• International Journal of Naval Architecture and Ocean Engineering
• /
• v.4 no.2
• /
• pp.96-111
• /
• 2012

Hull Mounted Sonar (HMS) is a long range submerged vehicle's hull-mounted passive sonar system which detects low-frequency noise caused by machineries of enemy ships or submerged vehicles. The HMS needs a sound absorption /insulation multi-layer structure to shut out the self-noise from own machineries and to amplify signals from outside. Therefore, acoustic analysis of the multi-layer system should be performed when the HMS is designed. This paper simplified the HMS multi-layer system to be an infinite planar multi-layer model. Also, main excitations that influence the HMS were classified into mechanical, plane wave and turbulent flow excitation, and the investigations for each excitation were performed for various models. Stiffened multi-layer analysis for mechanical excitation and general multi-layer analysis for turbulent flow excitation were developed. The infinite planar multi-layer analysis was expected to be more useful for preliminary design stage of HMS system than the infinite cylindrical model because of short analysis time and easiness of parameter study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.1185-1191
• /
• 2001

This paper discusses an experimental method for measuring the insertion loss (IL) performance of multi-layered insulations that are used in vehicles. Instead of two adjacent reverberation chambers which are generally used to measure the transmission loss (TL) of the large sound isolation materials, air-borne sound insulation tester was utilized to determine the IL and articulation index (AI) of standardized insulation materials. In comparison to reverberation chamber method, air-borne sound insulation tester method is more space-saving, more time-saving and more simple to the automotive acoustics. From the empirical results, it is found that the performances of insulation materials are closely connected with density of polyurethane foam, thickness of heavy layer, thickness of polyurethane foam, and application ratio to panel area.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.23 no.8
• /
• pp.1110-1118
• /
• 1999

This study was to examine the effects of garment types on thermal insulation using a thermal manikin. cotton polyester wool silk and rayon were selected as outer wears like a blouse a skirt slacks and one-piece for this study Acetate was chosen as a lining. Brief and upper innerwear with long sleeves(cotton) were also chosen as the innerwear. The results were as follows: 1. The thermal insulation of the garment of single layer was in proportion to the covering area of garment in all types of clothing. 2. On adding the innerwear or the lining or both the thermal insulation of the each garment of single layer were showed a different trends by garment types. The thermal manikin insulations of one-piece dress adding the innerwear was higher than those of blouse-skirt suits. The thermal insulation of one-piece dress adding the innerwear and lining was lower than those of blouse-skirt suits. 3. The increasing rates of thermal insulation of multi-layered garments had different value by garment types but garment made of rayon and silk were showed very high increasing rates of thermal insulation. 4. The increasing rates of the thermal insulation of one-piece dress added the lining the innerwear or both except polyester showed the highest value and then blouse-slacks suits' turn came ound Blouse-skirt suits had the lowest the increasing rates of thermal insualition value.

• Transactions of the Korean hydrogen and new energy society
• /
• v.32 no.6
• /
• pp.585-591
• /
• 2021

Liquefied hydrogen have advantage which reduces the volume by about 800 times or more compared to hydrogen gas, so it is possible to increase the storage density. However, liquefied hydrogen produced by cryogenic cooling of 20 K or less at normal pressure has a problem of maximizing the insulation effect that blocks heat introduced from the outside. Representative insulation technologies include vacuum insulation and multi-layer insulation materials and in general, heat blocking is attempted by combining insulation technologies. Therefore, in this study, the pressure of the internal vacuum layer was changed to 10^-1, 10^-2, 10^-3 and 10^-4 Torr to confirm the thermal insulation performance of the vacuum jacket valve for transporting liquefied hydrogen. As a result, it was confirmed that the insulation performance improved as the degree of vacuum increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.4
• /
• pp.333-338
• /
• 2007

The object of this study is to find the optimal insulation design conditions of a HTS power cable cryostat. The optimum condition of a cable cryostat is obtained by varying types of MLIs, cable core weights, spacer diameters, winding pitches and MLI layer numbers. As the weight of cable core is increased, conduction heat transfer from surroundings to cable cryostat is increased. But as the spacer pitch is increased from 120 mm to 200 mm, the heat leak of cable cryostat remains almost constant. The optimal number of MLI layers is suggested. Double ply MLI is more effective than triple ply MLI and the insulation effect is best when the number of MLI layers is 36.

• Journal of Bio-Environment Control
• /
• v.28 no.3
• /
• pp.255-264
• /
• 2019

In this study, we conducted the hot box tests to compare the changes in thermal insulation for the four types of multi-layer thermal screens by the used period after collecting them from the greenhouses in the field when they were replaced at the end of their usage. The main materials for these four types of multi-layer thermal screens were matt georgette, non-woven fabrics, polyethylene (PE) foam, chemical cotton, etc. These materials were differently combined for each multi-layer thermal screen. We built specimens ($70{\times}70cm$) for each of these multi-layer thermal screens and measured the temperature descending rate, heat transmission coefficient, and thermal resistance for each specimen through the hot box tests. With regard to the material combinations of multi-layer thermal screens, thermal insulation can be increased by applying a multi-layered PE foam. However, it is considered that the multi-layered PE foam significantly less contributes to heat-retaining than chemical wool that forms an air-insulating layer inside multi-layer thermal screens. For the suitable heat-retaining performance of multi-layer thermal screens, basically, materials with the function of forming an air-insulating layer such as chemical cotton should be contained in multi-layer thermal screens. The temperature descending rate, heat transmission coefficient, and thermal resistance of multi-layer thermal screens were appropriately measured through the hot box tests designed in this study. However, in this study, we took into consideration only the four kinds of multi-layer thermal screens due to difficulties in collecting used multi-layer thermal screens. This is the results obtained with relatively few examples and it is the limit of this study. In the future, more cases should be investigated and supplemented through related research.

• Journal of Bio-Environment Control
• /
• v.16 no.2
• /
• pp.89-95
• /
• 2007

This study was accomplished to compare energy saving effects of several heat insulation materials in greenhouse and to develop new automatic opening and closing equipment which is suitable to the most effective heat insulation material. To find out more effective heat insulation material, the magnitude of heat transfer occurred through aluminum screen (ALS), non-woven fabric (NWF), double-layer aluminum screen with chemical cotton sheet (DAL), and multi-layer fabric screen material quilted with non-woven fabric, chemical cotton, poly foam, and polypropylene (MLF) were compared relatively. The results showed that the relative magnitude of heat transfer occurred through MLF was lower than DAL and ALS by 23.3% and 43.0% respectively. MLF screen material was the most effective compared with other heat insulation materials. But because of thickness, there was a need of new mechanism for automatic operation in greenhouse. Accordingly, new screen system using MLF-thick but profitable for keeping warm in greenhouse-was developed. Opening & closing equipment was designed to roll MLF with pipe axis during opening process and pull MLF with string during closing process with electric motors, clutches, drums, and so on. In hot pepper cultivation and energy saving test during winter time, the early stage yield of pepper under MLF screen system was higher than NWF by 27%, and gasoline consumption of MLF screen system was lower than NWF by 46%.

• Journal of Bio-Environment Control
• /
• v.28 no.3
• /
• pp.273-278
• /
• 2019

The multi-layer insulating curtains used in the experiment was produced in six combinations using non-woven fabric containing aerogel and compared and analyzed by measuring heat flux and heat perfusion rates due to weight, thickness and temperature changes. Using silica aerogel, which have recently been noted as new material insulation, this study tries to produce a new combination of multi-layer insulating curtains that can complement the shortcomings of the multi-layer insulating curtains currently in use and maintain and improve its warmth, and analyze the thermal properties. The heat flux means the amount of heat passing per unit time per unit area, and the higher the value, the more heat passing through the multi-layer insulating curtain, and it can be judged that the heat retention is low. The weight and thickness of multi-layer insulation curtains were found to be highly correlated with thermal insulation. In particular, insulation curtains combined with aerogel meltblown non-woven fabric had relatively higher thermal insulation than insulation curtains with the same number of insulation materials. However, the aerogel meltblown non-woven fabric is weak in light resistance and durability, and there is a problem that the production process and aerogel are scattering. In order to solve this problems, the combination of expanded aerogel non-woven fabric and hollow fiber non-woven fabric, which are relatively simple manufacturing processes and excellent warmth, are suitable for use in real farms.

• Progress in Superconductivity and Cryogenics
• /
• v.22 no.1
• /
• pp.17-23
• /
• 2020

Cryogenic insulation systems, with proper materials selection and execution, can offer the highest levels of thermal performance. Insulations are listed in order of increasing performance and, generally, in order of increasing cost. The specific insulation to be used for a particular application is determined through a compromise between cost, ease of application and the effectiveness of the insulation. Consequently, materials, representative test conditions, and engineering approach for the particular application are crucial to achieve the optimum result. The present work is based on energy cost balance for optimizing the thickness of insulated chambers, using foamed or multi layered cryogenic shell. The considered insulation is a uniformly applied outer layer whose thickness varies with the initial and boundary conditions of the studied vessel under steady-state radial heat transfer. An expression of the optimal insulation thickness derived from the total cost function and depending on the geometrical parameters of the container is presented.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.52 no.6
• /
• pp.271-277
• /
• 2003

It is important to control layer current distributions of coaxial multi-layer HTS cables, because a homogeneous layer current distribution decreases AC loss and can supply the largest operational current. We have extended the theory that treat the operational current more than the critical current by considering V-I nonlinear characteristics of HTS tapes including flux flow resistance and contacting resistance between the cable and terminals. It is important to investigate the current distribution under the condition of operational current more than the critical current of cable, because the cable has experiences of fault current. In order to verify the extended theory, we have fabricated a two layers cable with the same twisting layer pitch. It was observed that almost all the operational current less than the critical current flowed on the outer layer because of its lower inductance. In case of operational current more than critical currents of layers, the flux flow resistances affect strongly current waveform and thereby the currents of layers were determined by the flux flow resistances. And we investigated breakdown characteristics in $LN_{2}$/paper composite insulation system for the application to a HTS cable. In this experiment, we got some information out of that the electrical characteristics of the insulation materials depends on the condition of butt gap.