查看更多>>摘要：Additive manufacturing technology with metal powder has facilitated the production of innovative and even more complex heat sinks. The layer-additive process offers a wide range of geometries that may be exploited for advanced cooling purposes and the final identification of the best heat sink configuration has to deal with other constraints imposed by the specific application. This contribution focuses on the thermal and fluid dynamic characterization of water cooling annular channels for applications in internal combustion engine components, where also the load-bearing capacity is requested together with the cooling performances. The heat transfer inside the annular channel was enhanced by pin fins arrays that were manufactured by selective laser melting technology in AISI 316L stainless steel. Four pin fins arrays that differ in dimensions and geometries were experimentally tested over a range of mass flow rates to compare their pressure losses and heat transfer performances against those of the smooth annular channel. Furthermore, the test coupons were analysed through optical non-destructive techniques to characterize their geometrical morphology in terms of conformity with the designed model, surface roughness and waviness. In the investigated channel Reynolds number range (from 2000 to 12,000), the pin fins arrays with the largest height-to-pin diameter ratio show better thermal performances (Nu/Nu(0) always greater than 2), however their heat sink efficiencies are above unity only for Re < 3000. In addition, the 45 degrees oriented pin arrangement seems the most promising geometry due to high thermal efficiency, lighter weight and slightly lower manufacturing cost.
查看更多>>摘要：An accurate heat and mass transfer model of a tumble drum has not been developed yet owing to complicated random motions of clothes in the tumble drum. In this study, heat and mass transfers of water from clothes to air, including the heat loss in the tumble drum of a clothes dryer, are measured with the temperature, humidity, airflow rate, and water content of clothes. The mass transfer rate increases as the air temperature, airflow rate, and water content of clothes increase; however, it decreases with an increase in the relative air humidity. The mass transfer rate enhancement is dominated by the increase in the temperature over the airflow rate; the increased temperature from 40 degrees C to 80 degrees C results in an increase in the mass transfer rate of 196%-238%, and the increased volumetric airflow rate from 2.5 CMM to 3.1 CMM leads to an increase in the mass transfer rate of 21%-23%. The heat loss in a tumble drum increases as the air temperature increases and continues to increase as the relative air humidity and water content of clothes decrease. Furthermore, although the heat loss is linearly proportional to the difference between the temperatures of ambient air and clothes, it has an insignificant relationship with the airflow rate. In addition, the prediction models of heat and mass transfers of water and heat loss in the tumble drum are developed using artificial neural network, exhibiting optimal agreements with the measured data. The developed prediction models can be used to optimize the tumble drum dryer, considering energy efficiency and short drying time.
查看更多>>摘要：The blade tip region of the gas turbine is exposed to an extreme operating condition with a high heat load. The conventional cooling concept that places cooling holes on the tip would consume a lot of cooling air and lead to a reduction in thermal efficiency. Whereas phantom cooling was supposed to help cool the tip region without using additional cooling air. In this paper, computational comparisons were conducted to forecast the tip phantom cooling effects caused by the blade ejections by employing the standard k-omega model. Then, phantom cooling performance was presented under the flat tip (FT) and the squealer tip (ST), with three tip clearances. Results show that the FT shows a better phantom cooling performance compared to the ST. The phantom cooling effects on the FT are distributed at the tip forepart and near the pressure side (PS). Whereas, for the ST, traces of phantom cooling are barely detected on the PS rim. Increasing the tip clearance would weaken the phantom cooling performance on the FT forepart but enhance it on the rear part. For the ST, its phantom cooling effectiveness values decrease as the tip clearance increases. A lower aerodynamic loss is obtained for the ST under any coolant MFR or tip clearance.
查看更多>>摘要：This paper presents an experimental investigation of the influence of multiple parameters on the thermal performance of variable conductance heat pipes (VCHPs) according to theoretical design and analysis. The operating characteristics of four VCHPs, such as the steady-state temperature, thermal resistance, and degree of self-control, were systematically analysed and compared. The design principles were examined considering the structural matching design, thermal-physical properties, and charging mass of the fluids. The examined types included the cold-gas reservoir VCHP (CGR-VCHP) and the hot-gas reservoir VCHP (HGR-VCHP), whose steady-state operating temperatures and thermal resistances were compared. The HGR-VCHP attained a higher degree of self-control than the CGR-VCHP for the same heat pipe (HP) structure size. The effects of the reservoir volume of the CGR-VCHP were experimentally and theoretically assessed. Compared to a small volume of 33.66 mL, a large volume of 43.27 mL increased the self-control, with dT(va)/dQ dropping from 0.272 K/J to 0.042 K/J. Moreover, the temperature difference decreased from 13.6 to 2.09 degrees C under the same heat load increase of 50 W. Both R22 and ammonia were chosen as working fluids due to their similar sensitivity factors. The self-control ability of the ammonia CGR-VCHP was higher than that of the R22 CGR-VCHP based on the obtained experimental and theoretically calculated results. This research provides valuable insights into VCHP multiparameter analysis, which are of great significance for the practical application of VCHPs in self-control thermal.
查看更多>>摘要：This work investigates the effects of an additively manufactured (AM) evaporator on two-phase loop thermosyphon performance. The thermosyphon employs a radially finned, air-cooled condenser connected to an aluminum side-heated evaporator by nylon tubing. Two evaporator surfaces were examined: one with smooth conventionally machined aluminum channels and the other with channels additively manufactured by selective laser melting (SLM). The loop thermal performance and the operational instabilities were characterized for different working fluid charge volumes using water and ethanol. The instabilities were quantified using the maximum fluctuation amplitude of the evaporator wall temperature. Results show that increasing the input power decreases the total resistance and lessens the corresponding instabilities. Low fluid charges result in better thermal performance and lower evaporator temperature instabilities, but they reduce the loop's maximum heat transport capacity. The peak in condenser resistance was found to serve as a good indicator for the end of geysering. Finally, the AM evaporator resulted in slightly higher thermal resistances compared with the conventionally machined version; however, it decreased temperature fluctuations at the heat source.
查看更多>>摘要：Combined cooling, heating and power (CCHP) systems have received wide attention for their potential of high efficiency and energy conservation. In this work, a novel CCHP system is designed coupling the solar thermal input (ST) system and the regenerative organic flash cycle (OFC) system. The OFC subsystem could recycle two kinds of heat sources to achieve cascade utilization of heat energy. The CCHP-ST-OFC system is evaluated by comparing with the conventional CCHP system and the CCHP-ST-ORC system (organic Rankine cycle). The effects of several operating parameters on the thermodynamic performance are discussed. Based on the negative feedback regulation, an operation strategy is proposed and applied to buildings to verify the thermodynamic economy. The results demonstrate that the electricity and heat provisions are 275.0 kW and 211.5 kW, which are 4.7 kW and 19.3 kW higher than the CCHP-ST-ORC system. The electricity of the OFC subsystem is 15.0 kW and 47% higher than the ORC system. Moreover, changing the smoke outlet temperature in the waste heat recovery equipment could effectively adjust the heat provision and power generation. The trend of the day and night power generation with the mass flow rate of the heat source is reversed. The energy provision and performance increased with the increasing partial load ratio of the internal combustion engine. The building case study reveals that the exergy efficiency of the CCHP-ST-OFC system is 38.7% and the primary energy ratio is 53.1%, respectively. Meanwhile, the natural gas consumption of the CCHP-ST-OFC system is 5.14 x 105 m3/year, with a 9% reduction than the CCHP-ST-ORC system.
Han, ZhenxingWickramaratne, ChaturaGoswami, D. YogiJotshi, Chand...
14页
查看更多>>摘要：Inorganic salts are potential phase-change materials for medium- and high-temperature thermal applications. It is essential to acquire knowledge of their behavior in latent heat thermal energy storage for the design of storage devices and the construction of an energy conversion and utilization system. In this study, a eutectic mixture of NaNO3 (mass ratio of 46%) and KNO3 was selected as phase change material, and a nitrate salt-based latent heat thermal energy storage unit was built to experimentally investigate its operating characteristics during charging and discharging. The thermophysical properties of the eutectic nitrate salt were measured and presented. The air outlet temperature remained almost unchanged during the melting of salt in the charging process, but it decreased gradually during the discharging process because the thermal resistance increased with the salt solidification. The melting time was shortened by 31.0% and 38.1% when the air inlet temperature was increased from 260 degrees C to 270 and 280 degrees C, respectively. The solidification time was shortened by 22.2% and 33.3% when the air inlet temperature was reduced from 210 degrees C to 200 and 190 degrees C, respectively. When the air mass flow rate was increased from 0.964 g/s to 1.446 and 1.962 g/s, the melting time was shortened by 32.4% and 57.4%, respectively, while the solidification was only shortened by 8% and 16%, respectively. The charging ratio or discharging ratio can be calculated through heat-loss evaluation to depict the thermal energy change in a charging or discharging process. The results indicated that charging ratio increased almost linearly with the melting of the salt. The air mass flow rate had a significant impact on this parameter. The influence of the air inlet temperature was gradually weakened with the increasing air inlet temperature. Owing to the coupling effect of heat loss and airflow, the influence of air parameters on the discharging ratio was weak. The effectiveness of storage indicates the extent to which the latent heat of salt can be utilized. It increased from 29.7% to 52.8% when the air inlet temperature was reduced from 210 to 190 degrees C. This study provides insights into the phase-change characteristics of the nitrate salt and the nitrate salt-based latent heat thermal energy storage unit.
查看更多>>摘要：A two-dimensional mathematical model of a regenerative heat exchanger for a ventilation system with a periodic change in the air flow direction is developed. This system allows a significant economy of the thermal energy for heating buildings in winter. Such devices are quite compact, has no moving details and do not require significant electrical power for their operation, while they can provide the ventilation needs of both whole buildings and individual rooms in multi-storey buildings. The definition of energy efficiency of a regenerative heat exchanger is formulated in terms of reducing the loss of thermal energy. It is shown, that regenerative heat exchanger can really reduce thermal energy losses by ventilation more than by 90%. Parametric studies are fulfilled using the method of numerical simulation and the influence of operating and design parameters of the heat exchanger on its energy efficiency is revealed. In numerical calculations, a group of parameters that most strongly affect the energy efficiency of the ventilation system is identified, and recommendations for optimizing these parameters are given.
Garcia, AntonioMonsalve-Serrano, JavierSari, Rafael LagoMartinez-Boggio, Santiago...
23页
查看更多>>摘要：This paper presents a novel simulation approach consisting of coupling fundamental and applicate aspects of Lithium-Ion battery simulations. A battery module representative of a complete battery pack is built using GT-AutoLion, consisting of a detailed electrochemical model and detailed cooling system modelled using the finite elements approach. The results show fresh and aged cylindrical cells submitted to different battery cooling flows. The cells are charged and discharged in high C(rates )to observe the performance of the proposed system in critical conditions. In addition, a battery thermal runaway code in Python is coupled to simulate the decomposition of the main components of the battery cell and their associated heat release during the battery operation. The concentration of the main species is tracked as well as the battery cells temperature distribution. The aged cells shown more probabilities of thermal runaway due to the increase of the internal resistance. However, it is possible to reduce the difference by increasing the cooling flow from 3 g/s to 50 g/s. When analysing the thermal runaway induced by a failure of a cell, the comparison shows that the mechanisms found in the bibliography shows a difference of 40 s in predicting the peak of heat release rate. Overall, the proposed framework confirms its capability of addressing the relevant phenomena during the battery operation, providing a way of improving the design phase from the battery cell to the battery pack.
查看更多>>摘要：To recover waste heat resources and improve the utilisation rate of waste heat, a cogeneration system based on bionics was designed. To maximise the utilisation rate of waste heat, the effects of different bionic channel structures (angular frequency omega = 20, 25, and 30 rad/s; amplitude A = 1, 2, and 3 mm; and phase shift alpha = 0 degrees, 90 degrees, and 1801 on the power generation characteristics were studied experimentally. The innovation of this study lies in designing bionic structures with different shapes and replacing traditional working fluids with nanofluids. The experimental results showed that, when the working medium was a CuO-H2O nanofluid, the temperature at the hot end of the thermoelectric plate increased by 7.19%. For different bionic structures, the thermoelectric conversion efficiency of waste heat utilisation equipment with omega = 30 rad/s, A = 3 mm, and alpha = 180 degrees was the highest, being 15.29%, 18.79%, and 6.97% higher than those with omega = 20 rad/s, A = 1 mm, and alpha = 0 degrees, respectively. The results of this study can provide guidance for the design and operation of the power generation characteristics of waste heat utilisation equipment.
NSTL
Elsevier