107,763 research outputs found
Film condensation heat transfer of low integral-fin tube.
No full textPhDFor condensation on horizontal low-finned tubes, the
dependence of heat-transfer performance on fin spacing has
been investigated experimentally for condensation of
refrigerant 113 and ethylene glycol. Fourteen tubes have
been used with inside diameter 9.78 mm and working length
exposed to vapour 102 mm. The tube had rectangular
section fins having the same width and height (0.5 mm and
1.59 mm) and with the spacing between fins varying from
0.25 mm to 20 mm. The diameter of the tube at the fin root
was 12.7 mm. Tests were also made using a plain tube
having the same inside diameter and an outside diameter
equal to that at the root of the fins for the finned tubes.
All tests were made at near atmospheric pressure with
vapour flowing vertically downward with velocities of 0.24
m/s and 0.36 m/s for refrigerant 113 and ethylene glycol
respectively. Optimum fin spacings were found at 0.5 mm
and 1.0 mm for refrigerant 113 and ethylene glycol
respectively. In earlier experiments for steam using the
same tubes, the optimum fin spacing was found to be 1.5 mm.
Maximum enhancement ratios of vapour-side heat-transfer
coefficient (vapour-side coefficient for a finned tube /
vapour-side coefficient for a plain tube. for the same
vapour-side temperature difference) were 7.5, 5.2 and 3.0
for refrigerant 113, ethylene glycol and steam
respectively.
Enhancement phenomena have also been studied
theoretically. Consideration has been given to a role of
surface tension forces on the motion and configuration of
condensate film. On the basis of this study, several
semi-empirical equations, to predict heat-transfer
performance, have been obtained. These are considered to
represent recent reliable data (present and other recent
works) satisfactorily
Forced-convection condensation heat-transfer on horizontal integral-fin tubes including effects of liquid retention
No full textPhDAccurate and repeatable heat-transfer data are reported for forced-convection filmwise
condensation of steam and ethylene glycol flowing vertically downward over two
single, horizontal instrumented integral-fin tubes and one plain tube. Vapour-side,
heat-transfer coefficients were obtained by direct measurement of the tube wall
temperature using specially manufactured, instrumented tubes with thermocouples
embedded in the tube walls. Both tubes had fin height of 1.6 mm and fin root diameter
of 12.7 mm, with fin thickness and spacing of 0.3 mm and 0.6 mm, respectively for
the first tube and 0.5 mm and 1.0 mm respectively for the second. Tests were
performed at atmospheric pressure for steam with nominal vapour velocities from
2.4 m/s to 10.5 m/s and at three pressures below atmospheric with nominal vapour
velocities from 8.4 m/s to 57 m/s for steam and 13 m/s to 82 m/s for ethylene glycol.
The data show that both the finned tubes provide an increase in heat flux at the same
vapour-side temperature difference with increasing vapour velocity. Visual
observations were made and photographs obtained of the condensate retention angle
at each combination of vapour velocity and pressure. It was observed that the
curvature of the meniscus was distorted by the increase in vapour velocity and in
many cases, the extent of condensate flooding changed compared to its value in the
quiescent vapour case.
In parallel, experiments involving simulated condensation on finned tubes were
conducted using horizontal finned tubes in a vertical wind tunnel. Condensate was
simulated by liquid (water, ethylene glycol and R-113) supplied to the tube via small
holes between the fins along the top of the tube. Downward air velocities up to 24 m/s
were used and retention angles were determined from still photograph. Eight tubes
with a diameter at the fin root of 12.7 mm were tested. Five tubes of which had fin
height of 0.8 mm and spacing between fins of 0.5 mm, 0.75 mm, 1.0 mm, 1.25 mm
and 1.5 mm and three tubes had fin height 1.6 mm with fin spacings 0.6 mm, 1.0 mm
and 1.5 mm. The results were repeatable on different days and suggested, for all tubes
and fluids, that the retention angle asymptotically approached a value around 80o to
85o (from either lower or higher values at zero vapour velocity) with increase in air
velocity. Good agreement was found with observations taken during the condensation
experiments
Free-convection condensation on single horizontal pin-fin tubes
No full textPhDNew experimental data are reported for free-convection condensation of ethylene
glycol and R-113 on three-dimensional pin-fin tubes. Effects of pin geometry and tube
thermal conductivity (for copper, brass and bronze giving a mean range of 400, 120 and
80 W/m K over the range of temperature of interest) were investigated. All tests were
performed at near atmospheric pressure with downward flowing vapour at low velocity.
Heat-transfer enhancement was found to be approximately twice the corresponding
active surface area of the tubes, i.e. the surface area of the parts of the tube and pin
surface not covered by condensate retained by surface tension. For ethylene glycol, the
best performing pin-fin tube gave a heat-transfer enhancement of 5.8, about 24 %
higher than the ‘equivalent’ two-dimensional integral-fin tube (i.e. with the same finroot
diameter, longitudinal fin spacing and thickness and fin height). For R-113, the
best enhancement was 5.9, about 10 % higher than the equivalent integral-fin tube.
For both fluids tested, vapour-side, heat-transfer enhancement was found to increase
with decreasing circumferential pin spacing and increasing pin height. Circumferential
pin thickness had little effect on heat-transfer enhancement. Effects of tube thermal
conductivity were found to be more significant for ethylene glycol than R-113.
Retention angle measurements were made under static conditions (without
condensation) and were found to be larger than for equivalent integral-fin tubes. An
expression for condensate retention angle on pin-fin tubes was proposed and found to
agree with the measured retention angles to ±15%.
A semi-empirical model for condensation heat transfer on horizontal pin-fin tubes has
been developed which accounts for the combined effect of gravity and surface tension.
The model predicts the majority of available data to ±20 %
Enhancement of Round Tube and Flat Tube-Louver Fin Heat Exchanger Performance Using Deluge Water Cooling
No full textAn experimental study has been conducted to evaluate the performance of a compact round-tube louver-fin condenser, each with frontal areas of 0.25 m2 in both dry and wet conditions. Deluge water cooling is achieved by incorporating a perforated bottom plate-type water distributor on top of the round tube heat exchanger. Water is used as a refrigerant, and enters the heat exchanger tubes at 35°C temperature. Ambient air and deluge cooling water are both maintained at 22°C temperature. Heat exchanger capacity and air-side pressure drop are measured with the heat exchanger angle set at 0° and 21° from vertical, with a frontal air velocity of 1.4 m/s and 3.5 m/s without deluge water cooling, and a frontal air velocity of 1.4 m/s with deluge water cooling. For both heat exchangers, the capacity was significantly enhanced with the use of deluge water cooling and with the heat exchanger angle set at 21° from vertical
Evaluation of Fin Efficiency and Heat Transfer Coefficient for Fined Tube Heat Exchange
No full textThis study discussed the estimation of the fin efficiency and the pure-heat transfer coefficient in the heat exchanger. One hundred twenty cases of plate fins having known heat transfer coefficients were tested numerically to investigate the validity of the previous classical theory on the fin efficiency. The conventional theory on the fin efficiency was only useful when the value of NTUf was near zero. However, it was not useful at high NTUf and low fin efficiency in the heat exchanger. A new definition of fin efficiency and a model for pure-heat transfer coefficient are suggested, which are applicable to the heat exchanger. The present model reduced error greatly than the classical model in the estimation of the pure-heat transfer coefficient at 0 \u3c mL \u3c 2, 0 \u3c NTUf \u3c 2.5
A true piece of cultural hybridity: Ginammi’s Psaltir s posledovanjem of 1638
No full textThe paper focuses on the activity of the Venetian printing house Ginammi, which printed books in Serbian and Croatian for the great part of the 17th century, thus acquiring undisputed primacy in the Balkan market. In 1638, house Ginammi published a Psaltir s posledovanjem, the last book in slavenosrpski to be published in Venice, which can also be regarded as a true specimen of the universality of the Baroque culture. In the first part, the paper investigates the activity of house Ginammi, with reference to the Venetian printing context. In the second part, Ginammi’s Psaltir s posledovanjem of 1638, its text and its illustrations, are analysed, thus showing how the finished work functions as a curious amalgamation of Medieval Serbian, Renaissance and Baroque visual imagery
Sound production and associated behavior of tagged fin whales (Balaenoptera physalus) in the Southern California Bight
No full textBackground: For marine animals, acoustic communication is critical for many life functions, yet individual calling behavior is poorly understood for most large whale species. These topics are important for understanding whale social behavior and can also serve as a baseline for behavioral studies assessing whale response to disturbance. Using a new technique for identifying the calling individual, we measured body orientation, dive behavior, and surface social behavior in relation to call production for tagged fin whales in Southern California. Results: Behavioral metrics associated with elevated call rates included shallow maximum dive depths (10–15 m), little body movement, negative pitch in body orientation, and moderate body roll. Calling whales were also more likely to be traveling than milling, in groups rather than solitary, and without change in group size compared to non-calling whales. Conclusions: These are the first descriptions of body posture and depths at which fin whales are most likely to call, and some possible sound propagation and/or anatomical reasons for these results are considered. The call behavior characterizations presented here will help in predicting calling behavior from surface behavior, informing interpretation of passive acoustic data, and determining the effects of anthropogenic sound on whales in Southern California.Peer reviewe
Emblemi u Orfelinovoj Istoriji Petra Velikog
No full textОва студија настаје из жеље да се осветли улога емблема као основног елемента за иконографију нумизматике петровске епохе, позивајући се првенствено на неке примере из бакрорезних медаља илустрованог издања Житија Петра Великаго Захарије Орфелина, прве монографије посвећене руском цару на неком словенском језику
Frosting Performance of Fin-and-Tube Evaporators with Small Copper Tubes Diameter
No full textIn modern heat pump systems, the heat exchangers use enhanced heat transfer surfaces for both air and refrigerant sides. In air conditioning applications, conventional 9.5 mm (3/8 inch) tube diameter fin-and-tube coils are slowly being replaced by microchannel heat exchangers. However, during heating mode the energy performance of heat pump systems with microchannel outdoor coils are generally lower than those of fin-and-tube direct-expansion evaporators due to a higher frequency of defrost cycles. A different approach might be to utilize fin-and-tube technology, which has proven records of excellent water drainage characteristics and good performance in frosting operating conditions, and enhance the air side heat transfer rates by introducing a larger number of small diameter copper tubes. In this paper, six fin-and-tube coils with copper tube diameter ranging from 5 mm (1/5 inch) to 7mm (8/29 inch) were experimentally investigated in frosting operating conditions. The laboratory experiments were conducted in an air flow wind tunnel at Oklahoma State University. Experimental data on heat transfer rate and air-side pressure drop across the coils were measured and the fin density and the tube diameter were varied in a parametric fashion during the experimental campaign. The performance of the fin-and-tube coils were also compared to those of a conventional 9.5 mm copper tube diameter fin-and-tube heat exchanger and of a microchannel heat exchanger that had similar air-side frontal area and at similar operating conditions of outdoor direct-expansion evaporators in heat pump systems for residential applications. The trends of the data during frosting operation suggested that reducing the tube diameter was beneficial for frosting performance at low fin density while was harmful at high fin density. The data showed that increasing the fin density increased the capacity but significantly reduced the time for heating service for the evaporator. Small copper tube diameter resulted in about 11% higher initial capacity at dry start conditions and about 4% higher average integrated capacity when considering the entire frost period. The data discussed in this paper serve as basis for future research on direct-expansion evaporators for air-source heat pump applications, in which the frosting of the outdoor heat exchangers is still one of the major concerns
Effect of Louver Angle on Performance of Heat Exchanger With Serpentine Fins and Flat Tubes in Periodic Frosting
No full textThis paper presents the results of an experimental study on the air-side pressure drop and overall heat transfer coefficient characteristics for serpentine-louvered-fin, microchannel heat exchanger in periodic frosting. It focuses on quantification of the effects of louver angle on heat transfer and pressure drop and on defrost and refrost times. Nine heat exchangers differing in louver angle and fin pitch (i.e. louver angle 15º to 39º and fin pitch 15 to 18 fpi) are studied. The face velocity was 3.5 ms/ and inlet air relative humidity of 70% and 80%. Effect of fin pitch and louver pitch on initial Colburn j0 factor and Fanning friction f0 factor during the start of the first frosting cycle are reported, and compared to the prediction by the Chang and Wang (1997)
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