Review of regenerator materials applicable for miniature Stirling cryocoolers

Kishor Kumar V. V. 대한설비공학회 2021 International Journal Of Air-Conditioning and Refr Vol.29 No.4

Miniature Stirling coolers are preferred to provide cryogenic cooling for Infra-Red (IR) sensors used for communication, military and space applications. They provide 0.25-1.5 W of cooling effect at 80 K. Miniature Stirling coolers used for space applications are time tested, reliable and have the maximum COP compared to other types of coolers. Helium is used as the working fluid because of its low boiling point, high thermal conductivity, high ratio of specific heats and inert gas properties.A regenerator is the primary heat exchanger in the system which periodically exchanges heat with the cold and hot gases passing through the regenerator material. The effectiveness of the regenerator is the most important parameter influencing the cooling effect produced by the system. For the optimum performance of the cryocooler, the regenerator should have maximum heat transfer area, minimum void volume, minimum pressure drop, large heat capacity ratio between matrix material and gas and minimum longitudinal conduction. Since some of these requirements are conflicting in nature, the design of the regenerator becomes a challenge in the overall design of the cooler. A state of the art review of regenerator materials, design and operation are presented in this paper. The different sources of regenerator losses and the issues related to regenerator design and optimization are discussed in detail. Results of various experimental and numerical investigations conducted on Stirling regenerator are discussed and the recent developments in material selection and design are highlighted.

Prediction of Darcy Permeability and Forchheimer’s Coefficient of Porous Structures Relevant to Regenerator of a Stirling Cryocooler Using a Correlation Based Method

V. V. Kishor Kumar,Biju T. Kuzhiveli 대한설비공학회 2017 International Journal Of Air-Conditioning and Refr Vol.25 No.2

A regenerative heat exchanger is the most vital component in the design of a Stirling cryocooler. Computational Fluid Dynamics (CFD) is the best technique for the design and prediction of the performance of a regenerator. The reliability of the simulation results depend on the accuracy of the Darcy permeability KK and Forchheimer’s inertial coefficient CfCf used for modeling the momentum transfer in porous media. Usually these coefficients are calculated from pressure drop data obtained from experiment. Because of the requirement of sophisticated equipments for the measurement and analysis of data, experimental study becomes expensive. This paper proposes a friction factor correlation-based method for the prediction of directional permeability and Forchheimer’s inertial coefficient of wire mesh structures relevant to Stirling cryocooler. The friction factor for the flow of helium through #325, #400 and #635 SS wire matrices with porosities of 0.6969, 0.6969 and 0.6312 are calculated using standard correlations and compared with the friction factor given by Clearman et al. based on steady flow experimental study. The friction factor obtained from Blass and Tong/London correlations are in agreement with that of Clearman et al. The viscous and inertial resistances are calculated from the friction factor obtained from Blass and Tong/London correlations. Using these values, the regenerator was modeled as a porous media in Fluent. From the steady flow simulation, pressure drop at different mass flow rates (0.08–1.44g/s) is obtained. The maximum deviation of predicted pressure drop from the reported experimental data is 15.14%. The Darcy permeability KK and Forchheimer’s inertial coefficient CfCf obtained from correlation-based method was used for modeling the oscillatory flow of helium through a #400 regenerator. The pressure amplitude and phase at regenerator exit were obtained at different frequencies. The average deviation of predicted pressure amplitude from the experimental data is 15.83%. The model could predict the phase angle also accurately. Therefore, the proposed method can be used to calculate the hydrodynamic parameters of woven wire screen matrices applied to Stirling cryocoolers.

Acreage estimation of kharif rice crop using Sentinel-1 temporal SAR data

Subbarao Nandepu V. V. S. S. Teja,Mani Jugal Kishore,Shrivastava Ashish,Srinivas Kumar Samayamantula,Varghese A. O. 대한공간정보학회 2021 Spatial Information Research Vol.29 No.4

Rice is one of the most important food crop in India covering about one-fourth of the total cropped area. India is the second largest producer and consumer of rice and accounts for 21% of the world’s total rice production. Rice is fundamentally a kharif season crop and grown in mainly rainfed areas. Recently there is a considerable increase in production, area and yield of rice crop in India. Temporal monitoring of crop area under cultivation is essential for the sustainable management of agricultural activities on both national and global levels. The present study is envisaged to estimate area under kharif rice using multi-temporal Sentinel-1 Synthetic Aperture Radar (SAR) data with dual polarization (VH and VV) in Bhandara district of Maharashtra. The geographical area of Bhandara district is 4087 square kilometres and lies in between 20640 030 ’ to 21600 180 ’ N latitude and 79440 930 ’ to 80080 700 ’ E longitude. The rice area is extracted using Random Forest (RF) classification techniques available in SNAP tool and validated using the ground observation collected from the field. An area of 1760 square kilometres was found under kharif rice out of 4087 square kilometres area of entire Bhandara district. The rice is predominant crop and covered around 43% of the total geographical area of Bhandara district during kharif season. The user accuracy (omission error), producer accuracy (commission error) for rice crop, overall accuracy and Kappa coefficients were 82.7, 90.0, 91% and 0.80, respectively. The study found that SAR data can be successfully used for acreage estimation with RF classifier.

A review on solar photovoltaic-powered thermoelectric coolers, performance enhancements, and recent advances

Kaiprath Jayadeep,V. V. Kishor Kumar 대한설비공학회 2023 International Journal of Air-Conditioning and Refr Vol.31 No.1

The average global temperature has increased by approximately 0.7 °C since the last century. If the current trend continues, the temperature may further increase by 1.4 – 4.5 °C until 2100. It is estimated that air-conditioning and refrigeration systems contribute about 15% of world electrical energy demand. The rapid depletion of non-renewable resources such as fossil fuels and the associated emissions lead to the development of alternative solutions which employ renewable energy resources for refrigeration. The conventional vapour compression (VC) and vapour absorption (or adsorption) (VA) refrigeration systems usually rely on fossil fuels for their operation which ultimately leads to large amount of CO 2 emissions. Thermoelectric (TE) refrigeration systems working on the principle of Peltier effect are an alternative for the conventional systems. The thermoelectric refrigerators will not produce any noise and vibration due to the absence of any moving parts. They are refrigerant-free as electrons act as heat carriers. The greatest advantage of a TE system is that it can directly be powered by solar photovoltaic (PVs) since they give a DC output. The main drawback of thermoelectric refrigeration system is their low coefficient of performance (COP). The COP of a thermoelectric cooler (TEC) operating with a temperature difference of 20 °C is about 0.5. The improvement of heat transfer at the hot side of the cooler is a key aspect for a better COP. A good thermoelectric material should possess high Seebeck coefficient, low-thermal conductivity, and high electrical conductivity. Since these three are interrelated, these parameters must be optimized. It is important to reduce the electric contact and thermal resistances and get an optimized configuration of thermoelectric cooler. The recent developments in material science has enabled the usage of better thermoelectric materials with a positive Thomson coefficient to produce a better cooling performance. The total efficiency of a TEC powered by solar cell is the product of PV system efficiency and the COP of the cooler. Therefore, the enhancement of PV system efficiency and the selection of materials with better thermoelectric performance are important in the design of solar-powered thermoelectric cooler. The performance of solar cell-powered TEC depends on solar insolation which varies with weather, climate, and geographic location. Due to the variation in insolation and unavailability of solar power in the night, a battery must be used to store the energy. This paper presents a comprehensive review about the thermoelectric coolers and the dependance of performance of TECs on various operating and design parameters. The results reported for the performance improvement of solar PV-powered thermoelectric coolers were critically analysed.

Isolation and Characterization of Mucous Exopolysaccharide (EPS) Produced by Vibrio furnissii Strain VB0S3

( Bramhachari ),( P. V. ),( P. B. Kavi Kishor ),( R. Ramadevi ),( Ranadheer Kumar ),( B. Rama Rao ),( Santosh Kumar Dubey ) 한국미생물생명공학회 2007 Journal of microbiology and biotechnology Vol.17 No.1

Effect of Wall Thermal Boundary Conditions on Flame Dynamics of CH4-Air and H2-Air Mixtures in Straight Microtubes

Singh, Aditya P.,Kishore, V. R.,Yoon, Y.,Minaev, S.,Kumar, Sudarshan Taylor Francis 2017 Combustion science and technology Vol.189 No.1

Burning velocities of DME(dimethyl ether)-air premixed flames at elevated temperatures

Varghese, R.J.,Kishore, V.R.,Akram, M.,Yoon, Y.,Kumar, S. Pergamon Press 2017 Energy Vol.126 No.-

This paper reports the measurement of laminar burning velocities of DME (dimethyl ether)-air mixtures at higher mixture temperatures using planar flames stabilized in a controlled temperature mesoscale diverging channel. The reliability of this technique for flame speed measurement at high mixture temperatures has been established through various numerical studies using detailed 3-D computational model for DME-air mixtures. The distribution of fuel-air mass flux, reaction zone, and flame shape indicate that a planar flame is indeed formed in both transverse and depth directions of the channel. The stabilized flame is independent of any stretch effects except mild hydrodynamic strain due to channel divergence (30-50 s<SUP>-1</SUP>), and measured values of laminar burning velocities are within +/-5% of the actual value. The experiments were carried out at various equivalence ratios (φ = 0.7-1.4) and elevated mixture temperatures (350-640 K). The burning velocities and temperature exponents were determined using the planar flames stabilized at different mixture inlet velocities and temperatures. Slightly rich mixtures (φ = 1.1) point to the maximum burning velocity, in good agreement with recent literature at ambient conditions. Temperature exponents for different equivalence ratios increase to both sides of φ = 1.1. Numerically calculated laminar burning velocities with different chemical kinetic schemes compared well with the measured burning velocities at higher mixture temperatures.

Smart City IoT System Network Level Routing Analysis and Blockchain Security Based Implementation

Bommu Samuyelu,M Aravind Kumar,Babburu Kiranmai,N Srikanth,Thalluri Lakshmi Narayana,G V. Ganesh,Gopalan Anitha,Mallapati Purna Kishore,Guha Koushik,Mohammad Hayath Rajvee,S S. Kiran 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.2

This paper demonstrates, network-level performance analysis and implementation of smart city Internet of Things (IoT) system with Infrastructure as a Service (IaaS) level cloud computing architecture. The smart city IoT network topology performance is analyzed at the simulation level using the NS3 simulator by extracting most of the performance-deciding parameters. The performance-enhanced smart city topology is practically implemented in IaaS level architecture. The intended smart city IoT system can monitor the principal parameters like video surveillance with a thermal camera (to identify the virus-like COVID-19 infected people), transport, water quality, solar radiation, sound pollution, air quality (O3, NO2, CO, Particles), parking zones, iconic places, E-suggestions, PRO information over low power wide area network in 61.88 km × 61.88 km range. Primarily we have addressed the IoT network-level routing and quality of service (QoS) challenges and implementation level security challenges. The simulation level network topology analysis is performed to improve the routing and QoS. Blockchain technology-based decentralization is adopted to enrich the IoT system performance in terms of security.