PREDICTION OF TURBULENT PLANE JET IN CROSSFLOW

In this article numerical predictions of turbulent plane jets discharged normal to a weak or moderate cross stream are presented. The Reynolds-averaged Navier-Stokes equations with the standard k- k turbulence model have been used to formulate the flow problem. The governing equations that are elliptic in nature are solved using the finite volume method. The predictions are presented to illustrate the flow pattern involved and to assess the performance of the standard k- k model by comparison with available experimental data for three different jet to cross stream velocity ratios (six, nine, and ten) and the agreement is found to be satisfactory.     

A CRITICAL INVESTIGATION INTO THE HEAT AND MASS TRANSFER ANALYSIS OF CROSSFLOW WET-COOLING TOWERS

The heat and mass transfer process of evaporative cooling in crossflow wet-cooling tower fills is investigated. The governing equations of the crossflow evaporative process are derived from first principles. A detailed account is given of how to solve these equations. The governing equations, according to the Poppe, Merkel, and e-NTU methods of analysis, are considered. The equations of the Poppe method of analysis are extended to give a more detailed representation of the transfer characteristic or Merkel number. The results of a crossflow wet-cooling tower fill analysis according to the Merket, Poppe, and e-NTU methods of analysis are presented. The differences between the results of these methods are evaluated.     

A THEORETICAL AND EXPERIMENTAL INVESTIGATION OF A RADIATIVE COOLING SYSTEM

A radiative cooling system is built in Irbid-Jordan and utilized to cool and store fluids by direct radiation to the low effective sky temperature. The radiative cooling system is built to verify the validity of a mathematical model proposed to describe the system dynamic thermal behavior. The constructed radiative system has the ability to create a 15°C reduction in the mean temperature of a 120 l capacity storage tank using 0.6 m² radiative cooling panel over one night and under climate conditions that vary within the range of 28–55% for relative humidity and 16–27°C for ambient temperature, which are the average spring conditions of Irbid-Jordan (Latitude=32.5°N, Longitude=35.5°E). This implies that the system can emit 13 MJ/(m².night) to the sky. It is found that the theoretical and the experimental predictions of the proposed model are in a qualitative good agreement.     

液体除湿空调实验台的性能分析及实验研究

针对上海气候环境条件设计制造了利用80℃以下低品位热源驱动的全新风送风LiCl液体除湿空调实验台,用于为100m2空调区域提供19℃以下的送风,独立承担室内热湿负荷.分析测试了系统送风温度的影响因素,表明再生热源温度是主要影响因素.该系统结构适合采用除湿再生同时运行模式,该模式下系统运行性能为:夏季工况新风制冷量为35～49kW,热力COP为0.72～0.98;秋季工况为17～29kW,热力COP为0.30～0.51.最后验证了除湿再生独立运行模式的可行性与实际效果:新风制冷量45kW,热力COP为1.1,为今后实验台的改进指明了方向.     

TURBULENT FORCED CONVECTIVE HEAT TRANSFER IN THE ENTRANCE REGION OF A CONFINED JET

Forced convective heat transfer in the entrance region of a confined turbulent jet is studied numerically. The solution of the transport equations is based on a combination of an iterative, finite-volume computational procedure using primitive dependent variables and a two-equation turbulence closure model. The separated flow zone, which extends as far as three pipe diameters, is observed to be a site of high turbulence. The heat transfer results show little sensitivity to the total number of grid points. The variation of the Nusselt number is influenced by the growth of the thermal boundary layer and the presence of the separated zone. Locations of the minimum and maximum Nusselt numbers are found to be functions of the Craya-Curtet number. Finally, the heat transfer predictions are clearly shown to be sensitive to the location of the grid point next to the wall.     

COMPUTATIONAL ANALYSIS OF TURBULENT FLUID FLOW AND HEAT TRANSFER OVER AN ARRAY OF HEATED MODULES USING TURBULENCE MODELS

A computational analysis is carried out using the standard k - l model and two low Reynolds number turbulence models as applied to developing turbulent fluid flow and heat transfer in a channel with surface-mounted heat-generating modules. The channel is assumed to be formed between two adjacent circuit boards with surface-mounted heat-generating modules mounted on a single side of each board. A detailed discussion of the computational model and the solution algorithm is given. Numerical experimentation is carried out with respect to mesh size and other mesh parameters. Calculation is performed for a Reynolds number range 2,000-7,000, and a Prandtl number of 0.7. The predictions of both pressure drop and heat transfer coefficient over the modules are compared with selected experimental data. The comparison showed that the low Reynolds number model based on Jones and Launder gives good predictions in a Reynolds number range of 2,000-5,000. At higher Reynolds numbers such as at Re=7,000, the standard k - l results in better predictions.     

CPC接收面上光强分布及其影响因素的理论和实验研究

将太阳源辐射的高斯模型与射线跟踪法相结合，提出一种计算ＣＰＤ聚光接受面上光强分布的新方法，并对其影响因素进行计算研究和实验证，表明该方法切实可行。     

低倍聚光光伏系统的实验研究

设计并建造了一台低倍聚光光伏发电系统,介绍了系统的结构,阐述了系统工作原理,并对其进行了实验研究,与固定安放的光伏系统进行了对比.根据实验结果,低倍聚光光伏系统在测量时段内的输出功率始终明显大于固定光伏系统,其总发电量是后者的3.18倍,这证明了这种光伏系统的优越性,所收集的电池温度、输出功率等数据对该类型聚光光伏系统的进一步研究有一定的参考价值.     

太阳能半导体冰箱实验研究与性能分析

该文提出一种太阳能半导体冰箱并进行了实验研究与性能分析，它依靠太阳电池驱动，通过热电制冷效应制冷。实验表明，该装置能够维持冰箱内温度在5-10℃，COP约0.3。冰箱性能与太阳辐射和热电制冷元件冷热端温差等条件有很大关系，存在分别使COP和制冷量达到最大值的最佳太阳辐照度。该冰箱可用于边远地区或户外郊游、甚查及施工等缺电条件下食品和饮料的冷藏保鲜以及医用疫苗的保管等。     

喷射式制冷系统工质研究

喷射式制冷系统的性能在很大程度上取决于制冷工质的选择.为了比较新的无污染工质对喷射式制冷系统的影响,建立了喷射式制冷系统分析和工质热物性计算的简单模型,研究了有无回热两种情况下不同工作温度时工质对系统性能的影响.     

喷射式制冷系统工质研究

喷射式制冷系统的性能在很大程度上取决于制冷工质的选择。为了比较新的无污染工质对喷射式制冷系统的影响，建立了喷射式制冷系统分析和工质热物性计算的简单模型，研究了有无回热两种情况下不同工作温度时工质对系统性能的影响。     

NUMERICAL SIMULATIONS ON THE HYDRODYNAMICS OF A TURBULENT SLOT JET IMPINGING ON A SEMICYLINDRICAL CONVEX SURFACE

This study presents the numerical simulations of flow characteristics of a turbulent slot jet impinging on a semicylindrical convex surface. The turbulent-governing equations are solved by a control-volume-based finite difference method with power-law scheme, and the well-known k  ? ε turbulence model associated with the wall function is used to describe the turbulent behavior and structure.

While the width of the slot nozzle is fixed at 9.38 mm, the diameter of the semicylinder is at 150 mm, and air is the working medium, the adopted modifying parameters here include the Reynolds number of the inlet flow (Re = 6000 ~ 20000), jet to impingement surface spacing (y / w = 7 ~ 13), and the entrainment or wall boundary is employed nearby the convex surface. The numerical simulations of flow fields indicate that the velocity distribution of the free jet region departs from the center with increasing y / w. When we increase Reynolds number Re, the variation of the velocity on the convex surface becomes rapid, and the turbulent kinetic energy increases.     

NUMERICAL INVESTIGATION OF AN INTERNAL LAYER IN TURBULENT FLOW OVER A CURVED HILL

The development of an internal layer in a turbulent boundary layer flow over a curved hill is investigated numerically. The turbulent flow equations are solved by a control volume based, finite-difference method. The turbulence is described by a multiple-time-scale turbulence model. Computational results show that the internal layer is a strong turbulence field that develops beneath the external boundary layer and is located very close to the wall. The turbulence field of the boundary layer flow over the curved kill is compared with that of a turbulent flow over a symmetric airfoil (which has the same geometry as the curved hill except that the leading and trailing edge plates were removed) to study the influence of a strongly curved surface on the turbulence field. The turbulence structure in the near-wall region of the curved hill is almost the same as that of the airfoil in most of the curved region even though the approaching external flows are quite different. Results show that the development of the wall shearing stress and separation of the boundary layer at the rear of the curved hill depend mostly on the streamline curvature and are only slightly influenced by the external boundary layer flow.     

一种强化太阳能换热的新型涡流发生器换热机理与实验研究

提出一种强化太阳能热风干燥器和集热器气侧换热的新型涡流发生器—斜截半椭圆柱体,并对其进行了实验研究及机理分析。在雷诺数为4000～38000的紊流范围内对矩形风道内分别布置单排一对直角三角翼、矩形翼、梯形翼、斜截半圆柱体、斜截半椭圆柱体等涡流发生器的强化传热效果和压降特性进行了对比实验。实验在稳态的气水逆流换热方式下进行,并固定各涡流发生器的高宽比为1/2,该迎流攻角为60°。结果表明,斜截半椭圆柱体是具有优越的强化气侧换热效果和低压降特性的新型涡流发生器。该对这种新型涡流发生器强化换热的机理作了初步分析。     

EXPERIMENTAL INVESTIGATION OF INTERFACIAL FRACTURE PARAMETERS AND CRACK INITIATION UNDER MECHANICAL AND THERMOMECHANICAL LOADING

Mechanically and thermomechanically stressed interface cracks in adhesively bonded bimaterials (PMMA-aluminum) with a large elastic and thermal property mismatch are experimentally studied. The elasto-optic effects are mapped as (sigmax+sigmay) contours in the PMAA halves and interfacial fracture parameters are estimated. Crack initiation under mechanical and thermomechanical loading conditions are shown to be controlled by different micromechanical processes. The results suggest that the micromechanical unlocking of microcavities and microprotrusions along the interface is primarily responsible for failure initiation under thermomechanical loading conditions. This is unlike the mechanical loading situations wherein fracture toughness is derived primarily from the breakage of interlocking microentanglements. The measured values of the fracture parameter DeltaIm(Kaiepsilon)T due to a temperature rise is a constant and much higher than its real counterpart (DeltapsiT (a) approxequal 76-82 degrees). The Delta(Kaiepsilon)T|cr thus obtained are much lower than the mechanical counterparts.     

A NUMERICAL STUDY OF JETS IN A REACTING CROSSFLOW

This article is concerned with computational modeling of the mixing of circumferentially placed round jets with a crossflow in a circular duct. This flow is relevant to many engineering applications including gas turbines and steel melting furnaces. Both nonreacting and reacting flows are considered. The fundamental characteristics that govern the mixing of the air and fuel streams are investigated. Further, the applicability of a laminar flamelet model for prediction of the combustion process is assessed through comparison of code predictions to experimental data.     

热泵间歇制热及土壤热响应特性的研究

研究了广东地区地源热泵机组间歇式运行模式下埋地管换热器的换热能力及土壤热响应特性。土壤源热泵系统的单U、双U埋地管换热器深30m,在连续运行工况下,系统运行12h后土壤温度变化很小,单U和双U井的土壤平均温度分别下降5.16℃和6.30℃,系统停机后自然恢复到初始温度需要长达75h。分别取开停时间比3h:5h和4h:5h进行实验,并比较了间歇和连续两种工况下地埋管换热能力的大小,发现间歇工况下单U井的换热能力可分别提高8.3%和7.6%,双U井可分别提高10.2%和3.1%。     

重力式热管串联运行的性能研究

对一种用于太阳能—土壤源热泵地板采暖系统中的碳钢/水重力式热管进行了实验研究。该热管全长0.8m,内外径分别为12mm和15mm。蒸发段采用水加热,冷凝段采用风冷。在不同的串联方式、倾角(-2°~90°)、热水温度(40~60℃)、热水流量(0.1~0.3m3/h)及蒸发段长度(30~180mm)下进行了串联热管的性能实验。实验结果表明:串联热管的传热功率和壁面温度均随供水温度和水流量的提高而持续增长,随倾角和蒸发段长度的增加而先增长后下降;串联热管在倾角为30°~40°、热水温度为60℃、热水流量为0.3m3/h、蒸发段长度为120mm、D型串联的条件下运行最佳。根据实验现象和数据分析了不同条件下串联热管的传热机理,给出了串联热管的工作特性。     

NUMERICAL INVESTIGATION OF HEAT TRANSFER UNDER CONFINED IMPINGING TURBULENT SLOT JETS

This work numerically in vestigates confined impinging turbulent slot jets. Eight turbulence models, including one standard and seven low-Reynolds-number k-epsilon models, are employed and tested to predict the heat transfer performance of multiple impinging jets. Validation results indicate that the prediction by each turbulence model depends on grid distribution and numerical scheme used in spatial discretization. In addition, spent fluid exits are set between impinging jets to reduce the cross-flow effect in degradation of the heat transfer of downstream impinging jets. The overall heat transfer performance can be enhanced by proper spent fluid removal.