• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.250-261
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• 1999

Based on a set of performance plots relating the design variables to the imposed conditions, an easy-to-use and versatile design procedure for chevron-type multipass plate heat exchangers is developed. In order for the present procedure to cover multipass with unequal passes and non-unity ratio of heat capacity rate, each stream number of transfer unit is adopted as the basic design variable instead of the exchanger number of transfer unit. It is found that there exists a unique relation between the stream and exchanger number of transfer units regardless of the chevron angle and the plate length. In addition, for a given value of the pressure drop the heat transfer area per unit mass flow rate can be expressed in terms of the stream number of transfer unit only. These two relationships in the form of simple plots constitute the framework of design. The sample results in comparison with the available data indicate that the present procedure includes the previous ones as a subset, and that every design method is affected essentially by the selection of specific correlations for the heat transfer coefficient and the friction factor.

• Journal of Korean Foot and Ankle Society
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• v.8 no.2
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• pp.126-130
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• 2004

Purpose: In this study, we tried to develop the technique of osteotomy for hallux valgus. The new modified technique of osteotomy was accomplished with even more greater stability, accurate correction of the deformity and more effective than 'chevron' osteotomy in terms of correction of the deformity. Materials and Methods: Between March 1998 and December 2001, 55 cases of new modified osteotomy for hallux valgus were performed for 39 patients, 16 of whom underwent operation of both feet. Operations were made for 34 women and 5 men whose average age was 46 years old (range, $20{\sim}71$ years). Average follow up period was three years (range, $2{\sim}5$ years), and during the follow up, the patients underwent physical examination and assessment with use of the American Orthpaedic Foot and Ankle Society's hallux-metatarso-phalangealinterphalangeal scale and standard foot radiographic measurements. Results: 37 patients (53 cases) out of 39 patients (55 cases) had no pain, good cosmesis, and all of the patients were satisfied with the results of the operation. Two had occasional mild discomfort. The average score according to the hallux-metatarso-phallangeal-interphalangeal scale was 93.2 points (range, $78{\sim}100$ points). The average preoperative intermetatarsal angle was $14.4^{\circ}$, which was decreased to $7.9^{\circ}$ after the osteotomy with an average correction of $6.5^{\circ}$ and The average preoperative hallux valgus angle was $34.1^{\circ}$, which was decreased to $11.1^{\circ}$ after the osteotomy with an average correction of $23^{\circ}$. This new modified technique would prevent the angulation or shortening at the osteotomy site and it was also even more stable at osteotomy site, and could do even more effective and accurate correction of the deformity than conventional Chevron osteotomy. Conclusion: New modified chevron osteotomy for the treatment of symptomatic hallux valgus was done in 55 cases, and the results were satisfactory in all cases. This method was more stable at the osteotomy site than conventional Chevron osteotomy and was also possible to do more accurate and more effective correction of the deformity. It was also easy to control the distal fragment of first metatarsal bone.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.269-277
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• 2002

Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

• Journal of Korean Foot and Ankle Society
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• v.12 no.1
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• pp.26-30
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• 2008

Purpose: The authors evaluated the differences between K-wires and Bold screw for fixing the proximal metatarsal chevron osteotomy of moderate and severe hallux valgus. Materials and Methods: There were 59 patients (81 feet) who were moderate and severe degree hallux valgus according to the classification of Mann. They all got the proximal chevron osteotomy when correcting the deformity. All patients were followed up at least 6 months. We divided the patients into 2 groups, K-wires fixed group as A, Bold screw fixed group as B. Group A were 42 patients (63 feet) and Group B were 18 patients (19 feet). Among the Group B, 2 feet who were failed to fix the oetotomy site with Bold screw, were fixed with K-wires during operation. We measured the AOFAS score preoperatively, postoperatively and at final follow-up, VAS score at 2 weeks after the operation. Also preoperative, postoperative and follow-up hallux valgus angle (HVA) and intermetatarsal angle (IMA) were measured for each patients. Results: Mean follow up period was 1.34 year (range: 6 months-6.16 years). Mean VAS score of group A was $3.21{\pm}1.7$ and group B $1.76{\pm}1.0$. Preoperative mean AOFAS score of group A was $45.61{\pm}8.3$, group B $44.41{\pm}8.9$, the final mean score of group A was $88.87{\pm}8.3$ and group B $92.47{\pm}4.4$. Preoperative mean HVA was $30.82{\pm}6.6$ degrees in group A and $32.88{\pm}14.5$ degrees in group B, the final mean angle of group A was $14.89{\pm}8.3$ degrees and group B $17{\pm}4.4$ degrees. The preoperative mean IMA of group A was $13.69{\pm}3.6 $degrees and group B $12.35{\pm}5.2$, the final mean angle of group A was $9.26{\pm}3.6$ degrees and group B $12.35{\pm}5.8$ degrees. Conclusion: There were no statistical differences in radiologic and clinical results (p>0.05) but, group B exceeded group A in VAS score (p=0.0007) and had no statistical significance in terms of reduction angle loss (p=0.06). Early returning to normal life activity may be possible for patients using Bold screws.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.220-225
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• 2001

The plate heat exchanger is characterized. by low pressure drop and high heat transfer coefficient. The experimental study has been performed on the condensation heat transfer and pressure drop characteristics of the plate heat exchangers in this study. In the present study, a brazed type plate heat exchanger was investigated at a chevron angle of $45^{\circ},\;55^{\circ},\;and\;70^{\circ}$ with R410A. Condensation temperatures were varied from $20^{\circ}C\;and\;30^{\circ}C$, and mass flux was ranged from $13{\sim}34\;kg/m^{2}s$ with constant heat flux ($=5\;kw/m^{2}$). The heat transfer coefficient and pressure drop increased with the chevron angle. Average condensation heat transfer coefficients and pressure drops are decreased with increasing condensation tempeature.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.477-482
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• 2001

An experimental study on the performance evaluation of a brazed plate heat-exchanger with 10RT of normal cooling capacity has been carried out. In the present study, a brazed type plate heat exchanger was tested at a chevron angle $25^{\circ}$ with refrigerant R-22. Mass flux was ranged from $23\;to\;58kg/m^{2}s$ in condensation, and from $22\;to\;53kg/m^{2}s$ in evaporation. The heat transfer coefficient and pressure drop increased with the mass flux increases. The water side pressure drop increased with the cooling water flow rate and chilled water flow rate increases, while mass flux has little affect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.129-134
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• 2009

In the present study, the characteristic of flow distribution in the channel of a plate heat exchanger is investigated numerically. In order to accomplish the efficient and fast analyses of the flow characteristics in the channel, a semi-microscopic analysis has been performed using a porous media model. For semi-microscopic analysis using porous media, the flow resistance coefficients are obtained through the result of pressure drop in the experimental data. The results showed that the variation of mass flow rate, geometry and chevron angle strongly depend on the flow distribution in the channel. Particularly, the chevron angle is most important factor for uniform flow distribution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.174-183
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• 2001

Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-404A. Data are presented for the following range of variables: the mass flux ($20~80kg/m^2s$), chevron angle($20^{circ}C,\;35^{circ}C,\;45^{circ}C$) and inlet pressure of he refrigerant (1.4 and 1.6 MPa). for both subcooled and tow-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation hat transfer coefficient and pressure drop was compared with the previously proposed correlations. Among them, Traviss correlation agreed with experimental results within -35~82% for heat transfer coefficient and -73~93% for pressure drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.1
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• pp.83-90
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• 2002

An experimental study on the performance evaluation of a brazed plate heat exchanger with 10USRT of normal cooling capacity has been carried out. In the present study, a brazed plate heat exchanger was tested at a chevron angle $25^{\circ}$with refrigerant R-22. Refrigerant mass flux was ranged from 23 to 58 kg/$m^2$s in condensation, and from 22 to 53 kg/$m^2$s in evaporation. The heat transfer coefficients and pressure drops are increased as the mass flux increases. The water side pressure drop is increased as the cooling water flow rate and chilled water flow rate increase, while mass flux has little effect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• Journal of Korean Foot and Ankle Society
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• v.24 no.4
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• pp.129-134
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• 2020

Purpose: This study compared the results of proximal and distal chevron osteotomy in patients with severe hallux valgus. Several recent studies have shown that the indications for distal metatarsal osteotomy with a distal soft-tissue procedure could be extended to include severe hallux valgus. Materials and Methods: This study analyzed 127 severe hallux valgus surgeries. Of these, 76 patients (76 feet) were excluded for lack of adequate follow-up and additional procedures (Akin procedure), leaving 51 patients (51 feet) in the study. The mean age of the patients was 58 years (21~83 years), and the mean follow-up duration was 18 months (12~32 months). The patients were divided into two groups. Group 1 underwent distal chevron osteotomy, and group 2 underwent proximal chevron osteotomy performed sequentially by a single surgeon. The patients were interviewed for the American Orthopaedic Foot and Ankle Society (AOFAS) score before and one year after surgery. The anteroposterior weight-bearing radiography of the foot was taken before and one year after surgery. Results: There were no significant differences in pain and function after one year in either group. Both groups experienced significant pain reduction and an increase in the AOFAS score. Significant improvement of the hallux valgus and intermetatarsal angle corrections was observed in both groups, and the sesamoid position was similar in each group. More improvement in radiographic correction of intermetatarsal angle was noted in group 2. Both procedures gave similar good clinical and radiological outcomes. Conclusion: This study suggests that a distal chevron osteotomy with a distal soft-tissue procedure is as effective and reliable a means of correcting severe hallux valgus as a proximal chevron osteotomy with a distal soft-tissue procedure.