• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.2
• /
• pp.79-86
• /
• 2009

The present study was investigates the effect of the parameters on the frost formation and heat transfer performance such as fin shape, air temperature and air velocity. Heat transfer rate and pressure drop by frost were experimentally investigated. Effect of the wet blub temperature and air velocity on the heat transfer performance has been also investigated. The heat transfer performance of the louver fin and tube type heat exchanger was higher by maximum of 0.85% than the corrugate fin type at the air temperature of $2.0/1.5^{\circ}C$. As the wet blub temperature of air were increased, the heat transfer rate, pressure drop and mass of frost of three test models were increased. Especially, the maximum heat transfer rate and maximum pressure drop were shown for the Type B louver fin heat exchanger. As an experimental result, the enhancement factor(EF) of louver fin and tube type heat exchanger was only $0.2{\sim}0.4$ due to the high pressure drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.6
• /
• pp.740-748
• /
• 1999

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different vertical tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare inner surface, groove inner surface, corrugated inner surface and spring inserted inner surface tubes. The additive concentration was about 0.08 mass%. The heat transfer coefficient was measured as a function of film Reynolds number in the range of 20~200. Experiments were tarried out at higher cooling water temperature of $35^{\circ}C$ to simulate an air cooling condition for several kinds of absorber testing tubes. The experimental results were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube. Especially, it is clarified that the tube with an inserted spring has the highest enhancement effect.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.246-250
• /
• 2006

In general, combustion characteristic of hybrid propulsion was shown with the regression rate depending on only massflow rate of oxidizer But this empirical relation was not represented well effect of the thermo-chemical properties of solid fuel. So, in this study, the combustion characteristics was studied with the mass transfer number(B number) of solid fuel instead of regression rate with various fuel. The PMMA, PP, and PE were used as fuel, and gas oxygen as oxidizer in this experiment. The mass flowrate of gas oxigen was controlled by the several chocked orifices that have different diameter, and the oxidizer supply range was $3.66\sim45.3g/sec$. As result, the empirical relation for mass flux of solid fuel was obtained with mass transfer number, and mass flux of oxidizer as follow; $\dot{m}^{'}_f\;=\;0.0175G^{0.55}B^{0.4}$.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.240-241
• /
• 2005

The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 4.57 mm, and length of 4 m. The experiments were conducted at mass flux of 200 to 700 kg/$m^2s$, saturation temperature of 0$^{circ}C$ to 20$^{circ}C$, and heat flux of 10 to 30 kW/$m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with test results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.6
• /
• pp.860-867
• /
• 2001

In this study, condensation heat transfer experiments were conducted with plate and shell heat exchangers(P&SHE) using R-22. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-22 in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45°. Downflow of the condensing R-22 in one channel releases heat to the cold upflow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-22 on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. A rise in the refrigerant mass flux causes an increase in the h(sub)r. Also, a rise in the average heat flux causes an increase in the h(sub)r. Finally, at a higher system pressure the h(sub)r is found to be slightly lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.10
• /
• pp.932-940
• /
• 2000

An experimental study on evaporative heat transfer characteristics in micro-fin tubes before and after expansion process has been performed with R-22. Single-grooved micro-fin tubes with outer diameter of 9.52 mm were used as test sections, and it was uniformly heated by applying direct current to the test tubes. Experiments were conducted at mass flow rates of 20 and 30 kg/hr. For each mass flow rate condition, evaporation temperature was set at 5 and $15^{\circ}C$and heat flux was changed from 6 to 11 kW/$m^2$ The evaporative heat transfer coefficient of micro-fin tubes after expansion is decreased because of the crush of fins and enlargement of inner diameter compared to that before expansion. Convective boiling effect decreased remarkably at higher quality range in the micro-fin tube after expansion, and the difference of the heat transfer coefficient in micro-fin tubes before and after expansion was greater for higher quality region. The evaporative heat transfer coefficient of the micro-fin tube after expansion was 19.9% smaller on the average than that before expansion.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.5
• /
• pp.357-363
• /
• 2008

In order to investigate $CO_2$ heat transfer coefficient and pressure drop by PAG oil concentration during $CO_2$ evaporation, the experiment on evaporation heat transfer characteristics in a horizontal micro-fin tube was performed. The experimental apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes($400{\sim}1200\;kg/m^2s$), heat fluxes($10{\sim}30\;kW/m^2$) and saturation temperatures ($-5{\sim}5^{\circ}C$), and PAG oil concentration($0{\sim}5\;wt%$). The variation of the heat transfer coefficient was different in accordance with the oil concentration. With the increase of the oil concentration, the evaporation heat transfer coefficient decreased and the delay of dryout by oil addition was found. Pressure drop increased with the increase of the oil concentration and heat flux, and the decrease of saturation temperature.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2000.04a
• /
• pp.714-719
• /
• 2000

This paper describes a transfer matrix approach to analyze the dynamics of a high sped flexible rotor system supported at 2 positions by five ceramic bearings. The rotor system is modelled as lumped parameters in which many factors are considered not only lumped inertia or mass, bending moment, shear force but also gyroscopic effect and unbalance. The equation of motion is derived in the transfer matrix form, from which the eigenvalues equation is also derived. The transfer natural frequencies and modes. The eigenvalues, eigenmodes, campbell diagram, whirling critical speed, whirling modes, and the response of unbalance are calculated and discussed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.2
• /
• pp.269-277
• /
• 2002

Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

• KSBB Journal
• /
• v.8 no.5
• /
• pp.417-423
• /
• 1993

The effect of moisture content of biocatalyst on the performance of a gas phase continuous bioreactor was investigated along with study on the mass transfer limitation. The biocatalysts whose moisture contents are 46.2% and 37.2%, respectively were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, following by slow dehydration method, and packed into a column. Relative production rate (RPR), acetaldehyde composition ($X_p$) and conversion (X) of biocatalysts (37.2%) are better than those of biocatalysls (46.2%), and it was considered that these are attributed to the mass transfer enhancement in the gas phase compared with the aqueous phase.