https://doi.org/10.6110/KJACR.2017.29.8.391

Jaehyeok Heo ; Dong-Won Lee ; Min-Hwi Kim ; Wonkeun Baik ; Rin Yun

Understanding of seawater fouling characteristics is critical in designing a heat exchanger adapted in an effluent utilization system for a power plant. We reviewed three types of fouling mechanisms of general, biological, and crystallizing for a plate-frame heat exchanger, to be used for heat exchanging with heated effluent from a power plant. Also, mathematical models for each type of seawater fouling were suggested. Actual thermal resistance calculated from seawater fouling models were compared and implemented in designing a plate-frame heat exchanger. The bio-fouling model revealed the largest thermal resistance and the highest number of plates for a plate-frame heat exchanger under the same heat load. Overall heat transfer coefficient and pressure drop of a plate-frame heat exchanger under fouling conditions was lower by 58 percent and higher by 2.85 times than those under clean conditions, respectively.

https://doi.org/10.6110/KJACR.2017.29.8.401

Myung Sung Lee ; Soo Whan Ahn

The effect of different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on local heat transfer distributions and pressure drops in a divergent channel with 30° inclined ribs on one wall or two walls was investigated for Reynolds numbers from 22,000 to 75,000. Top and bottom walls were insulated; two side walls were uniformly heated in the divergent channel. Heated walls were composed of 10 isolated coper sections and length-to-outlet hydraulic diameter ratio of 10. Rib height-to-outlet hydraulic diameter ratio was 0.1, and rib pitch-to-height ratio equaled 10. Results revealed that V-shaped continuous rib (case A) produced approximately 1.4 times higher average Nussselt number than in the parallel broken rib (case B), and V-shaped broken rib (case C) in the channel with two ribbed walls at Re = 54,000.

https://doi.org/10.6110/KJACR.2017.29.8.408

Hyunwoo Choi ; Jeong-Heon Shin ; Jun Seok Choi ; Seok Ho Yoon

Supercritical carbon dioxide (sCO₂) power system is emerging technology because of its high cycle efficiency and compactness. Meanwhile, PCHE (Printed Circuit Heat Exchanger) is gaining attention in sCO₂ power system technology because PCHE with high pressure-resistance and larger heat transfer surface per unit volume is fundamentally needed. Thermo-fluidic characteristics of sCO₂ in the micro channel of PCHE should be investigated. In this study, heat transfer characteristics of sCO₂ of various inlet conditions and cross-sectional shapes of single micro channel were investigated experimentally. Experiment was conducted at supercritical state of higher than critical temperature and pressure. Test sections were made of copper and hydraulic diameter was 1 mm. Convective heat transfer coefficients were measured according to each interval of the channel and pressure drop was also measured. Convective heat transfer coefficients from experimental data were compared with existing correlation. In this study, using measured data, a new empirical correlation to predict near critical region heat transfer coefficient is developed and suggested. Test results of single channel will be used for design of PCHE.

https://doi.org/10.6110/KJACR.2017.29.8.419

Sungjune Yang ; Youngjoo Kim ; Jun Hur ; Teasung Kim

In this study, energy loss due to ventilation load in the dock system was analyzed through simulation. Also, flow generated in the dock system of the warehouse was measured using manufactured measuring devices. Numerical simulation was conducted by simulating the most common picking tasks by examining the actual working environment. Incompressible and unsteady turbulent flows were assumed, and the turbulence model was the k-e standard model. Proper grid was selected through grid dependency test. Measurement was conducted using Honeywell and Vaisala sensors, and flow and temperature inside the warehouse were measured and compared with simulation results to validate simulation. When comparing amount of loss occurring in two hours and amount of loss occurring in 15 minutes, docking time of the former was eight times longer but energy loss was 3.8 times lower. Ventilation load occurring during the initial period after opening docking system accounted for a large proportion of total ventilation load. Also, comparing the load when the dock was closed and the load when the truck was parked, ventilation load was significantly higher than load due to heat conduction from the wall. Therefore, in improving the docking system, it is effective to reduce the gap by improving compatibility of the docking system and truck, rather than wall material.

https://doi.org/10.6110/KJACR.2017.29.8.429

Seungho Ha ; Junghoon Park ; Soohun Lee ; Kwang Ho Kim

There are three main methods to store heat energy; sensible heat storage, latent heat storage, and thermochemical heat storage. Thermochemical heat storage has the highest storage density among the three methods, so this study focused on the thermochemical heat storage method. Experiments were conducted in this study with Zeolite 13x as thermochemical material in a large-scale reactor with 8 kg of Zeolite 13x. Experiments analyzed storage density of Zeolite 13x with respect to four different heating temperatures (50℃, 100℃, 150℃, 200℃) in heat storage process. As a result, they showed 40~50 percent of storage efficiency in the experiment. Experiments also revealed that reactions between Zeolite 13x and water vapor were reversible and stable, but efficiency of the system was low, compared with sensible heat storage systems or latent heat storage systems.

https://doi.org/10.6110/KJACR.2017.29.8.437

Nae-Hyun Kim ; Hyun-Jin Kim

Because of improvement of living standards and increased use of ice at home, built-in ice makers are of interest. In this study, refrigeration cycle of a unitary ice maker for residential usage was optimized using R-404A. Optimization was achieved through a search for proper refrigerant charge amount. For the present ice maker producing ice for 24 cups, the optimum charge amount was 200 g. In this configuration, the ice making cycle time was 17 minutes 53 seconds, ice production was 1.27 kg/h and COP was 0.310. After initial start-up, condensation and evaporation temperatures gradually decreased with time. As ice builds in the cup, heat transfer performance of the evaporator decreases, that results in decrease of evaporation and condensation temperatures. Replacement of existing slit nozzles with individual circular hole nozzles improved ice production capacity by 10 percent. Through visualization of ice formation in the ice cup, growth rate of the ice in the cup was relatively uniform.