微胶囊流体微通道传热研究进展

相变微胶囊流体因相变潜热大和粒子之间的微对流效应,具有载热密度大,传热温差小的特点,在传热方面具有独特的优势。但其低导热率和高粘度限制了其应用范围。基于微胶囊流体在微通道内不同流动状态下的传热性能及强化微胶囊流体传热方面进行研究进展介绍,并分析总结微胶囊流体在暖通空调及相关领域的应用进展。

CO_(2)跨临界热泵高温化途径分析

CO_(2)作为一种环境友好的自然工质,以其为循环工质的跨临界热泵制热能力突出。建立CO_(2)跨临界增压和CO_(2)跨临界热泵理论分析模型,研究不同增压过程对热泵系统COP、气冷器中水的出口温度及质量流量的影响规律。结果表明,2种热泵高温化方案均会提升压缩机等熵效率、功耗和压缩机出口工质温度,且提升了气冷器出口水温,但COP和热水的质量流量有所降低。综合来看,随气冷器出水温度的增加,增大压缩机吸气过热度的循环耗功上升幅度较小,但COP下降幅度较大,可在小范围内提升热水温度;提高压缩机出口压强能获得更高的热水温度,可控范围更大,且COP降低幅度较小。

卓越工程师人才培养背景下能源与动力工程专业课程多元化实践教学方法研究

针对当前传统教学模式在实践创新型专业人才培养中存在的问题,以能源与动力工程专业热力设备原理、换热器原理与设计两门专业课程为例,探讨卓越工程师背景下多元化实践教学方法与常规教学模式的差异,提出课程教学过程中应加强多媒体课件设计、工程案例分析、校外工程师进课堂和实验、课程设计实际工程化及工程现场实践教学环节等多元化实践教学内容,让学生从基础知识、案例应用、实验现象与结果分析、工程现场实践等多角度开展全面的深度学习,提高学生的学习兴趣和综合实践能力,培养满足社会需求的卓越工程师人才。

一带一路背景下能源与动力工程专业人才培养国际化路径探索

针对当前传统人才培养模式在国际化人才培养中的不足,基于能源与动力工程专业,讨论了一带一路背景下人才培养新模式与常规培养方式的差异,从培养方案的改革,双语课程的建设,教师教学能力的提升及国际化,学生的创新及国际化等角度探索了能源与动力工程专业人才培养的国际化路径,以期提高学生的学习兴趣和综合实践能力,提升学生的专业国际化素养,培养出满足社会需求的新型国际化人才。

湿空气接触式换热过程建模与分析

以湿空气为研究对象,提出了一种空气全热吸收装置,建立了空气与盐溶液换热的理论模型,通过二分法分析换热过程,研究了直接接触式换热装置中空气进口温度、空气相对湿度和盐水进口温度、盐水质量流量对热质交换性能,以及凝结水量和换热量的影响。研究结果表明:空气进口温度升高和相对湿度增加会加强热质交换程度;盐水进口温度升高会削弱热质交换程度,而盐水质量流量的增加可以增强传质传热。

Experimental Investigation of the Operating Characteristics of a Pulsating Heat Pipe with Ultra-Pure Water and Micro Encapsulated Phase Change Material Suspension

The specific heat capacity of working fluid is an important influence factor on heat transfer characteristic of the pulsating heat pipe(PHP).Due to the relatively large specific heat capacity of micro encapsulated phase change material(MEPCM) suspension,a heat transfer performance experimental facility of the PHP was established.The heat transfer characteristic with MEPCM suspension of different mass concentrations(0.5% and 1.0%) and ultra-pure water were compared experimentally.It was found that when the PHP uses MEPCM suspension as its working fluid,operating stability is impoverished under lower heating power and the operating stability is better under higher heating power.At the inclination angle of 90°,the temperature at heating side decreases compared to ultra-pure water and the temperature at heating side decreases with the raising of MEPCM suspension mass concentration.The heat transfer characteristic of the PHP is positively correlated with the inclination angle and the 90° is optimum.The unfavorable effect of the inclination angle decreases with heating power increasing.When the inclination angle is 90°,the PHP with MEPCM suspension at 1.0% of mass concentration has the lowest thermal transfer resistance and followed by ultra-pure water and MEPCM suspension at 0.5% of mass concentration has the highest thermal transfer resistance.When the inclination angles are 60° and30°,the effect of gravity on the flow direction is reduced to 86.6% and 50% of that on the inclination angle of 90°,respectively,and the promoting effect of gravity on the working fluid is further weakened as the inclination angle further decreases.Due to the high viscosity of MEPCM suspension,the PHP with ultra-pure water has the lowest heat transfer resistance.When the inclination angles is 60°,the thermal resistance with MEPCM suspension at0.5% of the mass concentration is lower than that at 1.0% at the heating power below 230 W.The thermal resistance of MEPCM suspension tends to be similar for heating power of 230-250 W.At the heating power above 270 W,the thermal resistance with MEPCM suspension at 1.0% of the mass concentration is lower than that at 0.5%.

Heat Recuperation for the Self-Condensing CO_(2)Transcritical Power Cycle

The supercritical CO_(2)Brayton cycle has potential to be used in electricity generation occasions with its advantages of high efficiency and compact structure.Focusing on a so-called self-condensing CO_(2)transcritical power cycle,a model was established and four different layouts of heat recuperation process were analyzed,a without-recuperation cycle,a post-recuperation cycle,a pre-recuperation cycle and a re-recuperation cycle.The results showed that the internal normal cycle's share of the whole cycle increases with increasing the cooling pressure and decreasing the final cooled temperature.Heat load in the supercritical heater decreases with increasing the cooling pressure.From perspective of performance,the re-recuperation cycle and the pre-recuperation cycle have similar thermal efficiency which is much higher than other two layouts.Both thermal efficiency and net power output have a maximum value with the cooling pressure,except in the condition with the final cooled temperature of 31℃.Considering both the complexity and the economy,the pre-recuperation cycle is more applicable than the other options.Under 35℃of the final cooled temperature,the thermal efficiency of the pre-recuperation cycle reaches the peak 0.34 with the cooling pressure of 8.4 MPa and the maximum net power output is 2355.24 kW at 8.2 MPa of the cooling pressure.

Influence of Filling Ratio and Working Fluid Thermal Properties on Starting up and Heat Transferring Performance of Closed Loop Plate Oscillating Heat Pipe with Parallel Channels

Using ethanol or acetone as the working fluid, the performance of starting up and heat transfer of closed-loop plate oscillating heat pipe with parallel channels(POHP-PC) were experimentally investigated by varying filling ratio, inclination, working fluids and heating power. The performance of the tested pulsating heat pipe was mainly evaluated by thermal resistance and wall temperature. Heating copper block and cold water bath were adopted in the experimental investigations. It was found that oscillating heat pipe with filling ratio of 50% started up earlier than that with 70% when heating input was 159.4 W, however, it has similar starting up performance with filling ratio of 50% as compared to 70% on the condition of heat input of 205.4 W. And heat pipe with filling ratio of 10% could not start up but directly transit to dry burning. A reasonable filling ratio range of 35%-70% was needed in order to achieve better performance, and there are different optimal filling ratios with different heating inputs- the more heating input, the higher optimal filling ratio, and vice versa. However, the dry burning appeared easily with low filling ratio, especially at very low filling ratio, such as 10%. And higher filling ratio, such as 70%, resulted in higher heat transfer( dry burning) limit. With filling ratio of 70% and inclination of 75°, oscillating heat pipe with acetone started up with heating input of just 24 W, but for ethanol, it needed to be achieved 68 W, Furthermore, the start time with acetone was similar as compared to that with ethanol. For steady operating state, the heating input with acetone was about 80 W, but it transited to dry burning state when heating input was greater than 160 W. However, for ethanol, the heating input was in vicinity of 160 W. Furthermore, thermal resistance with acetone was lower than that with ethanol at the same heating input of 120 W.

Investigation on the Pinch Point Position in Heat Exchangers

The pinch point is important for analyzing heat transfer in thermodynamic cycles. With the aim to reveal the importance of determining the accurate pinch point, the research on the pinch point position is carried out by theoretical method. The results show that the pinch point position depends on the parameters of the heat transfer fluids and the major fluid properties. In most cases, the pinch point locates at the bubble point for the evaporator and the dew point for the condenser. However, the pinch point shills to the supercooled liquid state in the near critical conditions for the evaporator. Similarly, it shifts to the superheated vapor state with the condensing temperature approaching the critical temperature for the condenser. It even can shift to the working fluid entrance of the evaporator or the supereritical heater when the heat source fluid temperature is very high compared with the absorb- ing heat temperature. A wrong position for the pinch point may generate serious mistake. In brief, the pinch point should be founded by the itcrativc method in all conditions rather than taking for granted.

Experimental Investigation on the Performance of[APMIm][NTf_(2)]for Capturing CO_(2)from Flue Gas of the Cement Kiln Tail

Facing the global warming trend,humanity has been paying more and more attention to the Carbon Capture,Utilization and Storage.Large amounts of CO_(2)is emitted with burning fossil fuel as well as by some special industrial processes like the decomposition of calcium carbonate in a cement plant.The cement industry contributes about 7%of the total worldwide CO_(2)emissions and the CO_(2)concentration of flue gas of the cement kiln tail even exceeds 30%.Ionic liquid is considered to be an effective and potential material to capture CO_(2).In order to investigate the performance of ionic liquids for capturing CO_(2)from flue gas of the cement kiln tail,an experiment system was established and an ionic liquid,[APMIm][NTf_(2)](1-aminopropyl-3-imidazolium bis(trifluoromethylsulfonyl)imine),was tested using pure CO_(2)and simulated gas.The results showed that both physical and chemical absorption play roles while physical absorption dominates in the absorption process.Both the absorption capacity and rate decrease with raising the operating temperature.In the experiment with pure CO_(2),the absorption capacity is 0.296molCO_(2)⋅molIL−1 at 30℃ and 0.067molCO_(2)⋅molIL−1 at 70℃.Meanwhile,the ionic liquid can be regenerated for recycling without obvious changes of the absorption capacity.When the ionic liquid is used for flue gas of the cement kiln tail rather than pure CO_(2),a sharp decrease of the absorption capacity and rate was observed obviously.The absorption capacity at 30℃ dropped even to 0.038molCO_(2)⋅mol_(IL)^(−1),12.8%of that for pure CO_(2).Additionally,a natural desorption of CO_(2)from the ionic liquid was observed and affected the experimental results of the absorption capacity and the absorption-desorption rate to some extent.

Combustion Characteristic and Mechanism of a Mixture Working Fluid C_(3)H_(8)/CO_(2)

In the CO_(2)transcritical power cycle,conventional cooling water can hardly condense subcritical CO_(2)because its critical temperature is as low as 30.98°C.In order to avoid this condensing problem,CO_(2)-based mixtures have been proposed as working fluids for transcritical power cycle.They can raise the critical temperature by mixing a little C_(3)H_(8)as the secondary component to CO_(2).However,the flammability of the mixture may limit its application.This article investigated laminar flame speed of C_(3)H_(8)/CO_(2)which represents the mixture’s combustion characteristic by a so-called heat flux method and studied the inhibition mechanism of CO_(2)on the combustion based on the Premixed Laminar Flame-Speed Calculation reactor of Chemkin-Pro.The experimental results showed that the laminar flame speed shows a peak value with changing the equivalence ratio and accelerates with raising the mole fraction of the organic gas.Additionally,a slight upwards trend was observed for the corresponding equivalence ratio of the peaks.The flammable range for the equivalence ratio extended with the mole fraction of C_(3)H_(8)increasing.With the mole fraction of C_(3)H_(8)of 0.15,the maximum laminar flame speed was 12.8 cm/s,31.7%of that of the pure C_(3)H_(8).The flammable range was from 0.41 to 1.33,decreasing by 23.3%compared with that of C_(3)H_(8).A flammable critical mixing ratio was also found as 0.08/0.92 for C_(3)H_(8)/CO_(2)at the normal condition.By simulating,it was found that the most key free radical and elementary reaction which determine the inhibition of CO_(2)on the combustion are OH and H+O_(2)=O+OH,respectively.