多级矩阵结构冷却除湿器的除湿性能研究

为了降低空分系统压缩机功耗,提高压缩机运行可靠性,本文提出一种用于压缩机进气除湿的多级矩阵结构的冷却除湿器,并搭建了多级冷却除湿实验台,测试了除湿器的除湿性能。实验结果表明,在进口空气含湿量和温度固定为11.7 g/(kg干空气)和24.4 ℃时,当空气质量流量由0.48 kg/s增至0.78 kg/s,空气出口含湿量由7.1 g/(kg干空气)增至7.7 g/(kg干空气);在进口空气质量流量和温度固定为0.53 kg/s和25.2 ℃时,当冷却水温度由6.9 ℃升至11.9 ℃,空气出口含湿量由7.1 g/(kg干空气)增至9.4 g/(kg干空气)。同时,建立了除湿器内部传热传质过程的稳态数值模型,将模拟结果与实验结果进行对比。结果表明,该模型对于除湿器出口空气含湿量和温度的平均误差分别为8.6%和2.1%,显示出较好的可靠性。进一步模拟研究了多级矩阵结构与单级叉流结构冷却除湿器的除湿性能,发现采用多级结构可以有效提高除湿效率,在进口空气流量和冷却水质量流量分别为0.53 kg/s和0.3 kg/s时,多级结构的除湿量可以提高4.3%,除湿效率可以提高2.5%;通过增加填料模块的长度,可以提高除湿效率。当长方体填料模块体积固定为0.054 m3,模块长度由0.14 m增至0.28 m时,传质系数可由4.3 g/(m2?s)增至6.5 g/(m2?s),除湿效率由66.4%升至79.2%。     

A comparison of the finite element and control volume numerical solution techniques applied to timber drying problems below the boiling point

Drying is a process which involves heat and mass transfer both inside the porous material, where a phase change in moisture occurs from the liquid to the gaseous state, and in the external boundary layer of the convected hot dry air, which heats the porous medium. The equations which govern this process consist of three tightly coupled, highly non-linear partial differential equations for the unknown system variables of moisture content, temperature and pressure. Due to the inherently complex boundary conditions and intricate physical geometries in any practical drying problem, an analytical solution is not possible. In order to obtain a transient drying solution it is necessary to resort to a numerical technique. The numerical solution techniques which were employed in this research were the finite element method and the control volume method. The transient numerical results were compared and contrasted for two timber drying problems, first, at a dry bulb temperature of 50°C, and secondly, at 80°C, both cases being below the boiling point of water.     

An experimental investigation of saturated flow boiling heat transfer and pressure drop in square microchannels

In this study, saturated flow boiling characteristics of deionized water in parallel microchannels are investigated experimentally. The silicone microchannel heat sink consists of 29 parallel square microchannels having hydraulic diameters of 150 µm. Experiments have been conducted for four different values of the mass flux consisting of 51, 64.5, 78 and 92.6 kg/m²s and heat flux values from 59.3 to 84.1 kW/m². Inlet temperature of deionized water is kept at 50 ± 1 °C. Heat transfer and pressure drop are examined for varying values of the governing parameters. Simultaneous high-speed video images have been taken as well as temperature and pressure measurements. The flow visualization results lead to key findings for flow boiling instabilities and underlying physical mechanisms of heat transfer in microchannels. Quasi-periodical rewetting and drying, rapid bubble growth and elongation toward both upstream and downstream of the channels and reverse flow are observed in parallel microchannels.     

Experiments on the transition from the steady to the oscillatory marangoni convection of a floating-zone under various cold wall temperatures and various ambient air temperature effects

The transition from the steady to the oscillatory Marangoni convection of a floating-zone under various cold wall temperatures and various ambient air temperature effects have been investigated experimentally by heating the sample from above (opposite direction of Marangoni convection and buoyant forces). The heat transfer takes place mainly through conduction as well as the natural convection of the air around the cylindrical liquid bridge. The ambient airflow in the present work is varied by varying the cold wall temperature and ambient air temperature. In this study, the transition from the steady to the oscillatory Marangoni convection flow of a high Prandtl number fluid in a floating half-zone is visualized by means of the already proven method of the “light-cut-technique”. The test fluid zone is held in ambient air at +4 °C, +10 °C, +16 °C, +23 °C, and +28 °C. The onset of oscillations, the oscillation level, and oscillation pattern are investigated under various conditions. It is found that the critical temperature difference (ΔT_Cr) varies substantially when the cold wall temperature and the ambient air temperature are varied.     

电动客车用余热回收型热泵的换热器优化及性能实验研究

本文针对热泵空调系统在冬季低温工况下制热能力衰减问题,通过换热器设计优化,研发出基于喷射补气的余热回收型热泵空调系统,并进行了性能实验研究.结果表明:研制的准二级压缩电动客车热泵空调系统在低温条件下具有较好的制热性能.在环境温度为-20℃,车内温度为20℃,余热量为1.8 kW的制热工况下,相比于无余热回收工况,系统制...     

Modelling of reinforced polymer composites subject to thermo‐mechanical loading

A coupled finite element model is developed to analyse the thermo‐mechanical behaviour of a widely used polymer composite panel subject to high temperatures at service conditions. Thermo‐chemical and thermo‐mechanical models of previous researchers have been extended to study the thermo‐chemical decomposition, internal heat and mass transfer, deformation and the stress state of the material. The phenomena of heat and mass transfer and thermo‐mechanical deformation are simulated using three sets of governing equations, i.e. energy, gas mass diffusion and deformation equations. These equations are then assembled into a coupled matrix equation using the Bubnov–Galerkin finite element formulation and then solved simultaneously at each time interval. An experimentally tested 1.09 cm thick glass‐fibre woven‐roving/polyester resin composite panel is analysed using the numerical model. Results are presented in the form of temperature, pore pressure, deformation, strain and stress profiles and discussed. The maximum normal stress failure criterion is used in order to establish the load‐bearing capability of the composite panel. Significant pore gas pressure build‐ups (to 0.8 MPa and higher) have been perceived at high thermo‐chemical decomposition rates where the material experiences a complex expansion/contraction phenomenon. It is found that the composite panel experiences structural instability at elevated temperatures up to 300°C but retains its integrity even under moderate external loading. Copyright © 2005 John Wiley & Sons, Ltd.     

Numerical modeling of heat and mass transfer during the drying of granulated polymers in a packed bed

A model is proposed for calculating heat and mass transfer in a packed bed exposed to a drying agent. Results are presented from a numerical realization of the model for the drying of granulated polyamide of type PA-6.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 6, pp. 995–1000, December, 1990.     

大空间建筑下送风分层空调系统区域间换热特性研究

本文采用实验和计算流体力学(CFD)方法,研究了带有柱状下送风系统的大空间建筑中,由气流换热和温差导热组成的对流转移热的计算方法.在缩尺模型实验室中,研究了三种不同排风比的热环境和负荷特性,根据实验得到的中心线垂直温度分布和空调冷负荷验证了CFD模拟结果,并基于相似理论,将缩尺数值模型拓展至全尺寸工况模拟.结果表明:在...     

低温低压下工业铁粉的干燥特性及传热传质分析

本文通过搭建低温低压热泵干燥装置,研究了工业铁粉在不同低压下的干燥效果并分析了低温低压干燥过程中的传热与传质。结果表明:降低干燥环境压力会增大湿铁粉的除湿量,当环境压力从101 kPa降至10 kPa,除湿量增加2.5倍,且在10 kPa压力下铁粉含湿量能降至1%以下。当干燥空气为50℃,风速为0.5 m/s时,随着压力从101 kPa逐渐降至10 kPa,传质系数降低28.1%,传热系数降低68.4%,因此表征传热传质相对强度的刘易斯因子LF随着环境压力的降低而降低。当环境压力为10 kPa、风温为50℃时,流速从0.2 m/s增至2.0 m/s时,传质系数增加32.9%,传热系数增加67.8%,表明低压环境抑制了风速对传质系数的强化作用,因此LF随着风速的增加而增加。在10 kPa环境压力下,LF低至0.5~0.6,表明低压环境中质量扩散与热量扩散存在明显区别。     

Heat and Mass Transfer Measurements for Tray-Fermented Fungal Products

In this study, heat and mass transfer in static tray fermentation, which is widely used in solid-state fermentation (SSF) to produce fungal products, such as enzymes or koji, is investigated. Specifically, kinetic models of transport phenomena in the whole-tray chamber are emphasized. The effects of temperature, moisture, and humidity on microbial growth in large-scale static tray fermentation are essential to scale-up SSF and achieve uniform fermentation. In addition, heat and mass transfer of static tray fermentation of Trichoderma fungi with two tray setups??traditional linen coverings and stacks in a temperature?Chumidity chamber is examined. In both these setups, the following factors of fermentation were measured: air velocity, air temperature, illumination, pH, carbon dioxide (CO₂) concentration, and substrate temperature, and the effects of bed height, moisture of substrate, and relative humidity of air are studied. A thin (1 cm) bed at 28 °C and 95 % relative humidity is found to be optimum. Furthermore, mixing was essential for achieving uniform fermentation of Trichoderma fungi. This study has important applications in large-scale static tray fermentation of fungi.     

New experimental data of CO2 flow boiling in mini tube with micro fins of zero helix angle

Heat transfer and pressure drop characteristics of CO₂ flow boiling in mini tube with micro fins of zero helix angle were experimentally investigated. The working conditions cover mass flux from 100 to 600 kg m⁻² s⁻¹, heat flux from 1.67 to 8.33 kW m⁻², vapor quality from 0 to 0.9 and saturation temperature from 1 to 15 °C. The results show that the heat transfer coefficient increases with increasing vapor quality, but sharply decreases at vapor quality around 0.2~0.4 under most conditions, and the dryout vapor quality decreases with the increasing heat flux and saturation temperature. Pressure drop increases with increasing mass flux and heat flux, or decreasing saturation temperature, and mass flux is the major influence factors. The enhancement ratio of heat transfer coefficient is higher than that of pressure drop, which shows potentials of using such kind tubes to enhance the overall heat transfer performance. A heat transfer coefficient correlation and a pressure drop correlation for 0° helix angle micro-fin tube were developed, and they agree well with the experimental data.     

大容量螺杆式无霜空气源热泵系统特性研究

本文提出一种利用螺杆式压缩机余热进行辅助解吸的无霜空气源热泵系统,建立了一套余热回收无霜空气源热泵数学模型,并实验验证了模型的准确性,分析了环境温度、相对湿度、解吸循环空气温度和质量流量等参数对系统的影响.结果表明:该系统的余热量占解吸所需总能量的比例最高可达0.61;COP受解吸循环空气温度与质量流量的影响较小,受空...     

Development and analysis of a portable compressed liquid air cooling system for fast vehicle cabin cooling

Fast cooling of the cabin of parked vehicles under the sunshine has received considerable attention, especially when the vehicle cooling system does not have the capacity to perform such a task in a very short period of time. Most studies have focused on cooling the vehicle cabin throughout the parking period. In this paper, a novel portable cooling system is proposed to cool the vehicle cabin in 60 seconds. A three dimensional heat and mass transfer model is developed and used to evaluate the performance of the proposed cooling system. The proposed cooling system consists of an insulated container with a volume of 1.0 liter that is filled with compressed liquid air, which requires simple modification to the rear air vent system. The proposed system was able to lower the temperature of the vehicle by 12.0 °C and 15.2 °C for container pressures of 5.0 bar and 9.0 bar, respectively.     

On the development of high temperature ammonia–water hybrid absorption–compression heat pumps

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.     

An improved procedure for obtaining and maintaining well characterized partial water saturation states on concrete samples to be used for mass transport tests

A conditioning procedure is proposed allowing to install into the concrete specimens any selected value of water saturation degree with homogeneous moisture distribution. This is achieved within the least time and the minimum alteration of the concrete specimens. The protocol has the following steps: obtaining basic drying data at 50 °C (water absorption capacity and drying curves); unidirectional drying of the specimens at 50 °C until reaching the target saturation degree values; redistribution phase in closed containers at 50 °C (with measurement of the quasi-equilibrium relative humidities); storage into controlled environment chambers until and during mass transport tests, if necessary. A water transport model is used to derive transport parameters of the tested materials from the drying data, i.e., relative permeabilities and apparent water diffusion coefficients. The model also allows calculating moisture profiles during isothermal drying and redistribution phases, thus allowing optimization of the redistribution times for obtaining homogeneous moisture distributions.     

Influence of the annealing and defects on the VHCF behavior of an SLM AlSi10Mg alloy

In the paper, the influence of the annealing temperature on the Very High Cycle Fatigue (VHCF) of AlSi10Mg specimens produced through selective laser melting (SLM) is experimentally assessed. VHCF tests at 20 kHz are carried out on Gaussian specimens subjected to a heat treatment suggested by the system supplier (heating for 2 hours to 320°C and air cooling) and to a heat treatment proposed by the authors (heating for 2 hours to 244°C and air cooling). The defects originating failure and the conditional P‐S‐N curves are compared. Experimental results show that an annealing temperature of 320 ° C induces the spheroidization of the Si network, which enhances the ductility but has a negative effect on the VHCF response. On the contrary, by reducing the heating temperature to 244 ° C , the original as‐built microstructure is not altered and the minimization of the residual stresses permits to enhance the VHCF response.     

A simplified experimentally tested theoretical model to reduce water consumption of a direct evaporative cooler for dry climates

The aim of this study is to introduce a simple modified experimentally tested theoretical model to mainly reduce the water consumption rate of a direct evaporative cooler type (DEC). The convective heat transfer coefficient correlations are introduced to the fundamental governing equations of this model and the saturation effectiveness of the DEC is calculated. The saline water at different concentrations is used as a feed water to the presented model. The impacts of inlet ambient air conditions and the salinity ratios on the amount of consumed water and the supply air temperature are investigated. The experimental runs are performed on a commercial type DEC and an average operating sprinkled water temperature is found to be 2.5 °C higher than inlet WBT of air. At 200,000 PPM salinity ratio, a reduction in water consumption by about 1.5 L h⁻¹ is reached but with 8.6% increase in the supply air temperature.     

Evaporation of water droplets containing carbon nanotubes

The evaporation of water droplets containing carbon nanotubes has been experimentally studied. The droplets were evaporated in a flow of dry air at temperatures in a range of T ₀ = 20−200°C and Reynolds numbers designed on the initial diameter were Re = 500−2000. The results of measurements of the droplet surface temperature and evaporation rate show that the addition of ∼0.1 wt % nanoparticles to the base liquid (water) virtually does not change the laws of heat and mass transfer.     

Assessment and analysis of binary hybrid nanofluid impact on new configurations for curved-corrugated channel

The current numerical paper introduces the flow and heat transfer characteristics across a new configuration channel, namely: the curved-corrugated channel, using binary hybrid nanofluid. E-shaped baffles with different geometrical parameters have been employed while CuO / MgO-water nanofluid is experimentally prepared with different volume fractions 0.0–5%. Measured thermophysical properties is utilized to simulate the flow and heat transfer characteristics by adopting the κ-ε model. The influences of corrugations, baffles, and geometric parameters; gap ratio (GR = 0.2,0.3,0.4, and 0.5), blockage ratio (BR = 0.2,0.25,0.3, and 0.35), and pitch angle (β = 10°, 12.5°, and 15°) at different Reynolds number (8000–28000) are evaluated using thermal–hydraulic performance method. The outcomes show that vortex flow and increased turbulence will increase heat transfer due to influences of corrugations and baffles. It is confirmed that the flow variations governed by the geometric parameters of the design and the best performance produce at lowest pitch angle 10°, lowest gap ratio (GR = 0.2) and highest blocking ratio (BR = 0.35). Regards the fluid medium, CuO / MgO particles improve the thermophysical properties of the base fluid and thereby boost the thermal performance of the system. It has found new correlations between the Nusselt number, friction Factor and design parameters of tested channel with using binary hybrid nanofluid.