• Journal of the Korean Society for Heat Treatment
• /
• v.2 no.2
• /
• pp.68-83
• /
• 1989

Physical metallurgy aspects of gaseous ferritic nitrocarburising are reviewed in the light of basic studies undertaken since 1975 which have illustrated inconsistencies between the iron-carbon-nitrogen ternary phase diagram at $570^{\circ}C$ and the experimental observation of the co-existence of the ${\varepsilon}$ carbonitride phase and ferrite. Thermodynamic investigations by Xu and Li together with those by Slycke et al are reviewed to illustrate compatability between a modified isothermal section of the Fe-C-N system and the formation and growth of a monophased ${\varepsilon}$ structure under a variety of processing conditions. The implications of the modified diagram in terms of innovations in industrial ferritic nitrocarburising practice are discussed, together with limitations on the control of the process. The importance of the developing technology of black nitrocarburising for enhanced wear, fatigue, and corrosion resistance is emphasised. Basic studies and industrial status of austenitic nitrocarburising treatments are also reviewed, which highlight the importance of substrate strengthening for high load bearing applications of anti-scuff thermochemical treatments.

• Proceedings of the SAREK Conference
• /
• 2005.11a
• /
• pp.451-456
• /
• 2005

The mathematical model for the heat exchangers of absorber and desorber is made in the elementary control volume method and the thermodynamic properties of working fluid. water/ammonia mixture. are calculated by some fundamental subroutines in RefProp 7.0 and flash subroutines made by authors The simulation results show that two-stage cycle has higher COP than single stage if temperature lift is high: the performance of single stage compression cycle can be improved by increase of absorber pressure. but the performance of two-stage compression cycle can not be improved in this way : the compressor discharging temperature of two-stage compression is much lower than that of single stage cycle. which is very important to the safety operation of CA heat pump. Major parameter comparison between the cycles at their optimal configurations is also given.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.5
• /
• pp.382-389
• /
• 2017

The development of electronic technology has been rapidly achieved in the automotive industry. A trend that attaches electric equipment, including ECUs at vehicles, is observed. However, decrepit vehicles have several electrical noises and errors. The effect of electric noise on vehicles that are focused on smoke was investigated. Many researchers have argued that one of the reasons of the occurrence of smoke in vehicles is the inexact time of the occurrence of ignition. Moreover, various physical, chemical, and thermodynamic solutions were attempted to approach and many improvements were accomplished. However, in this study, the reduction of electrical and electronic noise is confirmed to improve the accuracy of the injection time on decrepit vehicles with electrical and electric technologies. Previous studies suggest that the distance between the pilot and main ignitions affect the occurrence of smoke and control the variance value of the distance between pilot and main ignitions with electric filter. Thus, the effect of reducing smoke occurred.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2033-2038
• /
• 2008

The CPLs(capillary pumped loops) are two phase heat transfer devices which enable active control of operating temperature of heat absorbing elements(or evaporators). Although the CPLs gain increasing interests as promising heat transfer devices for future missions such as spacecraft and commercial applications, their intrinsic complexity in operating principles makes the widespread use of these devices difficult. The key element and main cause of this complexity in operating principles is the two phase hydrodynamic accumulator or reservoir which controls the saturation state of the remaining loop and, particularly for the CPLs, it is separated from the evaporator. Thus, in this study, the operating characteristics of the CPL is investigated experimentally and theoretically. Mainly focusing on the role of reservoir the thermodynamic operating principle is examined first and the experimentally obtained steady state and transient state operating characteristics are discussed in detail.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.11
• /
• pp.1079-1088
• /
• 2001

A dynamic simulation model was developed to analyse the transient characteristics of a multi-inverter heat pump. The programs included a basic air conditioning system such as a evaporator, condenser, compressor, linear electronic expansion valve (LEV) and by-pass circuit. The theoretical model was derived from mass conservation and energy conservation equations to predict the performance of the multi-inverter heat pump at various operating conditions. Calculated results were compared with the values obtained from the experiments at different operation frequencies of compressor, area of the LEV and configuration of indoor units operation. The results of the simulation model showed a good agreement with the experimental ones, so that the model could be used as an efficient tool for thermodynamic design and control factor design of air-conditioners.

• Journal of the Korean Society for Heat Treatment
• /
• v.8 no.2
• /
• pp.127-136
• /
• 1995

The simultaneous addition of Al and Cr to the surface of Ni-and Fe-base alloy provides enhanced resistance to oxidation and corrosion in high temperatures. However, because of the large differences in thermodynamic stabilities of the volatile halides of Al and Cr, the codeposition of Al and Cr by halideactivated pack cementation is only possible for very specific, limited combinations of conditions. In this study, the experiments on the combinations of various metallic source powders and activators were conducted in order to obtain codeposition layers of Al and Cr on Ni with adequate composition by pack cementation. When Cr-Al masteralloy was used as a source powder, it was not easy to control Al and Cr content sensitively in the coating layers. On the other hand, when pure Cr and Al powder was used, ${\beta}$-NiAl layer containing about 20wt % Cr was obtained.

• Journal of Engineering Education Research
• /
• v.21 no.2
• /
• pp.3-6
• /
• 2018

A few thermodynamics texts are commonly found to have unrealistic example problems in which the process violates the second law of thermodynamics. This error would result from presentation order in the text which introduces first the first law for cycles, systems, and control volumes and then the second law later. In the presentation order, the example problems deal only with the first law without telling whether the process violates the second law. To correct this erroneous situation, it could be recommended to present the first law and the second law successively so that both laws could be applied simultaneously to the given example problems.

• Journal of Acupuncture Research
• /
• v.26 no.5
• /
• pp.117-125
• /
• 2009

Objectives : This study is to research the trend of the Moxibustion-related studies and to establish the hereafter direction for the study on Moxibustion. Methods : We reviewed the domestic articles published last ten years(2000~2009). Results : We have searched 45 articles in 4 journals of Korean Acupuncture & Moxibusion, Korean Oriental Medicine, Korean Meridian & Acupoint, Korean Oriental Internal Medicine. 1. There were the most research done 2003, 2008. Both of them have 8 articles. In other years there were 2 or more articles. 2. The pattern of study was as follow: the clinical studies were 23, studies of phisical Characteristics and new moxibustion method were 9, the philological study were 5, the reviewed studies were 3, the experimental studies were 2 and the others were 5. The rate of clinical studies was increased. 3. In the clinical studies, the case-control study and non case-control study were more than case study. The disease after stroke were the most predominant. The rates of direct moxibustion and indirect moxibusion were similar. 4. After beginning 2000s, there were more studies of thermodynamic Characteristics. In the mid 2000s, there were more studies of new moxibustion method appearing. Conclusions : We need more studies about various kinds of diseases, side effect and aftereffects. There should be convenient and useful methods of moxibustion.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.154-155
• /
• 2006

This study investigated a mechanism for controlling the shape of Cu nanocrystals fabricated using the polyol process, which considers the thermodynamic transition from a facetted surface to a rough surface and the growth mechanisms of nanocrystals with facetted or rough surfaces. The facetted surfaces were stable at relatively low temperatures due to the low entropy of perfectly facetted surfaces. Nanocrystals fabricated using a coordinative surfactant stabilized the facetted surface at a higher temperature than those fabricated using a non-coordinative surfactant. The growth rate of the surface under a given driving force was dependent on the surface structure, i.e., facetted or rough, and the growth of a facetted surface was a thermally activated process. Surface twins decreased the activation energy for growth of the facetted surface and resulted in rod- or wire-shaped nanocrystals

• Environmental Engineering Research
• /
• v.25 no.3
• /
• pp.384-392
• /
• 2020

The presence of high fluoride concentration (> 1.5 mg/L) in water causes serious health problems such as fluorosis, infertility, brain damage, etc., which are endemic to many places in the world. This study has investigated the fluoride removal capacity of the novel activated biochar (BTS) and hydrochar (HTS) using Teff (Eragrostis tef) straw as a precursor. Activated biochar with mesoporous structures and large specific surface area of 627.7 ㎡/g were prepared via pyrolysis process. Low-cost carbonaceous hydrochar were also synthesized by an acid assisted hydrothermal carbonization process. Results obtained from both adsorbents show that the best local maximum fluoride removal was achieved at pH 2, contact time 120 min and agitation speed 200 rpm. The thermodynamic studies proved that the adsorption process was spontaneous and exothermic in nature. Both adsorbents equilibrium data fitted to Langmuir isotherm. However, Freundlich isotherm fitted best for BTS. The maximum fluoride loading capacity of BTS and HTS was found to be 212 and 88.7 mg/g, respectively. The variation could primarily be attributed to a relatively larger Surface area for BTS. Hence, to treat fluoride contaminated water, BTS can be promising as an effective adsorbent.