demonstrated improved temperature control and reaction stability [19].

Computational Fluid Dynamics (CFD) has experienced significant advancement in thermo-fluid applications through enhanced numerical methods and computational capabilities. The integration of machine learning algorithms with traditional CFD approaches has revolutionized turbulence modeling, particularly in predicting complex flow phenomena with improved accuracy [20]. Notable progress has been made in mesh adaptation techniques, where dynamic mesh refinement strategies have enhanced the resolution of thermal boundary layers and multiphase interfaces [21]. The development of hybrid turbulent models has provided more accurate predictions of heat transfer in complex geometries while maintaining computational efficiency [22]. Additionally, recent advances in GPU-accelerated computing have enabled real-time simulations of thermal systems, which are particularly beneficial in industrial applications and design optimization [23]. The integration of uncertainty quantification methods with CFD analysis has improved the reliability of thermal predictions in engineering applications, especially in cases involving phase change and conjugate heat transfer [3]. The development of high-fidelity multiphysics models that couple CFD with other physical phenomena is particularly noteworthy, as they enable more comprehensive analysis of thermal systems [24].

As mentioned previously, research techniques have been significantly developed. In the experimental field, non-intrusive measurement techniques such as Particle Image Velocimetry (PIV) are now capable of resolving flow behavior in a 3D format for different length and time scales. Particularly notable examples of state-of-the-art measurement technology include the Spallation Neutron Source (SNS) [25] and the High Flux Isotope Reactor (HFIR) [26]. Both represent two distinct but complementary approaches to neutron science [27]. The SNS produces neutrons through a spallation process, where high-energy protons strike a heavy metal target, causing it to release neutrons in short, intense pulses—this time structure makes it particularly valuable for certain types of experiments like neutron scattering. The HFIR, in contrast, is a continuous neutron source that uses nuclear fission in a highly enriched uranium core to produce one of the highest steady-state neutron fluxes available for research. The application of neutrons from either the SNS or HFIR allows flow to be visualized in opaque channels, thereby allowing for the optimization of flow in heat exchangers.

Research into fluid mechanics and heat transfer is expected to continue developing and progressing for the sake of acquiring new knowledge and developing new technologies. However, limitations on experimental research on heat transfer and fluid flow still persist, including spatial and temporal aspects. Advancement is pivotal to improving current applications, in addition to enabling new concepts that can be transformed into mature technologies with a high level of market readiness.

3. Conclusions

The science of heat transfer and fluid mechanics has been the core of a wide range of technologies such as renewable energy and a variety of industrial sectors; this Special Issue presents research on their different related applications. The spatial and temporal scales of the researched phenomena indicate the versatility of thermo-fluid research. Experimental technologies have significantly progressed and contributed to the development of the subject matter over the last few decades. Recent advancements in Computational Fluid Dynamics (CFD) have significantly enhanced thermo-fluid application research by leveraging innovations in computational methods and the associated utilized technologies. Machine learning integration has improved the accuracy and efficiency of CFD simulations by enabling rapid predictions of fluid dynamics and optimizing performance in complex systems. This advancement and others have broadened CFD’s scope and applicability, positioning it as a vital tool for advancing thermo-fluid research and applications across various industries.