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排序方式: 共有83条查询结果,搜索用时 156 毫秒
1.
Data reduction for air-side performance of fin-and-tube heat exchangers   总被引:12,自引:0,他引:12  
The present study focuses on the data reduction method to obtain the air-side performance of fin-and-tube heat exchangers. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper recommends standard procedures for dry surface heat transfer in finned-tube heat exchangers having water on the tube-side. Inconsistencies addressed include the -NTU relationships, calculation of the tube-side heat transfer coefficient, calculation of fin efficiency, and whether entrance and exit loss should be included in the reduction of friction factors. Use of the recommended standardized methodology will provide more meaningful data for use in the development of correlations, or for performance comparison purposes.  相似文献
2.
根据轮胎温度场的单向解耦分析思想,形成了一个基于ABAQUS程序的轮胎稳态温度场的分析方法,单向解耦过程分为变形、损耗、热传导三个分析过程。变形分析中,采用了平衡态的超弹性材料模型;损耗分析中,依据变形分析获得的应力应变场,结合材料粘性损耗特性来获得损耗能量;热传导分析中,依据实测的轮胎胎侧温度场,提出了一种基于实验的数值反演方法来确定胎侧的对流热边界条件。由于轮胎胎侧的形状和结构细节,其对流热边界不同于旋转平圆盘的对流热边界,本文的数值反演方法避免了实测胎侧对流热交换系数的困难。  相似文献
3.
Prediction of cooling-coil performance under condensing conditions   总被引:5,自引:0,他引:5  
The possibility of predicting chilled-water cooling-coil performance under condensing conditions using dry-surface heat transfer correlations is examined. Experimentally determined wet-surface Nusselt number data are presented and compared with dry-surface data obtained from the same cooling coils. The wet-surface Nusselt numbers show considerable scatter; some of the results are higher than the corresponding dry-surface correlations, while others are lower. A sensitivity analysis is presented to illustrate that the wet-surface Nusselt numbers are very sensitive to the uncertainties in the measured inlet dew-point temperature and the measured heat transfer rate. It is demonstrated that the use of dry-surface Nusselt number correlations in a coil model result in wet-surface heat transfer predictions that are generally within 5 percent of the experimentally determined value.  相似文献
4.
纵向涡强化换热的实验研究   总被引:4,自引:0,他引:4  
姚刚  杨泽亮 《实验力学》2001,16(2):158-162
在流道内安装三角翼对涡发生器可以产生纵向涡旋,本文研究了Re=800-8000范围内,以空气作为介质,涡发生器对加热片的强化换热效果,并通过红外热像仪测量加热片面的温度场,结果表明:与光滑加热片换热面比较,加装三角翼对涡发生器后,强化换热效果明显。本文条件下,在雷诺数为6000时,加装涡发生器整体强化换热效果达到50.8%。  相似文献
5.
An experimental study has been conducted to investigate the condensate carryover phenomena in dehumidifying heat exchangers. Two wavy finned-tube coils were tested, for which the fin surfaces were treated to provide either low or high contact angles. The receding contact angle on the fins of the two coils were 70° and 10°, respectively. The distribution of condensate carryover was measured along the tunnel bottom downstream from the coil for different air frontal velocities. As the frontal velocity increases, the quantity of condensate carryover increases, and the condensate is blown further from the coil. The receding contact angle on the fin surface is a key factor controlling the condensate carryover characteristics. The coil having a 10° receding contact angle shows significantly less condensate carryover than the coil having a 70° receding contact angle. Numerous condensate droplets and bridges were observed on the fin surfaces of the 70° receding contact angle coil; however, few were seen for the 10° receding contact angle coil. The dominant carryover results from droplets formed from bridged condensate, and the diameter of the resulting droplets is approximately 3.0 mm.  相似文献
6.
An experimental study on the thermal performance of ground heat exchanger   总被引:4,自引:0,他引:4  
A knowledge of ground thermal properties is most important for the proper design of large GHE (ground heat exchanger) systems. Thermal response tests have so far been used primarily not only for in situ determination of design data for GHE systems, but also for the evaluation of grout material, heat exchanger types and groundwater effects. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in boreholes.  相似文献
7.
The naphthalene sublimation method was used to study the effects of span position of vortex generators (VGs) on local heat transfer on three-row flat tube bank fin. A dimensionless factor of the larger the better characteristics, JF, is used to screen the optimum span position of VGs. In order to get JF, the local heat transfer coefficient obtained in experiments and numerical method are used to obtain the heat transferred from the fin. A new parameter, named as staggered ratio, is introduced to consider the interactions of vortices generated by partial or full periodically staggered arrangement of VGs. The present results reveal that: VGs should be mounted as near as possible to the tube wall; the vortices generated by the upstream VGs converge at wake region of flat tube; the interactions of vortices with counter rotating direction do not effect Nusselt number (Nu) greatly on fin surface mounted with VGs, but reduce Nu greatly on the other fin surface; the real staggered ratio should include the effect of flow convergence; with increasing real staggered ratio, these interactions are intensified, and heat transfer performance decreases; for average Nu and friction factor (f), the effects of interactions of vortices are not significant, f has slightly smaller value when real staggered ratio is about 0.6 than that when VGs are in no staggered arrangement. A cross section area of flow passage [m2] - A mim minimum cross section area of flow passage [m2] - a width of flat tube [m] - b length of flat tube [m] - B pT lateral pitch of flat tube: B pT = S 1/T p - d h hydraulic diameter of flow channel [m] - D naph diffusion of naphthalene [m2/s] - f friction factor: f = pd h/(Lu 2 max/2) - h mass transfer coefficient [m/s] - H height of winglet type vortex generators [m] - j Colburn factor [–] - JF a dimensionless ratio, defined in Eq. (23) [–] - L streamwise length of fin [m] - L PVG longitudinal pitch of vortex generators divided by fin spacing: L pVG = l VG/T p - l VG pitch of in-line vortex generators [m] - m mass [kg] - m mass sublimation rate of naphthalene [kg/m2·s] - Nu Nusselt number: Nu = d h/ - P pressure of naphthalene vapor [Pa] - p non-dimensional pitch of in-line vortex generators: p = l VG/S 2 - Pr Prandtl number [–] - Q heat transfer rate [W] - R universal gas constant [m2/s2·K] - Re Reynolds number: Re = ·u max·d h/ - S 1 transversal pitch between flat tubes [m] - S 2 longitudinal pitch between flat tubes [m] - Sc Schmidt number [–] - Sh Sherwood number [–]: Sh = hd h/D naph - Sr staggered ratio [–]: Sr = (2Hsin – C)/(2Hsin) - T p fin spacing [m] - T temperature [K] - u max maximum velocity [m/s] - u average velocity of air [m/s] - V volume flow rate of air [m3/s] - x,y,z coordinates [m] - z sublimation depth[m] - heat transfer coefficient [W/m2·K] - heat conductivity [W/m·K] - viscosity [kg/m2·s] - density [kg/m3] - attack angle of vortex generator [°] - time interval for naphthalene sublimation [s] - fin thickness, distance between two VGs around the tube [m] - small interval - C distance between the stream direction centerlines of VGs - p pressure drop [Pa] - 0 without VG enhancement - 1, 2, I, II fin surface I, fin surface II, respectively - atm atmosphere - f fluid - fin fin - local local value - m average - naph naphthalene - n,b naphthalene at bulk flow - n,w naphthalene at wall - VG with VG enhancement - w wall or fin surface  相似文献
8.
In this paper, the authors adopt the model suggested by Lin and et al in [6–8] with some improvement in difference schemes. We especially focus on the details of water-heat exchange process in vegetation. For illustration, numerical simulation of the exchange process for wheat in Xu-Chen region in Shandong province is carefully made, the computational results turn out in good agreement with the experimental data. The study, as one of the subproject of 06-02-01 was financially supported by the Bureau of Resources and Environment, CAS and National Natural Science Foundation of China.  相似文献
9.
本文通过求解三维Navier-Stokes方程,导出计算挤压膜阻尼的公式,对Mulcahy所提出的模型作了改进,并提出了stokes数的间隙修正因子的概念. 改进后的挤压膜阻尼模型计及管子振幅的影响,在管子振幅很小的情况下,它与Mulcahy提出的模型相似,实际上可把Mulcahy提出的模型看成改进后模型的一个特例. 为了验证改进后的模型,对传热管在空气和静水介质中的阻尼进行了实验研究.结果表明理论计算值与实验测量值符合良好.  相似文献
10.
Wing-type vortex generators for fin-and-tube heat exchangers   总被引:2,自引:0,他引:2  
The effect of wing-type vortex generators on heat transfer and pressure drop of a fin-and-tube heat exchanger element was investigated. Local heat transfer was measured by liquid crystal thermography on the fin in the Reynolds number range of 600–2700. Flow losses were estimated from the measured pressure drop of an element. Delta winglets were used as vortex generators. Four fin-and-tube configurations were tested, an inline and a staggered arrangement, each with plain fins and with fins with a pair of vortex generators behind each tube. For the inline tube arrangement the vortex generators increase the heat transfer by 55–65% with a corresponding increase of 20–45% in the apparent friction factor. Results indicate that the vortex generators have the potential to reduce considerably the size and mass of heat exchangers for a given heat load.  相似文献
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