Huijin Xu

By Huijin Xu, Zhanbin Xing, Fuqiang Wang and Changying Zhao

Metal foams can be well used as ideal materials for various efficient heat transfer devices due to light weight, high specific, and high thermal conductivity. Nanofluids have higher thermal conductivities than traditional fluid, so it can be used as an efficient heat transfer characteristics medium. This paper focuses on heat transfer of nanofluid, metal foam and the combination of the two. The physical properties of nanofluid and metal foam are summarized. The characteristics of flow and heat transfer are introduced. This work creates a close connection between scientific research and practical applications of this dual heat transfer enhancement method.

Part of the book: Novel Nanomaterials

By Chen Yang, Huijin Xu and Akira Nakayama

A volumetric solar receiver receives the concentrated radiation generated by a large number of heliostats. Turbulent heat transfer occurs from the solid matrix to the air as it passes through the porous receiver. Such combined heat transfer within the receiver, including radiation, convection and conduction, is studied using a local thermal non-equilibrium model. Both the Rosseland approximation and the P1 model are applied to consider the radiative heat transfer through the solar receiver. Furthermore, the low Mach approximation is exploited to investigate the compressible flow through the receiver. Analytic solutions are obtained for the developments of air and ceramic temperatures as well as the pressure along the flow direction. Since the corresponding fluid and solid temperature variations generated under the Rosseland approximation agree fairly well with those based on the P1 model, the Rosseland approximation is used for further analysis. The results indicate that the pore diameter must be larger than its critical value to obtain high receiver efficiency. Moreover, it has been found that optimal pore diameter exists for achieving the maximum receiver efficiency under the equal pumping power. The solutions provide effective guidance for a novel volumetric solar receiver design of silicon carbide ceramic foam.

Part of the book: Foams

By Guojun Yu and Huijin Xu

The heat and/or mass transfer is crucial in various energy conversion and storage systems such as heat exchangers and energy storage systems, since they highly affect the efficiency of energy conversion and transport. Enhancing the heat and/or mass transfer within these systems is the most important means to improve system efficiency. Porous media have found wide application in enhancing the heat conduction, mass diffusion, or both, for different energy conversion and storage systems. In this chapter, a brief review on the application of different porous media for transport enhancement in various systems was made, indicating that using porous media is capable of enhancing the transport ability appreciably, sometimes being up to hundreds of times in some physical problems. This review could provide some insight into the transport enhancement design of various energy conversion and storage systems, which is especially important in the background of carbon neutralization.

Part of the book: Transport Perspectives for Porous Medium Applications

By Huijin Xu and Hao Luo

Amid the escalating severity of water scarcity, seawater desalination has emerged as a viable solution. Traditional seawater desalination technologies are fraught with numerous drawbacks, including high energy consumption, exorbitant costs, intricate structures, and adverse environmental impacts. In contrast, solar-powered seawater desalination technology has garnered significant attention due to its economic viability and environmental sustainability. This article undertakes a comprehensive study of the solar seawater desalination system, encompassing both direct and indirect methodologies, and delves into the strengths and weaknesses of diverse technologies, such as solar distillation, humidification-dehumidification, solar chimney, reverse osmosis, multi-effect distillation, and multi-stage flash evaporation. The direct approach harnesses solar energy to directly desalinate seawater, whereas the indirect method transforms solar energy into other energy forms for the purpose of seawater desalination. Simultaneously, an in-depth analysis of the benefits of solar-powered seawater desalination technology is conducted. Its economic merits include minimal infrastructure requirements and ease of local design, installation, and maintenance, albeit with a limited water production capacity per unit area. The costs associated with different technologies exhibit substantial variations and are subject to the influence of multiple factors. Future development trajectories are centered around enhancing efficiency, reducing costs, and achieving large-scale applications, exemplified by the exploration of hybrid rare-earth-driven desalination, forward osmosis, and dew point evaporation technologies, as well as the integration of advanced materials, intelligent control systems, and energy storage technologies.

Part of the book: Advances in Desalination Insights

By Yuhan Jin, Huijin Xu and Ruming Pan

The growing global energy demand and increasing environmental challenges have accelerated research into renewable energy utilization technologies. Biomass and solar energy, as promising renewable resources, can be combined through solar-driven pyrolysis/gasification for producing biofuels and biochar. This study reviews comprehensive numerical simulation methods for solar-driven biomass thermochemical conversion, focusing on solar heat source treatment methods, the equivalent porous media model of heat and mass transfer, and common reaction kinetics models. Three principal solar heat source modeling approaches are examined: temperature boundary, heat flux boundary, and Monte Carlo ray tracing (MCRT), with MCRT providing superior accuracy in capturing directional radiation in complex reactor geometries. The thermal analysis incorporates local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) approaches within the equivalent porous media model, along with the radiative transfer models including the Rosseland approximation, P1 approximation, and Discrete Ordinates (DO) method. LTNE is crucial for systems with pronounced solid-fluid temperature gradients, while the Rosseland and P1 approximation provide the efficient computational methods for media with high optical thickness. Three fundamental reaction kinetics models are presented for biomass pyrolysis: single-component single-step, single-component multistep, and multicomponent multistep reaction kinetic models. Multistep reaction kinetics models are shown to capture intermediate pathways and product distributions more realistically than single-step approaches. The numerical model coupling multi-physical fields can provide a solid theoretical basis for optimizing reactor design, regulating target products, and enhancing energy conversion efficiency. Future research should integrate high-fidelity simulations with experimental validation to enhance predictive accuracy and support scale-up of solar-driven biomass conversion systems.

Part of the book: Progress on Porous Media Research

By Huijin Xu and Bo Cheng

The rapid development of the shipping industry has made the problems of energy consumption and fresh water supply increasingly prominent. The exhaust gas emitted by marine diesel engines carries a large amount of medium and low-temperature waste heat, providing significant potential for its recovery and utilization. This article systematically reviews the research progress in this technical field. Firstly, the thermodynamic characteristics of ship exhaust gas and the basic principles of mainstream seawater desalination technologies, such as, reverse osmosis, multi-effect distillation, multistage flash evaporation, and adsorption desalination, are summarized. Based on this, two major types of tail gas waste heat desalination systems were analyzed in detail: the first is the tail gas direct-drive thermal system, and the second is the exhaust gas-power combined drive system. This chapter further starts from performance indicators such as, water production ratio and energy consumption, comparing the advantages and disadvantages of different technical paths. However, the wide application of this technology still faces several key challenges, including the constraints of the fluctuation of exhaust gas heat sources on the stable control of the system, and so on. The conclusion indicates that the technology of seawater desalination driven by the waste heat of ship exhaust gas has broad prospects. Future research directions should focus on intelligent adaptive control, efficient anticorrosion and antiash technology, and modular and miniaturized design of the system, among other areas.

Part of the book: Desalination Frontiers