Abstract The compressor of a refrigerator accounts for approximately 60-80% of the total energy consumption necessary for the refrigeration cycle. This study investigates the implementation of a pre-compression system featuring a vibrating nozzle, with the goal of enhancing the efficiency of a linear compressor. By utilizing this pre-compression system, the cooling capacity and efficiency of the compressor are expected to improve. The numerical results show that the pre-compression system leads to an improvement of approximately 1.7% in cooling capacity compared to the baseline model. Furthermore, an increase of approximately 0.1 in EER was observed, confirming the feasibility of incorporating a pre-compression system with a vibrating nozzle.

냉매 오충전은 에어컨에서 빈번하게 발생하는 고장 모드 중 하나로, 적정 충전량 대비 부족 및 과충전 모두 냉방 성능의 저하를 유 발하므로 충전된 냉매량을 정확하게 판단하는 것이 중요하다. 본 연구에서는 퍼지 군집화 기법을 통한 정상상태 식별을 통해 냉매 오 충전량을 다중 분류하는 모델을 개발하였다. 정상상태 식별을 위해 에어컨 운전 데이터에 대해 이동 평균 간의 차이를 활용한 퍼지 군 집화 알고리즘을 적용하였으며, IFDR를 통해 기존 연구된 정상상태 판단 기법들과 식별 결과를 비교하였다. 이후, 시스템 내 상관성 을 고려한 mRMR을 이용해 특징을 선택하였으며, 도출된 특징을 이용해 SVM 기반의 다중 분류 모델이 생성되었다. 제안된 방법은 시험 데이터를 통해 만족할 만한 분류 정확도와 강건성을 도출하였다.

In this paper, cycle performance analysis of two-stage compression two-stage expansion refrigeration system using eco-friendly refrigerants is presented to offer the basic design data for the operating parameters of the system. Eco-friendly refrigerant R600a(Isobutane) for freon refrigerant R22 were used working fluids in this study. The coefficient of performance(COP) of R600a is about 5% greater than that of R22 two-stage compression refrigeration system in the range of evaporation temperature –30℃∼-60℃. The coefficient of performance of two-stage compression and two-stage expansion refrigeration system decreases with the increasing condensation temperature and superheating degree but increases with the increasing evaporation temperature, subcooling degree and mass flow rate ration of intercooler.

This paper considers the influence of internal heat exchanger and capillary tube on the efficiency of small refrigeration system using eco-friendly refrigerants such as R290, R600a, R1270, and R717. A refrigeration system using such internal heat exchanger and capillary tube may improve performance, but may degrade performance. Therefore, this paper used a mathematical model in a normal state to understand performance characteristics as to what change occurs when internal heat exchanger and capillary tube are attached to eco-friendly refrigerant based on R134a. In addition, the effects of operating conditions such as refrigerant flow rate, evaporation temperature, condensation temperature, subcooling degree internal heat exchanger length and capillary tube length were analyzed. The result showed that the evaporation temperature, condensation temperature, subcooling degree, internal heat exchanger length and capillary tube length had an effect on the refrigeration capacity and compression power. Therefore, it is necessary to design a refrigeration cycle using an eco-friendly refrigerant by grasping these effects in detail.

본 연구에서는 CO2 가스 배출 저감 및 선박 폐열 회수 증대를 목적으로 선박 배기로 버려지는 폐열을 전기로 변환하는 ORC(Organic Rankine Cycle) 발전에 대해 시뮬레이션을 통한 냉매별 효율을 보여주고 있다. 상대적으로 고온인 배기가스의 폐열과 상대적으로 저온인 냉각해수를 이용하여 Aspen HYSYS 11을 이용하여 시뮬레이션을 수행하였다. 해수냉각 ORC 발전시스템의 시뮬레이션 결과, 작동유체 효율은 R717 냉매가 2.86 %로 가장 높았고, 다음 순으로 R152a, R134a, R143a, R125a로 나타났다.

The new thermal management models of linear compressors have been recently reported. These models adopt the simplified transient flow effects to shorten the excessive analysis time. Among the unsteady flow effects of the linear compressor, the effect of the gap flow between the compressor housing and the body due to the body vibration on the heat transfer performance was studied in this paper. For this study, a numerical analysis for the unsteady axisymmetric flows was performed by using CFD (Computational Fluid Dynamics). The results show that the high-speed refrigerant flows occurred in the gap between the compressor housing and the body, which contribute to increasing the heat transfer from high temperature refrigerants in the housing to the outside air. In addition, as the gap decreases, the refrigerant flow rate through the gap increases and the heat transfer rate increases as well.

In this paper, the performance characteristics of a cryogenic refrigeration system used in fields such as HMR(Home Meal Replacement) that require ultra-low temperatures of -50℃ using natural refrigerants according to the recent enforcement of the Atmosphere Environment Conservation Act were investigated. For this purpose, a 2-stage compression refrigeration system using R744(CO2) and a cascade refrigeration system using R747/R404A and R747/R717(NH3) were applied. The COP(coefficients of performance) of each refrigeration system were compared according to changes in evaporation and condensation temperature, subcooled and superheated degree. Although the coefficient of performance of the 2-stage compression refrigeration system using R744 was superior to that of the cascade refrigeration system, 2-stage refrigeration system was considered that various problems should be solved in practical terms. In addition, the COP of R744/R717 for various operating conditions showed similar results to R744/R404A, so the possibility of alternativeness could be confirmed in the cascade refrigeration system.

This paper focuses on the simulation of refrigeration cycle equipped with the adiabatic capillary tube, which is widely used in small vapor compression refrigeration systems. The present simulation is based on fundamental conservation equations of mass, energy and momentum. These equations are solved through an iterative process. The adiabatic capillary tube model is based on homogeneous flow model. This model is used to understand the natural refrigerants flow behavior inside the adiabatic capillary tube. Transport properties and thermodynamic of natural refrigerants are calculated by using EES(Engineering Equation Solver) program. The operating factors considered in this paper include condensation temperature, evaporation temperature, inner diameter tube and sub-cooling degree of the adiabatic capillary tube. Our simulation results are summarized as follows: as the size of the inner diameter tube increases, the pressure drop in the capillary tube decreases while the length of the capillary tube increases. We found that R-290 decreases by 20-22% on average, and R-600a significantly decreases below 50%, while R-1270 increases 17-19% on average, compared to R-134a.

Due to the concern on global warming, refrigerants having high GWP(Global Warming Potential) are being replaced to low GWP refrigerants. As for small slush maker, R-134a is being to replaced to R-290, whose GWP is 3. In this study, performance tests were conducted on the slush maker having dual evaporator, which was designed to operate using R-290. Results showed that the optimum refrigerant charge amount was 100g. At the charge amount, 61 minutes was needed to make a slush from a raw milk substance, which contained 10% sucrose. The power consumption was 0.89 kW, which yielded COP of 0.252. Tests were further conducted changing the outdoor air temperature. It was resulted that slush-making was possible at all outdoor temperatures except at an extreme temperature of 43°C. Even at the temperature, slush-making was possible if the machine operated with a single evaporator. The COP increased with the decrease of the outdoor temperature.

Improvement of living and life style led to increased sales of frozen milk products, such as ice creams or ice bars. These frozen milk products are commonly stored in a small refrigeration stocker. R-502, which has long been used as the refrigerant of a stocker, is being replaced with R-404A due to the ozone layer depletion issue. In this study, thermal analysis was conducted for the stocker, and the results are compared with experimental data. For the compressor analysis, performance curves were used. Evaporator or condenser was discretized into small volumes, and energy balance was applied. Capillary tube was also discretized into small volumes, and energy and momentum balance were applied. Comparison with the test data of the stocker having 500 liter internal volume revealed that the condensation or evaporation temperature was predicted well except for the initial start-up period. Slightly lower prediction (maximum 4oC) was obtained for the stoker room temperature at the initial operation period. The effect of radiation heat transfer for prediction of the stocker room temperature was assessed.

In this paper, we analyzed the characteristics of the mass flow rate and velocity of the refrigerant in response to a change in the number of holes and the diameter size(Type-1～4) of the valve guide refrigerant to flow from Pc to Ps when the pressure is constant. Type-1 is 40% higher mass flow flowing in the direction of Ps as compared with the Pc mass flow rate. Type-2 is 64% higher mass flow flowing in the direction of Ps as compared with the Pc mass flow rate. Type-3 is 50% higher mass flow flowing in the direction of Ps as compared with the Pc mass flow rate. Type-4 is 47% higher mass flow flowing in the direction of Ps as compared with the Pc mass flow rate.

In this paper, cycle performance analysis of two-stage compression and two-stage expansion refrigeration system using Natural refrigerants is presented to offer the basic design data for the operating parameters of the system. Alternative natural refrigerant R290(Propane), R600(Butane), R717(Ammonia), R1270(Propylene) for freon refrigerant R22 were used working fluids in this study. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, and mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of two-stage compression and two-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and two-stage expansion refrigeration system using alternative nreon refrigerants have an effect on COP of this system.

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system using alternative Freon refrigerants is presented to offer the basic design data for the operating parameters of the system. Pure alternative Freon refrigerant R32, R134a and near NARM(Non-Azeotropic Refrigerants Mixtures) R404A, R407C, R410A and ARM(Azeotropic Refrigerant Mixtures) R507A were used working fluids in this study. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of two-stage compression and one-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter- cooler of two-stage compression and one-stage expansion refrigeration system using alternative Freon refrigerants have an effect on COP of this system.

In this paper, cycle performance analysis of cascade refrigeration system using alternative FREON refrigerants are presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooled and superheated degree, and evaporating and condensing temperature, temperature difference of cascade heat exchanger in cascade refrigeration system. The COP of cascade refrigeration system increases with the increasing subcooled degree, but there is no significant changes with the increasing superheated degree. The COP of cascade refrigeration system depends on evaporating and condensing temperatures of cascade heat exchanger. Therefore, subcooled degree, evaporating and condensing temperature of cascade heat exchanger using alternative FREON refrigerants have an effect on the COP of this system. In this paper, COP of cascade refrigeration system using R23 for low temperature system and R507A for high temperature system is higher 8 ~ 29 % than using R13 for low temperature system and R22 for high temperature system.

In this paper, cycle performance analysis of cascade refrigeration system using natural refrigerants R744 for low temperature cycle, and R290, R600, R600a, R717 for high temperature cycle are presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooled and superheated degree, and condensing and evaporating temperature, temperature difference of cascade heat exchanger in cascade refrigeration system. The COP of cascade refrigeration system increases with the increasing subcooled degree, but there is no significant changes with the increasing superheated degree. The COP of cascade refrigeration system depends on evaporating and condensing temperatures of cascade heat exchanger. The COP of cascade refrigeration system using natural refrigerants is similar to the COP using freon refrigerant (R23 / R22). Points to be considered are th security, the attached facilities for natural refrigerants than COP.

HFC-134a is currently used as a refrigerant in automotive air conditioning system replacing the ozone depleting CFC-12 refrigerant. This paper was experimentally studied on the performance characteristics of an automotive air conditioning system with variations of charging refrigerant and compressor speed. An air conditioning system was composed of laminated type evaporator, parallel flow type condenser, vane rotary type compressor, externally equalized thermostatic expansion valve and receiver drier with specifications of Hyundai Sonata Ⅱ vehicle. And the automatic measuring system of air conditioner used KTE-1000BA developed by a KT ENG Co., Ltd.. of Korea. The optimum conditions which were tested as available parameters for better performance are indicated charging refrigerant 800 g and compressor speed 1700 rpm.

본 연구는 에어컨의 적정냉매충전량 진단을 위한 자료를 제공하기 위하여 수행하였다. 공기 온도 33∼35℃, 습도 55∼57%RH로 조절되는 실내에서 SONATA III(Hyundai motor Co., Korea)자동차의 에어컨시스템을 대상으로 냉매충전 및 성능시험장치를 구성하고 냉매충전량 변화에 따른 냉매라인의 측정량으로 각 지점 온도와 고압 및 저압을 측정하고 분석하였다. 냉매라인의 측정온도는 압축기, 응축기, 리시버드라이어 및 증발기의 입구와 출구 파이프표면온도와 응축기와 증발기벤트 입구와 출구의 송풍공기온도이다. 이들 각 온도와 압력은 정도의 차이는 있으나 모두 냉매충전량(Wr)에 따른 영향을 받으며, 이들을 측정하여 냉매충전 정도를 진단할 수 있는 것으로 나타났다. 엔진회전속도 2,000 rpm과 1,500 rpm에 따른 각 측정량의 변화양상은 차이가 나타나지 않아 에너지사용량이 낮은 1500 rpm이 시험 회전수로 적당할 것으로 판단된다. 냉매충전량에 가장 큰 영향을 입는 측정량은 증발기벤트 입출구온도차(Td)이며, 그 다음이 냉매라인 고압측의 압력(P1)으로 나타났다. 1,500 rpm에서 Wr이 350 g까지 증가함에 따라 Td는 급격히 증가하다가 350g에서 700g까지는 12.8℃에서 16.7℃로 완만하게 증가하였고, 700g을 초과하면서 완만하게 감소하였다. P1은 Wr이 400 g까지 증가함에 따라 급격히 증가하다가 400 g에서 700 g까지는 14.3 kgf/cm2에서 16.0 kgf/cm2으로 완만하게 증가하였고 700 g을 초과하면 급격하게 상승하였다. 에어컨사용설명서에 제시된 냉매충전량이 720 g인 것을 고려하면 1,500 rpm에서 적정냉매충전량 진단은 5%오차범위에서 증발기벤트 입출구 공기온도차가 15℃, 고압측압력 15 kgf/cm2일 때로 추정된다. 에어컨상태가 정상인 진단은 Td가 12℃이상과 P1이 14 kgf/cm²에서 16 kgf/cm² 사이일 때로 판단된다.