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¡¡ A general exergy balance equation [48] and the corresponding cost-balance equation [49] that are applicable to any component of thermal systems have been formulated. The exergy of material stream involved in the component of any thermal system was decomposed into thermal, mechanical and chemical exergy flows and an entropy-production flow. A unit exergy cost is assigned to each disaggregated exergy in the stream at any state. This methodology permits us to obtain a set of equations for the unit costs of various exergies by applying the cost-balance equation to each component of the system and to each junction. The monetary evaluations of various exergy costs as well as the production cost of thermal system are obtained by solving the set of equations. The lost costs of each component of the system can also be obtained by this method. Application to a 1000 kW gas turbine cogeneration system show that the unit exergy costs increase as the production process continues and that the production cost of electricity increase nearly proportional with the input cost [50]. The application of the proposed exergy and thermoeconomic analyses to 500-MW combined cycle plant [51] has revealed that the model provides the productive structure of the system considered, consequently could visualize the cost formation process and the productive interaction between components clearly. In the analyses, it has been found that the exergy and cost balance equations for the plant boundary play a crucial role for the determination of the production costs. A comparative study of thermoeconomic methodologies between the SPECO(Specific Cost) methodology proposed by Professor G. Tsatsaronis and our MOPSA(Modified Productive Structure Analysis) for the predefined CGAM cogeneration system has been done [50]. It has also been found that the unit cost of products is dependent on the chosen level of aggregation of the system only when one consider the entropy production rate as one of parameters to determine the unit cost of products, which suggest that the cost structure of energy system is interrelated by the irreversibilities occurred at each component [52]. Recently exergetic and thermoeconomic analysis were also performed for a 200-kW phosphoric acid fuel cell plant by using MOPSA and was found that the system might be viable economically when the initial investment cost per power is reduced to the level of the gas turbine co-generation plant of 1500 $/kW [53]. Recently optimal configuration and optimal operation condition of the cogeneration plant [54] and the economic evaluation of the plant [55] were determined by considering annual energy demand pattern of commercial building such as hotels and hospitals and apartments[56]. A study on the energy distribution technology for the Customized Smart Energy Solution (CSES) is in progress. [48] Si-Doek Oh, Hyo-Sun Pang, Si-Moon Kim and Ho-Young Kwak, "Exergy analysis for a gas turbine cogeneration systems," Journal of Engineering Gas Turbines and Power, Vol. 118, pp. 782-791, 1996. [49] Si-Moon Kim, Si-Doek Oh, Yong-Ho Kwon and Ho-Young Kwak, "Exeroeconomic analysis for thermal systems," Energy, Vol. 23, pp. 393-406, 1998. [50] Yong-Ho Kwon, Ho-Young Kwak, Si-Doek Oh, "Exergoeconomic analysis of gas turbine cogeneration systems," Exergy; Int. J., Vol.1, pp.31-40, 2001. [51] Ho-young Kwak, Duck-Jin Kim and Jin-Seok Jeon, "Exergetic and thermoeconomic analysis of power plant," Energy, Vol. 28, pp. 343-360, 2003. [52] Ho-Young Kwak, Gi-Taek Byun, Yong-Ho Kwon and Hyup Yang, "Cost structure of CGAM cogeneration system," International Journal of Energy Research, Vol. 28, pp. 1145-1158, 2004. [53] Ho-Young Kwak, Hyun-Soo Lee, Jung-Yeul Jung, Jin-Seok Jeon and Dal-Ryung Park, "Exergetic and thermoeconomic analysis of a 200-kW phosphoric acid fuel cell plant," Fuel, Vol. 83, pp. 2087-2094, 2004. [54] Si-Doek Oh, Ho-Jun Lee, Jung-Yeul Jung and Ho-Young Kwak, ¡°Optimal planning and economic evaluation of small scale cogeneration system," Energy, Vol. 33, pp.760-771, 2006. [55] Si-Doek Oh, Hoo-Suk Oh and Ho-Young Kwak, ¡°Economic evaluation for adoption of cogeneration system," Applied Energy, Vol. 84, pp.266-278, 2007. [56] Hyon Uk Seo, Jinil Sung, Si-Doek Oh, Hoo-Suk Oh, and Ho-Young Kwak, "Economic optimization of a cogeneration system for apartment houses in Korea," Energy and Buildings,Vol. 40, pp. 961-967, 2008. ¡¡
The effect of d.c. electric field on nucleate boiling heat transfer for various refrigerants R11, R113 and FC-72 in addition to the study on the convective boiling of refrigerant mixture of R11 and R113 [57] was investigated in a single-tube shell/ tube heat exchanger by using temperature control method of wall superheat [58]. Also the behavior of bubble under nonuniform electric field produced by wire electrode was studied by numerical calculation. Proper electrode configuration, appropriate electric field strength and wall superheat turn out to be all important factors to enhance the nucleate boiling heat transfer as well as to prevent reducing the electric field strength, which should be considered for electrohydrodynamic (EHD) augmented evaporator design and its operation [58], It has also been found that the electrical charge relaxation time of field is an important parameter for the enhancement of nucleate boiling heat transfer [59]. This can be realized by azeotropic mixture of R113+wt4% ethanol one having very short charge relaxation time of 0.005ses [60]. A "convective immersion cooling module" to enhance the the critical heat flux by increasing the nucleate boiling area in the heat spreader was developed [61]. An experimental study of thermosyphonic
boiling heat transfer in vertical tube and channel made by two parallel retangular plate with open
periphery was done to understand the effect of the gap size and pumping
action [62]. Also a new thermosyphon cooling module(TSCM)
was designed and fabricated to cool the mult-chip
module(MCM), which can be utilized in the telecommunication system [63]. The
cooling module patented in Korea(# 0211058) and in United States(# 5,859,763, 1999)
consists of a cold plate and an integrated condenser. With an allowable
temperature rise of 56 ¡É on the surface of the heater, the cooling
module TSCM can handle a heat flux of about 2.7 W/cm2 using R11 as
working fluid. More refined cooling module which has smooth transition from
transient to steady state without heat transfer crises at any heat flux level
was tested [64]. [57] Jae Ho Hong, Cheon-Ho Park, and Ho-Young Kwak, "Forced convective boiling in vertical tube for binary refrigerant mixtures of R11 and R113," KSME International Journal, Vol. 12, pp. 493-503, 1998. [58] Si-Doek Oh and Ho-Young Kwak, " A study of bubble behavior and boiling heat transfer enhancement under electric field", ASME, NE-Vol. 19, Thermal Science of Advanced Steam Generator/Heat Exchangers, pp. 1-14, 1996, Heat Transfer Engineering, Vol. 21, pp. 33-45, 2000. [59] Snag-Houn Han, Min-Kyun Na, Si-Deok Oh and Ho-Young Kwak, "Electrohydrodynamic(EHD) enhancement of boiling heat transfer with a lo-fin tube", KSME International Journal, Vol. 13, pp. 1999. [60] Si-Deok Oh, and Ho-Young Kwak, "Electrohydrodynamic (EHD) enhancement on boiling heat transfer of R113+wt4% ethanol mixture", Journal of Mechanical Science and Technology (KSME Int. J.), Vol. 20, pp. 681-691, 2006. [61] Yong-Sik Yoon, Hyup Yang, and Ho-Young Kwak, "Enhancement of the critical heat flux by using heat spreader," KSME International Journal, Vol. 17, pp. 1063-1072, 2003. [62] Jin-Seok Jeon, Jung Hee Na, Hong Chul Park, and Ho-Young Kwak, "An experiment on thermosyphon boiling in uniformly heated vertical tube and asymmetrically heated vertical channel," KSME International Journal, Vol. 15, pp.98-107, 2001. [63] Sang-Sig Nam, Sung-Bong Choi, Jae-Hee Kim and Ho-Young Kwak, "Transient characteristics of a two phase thermosyphon cooling module for multi-chip device", ETRI J. Vol. 20, pp. 284-299, 1998. [64] Min-Kyun Na, Jin-Seok Jeon, Ho-Young Kwak and Sang-Sig Nam, "Experimental study on a closed loop two-phase thermosyphon for cooling MCMs, Heat Transfer Engineering, Vol.22, pp.29-39, 2001. [65] Jung-Yeul Jung and Ho-Young Kwak, "Fluid flow and heat transfer in microchannels with rectangular cross section," Heat Transfer Engineering, in press, 2007. [66] Jung-Yeul Jung, Ki-Taek Byun, and Ho-Young Kwak, "Proteinaceous bubbles and nano particles flows in microchannel," Microfluidics and Nanofluidics, Vol. 1, pp. 177-182, 2005. [67] Jung-Yeul Jung, and Ho-Young Kwak, "Separation of micro particles and biological cells inside an evaporating droplet using dielectrophoresis," Analytical Chemistry, Vol. 79, pp. 5087-5092, 2007. [68] Jung-Yeul Jung and Ho-Young Kwak, "Effect of surface condition on boiling heat transfer from silicon chip with sub-micron roughness," International Journal of Heat and Mass Transfer, Vol. 49, pp. 4543-4531, 2006. [69] Jung-Yeul Jung, Hoo-Suk Oh, Dae Keun Lee, Kyong Bin Choi, Sang Keun Dong, and Ho-Young Kwak, "A Capillary pumped loop (CPL) with cone shaped capillary structure for cooling electronic device," Journal of Micromechanics and Microengineering, Vol. 18(1) paper #017002. [70] Jung-Yeul Jung, Hoo-Suk Oh, Ho-Young Kwak, "Forced convection heat transfer of nanofluids in microchannels," Submitted for publication, 2007. ¡¡
1. Invited Lecture at the Spring Meeting of Lorean Society of Mechanical Engineers(KSME); April 24-25, 1998, Jinju(Kyung Sang University) Korea. Bubble, bebble, toil and trouble : Sonoluminescence Phenomena and Star Formation Abstract The phenomenon og light emission from a oscillating gas bubble trapped in ultrasound field in water, SL, was discussed with spherical symmetry. Also the stability, spherical oscillation and gravitational collapse of Newtonian stars were stars were studied hydrodynamically. 2. Invited Lecture at the
Research Workshop on Nucleation Theory and Applications; April 12-20, 1999, Cluster Models in the Theory of Bubble Formation and Related Problems Abstract Using a new surface energy
for the formation of the critical cluster, models for the gas bubble
formation in gas-liquid solutions and for the vapor bubble formation within a
liquid under tension are presented in this paper. The energy related to
translational motion of molecule, which is lost during the dissolution
process is considered as the surface energy needed for the gas bubble
formation in solutions. Results from the model show good agreement with
experiments for various gases dissolved in water solutions. On the other
hand, the surface energy needed for the bubble formation is calculated from
the ¡¡ 3. Plenary Speakers at the
Fourth JSME-KSME Thermal Engineering Conference; Oct. 1-6, 2000, Bubble Dynamics/Sonoluminescence/Newtonian Stars Abstract The sonoluminescence phenomenon which is the light emission associated with the catastrophic collapse of a gas bubble oscillating under ultrasound may be understood by the analytical solutions for the Navier-Stokes equations in spherical symmetry. Further the homologous solutions of the Euler equation with Newtonian gravity yield many fruitful results such as stellar stability, spherical oscillation and collapse of Newtonian stars. All these results came from an effort to understand the dynamics of a thin shelled sphere of gas, a tiny bubble. ¡¡ 4. Keynote Lecture at the
Twelfth International Heat Transfer Conference, August 18-23, 2003, Bubble Nucleation; A Microscopic Phenomenon Abstract In this article, vaporous bubble nucleation
in liquid and the evaporation process of a liquid droplet at its superheat limit
were discussed based on clustering process of molecules (molecular cluster
model for bubble nucleation). A puzzling phenomenon of carbon monoxide gas
bubble formation in Fe-C-O melts was also discussed by the cluster model
based on the interaction between solute gas and solvent molecules. For the
vapor bubble formation, the energy barrier against bubble nucleation was
estimated by the molecular interaction due to ¡¡
1. Ho-Young Kwak and Yoon-Pyo Lee, "Shock and thermal waves emanating from a sonoluminescing gas bubble in Shock Focussing Effect in Medical Science and Sonoluminescence," Edited by R.C. Srivastava, D. Leutloff, K. Takayama and H. Gronig, Springer, 2003. Abstract The generation and propagation of the shock pulse from a sonoluminescing gas bubble whose wall acceleration reaches 1012m/s2 near the collapse is considered by using the bubble wall motion developed by Keller and Miksis in conjunction with the analytical solutions for the gas inside bubble and the Kirkwood-Bethe hypothesis for the outgoing wave. The propagation of the pressure wave inside the bubble, where there are in homogeneous of density, pressure and temperature induced by the rapid bubble collapse, is also treated. The propagation of a solition-like heat wave which is generated by "thermal spike" due to the rapid increase and subsequent decrease in the bubble wall acceleration is also discussed. ¡¡ 2. Ho-Young Kwak, "Vapor bubble nucleation: a microscopic phenomena," KSME International Journal, Vol. 18, pp. 1271-1287, 2004. Abstract In this article, vapor
bubble nucleation in liquid and the evaporation process of a liquid droplet
at its superheat limit were discussed from the viewpoint of molecular
clustering (molecular cluster model for bubble nucleation). For the vapor
bubble formation, the energy barrier against bubble nucleation was estimated
by the molecular interaction due to the 3. Ho-Young Kwak, "Bubbles:
Homogeneous Nucleation," Encyclopedia of Surface
and Colloid Science, 2nd Edition, pp. 1048-1071, CRC Press, 2006.
Key
words;
bubble nucleation, CO bubble in melts, droplet explosion, evaporation, gas
bubble, laser-induced cavitation, microcellular
foam, molecular cluster, quantum tunneling, superheat limit of liquid,
tensile strength, vapor bubble. 4. Ho-Young Kwak and Si-Doek Oh, "Exergetic and thermoeconomic analyses optimal planning of cogeneration systems" in Energy Efficiency Research Advances, ed. By D.M. Bergmann, Nova Science Publishers, Inc., 2008. Abstract Increasing demand in fossil fuels which will remain the dominant energy source to 2030 might cause a drastic change in global climate. To curb such fossil fuels demand and reduce CO2 emissions correspondingly, more efficient use of the fossil fuels are strongly required. In this article thermodynamic and economic evaluation methods and optimal planning of gas turbine cogeneration systems which can return fossil fuel energy savings up to 30% are treated. A general exergy balance equation that is applicable to any component of thermal system is presented. A cost-balance equation formulated by assigning a unit exergy cost to each disaggregated exergy stream in the exergy balance equation is also presented. Applications of the exergy and cost-balance equations to a gas turbine cogeneration are shown. A method to determine the optimal configuration and optimal operation mode of cogneration system is also presented based on the energy demand data for commercial buildings such as a hotel, a hospital and an office building.
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Invited Lectures
