荒煤气上升管余热回收装置的传热实验研究

2台不同导流角度的新型螺旋夹套式余热回收装置用于4.3m焦炉上升管进行传热特性实验研究,测试了荒煤气在一个结焦周期内的温度波动及总体传热效果.结果表明,荒煤气的温度随着结焦时间呈现周期性波动,最高可达825℃,荒煤气温度波动对传热量的影响较大,但对总体传热系数影响不大.稳定氮气侧流量190m3/h,入口温度30℃,91 #装置(导流角度4°)的,havg为30.23W/(m2·℃),92#装置(导流角度3°)的havg为25.2 W/(m2·℃).针对荒煤气的流动特性和本实验装置结构特点所提出的传热模型同实验数据匹配较好,最大相对误差控制在±20％以内.     

EFFECT OF NEAR-WALL MODELLING ON PREDICTION OF IMPINGEMENT HEAT TRANSFER

Due to enhanced transport characteristics, impinging jets are widely used in industry to dry large surface area products such as paper and textiles. The present numerical study concerns the modelling of convective heat transfer for impingement drying. Flow and heat transfer under a confined two dimensional turbulent air jet impinging on a flat surface were modelled by solution of two-dimensional Navier-Stokes and energy equations. The turbulence model used was the high-Re number version of the well known two-equation (κ-?) model and numerical solution was by the upwind finite difference scheme. The specific objective was to evaluate the accuracy of schemes for modelling the near-wall turbulent flow.

The mean flow properties such as centerline velocity decay and the pressure distribution at the impingement surface show no dependence on the near-wall model used. Heat transfer predictions were found to be quite sensitive to the choice of near-wall model. Best agreement between predictions and experiments was obtained for a Chieng-Launder type model with a new modification, use of k_p instead of k_v in the calculation of τ_w.     

EFFECT OF NEAR-WALL MODELLING ON PREDICTION OF IMPINGEMENT HEAT TRANSFER

Due to enhanced transport characteristics, impinging jets are widely used in industry to dry large surface area products such as paper and textiles. The present numerical study concerns the modelling of convective heat transfer for impingement drying. Flow and heat transfer under a confined two dimensional turbulent air jet impinging on a flat surface were modelled by solution of two-dimensional Navier-Stokes and energy equations. The turbulence model used was the high-Re number version of the well known two-equation (κ-ε) model and numerical solution was by the upwind finite difference scheme. The specific objective was to evaluate the accuracy of schemes for modelling the near-wall turbulent flow.

The mean flow properties such as centerline velocity decay and the pressure distribution at the impingement surface show no dependence on the near-wall model used. Heat transfer predictions were found to be quite sensitive to the choice of near-wall model. Best agreement between predictions and experiments was obtained for a Chieng-Launder type model with a new modification, use of k_p instead of k_v in the calculation of τ_w.     

HEAT AND MASS TRANSFER IN IMPINGEMENT DRYING

ABSTRACT

In industrial drying applications, efficient transfer of heat and mass between a drying medium and the material being dried is very critical for the overall economics of the operation. Impinging jets are therefore widely used for their enhanced tmnsport characteristics, especially for drying of continuous sheets of materials such as paper and textiles. In such applications, a thin sheet of material, as wide as 6m in cross machine direction, speeds at velocities as high as 90 km/hr under high velocity jets emerging from a confining surface parallel to the material surface. Many variables and effects need to k considered for proper design of such impinging jet systems: nozzle geometry and size, nozzle configuration, location of exhaust pons, nozzle-to-surface separation, jet-to-jet separation, cross flow, jet exit velocity and surface motion. For permeable materials, additional enhancement of heat and mass transfer that occur when some of the impinging gas is removed through the material makes this option an atmctive one.

Here, we review the above effects and offer predictive correlations from literature which may be used in the design of high velocity impinging jet systems.     

喷液流化床中传热特性

引言流化床反应器由于其特有的众多优点,尤其是传热效果好、床层温度均匀,而在工业上得到广泛的应用．然而随着工业的发展,生产能力的提高,对流化床的换热能力提出了更高的要求．于是出现了许多强化流化床传热的方法,例如乙烯氧氯化反应中的内置换热管法;乙炔制醋酸乙烯中的外加夹套法;催化裂化反应中的粒子循环法．在80年代初期出现了一种流化床带液操作的新方法,它在气相法聚乙烯生产中的应用（其操作工艺被简称为冷凝工艺）具有远大的前景．该工艺是在一般的气相法聚乙烯流化床反应工艺的基础上,在流程中添加易挥发的液体,使反…     

HEAT AND MASS TRANSFER IN IMPINGEMENT DRYING

In industrial drying applications, efficient transfer of heat and mass between a drying medium and the material being dried is very critical for the overall economics of the operation. Impinging jets are therefore widely used for their enhanced tmnsport characteristics, especially for drying of continuous sheets of materials such as paper and textiles. In such applications, a thin sheet of material, as wide as 6m in cross machine direction, speeds at velocities as high as 90 km/hr under high velocity jets emerging from a confining surface parallel to the material surface. Many variables and effects need to k considered for proper design of such impinging jet systems: nozzle geometry and size, nozzle configuration, location of exhaust pons, nozzle-to-surface separation, jet-to-jet separation, cross flow, jet exit velocity and surface motion. For permeable materials, additional enhancement of heat and mass transfer that occur when some of the impinging gas is removed through the material makes this option an atmctive one.

Here, we review the above effects and offer predictive correlations from literature which may be used in the design of high velocity impinging jet systems.     

CONDENSATION OF SINGLE TWO-PHASE BUBBLES IN AN IMMISCIBLE LIQUID: HEAT TRANSFER CHARACTERISTICS

An analytic expression has been derived for the steady rate of heat transfer from a two-phase bubble condensing in an immiscible liquid medium. The resistance offered by condensate film has been taken into account in terms of its thermal properties.

A comparison of predicted and experimentally observed values for the average Nusselt number shows satisfactory agreement.     

多孔铝内体积对流传热系数的测量

引　言多孔铝 (合金 )作为一种高孔隙率 (孔隙率 >0 9)多孔介质 ,具有明显的多功能性[1] .通孔型多孔铝是指多孔铝的内部孔隙互相连通 ,且外部流体可以通过 ,具有比表面积大、质量轻的特点 ,是开发强化换热装置的优选材料 ,有可能在新型紧凑式换热器、回热器、风冷冷凝器 (或冷却塔 )等换热设备研制过程中获得应用 .但流体流经多孔铝的　对流换热特性实验数据比较缺乏 ,对各种影响因素的研究也欠充分 .Hwang等[2 ] 测量了空气流经70 %、 80 %、 95 %三种孔隙率多孔铝的体积对流传热系数 ,但缺乏对孔隙密度、母材性质等影响的研究 .何德坪…     

RIB ORIENTATION EFFECTS ON HEAT TRANSFER PERFORMANCE IN FORCED CONVECTIVE BOILING

The effects of rib orientation to the direction of flow on the heat transfer performance of ribbed surfaces in forced convective boiling have been investigated experimentally. Test surfaces were manufactured from a stainless steel plate of 1.60 mm thickness on to which transverse rectangular ribs were machined. Rib height, length and spacing were kept constant at 0.50 mm, 1.00 mm and 0.50 mm respectively and rib orientation to the direction of flow was varied from 0° to 135°. In order to ensure good reproducibility of the experimental data, the effects of surface roughness were isolated by providing a constant surface micro-roughness for all test specimens and the effects of aging were also isolated. Experimental data are reported for heat transfer from ribbed surfaces to water boiling at atmospheric pressure for velocities ranging from 0.2 m/s to 1.4 m/s and inlet subcoolings from 5° to 30°C.     

CONVECTIVE HEAT TRANSFER DURING COATING OF PARTICLES IN TWO-DIMENSIONAL SPOUTED BEDS

ABSTRACT

This work deals with the evaluation of gas-to-particle convective heat transfer in a process of coating of particles in two-dimensional spouted beds. A detailed calculus routine is presented and two correlations of heat transfer coefficient, for the spout and annular regions are derived. The study is performed with two, two-dimensional spouted beds with different sizes and with two different particles, placebo and soybean.     

INVESTIGATION OF IMPINGEMENT HEAT TRANSFER COEFFICIENT AT HIGH TEMPERATURES

Very little information exists for the impingement heat transfer coefficient at high temperatures. All available empirical correlations are mainly based on experiments conducted at relatively low impingement temperatures, and thus cannot describe the heat transfer characteristics of the impingement air at high temperatures with sufficient accuracy. A comprehensive study of the impingement heat transfer coefficient at high temperatures is carried out and presented in this paper. The aim of the study is to give a summary of the experimental results of the impingement heat transfer covering a large impingement air temperature range from 100 to 700°C. Heat transfer measurements were carried out on a laboratory-scale test rig. The main parts of the rig were a fan, a gas burner for air heating, a heavily insulated nozzle array with 300 × 500 mm impingement surface, a 40 mm thick and 300 × 500 mm sized aluminium plate for determination of heat transfer, and a data acquisition system. The heat transfer rate was determined from the heat-up rate of the aluminium plate due to the high temperature jet impingement.     

HEAT TRANSFER IN THE THERMAL ENTRANCE REGION OF AN INTERNALLY HEATED FLOW

The passage of an electrical current through a liquid causes the evolution of heat and when the electrical conductivity depends on the temperature, the rate of evolution varies from point to point in the fluid. Within the thermal entrance region of a duct flow, competition between the rate of evolution and the rate of conduction to bounding surfaces, coupled with differences in residence time between points in planes perpendicular to the flow direction causes local maxima in the temperature field in such planes. The evolution of such temperature fields is studied here using Galerkin's method to approximate solutions of the appropriate differential equation. Temperature fields of this sort influence the electrophoretic migration of small particles in the process known as continuous flow electrophoresis.     

INVESTIGATION OF IMPINGEMENT HEAT TRANSFER COEFFICIENT AT HIGH TEMPERATURES

ABSTRACT

Very little information exists for the impingement heat transfer coefficient at high temperatures. All available empirical correlations are mainly based on experiments conducted at relatively low impingement temperatures, and thus cannot describe the heat transfer characteristics of the impingement air at high temperatures with sufficient accuracy. A comprehensive study of the impingement heat transfer coefficient at high temperatures is carried out and presented in this paper. The aim of the study is to give a summary of the experimental results of the impingement heat transfer covering a large impingement air temperature range from 100 to 700°C. Heat transfer measurements were carried out on a laboratory-scale test rig. The main parts of the rig were a fan, a gas burner for air heating, a heavily insulated nozzle array with 300 × 500 mm impingement surface, a 40 mm thick and 300 × 500 mm sized aluminium plate for determination of heat transfer, and a data acquisition system. The heat transfer rate was determined from the heat-up rate of the aluminium plate due to the high temperature jet impingement.     

HEAT TRANSFER IN THE THERMAL ENTRANCE REGION OF AN INTERNALLY HEATED FLOW

The passage of an electrical current through a liquid causes the evolution of heat and when the electrical conductivity depends on the temperature, the rate of evolution varies from point to point in the fluid. Within the thermal entrance region of a duct flow, competition between the rate of evolution and the rate of conduction to bounding surfaces, coupled with differences in residence time between points in planes perpendicular to the flow direction causes local maxima in the temperature field in such planes. The evolution of such temperature fields is studied here using Galerkin's method to approximate solutions of the appropriate differential equation. Temperature fields of this sort influence the electrophoretic migration of small particles in the process known as continuous flow electrophoresis.     

ANALYSIS OF CONVECTIVE HEAT TRANSFER DURING IMMERSION FRYING

ABSTRACT

Immersion frying was studied as a high temperature drying process and analogies drawn between periods found in drying and similar periods in immersion frying. Analysis of external heat transfer during immersion frying showed a highly complex system of free and forced convection augmented by boiling conditions. Oil flow was found to be driven downward by buoyancy forces due to cooling at the sample surface then upward due to entrainment in vapor bubbles during boiling conditions. Experimental work showed the convective heat transfer coefficient to be a dynamic property ranging from 300 to 1100 W/m²°C and to be strongly coupled with bulk movement of the oil. Heat flux measurements found a peak flux of nearly 30,000 W/m³. Based on analysis of bubble dynamics it is hypothesized that heat flux increases with increased oil degradation through a reduction in vapor bubble size and increase in bubble frequency due to changes in interfacial properties of the oil.     

液化气烘炉在罐式煅烧炉的应用

介绍了罐式煅烧炉利用液化气烘炉的工作原理、结构特点,并对应用过程、工艺流程进行了详细说明,液化气烘炉在罐式煅烧炉上的成功应用,为气体烘炉技术在罐式煅烧炉上的推广应用起到了很好的示范作用。     

离心流化床中气固传热特性的实验研究

本文使用玻璃细珠、黄砂和氧化铝球在不同操作条件下进行了离心流化床气固两相间传热特性的实验研究．测定了气体入口、出口和床层温度随时间的变化．分析了床层厚度、粒径、物料性质、床体转速和气体流速等因素对气固传热特性的影响．首次获得了离心流化床气固两相传热的准则方程．     

ANALYSIS OF CONVECTIVE HEAT TRANSFER DURING IMMERSION FRYING

Immersion frying was studied as a high temperature drying process and analogies drawn between periods found in drying and similar periods in immersion frying. Analysis of external heat transfer during immersion frying showed a highly complex system of free and forced convection augmented by boiling conditions. Oil flow was found to be driven downward by buoyancy forces due to cooling at the sample surface then upward due to entrainment in vapor bubbles during boiling conditions. Experimental work showed the convective heat transfer coefficient to be a dynamic property ranging from 300 to 1100 W/m²°C and to be strongly coupled with bulk movement of the oil. Heat flux measurements found a peak flux of nearly 30,000 W/m³. Based on analysis of bubble dynamics it is hypothesized that heat flux increases with increased oil degradation through a reduction in vapor bubble size and increase in bubble frequency due to changes in interfacial properties of the oil.     

CYLINDER-TO-BED HEAT TRANSFER IN AERATED VIBRATED BEDS OF SMALL PARTICLES

Cylinder-to-bed heat transfer in aerated vibrated beds was studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0-25 Hz and half-amplitude from 0-4 mm. Alumina and molecular sieve particles of sizes ranging from 27 μm to 1400 μm were used as the model particles. A single-orifice bottom plate was used to supply the air flow at rates varying from 0 to the minimum fluidizing velocity. For small-panicle beds which display resonant behaviour, the cylinder-to bed heat transfer coefficient remains close to the packed bed value as the frequency is increased. Close to the resonant frequency, it increases rapidly to reach a maximum at the resonant frequency. Thereafter, h decreases only gradually with further increase of frequency. The cylinder-to-bed heat transfer coefficients at resonance are much higher than those in packed beds (up to 19 times). The high heat transfer rates are due to particle mobility which reaches a maximum at the resonant point. Surface coverage is greatly affected by both the resonant frequency and aeration rates. It affects the heat transfer rate but is not rate limiting even at low bed bulk densities and surface particle coverage.     

BREAKDOWN OF A HEATED LIQUID INITIAL BREAKDOWN OF A HEATED LIQUID FILM IN COCURRENT TWO-COMPONENT ANNULAR FLOW: I. SMALL PERTURBATION MODEL

A small perturbation theory is developed for the breakdown of a thin evaporating liquid film draining down a heated tube subject to a non-negligible surface shear stress. ¹The film is always so thin that entrainment is negligible. The usual traveling wave is here not adequate, and a time-independent surface perturbation which is exponential in the flow and periodic in the cross-stream direction is assumed. The appropriate Orr-Summerfeld equation and boundary conditions are then derived. Comparison with experimental data, using a large effective contact angle, obtained from the lower bound of the eigenvalue spectrum, gives good agreement for the critical Reynolds number.