• Energy Research
• EU close
• Applied Thermal Engineering close

Abstract Numerical models allow the solving of dynamic and complex problems such as industrial processes. Reliable numerical models representing the unit operations and energy systems within plants can greatly increase the competitiveness of industries. Industrial plants besides the primary circuits related to the manufacturing processes, also include secondary circuits related to water circuits and commonly neglected as not being directly involved in the processes. Typical industrial water circuits (IWC) include: water cooling, gas washing circuits, water treatment, water transportation and quenching circuits. The OpenModelica environment allows users to perform modelling and simulation of processes in an accessible and open source way. There is however a lack of dedicated open source library including the variety of equipment and processes of typical IWC. Hence, this paper presents a library based on typical IWC and validated with real case studies from different industrial sectors. The validation has shown good agreements between the modelling and the real data and therefore applicable for a variety of applications such as: energy efficiency improvement, circuits design, equipment dimensioning, operational and maintenance conformity.

© 2019 The cryogenic industry has experienced remarkable expansion in recent years. Cryogenic technologies are commonly used for industrial processes, such as air separation and natural gas liquefaction. Another recently proposed and tested cryogenic application is Liquid Air Energy Storage (LAES). This technology allows for large-scale long-duration storage of renewable energy in the power grid. One major advantage over alternative storage techniques is the possibility of efficient integration with important industrial processes, e.g., refrigerated warehousing of food and pharmaceuticals. Heat exchangers are among the most important components determining the energy efficiency of cryogenic systems. They also constitute the necessary interface between a LAES system and the industrial process utilizing the available cooling effect. The present review aims to familiarise energy professionals and stakeholders with the latest achievements, innovations, and trends in the field of cryogenic heat exchangers, with particular emphasis on their applications to LAES systems employing renewable energy resources. Important innovations in coil-wound and plate-fin heat exchanger design and simulation methods are reviewed among others, while special attention is given to regenerators as a prospective component of cryogenic energy storage systems. This review also reveals that the geographical spread of research and development activities has recently expanded from well-established centers of excellence to rather active emerging establishments around the globe.

Abstract Thermal management of lithium-ion (Li-ion) batteries in Electrical Vehicles (EVs) is important due to extreme heat generation during fast charging/discharging. In the current study, a sandwiched configuration of the heat pipes cooling system (SHCS) is suggested for the high current discharging of lithium-titanate (LTO) battery cell. The temperature of the LTO cell is experimentally evaluated in the 8C discharging rate by different cooling strategies. Results indicate that the maximum cell temperature in natural convection reaches 56.8 °C. In addition, maximum cell temperature embedded with SCHS for the cooling strategy using natural convection, forced convection for SHCS, and forced convection for cell and SHCS reach 49 °C, 38.8 °C, and 37.8 °C which can reduce the cell temperature by up to 13.7%, 31.6%, and 33.4% respectively. A computational fluid dynamic (CFD) model using COMSOL Multiphysics® is developed and comprehensively validated with experimental results. This model is then employed to investigate the thermal performance of the SHCS under different transient boundary conditions.

Solar desiccant cooling systems, SDEC, could be an effective alternative to conventional cooling systems, which mainly depend on electrical energy. The main objective of this work was to determine experimentally the seasonal coefficient of performance, SCOP, of a SDEC system composed of a desiccant wheel, an indirect evaporative cooler and a thermal solar system, to control indoor conditions in a research lab room. The dependence of coefficient of performance on outdoor air conditions and percentage of renewable energy used by the SDEC system were also analysed. Experimental tests were carried out for six weeks during spring and summer seasons in Martos, Spain. The experimental results showed that the SDEC system independently adjusted the temperature and humidity of the supply air. 75% of the energy consumed by this air handling system comes from renewable sources. A seasonal coefficient of performance of the SDEC system of 2 was obtained for the period analysed. It is shown that the higher the outdoor temperature, the higher instantaneous COPs is. These results suggest that the use of SDEC systems in hot climates, such as southern European climates, could contribute to achieve the EU's energy goals within the frame of Nearly Zero Energy Buildings.

The ejector is a process equipment frequently used in refrigeration processes. There is currently a knowledge gap on the efficiency of ejectors operating with mixtures. To address this knowledge gap, we present a one-dimensional ejector model for mixtures, defined by spatially distributed mass-, energy- and momentumbalances for different zones, which together constitute the full ejector geometry. The recently developed delayed homogeneous relaxation model is used to describe the two-phase transition in the motive and suction nozzles. For evaporation of pure CO2 in the throat of the motive nozzle, the model yields an average error of 2.6% in the critical mass flow rate, which is significantly lower than the homogeneous equilibrium model that has an average error of 8.4%. A comparison to new experimental data shows that both models give excellent predictions of critical mass flow rates where condensation occurs in the throat, with an average error below 0.9%. New experimental data with CO2 are presented, which are used to regress two parameters in correlations that describe the momentum transfer between the primary and secondary stream in the mixer and diffuser sections. This leads to accurate reproduction of the pressure lift in five different ejector geometries, with a mean error of 2.3%. By using nonequilibrium thermodynamics, we derive formulae for the local exergy destruction in the ejector. The largest exergy destruction is located in the mixer, and originates in transfer of momentum between the primary and secondary streams. The local exergy destruction profiles through the mixer and diffuser are highly non-uniform, and deviate from the established guidelines for energy-efficient design characterized by equipartition of exergy destruction. This reveals a potential to increase the performance of ejectors by suitable adjustments to their geometric design. The mathematical model validated for pure CO2 is assumed to also be valid for mixtures rich in CO2. We show that minute concentrations of a second component can have a significant influence on the ejector performance. When fixing the inlet conditions and ejector geometry, we demonstrate that adding 2% H2 to a mixture of CO2 decreases the critical mass flow rate by 20%, while adding 2% SO2 increases the pressure lift by 1 bar.

In the present work, the multiphase flow dynamics in fluidized beds is modelled using the Two-Fluid Model (TFM) where the characteristics of a granular solid phase are described by the Kinetic Theory of Granular Flow (KTGF). A drag function and heat transfer coefficients are used to describe the interaction and heat exchange between different phases, respectively. The effective thermal conductivity is defined as a function of phase volume fraction and thermal properties and is used to calculate the heat transfer coefficient from immersed tube to fluidized beds. The effects of different tube shapes on the flow characteristics and local heat transfer coefficients are investigated and the time-averaged heat-transfer coefficient is compared with the experimental data in the literature. The simulated results show that the heat transfer processes are significantly influenced by the reintroduction of solid particles around the immersed surfaces and the heat transfer coefficients vary sensitively with the distribution of the solid phase. The simulated heat transfer coefficients are in the same order as the experimental data which indicates that it can be quantitatively employed to aid the configuration of heating tubes during industrial design of the fluidized bed reactors.

Loop heat pipes (LHPs) are efficient two-phase heat transfer devices that have found many space and terrestrial applications. This work addresses our insufficient understanding of LHP operation under gravity-assisted attitude, i.e. the condenser is located higher than the evaporator. A steady-state mathematical model of a LHP under gravity-assisted operation was established based on two driving modes: gravity driven mode and capillarity-gravity co-driven mode, determined by a defined transition heat load. The model was validated by the experimental results, and was employed to predict the operating characteristics of a LHP under the gravity-assisted attitude. Comparing to LHPs operating under horizontal or antigravity attitudes, some distinctive features have been identified, which include: i) the total mass flowrate in the loop shows a unique V-shape with the increase of applied heat load; ii) the steady-state operating temperature is much lower under the gravity driven mode, and is in similar values under capillarity-gravity co-driven mode and iii) the thermal conductance of the LHP increases with increasing positive elevation especially in the variable conductance zone. Such results contribute greatly to the understanding of the complicated operating principle and characteristics of LHPs especially for terrestrial applications.