共查询到20条相似文献,搜索用时 15 毫秒
1.
Sang Chun Lee Sang Chul Nam Tae Gon Ban 《Journal of Mechanical Science and Technology》1998,12(5):917-925
In an effort to develop a heat transfer enhancement technique for low temperature applications such as utilization of LNG
cold energy, an experiment was carried out to evaluate the heat transfer and the pressure drop performance for a spirally
indented tube using ethylene-glycol and water solutions and pure water under horizontal single-phase conditions. The test
tube diameter was 14.86 mm and the tube length was 5.38 m. Heat transfer coefficients and friction factors for both inner
and outer surfaces of the test tube were calculated from measurements of temperatures, flowrates and pressure drops. Correlations
of heat transfer coefficients in the spirally indented tube, which were applicable for laminar and turbulent regimes were
proposed for inner, and outer surfaces. The correlations showed that heat transfer coefficients for the spirally indented
tube were much higher than those for smooth tubes, increased by more than 8 times depending upon the Reynolds number. The
correlations were compared with other correlations for various types of surface roughness. The effect of the Prandtl number
on the heat transfer characteristics was discussed. The critical Reynolds number from the laminar flow to the turbulent flow
inside the spirally indented tube was found to be around Re=1,000. 相似文献
2.
Soo Whan Ahn ByungChang Lee WonCheol Kim Myung- Whan Bae Yoon Pyo Lee 《Journal of Mechanical Science and Technology》2002,16(9):1175-1182
The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling
increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed
to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various
solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the
increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000. 相似文献
3.
Soon Hyun Yoon Moon Kyung Kim Dae Hee Lee 《Journal of Mechanical Science and Technology》1997,11(4):476-483
Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally
investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity
and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width)
ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward
the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of
the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger
than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity
caused by more active mixing of the jet flow. 相似文献
4.
An experimental study was conducted to investigate the effects of air-side fouling and cleaning on the performances of various
condenser coils used in unitary air-conditioning systems. A total of six condenser coils with different fin geometry and row
number were tested. Performance tests were performed at three different conditions: clean-as-received, after fouling, and
after cleaning. In all cases, it was observed that the fouling was mostly confined to the frontal face of the heat exchanger
as reported in the previous investigations. The amount of deposited dust was more dependent on fin geometry for the single-row
heat exchangers than for the double-row heat exchangers. The predominant effect of fouling was to cause a more significant
increase in air-side pressure drop than a degradation in heat transfer performance. For the single-row heat exchangers, the
pressure drop increased by 28 to 31%, while the heat transfer performance decreased by 7 to 12% at the standard air face velocity
of 1.53 m/s depending on fin shape. For the double-row heat exchangers, the pressure drop increased by 22 to 37%, and heat
transfer performance decreased by only 4-5% at the same air face velocity. Once the contaminated coils were cleaned according
to the given cleaning procedure the original performance of the heat exchangers could almost be recovered completely. The
pressure drop could be restored within 1 to 7% and the heat transfer performance could be recovered to within 1 to 5% of the
originally clean heat exchangers. Therefore, it is concluded that a periodic application of the specified cleaning technique
will be effective in maintaining the thermal performance of the condenser coils. 相似文献
5.
It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer.
In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of
boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to
dimensionless parameters such as Sherwood number, Stanton number and Colburnj-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According
to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation
of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more
suitable for turbulent boundary layer. But average Sherwood number and average Colburnj-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar
boundary layer as well as turbulent boundary layer. 相似文献
6.
Nae-Hyun Kim Jung-Ho Ham Jin-Pyo Cho 《Journal of Mechanical Science and Technology》2008,22(3):545-555
The heat transfer and friction characteristics of fin-and-tube heat exchangers having herringbone wave fins were experimentally
investigated. Eighteen samples having different fin pitches (1.34 mm to 2.54 mm) and tube rows (one to four) were tested.
For all the samples, the waffle depth and the corrugation angle of the fin was 1.14 mm and 11.7o respectively. Results showed that the j factors were insensitive to fin pitch, while f factors increased as the fin pitch
increased. As the number of tube rows increased, both the j and f factors decreased. However, the effect of tube row diminished
as the Reynolds number increased, at least for j factors. Existing correlations failed to adequately predict the present data.
A new correlation was developed based on existing data, which significantly improved the predictions of the present data. 相似文献
7.
The boiling heat transfer characteristics of two-phase closed thermosyphons with internal grooves are studied experimentally
and a simple mathematical model is developed to predict the performance of such thermosyphons. The study focuses on the boiling
heat transfer characteristics of a two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal grooves.
A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tube is
also tested for comparison. Methanol is used as working fluid. The effects of the number of grooves, the operating temperature,
the heat flux are investigated experimentally. From these experimental results, a simple mathematical model is developed.
In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphon.
And also the effects of the number of grooves, the operating temperature, the heat flux are brought into consideration. A
good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the
predictions from the present mathematical model is obtained. The experimental results show that the number of grooves and
the amount of the working fluid are very important factors for the operation of thermosyphons. The two-phase closed thermosyphon
with copper tubes having 60 internal grooves shows the best boiling heat transfer performance. 相似文献
8.
Nae-Hyun Kim Do-Young Kim Jun-Hyun Hwang 《Journal of Mechanical Science and Technology》2008,22(12):2498-2508
The effect of inclination angle on the heat transfer and pressure drop characteristics of brazed aluminum heat exchangers
was experimentally investigated under wet conditions. Three samples having different fin pitches (1.25, 1.5 and 2.0 mm) were
tested. Results show that heat transfer coefficients are not affected by the inclination angle. However, friction factors
increase as the inclination angle increases with negligible difference between the forward and backward inclination. The effect
of fin pitch on the heat transfer coefficient and on the pressure drop is also discussed. Comparison of the dry and wet surface
heat transfer coefficients reveals that dry surface heat transfer coefficients are significantly larger than wet surface heat
transfer coefficients. Possible explanation is provided by considering the condensate drainage pattern. The data are also
compared with the existing correlation.
This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha
Nae-Hyun Kim is a Professor of Mechanical Engineering, University of Incheon. His area of interest spans boiling and condensation, heat
transfer enhancement and heat exchanger design. He has been active in heat transfer community, and was a Chairman of Thermal
Engineering Division of KSME. He holds several editorial position including Journal of Enhanced Heat Transfer. He is a recipient
of Asian Academic Award awarded by SAREK and JSRAE. 相似文献
9.
Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure
refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent
temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the
nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants
were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant
mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients
of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure
refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall
compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change
due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface
had a minor effect. 相似文献
10.
An experimental investigation on the flow pattern and pressure drop was carried out for both an adiabatic and a diabatic two-phase
flow in a horizontal tube with pure refrigerants R134a and R123 and their mixtures as test fluids. The observed flow patterns
were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire regions of mass
velocity in this study. The measured frictional pressure drop in the adiabatic experiments increased with an increase in vapor
quality and mass velocity. These data were compared to various correlations proposed in the past for the frictional pressure
drop. The Chisholm correlation underpredicted the present data both for pure fluids and their mixtures in the entire mass
velocity range of 150 to 600 kg/m2s covered in the measurements, while the Friedel correlation was found to overpredict the present data in the stratified and
stratified-wavy flow region, and to underpredict in the annular flow region. 相似文献
11.
Young-Ryoul Back Jae-Heon Lee Byung-Ha Kang Myung-Do Oh 《Journal of Mechanical Science and Technology》1994,8(3):219-230
Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically.
The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region.
The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be
studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding
the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique.
The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation
amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the
pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase
difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are
strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat
transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical
process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail,
and the aspects that must be included for an accurate simulation are discussed. 相似文献
12.
Jin Gi Paeng Kyung Hwan Kim Young Hwan Yoon 《Journal of Mechanical Science and Technology》2009,23(2):536-543
The air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement
and numerical computation. The heat exchanger consists of a staggered arrangement of refrigerant pipes with a diameter of
10.2 mm and a fin pitch of 3.5 mm. In the experimental study, the forced convective heat transfer was measured at Reynolds
numbers of 1082, 1397, 1486, 1591 and 1649 based on the diameter of the refrigerant piping and on the maximum velocity. The
average Nusselt number for the convective heat transfer coefficient was also computed for the same Reynolds number by using
the commercial software STAR-CD with the standard k - ɛ turbulent model. It was found that the relative errors of the average Nusselt numbers between the experimental and numerical
data were less than 6 percent in a Reynolds number range of 1082∼1649. The errors between the experiment and other correlations
from literature ranged from 7% to 32.4%. However, the literature correlation of Kim et al. is closest to the experimental
data within a relative error of 7%.
This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha
Jin-Gi Paeng recieved a bachelor’s degree in Aero Mechanical Engineering from Gyeong-sang National University in 2000. He then went on
to recieve his M.S. degrees from Changwon National University in 2004. Currently, he completed the doc-tor’s course and a
doctoral dissertation in 2007 and 2008, respectively. He will take a doctorate in 2008. 相似文献
13.
In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary
tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the
inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation
was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating
capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased,
the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios
of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the
waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio
of 40 vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90°. the pressure wave
was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency
of pressure oscillation was the highest. 相似文献
14.
Eun Soo Jeong 《Journal of Mechanical Science and Technology》1995,9(2):225-239
Effects of axial temperature gradient on heat transfer, momentum transfer and energy conversion mechanisms within a closed
cylinder-piston apparatus are analyzed. Assuming that the gas density change is small, the first-order and steady second-order
solutions of continuity, momentum and energy equations are obtained. The solutions show that there exists a steady circulating
flow and the magnitude of the steady axial velocity increases as the axial temperature gradient increases. There exists not
only an oscillating component of heat flux between the gas and the wall, but also a steady component whose direction depends
on axial temperature gradient. It is shown that heat is pumped from the wall near the piston to the wall near closed-end for
negative axial temperature gradient. Heat transfer relation for both oscillating pressure and oscillating flow conditions
is proposed. 相似文献
15.
To overcome the fouling problem that is common in heat exchangers for waste heat recovery, a new type of fluidized heat exchanger
was devised and tested. Fluidized bed heat exchangers are considered to be a good candidate for waste heat recovery flue gases
due to their demonstrated ability to avoid fouling or to clean out deposition on heat transfer surfaces, but have a major
drawback with significant pressure losses. These pressure drops typically associated with the distributor plate, which is
a key component in constructing any conventional fluidized bed system, limit the applicability of fluidized bed heat exchangers
for use as an energy saving device. In a new design, however, dilute gassolid particulate is maintained without having a distributor
plate. The main feature of this no-distributor-fluidized (NDF) heat exchanger is the self-cleaning action by ingested circulating
particles at minimal additional pressure loss. In the present study, a multi riser NDF heat exchanger of 7,000 kcal/hr capacity
was built to evaluate its heat transfer performance and fouling reduction characteristics. To experimentally simulate the
fouled condition, fuel rich combustion gas with soot was introduced to the heat exchanger, then a cleaning test was performed
by introducing glass bead particles (600μm) inside the gas passage of the heat exchanger unit. Through the present experimental
study, the performance degradation due to fouling was successfully demonstrated and the cleaning role of particle circulation
was identified. It was also demonstrated that small amounts of circulating particles contribute not only to the fouling reduction
on the gas side, but also to the heat transfer enhancement. Experimental operation data for 50 hours including accelerated
fouling are obtained to simulate the long-term behavior of the system. 相似文献
16.
This paper reports an experimental study on flow boiling of pure refrigerants R134a and R123 and their mixtures in a uniformly
heated horizontal tube. The flow pattern was observed through tubular sight glasses with an internal diameter of 10 mm located
at the inlet and outlet of the test section. Tests were run at a pressure of 0.6 MPa in the heat flux ranges of 5–50 kW/m2, vapor quality 0–100 percent and mass velocity of 150–600 kg/m2s. Both in the nucleate boiling-dominant region at low quality and in the two-phase convective evaporation region at higher
quality where nucleation is supposed to be fully suppressed, the heat transfer coefficient for the mixture was lower than
that for an equivalent pure component with the same physical properties as the mixture. The reduction of the heat transfer
coefficient in mixture is explained by such mechanisms as mass transfer resistance and non-linear variation in physical properties
etc. In this study, the contribution of convective evaporation, which is obtained for pure refrigerants under the suppression
of nucleate boiling, is multiplied by the composition factor by Singal et al. (1984). On the basis of Chen’s superposition
model, a new correlation is presented for heat transfer coefficients of mixture. 相似文献
17.
Journal of Mechanical Science and Technology - In a gas engine based cogeneration system, heat may be recovered from two parts: Jacket water and exhaust gas. The heat from the jacket water is often... 相似文献
18.
The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having
50, 60, 70, 80, 90 internal grooves. Three different working fluids (distilled water, methanol, ethanol) are used with various
volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination
angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and
boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The
experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill
charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively
high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube.
The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum
inclination angle for this study is 20°-30° from the horizontal position. 相似文献
19.
An experiment has been conducted on the flow and heat transfer characteristics of film coolant injected from a row of five
holes with compound angle orientations of 35° inclination angle and 45° orientation angle. The Reynolds number number based
on the mainstream velocity and injection hole diameter 3.58 x104. Three-dimensional velocity, film cooling effectiveness and heat transfer coefficient data are presented at three different
mass flux ratios of 0.5, 1.0 and 2.0. Flow entrainment has been found between the vortices generated by adjacent injectants.
The injectant with compound angle orientation entrains not only the mainstream boundary layer flow but also the adjacent injectant.
Because of the flow entrainment, the injectant. With compound angle orientation is characterized by a single vortex while
two bound vortices are usually observed in the case of simple angle injection. The strength of the secondary flow depends
strongly on the mass flux ratio, which shows significant influence on the film cooling effectiveness and heat transfer coefficient. 相似文献
20.
Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the
annuli with parallel flow, ten different annular arrangements are considered. For water (low rate in l,700<Re<13,000 regime,
data for Nusselt numbers are presented. The results show significant effects of both the pitch to trough height ratio (P/e) and the radius ratio (r
*). AsP/e becomes closer to 8 in the range below the radius ratio(r
*) of 0.5. Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (r*) of 0.5 because flow reattachment position becomes farther in the narrower clearance. 相似文献