• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.5
• /
• pp.728-734
• /
• 2004

Environmentally friendly refrigerants with zero ozone layer depletion potential are required to be used in refrigerators and air conditioners due to the difficulties related to ozone layer depletion and global warming. A rigorous study for the system performance with new refrigerants having zero ozone layer depletion potential is inevitable before adopting that as a new fluid. The HFC(Hydrofluorocarbon) potential has been recommended as alternatives. In this paper. system performance in the heat pump facilities were studied using R-290, R-600a. R-1270 as an environment friendly refrigerant. R-22 as a HCFC's refrigerant. The experimental apparatus has been set-up as a conventional vapor compression type heat Pump system. The test section is a horizontal double pipe heat exchanger. A tube diameter of 12.70mm with 1.315mm wall thickness is used for this investigation. The test results showed that the COP of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of COP was found in R-1270. The refrigeration capacity of hydrocarbon refrigerants were higher than that of R-22. The compressor work was obtained with the maximum value in R-1270 and the minimum one in R-22.

• KSTLE International Journal
• /
• v.1 no.2
• /
• pp.113-117
• /
• 2000

The rotary-vane compressor has become one of the most successful types of compressors because of its mechanical reliability, compactness, and adaptability to moderately high-speed operation in virtually an unlimited range of sizes. However recently, the depletion of the ozone layer due to the current refrigerant(R22) has been getting worse, and it is one of the world's pressing issues. In this paper, we will discuss the use of R410a in the compressor of a room air-conditioner as an alternative refrigerant and air-conditioning system to R22, since R410a has greater refrigerant characteristics than R22. Miniaturization of the rotary compressor for the new refrigerant and air-conditioning system is also possible, which reduces the prime cost of production, hence R410a is naturally a better refrigerant. But to apply the new HFC refrigerant system in refrigeration and air-conditioning systems, a significant redesign of the current refrigerant system is also required, because as the refrigeration changes, lubrication characteristics vary. Close attention must be paid to friction force and energy loss due to friction and wear at many sliding areas.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.2
• /
• pp.96-105
• /
• 2001

R410a which is one of HFC refrigerants is being considered to be a promising replacement for R22 widely used in domestic air conditioners. The rolling piston type rotary compressors for R410a have lower energy efficiency than those for R22 because of the high pressure difference between a suction chamber and a discharge chamber in the compression mechanism. in addition, the re-expansion gas loss of the rotary compressor for R410a which occurs a ta clearance volume in a discharge port becomes larger than that for R22 due to high density of R410a refrigerant. Therefore, Pressure-Volume analyses for various design parameters of a discharge system were carried out to improve efficiency of a R410a rotary compressor. The results such as performance dta, over-compression loss, and re-expansion loss were acquired by P-V analyses and analyzed quantitatively. As a conclusion, the optimal specifications of several design parameters of a discharge system were obtained by analyzing P-V diagrams.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.12
• /
• pp.2806-2818
• /
• 1997

It is generallyaccepted that broadband access technologies will play an important role in the National Information Infrastructure. However, the provision of direct fibers to residential and small business customers has always been considered a challenge. To accelerage the provision of Broadband Access Facilities, alternatibe paths could be identified and actaivated in parallel. In this paepr, we present an overview of the alternative access technologies focusing on xDSL, FTTx, HFC, HFR, and suggest the modeling of the access netetwork systems which is using of the technologies. Also to investigate the economics of each access systems, we derve the numerical equations which is summed up the al parameter including the labor cost of the model system. The proposed equation has a variable which is the cell size (or subsciber clusters) and calculate the real cost values which is normalized by the copper cable unit cost. From the numerical resutls, we conclude that the economic access method to provide these broadband capabilities is depended on the subscriber penetration, the patterns of subscriber distribution density and existing communication infrastructures. It can be expected that our analytical model and equations provides an elegant solution to choose the optimal broadband access technologies to residential and small business customers.

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.6
• /
• pp.871-879
• /
• 1998

The refrigerator consists of many components such as compressor condenser expansion valve evaporator and the cabinet which filled by urethane foam. In this paper the heat leakage of refriger-ator is measured by the new experiment method which is different from a present method, The devi-ation of the UA(overall heat transfer coefficient times area) between the simulation and experiments is about 7-8%. Using the modeling of various components of refrigeration system a performance analysos of CFC 12 and HFC 134a is performed numerically on the UA. As the results of this study according to increase the heat leakage the refrigeration load and mass flow rate of refrigerant are increased. And the increase of the mass flow rate results in the increase of the condensing and evapo-rating temperature. Therefore according to increase of the heat leakage the COP leads to increase because the increase of refrigeration capacity is larger than the increase if compressor power.

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.2
• /
• pp.181-189
• /
• 1998

A general steady-state model for simulation on domastic refrigerator has been developed. The system model consists of various standard components such as evaporator compressor condenser capillary tube and cabinet. Cabinet is not system component but influence characteristic on domastic refrigerator. The purpose of this paper is to compare between characteristics of HFC 134a with CFC 12 in the domastic refrigerator and to predict the steady state cycle performance which is various specifications of cycle components under the continuous running conditions. As the results of simulation the coefficient of performance of both condenser and evaporator increases with increasing UA the increasing rate for condenser is greater than for evaporator.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.2
• /
• pp.210-217
• /
• 1999

This paper reports the experimental results on heat transfer characteristics of R-22 and R-407C(HFC-32/125/134a 23/25/52 wt%) condensing inside horizontal smooth and finned tubes. The test condensers used In the study are double pipe heat exchangers of 7.5 mm ID, 9.5 mm OD smooth tube, and 60 finned micro-fin tube with 8.53 mm ID, 9.53 mm OD. Each of these tubes was 4 000 mm long tubes connected with an U-bend. These U type two-path test tubes are divided In 8 local test sections for the identification of the local condensing heat transfer characterisitcs and pressure drop, U-bend effects on condensing flows. Inlet quality is maintained 1.0, and refrigerant mass velocity is varied from 102.0 to $301.0kg/m^2{\cdot}s$. From the results, it was found that the pressure drop of the R-407C Increased, and heat transfer coefficient decreased compared to those of R-22. In comparison condensing heat transfer characteristics of micro-fm tube with those of smooth tube, increasing of condensing heat transfer coefficient was found outstanding compared to the increasing ratio of pressure drop. Furthermore, pressure drop In U-bend showed at most a 30 % compared to the total pressure drop in the test section.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.3
• /
• pp.435-449
• /
• 1995

In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.

• Science of Emotion and Sensibility
• /
• v.17 no.2
• /
• pp.101-110
• /
• 2014

High-frequency is sound produced in non-audible area, which couldn't be heard in daily life. The frequency range above 22Khz is called 'high-frequency' and its components are called 'HFC(High-Frequency Components)'. It is known that ocean wave sound is rich in HFC, because it brings serenity and causes ${\alpha}$-waves in human mind. When this natural sound is combined with high-frequency, it seems to give a pleasurable feeling, indicated by an ${\alpha}$-wave increase and a ${\beta}$-wave decrease. We call this phenomena "the hypersonic effects". In this experiment, subjects listened to the ocean wave sound simultaneously with corresponding frequencies similar to ocean wave frequency components created artificially in a electric circuit. Brain waves were measured by an EEG system with 8 channels using 8 electrodes on Fp1, Fp2, F3, F4, T3, T4, O1, and O2. The results showed that ${\alpha}$-wave increase and ${\beta}$-wave decrease were statistically significant while subjects were listening to the ocean wave sound along with the high frequency components, reflecting the hypersonic effect.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.1
• /
• pp.48-58
• /
• 2001

For the past few decades the vapor compression cycle with a solution circuit (VCCSC) has been known to provide high efficiency and variable capacity. In this study performance of a VCCSC cycle is examined through computer simulation. In the simulation heat exchangers were modelled by specifying UA or effectiveness values while the compressor performance was specified by an isentropic efficiency. Aqua/ammonia solution was chosen as the working fluid which can be used in the high temperature range. The results show that there exists an optimum operation condition which is dependent upon the temperatures of the external heat transfer fluids(HTFs). Besides the HTF\`s temperature, the maximum system pressure and the size of the solution heat exchanger are shown to have an influence on the optimum operation condition. Finally, as compared to a simple vapor compression heat pump with HFC134a, the COP of the VCCSC is shown to be 2∼22% higher.