共查询到20条相似文献，搜索用时 15 毫秒
1.
CUI Wen-zhi~ 《保鲜与加工》2004,(11):88-91
A new kind of evaporative heat transfer experiment for the cooling process of condensers is conducted. The test coil is immersed in an air-water bubbling layer. The air-water two-phase flow passes through the heating tubes of the coil. Due to the motion of the air bubbles in the water, a thin water film forms on the surface of the heating tubes. As the air bubbles passing by the tubes the water is evaporated into the air. The tubes of coil reject heat to the water film, and the evaporation of the water film then rejects heat to the air bubble stream. This heat transfer mode significantly increases the heat transfer coefficient between tubes and air. The consumption of the power of a water pump can be decreased. Moreover, the airflow rate required is less than that of an air-cooled condenser.The pressure drop of air through air-water bubbling layer and the heat transfer between the tubes and water are experimentally investigated in the paper. The results show that the factors affecting the pressure drop and the heat transfer coefficient involve the pore geometry of sieve plate, the height of the air-water bubbling layer, the air flow rate through the sieve plate and the heat flux of tubes. The heat transfer coefficient between tube and water is two times larger than that of falling film of water on the outer surface of tube. 相似文献
2.
With the influence of the different gas Reynolds number and liquid Reynolds number on falling film heat and mass transfer of subway station plate evaporative cooler, the experiment was carried out by non contact infrared thermal imaging technology under gas liquid cross flow condition. The results indicated that during the increasing of liquid Reynolds number the thickness of liquid film increased and the temperature difference between liquid film inlet and outlet decreased in determined heating water temperature which weakened the heat transfer of liquid film. However, the increase of liquid Reynolds number strengthened the liquid film turbulence that enhanced heat transfer. Under the synergistic effect of these two factors, there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat and mass transfer coefficient of liquid film. 相似文献
3.
Rectangle fin is widely used in different kinds of heat exchangrs. Convection heat transfercoefficient distribution over the fin surface is one of the theorehcal problems in research on enhancement of heat transfer. In this paper, a tube with an attached rectangular fin is used for a model and thefin surface is divided into a network of nodes by the finite difference techinque. When the wind velocityis u= 4. 5 m/s. the temperature distribution of discretization is obtained by experimental measurement,then the convection heat transfer coefficient of all nodes are soved by using the methed of inverse heatconduction problem. Through checking with heat balance methed, the results show that the solution cancorrectly express the actual heat transfer situation.This result is useful to experimental research onenhancement of heat transfer for finned for heat exchangers. 相似文献
4.
To research the influence of combustion chamber thermal boundary conditions on micro combustion characteristics in micro ICE, the laminar flow finite rate model is adopted to simulate the micro combustion process. Firstly, the influence of grid scale, the time step length and the maximum iterations per time step on accuracy of simulation results are explored. The results show that simulation results agree well with experimental results. And then, the influences of heat transfer coefficient, wall thickness and material on combustion characteristics are discussed. The results indicate that heat transfer coefficient has obvious influence on combustion characteristics. The pressure rise rate decreases, the ignition delays and the highest pressure value drops 2 atmospheres as heat transfer coefficient increases from 0 to 55 W/(m 2·K). The wall thickness and material have a little effect on combustion characteristics. This is because that the main heat transfer resistance in the heat flow path from cylinder to external environment lies between the outer wall and environment. 相似文献
5.
A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient. 相似文献
6.
Liu Hong Chen Yuanguo 《保鲜与加工》1991,(3):35-39
The present paper discribes experiment research of effect of the inclination on heat transfer on 9 kinds of plain tubes in atomosphere, working fluids are distill water and ethanel. Experinent result show very obvious effect of inclination of pool boiling heat transfer. The larger heat transfer increases, the larger the inclination does. The correlation obtained on 524 experiment data can be used for reference to engineering design in prospect of heat transger coefficient. 相似文献
7.
The experimental study of the flow resistance and heat transfer characteristics are conducted for water and ethylene glycol solution (66% Wt) flowing in the heat exchanger with small rectangular microchannels . The heat exchanger having the channels of 0.4 mm in width, 2.0 mm in height, and 20 mm in length is heated by a hearing rod at the bottom surface, the upper and two side surfaces are adiabatic. During experiments, the Reynolds number are ranged from 2 to 2 500. The experimental results show that the flow friction factor decreases and Nusselt number increases with increasing Reynolds number for water and ethylene glycol solution. At a fixed Reynolds number, the Nusselt number for ethylene glycol solution with larger Prandtl number is greater than that for water. Meanwhile, the correlations of flow resistance and heat transfer in the heat exchanger with small channels are obtained for engineering application. 相似文献
8.
In present paper, the suppression factor of Chen's model is determined, based on the force and heat balance on a vapour bubble and Clausius-Clapeyron equation, the active nucleate cavity size of flow boiling surface and its disperse characteristic. Furthermore, the correlation is attained using Chen' model and the present suppression factor from the experimental data of R134a and R22 for a smooth tube. The correlation agrees well with the experimental data. It demonstrates the present suppression factor is able to promote the accurate which predicts the heat transfer coefficient of flow boiling in Chen's model. 相似文献
9.
槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。 相似文献
10.
地埋管地源热泵换热器的换热性能受到不同地质结构的影响。以武汉和重庆地区的典型地质构成为边界条件,建立了三维地埋管的单孔双U管换热模型,通过模型计算,获得了两种地质条件下的地埋管换热性能,以重庆地区的地源热泵热响应测试结果以及工程运行数据出发,对模型的计算结果进行了验证,结果表明,模型吻合度较好,可以应用于工程分析。以模型为条件,进行地质结构对换热性能的影响度分析,预测了两地地埋管地源热泵的换热性能并计算得到换热器的平均换热系数分别为武汉地区K1=1.65（W/m·K）,重庆地区K2=1.51（W/m·K）。 相似文献
11.
建立了以容积换热系数为目标函数,工质流率U0、喷头喷孔直径di、导热油液位高度Z为决策变量的直接接触式换热器性能优化模型,同时进一步将液滴群行为与传热协同关系作为约束条件引入优化模型中,重点分析该约束条件对优化过程及结果的影响。运用遗传算法对原模型和补充模型进行了优化分析,结果表明：原模型优化后的容积换热系数达到了初始值的6.7倍;而补充模型最优值的迭代次数比原模型减小了约55%,同时最优值比原模型提高了0.3%。所以该约束条件不仅提高了迭代速率,还提高了寻求全局最优值的概率,使得最优解更逼近全局最优值。 相似文献
12.
Chen Li Li Longjan Zhang Hongji 《保鲜与加工》1993,(2):44-50
SIMPLE method is used to study the influence of aspect ratio on the natural
convection in an enclosure with five discrete heat sources on a vertical wall and an isothermal heat sink on another vertical wall. The range of aspect ratio is from 3. 0 to 12. 22. At high aspect ratio, multiple secondary flow cells can be found,which enhance heat transfer strongly and cause the highest heat transfer coefficient based on cooling area Nuc. With the decrease of aspect ratio,secondary flow cells become weaker gradually and finally reach the lowest Nuc at H/W = 7. 35. If H/W continues to decrease,natural convection is gradually developed,and heat transfer is improved. At H/W = 3. 67,Nuc becomes stable. Then the decrease of aspect ratio will not affect heat transfer. Besides, A heat transfer correlation including the influence of aspect ratio is .also provided. 相似文献
13.
Zhang Hongji Li Longjian 《保鲜与加工》1992,(2):32-39
The effect of the convective heat transfer in the entrance region of the tube on the temperature field and the maximum temperature of the tube material in the tube -mouth region of the high temperature heat exchange equipment is examined by numerical analysis. The computations on the basis of four different formulas for convection heat transfer coefficient are performed. The computed results indicate that the efect can not be ignored as for heat protection of the tube -mouth region and it is resapnable and secure that the mean convective heat transfer coefficient with taking account of the effect of the entrance region is used in the thermal design of the tube -mouth region. 相似文献
14.
A new mold slag with low content SiO2 and high content Al2O3 is designed in order to avoid or alleviate the reaction between Al and SiO2 during the continuous casting of high-Al steel, the acidity of this slag is adjusted by adding B2O3, and the effect of B2O3 content on the fusion property, viscosity property and heat transfer characteristics through the mold slag film of the mold slag is analyzed. The results show that the fusion temperature, viscosity, viscous flow activation energy decrease and heat flux through the slag film increases with the increase of B2O3 content in the range of 4%~10%; temperature time transformation (TTT) diagrams move to longer incubation time with the increase of B2O3, while the crystallization speed of mold fluxes decreases; under this experiment condition, the precipitation of CaF2 crystals can be restrained by the increase of B2O3 content in the mold slag. 相似文献
15.
The heat transfer process in the louvered fin heat exchanger is analyzed,and the corresponding physical and mathematical models on the coupled conduction-convective heat transfer for the louver fin geometry are proposed.The control volume-based finite element method(CVFEM) is employed to solve numerically the problem.The computed(results) reveal the flow structure and heat transfer in the geometry in detail.Compared with the empirical correlation of heat transfer and friction coefficients previously proposed,the computed results show better consistency with the experimental results. 相似文献
16.
抽穗扬花期高温胁迫对不同耐热性水稻生理指标的影响 总被引：1，自引：0，他引：1
高温热害对水稻生产造成了巨大的损失,其危害机理研究刚刚起步。为了研究不同耐热性水稻在高温胁迫下主要生理指标的变化情况,对其生理指标与耐热性的关系进行分析。结果表明:不同品种的水稻,耐热性存在差异,可以通过耐热系数筛选不同的耐热品种;高温胁迫对不同耐热性水稻的生理指标有较大的影响,绝大多数的生理指标随高温处理时间延长,表现出先增大,达到峰值后下降的趋势;耐热性强的水稻品种,各个生理指标的峰值出现的较晚,耐热性差的品种,较早达到峰值;耐热系数和生理指标相关分析表明耐热系数除与MDA含量呈正相关关系外,与各生理指标上呈负相关关系,其中与CAT酶活性相关系数到达了-0.75222**。高温胁迫下,水稻水稻生理指标会发生很大的变化;每个生理指标基本都有峰值出现,表明生物体高温热害是应激物质等调节存在反馈机制;高温胁迫时生理指标变化与耐热性有一定的相关性。 相似文献
17.
In the established model,
the cooling differences are considered between the surface of inner radius and that of
outer radius, and in the transverse direction of thin slab. And the conception for the
effective coefficient of spraying water in continuous casting is firstly put forward.
According to different casting speeds and different cooling zones, different time step
lengths are adopted. In this model the heat transfer differences are thought over among
vertical and curved zones, wide and narrow surfaces an well as angular zone of mould. The
method of the corrected equivalent specific heat is used to deal with latent heat. The
influence of forced convection is considered on heat transfer. Therefore, the model has
higher accuracy and is consistent with the practice. 相似文献
18.
Liao Qiang Xin Mingdao 《保鲜与加工》1993,(3):7-12
This paper presents the experimental results of convective heat transfer performance in 5 copper tubes with three dimensional internally extended surface, with flow of various test fluid in the Reynolds number range of 8,000 to 80,000. Water and mixture of ethylene glycol with water (the ethylene glycol weight content equals 55%) are chosen as test fluid. The effect of the physical properties for test fluid on heat transfer performance in the tubes with three dimensional internally extended surface is discussed. The heat transfer correlation is obtained by the experimental data. 相似文献
19.
In this paper, experimental results on heat transfer performance of a low integral-fin tube, thermoexcel-C tube (C tube) and a new horizontal double-side enhanced condenser tube (GC tube) have been reported for condensation of R-11. Within our experimental scope,the overall heat transfer coefficient of the GC tube can increase more than 5 times that of the smooth tube . And the relevant friction factor inside the GC tube can be 7 times that of the smooth tube. The Second law of thermodynamics was applied to develop a new criterion to assess the heat transfer performance of the GC tube,the C tube,the low integral-fin tube,and the DAC tube[1] (another doubleside enhanced condenser tube). The result shows the heat transfer performance of the GC tube is superior to the other tubes from a thermodynamical viewpoint. 相似文献
20.
Experimental study of condensation heat transfer of HC600a-oil mixture in a horizontal micro fin tube is performed to investigate the inflence of oil percentage, saturated pressure and mass flux on condensation heat transfer.The empirical correlation according to this study is well correlated by the experimental data. By comparing with other refrigerants, HC600a has no inflence on ozone depletion and better heat transfer characteristcs than CFC12 and HCFC134a. It is a promising substitute for CFC12. 相似文献