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.

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%.

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.

Modeling of Air Temperature for Heat Exchange due to Vertical Turbulence and Horizontal Air Flow

In order to calculate the air temperature of the near surface layer in urban environment,the surface layer air was divided into several layers in the vertical direction,and some energy balance equations were developed for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was taken into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area(with a horizontal scale of less than 500 m)and a large area(with a horizontal scale of more than 1 000 m)in Guangzhou in summer were used to validate the proposed model.The calculated results agree well with the measured ones,with a maximum relative error of 4.18%.It is thus concluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.

Numerical Method for Heat and Mass Transfer in Air Washer——1.Mathematical Solution for a Droplet Evaporating in Finite Surrounding Airstream

The main objective of this paper is to develop a simpleand efficient numerical model for estimation of heat and mass transfer between water spray drops and airstreamin horizontal parallel flow which enable us to accurateprediction of evaporative cooling performance.Thephysical process of a droplet evaporating in finite airflowhas been studied.Four basic differential equations havebeen developed with their numerical solutions providedby figures.

A Simplified Model for Analysis of Heat and Mass Transfer in an Indirect Evaporative Cooler

A simplified model for analysis of heat and mass transfer between air stream and flowing down water film in counter-flow plate heat exchanger which serves as an indirect evaporative cooler is theoretically analyzed in this paper. Indirect evaporative cooler is used for sensible cooling of air which then is used for air conditioning purposes. Mathematical model was developed allowing determining heat transfer surface, outlet air temperature and specific humidity of the air being cooled. To make the model simpler some simplifications have been incorporated. The model has high level of correctness and can be used to calculate and design different types of evaporative heat exchangers. Analysis of results of calculations by the help of the developed model prove that the surface of heat exchanger depends on the thickness of water film layer by the regularity of direct proportionality. Moreover, increasing of the water film thickness brings to the decreasing of the efficiency of evaporative type heat exchanger. The model can be used for correct calculation and design of an evaporative cooling air conditioning systems.

Near ground air temperature calculation model based on heat transfer of vertical turbulent and horizontal air flow

In order to calculate the air temperature of the near surface layer in urban environment,the surface layer air was divided into several sections in the vertical direction,and some energy balance equations were developed for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was taken into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area(with a horizontal scale of less than 500 m) and a large area(with a horizontal scale of more than 1 000 m) in Guangzhou in summer were used to validate the proposed model.The calculated results accord well with the measured ones,with a maximum relative error of 4.18%.It is thus concluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.

膜片式微通道预冷器换热微细管束振动分析与可靠性评价方法

针对预冷吸气式组合发动机的膜片式微通道预冷器换热微细管束振动可靠性问题,建立换热微细管固有振动特性计算方法与数学模型,研究预冷器换热微细管在高速气流冲击下的振动模式,给出综合考虑旋涡脱落激振、紊流抖振和弹性激振等多种共振模式的预冷器换热微细管束振动可靠性评价模型,揭示预冷器换热微细管振动可靠度的变化规律。研究结果表明,预冷器换热微细管的固有振动频率与换热微细管外径、壁厚、相邻支撑间隔板之间跨度以及材料特性等参数密切相关,其振型具有正弦函数的特征;预冷器换热微细管在高速气流冲击作用下存在旋涡脱落激振、紊流抖振、弹性激振等共振模式;预冷器换热微细管振动可靠度随外侧被冷却工质流速的增大呈现出先降低后提高并趋近于某一数值的变化规律;为防止预冷器换热微细管发生共振损坏,在结构设计中要充分结合工作剖面、流动换热特性等,合理设计换热微细管束结构参数。

填料蒸发预冷进风的机械通风空冷塔设计及其运行性能

为了解决机械通风空冷塔夏季机组出力不足,无法满足冷却需求的问题,设计了一种带有填料蒸发预冷进风的机械通风空冷塔,并利用Matlab编写计算程序,仿真研究了填料厚度、环境温度和环境湿度对所设计空冷塔运行性能的影响规律及其节能效果。研究表明:在环境温度为26℃,相对湿度为57%条件下,厚300 mm的CELdek7060填料蒸发预冷进风的预冷效果最好,空冷塔的排热率可提高20.57%;空冷塔的排热性能随环境温度升高而降低,且存在一个临界点温度为13.5℃,只有当环境温度高于此温度,填料蒸发预冷进风才可提升空冷塔的排热性能;在环境温度、相对湿度分别为35℃和57%时,填料蒸发预冷系统可使空冷塔的排热率提高96.96%,使出塔水温进一步降低2.80℃;在环境相对湿度为0%、环境温度为26℃时,填料蒸发预冷系统可使空冷塔的排热率提高81.14%,出塔水温进一步降低6.81℃。单塔每年节能收益约为13.84万元,具有良好的经济效益。

太阳能+空气能一体化热泵室外侧换热器气流组织及换热性能研究

常规空气源热泵在制热运行中,由于室外侧换热器冷风回流和迎面风速不均匀性过大,会导致换热性能恶化。为了解决这些问题,文章调整室外侧换热器结构并利用太阳辐射能量,提出了一种适用于公共建筑的新型太阳能+空气能一体化热泵室外机方案;建立了室外侧换热器数学模型,对常规空气源热泵室外侧换热器的气流组织及换热性能进行仿真分析,并通过实验验证模型的正确性;构建了涂敷太阳能吸收膜的单倒型和双倒型两种新型室外侧换热器结构,并对其气流组织及换热性能进行模拟研究。结果表明:单倒型和双倒型结构均能改善换热器迎面风速不均匀现象,其中双倒型结构改善效果更为明显,其外侧换热器和内侧换热器迎面风速不均匀度与常规空气源热泵室外侧换热器相比分别降低了46%和83%;在换热器面积、风机型号和数量相同的情况下,双倒型结构换热器空气侧换热量比单倒型结构提高了5.4%。该研究可提高热泵换热器换热效率,降低系统能耗,为太阳能耦合空气能一体化热泵相关研究提供理论支撑。

4.0 Mt/a加氢裂化装置运行过程中问题分析

以4 Mt/a柴油蜡油加氢裂化装置为例,通过分析其运行过程中缠绕管换热器压降低、石脑油分馏塔进料管线振动等热点和难点问题,提出相应的解决方法和措施,同时对大型加氢裂化装置进行了节能优化。结果表明:为实现缠绕管换热温度精准控制,在新装置设计阶段,应优先采用“X”形控制方式,在装置大型化后,根据装置运行特点和场地布置问题,应采取满足管道要求的优化方案。对于设置有石脑油稳定塔和石脑油分馏塔的工艺流程,需重点考虑介质特点,降低管线液击、管线振动所带来的影响。此外,优化新氢压缩机和普通离心泵的运行模式可为大型加氢裂化装置的平稳操作、节能降耗提供一定参考。

布雷顿循环冷端空冷换热器设计与变工况运行特性分析

作为布雷顿循环系统中的重要冷端部件,气体冷却器的性能对循环系统结构紧凑性和运行高效性有重要影响。分析了一种新型横流印刷电路板式换热器(printed circuit heat exchanger,PCHE)—板翅混合式气体冷却器的工作性能及影响因素,对该种换热器建立了一个数值计算模型,并编写MATLAB程序验证其可靠性;基于此,对该类冷却器进行了设计,其功率密度均在1 MW/m^(3)以上,属于紧凑型换热器;其次进行了变工况性能分析,给出了冷却器的压降和换热性能随循环工质和冷却空气进口状态的变化规律,并比较了布雷顿循环工质为超临界二氧化碳、氮气、空气时冷却器的换热特性和压降特性,结果表明,冷、热流体流量的改变对换热特性的影响最明显。研究结果对布雷顿循环空冷换热器的设计与运行具有参考意义。

浅析板管蒸发冷却式无霜空气源热泵及其设计应用

在常规板管蒸发冷却式冷水机组设计的基础上,借鉴了热源塔热泵系统使用防冻液喷淋的防冻措施原理,将其应用在板管蒸发冷却式冷热水机组上,并对板管蒸发式换热器及系统进行设计改进,使其适用于冬季制热工况,从而形成板管蒸发冷却式无霜空气源热泵机组。机组夏季采用板管蒸发式换热器作为冷凝器,相比于空气源热泵降低了冷凝温度,提高了系统的性能系数。冬季使用防冻液喷淋,设备运行无除霜循环,系统供热稳定,大大提高了室内侧的热舒适性。试验研究了不同溶液再生方式下的机组性能,结果表明:利用过冷热再生模式进行溶液再生时机组性能最优,在制热量不衰减的情况下性能系数仅下降了2.5%~5.1%。机组适用于夏热冬冷地区及部分纬度较低的寒冷地区。

液体硅酸钠用冷却输送装置的优化改进

液体硅酸钠因黏度高、易结晶,给其冷却输送带来了较大困难。介绍了一种新型液体冷却输送装置的结构、工作原理及技术特点。液体硅酸钠冷却输送应用效果证明,该新型装置在不改变流量的基础上提升冷却系统的运行效率,保证了高黏度液体冷却输送的高效和节能。

一体式多能源耦合热泵机组的性能研究

传统空气源热泵机组在低环境温度中运行的能效低,随环境温度的降低,制热量衰减严重,且存在潮湿天气下运行时结霜严重、化霜时影响用户采暖效果等问题。以一体式多能源耦合热泵机组为研究对象,建立了实验平台,通过测试对该热泵机组的性能系数(COP)进行分析研究。研究结果表明:1)一体式多能源耦合热泵机组采用模块化设计,安装快捷方便,系统控制简单,且初始投资较低。2)通过全流道双效集热板和风冷换热器可吸收自然环境中的太阳能、空气能、水汽能等多种能源,实现了一机多能源互补,有效解决了传统空气源热泵机组在环境温度低时能效低、在极端寒冷天气下不能正常运行的问题。3)在环境温度为2.2~3.8℃,日均太阳辐照度为476 W/m^(2)的条件下,一体式多能源耦合热泵机组的输出功率为72.3~76.1k W,COP在3.4~3.5之间,比传统空气源热泵机组的COP提高了22%左右。

电石法氯乙烯生产中的节能降耗措施

介绍了电石法氯乙烯生产中的节能降耗措施,包括采用双效换热器充分利用热量,蒸汽冷凝水闪蒸回收低压蒸汽,采用空冷器替代7℃水冷凝器等。

直接空冷火电机组乏汽余热利用技术

火电厂汽轮机排汽(乏汽)需要冷凝成液态水用于系统循环,湿冷、干冷机组都需要消耗大量能量来冷凝乏汽。北方缺水地区采用直接空冷火电机组,大量乏汽通过空冷岛散热。从热力学第二定律来看,乏汽已无做功能力,但是汽化潜热与做功能力无关,在能够提供真空环境确保乏汽流动性和需要加热远低于乏汽温度的工质的情况下,乏汽中的汽化潜热仍具有很高的回收价值。尤其对于直接空冷火电机组,其汽轮机排汽压力和温度均高于湿冷机组,可以采用汽水换热器直接回收乏汽热量加热厂区生水,降低电厂辅助蒸汽的消耗量,提高电厂收益。

Numerical Simulation and Experimental Studies of Air Treatment Process with Water Spray of One Row Parallel Flow

The main purpose of the present work is to make a further insight into the procedure of heat and mass transfer between water droplets sprayed and air stream in a direct evaporative air cooler used in air-conditioning system in textile mills. The thermodynamic models of the two-phase flow in such a air treatment system have been developed for one row parallel flow spray.The fields of temperature and relative humidity in spraylchamber, as well as the trajectories of sprayed drops have been obtained by calculation. A series of experiment aiming at quantifying the system performance and its influence factors have been conducted. It indicates that the increases of air velocity and water/air ratio while the decrease of nozzle density are favorable. Finally, the comparison between numerical simulation and experimental results have been carried out. Good agreements have been found for outlet air temperaturewhile a maximum error of 10% has been observed for air relative humidity.

电站空冷技术:研究现状及建议

空冷技术能够在电站冷端利用空气完成换热冷却,相比湿冷技术在节水、降耗、减排及降本方面具有独特优势。从系统设计与运行优化的角度出发,综述了直接空冷和间接空冷两大类空冷技术的研究进展。设计优化方面,换热器(凝汽器和散热器)的流动换热特性已获得广泛研究,相关优化一般从几何结构、位置布局等角度开展,然而目前凝汽器研究对象多局限于翅片管,针对管束整体的优化研究比较缺乏,散热器研究则需更全面地考虑几何参数的影响等;另外,由于风机(群)直接决定凝汽器的进气流量,其气动特性和集群效应研究成为重点,目前已形成多种分区方法和运行控制策略实施调优,但优化方案的经济性分析研究还有待深入。运行优化方面,为了削弱环境效应对空冷系统的负面影响,可以通过加装导流板等改善流场以扩展风的正向效应、开发控制预测模型进行防冻调控或设计防冻装置优化传热、设计开发各类清洗系统进行除垢等。当前研究在换热器设计优化的精度、广度和各类环境效应作用机理方面仍有进步空间,未来研究方向还包括新能源电站应用空冷的适应性分析,运用人工智能技术进行换热器设计、性能预测等。

制冷空调用换热器研究进展

为实现制冷空调行业的节能减排目标,研究具有轻量化、小型化和高效化的制冷空调用换热器至关重要。本文主要介绍强化换热技术在制冷空调用换热器中的应用,包括风冷式换热器、水冷式换热器和蒸发式冷凝器,以及适应低制冷剂充注量、低GWP工质的紧凑型高效换热器的研发进展,为换热器的优化设计提供借鉴。