Analysis of an Ultrathin Graphite-Based Compact Heat Exchanger

The emerging production of ultrathin graphite material is applied to thermal management in a numerical comparison of aluminum and graphite-based plate-fin heat exchangers. Considering anisotropic thermal conductivity in which out-of-plane transport is about two orders of magnitude lower than in-plane values, the ultrathin graphite-based solution outperforms aluminum by rejecting up to 20% more heat on a volumetric basis. Thermal and hydraulic performance is characterized for both solutions over a range of airflow rates in a notional water/air device. Laminar through fully turbulent regimes are considered. Steady and unsteady three-dimensional (3-D) conjugate simulations reveal a faster equilibration rate for the ultrathin graphite-based solution, minimizing thermal lag that must be accounted for in on-demand electronics cooling. Fin optimization studies predict equivalent conductance with graphite at one-tenth the thickness of aluminum. The combination of improved heat rejection, rapid response rate, and low material density make an ultrathin graphite-based solution uniquely suited to aerospace thermal management.     

Second-Law and Experimental Analysis of a Cross-Flow Heat Exchanger

This article presents a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems. This new heat exchanger was tested with an applicable experimental setup, considering temperatures, velocity of the air, and the pressure losses occurring in the system. These variables were measured and the efficiency of the system was determined. The irreversibility of the heat exchanger was taken into consideration, while the design of the heat exchanger was such that the minimum entropy generation number was analyzed with respect to the second law of thermodynamics in the cross-flow heat exchanger. The minimum entropy generation number depends on the parameters called the optimum flow path length and dimensionless mass velocity. Variations of the entropy generation number with these parameters are analyzed.     

紧凑式换热器表面瞬变测试的敏感性分析和数值模拟

提出了一种考虑纵向导热效应的紧凑式换热器表面平均传热系数瞬变测试方法.根据出口流体温度变化的实测数据,用Levenberg-Marquardt非线性曲线拟合,同时对理论模型中的纵向导热参数λl和进口流体温度变化时间常数τ ,以及传热单元数Ntu进行参数估计.敏感性分析和具有测量噪声的数值模拟实验表明,待求的反映换热面传热性能的Ntu参数估计值具有良好的精度.     

Detection of Fouling in a Cross-Flow Heat Exchanger Using Wavelets

Detection of fouling in a heat exchanger experiencing perfect steady-state conditions is not very difficult. But the challenge is to detect fouling when all inputs (inlet temperature of the fluids and the mass flow rates) are simultaneously varying. In this paper it has been considered that the mass flow rates can vary in a ratio of 2, and that the inlet temperatures can vary by about ±20%. This first approach is dedicated to show the feasibility of using the wavelet transform. It has been considered that getting simulated data is the best way. In fact, it is then possible to introduce an arbitrary fouling factor. Thus, in the first part of the paper the model of the heat exchanger is presented. It is developed using Simulink. The validation is carried out on an electrical heater, for which it is possible to find an analytical solution for transient states. It is also shown that steady states are accurately computed over a large range of the number of transfer units and heat capacity rate ratios. Then a brief overview of the wavelet transform is given. Then basic examples show that the wavelet transform can help to find the trend of time series. It is then applied to the analysis of the “wavelet-transformed” effectiveness of the heat exchanger. This analysis is carried out on a sliding observation window (to be able to detect fouling on-line). It is shown that fouling is detected at a very early stage.     

Experimental Study on Air Cooling Via a Multiport Mesochannel Cross-Flow Heat Exchanger

The air-side heat transfer and flow characteristics of cross-flow multiport slab mesochannel heat exchanger are investigated experimentally in this article. The multiport slab mesochannel heat exchanger consists of 15 finned aluminum slabs; each slab contains 68 flow channels of 1 mm circular diameter. The cold deionized water at a constant mass flow rate was forced to flow through the mesochannels, whereas the hot air at different velocities was allowed to pass through the finned passages of the heat exchanger core in cross-flow orientation. The heat transfer and fluid flow key parameters were examined in the region of the air-side Reynolds number in the range of 972–2758, with a constant water-side Reynolds number of 135. The effect of air-side Reynolds number on air-side Nusselt number was examined and a general correlation of Nusselt number with Reynolds number was obtained. The Nusselt number value was found to be higher in comparison with other research works for the corresponding Reynolds number range. The multiport mesochannel flat slab geometry has offered uniform temperature distribution into the core. This uniform temperature distribution leads to higher heat transfer over stand-alone inline flow tube bank.     

Analysis of Fin-Tube Joints in a Compact Heat Exchanger

This article deals with an analysis of fin-tube joints as functions of topological alterations of the joint fillet size. Based on numerical predictions of a joint topology formed by the surface tension driven reactive flow of molten metal, and subsequently verified by empirical evidence gathered through both laboratory and industrial testing, the topology alterations were identified for thermal integrity studies. Subsequently, thermal characteristics of corresponding fin-tube joints were determined in terms of two models of the thermal contact resistance. Model predictions of the fin efficiency with an altered topology of the joint zone were compared with the simulation results from a computational fluid dynamics study, and the results fit well. Numerical predictions of joint topology were devised using an in-house-developed finite-element code, and verified by the Surface Evolver code. Such prediction provided quantitative joint topology information that was needed in assessments of the joint thermal performance. Experimental data were obtained using a computer-controlled transparent hot zone with an ultra-high-purity nitrogen background atmosphere under tightly controlled conditions, and also by an analysis of the state-of-the-art manufacturing process data obtained from an industrial setting. It is demonstrated that a value of fin efficiency, assumed as recommended by traditional sizing design procedures, may drastically differ from actual values.     

高温紧凑板翅式换热器稳态和动态性能的研究

建立了紧凑板翅式换热器的动态数学模型.为了满足系统快速动态仿真的需要,采用容阻特性建模技术建立了紧凑板翅式换热器的仿真模型.在相同的运行条件下,对不同的高温板翅固体材料进行了稳态和动态仿真研究.结果表明:在不同的材料条件下,高温板翅式换热器的稳态性能基本相同;但不同材料的动态特性时间不同,硅碳陶瓷材料具有较小的延迟时间,常规高温合金材料延迟较大.     

应用遗传算法优化设计紧凑式换热器

应用遗传算法对锯齿型板翅式换热器的结构进行了优化设计.以预定的传热量、两侧压降、体积等设计要求为适应度函数,通过对设计变量构成的种群个体进行适应度评估以及选择、交叉、变异等遗传操作,得到符合设计约束的换热器最优结构参数(如翅高、翅长、间距,以及长、宽、高等).此外,对10次计算得到的设计参数进行了统计分析.结果表明:相关结构参数的不确定度很小,应用遗传算法可以快速方便地对紧凑式换热器的几何结构参数作出符合设计要求的选择.     

Transient Response of a Serpentine Finned-Tube Cross-Flow Heat Exchanger to a Step Change in Inlet Temperature

Abstract

An analysis of the thermal response of a finned-tube, liquid-to-gas cross-flow heat exchanger due to a step change in the liquid inlet temperature is performed. Closed-form solutions for the liquid and gas temperatures as functions of space and time are obtained via the Laplace transform technique for both small and large arguments of the modified Bessel function of the first kind. Using four physically important dimensionless parameters, the response of the liquid and average gas outlet temperatures are studied and presented in the time domain. The analysts is extended to a single-row serpentine coil geometry by accounting for U-tube bends. Using a typical heat exchanger geometry, the effects of the tube bends are shown to be significant. Relevant applications include automotive and HVAC heat exchangers and systems.     

紧凑式空气换热器在工业锅炉排烟余热利用上的应用

针对现有燃煤工业锅炉排烟温度偏高的问题,提出一种紧凑式的换热器,利用排烟余热加热空气,其结构采用独特的旁通烟道设计,并且在管束外增加了均流板,减少了阻力损失,在6．5t/h工业锅炉改造中得到成功应用。     

Design of a Compact Ceramic High-Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This article describes a compact silicon carbide ceramic, high-temperature heat exchanger for hydrogen production in the sulfur iodine thermochemical cycle, and in particular, to be used as the sulfuric acid decomposer. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H₂O, H₂SO₄, SO₃) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposer channels are coated with platinum to catalytically decompose sulfur trioxide into sulfur dioxide and oxygen. Hydrodynamic, thermal, and the sulfur trioxide decomposition reaction were coupled for numerical modeling. Thermal results of this analysis are exported to perform a probabilistic mechanical failure analysis. This article presents the approach used in modeling the chemical decomposition of sulfur trioxide. Stress analysis of the design is also presented. The second part of the article shows the results of parametric study of the baseline design (linear channels). Several alternate designs of the chemical decomposer channels are also explored. The current study summarizes the results of the parametric calculations whose objective is to maximize the sulfur trioxide decomposition by using various channel geometries within the decomposer. Based on these results, a discussion of the possibilities for improving the productivity of the design is also given.     

管壳式换热器的换热管强化传热技术浅述

介绍了管壳式换热器的换热管强化传热技术,分析了各自的原理、优缺点及推荐的使用场合。采用节能技术的换热器不仅提高了能源的利用率,而且减少了金属材料的消耗,对化工行业提高经济效益具有重要意义。     

Heat Transfer and Entropy Generation Analysis of an Intermediate Heat Exchanger in ADS

The intermediate heat exchanger for enhancement heat transfer is the important equipment in the usage of nuclear energy. In the present work, heat transfer and entropy generation of an intermediate heat exchanger (IHX) in the accelerator driven subcritical system (ADS) are investigated experimentally. The variation of entropy generation number with performance parameters of the IHX is analyzed, and effects of inlet conditions of the IHX on entropy generation number and heat transfer are discussed. Compared with the results at two working conditions of the constant mass flow rates of liquid lead-bismuth eutectic (LBE) and helium gas, the total pumping power all tends to reduce with the decreasing entropy generation number, but the variations of the effectiveness, number of transfer units and thermal capacity rate ratio are inconsistent, and need to analyze respectively. With the increasing inlet mass flow rate or LBE inlet temperature, the entropy generation number increases and the heat transfer is enhanced, while the opposite trend occurs with the increasing helium gas inlet temperature. The further study is necessary for obtaining the optimized operation parameters of the IHX to minimize entropy generation and enhance heat transfer.     

Analysis of a Parallel-Flow Heat Exchanger with a Heat Source

In this work, a modified analysis of a parallel-flow plate heat exchanger that takes into account a volumetrically uniform heat source in the hot fluid is presented. New expressions for the number of transfer units (NTU) and effectiveness of the heat exchanger are derived. These expressions are verified against the conventional effectiveness–NTU relations in the limit of zero heat source rate. This situation is of interest in applications such as the ammonia–water absorption absorber heat exchanger where a heat source is generated in the solution side. The model studies two cases based on the minimum and maximum heat capacities of the hot fluid. The results show that the number of transfer units and the effectiveness of the heat exchanger are the same for both cases. The analysis is applied to the absorber heat exchanger. Expressions of effectiveness and number of transfer units of a counterflow heat exchanger with a heat source in the hot fluid stream are also given from minimum and maximum heat capacities points of view.     

Stream-Symmetry of Heat Exchangers and Heat Exchanger Assemblies

Sufficient conditions are given for a heat exchanger or an assembly of heat exchangers to be invariant under the interchange of the two fluids. Analysis of this symmetry is performed on tht basis of geometrical or topological properties of the exchanger, and no prior knowledge of the exchanger solution is required. The 1-2 and 1-4 TEMA E, the split-flow TEMA G, and the divided-flow TEMA J shell-and-tube exchangers are discussed as examples. A t tent ion is drawn to possible erroneous interpretations of published F-charts for stream-unsymmetric eases.     

Optimum Design of Cross-Flow Shell and Tube Heat Exchangers with Low Fin Tubes

This paper presents a simple, efficient, robust, optimum design methodology for the design of a high heat transfer and low pressure drop cross-flow shell and tube heat exchanger with integral low fin tubes. This type of heat exchanger has the potential for application in the design of coolers in hypersonic wind tunnels to cool the air that emerges from the diffuser section of the wind tunnel. The methodology described here allows for the design and optimization of any type of heat exchanger that has constraints on pressure drop, as well as the design of an exchanger for very low pressure drop on the shell side fluid.     

三分椭圆螺旋折流板换热器

螺旋折流板换热器是以很小的压降实现强化传热的新型换热设备,但已有的1/4椭圆螺旋折流板方案不适合用于占管壳式换热器绝大多数的正三角形排列布管方案.文中介绍一种新型螺旋折流板换热器,由每层3块三分椭圆折流板首尾相接而形成壳侧螺旋通道,每块折流板的边都位于管束的自然间隔中.由于每块折流板的基准边与椭圆之长轴重合或平行,并与正三角形排列布管的各管孔的一条中心连线平行;另一条边也与另一方向的管孔中心连线平行,因而其管孔的定位划线和制造容易实现.     

管壳式与板式水水换热器性能比较

通过对管壳式与板式换热器结构特点、设计参数、安装检修、技术经济性等方面的性能比较,得出板式换热器优于管壳式换热器的结论.     

废热锅炉的设计

废热锅炉是国内某合成氨/尿素工程项目中的主要设备,这台设备的工艺包及工艺计算为国外某知名废热锅炉制造商提供,哈锅负责对其进行强度设计及产品制造。本文对废热锅炉的选材、结构设计、设计计算以及制造等问题进行较详细的论述和分析。