计及污垢影响的换热器热优化

本文利用熵产生数方法研究了气体和液体传热介质的顺流、逆流换热器的热力学完善性，结果表明，如给定冷、热流体的入口温度，在综合考虑传热、流动阻力和污垢的情况下，可用优化方法确定其它参数。     

管子管板检测机器人爬行脚的吊装负载能力研究

在爬行机器人携带无损检测（NDT）设备的情况下,为了保证其对立式换热器管子管板角焊缝检测过程的稳定性和可靠性,重点对立式换热器管子管板检测机器人的关键机构——爬行脚的负载能力进行了数值模拟分析和实验研究,应用Hypermesh和ANSYS Workbench联合仿真平台对爬行脚在充气和自锁工况下的结构强度和接触状态进行了仿真。模拟结果表明,在负载逐渐增加的过程中,两种工况下爬行脚与换热管内壁之间没有发生滑移失效,一直保持了良好的稳定性和可靠性。同时对爬行脚实验样机进行了开发和验证,并通过两种工况下的吊装负载实验,得到充气工况最大负载为38 kg,自锁工况最大负载为15 kg,验证了其良好的稳定性。     

涡节型、酒窝型强化管管内沸腾传热特性实验

以微型Capstone C30燃气轮机排放的烟气余热为热源,研究涡节结构强化管、酒窝结构强化管和光管管内沸腾换热特性。实验结果表明：涡节型结构强化传热管管内沸腾换热系数约为光管的1.6~2.1倍,管外对流传热系数约为光管的1.3~1.5倍,总传热系数约为光管的1.4~1.5倍;酒窝型强化传热管管内沸腾换热系数约为光管的2.1~2.5倍,管外对流传热系数约为光管的1.8~2.0倍,总传热系数约为光管的1.9~2.1倍。分析了涡节型强化传热管和酒窝型强化传热管较光管传热性能好的原因。     

Local heat transfer in the first baffle compartment of the shell-and-tube heat exchangers for staggered tube arrangement

A mass transfer measuring method based on absorption, chemical and coupled colour reaction is used to visualize and determine the shell side local heat transfer in the first baffle compartment of shell-and-tube heat exchangers with segmental baffles for staggered tube arrangement. Local mass transfer coefficients were transformed into heat transfer coefficients by using the analogy between heat and mass transfer. The local, per-tube and integral heat transfer coefficient distributions are presented.     

An improved scheme for determining heat transfer correlations from heat exchanger regression models with three unknowns

A nonlinear regression scheme for determining heat transfer correlations from overall heat exchanger measurements is presented. The proposed scheme is valid for any two-fluid heat exchanger data where only one fluid's thermal resistance varies. The resulting regression model has three unknowns; two are associated with the variable resistance, and the third is the sum of all other resistances. The model can be analyzed only by using nonlinear regression because it cannot be transformed into linear form. Unlike existing approximate methods of analysis (known as modified Wilson plots), the proposed scheme is guaranteed to converge if a solution exists. The scheme was successfully tested by analyzing data collected on a tube-fin heat exchanger with continuous plain fins.     

Synthesis and characterisation of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) Zr(IV) monothiophosphate composite cation exchanger: analytical application in the selective separation of lead metal ions

In this study, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) zirconium(IV) monothiophosphate composite cation exchanger was prepared by sol–gel precipitation method. The presence of sulphur in the cation exchanger enhances affinity towards the heavy metal ions which can improve the selectivity of the material. The selectivity studies showed that the material is selective towards Pb(II) ions. To characterise the material, several physicochemical properties were also studied which includes X-ray, scanning electron microscopy and transmission electron microscopy studies. The ion-exchange behaviour of this cation exchanger was studied by using some of the selected properties like ion-exhange capacity for various metal ions, elution, effect of eluent concentration, thermal effect on ion-exchange capacity (IEC). The results of IEC and physicochemical properties revealed that the material is nanocomposite, crystalline, chemically, mechanically and thermally stable. The analytical ability of this cation exchanger was demonstrated in binary separation of Pb(II) ions from a mixture of other metal ions. The recovery is qualitative and the separations are reproducible.     

Heat transfer augmentation and pumping power in double-pipe heat exchangers

One of the criteria for evaluating the performance of a heat exchanger with extended surfaces is the pumping power required for a specified heat duty. The results of an experimental project to relate the pumping power to heat transfer augmentation in a double-pipe heat exchanger are reported. The inner, electrically heated pipe was provided with external, rectangular, axial extended surfaces with interruptions. Heat transfer augmentation and friction factors were determined for different configurations with air as the fluid. Starting with continuous fins, cuts were introduced in the fins to give four ratios of the finssegment length to the gap between the segments, and finally all the fins were removed, which resulted in smooth pipes. Five different mass flow rates in two different inner pipes were employed. Lengths, surface areas, and pumping powers for finned pipes are compared with those for smooth pipes. The average heat transfer coefficient increases with an increase in the frequency of the interruptions. For equal heat transfer rates a significant reduction in the lengths can be achieved by interrupted fins. In many cases the reduction in the length is also accompanied by a reduction in the pumping power.     

Enhancement of heat transfer in compact heat exchanger by different type of rib with holographic interferometry

An experimental study was carried out to investigate enhancement of heat transfer in compact heat exchanger by keeping pressure drop constant in a given range. Two different test matrices, cylindrical and triangular, used to find the optimum ribs were compared with a smooth channel. The investigation was performed with both laminar and turbulent forced flow for Reynolds numbers from 250 to 7000. The geometric parameters, in order to satisfied manufacturer demands, were fixed at p/e=6.67 and the wall temperature was held constant at 50°C. The technique of holographic interferometry was used to determine the temperature distribution in the test duct. Velocity distribution was measured using laser doppler anemometer techniques. For comparison the technique of global measurement was also used. The results revealed that cylindrical ribs are optimum heat transfer for conversion of pressure drop. An 8% experimental error was found in global measurement compared to holographic interferometry.     

A study on the correlation between the thermal contact conductance and effective factors in fin–tube heat exchangers with 9.52 mm tube

The thermal contact resistance is a principal parameter interfering with heat transfer in a fin–tube heat exchanger. However, the thermal contact resistance in the interface between tubes and fins has not been clearly investigated. The objective of the present study is to examine the thermal contact conductance for various fin–tube heat exchangers with tube diameter of 9.52 mm and to find a correlation between the thermal contact conductance and effective factors such as expansion ratio, fin type, fin spacing and hydrophilic coating. In this study, experiments have been conducted only to measure heat transfer rate between hot and cold water. To minimize heat loss to the ambient air by the natural convection fin–tube heat exchangers have been placed in an insulated vacuum chamber. Also, a numerical scheme has been employed to calculate the thermal contact conductance with the experimental data. As a result, a new correlation including the influences of expansion ratio, slit of fin and fin coating has been introduced, and the portion of each thermal resistance has been estimated in the fin–tube heat exchangers with 9.52 mm tube.     

Heat transfer due to harmonic variation in the free stream temperatures in a flat plate exposed on both sides

The heat transfer through an infinite flat plate is studied when the temperatures of the two free streams surrounding it are varying harmonically with time and out of phase, with a delay period τ_d. The configuration is a simplified model for the heat transfer through the separating wall in the isochoric counter-current heat exchanger. The results show that apart from the τ_d effect, the perturbation parameters depend mainly on the cavity passing frequency f. At the thick plate solution, the combined passing frequency–delay time influences are significant only when the dimensionless frequency is smaller than 10. Within this range τ_d affects seriously not only the temperature perturbation amplitudes (which determine the thermal stresses) but also the heat fluxes and the accumulated energy ones. When f ≥ 10, the plate behaves as two separate semi-infinite slabs. Heat penetration delays greater than one cavity passing period may be possible.