不同加热方式下大尺寸物料的传热特性

以秸秆料包为原料,采用微波加热和电加热2种方法对其进行了加热试验,测得了料包内部的温度分布,并进行了对比研究.结果表明:微波加热迅速,均匀性好,但物料特性和加热过程中的化学反应对温度分布有重要影响;电加热时,料包内部温度沿导热方向单调递减,由于导热热阻的存在,使得沿导热方向分布的各层物料进入热解阶段的时间间隔逐渐增大,热平衡时各层物料间存在明显的温度梯度.在功率可对比的情况下,微波加热比电加热速度更快、效率更高.     

Flow Boiling Heat Transfer in A Minichannel with Enhanced Heating Surface

This paper presents the results of flow boiling in a 1.0-mm-deep minichannel with asymmetrical heating. The heating element for the working fluid (FC-72) is a single-sided enhanced alloy foil made from Haynes-230. Two types of enhanced heating surfaces, prepared by laser texturing and with microrecesses varied in terms of size, were used for investigations. The experimental research focused on the transition from single-phase forced convection to nucleate boiling, that is, the zone of boiling incipience and further development of boiling. Flow structure was observed through a glass pane. Owing to the liquid crystal layer placed on the opposite side of the enhanced foil surface, it was possible to observe the onset of flow boiling (as a “boiling front”) and to measure temperature distribution on the heating wall through another glass pane. The objective of the study is to determine void fractions for increasing heat fluxes supplied to the heating surface. The flow structure photos were processed in Corel graphics software and binarized. The analysis of phase volumes was developed in Techsystem Globe and NIS-Elements Advanced Research software. The results of experiments with both types of enhanced heating foil were compared.     

Turbulent Opposing Mixed Convection Heat Transfer in a Vertical Flat Channel with One-Side Heating

The paper presents experimental data on turbulent local heat transfer in a flat vertical channel with one-side heating for opposing mixed convection in wide ranges of airflow parameters (Re = 4 × 10³–4 × 10⁴; Gr_q = 1.7 × 10⁸–1.4 × 10¹⁰; pressures p = 0.2, 0.4, 0.6 MPa). Analysis has been performed by application of different buoyancy parameters. General correlation was suggested to predict the heat transfer rate. The experimental data were compared with the available correlations for vertical tubes.     

Heat Transfer Characteristics of Nanofluids in an Acoustic Cavitation Field

Heat transfer characteristics of nanofluids in an acoustic cavitation field have been investigated experimentally. The effects of acoustical parameters, nanofluids concentration, and fluid subcooling on heat transfer are determined in detail. Results show that acoustic cavitation and nanometer particles have a profound influence on single-phase convection and boiling heat transfer of a horizontal circular copper tube. The former is mainly ascribed to the impingement and disturbance of cavitation bubbles and anticipatory activation of smaller vapor embryos within the cavities, while the latter is caused by roughness modification of the tube surface. The above mechanisms are given based on the Schlieren photographs and optical observation. Acoustic cavitation has been shown to be a good way to reduce or eliminate boiling hysteresis.     

散热管道在温室内放热特性的分析

设施农业是我国现代化进程的一个重要内容，现代化温室作为设施农业的标志，正在受到大力发展和重点研究。本论文重点研究温室热水供热系统散热管道的热工性能。论文主要进行了以下工作：1.分析了温室热水供热系统的型式及散热管道的布置方式；2.对温室热水供热系统散热管道的热工性能进行理论分析和计算；3.在密闭小室内，对温室散热管道热工性能进行实际测试，并得出散热管道传热系数的实验公式。     

斯特林机加热管积碳对其换热与循环特性的影响

以柴油机尾气为碳源,考察发动机加热管内流体雷诺数、流体温度和积碳时间对积碳量的影响规律,分析积碳量对加热管换热特性以及对发动机运行性能的影响。研究表明:同一工况下,管内积碳量随积碳时间近似线性增加(180 h);积碳量受雷诺数和流体温度影响较大,雷诺数为10 434时,积碳量最大,管内流体温度为110℃时,积碳量为1.645 6 g,约为190℃时积碳量(0.165 1 g)的10倍;积碳量较少时,可以强化加热管的换热性能,但随着积碳量的增加,换热性能逐渐降低;利用SIMPLE模型考察了管内积碳对斯特林循环的影响,随着积碳量的增加,斯特林发动机的循环效率和循环功率都先增加后减少。结合效能分析,提出在循环功率降低到初始状态功率以下时,此时单位面积积碳量约为5.11~6.88 mg/cm~2,雷诺数在3 688~33 523范围内,建议对斯特林发动机进行积碳检测和清洗。     

返料换热型循环流化床工业锅炉燃烧传热特性

试验研究了一台将全部蒸发埋管布置在回料阀中的11,t/h返料换热型循环流化床工业锅炉的燃烧传热特性.结果表明,锅炉分离器及回料阀中均存在显著的燃烧份额,并随锅炉负荷的变化而变化;回料阀埋管内工质蒸发量随锅炉负荷增加而显著增加,但其蒸发份额基本保持稳定;基于回料阀内循环灰碳平衡,对锅炉满负荷条件下的循环灰量进行了估算,并对循环灰特性及锅炉低负荷性能进行了探讨.     

Heat Transfer Enhancement of an Automobile Engine Radiator using ZnO Water Base Nanofluids

In this research paper, the forced convective heat transfer enhancement of a Suzuki Mehran(VXR) 2016 radiator(heat exchanger) along with pressure drop and friction factor by utilizing Zinc oxide(Zn O) water based nanofluids has been experimentally studied. Three types of nanofluids with different volumetric concentrations of Zn O nanoparticles(0–0.3%) were employed in order to understand its effect on heat transfer enhancement. The experimental setup was completely designed as closely as possibl...     

热害矿井采暖期回风余热循环利用实例

本文以具有热害的某矿回风立井为例,结合井下局部降温与地面风-风换热装置,实现采暖期矿井回风余热的循环利用,达到了节能环保的效果,为相关设计提供参考和借鉴.     

Heat Transfer Characteristics of Gaseous Flows in Micro-Channel with Negative Heat Flux

Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with constant heat flux for which the value is negative for no-slip flow. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian method. The computations are performed for channels with constant heat flux ranging from ?10⁴ to ?10² W/m². The channel height ranges from 10 to 100 μ m and the aspect ratio of the channel height and length is 200. The stagnation pressure is chosen such that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in micro-channels with negative heat flux are compared with those of positive heat flux cases obtained in our previous work and also those of the incompressible flow in a conventional sized channel. In the case of fast flow, temperatures normalized by heat flux have different trends whether heat flux value is positive or negative. A correlation for the prediction of the wall temperature of the gaseous flow in the micro-channel is proposed. The rarefaction effect is investigated for the cases of channel height of 10 μ m with slip boundary conditions. The magnitudes of viscous dissipation term and compressibility term are also investigated. The effect of each term on heat transfer characteristics is discussed.     

Heat Transfer Research of a New Type of Radiant Floor Heating System

Abstract

In China, the energy policy of switching charcoal heating to electric heating is pushing hard. Radiant floor heating system (RFHS) with air-source heat pump system is considered to be a suitable scheme for energy retrofit. A new type of lightweight RFHS with the aluminum layer is put forward in this article, which has the benefit of lowering the supply water temperature by enhancing the heat transfer performance and homogenizing the floor surface temperature distribution. The theoretical model of the new lightweight RFHS is built and solved by the Matlab program. Experiments are conducted to study the thermal performance of the RFHS and verify the theoretical model. The effects of supply water temperature and water flow velocity on the thermal performances of the new RFHS are studied. Then, the effects of aluminum layer on the heat transfer performance of the new system are researched. Finally, comparative research of the new lightweight RFHS and traditional heavy RFHS is carried out. The results show that the average floor surface temperature, heat transfer rate, and annual exploitation cost of the new RFHS are all better than the traditional one.     

Heat Transfer Characteristics of a Quadratic Koch Island Fractal Heat Exchanger

Heat exchangers are widely used in the air conditioning and refrigeration industries, and any increase in their efficiency will have a positive effect on the industry as well. A new design of heat exchanger is proposed that will increase the heat transfer area significantly. The heat transfer area was increased by the use of fractals. Three techniques were used to investigate the heat transfer increase; analytical, numerical, and experimental methods. The results showed that the fractal heat exchanger has a higher heat transfer to overall volume ratio than a conventional tube-in-tube heat exchanger.     

Heat Transfer Performance of Microgroove Back Plate Heat Pipes with Working Fluid and Heating Power

Micro heat pipes(MHP) cooling is one of the most efficient solutions to radiate heat for high heat flux electronic components in data centers. It is necessary to improve heat transfer performance of microgroove back plate heat pipes. This paper discusses about influence on thermal resistance through experiments and numerical simulation with different working fluids, filling ratio and heat power. Thermal resistance of the CO₂ filled heat pipe is 14.8% lower than the acetone filled heat...     

热网监控系统在换热站中的应用

概述了牡丹江热电有限公司热网监控系统的构成、功能、应用及产生的节能效果。     

Improving Heat Transfer with Pool Boiling by Covering of Heating Surface with Metallic Spheres

Abstract

Boiling heat transfer (BHT) was investigated experimentally. Smooth copper walls were covered with single sphere layer and corresponding temperature difference and heat flux were measured. The results were compared with published data for several types of heating surfaces. Comparative analysis shows that surfaces covered with spheres have characteristics as good as the other systems, if not better.     

Research on the Heat Transfer Characteristics of a Loop Heat Pipe Used as Mainline Heat Transfer Mode for Spacecraft

An experimental research is conducted on the heat transfer characteristics of a loop heat pipe(LHP) used in the "mainline" heat transfer mode for spacecraft platform thermal control. The heat from multiple instruments scattered in different locations is collected by thermal control techniques such as axially grooved heat pipes and then transmitted to the radiant surface for dissipation through the LHP in an unified way. The research contents include the start-up characteristics, the operational stability characteristics, the operational blocking characteristics, the continuous blocking characteristics, the heat transfer capability, the thermal resistance, and the dynamic response characteristics under the change of the heat sink temperature. The results show that the higher the auxiliary starting power is, the easier it is to start the LHP; the higher the input power of the thermoelectric cooler is, the more beneficial it is to speed up the stabilization of the vapor-liquid interface in the condenser; the higher the blocking power, the shorter the blocking time of the LHP; the LHP can be operated stably within the heat sink temperature alteration process; the heat transfer ability is higher than 500 W with a systematic thermal resistance of 0.037°C/W.     

Investigation of the Heat Transfer Characteristics

In the present study a numerical investigation of the heat transfer in an annular combustion chamber of a typical industrial gas turbine was done using a Galerkin-based finite-element solution of the problem. Results were obtained for three basic cases: constant flux incident on the entire combustion segment, constant flux in three quadrants of the chamber and a different magnitude constant flux in the other quadrant, and different magnitude fluxes on the upstream and downstream portions of the chamber. The chamber Biot numbers, dimensionless heat flux, and dimensionless structural wall and thermal barrier coating thicknesses were found to have a crucial effect on the chamber temperature distribution. It was shown that changing the magnitude of the heat flux in a single quadrant prominently alters the temperatures throughout the wall in this area, leading to exceedingly steep temperature gradients. It was also found that any step decrease in downstream incident flux leads to a sharp drop in temperatures at the interface of the thermal barrier coating and the combustion gases.     

增压富氧燃烧流化床炉内传热特性

建立了增压富氧燃烧流化床锅炉炉内传热模型.通过模型计算,分析了颗粒粒径、空隙率、床层温度及系统压力等因素对炉内传热特性的影响.结果表明：随着颗粒粒径增大,传热系数减小;随着空隙率增大,传热系数减小;随着温度升高,传热系数增大;随着压力升高,传热系数增大,但增加的幅度明显变小,说明当压力升高到一定程度时,继续升高压力对传热没有太大影响.     

Determination of Heat Transfer During Gear Blank Quenching

This article presents experimental and numerical results for the quench of a gear blank in agitated and stagnant oil. The time history of temperature is determined with a whole-domain optimizer technique inverse solution method. This article offers a procedure to calculate the surface heat transfer on the quenched part by utilizing a straightforward minimization of an appropriate norm. The article presents 10 variations in setting up this inverse problem. The results indicate that dividing the boundary of the gear blank into four zones and assigning a fixed heat transfer coefficient or heat flux to each zone yields an average error of 40 K. This error can be reduced by either increasing the number of zones or by allowing the heat transfer coefficient or heat flux to vary within the zones. Of these possibilities, variation of heat transfer within the zones results in a greater reduction of the average error for the required level of computational effort.     

汽车尾气余热沥青加热装置的研究

针对公路养护的需要,研制了一种利用汽车尾气余热加热沥青的装置,它利用热管换热器回收汽车发动机排气的余热去加热沥青。实验结果表明该设备能够满足设计要求,是一种良好的节能、环保型公路养护设备。