• Transactions of the Korean hydrogen and new energy society
• /
• v.23 no.1
• /
• pp.19-25
• /
• 2012

The efficiency and life time of the Proton Exchange Membrane fuel cell (PEMFC) system is critically affected by incoming gas with humidity which should be maintained properly at normal operating conditions. Typically, incoming gas of automotive fuel cell is humidified by external humidifier but the characteristics of device is rarely reported. In this study, characteristics of water transfer in the membrane humidifiers have been experimentally investigated for flow rates of gas and for different flow arrangement under steady state condition. At first, capability of mass transfer through the membrane is examined at constant temperature. Then, the temperature distribution effect on the capability of mass transfer is tested over various inlet conditions. In summary, this research presents the mass transfer capability of hydrophilic membrane over various operating conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.8 no.4
• /
• pp.537-549
• /
• 1996

A numerical study of heat and mass transfer has been carried out for a frost formation process on a circular cylinder in a cross flow including the effect of buoyancy. Studies include cases of low and high Reynolds number flows. The effect of normal velocity at the surface which is produced due to mass transfer was included in the analysis as well as heat transfer contribution generated due to mass transfer. Variations of heat transfer and frost growth both in time and in the circumferential direction have been obtained for various buoyancy parameters. The effect of flow directions(identical or opposite directions to the gravity) has been studied to yield different frost growth. Our results have been compared with existing experimental data and are in good agreement. Buoyancy analyses for a high Reynolds number flow agree with full numerical solutions for the case of having the same flow direction as gravity. However, for the opposite direction case, the boundary layer analyses would not be applicable to predict frost growth except the region near the stagnation point.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.11a
• /
• pp.707-710
• /
• 2004

This paper reported the results of mock-up test on mass concrete for transfer girder using setting time difference of super retarding agent(SRA). According to test results, two mock-up structures were made. Plain concrete without placing layer reached maximum temperature after 24hours since placement and caused surface hydration cracks at top section. However, concrete with placing layer reached maximum temperature after 72hours and surface temperature was higher than center temperature, which did not cause surface crack. After form removing, no crack was observed at side surface of plain concrete, while concrete using SRA at mid section had surface scaling and settling crack. According to coring results, concrete with placing layer had a penetration crack from top section to bottom section. Therefore, the setting time difference method to reduce hydration heat will have difficulty in applying the mass concrete for transfer girder.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.1
• /
• pp.61-69
• /
• 2015

The objective of this study is to experimentally investigate the mixed flow behaviors and oxygen transfer characteristics of a vertical orifice ejector. The experimental apparatus consisted of an electric motor-pump, an orifice ejector, a circulation water tank, an air compressor, a high speed camera unit and control or measurement accessories. The mass ratio was calculated using the measured primary flow rate and suction air flow rate with experimental parameters. The visualization images of vertically injected mixed jet issuing from the orifice ejector were qualitatively analyzed. The volumetric oxygen transfer coefficient was calculated using the measured dissolved oxygen concentration. At a constant primary flow rate, the mass ratio and oxygen transfer coefficient increase with the air pressure of compressor. At a constant air pressure of the compressor, the mass ratio decreases and the oxygen transfer coefficient increases as the primary flow rate increases. The residence time and dispersion of fine air bubbles and the penetration of mixed flow were found to be important parameters for the oxygen transfer rate owing to the contact area and time of two phases.

• Preventive Nutrition and Food Science
• /
• v.8 no.3
• /
• pp.230-234
• /
• 2003

Mass transfer characteristics during osmotic dehydration of carrots were studied as functions of immersion temperature and time, and sugar and salt concentrations. The effect of osmotic dehydration on the degree of browning of air-dried carrots was also evaluated. Increasing the immersion temperature and time, sugar concentration, and salt addition increased water loss, sugar gain, molality and rate of dehydration. The water loss and increases in solids, and molality were rapid in the beginning of the process and then increased slowly during remainder of the process. Increasing 1 or 2% salt concentration in the 40$^{\circ}$Brix sugar solution at 6$0^{\circ}C$ increased water loss and solid gain. Salt addition was not able to significantly affected on water loss and solid gain compare to temperature (40～8$0^{\circ}C$) and sugar concentration (20～60$^{\circ}$Brix) changes due to the low salt concentration. A minimum degree of browning of the air-dried carrots (O.D. = 0.048) could be achieved using binary solutions (40$^{\circ}$Brix sugar solution with 2% salt addition) with 24 min of immersion time compared to control (O.D. = 1.308) or blanching with 24 min of immersion time (O.D. = 0.174).

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.27 no.5
• /
• pp.903-907
• /
• 1998

Mass transfer characteristics during osmotic dehydration of mushrooms(Agaricus bisporus) in sugar solution were studied as a function of sugar concentration, immersion time and temperature, and the effect of osmotic dehydration on browning inhibition of air-dried mushrooms was also evaluated. Increasing the sugar concentration, immersion time and temperature increased moisture loss, sugar gain, molality and rate parameter. The changes of sugar gain and rate parameter were more significantly affected by concentration than by temperature of sugar solutions, while 1$0^{\circ}C$ increase in temperature or 10 Brix increase in concentration had the same effect on water loss. Water loss, sugar gain, molality were rapid in the first period of osmotic dehydration especially in the case of higher concentration and temperature of sugar solutions. Effects of osmotic dehydration in sugar solution(60 Brix, 8$0^{\circ}C$) with 18 min of immersion time(O.D.=0.099) rior to air dehydration on browning inhibition of dried mushrooms were more significant than blanching in water(8$0^{\circ}C$) with the same immersion time(O.D.=0.330) and the control (O.D.=0.559).

• Bulletin of the Korean Chemical Society
• /
• v.25 no.10
• /
• pp.1538-1544
• /
• 2004

Fragmentations and proton transfer reactions of mono-, di-, and triethanolamines were studied using FTMS. It was found that the most abundant fragment ion was $[M-CH_2OH]^+$. The $[M-CH_2OH-H_2O]^+$ was observed in the mass spectra of diethanolamine and triethanolamine. By increasing the ion trapping time in the ICR cell, the $[M+H]^+$ and $[M+H-H_2O]^+$ ions were notably increased for all the samples while the $[M+H-2H_2O]^+$ was observed in the mass spectra of diethanolamine and triethanolamine. The proton transfer reactions between the fragment ions and neutral molecules occurred predominantly by increasing the ion trapping time. The rate constants for the proton transfer reactions were calculated from experimental results. The proton transfer reaction of $CHO^+$ was the fastest one, which is consistent with the heats of reaction. The rate constants for proton transfer reactions of triethanolamine were much slower than those of ethanolamine and diethanolamine because of the steric hindered structure of triethanolamine. The plausible structures of observed ions and heats of reaction for proton transfer were calculated with AM1 semiempirical method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.2
• /
• pp.109-118
• /
• 2013

The absence of a simple and general analytical model has been a problem in the design and analysis of desiccant-assisted air-conditioning systems. In this study, such an analytical model has been developed based on the approximate integral solution of the coupled transient ordinary differential equations for the heat and mass transfer processes in a desiccant wheel. It turned out that the initial conditions should be determined by the solution of four linear algebraic equations including the heat and mass transfer equations for the air flow as well as the energy and mass conservation equations for the desiccant bed. It is also shown that time-averaged exit air temperature and humidity relations could be given in terms of the heat and mass transfer effectiveness.

• Journal of Power System Engineering
• /
• v.3 no.1
• /
• pp.74-79
• /
• 1999

This paper describes formulation for algorithm of time historical response analysis of vibration for straight-line structure. This method is derived from a combination of the transfer stiffness coefficient method and the Newmark method. And this present method improves the computational accuracy of the transient vibration response analysis remarkably owing to several advantages of the transfer stiffness coefficient method. We regarded the structure as a lumped mass system here. The analysis algorithm for the time historical response was formulated for the straight-line structure containing crooked, tree type system. The validity of the present method compared with the transfer matrix method and the Finite Element Method for transient vibration analysis is demonstrated through the numerical computations.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.128-131
• /
• 2004

This paper is to investigate the mock up test results of mass concrete for transfer girder using setting time difference with super retarding agent(SRA) to reduce hydration heat. According to test results, the temperature history of plain concrete without placing lift had a steep rising curvature, and plain concrete had a big temperature difference between surface and middle section of mass concrete, which may result in occurrence of temperature crack. However, considering placing method B, because setting time of middle section concrete was retarded with an increase in SRA contents, higher hydration heat temperature was observed at surface section concrete compared with that at middle section concrete at early age, which can lower the possibility of hydration heat crack. In case of placing method C, although peak temperature of hydration heat was much lower, at early age, high crack occurrence possibility of the hydration heat attributable to the big temperature difference between middle section and bottom section of concrete was expected at bottom section concrete. Therefore, the structure above the ground like transfer girder is not applicable to consider the placing method C.