Semiconductor Science and Information Devices

Convection Heat Transfer from Heated Thin Cylinders Inside a Ventilated Enclosure

2022-10-09T10:47:55+08:00

Experimental study was conducted to determine the effect of velocity of axial fan, outlet vent height, position, area, and aspect ratio (h/w) of ventilated enclosure on convection heat transfer. Rectangular wooden ventilated enclosure having top and front transparent wall was made up of Perspex for visualization, and internal physical dimensions of box were 200 mm × 200 mm × 400 mm. Inlet vent was at bottom while outlet vents were at the side and top wall. Electrically heated cylindrical heat source having 6.1 slenderness ratio was fabricated and hanged at the centre of the enclosure. To calculate heat transfer rates, thermocouples were attached to the inner surface of heat source with silica gel. Heat source was operated at constant heat flux in order to quantify the effect of velocity of air on heat transfer. It was observed that average Nusselt number was increased from 68 to 216 by changing velocity from 0 to 3.34 m/s at constant modified Grashof number i.e. 5.67E+09. While variation in outlet height at the front wall did not affect heat transfer in forced convection region. However, Nusselt number decreased to 5% by changing the outlet position from top to the front wall or by 50% reduction in outlet area during forced convection. Mean rise in temperature of enclosure increased from 8.19 K to 9.40 K by increasing aspect ratio of enclosure from 1.5 to 2 by operating heat source at constant heat flux i.e. 541.20 w/m2.

Experimentation on Optimal Configuration and Size of Thin Cylinders in Natural Convection

2022-10-09T10:47:55+08:00

In this paper, an experimental study of laminar, steady state natural convection heat transfer from heated thin cylinders in an infinite air medium has been reported. Two electrically heated cylinders having the same slenderness ratio (L/D) i.e. 6.1 but different diameters i.e. 3.8 cm and 5.08 cm were used. 105 experiments were carried out to study the effect of diameter and inclination angle of thin cylinder on natural convection heat transfer. After mandatory corrections of radiation and endcap heat losses, convective heat transfer results were presented in the form of local and average dimensionless numbers. For vertical configuration of thin cylinder, Nusselt number was varied from 52.99 to 95.10 corresponding to 1.28×108≤Ra*L≤1.08×1010. While for horizontal configuration,Nusselt number was varied from 10.74 to 17.78 corresponding to 9.42×104≤Ra*D≤8.17×106. Results were compared with the published data and found satisfactory as the maximum percentage difference was only 3.09%. The essence of research is that the heat transfer coefficient increases with decrease in diameter and increase in inclination angle. Smoke flow visualization was done to capture patterns of fluid flow. Finally, comparison was made to quantify increase in Nusselt number from slender cylinder as compared to the flat plate.

Electronic Structure of CdS Nanoparticles and CdSe/CdS Nanosystems

2022-10-09T10:47:55+08:00

The electronic states of “wurtzite” CdS nanoparticles and CdSe/CdS nanosystems with up to 80 pairs of Cd-Se or CdS atoms were calculated.The results for CdS particles were compared with the results obtained earlier for CdSe particles of the same size and with published calculations of other authors. The calculated gap values in the range of 2.84 eV ~ 3.78 eV are typical for CdS particles of studied sizes in accordance with results of published data. The CdSe/CdS nanosystems were considered as layered ones and as quantum dots. The layered CdSe/CdS systems with twolayer CdS coverings can be interpreted in terms of combinations of two semiconductors with different energy band gaps (2.6 eV and 3.3 eV), while analogous systems with single-layer CdS coverings do not demonstrate a two-gap electron structure. Simulation of a CdSe/CdS quantum dot shows that the single-layer CdS shell demonstrates a tendency for the formation of the electronic structure with two energy gaps: approximately of 2.5 eV and 3.0 eV.

Air Pollution Monitoring System Using Micro Controller Atmega 32A and MQ135 Gas Sensor at Chandragiri Municipality of Kathmandu City

2022-10-09T10:49:59+08:00

Air is one of the essential elements of human’s surroundings. The earth’s atmosphere is full of air which contains gases such as Nitrogen, Oxygen, Carbon Monoxide and traces of some rare elements. But quality of the air has been degrading for some decades due to various activities conducted by the human beings that directly or indirectly affect the atmosphere leading to the air pollution. There are different techniques to measure air quality.However, with the evolution of time the expensive and less efficient analog devices have been replaced by more efficient and less expensive electronics device. In this research, MQ135 sensor is used to measure air quality of a particular location. I2C display is used to monitor the data. Indeed, with the increasing in number of vehicles, unplanned urbanization and rapid population growth, air pollution has considerably increased in the last decades in various areas of Kathmandu. Thus, this project ‘Air Pollution Monitoring System’ was focused on collection of the data specific location of Chandragiri municipality of Kathmandu city. In conclusion,analysis of the data is done with the help of origin software which shows that the Arduino device in this device works perfectly for measuring the air pollution. Air quality of the selected area is found to be less than 500 PPM which concludes that the air quality of this area is normal.

Signal and Power Integrity Challenges for High Density System-on-Package

2022-10-09T10:47:55+08:00

As the increasing desire for more compact, portable devices outpaces Moore’s law, innovation in packaging and system design has played a significant role in the continued miniaturization of electronic systems.Integrating more active and passive components into the package itself, as the case for system-on-package (SoP), has shown very promising results in overall size reduction and increased performance of electronic systems.With this ability to shrink electrical systems comes the many challenges of sustaining, let alone improving, reliability and performance. The fundamental signal, power, and thermal integrity issues are discussed in detail, along with published techniques from around the industry to mitigate these issues in SoP applications.