单相逆流换热器温度分布及(火用)传递特性的研究

借鉴无相变逆流换热器对数平均温度的推导方法,导出了无相变换热器中流体及换热管内、外壁的温度分布,并基于热力学第一、第二定律及非平衡热力学理论,以某高压加热器过热段为例,分别求出了换热过程中蒸汽至管外壁和管内壁至给水的传(火用)系数,从(火用)传递的角度分析了无相变管壳式换热器的换热性能,为优化换热器结构提供了理论参考依据.     

基于粒子群优化算法的板式换热器优化设计

从板式换热器的结构出发,通过对板式换热器中的流程组合数和冷热流体流速优化分析,得出板式换热器最优结构参数的数学模型,并且结合实例,运用粒子群算法对其进行求解,最终得到更为合适的流程组合数和流体流速,使设计的板式换热器更经济,效率更高。     

地热-高温水源热泵供热系统的分析

运用能量系统的为(火用)分析方法.建立地热-高温水源热泵供热系统的炯分析理论模型.以实际工程项目为例,分析和讨论了系统运行条件下的能量有效利用,并计算了地热-高温热泵供热系统的火甩效率和各部分(火用)损失、(火用)效率.从计算结果看出,板式换热器的火用损失所占比例较大.     

一种板壳式换热器传热准则关系式的实验分析

基于板式换热器的研究成果,对板壳式换热器进行实验研究,利用等流速法求解传热准则关系式.通过控制冷流体、热流体流速相同,对1/1流程组合的板壳式换热器进行实验,并对比和分析实验数据.结果表明:利用板式换热器的经验值拟合得到的传热准则关系式在不同定性温度下并不相同;1/1流程组合板壳式换热器冷流体、热流体的传热准则关系式的参数均为定值,即系数为0.182 5,雷诺数指数为0.75,普朗特数指数为0.34;板壳式换热器的传热准则关系式与板程流程数无关,且与壳程1流程和2流程也无关,但与3流程和4流程则呈现出系数相关的结论,3流程和4流程的系数分别为1流程的0.82倍和0.68倍.     

基于ANSYS FLUENT的板式换热器性能仿真

板式换热器作为海水淡化设备的关键部件，换热器的结构对于整个设备的正常运行、使用寿命以及海水淡化处理的效果都起着关键作用。但长期以来板式换热器的结构设计主要依赖于经验公式，缺乏可靠的设计分析方法。因此，根据板式换热器的结构，通过质量守恒方程、动量守恒方程以及能量守恒方程建立换热器的能量传递数学模型，采用湍流(RNG k-ε)模型建立质量传递模型。使用ANSYS FLUENT建立了板式换交换器的三维几何模型。并模拟了不同工况下的热力学性能。根据模拟结果分析了压力场、温度场、速度场和流动情况。比较分析了换热器在不同流量和冷热流体温差下的传热性能和阻力性能。为了提高板式换热器的效果可通过增加冷流体的流速和增加冷流体和热流体之间的温差来确保更大的传热系数，从而提升换热器的热交换性能。研究结果为不同工况条件板式换热器使用及设计提供了理论支持。     

波纹板式换热器传热与流动特性分析

通过数值模拟的方式,对一种用于低粘度流体的波纹板式换热器的传热特性和阻力性能进行分析,以控制变量法分析了流体速度对传热特性及阻力性能的影响;搭建了板式换热器测试平台,验证了数值模拟结果的正确性和可行性;用等速法拟合了Nu-Re与Eu-Re的相关准则式,并采用JF因子评价换热器综合性能。结果表明：模拟结果与实验结果相比误差在10%以内;当流体流速小于1.0 m/s时,换热器传热系数和压降随着流速的增大而增大,但综合换热性能逐渐变差,在此流速范围内,总传热系数随冷流体进口温度升高而增大。     

新型蜂窝板式换热器实验与模拟分析

板式换热器在工业生产中广泛应用,采用数值模拟和实验相结合的方法对新型蜂窝板式换热器进行研究。结果表明:数值模拟和实验结果在合理的误差范围内,验证了数值模拟的可靠性。新型板式换热器内部蜂窝结构附近的速度场出现规律的周期性变化,流体湍流强度增加,Nu和阻力系数f随焊孔直径和蜂窝直径的增加而增大,通过对蜂窝板在3 000≤Re≤25 000的数据结果进行关联,得到了蜂窝板流动换热的准则关系式,为蜂窝板式换热器的优化提供了理论依据,并为工业生产提供参考。     

板式换热器性能的数值模拟

建立了人字形板式换热器冷热双流道的流体流动与传热计算模型,利用计算流体力学软件对5组不同速度工况下换热器内流体的流动和传热进行了数值模拟,分析了换热器流道内的速度场、温度场和压力场.结果表明:数值模拟得到的板式换热器进、出口温差和压降与试验测量值的误差均小于6%;换热器内流体的流动和传热存在明显的不均匀性,导致其进、出口的另一侧出现明显的传热"死区";换热器的总传热系数和流道阻力均随着流体流速的增大而增大.     

基于火积耗散热阻的新型板式省煤器传热分析

建立了新型板式省煤器的传热模型,计算了新型板式省煤器的火积耗散热阻以及空气侧压降,分析了新型板式省煤器结构参数及空气流速变化时,火积耗散热阻及空气侧压降的变化情况。研究结果表明:增大长轴可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,并且空气侧压降变化幅度不大;增大短轴可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大;减小板束间距可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大,尤其是在板束间距小于20 mm时,继续减小板束间距会造成空气侧压降急剧增大;增大空气进口流速可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大,对换热器的磨损也会增加。     

供热板式换热器的性能试验分析

供热用板式换热器与其他行业用板式换热器相比独具一些特点。首先它所承担的换热量变化范围很大。第二是,换热器两侧流体的温度是随着室外空气温度的变化而变化的,变化后的参数仍要满足不同热用户(多为采暖和热水供应热用户)的供热要求。第三是,冷热流体设计供回水温度不同时,两者的设计流量可能不同,使两种流体的流程组合有变化。第四是,在使用过程中由于板片上沉积污垢对其传热性能及水力阻力都会有影响。这些特点使得研究在实际供热条件下板式换热器的热工特性和水力特性成为一个重要课题。     

一维非稳态导热过程(火用)传递的规律及计算

对平壁在导热第三类边界下的一维非稳态导热过程中的Yong传递进行计算，并将导温系数在定值与变值下的计算结果加以比较，以非稳态条件下Yong传递的时空分布规律进行分析。结果表明，Yong流密度随时间按指数规律递减，而Yong传递数却按指数曲线递增。在密度和比热近似不变的条件下，导温系数对温度场分布、Yong传递系数及Yong流密度有决定性的影响。     

板式相变贮能换热器传热模型和热性能分析

建立了板式相变贮能换热器的无量纲传热模型。它对流体入口流量、入口温度随时间变化情况和需考虑入口效应及添加肋片的情况均适用。模型解和文献准稳态解吻合。作为算例,藉此模型从各时刻的流体温度、相变界面随空间的分布情况和相变蓄热比、相变传热效率、传热系数、完全相变截面位置随时间的变化情况六个角度分析了一板式相变贮能换热器的相变传热性能。该模型可为板式相变贮能换热器的结构优化设计和热性能分析提供帮助。     

Frost distribution characteristics of laminar airflow on cold surface of mini-channels

This study was performed for simulating frosting characteristics that occurred on the surface of plate fins of the outside heat exchanger. Test section with local cooling modules at the central part was made as the rectangular cross sectional passage to imitate the outside heat exchanger. Local frost thickness distributions for test conditions having three experimental parameters (plate wall temperature, air humidity and velocity) were presented. Leading edge effect of the plate was clearly confirmed from the measured frost thickness distributions. The central part of the plate had the highest frost thickness because cooling devices were installed at the center of the plate. Due to different heat and mass transfer characteristics of upstream flow and downstream flow, the frost thickness of upstream area was much higher than that of downstream. The effects of plate surface temperature, humidity and velocity of inlet flow on frost thickness, and sensible and latent heat fluxes were analyzed.     

间接蒸发冷却板式换热器的(火用)效率分析

在考虑壁面两侧空气温度实际变化的前提下,对间接蒸发冷却传热过程中影响yong效率的主要因素,如一次空气进口温度、一、二次空气流速之比,二次空气相对湿度,一、二次通道宽度之比以及壁面润湿率进行了分析研究,为实际换热器设计提供理论依据。     

Exergy transfer effectiveness on heat exchanger for finite pressure drop

In this paper, exergy transfer effectiveness is defined to describe the performance of heat exchangers operating above/below the surrounding temperature with/without finite pressure drop. It is discussed systemically that the effects of heat transfer units number, the ratio of the heat capacity of cold fluids to that of hot fluids and flow patterns on exergy transfer effectiveness of heat exchangers. Furthermore, the results of exergy transfer effectiveness with a finite pressure drop are compared with those without pressure drop when different objective media, such as ideal gas and incompressible liquid, etc. are applied. The detailed comparisons of the exergy transfer effectiveness with heat transfer effectiveness are also performed for the parallel flow, counter flow and cross flow heat exchangers operating above/below the surrounding temperature.     

Investigation of heat transfer and pressure drop in plate heat exchangers having different surface profiles

It would be misleading to consider only cost aspect of the design of a heat exchanger. High maintenance costs increase total cost during the services life of heat exchanger. Therefore exergy analysis and energy saving are very important parameters in the heat exchanger design. In this study, the effects of surface geometries of three different type heat exchangers called as PHE_flat (Flat plate heat exchanger), PHE_corrugated (Corrugated plate heat exchanger) and PHE_asteriks (Asterisk plate heat exchanger) on heat transfer, friction factor and exergy loss were investigated experimentally. The experiments were carried out for a heat exchanger with single pass under condition of parallel and counter flow. In this study, experiments were conducted for laminar flow conditions. Reynolds number and Prandtl number were in the range of 50 ? Re ? 1000 and 3 ? Pr ? 7, respectively. Heat transfer, friction factor and exergy loss correlations were obtained according to the experimental results.     

壳管式海水换热器污垢状况的火用评价方法研究

分析了壳管式海水换热器管程结垢后换热强度及流动压降变化对换热器火用损失的影响,提出了一种利用(火用)损失系数评价换热器污垢状况的方法.该方法比通过检测污垢热阻评价换热器污垢状况的方法更全面,更简捷.     

不同螺旋角度螺旋折流板换热器传热性能与压降的研究

本文对螺旋折流板换热器和传统的弓形折流板换热器进行了壳程传热性能和压降特性的对比，同时通过实验方法对8°、12°、18°、25°、30°、40°螺旋角无搭接的螺旋折流板换热器进行了壳程传热性能和压降特性的研究，得出螺旋折流板换热器的螺旋流动强化了传热，螺旋折流板换热器的压降比弓形折流板换热器的压降小。     

Thermodynamic Evaluation of Transcritical CO_2 Heat Pump Considering Temperature Matching under the Constraint of Heat Transfer Pinch Point

The non-linear temperature glide in the supercritical CO_2 cooling process makes the heat transfer pinch point of heat exchanger show multiplicity,like size,location distribution and quantity,which makes the thermodynamic performance of the CO_2 transcritical cycle more complex and eventually affects the evaluation of the optimal operating state of the system.Based on the second law of thermodynamics and the constraints of heat transfer pinch,a thermodynamic evaluation method of CO_2 transcritical heat pump system was proposed according to the degree of temperature matching.The influence mechanism of multi-characteristic change of heat transfer pinch point on temperature matching degree and the effect of temperature matching degree on thermodynamic performance of CO_2 transcritical heat pump system were discussed.The relationship between temperature matching degree,COP and exergy efficiency of the system was analyzed.It is considered that the change of temperature matching index value can clearly characterize the change trends of COP and exergy efficiency.That is,the smaller the temperature matching degree is,the closer the temperature distribution of heat transfer fluids on both sides of the heat exchanger is to Lorenz cycle,and the greater the COP and exergy efficiency are.Furthermore,by monitoring the outlet temperature of the CO_2 cooler,which has an essential relationship with the temperature matching degree during the heat exchange process,the deviation between actual and optimal working condition can be judged online,which is beneficial to real-time evaluation of the working state of the system.