Applied Thermal Engineering最新文献

Innovative technologies are required to mitigate the challenges of climate change. A reversible high-temperature heat pump (HTHP) − organic Rankine cycle (ORC) system can be used for effective utilisation of industrial waste heat in the lower temperature band <100 °C. The system can provide useful process heat for industrial processes by operating in HTHP mode or generating power in ORC mode. This paper presents the experimental investigation of the reversible system in both HTHP and ORC modes. A single scroll unit was selected for the compressor (HTHP) and expander (ORC) roles, keeping the system compact. A HCFO refrigerant, R1233zd(E), with a low GWP value, was chosen as the working fluid for both operating modes. When operated in HTHP mode, a maximum compressor overall isentropic efficiency of 73.4 % and a COP_mech of 4.8 (ΔT_lift,rside = 41 K, T_sf,ev,in = 60 °C) was obtained. In ORC mode, the maximum net power output was 512.4 W (T_sf,ev,in = 90 °C, r_p = 2.3), overall cycle efficiency was 3.01 %, and overall isentropic efficiency of the expander was 54.6 %. The technical limitations encountered, and solutions put in place during the experimental testing campaign are discussed in detail.

The condenser plays a crucial role as one of the key components in a power plant, directly influencing its overall efficiency. Any alteration in the power plant’s efficiency has a substantial impact on both energy consumption and the environment. The holding steam ejector (HSE) is essential for condenser operation by creating a vacuum and effectively removing air. The primary objective of this study is to evaluation the motive flow temperature (MFT) by considering various parameters such as steam price, production entropy, air suction, and entrainment ratio (ER). The investigation focuses on different temperatures within the power plant condenser. The study examines the changes in MFT within the range of 350 ˚C to 400 ˚C, as well as the variation in condenser temperature (CDT) spanning from 47 ˚C to 67 ˚C. The results demonstrate that varying the MFT impacts the functional parameters of the HSE. As the MFT increases, there is an increasing trend in the ER. Simultaneously, there is a decreasing trend observed in the cost of steam production, production entropy, and air suction. When the MFT increased from 350 ˚C to 400 ˚C, the suction air mass flow rate for temperatures of 47 ˚C, 57 ˚C and 67 ˚C decreases by 2.22%, 2.09% and 1.99%, respectively. These results highlight the influence of temperature on various parameters, showcasing how adjustments in the MFT and CDTs can affect the flow characteristics and associated factors in the system.

To enhance the accuracy of lithium battery thermal models, this study investigates the impact of temperature-dependent convective heat transfer coefficients on the battery’s air cooling and heat dissipation model, based on the sweeping in-line robs bundle method proposed by Zukauskas. By calculating and fitting the relationship between the convective heat transfer coefficient and temperature at flow rates of 0.05 m/s, 0.15 m/s, 0.25 m/s, and 0.35 m/s, it was found that the relationship is complex. An electrochemical-thermal coupling model was established using the operational characteristics of lithium batteries, and a thermal runaway reaction kinetics model was created using isothermal thermal runaway experiments and least squares optimization. The temperature-dependent convective heat transfer coefficient was then integrated into both models. Numerical simulations revealed that during normal discharge, the maximum temperature difference in the battery when the convective heat transfer coefficient is a function of temperature is less than 1 % compared to when it is constant. However, in the high-temperature thermal runaway model, the impact of temperature-dependent convective heat transfer coefficients on the thermal runaway critical parameters is minimal at flow rates of 0.05 m/s and 0.15 m/s. When the flow rate increases to 0.25 m/s and 0.35 m/s, the impact on the trigger time of thermal runaway is 17.34 % and 18.07 %, respectively. Experimental validation and research results indicate that the temperature effect on the convective heat transfer coefficient should be considered in high-temperature thermal runaway and thermal management models to calculate the convective heat transfer more accurately within the battery pack, improving model accuracy and reducing the risks of thermal runaway.

Low-temperature solar collectors coupled with thermal energy storage can enable stable and carbon-free energy production. This work proposes a fully integrated organic Rankine cycle (ORC) with solar field and thermocline direct energy storage. The organic fluid remains liquid inside the solar field and the thermal energy storage, leading to a trilateral-like thermodynamic cycle. As opposed to other trilateral (flash) cycles, the proposed system distinguishes itself by including a turboexpander to deal with two-phase expansion, leading to higher conversion efficiency. In particular, with the same turbine efficiency, the proposed cycle outperforms alternative integrated ORC-solar field configurations by 1.5–3.8 percentage points in thermodynamic cycle efficiency for maximum temperatures between $400\text{–}600K$. The equivalent electric energy density also increases by 30% to 60%. The problem of the two-phase turbine is tackled by relying on a recently proposed radial-inflow turbine concept. The centripetal stator leverages the retrograde shape of the saturation curve to achieve a complete liquid-to-vapor expansion. As a result, the rotor can handle dry organic vapors without experiencing mechanical damage or additional losses from two-phase interactions. Preliminary turbine designs, obtained through optimization of a validated meanline method, consistently yield isentropic total-to-static efficiencies exceeding 85%, confirming the potential of the proposed system.

One of the most significant limitations to the advancement of electronics is the issue of heat dissipation. Currently, air cooling remains the most widely used method for heat dissipation due to the advantages of low cost and ease of maintenance. However, the traditional air-cooling method based on an all-solid heat sink is unable to keep pace with the rapid advancement in thermal power of electronics due to its limitation in area expansion by only solid fins. This study proposes an aluminum-based three-dimensional thermosyphon (3D-TS) coupling boiling-condensation heat transfer and forced air cooling as a means of overcoming the limitations of conventional air-cooling methods. Additionally, the incorporation of micro pin-fins enhances the boiling heat transfer and the overall performance of the three-dimensional thermosyphon. The performance of the three-dimensional thermosyphon is experimentally studied and analyzed under different volumetric flow rates using the environmentally friendly refrigerant R1233zd(E) as the working fluid. The results indicate that the total thermal resistance exhibits a biphasic response to heating power, with a decrease initially followed by an increase. This response is primarily attributed to the boiling mode on the substrate. Moreover, the micro pin-fins significantly enhance the boiling heat transfer on the substrate of the three-dimensional thermosyphon, enabling the three-dimensional thermosyphon to reach a minimum thermal resistance of 0.075 K/W and a maximum thermal dissipating power of 650 W with the temperature of the heating source below 85 °C. The three-dimensional thermosyphon proposed in this work is capable of meeting the cooling requirements of the majority of high-performance chips. This paper offers a valuable reference and guidance for the design and optimization of the phase-change devices.

Pulsating heat pipe (PHP) is a kind of efficient passive phase-change cooling device. The pulsating behaviors of the two-phase flow inside PHP significantly affect the heat transfer performance for PHP, the investigation of which will greatly contribute to the optimal design of PHP for electronic heat dissipation in small space. In the present work, the heat transfer performance of PHP is optimized via structure analysis and modeling calculation. A new “spring-mass-damper” model in terms of separated phase flow mode is established, where the frictional pressure loss of the real two-phase flow pattern − slug flow in PHP is considered. Besides, a prototype of PHP with adjustive-structured channel (ASCPHP) is proposed. The heat transfer performance of ASCPHP is evaluated with the newly established model. With theoretical computation method, the frequency of ASCPHP the superiority of ASPHP is also confirmed by comparison with other types of PHPs.

Branched or tree-shaped networks of microchannels are often preferred heatsink designs for microelectronic cooling due to their ability to offer a substantially large surface area-to-volume ratio. Designing an optimized tree-shaped heatsink in terms of hydrothermal performance poses challenges due to the intricate geometry and small-scale fluid–structure interactions involved, making prototyping challenging. We propose a systematically designed microchannel network heat exchanger inspired by tree branching patterns, aiming for ease in rapid prototyping and improved flow distributions offering enhanced thermal performance. Starting from a simpler geometrical consideration, we systematically improve the design by introducing a pin fin at the junction for improved flow distribution and then by imparting a converging angle in the channel for enhanced thermal performance. Additionally, we conduct an entropy generation analysis to examine the thermal performance of various nanofluid concentrations within the proposed device and witness significant thermal performance improvement that can benefit the thermal management of microelectronic components and other cooling applications.

Flexible composite phase change materials (CPCMs) have been extensively studied in the thermal management of cylindrical lithium-ion batteries and proven to have a good cooling effect. However, passive cooling of pouch lithium-ion batteries with severe uneven temperature distribution has not received the attention it deserves. The thermal management of pouch battery based on passive cooling of flexible PCMs considering the heat-generating structure of pouch batteries needs to be further studied. Herein, CPCMs with different thermal conductivity were prepared, and four different distribution modes of CPCMs, including partial coverage and complete coverage, were applied to thermal management of pouch battery. Results indicated that the maximum temperature (T_max) and maximum temperature difference (ΔT_max) can be kept separately within 35 °C and 5 °C in the passive thermal management of a single battery except upper coverage at discharge rate of 5C, and the middle coverage (case B) showed excellent temperature control in partial coverage cases. Equally noteworthy was that the increase in thermal conductivity increased the ΔT_max in partial coverage cases, while showing the opposite trend for full coverage (case ABC). Furthermore, only passive cooling of pouch battery pack did not meet the safety requirements under the discharge rate cycle of 5C. Under the active–passive combination mode, case B can control the T_max (32.22 °C) and ΔT_max (4.69 °C) within a safe range, which was superior to case ABC (T_max = 35.53 °C, ΔT_max = 5.04 °C). This conclusion provides technical support for the pouch battery to seek economic, stable and efficient thermal management.

Oxygen-enriched combustion is widely used in industrial furnaces. To elucidate the multi-physics properties of reheating process, this study numerically explores the flow and combustion characteristics of syngas oxygen enrichment combustion in an industrial-scale walking beam type reheating furnace. The findings demonstrate that gas flow patterns at the furnace inlet primarily encompass the billet periphery, enhancing heat transfer efficiency. Oxygen-enriched combustion achieves lower temperature differences, higher heating temperature and CO₂ emissions. Additionally, increasing levels of oxygen enrichment correlates with elevated temperatures, though the increments diminish progressively. Specifically, temperatures at the outlet of the preheating section range from 1100 K to 1200 K, with the middle region of the heating section displaying slightly lower temperatures compared to the areas adjacent to the burner. High temperature zones are primarily concentrated around the burners in soaking and heating sections. In terms of heating temperature and thermal uniformity, 30 % oxygen-enriched condition yields superior performance, evidenced by higher heating temperatures and reduced temperature differentials. Moreover, oxygen-enriched combustion enlarges CO₂ emissions, with a 124.5 % enhancement observed. The lowest NO emission content at the outlet occurs during combustion with 21 vol% air and 45 vol% oxygen enrichment, however, these values remain relatively high. The insights derived from this study provide a foundational framework and guiding principles for furnace design and optimization of multi-gradient oxy-enriched combustion.

A review of the jet’s flow dynamics, coherent structures, and heat transfer characteristics is presented. The goal is to have a bird-eye view on the understanding of this complex flow field in light of the latest research. The focus is placed only on the heat transfer by a single slot or circular jet impinging on a flat surface. The influence of various variables or parameters on the target wall heat transfer is discussed. Jet heat transfer correlations are compared with experimental data close to a Reynolds number of 20,000 and a jet outlet-to-target wallspacing of two diameters. The recent state of the art, high fidelity Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) studies on an impinging jet are discussed and compared with the available experimental data. Different reasons for the occurrence of secondary peaks in the Nusselt number distributions as interpreted by various researchers are presented. The review shows that despite of the variety of existing research on impinging jets, there is still a need of further research on this subject.