Computational and Experimental Study of Cooling Process in Coke Dry Quenching Experimental Shaft

Owing to its merits in energy savings, environmental protection and coke quality improvement, the Coke Dry Quenching (CDQ) technology is favorite in coke making industry today. In order to validate the mathematical model developed for the cooling process of real CDQ shaft, the one-seventh scale experimental setup was established. With the air as the working fluid and the coke as the packed bed, the coke and gas temperatures and the pressure drop in the cooling shaft were measured. A mathematical model based on the non-Darcian and non-thermal equilibrium model for the cooling process of the CDQ experimental shaft was presented. The computational results were compared to the experimental data. It was found that most numerical predictions were supported by the measured values.     

A Novel Approach for Energy Efficiency Prediction of Various Natural Draft Wet Cooling Towers Using ANN

Cooling tower is crucial equipment in the cool-end system of power plant and the natural draft counter-flow wet cooling tower(NDWCT) gets wide application. The artificial neural network(ANN) technique is becoming an effective method for the thermal performance investigation of cooling towers. However, the neural network research on the energy efficiency performance of NDWCTs is not sufficient. In this paper, a novel approach was proposed to predict energy efficiency of various NDWCTs by using Back Propagation(BP) neural network: Firstly, based on 638 sets of field test data within 36 diverse NDWCTs in power plant, a three-layer BP neural network model with structure of 8-14-2 was developed. Then the cooling number and evaporation loss of water of different NDWCTs were predicted adopting the BP model. The results show that the established BP neural network has preferable prediction accuracy for the heat and mass transfer performance of NDWCT with various scales. The predicted cooling number and evaporative loss proportion of the testing cooling towers are in good agreement with experimental values with the mean relative error in the range of 2.11%–4.45% and 1.04%–4.52%, respectively. Furthermore, the energy efficiency of different NDWCTs can also be predicted by the proposed BP model with consideration of evaporation loss of water in cooling tower. At last, a novel method for energy efficiency prediction of various NDWCTs using the developed ANN model was proposed. The energy efficiency index(EEI) of different NDWCTs can be achieved readily without measuring the temperature as well as velocity of the outlet air.     

Cooling Performance of an Impingement Cooling Device Combined with Pins

Experimental study and one dimensional model analysis were conducted to investigate cooling performance of an integrated impingement and pin fin cooling device. A typical configuration specimen was made and tested in a large scale low speed closed-looped wind tunnel. Detailed two-dimensional contour maps of the temperature and cooling effectiveness were obtained for different pressure ratios and therefore different coolant flow-rates through the tested specimen. The experimental results showed that very high cooling effectiveness can be achieved by this cooling device with relatively small amount of coolant flow. Based on the theory of transpiration cooling in porous material, a one dimensional heat transfer model was established to analyze the effect of various parameters on cooling effectiveness. It was found from this model that the variation of heat transfer on the gas side, including heat transfer coefficient and film cooling effectiveness, of the specimen created much more effect on its cooling effectiveness than that of the coolant side. The predictions of the one-dimensional mode were compared and agreed well with the experimental data.     

Case Study of Indirect Adiabatic Cooling System in Historical Building

The objective of the present study is to investigate the efficiency of indirect adiabatic chiller-based cooling system efficiency dependence of outdoor air humidity. The system is located in historical building, in temperate climate of Latvia. The data about electricity consumption, water consumption, chiller operation stages, cooling average temperatures and outdoor air parameters have been acquired for the period of 2.5 month, during the cooling season. Using data collected by BACnet based BMS controllers and adiabatic chiller control system, we have analyzed operation efficiency of the chiller and its dependence of outdoor air humidity. Data range for the period from August 1st till October 13th, 2011 was taken for deeper analysis, which showed that in temperature range 22.0 ± 0.5 ℃ for the studied period of time chiller＇s COP is slightly dependent on the outdoor air moisture.     

Enhancement of Thermo-Flow Performances by Windbreakers for Two-Tower Indirect Dry Cooling System

The winds will greatly weaken the cooling performance of indirect dry cooling system with twin towers.The exterior windbreakers are recommended to restrain the wind adverse effects in this paper.The macro heat exchanger model was adopted to simulate the heat exchange between circulating water and ambient air.The performances of natural draft dry cooling system(NDDCS)with and without exterior windbreakers were numerically studied.The pressure,velocity and temperature distribution of cooling air in wind angles of 0°,45°and 90°was obtained and presented.The results show that in all wind directions,the performances for lateral sector of towers with windbreakers are significantly improved,but the low-pressure zone appears unexpectedly for the rear sectors,which reduces the air flow rate.The cooling performances of the twin towers with or without windbreakers decrease at first but then recover with the wind velocity increasing.Besides,the optimal flow and heat transfer performances appear in the wind angle of 0°.The cooling performances can be significantly improved in all three wind directions due to windbreaker configuration.     

Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine. Part Ⅱ： Grooved Surfaces

The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000-40000 r/min and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature.     

Experimental and Numerical Evaluation of the Performance of Supersonic Two-Stage High-Velocity Oxy-Fuel Thermal Spray （Warm Spray） Gun

The water-cooled supersonic two-stage high-velocity oxy-fuel (HVOF) thermal spray gun was developed to make a coating of temperature-sensitive material,such as titanium,on a substrate.The gun has a combustion chamber (CC) followed by a mixing chamber (MC),in which the combustion gas is mixed with the nitrogen gas at room temperature.The mixed gas is accelerated to supersonic speed through a converging-diverging (C-D) nozzle followed by a straight passage called the barrel.This paper proposes an experimental procedure to estimate the cooling rate of CC,MC and barrel separately.Then,the mathematical model is presented to predict the pressure and temperature in the MC for the specific mass flow rates of fuel,oxygen and nitrogen by assuming chemical equilibrium with water-cooling in the CC and MC,and frozen flow with constant specific heat from stagnant condition to the throat in the CC and MC.Finally,the present mathematical model was validated by comparing the calculated and measured stagnant pressures of the CC of the two-stage HVOF gun.     

Research on cooling effectiveness in stepped slot film cooling vane

As one of the most important developments in air cooling technology for hot parts of the aero-engine,film cooling technology has been widely used.Film cooling hole structure exists mainly in areas that have high temperature,uneven cooling effectiveness issues when in actual use.The first stage turbine vanes of the aero-engine consume the largest portion of cooling air,thereby the research on reducing the amount of cooling air has the greatest potential.A new stepped slot film cooling vane with a high cooling effectiveness and a high cooling uniformity was researched initially.Through numerical methods,the affecting factors of the cooling effectiveness of a vane with the stepped slot film cooling structure were researched.This paper focuses on the cooling effectiveness and the pressure loss in different blowing ratio conditions,then the most reasonable and scientific structure parameter can be obtained by analyzing the results.The results show that 1.0 mm is the optimum slot width and 10.0 is the most reasonable blowing ratio.Under this condition,the vane achieved the best cooling result and the highest cooling effectiveness,and also retained a low pressure loss.     

Thermal characteristics of air-water spray impingement cooling of hot metallic surface under controlled parametric conditions

Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper.The controlling input parameters investigated were the combined air and water pressures,plate thickness,water flow rate,nozzle height from the target surface and initial temperature of the hot surface.The effects of these input parameters on the important thermal characteristics such as heat transfer rate,heat transfer coefficient and wetting front movement were measured and examined.Hot flat plate samples of mild steel with dimension 120 mm in length,120 mm breadth and thickness of 4 mm,6 mm,and 8mm respectively were tested.The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface.Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e,4 mm thick plates.Increase in the nozzle height reduced the heat transfer efficiency of spray cooling.At an inlet water pressure of 4 bar and air pressure of 3 bar,maximum cooling rates670℃/s and average cooling rate of 305.23℃/s were achieved for a temperature of 850℃ of the steel plate.     

Experimental Investigation of Solar Chimney Power Plant

The paper investigated the performance of a solar chimney, by measuring the chimney air temperature and velocity. A short solar chimney prototype was designed and constructed at Botswana Technology Center. A wind turbine was installed to rotate a small DC generator. Temperatures and velocities were measured at different times of the day with thermocouples and hotwire anemometer, respectively. Irradiance was measured with pyranometer. A Delta-T data logger was used to store data at intervals of 30 s. Various graphs depicting the influence of irradiance on temperature, velocity and power have been plotted. Irradiance was found to affect the chimney temperature and subsequently affects chimney air velocity and power produced. Ambient air （wind） velocity was found to have influence on the performance of the solar chimney by increasing chimney air velocity.     

自然通风高位收水冷却塔性能对比分析

以某逆流式自然通风常规冷却塔为研究对象,对其相同尺寸的高位收水冷却塔进行对比仿真分析,研究布置高位收水装置对冷却塔效果的影响。在多种运行工况下分别对常规冷却塔和高位收水冷却塔进行模拟计算,分析高位收水装置布置前后塔内空气流动和温度变化,以及冷却水平均温降的变化。结果表明,相较于常规冷却塔,同种条件下高位收水塔内通风量增加了约20%,改善了空气与冷却水之间的传质传热,使得冷却水温降提高了约30%。     

Numerical investigation of free-cooling system using plate type PCM storage

Free cooling night ventilation is the process of storing the coolness in the night time and releasing this coolness in hot day time. In this paper, a numerical study was carried out to simulate and to find out the optimum design for plate type storage filled with phase change material (PCM) which is used in night ventilation systems. The effect of different parameters such as thickness of PCM-plates, inlet air temperature and air mass flow rates on melting front, cooling power, outlet temperature and thermal performance of heat exchanger was studied. The results showed that cooling power can be increased by increasing the mass flow rate. Also, the thickness of the plates in the storage device plays an important role in the thermal performance of the unit and has a linear relation with the melting process duration of PCM for considered configuration.     

Improved cooling performance of large motors using fans

This paper studies the cooling performance by axial fans with forward-swept and inclined blades and a structure with low ventilation resistance for large-capacity open-type motors. The ventilation resistance of axial fans for motors is much greater than that of common fans for creating draughts. Flow separates remarkably on the blades' surfaces and fluid noise is large. We reduced the ventilation resistance inside an electric motor and adopted axial fans with forward-swept and inclined blades. We confirmed by wind tunnel experiment that the flow rate with this combination increases remarkably compared with the conventional ventilation structure and axial fans. Numerical fluid analysis was performed on the flow around the blade at this flow rate. It was confirmed that no flow separation appeared for the air flow along the blade surfaces. This was also observed in a flow visualization experiment. Furthermore, an actual motor with both the low-ventilation-resistance structure and axial fans with forward-swept and inclined blades showed that the flow rate of cooling air increased by 80% compared with that of conventional machines, and the average temperature rise of stator windings decreased by 30%. Thus, the cooling performance was greatly improved.     

Improving indoor conditions of a Thai-style mushroom house by means of an evaporative cooler and continuous ventilation

The paper discusses the effect of an evaporative cooling process and continuous ventilation for improving the indoor conditions of a conventional Thai-style mushroom house. A numerical model describing the behaviour of the Thai-style mushroom house model was developed. It was validated by comparing its output with that of the experiment of a small model of a mushroom house. It was found that the combination of evaporative cooling and continuous ventilation reduced the temperature and increased the relative humidity of air inside a mushroom house that is suitable for growing Lentinus.     

Experimental study for comparison of thermal comfort and air age between two combined ventilation systems with chilled ceiling considering occupant density

Due to the global spread of diseases and epidemics, the need to maintain a clean indoor atmosphere has received increasing attention in recent years. Therefore, there will be a need to clearly estimate and define the areas that affect human exposure to pollutants, taking into account the occupied density, which is the primary importance of this research. The capacity of the chilled ceiling combined with mixing ventilation and personal ventilation systems has been studied and compared to the chilled ceiling with mixing ventilation in terms of mean air age, temperature distribution, CO₂ concentration, and thermal efficiency, with the best flow rate of the proposed system considering the occupied density in a thermally insulated office room experimentally in the climate of Iraq (Hilla, a hot and dry climate). Twelve tests were performed for four different cooling loads with cooled ceilings (0%, 0.25%, 50%, and 80%), at a constant supply air flow rate with two PV airflow modifiers for three cases. As the cooling load treated by a chilled ceiling increased, the average air temperature increased with height in all cases. The lowest values of average air age appeared in the occupied area in the case of a chilled ceiling with mixing ventilation. This study shows that the chilled ceiling combined with a mixing ventilation and personal ventilation system with a flow rate of 7.5 L/s provides thermal comfort and higher air quality in the occupied area. based on the values of air exchange efficiency and occupants’ air exchange efficiency. As a result, a flow rate of 7.5 L/s is the best option for protecting occupants from direct pollution in the breathing zone and in the surrounding microclimate, because the lower the ventilation rate, the less air is changed for occupants.     

动力锂电池组非稳态射流强化换热数值模拟

为动力锂电池组设计了通风冷却系统,在控制总通风量的前提下,研究了非稳态射流对动力锂电池组的冷却效果,针对26650型锂电池组射流冲击方案进行数值模拟分析,揭示非稳态射流送风周期、送风变化量对电池组温升和温度均匀性的影响。研究结果表明:冲击射流的非稳态特性改善了电池组温度场的均匀性,对电池组总温升影响不明显。     

The effect of the London urban heat island on building summer cooling demand and night ventilation strategies

This paper investigates the effect that increased air temperature due to the London heat island has on the effectiveness of stack night ventilation strategies for office buildings. Stack ventilation was investigated as the most suitable night ventilation strategy because this is largely independent of wind variations affected by local urban morphology. The paper presents a summary of the results of air temperature measurements carried out in London in 1999/2000 which were used to quantify the London Urban Heat Island Intensity. It then presents data for two representative weeks, one with extreme hot weather and one with typical hot weather in the centre of the London heat island and a rural reference site. These data are used to carry out a parametric analysis by using a thermal and air flow simulation tool specifically designed for offices in SE England. A reference and optimised office module are described. A comparison of the building types based in the same location suggests that during the typical hot week the rural reference office has 84% energy demand for cooling compared to a similar urban office. A rural optimised office would not need any artificial cooling and would be able to maintain temperatures below 24 °C. An urban optimised office would not be able to achieve this. A rural optimised office would need 42% of the cooling required for an optimised urban office. A comparison of the optimised to the reference office module suggests that an urban optimised office reduces the cooling demand to 10% of the urban reference office.     

Review on free cooling of buildings using phase change materials

The concept of Green building is gaining importance in the present energy scenario and related environmental issues. Free cooling or ventilation cooling is truly a green concept since even 1 g of carbon is not burnt for the purpose of cooling. Also it ensures that a good indoor air quality is maintained in the building. In this paper a detailed review of work carried out by various researchers on free cooling or ventilation cooling is presented. In addition the major challenges and facts posed in the use of phase change material for free cooling system design such as thermal resistance of air and phase change materials, geometry of encapsulation are discussed in detail. Also the method of energy efficient charging and discharging, effect of phase change temperature, insulation and geographical location are also discussed in this paper. This paper also provides lists the PCM candidates used for free cooling.     

Effects of window size and thermal mass on building comfort using an intelligent ventilation controller

A prototype microcomputer-controlled thermostat was developed that can manage airflow according to cooling the needs in a building and the resources in the environment. This intelligent control system measures both indoor and outdoor temperature and uses decision rules to control a whole-house fan, in addition to the furnace and air conditioner. No such residential thermostat is currently commercially available. This paper presents the controller strategy that optimizes cooling with outdoor air. This paper also quantifies the effects of modifying the amount of thermal mass and the window area on indoor comfort when using this controller. These test confirm that smaller windows and more mass performed better than larger windows and less mass, and that higher volumes of controlled ventilation outperformed fixed ventilation rates.     

Integration of variable refrigerant flow and heat pump desiccant systems for the cooling season

Energy saving and indoor air condition enhancing potentials by integrating the variable refrigerant flow (VRF) and heat pump desiccant (HPD) systems were investigated in a field performance test during a cooling season. Three different operating modes: non-ventilated, HPD ventilation assisted and HPD ventilation–dehumidification assisted VRF systems were investigated. The HPD systems operated in the ventilation–dehumidification mode dehumidify the outdoor air and supply it to the indoor air during the ventilation. It was found that the VRF systems provided an average of 97.6% of the total cooling energy for the HPD ventilation assisted mode. The remainder was the recovered cool by the HPD systems during ventilation. The VRF systems provided an average of 78.9% of the total cooling energy for the HPD ventilation–dehumidification assisted mode. The remainder was covered by the HPD systems which provided additional sensible and latent cooling. Overall, among the three operating modes, it is concluded that the HPD ventilation–dehumidification assisted VRF outdoor units consume less energy than the HPD ventilation assisted ones, but more than the non-ventilated ones, while providing the best indoor thermal comfort and indoor air quality conditions. For the total system, the HPD ventilation–dehumidification assisted VRF systems consume less energy than the HPD ventilation assisted ones.