• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.3
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• pp.265-270
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• 2012

A finned tube type heat exchange module has been proposed for a multi-burner water tube boiler. Fin density and length increase in streamwise direction to equalize the evaporation for each module, which makes it difficult to apply conventional bulk design procedure. The design program has been improved by updating data for every row of tubes along the flow. A numerical simulation has been also conducted to evaluate the effect of inlet conditions and validated with experiment. The heat transfer of the first row has been underpredicted by the conventional Zhukauskas correlation, since the acceleration of the flow due to the blockage is not fully inflected. The fin tip temperature is also underpredicted by Bessel solution, because of the interaction with neighboring fins.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.528-533
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• 2007

A finned tube type heat transfer module has been proposed for a multi-burner water tube boiler. Fins change their geometry along the streamwise direction to maximize the performance, which makes it difficult to apply conventional bulk analysis. The design program has been improved by updating data for every row of tubes along the flow. A numerical simulation has been also performed to evaluate the effect of inlet conditions and validated with experiment. The heat transfer of the first row has been underpredicted by the conventional Zhukauskas correlation, where the acceleration of the flow due to the blockage is not fully inflected. The fin tip temperature is also underpredicted by Bessel solution, because of the interaction with neighboring fins.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.163-168
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• 2001

Vibration problems occurred in an air cooled heat exchanger with axial flow fan for a petrochemical plant were investigated. Experimental field test and theoretical verification were performed. To find the main cause of the high vibration of the fan at the air inlet of the axial fan, the frequency spectrum was measured. The natural frequency of the driving support of the heat exchanger was numerically calculated. Both of the measured and the natural frequency were approximately equal to the blade passing frequency. Because it was difficult to modify the structure of the driving support during the normal operation of the plant, the blade number of the fan was increased, which greatly reduced the vibration level of the heat exchanger.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.75-81
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• 2000

Vibration problems induced by an air cooled heat exchanger with axial flow fan were investigated during the operation of a petrochemical plant. Two different studies were done; one was experimental field test and the other was theoretical verification. To find main cause of the blade passing frequency of the fan after installing additional blockage board at the air inlet of the axial fan, the frequency spectrum was measured. The vibrations of the blade passing frequency became higher. The natural frequency of driving support of the heat exchanger was theoretically calculated. It was approximately equal to the blade passing frequency. During the normal operation of the plant, it was impossible to modify the structure of the driving support. Instead, the blade number was increased to reduce vibration level. It increased the ratio of the forcing frequency to the natural frequency of the driving support over the resonance region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.397-404
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• 2012

In this research, a numerical study was carried out on the mixing and flow characteristics of a vane-type static mixer for the reduction of $NO_x$ in the SCR systems from the diesel exhaust environments. The mixer was located at a distance of 57 times the pipe diameter away from the inlet. The analyses were performed by changing various parameters such as vane angles, blockage ratio, and location of the vane. Flow characteristics through the mixer were characterized by the uniformity index, swirl number, and pressure drop. The results show that uniformity index, pressure coefficient and swirl number are substantially influenced by the vane angle, blockage ratio and position of the vane of the mixer. In particular, the swirl number was increased when the vane was located near the pipe wall, or the vane angle was increased or scale was extended.

• Nuclear Engineering and Technology
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• v.39 no.2
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• pp.143-148
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• 2007

Spent nuclear fuel generated at nuclear power plants must be safely stored during interim storage periods. A dry storage cask to safely store the spent nuclear fuel should be able to adequately emit the decay heat from the spent nuclear fuel. Therefore, heat removal tests using a half scale dry storage cask have been performed to estimate the heat transfer characteristics of a dry storage cask under normal, off-normal, and accident conditions. In the normal condition, the heat transfer rate to an ambient atmosphere by convective air through a passive heat removal system reached 83%. Accordingly, the passive heat removal system is designed well and works adequately. In the off-normal condition, the influence of a half blockage in the inlet on the temperature appears minimal. In the accident condition, the temperature rose for 12 hours after the accident, but the temperature rise steadied after 36 hours.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.7
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• pp.596-602
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• 2006

Ice adhesion and blockage problems have been issued in continuous ice slurry making process. So we composed continuous ice slurry making device using a commercial small plate heat exchanger (PHX), and investigated character of ice formation. An experiment of ice formation was peformed with an aqueous solution of ethylene glycol 7 mass%. In the experiment, the effect of the pressurization on ice slurry formation during the cooling process was investigated. The pressurization test for the aqueous solution was performed by setting valves at the PHX inlet and outlet. At the results, the time of continuous ice formation increased as the pressure of the plate heat exchanger increased for cooling temperature of $-5^{\circ}C$. Also continuous ice formation at the cooling temperature of $-7^{\circ}C$ showed a possibility. It was found that the pressurization may contribute to suppress the dissolution of supercooled aqueous solution in the PHX.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.6
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• pp.317-323
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• 2013

A multi-perforated tube indicates the existence of multiple holes of various shapes on the surface of a long cylinder-type or rectangular tube, and a hole installed on the surface is called an orifice, as it is relatively small in size, compared with the surface area of the tube. In this study, the flow characteristics of a circular multi-perforated tube with many orifices on the surface were investigated experimentally and numerically. The volume flowrate issuing from each orifice, discharge angle, effective flow area ratio, and the flow fields around the orifices were measured and visualized, with the variation of the orifice area ratio, at the same blockage ratio. The volume flowrate distributions along the flow direction of the multi-perforated tube tends to be more uniform, as larger orifices were positioned at the inlet side of the multi-perforated tube, compared with no orifice area change along the flow direction.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.64-73
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• 1998

In twin spool aero-engine, there may be a S shaped annular duct between high pressure and low pressure spools. The flow passing this S shaped duct experiences the flow acceleration and deceleration due to the convex and concave surface of the duct as well as the increase of blockage according to the boundary layer growth along the surfaces. So, the high pressure compressor which is located behind the S shaped duct is influenced by the non-uniform flow field generated by the geometry of inlet duct. To study the influence of the S shaped duct on the centrifugal stage, performance tests were implemented for the compressor with straight cylindrical inlet duct and with S shaped inlet duct, respectively. The test results showed that the performance, such as pressure ratio and efficiency, of the compressor with S shaped duct was worse than that of the compressor with cylindrical duct. And the compressor with S shaped duct had reduced maximum flow rate around design speed. To investigate the cause of performance degradation, flow anlaysis was performed for the impeller in front of which is located S shaped annular duct. The result of CFD showed the strong acceleration of the flow in the axial direction around the inducer tip region which caused the increase of relative mach number and the decrease of incidence angle of the flow.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.64-75
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• 2008

During an experimental investigation on a 3-bladed and a 4-bladed axial inducer, a severe surge instability was observed in a range of cavitation number where the blade passage is choked and the inducer head is decreased from noncavitating value. The surge was stronger for the 4-bladed inducer as compared with a 3-bladed inducer with the same inlet and outlet blade angles. For the 4-bladed inducer, the head decreases suddenly as the cavitation number is decreased. The surge was observed after the sudden drop of head. This head drop was found to be associated with a rapid extension of tip cavity into the blade passage. The cause of surge is attributed to the decrease of the negative slope of the head-flow rate performance curve due to choke. Assuming that the difference between the 3 and 4-bladed inducers is caused by the difference of the blockage effects of the blade, a test was carried out by thickening the blades of the 3-bladed inducer. However, opposite to the expectations, the head drop became smoother and the instability disappeared on the thickened blade inducer. Examination of the pressure distribution on both inducers could not explain the difference. It was pointed out that two-dimensional cavitating flow analyses predict smaller breakdown cavitation number at higher flow rates, if the incidence angle is smaller than half of the blade angle. This causes the positive slope of the performance curve and suggests that the choked surge as observed in the present study might occur in more general cases.