• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.72-82
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• 2005

The objective of this paper is to describe the optimization of design parameters in a large-sized commercial bus heater system by using CFD(computational fluid dynamics) analysis and Taguchi method. In order to obtain the best combination of each control factor which results in a desired performance of heater system, the parameter design of the Taguchi method is adopted for the robust design considering the dynamic characteristic. The research activity may be divided into four phases. The first one is analyzing the problem, i.e., ascertaining the influential factors. In the second phase the levels were set in such a way that their variation would significantly influence the response. In the third phase the experimental runs were designed. In the final phase the planned runs were carried out numerically to evaluate the optimal combination of factors which is able to provide the best response. In this study, eight factors were considered for the analysis: one with two level and seven with three level combinations comprising the $L_{18}(2^1{\times}3^7)$ orthogonal array. The results of this study can be summarized as follows ; (i)The optimum condition of control factor is a set of <$A_2\;B_1\;C_3\;D_3\;E_1\;F_2\;G_3\;H_2$> where A is shape of the outer fin, B is pitch of the outer fin, C is height of the outer fin, D is the inner fin number, E is the inner fin height, F is length of the flame guide, G is diameter of the heating element and H is clearance between air guide and heating element. (ii)The heat capacity of heated discharge air under the optimum condition satisfies the equation y=0.6M w here M is a signal factor. (iii)The warm-up rate improves about three times, more largely as com pared with the current condition, which results in about 9.2minutes reduction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.729-737
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• 2006

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 staggered arrangement of refrigerant pipes of 10.2 m diameter and the pitch of fins is 3.5 m. In the experimental study, the forced convective heat transfer is measured at Reynolds number of 1082, 1397, 1486, 1591 and 1649 based on diameter of refrigerant piping and mean velocity. Average Nusselt number for the convective heat transfer coefficient is also computed for the same Reynolds number by commercial software of STAR-CD with standard $k-{\varepsilon}$ turbulent model. It is found that the relative errors of average Nusselt numbers between experimental and numerical data are less than 6 percentage in Reynolds number of $1082{\sim}1649$. The errors between experiment and other correlations are ranged from 7% to 32.4%. But the correlation of Kim at al is closest to the experimental data within 7% of the relative error.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.2
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• pp.102-107
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• 1996

It is difficult to analyze the high speed rolling missile with the generally used missile body fixed coordinates. In this study, we formulate the dynamic equations of the high speed rolling missile with the principal axis of inertia, and make the analytical model of one axis steering missile using pitch/yaw symmetry and complex summation method. With this model we analyze the control characteristics and propose the design considerations of high speed rolling missile with one axis control fin using PNG law in conjuntion with a seeker signal.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.570-575
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• 2001

An experimental study is performed to investigate the characteristics of vortex shedding behind a circular cylinder with serrated fins using hot-wire anemometer. Strouhal numbers which are calculated using outer diameter of a circular cylinder with serrated fins are higher than that of a circular cylinder. Fin thickness and pitch are closely related with vortex shedding frequency and play increasing or decreasing vortex shedding after transient Reynolds numbers. Strouhal numbers using effective diameters which are proposed in this paper agree with that of a circular cylinder. After transient Reynolds number, a trend of Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter.

• Journal of Mechanical Science and Technology
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• v.14 no.12
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• pp.1421-1428
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• 2000

The characteristics of heat transfer and pressure drop for fully developed turbulent flow in a tube with circumferential fins and circular were experimentally studied. The various spacing and sizes of circumferential fins and circular disks were selected as design parameters, while the effects of these parameters on heat transfer enhancement and pressure drop were investigated. In order to quantify the effect of heat transfer enhancement and the increase of pressure drop due to the fins and disks in a tube, the Nusselt numbers and the friction factors for various configurations and operating conditions were compared to those for a corresponding smooth tube. The results showed that the heat transfer rate was significantly enhanced by increasing the height of circumferential fins and decreasing the pitch of circumferential fins. On the other hand, the influence of the disk size and the fin-disk spacing were not significant. Based on the experimental results, a correlation for estimating the Nusselt number was suggested.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.22-28
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• 2001

Heat transfer and pressure distribution for heat exchanger type of domestic gas boiler are different from shape, pitch, thickness of fin and array of pipe respectively. In order to measure the pressure distribution across the heat exchanger, a suction type wind tunnel was constructed and velocity distribution was measured for pilot tube(4 point) of rack type. The experiments were performed for 5 different air flow mass, rpm=3,6,9,12,15 and transverse axis of heat exchanger(x-length) is 5cm respectively. Results showed that above 9.5m/s, pressure distribution dispersion for wet type of heat exchanger is on the increase and above 5.5m/s, pressure distribution dispersion for dry type of heat exchanger is on the increase. Also, pressure distribution dispersion by comparing two different types heat exchanger, dry type of heat exchanger showed a higher augmentation than wet type of heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.355-367
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• 2004

The heat transfer and friction characteristics of the heat exchangers having sinusoidal wave fins were experimentally investigated. Twenty-nine samples having different waffle heights (1.5 mm and 2.0 m), fin pitches (1.3mm to 1.7mm) and tube rows (one to three) were tested. Focus was given to the effect of the waffle configuration (herringbone or sinusoidal) on the heat transfer and friction characteristics. Results show that the sinusoidal wave geometry provides higher heat transfer coefficients and friction factors than the herringbone wave geometry, and the difference increases as the number of row increases. The i/f ratios of the herringbone wave geometry, however, are larger than those of the sinusoidal wave geometry. Compared to the herringbone wave geometry, the sinusoidal wave geometry yielded a weak row effect, which suggests a superior heat transfer performance at the fully developed flow region. Possible explanation is provided considering the flow characteristics in wavy channels. Within the present geometric range, the effect of the waffle height on the heat transfer coefficient was not prominent. The effect of the fin pitch was also negligible. Existing correlations highly overpredicted both the heat transfer coefficients and friction factors. A new correlation was developed using the present data.

• Journal of Fisheries and Marine Sciences Education
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• v.6 no.1
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• pp.58-76
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• 1994

Heat transfer and pressure drop measurements are made on low integral-fin tubes in turbulent water flow condition. The integral-fin tubes investigated in this paper are nominally 19mm in diameter. Eight tubes have been used with trapezoidally shaped integral-fins having fin density from 748 to 1654 fpm and 10, 30 grooves. Plain tube having same diameter as finned tube is also tested for comparison. Experiments are carried out using R-11 as working fluid. The refrigerant condensates at a saturation state of $30^{\circ}C$ on the outside tube surface cooled by coolant. The amount of noncondensable gases present in the test loop is reduced to a negligible value by repeated purging. For a given heat input to the boiler and given cooling water flow rate, all test data are taken on steady state. The heat transfer loop is used for testing single long tubes and cooling water is pumped from a storage tank through filters and flowmeters to the horizontal test section where it is heated by steam condensing on the outside of the tube. The pressure drop across the test section is measured by means of pressure gauge and manometer. Each tube tested is cleaned with sodium dichromate pickling solution and well rinsed with water prior to installation in the test section. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, heat transfer of finned tube is enhanced up to 4 times as that of a plain tube at constant Reynolds number and up to 2 times at constant pumping power. 2. Friction factors are up to 1.6~2.1 times those of plain tube. 3. At a given Reynolds number, Nusselt number decrease with increasing pitch to diameter. 4. The constant pumping power ratio for low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.746-753
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• 2005

Adsorption chillers have been receiving considerable attentions as they are energy-saving and environmentally benign systems. In order to evaluate adsorption rates, experiments were performed in the batch type adsorption apparatus. Three types of silica gels were investigated under an assortment of experimental conditions that are representatives of the actual operating environments in the adsorber of adsorption chillers. Experimental results revealed the effects of silica gel particle size, bed temperature, and fin pitch of fin tube on the adsorption rate. The $0.25\~1.18mm$ particle size of silica gel with high adsorption rate was selected as a suitable adsorbent. The measured adsorption rate became bigger with decreasing particle size. From the comparison of adsorption rate, it is found that the fin tube has about $21\%$ higher value than that of the bare tube. The effect of heat and mass flux is found to be more significant in the fin tube than in the bare tube.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.476-482
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• 2006

An experimental study has been performed to investigate the characteristics of air-side heat transfer and friction of a fined tube heat exchanger under heating conditions. Air enthalpy calorimeter was used to obtain the performance evaluation and analysis of the fined tube heat exchanger. Eight finned tube heat exchangers with slit fin, louver fin, and plain fin were used. The air-side heat transfer coefficient was calculated by the log-mean-temperature-difference. Air-side heat transfer and friction were presented in terms of j factor and friction factor on Reynolds number. From the experimental result, it was found that the variations of air-side heat transfer and friction of fined tube heat exchanger with the change of the fin configuration, row number, fin pitch, and tube circuit were obtained. j factor and friction factor decreased with Reynolds number increased. The tube circuit affected the air-side heat transfer and friction. In the case of slit and louver fin, j factor of 1st row was higher than that of 2nd row. But, with increasing Re, j factor was reversed. The characteristics of j factor and friction factor of 2nd row heat exchanger were different according to the kind of fins.