자연냉매용 이원 냉동시스템의 운전 조건 변화에 따른 최대 성능 예측 = Prediction on Maximum Performance According to Operation Condition of a Binary Refrigeration System Using Natural Refrigerants.

국문 초록 (Abstract)

본 논문에서는 자연냉매 R744(이산화탄소)를 저온사이클에 작동유체로 사용하는 이원 냉동시스템에서 최대 성능 예측을 위한 운전조건을 선정하기 위한 저온 냉동시스템의 설계자료를 제공하고자 한다.

본 논문에서 고려한 작동변수는 증발온도(Tₑ), 응축온도(T𝑐), 과열도(ΔTₛᵤₕ), 과냉각도(ΔTₛᵤ𝚌), 압축효율(η𝑐), 캐스케이드 열교환기 온도차(ΔT𝚌ₐₛ) 등이다. 이에 대한 주요 결과를 요약하면 다음과 같다.

저온영역 -50℃ ~ -30℃에서 R744-R717용 이원 냉동시스템의 증발온도(Tₑ)와 과열도(ΔTₛᵤₕ)가 증가할수록 시스템의 성능계수(COP)는 증가하였으나, 응축온도(T𝑐)와 과열도가 증가할수록 COP는 감소하였다.

저온사이클(R744)과 고온사이클(R717)에 모두 과냉각도(ΔTₛᵤ𝚌)가 주어질 때 이원 냉동사이클의 성능계수(COP)가 가장 높게 나타났으며, 저온사이클과 고온사이클의 과냉각도 증가에 따라 COP는 증가하였다.

캐스케이드 증발온도(T𝚌ₐₛ,ₑ)가 증가할수록 고온사이클의 성능계수(COPₕ)는 증가하는 반면 저온사이클의 성능계수(COPₗ)는 감소하며, 전체 사이클의 성능계수(COP)는 거의 일정한 것으로 나타났다.

압축효율(η𝑐)이 증가할수록 이원 냉동사이클의 성능계수(COP)는 증가하였고, R717용 고온사이클의 증발온도(T𝚌ₐₛ,ₑ) 감소에 따라 성능계수는 증가 후 감소하는 경향을 보였다. 압축효율이 낮을 때는 R744용 저온사이클의 성능계수(COPₗ)가 가장 높았으며, 반면 압축효율이 높을 때는 저온사이클과 고온사이클의 성능계수(COPₗ, COPₕ)가 모두 가장 높게 나타났다.

또한 과열도(ΔTₛᵤₕ), 과냉각도(ΔTₛᵤ𝚌), 압축효율(η𝑐), 증발온도(Tₑ), 응축온도(T𝑐), 캐스케이드 온도차(ΔT𝚌ₐₛ)는 R744와 R717용 이원 냉동사이클의 성능계수에 영향을 미치며, 각 인자별로 성능을 최대로 하는 최적 캐스케이드 증발온도(T𝚌ₐₛ,ₑ,ₒₚₜ)가 존재함을 확인하였다.

따라서 다중회귀분석을 통해 최대 성능계수(COPₘₐₓ)와 최적 캐스케이드 증발온도(T𝚌ₐₛ,ₑ,ₒₚₜ)에 대한 수학적 방정식을 제안하였다.

다국어 초록 (Multilingual Abstract)

In this paper, design data for a low-temperature refrigeration system are provided to select operating conditions for predicting maximum performance in a binary refrigeration system using natural refrigerant R744 (carbon dioxide) as the working fluid in the low-temperature cycle.

The operating variables considered in this paper are evaporation temperature (Tₑ), condensing temperature (T𝑐), superheating degree (ΔTₛᵤₕ), subcooling degree (ΔTₛᵤ𝚌), compression efficiency (η𝑐), and cascade temperature difference (ΔT𝚌ₐₛ).

The main results are summarized as follows: In the low-temperature range of -50℃ to -30℃, the COP of the R744-R717 binary refrigeration system increased as the evaporation temperature (Tₑ) and superheating degree (ΔTₛᵤₕ) increased, but the COP decreased as the condensing temperature (T𝑐) and superheating degree increased.

When the degree of subcooling (ΔTₛᵤ𝚌) was applied to both the low-temperature cycle (R744) and the high-temperature cycle (R717), the coefficient of performance of the binary refrigeration cycle was the highest, and it increased as the subcooling degree increased in both cycles.

As the cascade evaporating temperature (T𝚌ₐₛ,ₑ) increases, the coefficient of performance of the high-temperature cycle (COPₕ) increases, while that of the low-temperature cycle (COPₗ) decreases, and the coefficient of performance of the entire cycle (COP) remains almost constant.

It was confirmed that factors such as superheating degree (ΔTₛᵤₕ), subcooling degree (ΔTₛᵤ𝚌), compression efficiency (η𝑐), evaporation temperature (Tₑ), condensing temperature (T𝑐), and cascade temperature difference (ΔT𝚌ₐₛ) affect the coefficient of performance of the R744-R717 binary refrigeration cycle, and that each factor has an optimal cascade evaporating temperature (T𝚌ₐₛ,ₑ,ₒₚₜ) that maximizes performance.

Therefore, mathematical equations for the maximum coefficient of performance (COPₘₐₓ) and the optimal cascade evaporating temperature (T𝚌ₐₛ,ₑ,ₒₚₜ) were proposed through multilinear regression analysis.

목차 (Table of Contents)

• Ⅰ. 서 론 ·············································································································1
• 1. 연구의 목적 ·································································································1
• 2. 연구의 방법 및 범위 ·················································································3
• 3. 논문의 구성 ·································································································5
• Ⅱ. 성능 분석 ····································································································7
• Ⅲ. 결과 및 고찰 ····························································································16
• 1. 증발온도의 영향 ·······················································································16
• 2. 과열도의 영향 ···························································································18
• 3. 응축온도의 영향 ·······················································································22
• 4. 과냉각도의 영향 ·······················································································24
• 5. 압축효율의 영향 ·······················································································28
• 6. 캐스케이드 열교환기 온도차의 영향 ···················································32
• 7. 수학적 방정식의 적용 ·············································································34
• Ⅳ. 결 론 ···········································································································40
• 참고문헌 ·········································································································42
• Abstract ··········································································································45