速热式热水器缓冲包装设计研究

本文以一款速热式热水器包装为研究对象,对于市场应用范围较广的EPS缓冲垫层进行分析,找出现有方案的不足。通过瓦楞纸板组合结构的设计,完成此产品EPS包装方案的替代。简要介绍瓦楞纸板方案设计策略及各部分功用,并进行模拟运输实验验证。

Simulation study on combustion system of tankless gas water heater

This paper simulates the combustion system of a regular tankless gas water heater under different static pressure conditions.The simulation results are in accordance with the test results.It proves that the used physical and mathematical models are reasonable.The results show that the flame height and the excess air ratios depend on the system pressure drop but not on the absolute pressure at the combustion chamber.The pressure drop and the amount of combustion air have an inverse relationship with CO generation,and they also impact on the temperature and velocity fields.To reduce CO emission,a stronger fan is needed to provide extra pressure head to ensure that enough combustion air is introduced into the system.This study provides a useful research tool to develop products through computational fluid dynamic analysis and laboratory testing.

Soil respiration under three different land use types in a tropical mountain region of China

Soil respiration (SR) Wis one of the largest contributors of terrestrial CO_2 to the atmosphere.Environmental as well as physicochemical parameters influence SR and thus, different land use practices impact the emissions of soil CO_2. In this study, we measured SR, bi-monthly, over a one-year period in a terrace tea plantation, a forest tea plantation and a secondary forest, in a subtropical mountain area in Xishuangbanna, China. Along with the measurement of SR rates, soil characteristics for each of the land use systems were investigated. Soil respiration rates in the different land use systems did not differ significantly during the dry season, ranging from2.7±0.2 μmol m^(-2) s^(-1) to 2.8±0.2 μmol m^(-2) s^(-1). During the wet season, however, SR rates were significantly larger in the terrace tea plantation(5.4±0.5 μmol m^(-2)s^(-1)) and secondary forest(4.9±0.4 μmol m^(-2)s^(-1)) than in the forest tea plantation(3.7±0.2 μmol m^(-2) s^(-1)).This resulted in significantly larger annual soil CO_2 emissions from the terrace tea and secondary forest,than from the forest tea plantation. It is likely that these differences in the SR rates are due to the 0.5times lower soil organic carbon concentrations in thetop mineral soil in the forest tea plantation, compared to the terrace tea plantation and secondary forest.Furthermore, we suggest that the lower sensitivity to temperature variation in the forest tea soil is a result of the lower soil organic carbon concentrations. The higher SR rates in the terrace tea plantation were partly due to weeding events, which caused CO_2 emission peaks that contributed almost 10% to the annual CO_2 flux. Our findings suggest that moving away from heavily managed tea plantations towards low-input forest tea can reduce the soil CO_2 emissions from these systems. However, our study is a casestudy and further investigations and upscaling are necessary to show if these findings hold true at a landscape level.

Large Area Thermionic Cathode and Its Prilimiary Experimental Results

A 2MeV thermionic cathode test stand was established to meet the requirement of the large area thermionic cathode system.A 100ram in diameter type'B'thermionic dispenser cathode was developed.A 1000A emission current was produced at the voltage of the diode about 1.8MV,the pulse width about 90ns(FWHM),and the cathode temperature about 1350℃.The emission current density is 12A/cm^2.The results indicate that a large area thermionic cathode which produces high quality and high current electron beams is visible.The results also indicate that the ability of cathode emission relies on the diode-vacuum and cathode-temperature.

Velocity Profiles between Two Baffles in a Shell and Tube Heat Exchanger

Heat exchangers are extensively utilized for waste heat recovery,oil refining,chemical processing,and steam generation.In this study,velocity profiles are measured using a 3D particle image velocimetry(PIV)system between two baffles in a shell and tube heat exchanger for parallel and counter flows.The PIV and computational fluid dynamics results show the occurrence of some strong vectors near the bottom.These vectors are assumed due to the clearance between the inner tubes and the front baffle.Therefore,the major parts of the vectors are moved out through the bottom opening of the rear baffle,and other vectors produce a large circle between the two baffles.Numerical simulations are conducted to investigate the effects of the baffle on the heat exchanger using the Fluent software.The k-εturbulence model is employed to calculate the flows along the heat exchanger.

A New Method of Thermal Protection by Opposing Jet for a Hypersonic Aeroheating Strut

This paper presents the numerical investigation of thermal protection of scramjet strut by opposing jet in supersonic stream of Mach number 6 with a hydrogen fueled scramjet strut model using CFD software. Simulation results indicate that when a small amount of fuel is injected from the nose of the strut, the bow shock is pushed away from the strut, and the heat flux is reduced in the strut, especially at the leading edge. Opposing jet forms a recirculation region near the nozzle so that the strut is covered with low temperature fuel and separated from free stream. An appropriate total pressure ratio can be used to reduce not only aerodynamic heating but also the drag of strut. It is therefore concluded that thermal protection of scramjet strut by opposing jet is one of the promising ways to protect scramjet strut in high enthalpy stream.

Velocity Profiles between Two Baffles in a Horizontal Circular Tube

The shell and tube heat exchanger is an essential part of a power plant for recovering heat transfer between the feed water of a boiler and the wasted heat.The baffles are also an important element inside the heat exchanger.Internal materials influence the flow pattern in the bed.The influence of baffles in the velocity profiles was observed using a three-dimensional particle image velocimetry around baffles in a horizontal circular tube.The velocity of the particles was measured before the baffle and between them in the test tube.Results show that the flows near the front baffle flow were parallel to the vertical wall,and then concentrate on the upper opening of the front baffle.The flows circulate in the front and rear baffles.These flow profiles are related to the Reynolds number(Re) or the flow intensity.The velocity profiles at lower Re number showed a complicated mixing,concentrating on the lower opening of the rear baffle as front wall.Swirling flow was employed in this study,which was produced using tangential velocities at the inlet.At the entrance of the front baffle,the velocity vector profiles with swirl were much different from that without swirl.However,velocities between two baffles are not much different from those without swirl.