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Applied thermal engineering
Elservier Science Ltd.
Applied thermal engineering

Elservier Science Ltd.

1359-4311

Applied thermal engineering/Journal Applied thermal engineeringISTPSCIEI
正式出版
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    Investigation on the cooling performance of a buoyancy driven earth-air heat exchanger system and the impact on indoor thermal environment

    Long T.Li Y.Qiao Z.Lu J....
    16页
    查看更多>>摘要：The feasibility and cooling performance of a pure buoyancy-driven earth-air heat exchanger system (B-EAHE) with the assistance of combined effect of solar chimney and thermal mass were verified and revealed by a full-scale experimental study. The experimental results showed that the EAHE pipe diameter plays an important role in the system performance, and the airflow rates reach peak values of approximately 252 m3/h and 166 m3/h for the EAHE pipes with diameters of 0.3 m and 0.2 m, respectively. The air temperature differences between the inlet and outlet of the EAHE were approximately 12.5 °C and 13.0 °C in maximum, and 4.8 °C and 4.78 °C in average for the EAHE pipes with diameters of 0.2 and 0.3 m. In addition, the amplitude of indoor air temperature was further attenuated under the regulation of the B-EAHE system. The air temperature inside reference chamber varies from 28.3 to 35.1 °C, while the air temperature inside test chamber with 0.3 m diameter pipe ranges from 28.5 to 30 °C, which is approximately 2 °C lower than that for test chamber with 0.2 m diameter pipe. Moreover, higher energy saving potential is justified by the 0.3 m diameter pipe with peak cooling capacity of 1179 W compared with the 0.2 m diameter pipe with peak cooling capacity of 629 W. It is concluded that the B-EAHE system is able to achieve 24 h periodically fluctuating natural ventilation and passive cooling, and to improve the indoor thermal environment greatly in hot summer conditions.
      原文链接:
    • NSTL
    • Elsevier

    Heat transfer performance of an automotive radiator with MWCNT nanofluid cooling in a high operating temperature range

    Cardenas Contreras E.M.Bandarra Filho E.P.
    12页
    查看更多>>摘要：This study investigates the heat transfer performance of multiwalled carbon nanotube nanoparticles (MWCNT) dispersed in a binary mixture of water-EG (ethylene glycol) at a volumetric ratio of 50:50 in an automotive radiator. The nanofluids were prepared using the two-step synthesis method at volumetric ratios of 0.025%, 0.05% and 0.1%. The UV–vis spectrophotometry method was used to evaluate the colloidal stability of the samples, reporting the absorbance-concentration relationship according to the Beer-Lambert law. Thermophysical properties such as thermal conductivity and viscosity were measured experimentally and compared with correlations in the literature. The influence of nanoparticle concentration as well as the coolant inlet temperature, of up to 105 °C, on the heat transfer rate and in the overall heat transfer coefficient were evaluated experimentally. The air velocity was maintained constant at 2 m/s and the coolant mass flow rate ranged between 0.09 kg/s and 0.11 kg/s. The maximum increases for the heat transfer rate and for the overall heat transfer coefficient were 4.6% and 4.4%, respectively. The results show that the increase in the concentration of nanoparticles can improve the performance in heat transfer, although the performance decrease for high nanofluid inlet temperatures in the radiator was significant. Finally, the stability of the nanofluids was reassessed after performing tests on the radiator, demonstrating high aggregation and sedimentation of nanoparticles.
      原文链接:
    • NSTL
    • Elsevier

    Approximation of the compression process to isothermal in a reciprocating compressor with a liquid piston

    Shcherba V.E.Pavlyuchenko E.A.Nosov E.Y.Yu Bulgakova I....
    12页
    查看更多>>摘要：The implementation of the isothermal process of gas compression in the compressor increases the indicator efficiency up to 20%, which is a determining increase in their operation and saves a significant amount of energy and financial resources, as compressor units consume up to 10% of the energy consumed by production sector. Its implementation is possible in many ways: by changing the heat exchange surface (injection of coolant during compression), changing the heat transfer coefficient, changing the speed of gas compression, etc. The article considers a scheme for gas compression in a cylinder with a liquid piston having a variable speed to ensure an isothermal compression process, and a design of piston hybrid power machine, which brings the gas compression process closer to isothermal. According to theoretical studies, we determine the speed of the liquid piston for the implementation of the isothermal compression process, the amount of liquid required to supplied to the cylinder and the amount of liquid to be be drained from the pump into the gas cap. Using the method of mathematical modeling, according to the fundamental laws of conservation of energy, mass and motion, a mathematical model of a two-stage piston hybrid power machine with a liquid piston and a gas cap has been developed. The performance of the machine is verified by the created prototype, a test stand for its research and a series of experimental studies. As a result of the numerical experiment, we determined the physical picture of the processes in the machine, the absolute and relative flow rates of liquid into the gas cap and into the working cavity for isothermal compression process. The comparative analysis of the relative and absolute flow rates of the liquid and the instantaneous velocities of the piston identified areas by the angle of rotation where the isothermal compression process or close to it is carried out and where it is difficult. The performed parametric analysis verified that reducing the temperature of the walls and the diameter of the cylinder improves the implementing of the isothermal compression process. Using the findings, the results of the conducted patent analysis on the design features of the PHPM, we offered ways to implement the isothermal compression process, new two-stage PHPM designs with a liquid piston having high weight, size and energy indicators.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation on a two-bed adsorption refrigeration system with mass recovery

    Wang Y.Li M.Du W.Liu Q....
    8页
    查看更多>>摘要：In a two-bed continuous refrigeration system, the adsorbers often switch between desorption and adsorption states. Due to this frequent switching, the refrigeration capacity is easily wasted, and energy consumption is increased, resulting in generally low refrigeration performance. In this paper, a novel continuous adsorption refrigeration system using mass recovery was built and experimentally studied. Two adsorbent tubes and activated carbon-methanol were used as the adsorbers and the working pair, respectively. The two adsorbers were separately powered by an electrical heater and hot water. Two aspects of mass recovery were researched and compared: the system performance of processes without and with mass recovery and the system performance at different mass recovery times. The results demonstrate that the mass recovery process enhances the refrigeration performance of the system. The coefficients of performance (COPs) of cycles with mass recovery (180 s) and without mass recovery are 0.122 and 0.107, respectively; mass recovery increases the COP by 14.02%. It is also indicated that there is an optimal mass recovery time for the refrigeration cycle, which is 180 s in this study. Compared with those of 160 s and 200 s cycles, the COP of the optimal system increases by 2.52% and 6.09%, respectively.
      原文链接:
    • NSTL
    • Elsevier

    Numerical investigation on melting behaviour of phase change materials/metal foam composites under hypergravity conditions

    Ding C.Zhang C.Ma L.Sharma A....
    14页
    查看更多>>摘要：The integration of electronic devices in aerospace vehicles leads to a significant increase in the heat dissipation, which makes thermal management a severe challenge. Due to the high thermal energy storage capacity and the excellent thermal diffusivity, phase change materials (PCM)/metal foam composite is a potential thermal management material. In order to deepen the understanding of melting behaviour of PCM/metal foam under hypergravity, the numerical model considering natural convection, flow resistance of metal foam, and non-equilibrium heat transfer is proposed, and the effects of inclination angle, hypergravity value, metal foam porosity, and pore density on the melting are analyzed. It shows that the inclination angle has a great influence on the morphology of the melting interface, while has limited influence on the variation of PCM liquid fraction. As the inclination angle changes from 0° to 180°, the heated wall temperature first decreases, and then increases after reaching the lowest value at 45°, which is the optimal inclination angle. With the rise of hypergravity value, natural convection is enhanced, the heated wall temperature is reduced, while the hypergravity value has limited effect on the PCM liquid fraction. Furthermore, with the increase of metal foam porosity, natural convection is enhanced, while the heated wall temperature and the melting time become larger. When the porosity is larger than 0.95, the effect of metal foam on natural convection suppression is greater than that of heat conductivity enhancement, leading to that the performance of PCM/metal foam is worse than that of the pure PCM. Besides, with the decrease of pore density, natural convection is enhanced, the heated wall temperature becomes lower. Therefore, metal foam with lower pore density is preferred. This paper provides guidance to the optimal design of PCM-based heat sink for aerospace applications.
      原文链接:
    • NSTL
    • Elsevier

    Review of analytical studies of melting rate enhancement with fin and/or foam inserts

    Zhao C.Opolot M.Hooman K.Liu M....
    24页
    查看更多>>摘要：Phase change materials (PCMs) are extensively used in thermal energy storage (TES) applications but most of them own poor thermal conductivities. Melting of a PCM can be thermally enhanced by means of inserting high-conducting fin and/or foam structures, nevertheless, relevant design guideline for a PCM system with these thermal enhancers is yet absent partly because our interpretation of such systems is limited to particular experiments or simulations that usually valid only over a certain (and narrow) range of parameter values. In order to develop such guideline for practicing engineers, one must gain a comprehensive understanding of melting characteristics under different conditions. Hence, this review concerns only on theoretical works of melting with/without fin and foam structures. Isothermal melting without inserts inside a rectangular box under lateral, basal and inclined heating conditions will be firstly reviewed, afterwards, heat transport dimensions of melting in horizontal cylinder and sphere are clarified. Of a PCM system fin structures can be classified into straight and non-straight fins, whereas the former can be further subdivided into “short” lumped fins and “long” semi-infinite fins. Comparatively, only a few works of non-straight fins and porous foams are perceived due mainly to their irregular and complicated structures. Furthermore, different criteria for evaluating the performance of melting rate enhancement are summarized. Accordingly, the research gaps of theoretical works are remarked and several recommendations are introduced.
      原文链接:
    • NSTL
    • Elsevier

    Experimental performance of a LED thermal management system with suspended microencapsulated phase change material

    Ye J.Mo S.Jia L.Chen Y....
    9页
    查看更多>>摘要：Effective thermal management is crucial for electronic devices, while microencapsulated phase change material (MPCM) has great potential in the field of electronic heat dissipation. However, no existing study has conducted experimental research on the influence of MPCM suspension (MPCMS) on the thermal management performance of electronic devices. In the present study, improvement in the thermal management of LED by using MPCMS as coolant was experimentally demonstrated. The morphology, phase-change and thermophysical properties of the MPCM were observed. Experimental results indicate that the TEC-MHS system that uses MPCMS as coolant exhibited enhanced cooling capacity compared with the system that uses water. A dimensionless thermophysical factor was defined to study the effect of variation in thermophysical properties on cooling performance. Interestingly, the highest thermophysical factor and the best cooling performance were achieved at the same MPCMS concentration. The variation of cooling performance with the ambient temperature and flow rate of MPCMS were found to be attributed to the phase change of MPCM. The experimental results indicate that increased MPCMS concentration does not always lead to improvement of the cooling performance, while the thermophysical and phase change properties of MPCM play critical roles.
      原文链接:
    • NSTL
    • Elsevier

    A passive thermal management system with thermally enhanced water adsorbents for lithium-ion batteries powering electric vehicles

    Yue Q.L.Sun J.Xu J.B.Zhao T.S....
    9页
    查看更多>>摘要：Efficient thermal management is crucial for ensuring the safety and performance of lithium-ion batteries powering electric vehicles. Here, we develop a passive battery thermal management system with thermally enhanced water adsorbents by evenly loading MIL-101(Cr) particles onto a copper foam. MIL-101(Cr) particles can absorb water from the ambient and release water at an elevated temperature to dissipate heat, while the copper foam acts as a thermal conductive network to transfer the heat among the particles. The cooling performance of the system is tested under various battery working conditions. Results show that the thermal conductivity of the composite water adsorbent is increased to 1.9 W m?1 K?1, nearly 10 times of the pure MIL-101(Cr). Compared with natural cooling, air cooling and solid–liquid phase change material cooling, the proposed passive cooling method reduces the battery temperature by 7.5, 2.6, and 2.1 °C, respectively, at 3 C discharge. Additionally, the battery temperature and the temperature difference are confined below 37.6 and 1.5 °C in the dynamic discharge–charge cycling test. All these encouraging results indicate that the developed passive thermal management system achieves high cooling capability, good temperature uniformity, and zero energy consumption, which possesses a broad application prospect in electric vehicles.
      原文链接:
    • NSTL
    • Elsevier

    Performance of enhanced geothermal system with varying injection-production parameters and reservoir properties

    Wang K.Liu Z.Zeng T.Wang F....
    17页
    查看更多>>摘要：The injection-production parameters and reservoir properties significantly affect the heat extraction performance of the enhanced geothermal system (EGS), while quantitative rankings of the effecting parameters have been yet unknown. This paper is devoted to investigating numerically the heat extraction performance of EGS by three-dimensional reservoir models under the influence of varying injection-production parameters and reservoir properties. A thermal-hydro-mechanical (THM) coupled model is used to quantify the complicated heat extraction process of EGS. Three-dimensional geothermal reservoir models containing random fracture networks are established based on the Monto Carlo algorithm to quantify the effect of fracture numbers in the process of heat extraction. The parameter sensitivity of the injection-production parameters (injection mass flow rate and injection temperature) and the reservoir properties (rock matrix porosity, fracture permeability, and rock matrix permeability) on the heat extraction performance are ranked and evaluated over the Qiabuqia enhanced geothermal system. It is found the heat extraction performance shows non-monotonic relationships with the fracture numbers in the three-dimensional reservoir model, which indicates the necessity of EGS fracture optimization. The injection mass flow rate turns out the first while the fracture permeability and injection temperature are the secondary dominating factors affecting the heat extraction performance among the evaluated parameters. The outcomes are beneficial to the high-efficiency construction, operation, and optimization of the EGS especially those with similar conditions to the Qiabuqia EGS.
      原文链接:
    • NSTL
    • Elsevier

    Local heat exchanger network optimization of industrial coal-to-olefin process based on hot direct feed/discharge strategy

    Liu S.Li D.Yang S.Qian Y....
    14页
    查看更多>>摘要：Chemical process comprises multiple units that are linked together through process streams. Though it has the advantages of operation independence and flexibility, it will lead to considerable energy consumption and equipment investment. Existing studies have placed more stress on the heat integration and steam reduction for single unit. However, it is rarely optimized for the linking stream. In this study, local heat exchanger network was optimized based on the proposed hot direct feed/discharge strategy. On the whole, the heat integration consists of the integrations in the hot direct feed/discharge region and the downstream process. This strategy was capable of regulating the temperature distribution and improving the freedom of energy comprehensive optimization. The heat integration for downstream process was re-optimized under the principle of minimum steam consumption, where minimum steam flowrate was determined using the latent heat and the sensible heat of steam simultaneously. As revealed from the results, the optimal design decreased hot utility and cold utility by 32.24 MW and 29.14 MW. The steam condensate contributed 6.0 MW heat, which was provided by the latent heat of steam originally. Furthermore, as demonstrated from techno-economic analysis, an annual increment of 3.09 M$ benefit was achieved in a 0.6 Mt/y coal-to-olefins (CTO) process.
      原文链接:
    • NSTL
    • Elsevier