• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.39-49
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• 2001

Investigation of the performance of an autocascade refrigeration system using the refrigerant mixtures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) has been carried out by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions ranging from 10/90 to 30/70 by weight. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in the autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results match quite well with those obtained from the simulation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.928-936
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• 1999

An experimental study was performed to investigate characteristics of an inverter driven water-to-water refrigeration system with a variation of compressor frequencies and expansion devices. The frequency of a compressor varied from 30Hz to 75Hz, and performance of the systems applying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve(EEV) were measured. The load conditions were altered by varying the temperature of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test conditions were deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimum control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in an inverter refrigeration system due to active control of flow area with a change of compressor frequency and load conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.880-890
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• 1999

The purpose of this study is to investigate the performance of an autocascade refrigeration system using the refrigerant miktures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) as working fluids by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions in the range of from 10/90 to 30/70 by weight percentage. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results show similar trend with those from the simulation.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.439-444
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• 2005

Steady state simulation and dynamic simulation were performed to analyze the operational characteristics of a multi-type refrigeration system, Fully distributed model was adopted to simulate the steady state and transient responses of the system. The main aim was to see the effect of one indoor unit on the other unit. Numerical simulations were carried out for various operation conditions of an indoor unit - secondary fluid inlet temperature, mass flow rate and expansion valve opening. The results showed that the inlet temperature and mass flow rate of the secondary fluid of one indoor unit had minor effect on the operation of the other unit. However, the opening of the expansion valve had significant effect on the performance of the other unit.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.1
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• pp.39-46
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• 1994

Experiments on the performance of refrigeration system using alternatives to R12 are carried out. The condenser and the evaporator are concentric-tube heat exchangers of counter-flow type and the compressor is driven by a variable speed motor. In this study, R134a, R152a, R22/142b(50 : 50 by mass) are adopted as alternatives to R12. Tests are performed by varying the inlet and outlet temperatures of secondary fluids of evaporator and condenser under the condition of constant compressor speed, degree of superheating and degree of subcooling. Results show that R134a has refrigeration capacity close to that of R12 and requires the greatest compressor power compared with that of others. And the system using R152a shows the best performance from the viewpoint of refrigeration capacity, compressor power and coefficient of performance. R22/142b is superior to R12 in the above points.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.6
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• pp.242-247
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• 2016

This study analyzed the energy consumption of a building pump system that was originally equipped with a primary-secondary zone pump system. Using the HYSYS program the energy consumption of the primary pump system was compared with the primary-secondary zone pump system. The primary-secondary zone pump system consumes less energy than the originally designed primary pump system. When the distance between the machine room and each building is assumed to be equal, the primary pump system can be more efficient than the primary-secondary zone pump system with decreasing the distance. When the distance is 120 m, the primary system consumes less total annual energy than the primary-secondary zone pump system and saves 2,773 kWh. The suggested energy evaluation program can be useful if the designer seeks a more efficient pump system.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.1
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• pp.1-10
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• 2005

Screw compressor chillers are widely used in refrigeration for capacity over 30 RT. In general, chillers operate under part-load conditions during most of the time. Therefore, information on the characteristics of part-load is very important for better chiller performance and energy economy. In this study, performance tests of screw chiller with economizer using R22 and R407C under part-load conditions have been performed for various secondary fluid temperatures. Adoption of an economizer system increased the cooling capacity and improved COP except for lower part-load condition when economizer volume ratio is 1.01. For the same cooling capacity condition at part-load, COP's of both non-economizer and economizer system showed similar values.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.11
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• pp.902-909
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• 2003

Screw compressor type chillers are widely used in refrigeration for capacity over 30 RT. In general, chillers operate under part-load conditions. Therefore, information on characteristics at part-load is very important in view of chiller performance and energy economy. In this study, performance tests of part-load and economizer system using R22 and R407C have been performed for various secondary fluid temperatures. Adoption of an economizer system increased the cooling capacity and improved COP except for lower part-load condition when injection volume ratio is 1.01. For the same cooling capacity condition at part-load, COP of both non-economizer and economizer system showed similar values.

• Tribology and Lubricants
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• v.18 no.4
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• pp.291-298
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• 2002

In this study, a numerical analysis f3r the piston secondary dynamics and lubrication characteristics of small refrigeration reciprocating compressors is presented. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic forces and moments as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, and pin location on the stability of the piston, the oil leakage, and friction losses.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.350-356
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• 2003

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the variation in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the lubrication characteristics as functions of crank angle under compressor running conditions. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction tosses.