Positive Pressure Conditions Research Articles

Moist air permeability characteristics of flexible contact gaskets used in refrigerators

Flexible contact gasket is a significant component affecting the sealing performance of the refrigerator. However, few studies were conducted on the permeability characteristics of moist air through refrigerator gaskets. The purpose of this study is to explore the permeability characteristics including permeation paths size, flow type, modeling and temperature-humidity-pressure-structure effect. The characteristic scale of the interface of permeation paths is observed as 10−5 m in the free-state by atomic force microscope. The equation of Knudsen number and contact stress relation is established to judgment the flow types. By comparing the critical and simulated contact stresses, it is inferred that moist air simultaneously occurs slip, transition and free-molecular flows. A multi-scale coupling model of permeation rate is constructed to obtain the apparent permeability coefficient characterizing the permeability intensity. The air pressure difference affects the permeability characteristics in the form of direct driving force and changing the contact stress of the interfaces. Free-molecular flow mainly occurs under the negative pressure condition with inhalation coefficient of 2.26 × 10−5∼2.84 × 10−5 m2, while the slip flow mainly occurs under the positive pressure conditions with exhalation coefficient of 2.87 × 10−5∼4.65 × 10−5 m2. The essence of enhancing the sealing performance of structural improvement is to increase the contact stress and length of permeation path. By increasing the height, increasing the inclination angle, adding the auxiliary edges and adding an auxiliary airbag, the inhalation coefficient of moist air, the exhalation coefficient of moist air and the inhalation coefficient of water vapor are decreased by 54.82 %, 51.46 % and 66.04 %.

The techno-economic-environmental analysis of a pilot-scale positive pressure biomass gasification coupled with coal-fired power generation system

Biomass gasification coupled with coal-fired power generation (BGCPG) is of great significance for alleviating energy shortages and environmental pollution. Here we propose, analyze and validate a BGCPG system under positive pressure for cleaner applications based on a pilot-scale fluidized bed gasification plant and discussed the possibility of higher economic output and operating stability with reduced pollution emissions. Then the effects of temperature, air equivalence ratio and operating pressure were experimentally investigated for parameter optimization. The processes under positive and negative pressure were simulated and compared based on the pilot-scale experimental data, and the effects of the mixing ratio and operating pressure were investigated. Furthermore, the economic and sensitivity analyses were conducted for both a traditional coal-fired power plant and simulated BGCPG systems. The results demonstrated that the gas calorific value, gas yield, and gasification efficiency increased with the gasification temperature increasing, whereas the opposite trend was observed for the gas calorific value with the air equivalence ratio increasing. The positive pressure operation had little influence on the gasification process. The flue gas flow rate increased, and the furnace temperature decreased with an increase in the mixing ratio of biomass and coal. The reduction in fuel NOx and SOx was caused by the decreasing coal content, whereas the decrease in thermal NOx and boiler thermal efficiency was due to the increasing exhaust temperature. Compared with functioning under negative pressure, operation under positive pressure at a 20% mixing ratio could effectively reduce the pollutant emissions of SOx, NOx and dust by 5.64%, 8.8% and 20%, respectively. The generation costs of the BGCPG system under negative and positive pressure conditions were 0.05593 $/kW·h and 0.05582 $/kW·h respectively, indicating that a positive operating pressure would increase the economic benefit of a 660 MW generator by 5.808 × 105 $/year. These findings suggest the effectiveness of clean power generation with a higher economy and lower pollution emissions.

Derivations of Positive Pressure Condition for Development of Foldable Safe Pathway in Railway Tunnel Fires

Derivations of Positive Pressure Condition for Development of Foldable Safe Pathway in Railway Tunnel Fires

G-23 トラップの性能試験法に関する研究 : (その1)正圧時の封水損失特性

G-23 トラップの性能試験法に関する研究 : (その1)正圧時の封水損失特性

Centrifuge Rubber Suspension Spring Characteristics of the Experimental Research

This article has carried on the description about characteristic of rubber damping spring. According to different pressure and different temperature, The paper has carried on analysis using both static and dynamic test method. Obtaining the conclusion that the pressure change has little effect on the shear stiffness of rubber spring in positive pressure conditions,. Environmental temperature on the performance have larger effect. Therefore, we should carry on temperature test in the use of rubber elasticity components to ensure that the rubber spring meet the requirements in a certain temperature range

Experimental study of a novel CaCl 2/expanded graphite-NH 3 adsorption refrigerator

A novel CaCl 2/expanded graphite-NH 3 adsorption refrigerator is developed and tested. Only three valves are installed in this refrigerator and they all work at the same positive pressure condition, so the operating reliability of the refrigerator is greatly improved. The experimental results show that the refrigerating power Q CP, COP, SCP, electricity COP El, and volume refrigerating density Q CP-V of the refrigerator are 11.4 kW, 0.27, 422.2 W/kg, 32.6 and 57 kW/m 3, respectively, under the following conditions: the temperature of heating vapor is from 120 °C to 140.3 °C, the cooling water temperature is 25 °C, the evaporation temperature is −15 °C, the heating/cooling time is 25 min including 45 s mass recovery time. The SCP and volume refrigerating density of this refrigerator are about 1.8 times and 1.5 times that of the maximum of the former test results by other researchers.

Experimentelle Grundlagen - Druckwerte unter Vakuumtherapie-Schwämmen - eine In-vitro- und In-vivo-Untersuchung

Measurement of the pressure during V.A.C.(R)-therapy in superficial parts of the affected soft tissue as well as at the soft tissue/foam-interface, measurement of pressure values along bigger distances in the foam and the comparison of pressure transfer between polyurethane and polyvinyl-alcohol foams. A multi-channel electronic transducer-tipped catheter system based on the piezo-resistant principle was used. Measurement was performed on a plain table surface, at a bovine muscle as well as in human tibial anterior muscle of a patient after fasciotomy. Applied pressure values by V.A.C.(R)-therapy-units were 50 to 200 mm Hg (continuous suction modus). 100 % pressure transition through vacuum-therapy-foams to wound surface, almost 100 % pressure transition even along 60 cm in very large polyurethane-foams using only one trac-pad connector. Pressure values > 125 mm Hg using polyvinyl-alcohol-foams showed a reduction of up to 25 % in distances > 15 cm from trac-pad-connector. On the surface of the affected soft tissue there are negative and positive pressure values (25 % quartile: - 25 mm Hg; 75 % quartile: + 15 mm Hg). Pore walls of the foam can produce positive pressure conditions resulting in soft tissue compression and consecutively hypoperfusion or ischemia. V.A.C.(R)-therapy seems to produce an heterogeneity of pressure distribution at the wound ground leading to pressure gradients and facilitating drainage of interstitial fluid. This mechanism could explain the anti-edema effects of V.A.C.(R)-therapy resulting indirectly in an increased nutritive perfusion.

負圧領域における抵抗容量系の空気圧応答

A vacuum is frequently utilized for handling systems in factory automation. Because of the vacuum pressure, the change in state of air may differ from that of positive pressure systems during charge or discharge. However, pressure and temperature responses in the vacuum condition have not been examined up to now. Therefore, in this study the pressure and temperature responses of RC circuit in the vacuum condition is investigated. As a result, the research can be summarized as follows: 1) When the positive and vacuum pressure are compared in the same pressure ratio, it is found that the heat transfer rate is larger in the positive pressure case, because of the larger mixing effect.2) The temperature responses are determined by the thermal-time constants. Since the vacuum pressure gets smaller thermal-time constants which concern the air density, the temperature responses show a smaller variation than those of positive pressure. Therefore, the pressure response is slower in the case of negative pressure.The analysis method of pressure responses used in positive pressure conditions is feasible in the vacuum condition. This has been verified by experiment.

The numerical simulation of thermal-gradient CVI process on positive pressure condition

Normally, carbon/carbon (C/C) composites are manufactured by negative pressure CVI process. The products manufactured by this process may have higher density, but it takes a very long time and the reaction gases cannot be utilized adequately. The experimental results indicated that the densification rate of C/C composites can be greatly increased and the reaction gas can be utilized more adequately by applying positive pressure chemical vapor infiltration (CVI) process. However, the density homogeneity of the products manufactured by this process is relatively lower. To solve this problem, numerical simulation technology is applied to analyze the characters and feasibility of thermal-gradient CVI (TCVI) process on positive pressure condition. The result indicates that the thermal-gradient CVI process can increase the density homogeneity and densification rate of C/C composites greatly.

Anisotropic asymptotic behavior in chaotic inflation

We show that homogeneous cosmological models which are coupled to a scalar field can only approach isotropy at infinite times if the underlying Lie group is admitted by a Friedmann-Robertson-Walker model. This result generalises a theorem of Collins and Hawking for matter satisfying the positive pressure condition to scalar fields with an arbitrary positive, convex potential having a local minimum at φ 0 with V[ φ 0]=0.