• 설비공학논문집
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• 제7권1호
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• pp.112-119
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• 1995

Measurements of the local heat transfer coeffcients on a spherically concave surface with a round impinging jet are presented. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers used were 1,000, 23,000 and 50,000 and the nozzle-to-jet distance was L/d=2, 4, 6, 8, 10. Presented results are compared to previous measurements for flat plate. In the experiment, the local heat transfer Nusselt numbers on a concave surface are higher than those on a flat plate. Maximum Nusselt number at all region occured at L/d=6 and second maximum in the Nusselt number occured at R/d=2 for both Re=50,000 and Re=23,000 in case of L/d=2 and for only Re=50,000 in case of L/d=4. All other cases exhibit monotonically decreasing value of the Nusselt number along the curved surface.

• 대한설비공학회지:설비저널
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• 제8권4호
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• pp.213-220
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• 1979

A number of methods has been developed for calculation of heat transfer in the vertical round tube under conditions of forced convection with uniform heat flux at wall. I would like to express hereby one of applications of this study in the design of heat exchanger instruments for water flow at $15.8^{\circ}C(p_r=8)$ used frequently in our daily life. Also all the results are investigated for forced convective heat transfer in the case of heated water-flow at uniform wall heat flux in the vortical round copper tube, where the ratio of length to diameter will be 44. They are well in agreement with Gratz and Kraussold equation respectively in laminar and transition flow range. In turbulent flow in the range from Re=10,000 to 65,000, the experimental formula Is show as follows ; Nu=0.023 $R_e^{0.814}\;P_r^{0.4}$. And this is agreed with Dittus - Boelter equation when Reynolds number exponent increases from 0.80 to 0.814.

• 설비공학논문집
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• 제25권5호
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• pp.279-288
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• 2013

Heat transfer and pressure drop characteristics of fin-and-tube heat exchangers having sine wave fins and oval tubes were investigated. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7 mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. The effect of fin pitch on the j and f factors was negligible. The effect of the tube row on the j factor, however, was different from that of common fin-and-tube heat exchangers having plain fins and round tubes. The highest j factor was obtained for a two-row configuration, while the lowest one was obtained for a one-row configuration. A possible reason was attributed to the flow mixing characteristics of the sine wave channel of the present geometry. Comparison with a plain fin-and-tube heat exchanger having 15.88 mm O. D. round tube reveals that the present oval fin-and-tube heat exchanger shows generally superior thermal performance, except for the one-row configuration.

• 태양에너지
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• 제20권4호
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• pp.1-8
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• 2000

The suggested year round solar air conditioning system has been developed for cooling and heating. In particular, this system focused on cooling and dehumidification and it could reduce a peak time owing to the use of air conditioners in summer. This study was performed to find out how much heating loads could be saved and furthermore whether this suggested system would be possible to do heating without a switch of system in real situations. Through model house experiments, the following conclusions were obtained. 1) The collector efficiency was 36% at maximum, but more improved structure of suggested collector could increase its efficiency. 2) The temperature of outlet air was about $30^{\circ}C$ and it could reduce heating loads. 3) Measured temperature and calculated one agreed well within ${\pm}1.5^{\circ}C$.

• 설비공학논문집
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• 제19권1호
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• pp.43-50
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• 2007

In recent years the importance of the preservation of cultural artifacts like ancient tombs has been widely accepted domestically and internationally with increasing value of cultural artifacts. However not much technical attention has been paid for the facilities and systems to preserve these artifacts. As a part of the present study, the temperature and relative humidity inside a selected artifact, Shinkwan-ri tomb, have been monitored for a year round to improve the understanding of the indoor thermal environment. In this study, using the Computational Fluid Dynamics calculated the velocity and temperature distribution and offered basic data which are necessary for the best fitted design of tomb air-conditioning device. Through the result of this study, the generation of temperature variation was identified by natural convection. It enables us to get the possibility of humidity variation

• 설비공학논문집
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• 제12권5호
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• pp.519-524
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• 2000

The purpose of this study is to develop a low temperature waterless container for live fish transportation which is economical and efficient The principle of the waterless transportation is that a live fish becomes asphyxial at about $5^{\circ}C$can survive without water for a long time. A low temperature waterless container is developed for this purpose, which utilizes thermoelectric modules for rather smaller and lighter cooling system with precise temperature control devise compared to the existing mechanical system. At first, we succeeded in making flounders alive in the waterless container for 24 hours. Also when flounders were transported in a round trip from Inchon to Pusan in the waterless container, carried in a car, they survived in the waterless container for over 21 hours.

• 설비공학논문집
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• 제16권1호
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• pp.8-15
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• 2004

Since the vehicle is regarded as the third living space, the comfortable conditions are required in the passenger compartment. For this reason, customers are concerned about the filtering performances and the importance of filter media has been greatly placed. Therefore the dust holding capacity, the efficiency of these filter media (dry paper, wet paper, non-woven) and the configuration of air filter for vehicle were measured in this study. The following results were obtained on the basis of air filter test. It shows that the thickness and poresize of filter media should be lower for the higher efficiency. The measurement result shows that the performance of round shape filters are higher than the square shape filters. The dust holding capacity of the wet paper and the non-woven paper is higher than the dry paper. As a result, this research can provide an important design parameter and product guidance of the intake air filter for vehicular engine.

• Structural Engineering and Mechanics
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• 제37권6호
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• pp.633-648
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• 2011

This paper investigates the aspect-ratio locking of the isoparametric 8-node quadrilateral (QUAD8) element. An important finding is that, if finite element solution is carried out with in exact arithmetic (i.e., with no truncation and round off errors), the locking tendency of the element is completely avoided even for aspect-ratios as high as 100000. The current finite element codes mostly use floating point arithmetic. Thus, they can only avoid this locking for aspect-ratios up to 100 or 1000. A novel method is proposed in the paper to avoid aspect-ratio locking in floating point computations. In this method, the offending terms of the strain-displacement matrix (i.e., $\mathbf{B}$-matrix) are multiplied by suitable scaling factors to avoid ill-conditioning of stiffness matrix. Numerical examples are presented to demonstrate the efficacy of the method. The examples reveal that aspect-ratio locking is avoided even for aspect-ratios as high as 100000.

• 설비공학논문집
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• 제18권2호
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• pp.180-185
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• 2006

This study has been conducted in order to develop a temperature-controlled round pan diffuser with variable-openings. Flow visualization was performed to investigate the airflow patterns according to gap openings. The velocity profiles were measured using an omni-directional anemometer for two cases, i.e. a horizontal and a vertical discharge conditions. Numerical simulation also confirms there is a narrow range of gap openings where a horizontal discharge shifts to a vertical discharge. The air distribution performance index increases abruptly when the air discharge shifts from vertical to horizontal direction.

• 설비공학논문집
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• 제10권5호
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• pp.509-522
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• 1998

An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.