• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.172-181
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• 1993

Pseudo-Brayton cycle is defined as an ideal Brayton cycle admitting the difference between heat capacities of working fluid during heating and cooling processes. The endo-pseudo-Brayton cycle which is a pseudo-Brayton cycle with heat transfer processes is analyzed with the consideration of maximum power conditions and the results were compared with those of the endo-Carnot cycle and endo-Brayton cycle. As results, the maximum power is an extremum with respect to the cycle temperature and the flow heat capacities of heating and cooling processes. At the maximum power condition, the heat capacity of the cold side is smaller than that of heat sink flow. And the heat capacity of endo-Brayton cycle is always between those of heat source and sink flows and those of the working fluids of pseudo-Brayton cycle. There is another optimization problem to decide the distribution of heat transfer capacity to the hot and cold side heat exchangers. The ratios of the capacies of the endo-Brayton and the endo-pseudo-Braton cycles at the maximum power condition are just unity. With the same heat source and sink flows and with the same total heat transfer caqpacities, the maximum power output of the Carnot cycle is the least as expected, but the differences among them were small if the heat transfer capacity is not so large. The thermal efficiencies of the endo-Brayton and endo-Carnot cycle were proved to be 1-.root.(T$_{7}$/T$_{1}$) but it is not applicable to the pseudo-Brayton case, instead it depends on comparative sizes of heat capacities of the heat source and sink flow.w.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.228-228
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• 2017

Rice production and quality could be changed by temperature condition. Extremely high temperature event have been occurred more frequently for global warming. To increase rice quality against to global warming, breeding of heat tolerance rice cultivar is needed. Ilmi which is the one of Korean leading rice cultivar shows heat stress resistant character during ripening stage. Yield and quality (brown and milled rice) of Ilmi did not show significant different under high temperature condition compared to control condition. However, the main physiological characters for heat resistance of Ilmi have been not investigated yet. Therefore we try to investigate the heat tolerance characters of Ilmi. Two rice cultivars, Ilmi and Ilpum-which is heat susceptible rice cultivar, were cultivated under natural condition in wagnor pot until heading was appeared. After checking heading date, each material was cultivated under different temperature condition, heat($32/22^{\circ}C$) and control($26/16^{\circ}C$) condition. Anti-oxidant enzyme activity was checked during ripening stage in each material. Catalase and ascorbic peroxidase activity of leaf under heat stress condition were higher in Ilmi than Ilpum especially early ripening stage. Analyzing of stress resistance using $H_2O_2$, the flag leaf of Ilmi showed more green color than Ilpum with higher chlorophyll content than those of Ilpum. We also checked the amount of $H_2O_2$ content in young leaf of each material by treating high temperature. $H_2O_2$ content in each material was increased according to treatment time. However $H_2O_2$ content of young leaf in Ilmi was less than those in Ilpum. Also catalase and ascorbic peroxidase activity in leaf increased much faster in Ilmi than Ilpum. With those data, we confirmed that heat stress resistance of Ilmi is due to the higher anti-oxidant activity against to stress condition. We will investigate the heat tolerance characters of Ilmi more in further study to enhance the breeding effect of heat stress tolerance rice.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.349-354
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• 1991

The power output behavior of the binary cycle composed of two Carnot cycles is analyzed with considering heat transfer processes, in which the finitely constant temperature differences between heat sources and working fluids exists. The power output has the maximum value as an extremum for cycle temperatures and capacities of heat exchangers. In the internally reversible cycle, the power output is independent of the cycle temperature in the intermediate heat exchanger. In this case when the total capacities of heat exchangers are given, three heat exchangers have the same capacities at the maximum power output condition. In addition, when the cycle is not extremum for cycle temperatures and capacities of heat exchangers. At the maximum power output condition, the capacity of heat exchanger at the cold side is slightly more than the hot side as the cycle effectiveness decreases.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.2
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• pp.43-52
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• 2017

Heat treatment condition for dissolution of the M23C6 carbides in 2.25Cr-1Mo-V-Ti material for thermal power plant tube was investigated using a dilatometer method. 2.25Cr-1Mo-V-Ti material was heat-treated at $900{\sim}1,100^{\circ}C$ for 0, 10, 30 min to find the proper dissolution condition of M23C6 carbides. The phase identification and volume fraction of the carbide were measured by using OM, SEM, EBSD and TEM analysis. Optimal heat treatment condition of M23C6 carbide dissolution was selected by predicting dissolution temperature of carbide using Bs points appeared at dilatometer curve. Experimental results showed that the conditions of carbide dissolution was 900, 1,000, $1,100^{\circ}C$ for 30 min. Eventually, the optimal heat treatment condition for dissolution was 30 min at $1,000^{\circ}C$ considering the minimum coarsening of Austenite grain size.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2657-2666
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• 1995

In this study, the effects of design factors of finned-tube heat exchanger, such as fin spacing and fin array on the frost growth and heat exchanger performance are investigated under a frosting condition. The results show that the amount of frost, frost density and blockage ratio of air flow passage increase with decreasing fin spacing. Heat transfer rate increases momentarily at the initial stage of frosting and then decreases. After that heat transfer rate continues to increase again to reach a maximum value and then decreases dramatically. It is shown that the time required for heat transfer rate to reach a maximum value becomes shorter with decreasing fin spacing, and after a maximum value, heat transfer rate decreases very fast. The maximum allowable blockage ratio is introduced to determine the operation limit of a finned-tube heat exchanger operating under frosting condition and is obtained as a function of fin spacing. It is also shown that heat transfer rate of heat exchanger with staggered fin array increases about 17% and the amount of pressure drop of air increases about 1~2 mmH$_{2}$O, compared with those of in-line type heat exchanger under frosting condition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.225-229
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• 1990

As a basic study of optimal design conditions of refrigeration systems, the reversed carnot cycle, including heat transfer processes through the finite temperature differences between heat sources and the working fluids, is analyzed with the capacity of heat exchanger as a design parameter. When the temperatures of heat sources and the input work are fixed as constants, the optimal design condition is obtained as an optimum ratio of capacities of heat exchangers, which is exactly unity when the exergy output and effectiveness are maximum. In addition, the optimum ratio is slightly increased from unity as the irreversibility of the cycle increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.33-42
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• 1999

The effects of wan thermal boundary condition were investigated for a uniform wall temperature, a uniform wall heat flux, and for coupled heat conduction In the channel wall with transverse rectangular ribs. Numerical investigations for steady laminar flow show behavior similar to that observed experimentally in the separated flow region for flow over a cylinder. Conjugate heat transfer with a low solid-fluid thermal conductivity ratio does not lead to the same results as for the uniform heat flux boundary condition, and heat transfer reversal is found on the back sides of the ribs.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.325-335
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• 1992

In this work, direct contact 4-stage fluidized bed heat exchanger is experimentally studied to develop a new type of heat exchanger which recovers the energy contained in the high temperature waste gas exhausted from the industrial furnaces. A sand is used as a heat transfer medium in this experiment. To determine the optimum operating condition, 11 different perforated plates which have a different free area ratio with different hole diameter are used in the experiment. From the room temperature experiment, the pressure drop which is caused by fluidized bed formation is observed. The high temperature experiment is carried out to seek the optimum operating condition of high heat efficiency at low heat exchanger operation cost. The results of experiment are as following. The pressure drop in the high temperature condition can be predicted from the results of the room temperature experiment. And Nusselt number becomes smaller due to the increased interference between sand particles as Reynolds number increases when the dilute phase fluidized beds are formed in nigh temperature condition. But heat transfer amount through the total sand surface area become larger due to the large resident amount of sand. Considering the heat transfer amount and the heat exchanger operation cost, perforated plates which have either a 30% or 35% of free area ratio with 15mm of hole diameter are best fitted for our goal of this work. The values of .phi. which is a dimensionless number representing the absorption heat amount per unit sand rate are in the range from 0.4 to 0.5, when Reynolds number of waste gas ranges from 25-30 with these perforated plates.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

• Nuclear Engineering and Technology
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• v.39 no.2
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• pp.143-148
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• 2007

Spent nuclear fuel generated at nuclear power plants must be safely stored during interim storage periods. A dry storage cask to safely store the spent nuclear fuel should be able to adequately emit the decay heat from the spent nuclear fuel. Therefore, heat removal tests using a half scale dry storage cask have been performed to estimate the heat transfer characteristics of a dry storage cask under normal, off-normal, and accident conditions. In the normal condition, the heat transfer rate to an ambient atmosphere by convective air through a passive heat removal system reached 83%. Accordingly, the passive heat removal system is designed well and works adequately. In the off-normal condition, the influence of a half blockage in the inlet on the temperature appears minimal. In the accident condition, the temperature rose for 12 hours after the accident, but the temperature rise steadied after 36 hours.