• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권3호
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• pp.257-268
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• 2014

The objective of the present study is to investigate thermal diffusion and radiation effects on unsteady MHD flow past a linearly accelerated vertical porous plate with variable temperature and also with variable mass diffusion in presence of heat source or sink under the influence of applied transverse magnetic field. The fluid considered here is a gray, absorbing/emitting radiation but a non-scattering medium. At time t > 0, the plate is linearly accelerated with a velocity $u=u_0t$ in its own plane. And at the same time, plate temperature and concentration levels near the plate raised linearly with time t. The dimensionless governing equations involved in the present analysis are solved using the closed analytical method. The velocity, temperature, concentration, skin-friction, the rate or heat transfer and the rate of mass transfer are studied through graphs in terms of different physical parameters like magnetic field parameter (M), radiation parameter (R), Schmidt parameter (Sc), Soret number (So), Heat source parameter (S), Prandtl number (Pr), thermal Grashof number (Gr), mass Grashof number (Gm) and time (t).

• 상하수도학회지
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• 제25권4호
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• pp.503-510
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• 2011

Ammonia in water which is toxic to human, its concentration is regulated below 0.5 mg/L in drinking water. Current study aimed to develop appropriate models for ammonia stripping using hollow fiber membrane contactor. Two different models were developed during the study. Model 1 was assumed only free ammonia ($NH_3$) transfer in stripping process, whereas the Model 2 was assumed with total ammonia ($NH_3+{NH_4}^+$) transfer. Ammonium chloride ($NH_4CI$), sodium hydroxide(NaOH) were used to make ammonia solution, which was concentration of 25 mg as N/L at a pH of 10.5. The experimental conditions were such that, the liquid flow was in tube-side in upward direction and t he gas flow was on shell-side in downward direction a t room temperature. The experimental and modeling results showed that marginal difference were observed at low gas flux. However the difference between the both models and experimental value were increased when the gas flux was increased. The study concludes that the Model 1 with free ammonia is more appropriate when both models were compared and useful in ammonia stripping process at low gas flux.

• 대한기계학회논문집B
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• 제23권1호
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• pp.149-157
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• 1999

Heat transfer in a duct is augmented remarkably by rib turbulators. However, increasing friction loss is accompanied due to ribs disturbing flows. Hence, pressure drops and heat transfer are considered simultaneously to decide heat/mass transfer performance in a rib-roughened duct. In the present study, the effects of rib cross section shape on pressure drop through a duct are investigated as well as those on heat transfer characteristics. The results show that the characteristics of heat/mass transfer and friction loss in the duct roughened with triangular ribs are similar to those with square ribs, while significantly different from those with semicircular ribs. The best performance in the duct is obtained by using semicircular shaped ribs among three types of ribs for the large rib angles of ${\alpha}{\geq}63^{\circ}$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.218-225
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• 2008

When the heat release and acoustic pressure fluctuations are generated in the combustor by irregular combustion, these fluctuations affect the mass flow rate of the propellants injected through the injectors. Also, the variations of the mass flow rate by these fluctuations again bring about irregular combustion and furthermore that is related with combustion instability. Therefore, it is very important to identify the mass variation for the pressure fluctuation on the injector and to investigate its transfer function. So, we first have studied quantifying the variation of mass flow rate generated in simplex swirl injector by injection pressure fluctuation. To acquire the transient mass flow rate in orifice with time, we have tried to measure of the flow axial velocity and liquid film thickness in orifice. The axial velocity is acquired through theoretical approach after measuring the pressure in orifice and the flow area in the orifice is measured by electric conductance method. As results, mass flow rate calculated by axial velocity and liquid film thickness measuring in orifice accorded with mass flow rate acquired by direct measuring method in the small error range within 1 percents in steady state and within 6 percents as average mass flow rate in pulsated state. Hence this method can be used to measure the mass flow rate not only in steady state but also in unsteady state because the mass flow rate in the orifice can acquire with time and this method shows very high accuracy based on the experimental results.

• 한국태양에너지학회 논문집
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• 제27권3호
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• pp.143-148
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• 2007

It is essential to know the flow characteristics at the risers of Flat-plate solar collector for optimum design. For flat-plate solar collector, it is difficult to experimentally study the effect for the number of riser in the collector for the economic problem. So, this study was performed to show the flow characteristics of flat-plate solar collector with the number of riser using commercial code FLUENT 6.0. The base collector size is chosen with $2\;m^2$ as 1m by 2m in this study, the mass flow rate was estimated 0.04 kg/s using the mass flow rate of 0.02 kg/s per collector area for the certificate test. The number of riser is selected 4, 6, 8, 10, 12, and 14. Through the simulation, the conditions with the risers of 10 or 12 is shown as the optimum design conditions for conventional flat-plate solar collector considering lower pressure drop and more uniformly distributed mass flow rate for higher heat transfer rate without considering heat transfer.

• 대한기계학회논문집B
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• 제32권3호
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• pp.207-215
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• 2008

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. At the Reynolds number of $2.09{\times}10^5$, heat/mass transfer coefficients are measured for the tip gap height-to-chord ratio, h/c, of 2.0% at turbulence levels of Tu = 0.3 and 14.7%. A tip-surface flow visualization is also performed for h/c = 2.0% at Tu = 0.3%. The results show that there exists a strong flow separation/re-attachment process, which results in severe local thermal load along the pressure-side corner, and a pair of vortices named "tip gap vortices" in this study is identified along the pressure and suction-side tip corners near the leading edge. The loci and subsequent development of the pressure- and suction-side tip gap vortices are discussed in detail. The combustor-level high inlet turbulence, which increases the tip-surface heat/mass transfer, provides more uniform thermal-load distribution.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1207-1217
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• 1997

The present work experimentally investigated the effects of mass flux, heat flux, inlet quality on the heat transfer performance inside the U-bend of smooth and microfin tube using R-22 and R-407C refrigerants. The parameters were 200 and 400 kg/m$^{2}$ s for mass flux, 6 and 12 kw/m$^{2}$ for heat flux, 0.1 and 0.2 for inlet quality under the pressure of 0.65 MPa. The apparatus consisted of the test section of four straight sections and three U-bends, preheater, condenser, refrigerant pump, mass flow meter etc. The average heat transfer coefficient at the downstream straight section after U-bend was affected by U-bend due to the centrifugal force and mixing of two-phase flow in the U-bend. The average heat transfer coefficient at the U-bend was 4 ~ 33 % higher than that at the straight section. The average heat transfer coefficients were affected in the order of mass flux, heat flux and inlet quality. The average heat transfer coefficients in the microfin tube were lager by 19 ~ 49% and 33 ~ 69% than that in the smooth tube at the straight section and at the U-bend separately. The average heat transfer coefficients for R-407C were larger by 33 ~ 41% and 17 ~ 29% than that for R-22 in the smooth tube and the microfin tube separately.

• 설비공학논문집
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• 제13권1호
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• pp.9-17
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• 2001

In this study, flow boiling experiments were performed using R-134a on a plain tube bundle. Tests were conducted for the following range of variables; quality from 0.1 to 0.9, mass flux from $8\;kg/m^2s$ to $26\;kg/m^2s$ and heat flux from $10\;kW/m^2s$ to $40\;kW/m^2s$. The heat transfer coefficients were strongly dependent on the heat flux. However, they were almost independent on the mass flux or quality. The data are compared with the modified Chen model, which satisfactorily () predicted the data. Original Chen model, however, did not adequately predict the effect of quality. The reason may be attributed to the flow pattern of the present test, where the bubbly flow prevailed for the entire test range. The heat transfer coefficients of the tube bundle were 6~40% higher than those of the single tube pool boiling.

• Journal of Advanced Marine Engineering and Technology
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• 제17권3호
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• pp.24-32
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• 1993

Experimental data on the heat transfer characteristics of HCFC-123 and CFC-11 during condensation in horizontal smooth tube are presented. The experimental apparatus consisted of a closed working fluid loop, coolant loop, and measuring system. The major components of the working fluid loop made of a refrigerant pump, boiler, superheater, refrigerant flow meter, receiver and test section. The tube-in-tube type test section was made of smooth tube which were constructed form 9.52 mm outer diameter of smooth copper tube with 50 mm outside diameter of PVC tube duct. The ranges of parameter, such as refrigerant mass velocity, coolant flow rate, and quality were 90-325kg/($m^2$.s), 60-360kg/h, 5-95% respectively. Data were obtained under steady state condition for annular flow. As a result of these, the condensation heat transfer coefficients for HCFC-123 were slightly lower than those of CFC-11 from 8% to 15% inside horizontal smooth tube. Furthermore, a new generalized correlation for the heat transfer coefficients of HCFC-123 and CFC-11 during condensation inside horizontal smooth tube is proposed.

• 동력기계공학회지
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• 제17권6호
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• pp.54-62
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• 2013

A numerical analysis is performed to evaluate mass flow balance in the heat exchanger for the dehumidifier. To improve the mass flow balance for maximum heat transfer performance, inlet, outlet and baffle are changed. Mass flow balance is evaluated by non-uniformity of flow which is the same concept with the standard deviation. Usually, there will occur many paths between the inlet and the outlet, however, it will follow shortest and low resistance ways. The uniform distribution of flow is numerically analyzed for several types of heat exchangers. Making the shortest way between the inlet and the outlet is most important factor. Two types of heat exchangers are installed in the dehumidifier and 4 cases of Type A heat exchangers and 3 cases of Type B heat exchangers are evaluated and optimized. The result of this research is applied to design heat exchanger for commercial dehumidifiers.