• Journal of Advanced Marine Engineering and Technology
• /
• v.27 no.1
• /
• pp.108-116
• /
• 2003

In this paper, the experimental results of condensation heat transfer were reported for the plate and shell heat exchangers(P&SHE) using R-l34a. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-l34a 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$^{\circ}$. Downflow of the condensing R-l34a in one channel releases heat to the cold up flow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-l34a 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. Condensation heat transfer coefficients were increased when the refrigerant mass flux was increased. A rise in the average heat flux causes an slight increase in the hr. Finally, at a higher system pressure the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.1
• /
• pp.50-56
• /
• 2008

Experimental results for forced convection condensation of Refrigerant-22 and ternary Refrigerant-407C(HFC-32/125/134a 23/25/52 wt%) which is being considered as a substitute R-22 inside a horizontal micro-fin tube are presented. The test section was horizontal double-tube counterflow condenser with a length 4,000 mm micro-fin tube, having 8.53 mm ID, 0.2 mm fin height and 60 fins. The range of parameters of mass velocity were varied from 102.1 to 301.0 kg/(m2.s) and inlet quality 1.0. At the given experimental conditions. the average heat transfer coefficients for R-407C were lower than that for R-22 at a micro-fin tube. Over the mass velocity range tested. the PF(penalty factor) for R-22, R-407C were lower than the increasing ratio of heat transfer area by fins, and the EF(enhancement factor) for R-22, R-407C were higher than the increasing ratio of heat transfer area by fins.

• 연구논문집
• /
• s.34
• /
• pp.39-46
• /
• 2004

The compressors in the air conditioner have the role of the pressurization and circulation of the refrigerant. The hermetic reciprocating compressors driven by rotary motor have been used for the air conditioner. The linear compressor has very simple structure and enhancement in the efficiency in comparison to that of conventional reciprocating compressor. The linear compressors are widely used for the small cryogenic refrigerator (below 1 kW), such as the Stirling refrigerator and pulse tube refrigerator. In the cryogenic application, the pressure ratio of the linear compressor is below 1.5, but the linear compressor for the air conditioner should overcome the high pressure ratio and the large pressure difference between the each sides of the piston. The resonance characteristics of the linear compressor has the significant impacts on the power consumption. To minimize the power consumption, the linear compressor should be operated at the resonance point. In the resonance characteristics, the role of the mechanical and gas spring should be considered. In present study, the cycle of the analysis of the vapor compression refrigeration cycle with the different refrigerants (R134a, R4l0a, R600a) and the designs of the linear compressor are performed. The effects of the stiffness of the mechanical spring on the electromagnetic forces would be discussed. Finally, the results show the design specification of the linear compressor for the air conditioner.

• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.6
• /
• pp.715-722
• /
• 2007

Experiments were conducted for the investigation of pressure drop inside horizontal micro-fin tubes during the condensation of R-22 and ternary refrigerant. R-407C(HFC-32/125/134a 23/25/62 wt%) as a substitute of R-22. The condenser is a double-tube and counterflow type heat exchanger which is consisted with micro-fin tubes having 60 fins with a length of 4000mm, outer diameter of 9.53mm and fin height of 0.2mm. The mass velocity varied from 102.1 to $301.0kg/(m^2{\cdot}s)$ and inlet quality was fixed as 1.0. From the experimental results. the pressure drop for R-407C was considerably higher than that for R-22. The value of PF(penalty factor) for both of refrigerants was not bigger than the ratio of micro-fin tube area to smooth tube area. Based on the experimental data. correlation was Proposed for the prediction of frictional pressure drop during the condensation of R-22 and R-407C inside horizontal micro-fin tubes.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.12
• /
• pp.1831-1843
• /
• 2001

In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d$_{p}$ = 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m$^2$s G 26 kg/m$^2$s, 10 kW/m$^2$ q0 40 kW/m$^2$and 0.1 $\chi$ 0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d$_{p}$ = 0.27 mm) compared with that for R-123 (d$_{p}$ = 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.7
• /
• pp.980-991
• /
• 1998

In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m$\^$2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.

• Journal of Fisheries and Marine Sciences Education
• /
• v.14 no.2
• /
• pp.177-190
• /
• 2002

An experimental study was carried out to make clear heat transfer characteristics in flow boiling of binary mixtures of refrigerants R134a and R123 in a uniformly heated horizontal tube. Experiments were run at a pressure of 0.6 MPa both for pure fluids and mixtures in the ranges of heat flux $10{\sim}50{kW/m}^2$, vapor quality 0~100% and mass flux 150-600 $kg/m^2s$. Heat transfer coefficients of mixtures were reduced compared to the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant. Total pressure drop during two-phase flow boiling in a horizontal tube consists of the sum of two components, that is, the frictional pressure drop and pressure drop due to acceleration. The frictional pressure drop is the most difficult component to predict, and makes the most important contribution to the total pressure drop. On the other hand, the acceleration pressure drop resulting from the variation of the momentum flux caused by phase change is generally small as compared to the frictional pressure drop. There is no significant difference in measured pressure drop between mixtures and pure fluids. The correlation of Martinelli and Nelson predicted most of the present data both for pure and mixed refrigerants within 30%.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.3
• /
• pp.197-201
• /
• 2017

Most fishing vessels use an ice cooling system to manage and store captured fish. However, it is difficult to maintain an adequate temperature and salt concentration as well as operating time limitations in ice cooling systems. The purpose of this study is to investigate the heat transfer characteristics of flooded-type evaporators for a seawater cooling system to maintain proper seawater temperature in a fish tank. Experiments were conducted to investigate the heat transfer characteristics by changing the seawater temperature, flow rate, and saturation temperature of the refrigerant. It was confirmed that the heat transfer coefficient of an aluminum-brass tube was approximately 10% higher than that of a copper-nickel tube at the same heat flux. Furthermore, it was confirmed that applying the aluminum-brass tube to the heat transfer tube of a seawater heat exchanger was effective in terms of heat transfer. A comparison of the overall heat transfer coefficient of a single-tube heat exchanger and the flooded-type multi-tube heat exchanger for an 18-kW cooling system showed that the heat transfer coefficient of the single-tube heat exchanger was 25% higher under the same conditions. These results are considered to be important data for designing a flooded-type multi-tube heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.3
• /
• pp.208-215
• /
• 2011

In this work, pool boiling heat transfer coefficients(HTCs) of R22, R123, R134a, and R245fa are measured on both horizontal plain and 26 fpi low fin tubes. The pool boiling temperature is maintained at $7^{\circ}C$ and heat flux is varied from 80 $kW/m^2$ to 10 $kW/m^2$ with an interval of 10 $kW/m^2$. Wall temperatures are measured directly by thermocouples inserted through holes of 0.5 mm diameter. Test results show that HTCs of high vapor pressure refrigerants are usually higher than those of low pressure fluids in both plain and low fin tubes. On a plain tube, HTCs of R245fa are 23.3% higher than those of R123 while on a 26 fpi low fin tube, HTCs of R245fa are 46.3% higher than those of R123. The fin effect is more prominent with low vapor pressure refrigerants than with high vapor pressure ones due to a sweeping effect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.12
• /
• pp.924-930
• /
• 2018

The objective of this study was to investigate heating performance characteristics of electric heat pump system in a fuel cell electric vehicle (FCEV). In order to analyze heating performance characteristics of electric heat pump system with plate-type heat exchanger using stack coolant to evaporate the refrigerant, R-134a, each component was installed and tested under various operating conditions, such as air inlet temperature of inner condenser and compressor speed. When the air inlet temperature of inner condenser was varied from $0.0^{\circ}C$ to $-20.0^{\circ}C$, heating capacity was not quite different due to similar temperature gap between inlet and outlet of inner condenser with electric-driven expansion valve (EEV). However, COP increased until certain EEV opening, especially under 45.0%, because of decreasing power consumption. According to the compressor speed variation from 2,000 to 4,000 RPM, heating capacity and COP were found to have opposite trend. In the future works, stack coolant conditions as the heat source for tested heat pump system were analyzed with respect to heating performance, such as heating capacity and COP.