S. Kasthurirengan

Investigations into the thermal performance of multilayer insulation (300- 77 K) Part 1: Calorimetric studies

The thermal performance of multilayer insulation (MLI), consisting of double aluminized Mylar radiation shields and nylon net thermal spacers, was evaluated using a double guarded cylindrical calorimeter and a tank calorimeter over the temperature range 300-77 K. The degradation in the effective thermal conductivity of MLI was evaluated to be 1.68 using the calorimeters. The optimum number of layers for the MLI was 40 to 50 at a layer density of 25 layers

Optimization of thermoacoustic refrigerator using response surface methodology

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Optimization of thermoacoustic primemover using response surface methodology

. The temperature profile and heat flux through the MLI were obtained as a function of vacuum level for different numbers of insulation layers. The temperature profile of the MLI indicates the relative predominance of the conduction and radiation components of heat transfer through the insulation. It is observed that for a given number of layers, the temperature of a specific layer between the cold and warm boundaries decreases with an increase in chamber pressure and vice versa.

Investigations into the thermal performance of multilayer insulation (300-77 K) Part 2: Thermal analysis

Thermoacoustic refrigerator (TAR) converts acoustic waves into heat without any moving parts. The study presented here aims to optimize the parameters like frequency, stack position, stack length, and plate spacing involving in designing TAR using the Response Surface Methodology (RSM). A mathematical model is developed using the RSM based on the results obtained from DeltaEC software. For desired temperature difference of 40 K, optimized parameters suggested by the RSM are the frequency 254 Hz, stack position 0.108 m, stack length 0.08 m, and plate spacing 0.0005 m. The experiments were conducted with optimized parameters and simulations were performed using the Design Environment for Low-amplitude ThermoAcoustic Energy Conversion (DeltaEC) which showed similar results.

Use of narrow-pore filters in He II transfer devices - new results

Thermoacoustic engines are energy conversion devices that convert thermal energy from a high-temperature heat source into useful work in the form of acoustic power while diverting waste heat into a cold sink; it can be used as a drive for cryocoolers and refrigerators. Though the devices are simple to fabricate, it is very challenging to design an optimized thermoacoustic primemover with better performance. The study presented here aims to optimize the thermoacoustic primemover using response surface methodology. The influence of stack position and its length, resonator length, plate thickness, and plate spacing on pressure amplitude and frequency in a thermoacoustic primemover is investigated in this study. For the desired frequency of 207 Hz, the optimized value of the above parameters suggested by the response surface methodology has been conducted experimentally, and simulations are also performed using DeltaEC. The experimental and simulation results showed similar output performance.

Studies on Performance of Thermoacoustic Prime Mover

Simple analytical methods have been employed for heat transfer analysis of experimental data obtained through calorimetric investigations on multilayer insulation (MLI). Sectional heat transfer analysis has shown that the effective thermal conductivity of the MLI varies from section to section of the insulation structure and it has a peak which lies between the middle and warm boundary regions of the MLI. This could be attributed to a peak in residual gas conduction in this region. The theoretical estimation of heat flux through MLI, using a simple analytical model, is also discussed in this paper. This model takes into consideration the non-linear temperature profile of the insulation. The computed heat flux using this model gives a lower (2 to 4 times) value in comparison with the heat flux estimated from calorimetric measurements. A refined model has been suggested which includes the residual gas conduction also in MLI.

Experimental studies on cool-down and mass flow characteristics of a demountable liquid nitrogen transfer line

With the aim of finding simple methods for the fabrication of He II refilling devices, He II flow has been studied through filters made from various fine powders (oxides and metals, grain sizes in the range 0.05–2 μm) by compacting them under pressure. The results obtained for the different states of He II flow, especially in the “breakthrough” and “easy flow” range, are explained by the fountain effect, He II hydrodynamics and the choking effect. According to the results, pressedpowder filters can be classified into three groups with different flow characteristics, of which the “good transfer filters” with a behaviour neatly described by simple theory are suitable for use in He II refilling devices.

Development of pilot plant for cryogrinding of spices : A method for quality improvement

Thermoacoustic engines are the devices that convert thermal energy into acoustic energy without moving parts. The main objective of this study is to analyze the performance of a thermoacoustic prime mover measured in terms of onset temperature difference, frequency, and pressure amplitude by varying resonator, stack length, and plate thickness. From the experiments, it is observed that onset temperature difference and pressure amplitude increases with increase in resonator and stack length with minimum plate thickness, whereas the frequency increases with decrease in resonator and stack length with higher plate thickness. The experimental results are compared with simulated results via Design Environment for Low Amplitude Thermoacoustic Energy Conversion software (Los Alamos National Laboratory, Los Alamos, New Mexico, USA).

Studies on helium flow in experimental loops with different impedances operated with fountain effect pumps

A demountable transfer line has been designed and fabricated to carry out experimental studies on cool-down time and mass flow characteristics of a liquid nitrogen transfer line held in a horizontal position. The effects of varying degrees of vacuum in the interspace on the cool-down time and mass flow rates have been evaluated. It has been found that during the initial phase of cool-down, lines with coarse vacuum perform better than high-vacuum-insulated lines. The performances of multilayer-insulated lines and lines with interspace medium of carbon dioxide have been evaluated as well as that of bare line exposed to an ambient environment. An experimental correlation has been developed to predict the cool-down time as a function of vacuum level and supply dewar pressure.

Experimental and theoretical investigation of thermoacoustic prime mover

The development of a pilot plant for cryogrinding of spices is discussed in this paper. The unit has an indigenously designed and developed cryogenic screw cooler for optimal utilization of liquid nitrogen along with a digital signal processing system (DSP) for liquid nitrogen spray and automatic temperature control. In the first part, the advantages of cryogrinding over conventional grinding are described. The latter part discusses the details of the pilot plant, along with preliminary experimental studies using pepper as the sample. Experimental results clearly indicate the quality improvement of the cryoground spice in terms of increased volatile oil contents and flavour components.