Shading effects on the winter thermal performance of the Trombe wall air gap: An experimental study in Dalian

There has been little research on the application of shading devices in the air gap of the Trombe wall in China. Experiments on the thermal performance of an advanced Trombe wall with shading in the air gap was conducted in a passive solar house in Dalian. The thermal performance was investigated with regard to the simultaneous temperatures, heat gain and their acquisition of the Trombe wall. By analyzing experimental data, an investigation was carried out on the heat preservation effect by the shading device on a winter night. The theoretical optimum fixed location of the shading in the air gap for minimizing the heat loss was also discussed. Finally, the influence of shading on improving indoor thermal comfort was discussed using the concept of the building envelope response factor (BER) presented earlier by Lukic [The transient house heating condition—the building envelope response factor (BER). Renewable Energy 2003;28(4):523–32].     

An experimental and mathematical study of efforts of a novel photovoltaic‐Trombe wall on a test room

A novel photovoltaic‐Trombe wall (PV‐TW) is proposed and investigated experimentally and theoretically in this paper. The PV‐TW was installed at the south‐facing external wall of an environmental chamber that carried two identical test rooms. Both of the test rooms have a double window of the same size. One test room was installed with the PV‐TW (known as the PV‐TW room), and the other without PV‐TW (known as the reference room). The influence of the PV‐TW on the thermal environment of the test room was investigated under different operating conditions. The experimental results show the dual benefits of the PV‐TW system: improving the room thermal condition and at the same time generating electricity. Compared with the reference room, the maximum indoor temperature was found to be 5–7°C higher in winter, and the daily electrical output reached about 0.3 kWh with a PV cell area of 0.72 m². Also, a detailed model is given to evaluate the performance of PV‐TW theoretically, and the PV‐TW room is simulated under one certain operating condition. The simulated and measured air temperatures of PV‐TW room are found to be in good agreement. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimum design of Trombe wall system in mediterranean region

Thermal, environment and economic impact of Trombe wall system for residential building in Mediterranean region will be studied in this paper. Moreover, optimum size of this system will be determined by using Life Cycle Cost (LCC) criterion. This will lead to develop an approach for designing the most economic residential building in Mediterranean region.Hour-by-hour energy computer simulations were run with TRNSYS program to analyze the performance of Trombe wall. Then, a complete economical equations of LCC have been built and optimized for variable Trombe wall area ratio as a function of economic and thermal parameters.The optimum Trombe wall area ratio from thermal and economical point of view is 37%. This optimum ratio has reduced LCC by 2.4%. Moreover, about 445 kg CO₂ will be reduced annually.     

青岛农村地区Trombe墙结构对室内环境的影响

Trombe墙结构是一种依托于房屋南墙,以热压来提高室内热舒适性的结构。文章利用数值计算方法分析了夏季青岛地区Trombe墙结构和北窗的位置、尺寸对室内环境的影响,研究结果表明:夏季,Trombe墙结构不会使室内温度升高,并可以强化室内的自然通风,提高房间的热舒适性;随着北窗位置的改变,室内空气最高流速的位置也会发生改变,当北窗距屋顶高度为0.5 m时,室内高度约为1.7 m处,空气平均流速约为0.075m/s;随着北窗宽度的逐渐增加,Trombe墙结构可有效增大从北窗流入室内的空气流量,并使得室内空气流速略有下降,当北窗宽度为1.4 m时,室内气流的整体流速最大。     

An experimental study of axial conduction through a thermosyphon pipe wall

The effect of the axial conduction through the pipe wall on the performance of a thermosyphon was experimentally investigated in this study. Two 2-phase closed thermosyphons were tested; each had the same dimensions, materials and partially filled with R134a. The only difference between them was that one had a thermal break within the adiabatic section that resisted axial conduction between the evaporator and the condenser sections. The thermosyphons were heated by a constant-temperature hot bath and cooled by water via a concentric heat exchanger. The experiments were performed for different bath temperatures and different fill ratios. It was found that the axial conduction through the pipe wall caused an increase in the overall heat transfer coefficient, evaporation heat transfer coefficient and condensation heat transfer coefficient of the thermosyphon. However, the fraction of heat transfer associated with axial conduction decreased as the heat flux increased. For small heat flux (T_b = 30 °C), the increment of the evaporation and condensation heat transfer coefficient contributed by axial conduction reached 100% and 25%, respectively. For high heat flux (T_b = 60 °C), the increment was negligible (less than 1%).     

The effect of Trombe wall on indoor humid climate in Dalian, China

The paper clarified the effect of humidity adjustment of Trombe wall on indoor environment by the experimental comparison between a passive solar cell and a reference cell. Theoretical analysis on indoor humidity adjustment of Trombe wall in the passive solar cell is also performed based on steady moisture transfer theory. Simultaneously, the experiment proved that the passive solar cell could provide a relatively comfortable indoor environment.     

Mothballing in power markets: An experimental study

The deregulation of many electricity markets over the last two decades raises a number of issues, among which: securing adequate investments in capacity, and the possibility of cyclical behavior in capacity, are important for security of supply. A number of policies and market mechanisms aiming for capacity adequacy and market stability exist; in this paper we focus on one of these, mothballing of generation capacity. In electricity markets, mothballing is the possibility for a power generation company to temporarily withdraw generation capacity for a time, often for a year or more. Our hypothesis is that mothballing will help to stabilize markets, but at the same time increase prices. We test this hypothesis using laboratory experiments, with a simplified model of a generic electricity market. We report an experiment with twelve markets, where subjects make investment decisions; half of them had full capacity utilization (T1) and the other half had the option to mothball capacity (T2). The predictions of the effects of mothballing were confirmed in the experimental markets: prices and generation capacity exhibit clear cycles in T1, and damped cycles in the second set of experiments, T2. Furthermore, mothballing leads to higher prices on average.     

An experimental study of convective heat transfer in silicon microchannels with different surface conditions

An experimental investigation has been performed on the laminar convective heat transfer and pressure drop of water in 13 different trapezoidal silicon microchannels. It is found that the values of Nusselt number and apparent friction constant depend greatly on different geometric parameters. The laminar Nusselt number and apparent friction constant increase with the increase of surface roughness and surface hydrophilic property. These increases become more obvious at larger Reynolds numbers. The experimental results also show that the Nusselt number increases almost linearly with the Reynolds number at low Reynolds numbers (Re<100), but increases slowly at a Reynolds number greater than 100. Based on 168 experimental data points, dimensionless correlations for the Nusselt number and the apparent friction constant are obtained for the flow of water in trapezoidal microchannels having different geometric parameters, surface roughnesses and surface hydrophilic properties. Finally, an evaluation of heat flux per pumping power and per temperature difference is given for the microchannels used in this experiment.     

Performance of coupled novel triple glass and phase change material wall in the heating season: An experimental study

A Trombe wall that uses a phase change material (PCM) as the heat storage medium is usually called a PCM Trombe wall or PCM wall. A research project was conducted to investigate the performance of coupled novel triple glass (NTG) and PCM wall, which is simply called PCM wall in this paper, as a solar space heater. The south façade of a test room was constructed using PCM walls. Rubitherm® GR35 and GR41 were incorporated into the plaster of the walls as PCM. The ratio of the solar energy gain provided by the PCM walls to the heat load of the test room per month varied from 4% to 70%; daily overall efficiency of the PCM walls varied from 20% to 36%; and solar transmittance of the NTG varied from 0.45 to 0.55 during the heating period. The overall efficiency of the PCM wall including GR35 was higher than that of the PCM wall including GR41.     

An experimental and numerical study on the effect of the wall in a thermocline-type cylindrical enclosure—I Experments

In this, the first part of a two-part paper, axisymmetric natural convection flows in a thermocline-type cylindrical enclosure are studied experimentally with a laser Doppler velocimeter. A numerical model was developed using these experimental data and it is presented in the second part of this study. These enclosures find application as storage systems in solar energy power plants. It is shown that the walls of the container can have a strong effect in destroying the thermocline. This effect was studied for an initially established thermocline where the hot fluid (in the top) and the cold fluid (in the bottom) are separated by an adiabatic partition, and the container is well insulated outside.The flowfield that results from this initial condition is symmetric with respect to the partition (except for variations in the fluid and wall properties which were neglibible in our experiments), and it was only necessary to study the development of the initially cold fluid.Both the axial and radial components of the velocity were measured as a function of time and position. Two Rayleigh numbers (based on the temperature difference) were studied: 3.7 × 10⁸ and 7.5 × 10⁸. The velocities measured ranged between 0.01 cm/sec and 0.45 cm/sec. The error for typical velocities near the wall is ±10 per cent. Very good agreement was found with an available numerical solution.     

An experimental and modeling study of iso-octane ignition delay times under homogeneous charge compression ignition conditions

Autoignition of iso-octane was examined using a rapid compression facility (RCF) with iso-octane, oxygen, nitrogen, and argon mixtures. The effects of typical homogeneous charge compression ignition (HCCI) conditions on the iso-octane ignition characteristics were studied. Experimental results for ignition delay times, τ_ign, were obtained from pressure time-histories. The experiments were conducted over a range of equivalence ratios (?=0.25-1.0), pressures (P=5.12-23 atm), temperatures (T=943-1027 K), and oxygen mole fractions (χO₂=9-21%), and with the addition of trace amounts of combustion product gases (CO₂ and H₂O). It was found that the ignition delay times were well represented by the expression

     

An experimental study of void fraction and heat transfer under upward and downward flow boiling conditions

Heat transfer coefficient and actual void fraction have been measured during upflow and downflow boiling of water in an annular channel. At the same values of pressure, mass flux, heat flux and flow quality significant difference of void fraction has been established in upflow and downflow. The upflow and downflow heat transfer coefficients did not deviate significantly from each other, if compared at identical values of pressure, mass flux, heat flux and actual void fraction.     

An experimental study of coal gasification

Experiments were carried out on a 2 m diameter gas generator for a ceramics factory to study the effects of air-supply pressure, steam-saturation temperature and generator-gas exit temperature on fuel heating value. A total of 64 gasification experiments was performed using a standard coal mixture. Gaseous fuels with heating values ranging from 1100 to 1400 cal/liter were obtained. The heating value of the gas could be raised by up to 27% by maintaining the three process variables close to their optimum values, i.e. air-supply pressure=43 cm of H₂O, steam-saturation temperature=55°C, and generator gas-exit temperature=160°C.     

An experimental and analytical comparison study of power management methodologies of fuel cell-battery hybrid vehicles

The implementation of fuel cell vehicles requires a supervisory control strategy that manages the power distribution between the fuel cell and the energy storage device. Some of the current problems with power management strategies are: fuel efficiency optimization methods require prior knowledge of the driving cycle before they can be implemented, the impact on the fuel cell and battery life cycle are not considered and finally, there are no standardized measures to evaluate the performance of different control methods. In addition to that, the performances of different control methods for power management have not been directly compared using the same mathematical models. The proposed work will present a different optimization approach that uses fuel mass flow rate instead of fuel mass consumption as the cost function and thus, it can be done instantaneously and does not require knowledge of the driving cycle ahead of time. Also this study presents an experimental approach to validate the mathematical simulation results.     

Concentration of liquid foods using desiccants: An experimental study

Liquid foods are often partially dehydrated to reduce their water content so as to enhance their storage stability. Evaporation, which consumes large amounts of energy, is the most widely used operation for concentrating liquid foods. The paper describes a novel system to concentrate liquid foods by using liquid desiccants. In the proposed system, water vapour, evaporated from the liquid food at reduced pressure, passes to the liquid desiccant, where it is absorbed while liberating its latent heat. The liquid desiccant temperature thereby increases. The warm liquid desiccant can then be used to provide a portion of the thermal energy for the evaporation of the water in the liquid food. A vertical, double-falling-film evaporator which uses calcium chloride solution was built and was used to concentrate liquid foods. The experimental set-up was tested to study the influence of the liquid-desiccant flow rate, the liquid-food flow rate, and the liquid-desiccant concentration and temperature. Some of the experimental results are discussed in this paper.     

Transpiration cooling of a rotating disk: An experimental study

Heat-transfer coefficients were experimentally determined for a transpiration-cooled rotating disk. A theoretical analysis by previous investigators, based on an assumption of constant properties, was inadequate for predicting results in the present study of air injected into an air environment. However, a simple density ratio was sufficient to realign predicted and experimental results. The range of experiments included injection rates of 0·35–1·04 lb/min ft² and rotation Reynolds numbers of 19 000 – 51 000. The ratio of $\text{h}\text{h}{}_0$ (h₀ = coefficient for impermeable disk) varied from 0·69 to 0·21. Over the range studied, a semi-logarithmic equation correlates the data within 10 per cent.     

Methanol and ethanol steam reforming in membrane reactors: An experimental study

In this work a comparison between methanol steam reforming (MSR) reaction and ethanol steam reforming (ESR) reaction to produce hydrogen in membrane reactors (MRs) is discussed from an experimental point of view.     

装载机热管理仿真与试验研究

通过一维/三维耦合仿真方法进行装载机热管理仿真计算,建立装载机整车三维模型,利用Fluent商业软件计算发动机舱内的空气流动。计算结果表明:散热器进风不均匀,散热器上部与下部形成热风回流,整机左右两侧进风口的进风不畅和风扇周围形成多处涡流;利用三维仿真得到的散热器进口风量,在一维仿真中反推机舱阻力系数,利用KULI商业软件,计算发动机出水温度、液压油散热器进口温度、传动油散热器进口温度;通过仿真数据与试验数据的对比,验证了一维/三维耦合仿真的准确性。     

An experimental and numerical study on the effect of the wall in a thermocline-type cylindrical enclosure—II Numerical model

In this, the first part of a two-part paper, axisymmetric natural convection flows in a thermocline-type cylindrical enclosure are studied experimentally with a laser Doppler velocimeter. A numerical model was developed using these experimental data and it is presented in the second part of this study. These enclosures find application as storage systems in solar energy power plants. It is shown that the walls of the container can have a strong effect in destroying the thermocline. This effect was studied for an initially established thermocline where the hot fluid (in the top) and the cold fluid (in the bottom) are separated by an adiabatic partition, and the container is well insulated outside.The flowfield that results from this initial condition is symmetric with respect to the partition (except for variations in the fluid and wall properties which were neglibible in our experiments), and it was only necessary to study the development of the initially cold fluid.Both the axial and radial components of the velocity were measured as a function of time and position. Two Rayleigh numbers (based on the temperature difference) were studied: 3.7 × 10⁸ and 7.5 × 10⁸. The velocities measured ranged between 0.01 cm/sec and 0.45 cm/sec. The error for typical velocities near the wall is ±10 per cent. Very good agreement was found with an available numerical solution.     

沉浸式污水源热泵系统夏季变工况性能实验研究

介绍了污水源热泵实验台的实验装置、测点布置和测试原理,并对不同工况下系统性能及沉浸式污水换热器阻力进行了测试.测试结果表明,当污水温度升高时,热泵系统的制冷量及COP随之降低,对普通热泵机组来说,为保证热泵系统的正常运行,系统污水温度有一个最高的限制要求.当污水流量增加,热泵系统制冷量也随之增加,当流量增加到一定值时,流量的变化对系统性能的影响降低.