共查询到20条相似文献,搜索用时 62 毫秒
1.
Jorma Heikkinen 《Heat and Mass Transfer》2007,43(4):341-350
The fin efficiency in a heat exchanger element that is a simplification of one row in a tube-and-fin heat exchanger was theoretically
examined within wide ranges of the affecting variables: the conventional fin efficiency and the isothermal effectiveness of
the heat exchanger. These variables are suggested for use also in the further studies. An analytical solution can be found
for the case of a constant heat transfer coefficient. The ambient temperature variation alone decreases the fin efficiency
less than 4%. The local heat transfer coefficient obtained from the numerical fluid flow simulations is strongly affected
by the fin properties because the thermal boundary conditions for the fluid flow changes. On a poorly conducting fin surface
the heat transfer coefficient in front of the fin base is much larger than on an isothermal fin because the heat flux is increasing
in the flow direction. At low fin efficiencies this compensates for the decrease in fin efficiency due to ambient temperature
variation. 相似文献
2.
A three-dimensional numerical study was made to investigate effects of fin angle, fin surface emissivity, and tube wall temperature on heat transfer enhancement for a longitudinal externally-finned tube placed vertically in a small chamber. The numerical model was first validated through comparison with experimental measurements and the appropriateness of general boundary conditions was examined. The numerical results show that the mean Nusselt number increases with Rayleigh number for all the fin angles investigated. The maximum heat transfer rate per mass occurs when the fin angle is about 60° for fin surface emissivity between 0.7 and 0.8 and 55° when the surface emissivity increases to 0.9. With increasing tube wall temperature, both the natural convection and radiation heat transfer are enhanced, but the fraction of radiation heat transfer decreases in the temperature range studied. Radiation fraction increases with increasing fin surface emissivity. Both convection and radiation heat transfer modes are important. 相似文献
3.
A simulation model of a fin-and-tube heat exchanger is presented. The effect of the relative humidity, air speed, fin base
temperature, and inlet air temperature on the estimation of the overall heat-transfer coefficient and fin efficiency under
wet conditions is also investigated. This model considers a non-uniform airflow velocity as well as a variable sensible heat
transfer coefficient. 相似文献
4.
Atipoang Nuntaphan Tanongkiat Kiatsiriroat 《Experimental Thermal and Fluid Science》2007,31(8):1103-1109
This research investigates the effect of fly-ash deposit on thermal performance of a cross-flow heat exchanger having a set of spiral finned-tubes as a heat transfer surface. A stream of warm air having high content of fly-ash is exchanging heat with a cool water stream in the tubes. In this study, the temperature of the heat exchanger surface is lower than the dew point temperature of air, thus there is condensation of moisture in the air stream on the heat exchanger surface. The affecting parameters such as the fin spacing, the air mass flow rate, the fly-ash mass flow rate and the inlet temperature of warm air are varied while the volume flow rate and the inlet temperature of the cold water stream are kept constant at 10 l/min and 5 °C, respectively.
From the experiment, it is found that as the testing period is shorter than 8 h the thermal resistance due to the fouling increases with time. Moreover, the deposit of fly-ash on the heat transfer surface is directly proportional to the dust–air ratio and the amount of condensate on heat exchange surface. However, the deposit of fly-ash is inversely proportional to the fin spacing. The empirical model for evaluating the thermal resistance is also developed in this work and the simulated results agree well with those of the measured data. 相似文献
5.
In the present study, the heat transfer characteristics in dry surface conditions of a new type of heat exchanger, namely
a helically coiled finned tube heat exchanger, is experimentally investigated. The test section, which is a helically coiled
fined tube heat exchanger, consists of a shell and a helical coil unit. The helical coil unit consists of four concentric
helically coiled tubes of different diameters. Each tube is constructed by bending straight copper tube into a helical coil.
Aluminium crimped spiral fins with thickness of 0.5 mm and outer diameter of 28.25 mm are placed around the tube. The edge
of fin at the inner diameter is corrugated. Ambient air is used as a working fluid in the shell side while hot water is used
for the tube-side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates
are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. The effects of the inlet conditions of both
working fluids flowing through the heat exchanger on the heat transfer coefficients are discussed. The air-side heat transfer
coefficient presented in term of the Colburn J factor is proportional to inlet-water temperature and water mass flow rate.
The heat exchanger effectiveness tends to increase with increasing water mass flow rate and also slightly increases with increasing
inlet water temperature. 相似文献
6.
Valery Ponyavin Yitung Chen Anthony E. Hechanova Merrill Wilson 《Heat and Mass Transfer》2008,44(11):1379-1389
The present study addresses fluid flow and heat transfer in a high temperature compact heat exchanger which will be used as
a chemical decomposer in a hydrogen production plant. The heat exchanger is manufactured using fused ceramic layers that allow
creation of channels with dimensions below 1 mm. The main purpose of this study is to increase the thermal performance of
the heat exchanger, which can help to increase the sulfuric acid decomposition rate. Effects of various channel geometries
of the heat exchanger on the pressure drop are studied as well. A three-dimensional computational model is developed for the
investigation of fluid flow and heat transfer in the heat exchanger. Several different geometries of the heat exchanger channels,
such as straight channels, ribbed ground channels, hexagonal channels, and diamond-shaped channels are examined. Based on
the results, methods on how to improve the design of the heat exchanger are recommended. 相似文献
7.
Ke-Wei Song Liang-Bi Wang Ju-Fang Fan Yong-Heng Zhang Song Liu 《Heat and Mass Transfer》2008,44(8):959-967
Tube bank fin heat exchanger is one of the most compact heat exchangers, and it is widely used in industry equipments. The
flat tube bank fin heat exchangers with vortex generators (VGs) have significant good heat transfer performance, and are used
as radiators of locomotive. Here, we study heat transfer enhancement of a new fin where VGs are mounted on both surfaces of
the fin. The heat transfer performance of this pattern is evaluated by a numerical method, and the results are compared with
those obtained, under identical mass flow rate, when the VGs are mounted only on one surface of the fin. The results reveal
that using this new pattern the height of VGs can be reduced and still obtain satisfactory heat transfer enhancement, while
the pressure drop is reduced. The results also reveal that if VGs on one surface of the fin is determined, the locations where
VGs are mounted on other surface of the same fin are very important, with configurations studied in this paper, depending
on the value of Reynolds number, there exists an optimum location with which best heat transfer performance can be obtained. 相似文献
8.
A numerical scheme has been developed for computing fluid flow and heat transfer in periodically repeating geometries. Unstructured solution-adaptive meshes are used in a cell-centred finite volume formulation. The SIMPLE algorithm is used for pressure‒velocity coupling. For periodic flows the static pressure is decomposed into a periodic component and one that varies linearly in the streamwise direction. The latter is computed from the imposition of overall mass balance at the periodic boundary. A subiteration between the periodic pressure correction equation and the correction to the linear component is used. For heat transfer a formulation using the physical rather than the scaled temperature is employed. The scheme is applied to both laminar and turbulent computations of periodic flow and heat transfer in a variety of heat exchanger geometries; comparison with published computations and experimental data is found to be satisfactory. © 1997 John Wiley & Sons, Ltd. 相似文献
9.
A methodology for determining the optimum pin fin profile is introduced to minimize the fin volume for a constrained heat transfer rate under dehumidifying surface conditions. In this methodology, the mass transfer is evaluated using the polynomial variation of humidity ratio with temperature. A scheme is developed for solving the optimum conditions derived as a function of unknown temperature-dependent parameter and tip temperature under both the fully and partially wet surface conditions. The effect of psychrometric properties of the surrounding air on the optimum wet fin profile has been examined. The analysis presented in this study is pertinent to the dry, fully wet, and partially wet surface conditions. In every case study of optimum wet fins, the excess temperature at the tip vanishes with respect to the surrounding temperature. A non-linear temperature distribution in the optimum wet fin has been identified. 相似文献
10.
In the present study, the potential of rectangular fins with 30° and 90° angle and 10 mm offset from the horizontal direction for heat transfer enhancement in a plate fin heat exchanger is numerically evaluated with conjugated heat transfer approach. The rectangular fins are mounted on the flat plate channel. The numerical computations are performed by solving a steady, three-dimensional Navier–Stokes equation and an energy equation by using Fluent software program. Air is taken as working fluid. The study is carried out at Re = 400 and inlet temperatures, velocities of cold and hot air are fixed as 300, 600 K and 1.338, 0.69 m/s, respectively. Colburn factor j versus Re design data is presented by using Fluent. The results show that the heat transfer is increased by 10 % at the exit of channel with fin angle of 30° when compared to channel without fin for counter flow. The heat transfer enhancement with fins of 30° and 90° for different values of Reynolds number with 300, 500 and 800 and for varying fin heights, fin intervals and also temperature distributions of fluids on the top and bottom surface of the channel are investigated for parallel and counter flow. 相似文献
11.
This paper presents the analysis of heat transfer in a partially wet annular fin assembly during the process of dehumidification. In past studies, both fully dry and fully wet fins have been analyzed. New analytical formulation leading to a closed-form solution has been developed for a partially wet fin, which is most common in dehumidifier coil operation during air conditioning. The parameters that influenced the heat transfer rate in the finned tube structure are ratio of fin and wall thermal conductivities, ratio of fin thickness to fin pitch, ratio of wall thickness to fin pitch, ratio of fin length to fin pitch, cold fluid Biot number, ambient Biot number, the relative humidity and dry bulb temperature of the incoming air, and the cold fluid temperature inside the coil. Calculations were carried out to study the performance of the heat exchanger. The computed results included the temperature distribution in the wall and the fin and the fin efficiency. 相似文献
12.
Hideo Inaba Fujio Komatsu Akihiko Horibe Naoto Haruki Akito Machida 《Heat and Mass Transfer》2008,44(11):1305-1313
This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube
heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were
conducted under various conditions of air flow rate (0.5–1.0 m/s) and the temperature of brine (14–20°C) that was the heat
transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected
by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted.
Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger
is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of
non-dimensional temperature on them is larger than Reynolds number . 相似文献
13.
Performance of horizontal copper heaters with a transverse fin structure was investigated for pool boiling heat transfer and critical heat flux limits. Data were obtained for 5.1 and 7.6 cm diameter structured cooper and brass heaters in saturated R-113 boiling at pressures ranging between 0.037 and 1 atm. The fin structure consisted of 0.16 cm×0.16 cm×0.32 cm high square fins with an interfin spacing of 0.16 cm. Following a similar methodology to Haley and Westwater1, a numerical analysis of the heat transfer phenomenon was performed by solving the one-dimensional fin conduction equation with a non-linear heat transfer boundary condition obtained from the previously reported data for R-113 boiling on plain surfaces. The predictions agreed with the data at the 1 atm pressure levels but showed deviations at the low pressure levels. The results showed that, compared with plain surface heaters of the same diameters the finned structured surfaces investigated: (a) decreased the wall temperature differences for a given heat flux and saturated pool boiling conditions, thus improving the nucleate boiling heat transfer coefficients, and (b) increased the critical heat flux limits, calculated as the power input divided by the heater projected area, by a factor of 2–2.5. 相似文献
14.
A combination of uniform-thickness annular fins evenly spaced on a tube is a common extended-surface heat exchanger configuration. An analytical model is developed and is verified by comparing total heat transfer predicted by the model to available experimental data. A direct-pattern search technique is applied to the model to optimize the fin/ tube geometry. Optimum dimensions and spacing of fins are established to provide the maximum free convection heat transfer from a fin/tube combination. The optimum arrangement is dependent on fin thermal conductivity, tube diameter, volume of fin material per unit length of tube, and temperature difference between the tube and the surrounding air. Calculated results indicate that a fin in the optimum fin/tube system is shorter and thicker than an isolated fin optimized for minimum material (with no consideration of the effects of fin spacing). 相似文献
15.
Using a quasi-static approach valid for Stefan numbers less than one, we derive approximate equations governing the movement
of a phase change front for materials which generate internal heat. These models are applied for both constant surface temperature
and constant surface heat flux boundary conditions, in cylindrical, spherical, plane wall and semi-infinite geometries. Exact
solutions with the constant surface temperature condition are obtained for the steady-state solidification thickness using
the cylinder, sphere, and plane wall geometries which show that the thickness depends on the inverse square root of the internal
heat generation. Under constant surface heat flux conditions, closed form equations can be obtained for the three geometries.
In the case of the semi-infinite wall, we show that for constant temperature and constant heat flux out of the wall conditions,
the solidification layer grows then remelts. 相似文献
16.
3D numerical simulation on fluid flow and heat transfer characteristics in multistage heat exchanger with slit fins 总被引:1,自引:0,他引:1
In this paper, a numerical investigation is performed for three-stage heat exchangers with plain plate fins and slit fins
respectively, with a three-dimensional laminar conjugated model. The tubes are arranged in a staggered way, and heat conduction
in fins is considered. In order to save the computer resource and speed up the numerical simulation, the numerical modeling
is carried out stage by stage. In order to avoid the large pressure drop penalty in enhancing heat transfer, a slit fin is
presented with the strip arrangement of “front coarse and rear dense” along the flow direction. The numerical simulation shows
that, compared to the plain plate fin heat exchanger, the increase in the heat transfer in the slit fin heat exchanger is
higher than that of the pressure drop, which proves the excellent performance of this slit fin. The fluid flow and heat transfer
performance along the stages is also provided. 相似文献
17.
Wanling Hu Mei Su Liangcheng Wang Qiang Zhang Limin Chang Song Liu Liangbi Wang 《Heat and Mass Transfer》2013,49(9):1271-1285
In real application, once the pattern of fin is determined, fin spacing of tube bank fin heat exchanger can be adjusted in a small region, and air flow velocity in the front of the heat exchanger is not all the same. Therefore, the effects of fin spacing on heat transfer performance of such heat exchanger are needed. This paper numerically studied the optimal fin spacing regarding the different front flow velocities of a circular tube bank fin heat exchanger with vortex generators. To screen the optimal fin spacing, an appropriate evaluation criterion JF was used. The results show that when front velocity is 1.75 m/s, the optimal fin spacing is 2.25 mm, when front velocity is 2.5 m/s, the optimal fin spacing is 2 mm, and when front velocity is higher than 2.5 m/s, the optimal fin spacing is 1.75 mm. 相似文献
18.
XueHong Wu WenHui Zhang YanLi Lu QiuPing Gou ZhiMing Luo 《Heat and Mass Transfer》2014,50(9):1251-1259
In this paper, the semi-dimpled slit fin is proposed and the characteristics of heat transfer and fluid flow are analyzed based on the orthogonal experiment design method. A serial studies on the effects of fin pitch, arrangement of semi-dimple, dimple radius on heat transfer and flow characteristics of semi-dimpled slit fin are investigated. The computational results show fin pitch (Fp) has significantly effected on the performance of heat transfer and fluid flow, the influence of arrangement of semi-dimple, the dimple radius (R) and the opening direction of semi-dimples dwindle. At the same time, compared to the general semi-dimpled slit fin, the heat transfer coefficient and JF factors of the optimized fin increase by 10.7–25.1 and 2.6–7.7 %, respectively. When Re ≤ 1,521, the overall performance of slit fin is better than that of optimized fin; while Re > 1,521, the overall performance of optimized fin is better than that of slit fin. Finally, the performance evaluation plot of enhanced heat transfer of heat exchanger is applied to analyze the optimized fin, it can be seen that optimization fin have better heat transfer performance under the same power consumption. 相似文献
19.
Isak Kotcioglu Sinan Caliskan Veysel Ozdemir Senol Baskaya 《Heat and Mass Transfer》2009,45(10):1239-1246
In the present study, sizing of a single pass cross flow heat exchanger with unmixed fluid streams has been investigated.
The heat exchanger is a cross flow heat exchanger. It has overall dimensions of 20 × 20 × 20 cm. Two the most common heat
exchanger design problems are the rating and sizing problem. Sizing problems deal with designing an exchanger and determining
its physical size to meet the specified heat duty, pressure drops and other considerations. It means the determination of
the exchanger construction type, flow arrangement, heat transfer surface geometries and materials, and the physical sizes
of an exchanger to meet specified heat transfer and pressure drop. In this study, the physical size (length, width, height,
mass flow rates of both fluids and surface areas on each side of the exchanger) are determined. Inputs to the sizing problem
are surface geometries, fluid mass flow rates, inlet and outlet fluid temperatures and pressure drop on each side. Dimensions
of L
a
, L
b
, and L
c
for the selected surfaces were investigated such that the design meets the heat duty and pressure drops on both sides exactly. 相似文献
20.
Cristian CuevasDanielle Makaire Laurent DardennePhilippe Ngendakumana 《Experimental Thermal and Fluid Science》2011,35(1):154-164
In the present study, a whole heat exchanger with a hydraulic diameter of 2.3 mm is tested, which is a minichannel heat exchanger according to the Kandlikar classification. This is a louvered fin and flat tube heat exchanger currently used in car cooling systems, also known as radiator. A glycol-water mixture (60/40 in volume) circulates through the tubes at flows ranging from 100 to 7800 l/h and at a supply temperature of 90 °C. This fluid is cooled with ambient air at a temperature of 20 °C and at frontal air velocities varying between 0.5 and 7 m/s. The thermohydraulic performance of the heat exchanger is compared with the classical correlations given in the literature for the heat transfer and the friction factor calculation. On the glycol-water side the heat exchanger is characterized for Reynolds numbers from 30 to 8000. A first comparison is carried out with the correlations available in the literature with a purely predictive model by obtaining a predictive value with a systematic under prediction lower than 10%. In a second step a semi-empirical model is considered to identify the experimental heat transfer coefficients for this application. 相似文献