探讨螺旋板换热器的传热计算

本文讨论了在传热计算中螺旋板换热器与单壳程、单管程列管式换热器的差异。螺旋板换热器的传热计算在以往采用了与列管式换热器相同的方法 ,从对数平均温度差Δtm 的计算式可知 ,其中作了某种假设 ,一是传热只在某些流道间进行 ,一是热流体两侧的冷流体的温度相等 ,这与实际不符。考虑到螺旋板换热器本身的特点 ,由于热流体所在流道的内外两侧实际上存在传热 ,而且两侧流体的温度并不相同 ,在传热计算中应予考虑。本文从微积分着手 ,导出了一种新的计算方法。

Anti-apoptotic effect of banhasasim-tang on chronic acid reflux esophagitis

To evaluate the anti-apoptotic effect of banhasasim-tang (BHSST) on chronic acid reflux esophagitis (CARE) using a rat model. METHODSA surgically-induced CARE model was established in Sprague-Dawley rats. The modeled rats were divided into a treatment group or untreated group, and given BHSST (1 g/kg body weight per day) or water, respectively, for 15 consecutive days (n = 7 each group). Changes in expression of proteins related to nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and apoptosis were assessed by western blotting. Changes in esophageal pathology were analyzed by gross and histological examinations. RESULTSThe CARE exposure modeled rats showed increased levels of the NADPH oxidase subunit, NOX4 and p47phox in the esophagus. The BHSST treatment completely resolved these CARE-related increases. The CARE rats also showed markers of cytokine stress, including elevated levels of TNF-α and reactive oxygen species as well as of the consequent increase in JNK activation, and subsequent decrease in pro-survival gene expression, such as of Bcl-2. BHSST treatment resolved the CARE-related changes. BHSST also exerted an anti-apoptotic effect, as evidenced by altered expression of the apoptosis-related genes for bax, cytochrome c, and caspase 3. Finally, the BHSST treatment markedly ameliorated the CARE-related esophageal mucosal ulcerations. CONCLUSIONIn the rat model of CARE, BHSST can suppress development of esophageal mucosal ulceration via regulation of reactive oxygen species-dependent apoptosis.

Nitrogen budget in the Changjiang River drainage area

We established a budget model of nitrogen （N） inputs and outputs between watersheds and waterbodies to determine the sources of riverine N in the Changjiang （Yangtze） River drainage area. Nitrogen inputs in the budget included N from synthetic fertilizer, biological fixation by leguminous and other crops, wet/dry atmospheric deposition, excreta from humans and animals, and crop residues. The total N input was estimated to be 17.6 Tg, of which 20% or 3.5 Tg N was transported into waterbodies. Of the total N transported into waterbodies, the largest proportion was N from animal waste （26%）, followed by N from atmospheric wet/dry deposition （25%）, synthetic fertilizer N （17%）, N in sewage wastes （17%）, N in human waste from rural areas （6%） and industrial wastewater N （9%）. We studied the spatial patterns of N inputs and outputs by dividing the Changjiang River drainage area into four sub-basins, from upstream to downstream： the Tongtian River drainage area （TTD, the headwater drainage area, 138 000 l^n2, less disturbed by human activities）; the Jinsha River drainage area （JSD, 347 000 km2, less disturbed by human activities, approx. 3 500 km upstream of the Changjiang estuary）; the Pingshan-Yichang drainage area （PYD, 520 500 krn2, large-scale human disturbance, about 2 000 km upstream of the Changjiang estuary）; and the Yichang-Datong drainage area （YDD, 699 900 km^2, large-scale httman disturbance, approx. 620 km upstream of the Changjiang estuary）. The average N input into waterbodies was 2.3, 7.3, 24.1, and 28.2 kg N/ha in the TTD, JSD, PYD, and YDD sub-basins, respectively, suggesting an increase of N-components of more than 10 times from upstream to downstream areas.

Simulation of DPM distribution in a long single entry with buoyancy effect

Diesel particulate matter(DPM) is considered carcinogenic after prolonged exposure. With more dieselpowered equipment used in underground mines, miners' exposure to DPM has become an increasing concern. This paper used computational fluid dynamics(CFD) method to study DPM distribution based on an experiment conducted by the Diesel Emissions Evaluation Program(DEEP) in Canada. Twenty-four cases were simulated where the emissions from both truck and load-haul-dumps(LHDs) were examined.Each vehicle was placed in two stream wise locations, and the vehicles were oriented either facing or with the rear end toward the main fresh airflow. A species transport model with buoyancy effect was then used to examine the DPM dispersion pattern. High DPM regions were identified downstream,around, and even upstream of diesel engines. This can provide guidelines for good working practices and selection of diesel emission reduction technologies underground.

Residents' Attitude to Pay for Urban River Restoration:Empirical Evidence from Cities in Yangtze Delta

Public willingness to pay （WTP） for urban rivers res- toration was investigated in Shanghai, Nanjing and Hangzhou in China with a sample of 1,285. The factors influencing positive WTP against zero WTP are analyzed using a binary logit model. The results indicate that income, Huff （residential registration） status, household size, home property ownership, riverfront access, and attitudes toward current water quality arc statistically signifi- cant in the likelihood of positive WTR It is also found that respon- dents without local Huff are less willingness to pay positively in pooled sample and Shanghai sample. In the group holding property right of house but without local Huff is less willingness to pay positively in Hangzhou. Respondents in Nanjing are more will- ingness to pay positively than those in Hangzhou. Most common arguments against to pay for the restoration are ＂government＇s duty＂, ＂low income＂, ＂non-local-Huji＂ and ＂lack of trust in the government in how it spends money＂. The results are generally consistent with the hypothesis and specific situations in China. The findings make some contributions to the non-market valua- tion studies as well as provide useful information for public policy making in China.

Effective Channel Length Degradation under Hot-Carrier Stressing

This article describes the effective channel length degradation under hot carrier stressing. The extraction is based on the IDs-Vcs characteristics by maximum transconductance （maximum slope of IDs ＆ VGS） in the linear region. The transconductance characteristics are determine for the several devices of difference drawn channel length. The effective channel length of submicron LDD （Lightly Doped Drain） NMOSFETs （Metal Oxide Semiconductor Field Effect Transistor） under hot carrier stressing was measured at the stress time varying from zero to 10,000 seconds. It is shown that the effective channel length was increased with time. This is caused by charges trapping in the oxide during stress. The increased of effective channel length （△Leff） is seem to be increased sharply as the gate channel length is decrease.

Visualization Investigation on Flowing Condensation in Horizontal Small Channels with Liquid Separator

A simultaneous visualization and measurement experiment was carried out to investigate condensation flow pat- terns and condensing heat transfer characteristics of refrigerant R14 lb in parallel horizontal multi-channels with liquid-vapor separator. The hydraulic diameter of each channel was 1.5 mm and the channel length was 100 ram. The refrigerant vapor flowing in the small channels was cooled by cooling water. The parallel horizontal mul- ti-channels were covered with a transparent silica glass for visualization of flow patterns. Experiments were per- formed at different inlet superheat temperatures （ranging from 3~C to 7~C）. Mass velocity was in the range of 82.37 kg mZs1 to 35.56 kg m-2s1. It was found that there were three different flow patterns through the mul- ti-channels with the increase of mass velocity. The flow patterns in each channel pass almost tended to be same and all of them were annular flows.＇ The efficiency of the liquid-vapor separator with U-type was related to vapor mass velocity and the pressure in the small channels. It was also found that the heat transfer coefficient increased with the increase of the mass velocity while the cooling water mass flow rate increased. It increased to a top point and then decreased. It increased with the increase of superheat in the low superheat temperature region.

Prediction of Turbulent Flow Structure in a Fully Developed Rib-Roughened Narrow Rectangular Channel

Fully developed turbulent water-flow structure over one-side repeated-ribs in narrow two-dimensional rectangular channels was investigated experimentally by Particle Image Velocimetry （PIV） and analytically by the standard k-ε and nonlinear k-ε turbulent models. Two rib-pitch to height ratios （p/k） of 10 and 20 were investigated while the rib height was held constant at 4 mm. The rib height-to-channel equivalent diameter ratio （k/De） was 0.1. The streamwise mean velocity and turbulent kinetic energy distributions at six selected axial stations from the center rib for the two Reynolds number （Re） of 7,000 and 20,000 were obtained and compared with the predicted one. The performance ability in predicting separating and reattaching turbulent water-flow between the standard K-ε and nonlinear k-ε models had yielded no clear conclusion. A large-scale turbulent eddy was generated by the rib promoter and then propagated into the mainstream flow, which led to the deformation of the velocity profile. The turbulent kinetic energy was increased about two times higher at p/k = 20 than that at p/k =10 under the two Reynolds numbers. The effect of the p/k value and the Reynolds number （Re） on reattachment length （XR） was investigated and showed that the p/k and Re had no significant effect on the reattachment length beyond a critical value of Re = 15,000 where XR was found to be approximately 4 times of the rib height under water-flow condition.

Peristaltic flow of Williamson fluid in a convected walls channel with Soret and Dufour effects

Peristaltic flow of magnetohydrodynamic （MHD） Williamson fluid in a symmetric chan- nel is addressed. Modeling is given with Sorer and Dufour effects. Channel walls have compliant properties. Analysis has been carried out through long wavelength and low Reynolds number approach. The obtained series solutions for small Weissenberg number are developed. Impact of variables reflecting the salient features of wall properties, Blot numbers and Soret and Dufour on the velocity, temperature and concentration has been point out. Trapping phenomenon is also analyzed.