Energy Efficient Air Conditioning System Using Geothermal Cooling-Solar Heating in Gujarat, India

It is well known that one unit of electrical energy saved is equal to more than two units produced. One way of economizing the power is utilization of energy efficient systems at all locations. In the present study, the air conditioning system is analysed and an innovative way is suggested. We use natural low temperature of shallow sub surface (1 - 3 m) of the earth—geothermal cooling system. It is known that majority of the households and the apartment complexes in India have two tanks for water storage. One is the underground water sump and the other is the overhead water tank. In our study, we use these two water storage systems for space cooling during summer and also for heating during winter. The main aim of our paper is air-conditioning of the space in an economic way to save electricity. It is based on a simple idea of transferring the low temperature from underground water sump to the room in the house using water as a mode of transport. Since India is a tropical country located at low latitude, most of the year, the air temperature is high and demands space cooling. However, for a couple of months during severe winter months (Dec.-Jan.) at Ahmedabad, heating of the space is required. For heating the space, we suggest to use the well-known solar water heater. Effective use of heat exchanger is shown through computation, modelling schemes and lab experiment. We recommend geothermal cooling for 10 months in a year and solar hot water system during 2 months of winter. It is observed that the ambient air temperature of 35°C - 40°C in the room can be brought down to 26°C without much consumption of electricity. In a similar manner, the room temperature at night (13°C) during winter in Ahmedabad can be increased to 27°C through circulation of water from solar water heater in the heat exchanger.

Application Research of Intake-Air Cooling Technologies in Gas-Steam Combined Cycle Power Plants in China

The generated power and efficiency of gas-steam combined cycle (GSCC) power plants depend on the temperature of the inlet air greatly. Based on the analysis of basic theory of inlet air cooling technologies, the application of evaporative cooling system and the absorption cooling system in GSCC power plants are discussed in this paper. Moreover, in China with high temperature and humidity, applied research and simulation analysis of the above two different cooling systems are conducted separately, the research results of which can provide certain reference for optimal design and economic operation of inlet air cooling system for GSCC power enterprises in China.

Cooling effect of convection-intensifying composite embankment with air doors on permafrost

One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, their effects might not meet large-width expressway requirements. The convection-intensifying composite embankment composed of perforated ventilation ducts and crushed-rock layers was numerically studied to investigate its cooling effects. Adopting a numerical model, the temperature fields for two kinds of composite embankment with and without air doors were analyzed considering air flow and heat transfer characteristics in porous media. The results show that wind velocity in the crushed-rock zone is intensified by the perforated ventilation duct. The underlying permafrost temperature obviously decreases, and the 0 °C isotherm position rises significantly due to composite embankment. The composite embankment with air doors is more effective than that without air doors. Therefore, the new convection-intensifying composite embankment is potentially a highly efficient cooling measure for construction in permafrost regions.

Study on Air Film Formation Mechanism and Cooling in Large-Span Air-Conditioning Plant Rooms without Natural Wind

Large-span air-conditioning plant rooms have a large roof area and suffer from serious solar radiation in summer. The outside roof surface temperature is very high, so cooling load of roof occupies a large proportion in the envelope structure cooling load of large-span air-conditioning plant rooms. Based on the Coanda airfoil air induction unit, the author combined with exhaust air in large-span air-conditioning plant rooms to design the roof air film cooling system of large-span air-conditioning plant rooms. The adherence air film formed on the outside surface takes away heat on the outside surface of the roof, so as to reduce outside roof surface temperature of the roof, decrease heat transfer temperature difference between inside and outside roof surfaces of, and reduce roof cooling cold. Furthermore, the mathematical model and numerical simulation method of considering fluid-structure interaction for heat transfer and influences of solar radiation on air film formation of outside surface and cooling were constructed. Moreover, the numerical simulation method was conducted the validation of effectiveness. Also, the author discussed the air film formation mechanism and air film cooling ability of outside surface in large-span air-conditioning plant rooms without natural wind, developed a new air film cooling technology for the roof of large-span air-conditioning plant rooms, and supplemented the existing roof cooling technology.

Air Cooling of Mini-Channel Heat Sink in Electronic Devices

Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.

Research and Demonstration of Direct Air-Cooling System for 600-MW Fossil-Fired Power Plants

Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.

Achieving Cooler Soil as an Effective Heat Sink for Earth-to-Air Heat Exchanger (EAHE) Cooling Technology in Malaysia Tropical Climate

This research is intended to explore the capacity of Malaysia soil in becoming a more effective heat sink for the application of Earth-to-Air Heat Exchanger (EAHE) Cooling Technology in Malaysia. EAHE Cooling Technology consists of buried pipes underground where the ambient air is channeled through from the pipe inlet and produces cooler air at its outlet. Within the buried pipes, heat exchange process occurs between the air and the soil that surrounding the pipe. This building cooling technology has been applied in many countries, mostly in temperate or hot and arid climate where the diurnal temperature is large. However, minimal resources were found on the study of EAHE application to buildings in Malaysia, hence there is room to develop. A parametric study on EAHE cooling application in Malaysia was done through field experiment and concluded that among many parameters affecting the technology performance, the soil temperature which surrounded the pipe was the most influential factor. The study recommended to further reduce the soil temperature to achieve a cooler outlet temperature. In response to that, this research conducted a parametric study of soil temperature under three different soil surface conditions: bare, shaded with timber pallettes and insulated with used tyres at 1.0 m and 1.5 m underground. The data was logged for a month and the result has shown significant reduction in the soil temperature underground below the shaded and insulated soil surface as compared to below bare soil surface condition. The insulated soil surface produced the best result where the soil temperature was reduced up to 26.9°C. The main contribution of this paper is to highlight that the soil surface treatment can be used to reduce solar heat gain within the soil underground and thus improving the performance of EAHE Cooling Technology particularly for the application in Malaysia tropical climate.

Experimental Investigation of the Cooling Capacity of Gaseous Carbon Dioxide in Free Jet Expansion for Use in Portable Air-Cooling Systems

This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.

Analysis of Air-Cooling Battery Thermal Management System for Formula Student Car

Designing a good energy storage system represents the most important challenge for spreading over a large scale of electric mobility. Proper thermal management is critical and guarantees optimum working temperature in a battery pack. In the various battery thermal management technologies, air cooling is one of the most used solutions. The following work analyzes the cooling performance of the air-cooling thermal management system by choosing appropriate system parameters and analyzes using CFD simulations for accurate thermal modeling. These parameters include the influence of airflow rate and cell spacing on the configuration. The outcome of the simulations is compared using parameters like maximum temperature, and temperature distribution in the battery module to obtain optimum results for further applications. Finally, the simulations of the optimal solution will be compared to experimental results for validation.

新型迷你通道-相变热沉实验研究

电子元件的集成化、微型化等特点加剧了芯片的热问题,基于相变材料的被动式冷却技术已无法满足功率波动的高功率电子设备的需求。本文将相变技术与主动冷却技术相结合,提出了一种用于风冷散热的新型迷你通道-相变热沉结构。该结构改善了相变材料导热性能差的问题,也解决了相变材料熔化后泄漏的问题。通过实验测试了不同热流密度、不同风速对其热控性能的影响,总结了热沉的蓄放热特性,并与未填充相变材料热沉的热控性能进行了对比。实验中热流密度变化范围为1.81~3.47 W/cm^(2),风速变化范围为0~4 m/s。研究表明:热流密度的增大和风速的降低均会导致热沉温控时间的缩短。2 m/s风速足以满足热流密度小于2.91 W/cm^(2)的芯片散热需求,4 m/s风速可以在热流密度为3.47 W/cm^(2)的情况下将热沉底面温度维持在70℃。与未填充相变材料热沉相比,本研究提出的热沉可以起到延长温控时长,降低稳态温度的作用。此外,风扇的开启可以有效缩短热沉的冷却时间,对于间歇性工作的电子设备具有重要的应用意义。研究结果可为迷你通道-相变热沉在实践中的应用提供参考依据。

HTR-PM汽轮机轴封蒸汽断供原因分析及解决方案

介绍了高温气冷堆示范工程(HTR-PM)汽轮机轴封系统,并且对轴封蒸汽断供的原因进行了分析,提出了可以采用蒸汽发生器及管道内余汽供轴封、辅助电锅炉至轴封供汽管道改造、高温空气供轴封这3种解决方案。对3种方案进行对比,分析其在成本、可靠性和运行限制方面的优缺点,结果表明3种方案均是可行的。研究结果为HTR-PM汽轮机轴封蒸汽断供问题的解决提供了参考。

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.

具有时滞效应的air2stream河流水温模型及应用研究

高精度河流水温模型对于深入了解水温的时空变化特征和河流生态修复具有重要意义。基于数据驱动的air2stream模型在保证预测精度的同时,避免了计算的复杂性,已成为河流水温模拟常用的模型。由于水的热惯性及水文条件等的影响,河流水温变化往往显著滞后于气温变化,而air2stream原模型并未考虑滞后效应,导致该模型在流量未知情况下实际精度偏低。为解决该问题,采用气温-水温皮尔逊相关系数计算时滞天数,构建具有时滞的air2stream新模型,进一步根据长江中下游地区两个监测站的多年实测数据验证新模型的有效性和稳定性。结果表明:新模型在不引进额外观测数据的条件下具有更高精度且性能更稳定。相比原模型,在两个监测站新模型的均方根误差分别降低约4.29%和5.85%。新模型具有精度高、水文要素需求少的特点,可为长江中下游的水环境影响评价和生态保护提供依据。

Field experimental study on the cooling effect of mine cooling system acquiring cold source from return air

With the increase of mining depth, more and deeper coal mines are limited by heat disaster. The cooling energy in deep mine cooling system comes from mine water inrush or ground cooling tower, but we cannot adopt the two methods because mine water inrush in many old coal mines in China is limited. What is more, the cooling pipelines cannot be put in narrow pit-shaft. To settle the problem above, according to the characteristics of Zhangxiaolou Coal Mine, this paper adopts the deep mine return air as the cooling energy for deep mine cooling system. In addition, we carried out cite test to extract cold energy from return air. Through monitoring the water quantity, water temperature of cooling system and air temperature, we got the thermodynamic equilibrium parameters during the cooling energy acquisition analysis and the effect of cooling system that the temperature and humidity on working face are respectively reduced to 8-12 ℃ and 8-15% through cooling. This research offers experimental reference for deep mine cooling which lacks cooling energy.

高温环境因素对固-液混合燃料物理稳定性的影响

固-液混合燃料的物理稳定性对于燃料的质量和安全性均有重要的意义。高温环境引发的易挥发液体组分的气化将对燃料的物理稳定性产生极为复杂的影响。通过自主设计的实验装置模拟、加速燃料物理稳定性改变,并分别从液体燃料析出及密度分布变化趋势,分析高温环境因素的作用。结果表明:自然堆垛状态下燃料的顶部受饱和蒸汽压的改变影响较大,而中部、底部则由于燃料的紧密堆积,形成各自独立的气液平衡。同时,液体燃料于高温环境中对固体的润湿效果随之增强,更有利于液体组分完成对固体颗粒的吸附。在303~333 K的温度条件下,固液体积比为1.25∶1,硝基甲烷占液体组分40%的固-液混合燃料保持最佳的物理稳定性。

Optimization of rhizosphere cooling airflow for microclimate regulation and its effects on lettuce growth in plant factory

In plant factories,the plant microclimate is affected by the control system,plant physiological activities and aerodynamic characteristics of leaves,which often leads to poor ventilation uniformity,suboptimal environmental conditions and inefficient air conditioning.In this study,interlayer cool airflow(ILCA)was used to introduce room air into plants’internal canopy through vent holes in cultivation boards and air layer between cultivation boards and nutrient solution surface(interlayer).By using optimal operating parameters at a room temperature of 28℃,the ILCA system achieved similar cooling effects in the absence of a conventional air conditioning system and achieved an energy saving of 50.8% while bringing about positive microclimate change in the interlayer and nutrient solution.This resulted in significantly reduced root growth by 41.7% without a negative influence on lettuce crop yield.Future development in this precise microclimate control method is predicted to replace the conventional cooling(air conditioning)systems for crop production in plant factories.

Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.

Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device

This paper presents an analytical solution for the thermoelastic stress in a typical in-plane＇s thin-film micro- thermoelectric cooling device under different operating con- ditions. The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained, and the characteristics, including maximum temperature dif- ference and maximum refrigerating output of the thermo- electric device, are discussed for two operating conditions. Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the tempera- ture difference are formulated based on the theory of mul- tilayer system. The results demonstrate that, the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses. The stress distributions in layers of semiconductor thermoelements, insulating and support- ing membrane show distinctly different features. The present work may profitably guide the optimization design of high- efficiency micro-thermoelectric cooling devices.

Influence of Different Vortex Generators on Heat Transfer in Direct Air-Cooled Condensers

通过数值模拟研究了矩形小翼、三角小翼、梯形小翼、柱面梯形翼、柱面三角翼和柱面矩形翼等6种涡流发生器分别安装于直接空冷凝汽器单排蛇形翅片扁管中的压降和换热性能。Re数在600~1800范围内,涡流发生器采用相同高宽比、尾高、攻角以及安装位置。结果表明：矩形小翼的换热及压降增大最多,Re=1729时,相比平直翅片分别增加了14.27%和18.32%。Re=1 729时,柱面梯形翼的压力损失比矩形小翼少4.7%,换热低1.5%。当以（j/j0）/（f/f0）1/3作为综合换热性能评价标准时,柱面梯形翼的综合换热性能最好。另外,考察了柱面梯形翼倾角的影响（0°、6°、12°、20°、24°和26°）,相同工况下,倾角为12°的柱面梯形翼换热最好（较平直翅片增强4.29%~14.1%）、压降最小（增大7.5%~12.8%）且综合换热性能最好。柱面梯形翼因其迎流面积与斜边长度的匹配以及流线型柱面,具有良好的强化传热效果以及较小的压降。

Energy, Exergy and Thermoeconomics Analysis of Water Chiller Cooler for Gas Turbines Intake Air Cooling

Gas turbine (GT) power plants operating in arid climates suffer a decrease in output power during the hot summer months because of the high specific volume of air drawn by the compressor. Cooling the air intake to the compressor has been widely used to mitigate this shortcoming. Energy and exergy analysis of a GT Brayton cycle coupled to a refrigeration air cooling unit shows a promise for increasing the output power with a little decrease in thermal efficiency. A thermo-economics algorithm is developed to estimate the economic feasibility of the cooling system. The analysis is applied to an open cycle, HITACHI-FS7001B GT plant at the industrial city of Yanbu (Latitude 24o 05” N and longitude 38o E) by the Red Sea in the Kingdom of Saudi Arabia. Result show that the enhancement in output power depends on the degree of chilling the air intake to the compressor (a 12 - 22 K decrease is achieved). For this case study, maximum power gain ratio (PGR) is 15.46% (average of 12.25%), at an insignificant decrease in thermal efficiency. The second law analysis show that the exergetic power gain ratio drops to an average 8.5%. The cost of adding the air cooling system is also investigated and a cost function is derived that incorporates time-dependent meteorological data, operation characteristics of the GT and the air intake cooling system and other relevant parameters such as interest rate, lifetime, and operation and maintenance costs. The profit of adding the air cooling system is calculated for different electricity tariff.