固体吸附式制冷系统中吸附剂粒径及吸附床总孔隙率对吸附床传热性能的影响研究

文章采用数值模拟方法研究了圆筒型吸附床的二维非稳态脱附传热过程,并基于综合导热系数和接触热阻分析了吸附剂的粒径和吸附床的总孔隙率对吸附床传热性能的影响,以及吸附床的总孔隙率与吸附剂粒径的最优组合。分析结果表明:当吸附床的总孔隙率较大时,吸附剂粒径对吸附床传热性能的影响更为明显,且吸附剂粒径越小,吸附床的传热性能越好;随着吸附剂粒径逐渐增大,吸附床总孔隙率对吸附床传热性能的影响呈现出不同的变化趋势;当吸附剂的粒径较小且吸附床的总孔隙率较大时,吸附床的传热性能最优。     

一种新颖的太阳能制冷管及其性能实验研究

一种新颖结构的太阳能吸附制冷管,其吸附床由一种具有高强度,高吸附性能和导热性能,并对太阳能具有高吸收率的复合吸附剂块组成,与已有的太阳能制冷系统相比,每根冷管生成一个制冷系统,结构简单,密封性好,同时吸附床可直接吸收太阳辐射,提高了对太阳能的有效利用。实验表明,在未采用专门的集热装置,吸附床向阳面温度仅为７５℃左右的情况下,冷管的性能,系数可达８％左右。     

固体吸附式制冷系统中吸附床内传热过程的数值模拟

对一简化吸附床模型中传热过程进行理论分析,对吸附床内的热传导方程和换热管内流体的能量控制方程进行离散并利用控制容积法进行模拟数值计算,在计算模型中加入随时间变化的边界条件,得到吸附床内吸附剂和换热管内流体的两种互相耦合的温度分布,为吸附床的实际优化设计提供理论依据。     

太阳能制冷吸附材料导热系数实验研究

设计了一套测定堆积状态下不同尺寸吸附材料导热系数的实验装置,对吸附剂有效导热系数随颗粒尺寸及温度的影响进行实验分析。结果表明:硅胶的导热系数随粒径的增大而增大,SAPO-34的导热系数随粒径的增大而减小,且两者的导热系数均随温度的升高而增大,硅胶的导热系数整体大于SAPO-34的导热系数。     

太阳能吸附器中强化热传导性能的实验研究

针对太阳能吸附式制冷循环过程中，吸附剂热传导性能低的特点，研究采用高分子复合强化吸附剂提高其传热性能。发现少量导热高分子材料在吸附剂颗粒表面形成均匀连续的导热网，可使吸附剂的有效导热系数提高２—４倍，且吸附性能变化不大。     

太阳能吸附器中强化热传导性能的实验研究

针对太阳能吸附式制冷循环过程中,吸附剂热传导性能低的特点,研究采用高分子复合强化吸附剂提高其传热性能.发现少量导热高分子材料在吸附剂颗粒表面形成均匀连续的导热网,可使吸附剂的有效导热系数提高2-4倍,且吸附性能变化不大.     

13X-APG粒状沸石在固定床吸附器中的CO2吸附特性

以13X-APG粒状沸石为吸附剂,通过测量其在固定床吸附器中的吸附穿透曲线,研究了该吸附剂对CO2的动态吸附特性,考察了气体温度、气体流量、吸附剂颗粒大小对吸附剂吸附CO2性能的影响,获得了吸附过程中吸附床的温度变化。结果表明,随着气体温度的升高以及吸附剂颗粒粒径的增大,吸附剂对CO2的吸附量逐渐减小;吸附量随气体流量的变化不大;在吸附过程中,小粒径吸附剂的吸附床温度变化显著。     

沸石分子筛-水吸附工质对的吸附性能及导热性能

吸附工质对的吸附和传热性能是研究吸附式干燥、除湿及制冷的重要基础，由于吸附量与导热系数和吸附材料的性质、温度、压力等许多因素有关，需要通过实验来确定。该文通过对几种沸石分子筛的性能实验研究，测定了其最大吸附量、密度、吸附等压线及导热系数等一系列性能参数及其影响因素，并给出了实际循环过程中吸附床的温度、压力与吸附量之间的关系。研究表明沸石对水的吸附基本满足D—A方程，而沸石导热系数受温度以及吸附量的影响较大，随着温度及吸附量的增加而增加。     

吸附式制冷系统传热传质过程的数值模拟

建立了沸石－水吸附式制冷系统吸附床在非第一类边界条件时的二维传热传质模型。考虑了工质对的吸附特性对脱附过程的影响,讨论了肋片数量、肋片物性参数,吸附床的有效导热系数,接触热阻等参数对脱附时间的影响。结果表明,增加肋片可以改善吸附床的性能,其中肋片的数量和接触热阻的影响较大,肋片的物性参数影响不大。     

吸附制冷系统吸附床传热过程的数值模拟

为缩短吸附制冷周期,采用两床交替吸附/解吸结构,并采用管内走传热介质,管外填充吸附剂的吸附式制冷系统。建立了相应的数学模型。用数值方法对模型进行了求解,着重对吸附床温度场分布进行了数值模拟,并对吸附床内压力,某些点温度以及吸附量随时间的动态变化进行了模拟,得出的结果与实际情况吻合较好,说明此吸附制冷系统有较好的传热效果,为吸附床的优化设计提供了参考依据。     

Study of the Effect of Fin-and-Tube Heat Exchanger Fouling on its Structural Performance

This paper presents the thermal and structural analysis of high temperature fin-and-tube heat exchanger. Water flowing in tubular space and flue-gas flowing in the intertubular space, were considered as working fluids. The effect of limescale fouling on thermal and structural performance of heat exchanger was studied. The analysis considered an industrial heat exchanger, which failure occur from time to time. The expert inspection, after the failure indicated the existence of fouling layer within the heat exchanger tubes. In order to understand the reasons of heat exchanger failure, a detailed fluid flow analysis (both in the tubular and intertubular spaces) was performed. The analysis indicated that the silicate limescale fouling layer with thermal conductivity of 0.35 W/(mK) and thickness up to 1.5 mm existing in the tube, may increase the tube wall temperature even more than 150°C. The study also includes the impact of outer tube wall surface fouling with thickness of 0.2 mm and heat transfer coefficient of 2 W/(mK). As a result, the compressible stresses may increase over three times compared to the situation where the tube wall fouling does not exist.     

350 MW余热锅炉变工况运行特性分析

  目的  整体煤气化联合循环（IGCC）发电技术是高效、低碳的发电技术,余热锅炉是IGCC的组件之一。文章旨在研究余热锅炉变工况运行特性以提高整体煤气化联合循环发电技术的效率。  方法  通过分析余热锅炉的工作原理及传热传质原理,使用MATLAB软件展开编程计算,探究给水温度、给水压力、液相换热系数以及气相换热系数与余热锅炉内吸热量的关系。  结果  结果发现,当液相换热系数在200～1 000 W/(m2·K)和气相换热系数在20～100 W/(m2·K)范围内时,如果给水温度从30 ℃增加到100 ℃或给水压力增加,余热锅炉的吸热量将不断减少。反之,假设给水温度在30～100 ℃范围内,当液相换热系数从200 W/(m2·K)增加到1 000 W/(m2·K)或气相换热系数从20 W/(m2·K)增加到100 W/(m2·K)时,余热锅炉的吸热量不断增加。  结论  在液相换热系数与气相换热系数不变的情况下,给水温度或给水压力增加,余热锅炉的吸热量会减少;在给水温度与给水压力不变时,液相换热系数或气相换热系数增加,余热锅炉的吸热量会增加。     

Forced convection in metallic honeycomb structures

The heat transfer and pressure drop characteristics of sandwiched metallic honeycomb structures, with one face-sheet heated by constant heat flux and cooled by forced air convection, have been investigated both experimentally and numerically. Six test samples, made of two materials with different thermal conductivities (16.2 W/(mK) for stainless steel and 401 W/(mK) for pure copper), were evaluated. The effect of cell shapes was also explored using samples with square, diamond, trapezoidal and hexagonal shapes. Good agreements between experimental and numerical results were obtained for both the friction factor (pressure drop) and heat transfer rate. The results show that the overall pressure drop is correlated with surface area density and cell shape, whereas the overall heat transfer rate is a function of surface area density, cell shape, the ratio t/H, and the thermal conductivity of the solid material. Comparisons with other heat sink media have also been made. They indicate that the metallic honeycomb structures investigated are excellent candidates for heat sink applications.     

秸秆压缩块插孔纤维混凝土空心砌块墙体保温性能试验研究

采用热箱法测定了空心混凝土砌块和秸秆混凝土砌块的传热系数。试验结果表明:所测定单排单孔空心混凝土砌块平均传热系数K=1.78W/(m2.K),单排双孔空心混凝土砌块平均传热系数K=1.57W/(m2.K),秸秆压缩块混凝土砌块平均传热系数K=1.08W/(m2.K)。秸秆混凝土砌块作为墙体保温材料具有很好的隔热保温性能。     

一体式再生燃料电池温度和热流密度非原位同步测量

一体式再生燃料电池的热流密度和温度分布的研究对电池热管理具有重要的意义。本文将自制的薄膜传感器植入一体式再生燃料电池中,进行非原位实验研究。在给定不同气体预热温度下,测量了一体式再生燃料电池内部热流密度和局部温度,并根据已得到的温度和热流密度计算出局部表面传热系数。结果表明,在不同的气体预热温度下,流道内气体的温度和气体扩散层表面的温差维持在3℃左右。气体扩散层表面的热流密度整体呈现出下降的趋势。靠近加热棒处的温度最高,但热流密度最低。相同的气体预热温度下,流道内气体和气体扩散层表面的温差对换热量的影响要大于温度梯度的影响;气体预热温度的上升对表面传热系数h的影响不大。30℃时,表面传热系数h值在450 ~ 750 W/(m²?K) 之间。40℃时,表面传热系数h在450 ~ 650 W/(m²?K)之间。     

Experimental Investigation of Heat Transfer Enhancement in Rectangular Duct with Pentagonal Ribs

Rib turbulators are extensively used in augmentation of convective heat transfer in several applications related to heat exchange and cooling in thermal energy systems. Present experimental investigation examines the local heat transfer and friction factor characteristics of pentagonal ribs mounted on bottom heated wall of a rectangular channel. The emphasis is towards assessing and analysing the potential impact of varying chamfering angle (0 to 20°) and rib pitch to height ratio (6 to 12) on the overall heat transfer enhancement and its distribution on the surface. Experiments are performed at different Reynolds numbers ranging from 9400 to 58850. Liquid crystal thermography is applied to measure surface temperature distribution and finally to demonstrate the local heat transfer coefficient over the ribbed surface. The results depict that the local augmentation Nusselt number distribution is axisymmetric and shows 2-dimensionalty in heat transfer distribution. Pentagonal ribs show a significant improvement for the low heat transfer zones in leeward vicinity of the square rib, specially prominent at higher Reynolds number, and therefore seen as the potential benefit in terms of obviating the hotspots. It is observed that the pentagonal ribs lead to superior heat transfer enhancement in conjunction with significant reduction in pressure penalty as compared to square ribs and thus ensures an enhanced thermo-hydraulic performance.     

Experimental Study of Heat Transfer and Pressure Loss in Channels with Miniature V Rib-Dimple Hybrid Structure

Abstract

In order to increase the thermal efficiency, the gas turbines are designed to operate at higher temperature, which requires highly efficient cooling structures for turbine blades. The dimples and ribs are effective surface structures to enhance the convective heat transfer in the gas turbine blade internal cooling. In the present study, a novel hybrid cooling structure with miniature V-shaped ribs and dimples is presented, and the heat transfer and pressure loss characteristics are obtained experimentally. The heat transfer performance of the rib–dimple structures, which include three different rib height-to-hydraulic diameter ratios of 0.017, 0.029 and 0.044 and one dimple configuration with the dimple depth-to-diameter ratio of 0.2, are studied by using the transient liquid crystal thermography technique for turbulent flow in rectangular channels within the Reynolds number range from 10,000 to 60,000. It is found that the miniature V-shaped ribs arranged upstream the dimples can significantly improve the heat transfer performance of the dimples, resulting in a more uniform heat transfer distribution on the surface. The V rib-dimple hybrid structure in the channel shows much higher heat transfer enhancement than the counterparts with only the dimples in the channels.     

Design and performance prediction of a novel double heat pipes type adsorption chiller for fishing boats

A novel double heat pipe type adsorber, which uses compound adsorbent of CaCl₂ and expanded graphite to improve the adsorption performance, is designed. The double heat pipes are integrated into the adsorbers in order to solve the problem of the corrosion between seawater and the steel adsorber in ammonia system and improve the heat transfer performance of the adsorber. There are two kinds of heat pipes integrated with the adsorber. One is the split type heat pipe for heating the adsorber in desorption phase, the other one is the two-phase closed thermosyphon heat pipe for cooling the adsorber in adsorption phase. The performance of two-adsorber adsorption chiller integrated with double heat pipes is predicted. The heat transfer performance of the heat pipes can meet the heat demands for adsorption/desorption of the adsorbent when the heating/cooling time is 720 s and mass recovery time is 60 s. When the exhaust gas temperature is 550 °C, the cooling water temperature is 25 °C, the inlet and outlet chilled water is −10 and −15.6 °C, respectively; the simulation results show that the cooling power and COP of this adsorption system are 5.1 kW and 0.38, respectively.     

Heat transfer in rectangular channels with transverse and V-shaped broken ribs

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces of pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distribution of the heat transfer coefficient in channels with rib turbulators. This issue was tackled by means of the steady-state liquid crystal thermography: a pre-packaged liquid crystal film was glued onto the heated surface, and the colour map was taken by a video camera at the steady state of a given experiment. After calibration tests to assess the colour-temperature relationship had been performed, local heat transfer coefficients were obtained by applying custom-made software to process the digitised colour images. Liquid crystal thermography was applied to the study of heat transfer from a rectangular channel (width-to-height ratio equal to five) having one surface heated at uniform heat flux and roughened by repeated ribs. The ribs, having rectangular or square sections, were deployed transverse to the main direction of flow or V-shaped with an angle of 45 or 60 deg relative to flow direction. The effect of continuous and broken ribs was also considered. Local heat transfer coefficients were obtained at various Reynolds numbers, within the turbulent flow regime. Area-averaged data were calculated in order to compare the overall performance of the tested ribbed surfaces and to evaluate the degree of heat transfer enhancement induced by the ribs with respect to the smooth channel.     

不同加热功率下充液率对无芯环路热管性能的影响

设计了以铝为管材、丙酮为传热工质的无芯环路热管。其蒸发段采用加热带加热,冷凝段用风冷降温。热管依靠蒸发压头使工质循环,并依靠重力作用,使冷凝液回流到蒸发段。搭建试验台并研究了不同加热功率下充液率对无芯环路热管的传热温差、传热量、热效率、热阻和当量导热系数的影响。结果表明:加热功率为150.00 W、充液率为30%时,无芯环路热管的均温性最好;传热温差和热阻均最小,分别为6.75℃、0.045 K/W。传热量132.00 W、热效率0.88、当量导热系数168 125 W/(m·K),均达到最大值。所以,该无芯环路热管在本实验研究范围内的最佳工作条件为加热功率150.00 W、充液率30%。