冷却水污垢热阻预测的支持向量机法动态模拟实验研究

利用天然水通过管壳式模拟换热器来动态模拟冷却水系统的流动传热和污垢形成过程,实验中恒定壁面材料、加工方式和流速、水温等运行参数,突出研究水质参数对污垢形成的影响。文中基于污垢形成机制的初步认识,定性分析了硬度(钙、镁离子)、碱度、pH值、溶解氧、浊度、铁离子浓度等水质因素对污垢形成的影响,将其和时间作为输入量,污垢热阻作为输出变量,建立基于支持向量机的冷却水污垢热阻预测模型,并以另一运行周期数据检验模型预测精度,计及实验系统的不确定度,平均误差为8.874%;与美国管壳式换热器制造商协会(Tubular Heat Exchanger Manufactures Association,TEMA)标准推荐数据相比,本法所得污垢特性内涵更丰富,热阻除其渐近值,还有时变性;可靠性增强,逼真度高;可操作性强。

A novel experimental setup with sand trunk for heat extraction of geothermal heat exchanger

A novel experimental setup was developed to study the heat extraction of geothermal heat exchanger(GHE)in different operational modes under adiabatic and isothermal boundaries.The experimental setup consists of a sand trunk,a tailored water chiller,a natural cold source unit,two water boxes containing hot water and cool water,and a data acquisition system.The experimental results indicate that the volume flow rate of the entering water is a main factor affecting the heat extraction;furthermore,the heat extraction value per meter pipe decreases gradually along the heat extraction pipe and increases with the increase of the incoming water volume flow rate.Therefore,this novel experimental setup may be helpful to further study the operation performance of GHE in different types of soil.

Simulation of Gas-Fired Triple-Effect LiBr/Water Absorption Cooling System with Exhaust Heat Recovery Generator

An exhaust heat recovery generator is proposed to be integrated with conventional gas-fired triple-effect LiBr/water absorption cooling cycles to improve system energy efficiency. As a case study, simulation of the novel cycle based on promising parallel flow with cooling capacity of 1 150 kW is carried out under various heat recovery generator vapor production ratios ranging from 0 to 3.5%. The life cycle saving economic analysis, for which the annual gas conservation is estimated with Bin method, is employed to prove the worthiness of extra expenditure. Results show that the optimum gas saving revenue is obtained at 2.8% heat recovery generator vapor production ratio with 42 kW exhaust heat recovered, and the system energy efficiency is improved from 1.78 to 1.83. The initial investment of exchanger can be paid back within 7 years and 9 000 CNY of gas saving revenue will be achieved over the 15-year life cycle of the machine. This technology can be easily implemented and present desirable economic effects, which is feasible to the development of triple-effect absorption cycles.

Pressure drop of the film-enlarged tube bundles in air-water two-phase cross flow in evaporative air cooler

An experiment was carried out to investigate the relation of the maximum velocity of air passing through narrowest passage, mass flux of spray water in one square meter in one hour and the pressure drop of tube bundles. Twelve equations were obtained for the relation. The results show that the pressure drop of the tube bundles increases with increase of the maximum velocity of air and the mass flux of spray water. Comparing the pressure drop of the bare tube bundles with that of the film-enhanced tube bundles, it is found that the pressure drop of the film-enhanced tube bundles is lower about 11% and the surface roughness of the film-enhanced plates is a main factor that influences the pressure drop. The data and method obtained in the paper can be used to compute the pressure drop of the film-enhanced tube bundles and is helpful for selection of fan.

Numerical simulation of heat transfer process in cement grate cooler based on dynamic mesh technique

A grate cooler is key equipment in quenching clinker and recovering heat in cement production. A two-dimensional numerical model based on a 5000 t/d cement plant is proposed to for a study on the gas-solid coupled heat transfer process between the cooling air and clinker in a grate cooler. In this study, we use the Fluent dynamic mesh technique and porous media model through which the transient temperature distribution with the clinker motion process and steady temperature and pressure distribution are obtained. We validate the numerical model with the operating data of the cooling air outlet temperature. Then, we discuss the amount of mid-temperature air outlet and average diameter of clinker particles, which affect the heat effective utilization and cooling air pressure drop in clinker layer. We found that after adding one more mid-temperature air outlet, the average temperature of the air flowing into the heat recovery boiler increases by 29.04℃ and the ratio of heat effective utilization increases by 5.3%. This means heat recovery is more effective on adding one more mid-temperature air outlet. Further, the smaller the clinker particles, the more is the pressure drop in clinker layer; thus more power consumption is needed by the cooling fan.

Long-term precipitation change by hourly data in Haihe River Basin during 1961–2004

Hourly summer precipitation data recorded at 21 stations during 1961-2004 in the Haihe River Basin in North China were an alyzed. The results show that the precipitation frequency and amount and the morning peak mainly relating to longduratiol rainfall events decreased during this period, whereas the normalized afternoon peak mainly relating to short-duration event： increased, which may suggest that the proportion of short-duration rainfall has increased as the total summer rainfall has de creased. For short-duration events, the mean intensity and peak intensity increased at most stations and the time to peak inten sity decreased, which may be attributable to the higher thermal contrast between the warmer lower surface and cooler uppe level. In the case of long-duration events, the total amount was significantly correlated with the East Asian summer monsool index for the period 1961-2001 （correlation coefficient of 0.63）. Although the total amount of rainfall in long-duration event： decreased in the basin, the mean intensity and peak intensity, as well as the extreme hourly precipitation, increased in the western basin and decreased in the eastern basin.

Applicability of cement-based grout for ground heat exchanger considering heating-cooling cycles

The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.