• Energy Research

With social development and economic enhancement, energy is facing significant worldwide demand, and fossil fuels are the prime energy sources for various energy systems over past decades. Furthermore, among fuel-consumed applications, power plants are the primary source of energy consumption. There is a lot of waste heat and steam accompanied by the latent heat produced in the exhaust flue gas. Therefore, the latent heat recovery from the flue gas plays an important role in increasing the efficiency of the system and saving water. To recover the heat and mass in power plants, three primary methods are proposed to condense the vapor based on previous studies: (1) flue gas condensation technology, (2) liquid desiccant-based dehydration (LDD) technology and (3) membrane technology. This paper mainly reviews and summaries the indirect cooling technology in flue gas condensation technology. The numerical simulation and theory of flue gas condensation are introduced. Different heat exchanger types and conducted experiments are also summarized. The performance of the indirect cooling technology is affected not only by its own configuration and design but also by the flue gas inlet temperature, velocity, water vapor mass fraction, etc. The major concerns and outlook of practical applications for further study are attributed to the heat exchanger size and cost, acid corrosion, ash accumulation in flue gas, etc.

Abstract Two-phase traditional thermosyphons (TTS) are passive heat exchangers with low thermal resistance for heat transfer. An advanced thermosyphon system named falling-film thermosyphon (FFTS) is developed and introduced in this paper, which eliminates several limits of TTS and improves heat transfer performance. FFTS applications are preferred for large-scale heat transfer applications. In this work, a tube bank of FFTS modules is integrated into a power plant to condense water vapor of the flue gas. Axial- and cross- flow are both analyzed with inline and staggered arrangements. The numerical simulation of vapor condensation in the flue gas is developed, and the results are compared to previously published experimental data. The accuracy of model is validated. The Non-dominated Sorting Genetic Algorithm, version 2 (NSGA-II) is implemented to improve the thermal performance with low material consumption and pressure drop for tube banks. Several parameters of the configuration are optimized. As a result, smaller diameter tubes with longer length can gain better heat transfer performance, however, resulting in a higher pressure drop. The optimized arrangements can improve 60-70% condensation rate and reduce up to 80% material consumption with allowable pressure loss compared to a baseline geometry.

Abstract To improve the thermal management performance of Li-ion power battery packs, this paper investigates HP/PCM (heat pipe/phase change material) coupled thermal management (TM). The significant purposes are to reveal internal coupled heat transfer mechanism, and propose a critical application range of coupled TM. To achieve this goal, lumped parameter method and finite difference method are adopted to build the mathematical modelling. Based on the simulation, the superiority of temperature control in coupled TM can be confirmed, and its internal heat flux distribution is calculated to reveal the principle of temperature control effects. Further parametric study is carried out to analyze their variation trend over different working conditions, whereupon both coupled heat transfer mechanism and critical application range are obtained. Results demonstrate that coupled TM achieves lower battery surface temperature and longer control time compared with single HP and PCM TM, respectively. It also shows that internal coupled heat flux distribution transits from PCM-dominated to HP-dominated, and ultimately almost depends on HP. Furthermore, based on the data of parametric study, coupled TM plays superiority when h

Abstract As energy demands and environmental contaminants are facing significant challenges, advanced techniques and high-efficient thermal systems are extensively explored to protect the environment and save energy. Thermosyphons (TSs) are widely conducted as outstanding passive thermal transport devices, which can have high effective thermal conductivities. Nowadays, thermosyphons have been recognized in conjunction with phase change materials (PCMs) to improve the performance of the latent heat thermal energy storage systems. The primary purpose of the integration is to embed the high-efficient thermal conductor into the thermal storage unit to transfer and reserve a significant value of heat efficiently. This review documents applications of coupling TSs and PCMs, general design procedures, and numerical analysis of heat transfer for the systems based on the thermal network approach. Various applications are sorted and compared to reveal the potential advantages of the integration of TSs with PCMs. Moreover, this review also discusses the opportunities and challenges based on a comprehensive framework for the benefit of designers and engineers to implement the combination of TSs and PCMs.

Abstract Water harvesting from humid gas streams is central to fresh-water production, desalination, and particulate removal from combustion gas streams. Two-phase thermosyphons are well suited for these applications due to their very low thermal resistance, but have several operating limits at the high heat flows required for such applications. This work introduces the falling-film thermosyphon for large-scale condensation applications. Working fluid is pumped to the top of the evaporator to provide the evaporating liquid film on the inner tube wall, rather than by vapor condensation. The flooding, dry-out and pool-boiling limits are eliminated, resulting in significantly higher maximum heat fluxes for the same physical evaporator size. Additionally, the condenser no longer needs to be located vertically above the evaporator, which allows for a standard steam condenser to be used. A model for the condensation process in humid air was developed that estimates the fluid and heat transfer and is confirmed experimentally. Other benefits include the use of a high-thermal-conductivity polymer material for the evaporator section to minimize corrosion, and the ability to impose a temperature boundary condition on the evaporator, which is made possible due to the elimination of a liquid pool.

Abstract In this work, a series of novel multi-energy driven composite phase change materials (PCMs) were fabricated with paraffin wax (PW) as PCM, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) as the thickening agent, and reduced graphene oxide aerogel (rGOA) as multi-energy capture agent and support material. When the mass fraction of SEBS is in the range of 5 wt%-15 wt%, the composite PCMs can be formed as form-stable PCMs (FSPCMs) by the physical reaction. The enthalpy value of PW/SEBS5/rGOA is measured as high as 226 J/g. The prepared FSPCMs show a good thermal reliability due to little reduction of enthalpy value after 200 accelerate cycles. And the prepared FSPCMs present a good thermal stability according to the thermogravimetric analysis. The thermal conductivity results show that rGOA slightly improves the thermal conductivity of the FSPCMs. Moreover, the prepared FSPCMs show excellent photo-thermal and electro-thermal conversion performance with the help of rGOA which can harvest the photons and electrons. As a result, the PW/SEBS/rGOA PCMs have great promise in areas such as solar/electrical energy collection, thermal energy storage, and thermal management.