Investigation on standing wave thermoacoustic generator using DeltaEC

There is currently an urgent demand to reuse waste heat from industrial processes with approaches that require minimal investment and low cost of operation. Thermoacoustic generator (TAG) is a device that converts heat energy into useful work through the use of acoustic wave, porous media (honeycomb ceramic celcor) and heat exchangers that are all enclosed in a custom-defined resonator. This paper reports the basic design of thermoacoustic generator that is tested using a design software known as a Design Environmental for Low-amplitude Thermoacoustic Energy Conversion (DeltaEC). Many studies have highlighted the relationships between the geometry of the stack and the performance of the device. In this study, attention is given on the impact of the length of stack which was found to be the best at a length of 0.6 m when the frequency of the flow is at 127.4 Hz. Performance indicators like the acoustic power and the temperature difference across the stack have been used to analyse the results. The result shows that the highest acoustic power can be achieved when the generator that work with air at an atmospheric pressure is designed with a resonator of 2.14 m long and a stack with a length of 0.6 m. The maximum value for acoustic power is predicted to be as much as 24.01 kW

The effect of porous materials on temperature drop in a standing wave thermoacoustic cooler

Thermoacoustics is a principle of sciences that offers an alternative solution for cooling system with a technology that is green and sustainable. The thermoacoustic energy conversion takes place mostly within the area of the porous structure that forms the core of the system. In this study, the effect of changing the material of the porous structure on the performance of the thermoacoustic refrigerating system is reported. Experiments were performed under standing wave environment with two different resonance frequencies with air at atmospheric pressure. The porous stack was chosen to be with three different materials of polycarbonate, ceramic and stainless steel. The results show that the use of ceramic celcor as the porous material provides the biggest temperature difference which means that thermoacoustic performance is better. The performance is even better when the system is working with higher resonance frequency. At atmospheric pressure condition with air as working medium, the thermoacoustic cooler with ceramic porous material is capable of producing temperature difference of 39.16C when operating at a frequency of 202.1 Hz

Cell Arrangement of Lithium-ion Battery Pack for Improvement in Cooling Performance of Air-Cooled Battery Thermal Management System

งานวิจัยนี้ได้ทำการศึกษาเชิงตัวเลขของระบบจัดการความร้อนของชุดแบตเตอรี่ด้วยอากาศ เนื่องจากต้นทุนการผลิตที่ต่ำ, โครงสร้างการจัดเรียงที่ไม่ซับซ้อน และความเสถียรภาพของระบบที่สูง โดยทำการศึกษาชุดแบตเตอรี่ลิเธียมไอออนรุ่น 1860B จำนวน 40 เซลล์ ที่มีโครงสร้างการจัดเรียงเซลล์ที่แตกต่างกัน ได้แก่ แนวเดียวกัน, แนวเยื้อง และแนวสลับ เพื่อเปรียบเทียบสมรรถนะการระบายความร้อนของแต่ละรูปแบบ นอกจากนี้ อิทธิพลของความเร็วอากาศ และอัตราการคายประจุก็ถูกใช้ในการวิเคราะห์ร่วมด้วย เพื่อควบคุมให้เซลล์แบตเตอรี่ทำงานอยู่ภายในช่วงอุณหภูมิที่เหมาะสม ซึ่งมีค่าไม่เกิน 40C โดยแบบจำลองความร้อนที่เกิดขึ้นในเซลล์แบตเตอรี่ถูกจำลองขึ้นโดยอาศัยข้อมูลการทดสอบเซลล์แบตเตอรี่ภายใต้อุณหภูมิแวดล้อมต่าง ๆ จากผลการจำลองพบว่า เมื่อความเร็วของอากาศเพิ่มขึ้น ส่งผลให้ระบบระบายความร้อนมีประสิทธิภาพเพิ่มขึ้น โดยชุดแบตเตอรี่ที่ทำงานอย่างต่อเนื่องภายใต้อัตราการคายประจุ 0.5C อาจไม่จำเป็นต้องพึ่งพาระบบระบายความร้อนด้วยอากาศแบบบังคับ และในกรณีที่ชุดแบตเตอรี่ทำงานด้วยอัตราการคายประจุ 1C การระบายความร้อนจำเป็นต้องมีความเร็วของอากาศอย่างน้อย 1 m/s เพื่อควบคุมอุณหภูมิของเซลล์แบตเตอรี่ให้อยู่ภายในช่วงที่กำหนด แต่ระบบจัดการความร้อนด้วยอากาศไม่สามารถควบคุมอุณหภูมิของเซลล์แบตเตอรี่ได้ในกรณีที่มีการคายประจุอย่างรวดเร็ว นอกจากนี้ การจัดเรียงเซลล์ที่เหมาะสมที่สุดในแง่ของประสิทธิภาพการระบายความร้อนคือการจัดเรียงแบบแนวเดียวกัน และช่องว่างที่เหมาะสมระหว่างเซลล์ที่อยู่ติดกันคือประมาณ 1.5 มม.Air-cooled thermal management system has been numerically studied due to low manufacturing cost, simple layout structure and high reliability of the system. A set of Lithium-ion battery pack 18650B consisting of 40 cells was investigated under different cell arrangement structures, i.e., inline, offset, and staggered configurations in order to evaluate their cooling performances. Additionally, the effects of inlet velocity and discharge rate were taken into consideration to guarantee the temperature of batteries in operation within an optimal range, i.e., not over 40 °C. The heat simulation model of battery cells was developed based on the data acquired from the test under various ambient temperatures. The simulation results revealed that the increased air velocity resulted in better cooling performance of the system. The continuously operating battery pack under the discharge rate of 0.5C may not rely on the forced air-cooling system. When the battery pack discharging of 1C-rate, it required at least the air velocity of 1 m/s for cooling the battery within the optimal working temperature range. However, the forced-air cooling strategy was unable to control the temperature of the battery cell in case of fast discharging rate. Furthermore, the best cell arrangement in terms of cooling performance is the inline configuration and the appropriate gap between adjacent cells is about 1.5 mm

Experimental and numerical studies of one-directional and bi-directional flow conditions across tube banks heat exchanger

Bi-directional flow condition imposes different fluid dynamics and temperature changes compared to that of the usual one-directional flow condition. Bi-directional flow can be found in applications like thermoacoustic systems that offer a green technology for at least two major applications: refrigeration and power production. The technology is appealing as an alternative to traditional systems as it offers the replacement for the use of harmful working media and exhausted resources with the use of inert gaseous with relatively fewer moving mechanisms. As the fluid dynamics and heat transfer of bi-directional flow in a thermoacoustic working environment is less known, it is difficult to estimate losses and gain, especially during the design stage. This paper reveals the differences to be expected in the behaviour of flow and heat transfer through experimental as well as Computational Fluid Dynamics (CFD) results of one-directional and bi-directional flow conditions. Two different drivers were used to create the two different flow conditions: a loudspeaker for the bi-directional flow and a centrifugal blower for the one-directional flow. Both conditions were monitored based on flow amplitude that is calibrated between the two drivers. Results of velocity, temperature and, vorticity are recorded for Reynolds number that ranges between 270 and 1700. Analyses are supplemented with data from validated two-dimensional computational fluid dynamics models that were solved using the Shear-Stress-Transport (SST) k-ω turbulence model with second-order accuracy for all equations. Interesting features of differences in temperature and velocity changes between the one-directional and the bi-directional flows are reported. The temperature and velocity at upstream and downstream locations of the tube banks heat exchanger are almost the same for bi-directional cases but are significantly different when a one-directional flow is flowing over the heated tubes. In addition, the interplay between natural and forced convections is seen to affect the results that were recorded for the two flow conditions. The presence of thermally developing and fully developed regions is also discussed. The results indicate that the heat transfer behaviour of bi-directional flow is not the same as in the one-directional flow and the future calculation for heat transfer for bi-directional flow conditions of thermoacoustic must be carefully done with consideration of changes of flow conditions between the one-directional and the bi-directional flow conditions so that error could be minimized in the evaluation of the system’s performance