• Journal of the Korean Solar Energy Society
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• v.21 no.4
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• pp.63-71
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• 2001

This work has been carried out to find the ideal operating conditions for solar vacuum tube collectors which are widely used at present. Various types of solar collectors including a flat plate one were experimentally tested and examined to determine their thermal efficiencies and operating characteristics. Generally, solar vacuum tubes can be classified into two groups according to their design features. Of these, one is characterized by the insertion of a metallic device(such as a finned heat pipe) in an evacuated glass tube for the collection and transportation of solar energy. The other utilizes double glass tubes where the smaller one is contained inside the bigger one and soldered to each other after the small gap between them is evacuated. Both of these solar collectors are designed to minimize convection heat losses by removing the air which is in direct contact with the absorber surface. The performance of the former type can be readily analyzed by applying the relevant correlations developed for flat plate solar collectors. This has been demonstrated in the present study for the case of a solar collector where a heat pipe is inserted in an evacuated tube.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.71-80
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• 1985

The various sizes of wires are attached to the outside of the inner tube in a double pipe heat exchanger to enhance the thermal performance. The diameters of the wires range from 0.5mm to 1.6mm while the pitches are chosen between 5mm and 50mm. Experiments have been performed with the range of Reynolds numbers from 15000 to 30000 in annular space where air flows. The friction factors are increased by 1.5 to 4.5 times depending on the sizes and the pitches of the wires. However, the Nusselt numbers are increased by the factors of 1.8 to 2.8 within this experimental range. It is suggested that there should be an optimum configuration rendered when the weighting values of the heat transfer promotion and the pumping power are given.

• The KSFM Journal of Fluid Machinery
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• v.16 no.4
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• pp.5-9
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• 2013

An experimental investigation has been carried out in order to evaluate characteristics of wetted-type multi-path ultrasonic flowmeters. The multi-path ultrasonic flowmeters were installed at various entrance and exit locations for several cases of pipe fitting(straight, $90^{\circ}$ double elbow) and valve(gate valve, butterfly valve). We measured the flow-rate at each location. The measurement data of test flowmeter were compared with the measured data of reference flowmeter. The uncertainties of reference flowmeter and test flowmeter are 0.3 %, 0.4 %, respectively. The results demonstrate the effects of flowmeter location as well as the measurement errors in flow rate. The distance between the flow disturbance factor and a flowmeter was an important element of the test.

• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.3
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• pp.113-121
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• 1994

Since it is difficult to expect the normal production of plants in greenhouses during hot summer season in Korea, certain provisions on the control of extreme environmental factors in summer should be considered for the year-round cultivation in greenhouses. This study was carried out to find a method to suppress the temperature rising of nutrient solution by cooling, which is able to contribute to the improvement of the plant growth environment in hydroponic greenhouse during hot summer season. A mechanical cooling system using the counter flow type with double pipe was developed for cooling the nutrient solution efficiently. Also the heat transfer characteristics of the system was analysed experimentally and theoretically, and compared with the existing cooling systems of nutrient solution. The cooling capacities of three different Systems, which used polyethylene tube in solution tank, stainless tube in solution tank, and the counter flow type with double pipe, were evaluated. The performance of each cooling system was about 41 %, 70% and 81 % of design cooling load in hydroponic greenhouse of 1 ,000m$^2$ on the conditions that the flow rate of ground water was 2m$^3$/hr and the temperature difference between two liquids was 10 ˚C According to the results analysed as above, the cooling system was found to have a satisfactory cooling capability for regions where ground water supply is available. Fer the other regions where ground water supply is restricted, more efficient cooling System should be developed.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.4
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• pp.398-408
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• 2009

Crude oil carriers or product oil carriers are confronted with sea pollution due to hull damage from various accidents. To reduce the oil spillage of tankers, IMO(International Maritime Organization) and OPA 90(Oil Pollution Act 1990) adopted the hull structures of double skin type. In this study, oil spillage test of the double skin tanker with 1/100 scaled model was carried out under damaged condition due to collision and grounding accidents. A new structural type of oil tanker was also tested with pipe and valve system arranged in double side and single bottom hulls. Their results were compared with that of conventional type double hull on the view point of ship safety and oil spillage.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.356-361
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• 2012

Recently, even though the researches on renewable energy like geothermal, wind, solar energy have been performed widely, its use-rate in total energy is still low. This study was carried out to investigate the performance of hybrid heating system, which consisted of solar collector of thermosyphon tube type and X-L pipe boiler. Especially, new type of solar collector was tried and compared with double tube type and, futhermore, performance and safety on X-L pipe boiler were investigated. As the results, efficiency of solar collector of thermosyphon tube type was higher 20.7% than that of double tube type, mainly due to its structural characteristics. It was also confirmed that temperature of special heat medium used X-L pipe boiler rose up about 20% rapidly in comparison with that of pure water.

• Journal of Bio-Environment Control
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• v.4 no.1
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• pp.17-24
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• 1995

This study was carried out to make fundamental data for structural safety test of pipe- houses. Experiment on the stress distribution of pipe- houses was conducted to find suitable structural analysis model by examination of end support conditions of pipe. Besides, the loading test and the pile driving test were done to find pull-out capacity and bearing capacity of pipe on the assumption that pipe is pile foundation. For single span pipe - house, the theoretical results assuming the end support condition of pipe is fixed under ground agreed closely with the experimental results of stress distribution. On the other hand for double span pipe -house, the end support conditions of pipe were fixed support when vertical load is applied, and hinged one when horizontal load is applied. The pull - out capacity and allowable bearing capacity of the pipe portion that was buried in the grounds that were soft soil of paddy field and medium or hard soils of dry field derived from experimental results.

• Structural Engineering and Mechanics
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• v.57 no.6
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• pp.1125-1142
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• 2016

Tunneling is one of the challenging tasks in civil engineering because it involves a variety of decision making and engineering judgment based on knowledge and experience. One of the challenges is to construct tunnels in risky areas under shallow overburden. In order to prevent the collapse of ceilings and walls of a large tunnels, in such conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. This research deals with the numerical modeling of L-profiles and pipe fore-poling pre-support systems in the adit tunnel in northwestern Iran. The first part of the adit tunnel has been drilled in alluvial material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the results of numerical modeling done using FLAC3D, as well as observations during drilling, indicate the tunnel instability. To improve operational safety and to prevent collapse, pre-support systems, including pipe fore-poling and L-profiles were designed and implemented. The results of the numerical modeling coupled with monitoring during operation, as well as the results of instrumentation, indicate the efficacy of both these methods in tunnel collapse prevention. Moreover, the results of modeling using FLAC3D and SECTION BUILDER suggest a double angle with equal legs ($2L100{\times}100{\times}10mm$) in both box profile and tee array as an alternative section to pipe fore-poling system while neither $L80{\times}80{\times}8mm$ nor $2L80{\times}80{\times}8mm$ can sustain the axial and shear stresses exerted on pipe fore-poling system.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.85-89
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• 2011

Waste water is disposed to sewage disposal plant by underground PE double wall pipes. Various processes have been introduced to join PE pipes, but most of these methods have many disadvantages such as costs, lack of reliability and difficulties in joining, etc. Recently butt welding has been paid much attention to joint PE pipes as this process has many advantages such as cost, safety and reliability. In this study, newly developed heat plate, a patent-pending heat plate with a groove, was used to butt-weld PE double wall pipes with different misalignment gaps to simulate real underground conditions, and the butt welding temperature of PE pipe was determined by thermal analysis (Thermal Gravimetric Analysis, Differential Scanning Calorimetry and Dynamic Mechanical Analysis). The resulting joining characteristics of double wall pipes were compared with those from a conventional heat plate, in terms of stiffness, flattening and leakage tests. The results from the stiffness and flattening test showed that there were no big differences between the butt-welded joints made from these two plates. From the leakage test, although PE pipes welded with a conventional heat plate did leak below the required test conditions (10 min. at 0.75kgf/cm2), the pipes welded with a patent-pending grooved heat plate did not show any leakage even at a pressure 1.5 times higher than the required conditions. It was noted that by utilizing a grooved heat plate more complete fusion at the pipe joints could be obtained, which in turn induced a high quality joints.