• Title/Summary/Keyword: Internal heat exchanger (IHX)

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Experimental Study on Optimal Design of Internal Heat Exchanger for $CO_2$ System ($CO_2$ 시스템에서 내부열교환기 최적설계에 대한 실험적 연구)

  • Kim, Dae-Hoon;Lee, Sang-Jae;Choi, Jun-Young;Lee, Jae-Heon;Kwon, Young-Chul
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2085-2090
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    • 2007
  • This paper describes the possible way to improve the capacity, the efficiency and the pressure drop of $CO_2$ system. It is considered the use of an internal heat exchanger (IHX) to improve the performance of the $CO_2$ system. Experiment was performed by changing a tube shape, a tube number and a tube length of IHX to investigate the performance of IHX for $CO_2$ system. The focus of the present study is to obtain the concept on IHX optimal design. Experimental results show that design parameters are closely related with the capacity and the pressure drop of $CO_2$ system. In the transcritical $CO_2$ cycle, the system performance is very sensitive to the IHX design. System performance on operation condition and shape of IHX is also introduced.

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Operating Characteristics of Internal Heat Exchanger for $CO_2$ Geothermal Heat Pump in the Heating Mode (난방모드 시 $CO_2$ 지열히트펌프의 내부열교환기에 대한 운전특성)

  • Kim, Jae-Duck;Lee, Sang-Jae;Kim, Seon-Chang;Kim, Young-Lyoul
    • Proceedings of the SAREK Conference
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    • 2009.06a
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    • pp.1226-1231
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    • 2009
  • This paper presents operating characteristics of internal heat exchanger(IHX) for $CO_2$ geothermal heat pump in the heating mode. Mass flow rate of $CO_2$, inlet temperatures of $CO_2$ at high and low pressure side were selected as main effect factors by using fractional factorial DOE(Design of Experiments). And RSM(Response Surface Method) was used in optimization phase. The results show that heat transfer rate of IHX increases when either inlet temperature of low pressure side decreases or inlet temperature of high pressure side increases. Effectiveness of IHX increases with increasing of inlet temperature of either high pressure side or low pressure side. Finally, performance contour map was provided over the operation ranges of the main design factors.

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Experimental Study on Cooling Performance of Internal Heat Exchanger for CO2 Refrigerant System (이산화탄소 냉매 시스템용 내부 열교환기의 냉방성능에 관한 실험적 연구)

  • Kim, Dae-Hoon;Kwon, Young-Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.9 no.3
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    • pp.587-592
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    • 2008
  • In order to investigate the performance of an internal heat exchanger for $CO_2$ refrigerant system, the experiment was performed. Four kinds of internal heat exchangers(IHX) were used. The effects on the IHX length, the number of tube, the operating condition and the type of IHX were investigated. With increasing of the IHX length, the capacity and efficiency increased. The pressure drop of the low-side was larger compared with that of the high-side. As the temperature of the gas cooler increased, the capacity and efficiency increased linearly. The operation condition of evaporator was suggested as two phase region rather than superheat region. The capacity and efficiency of the micro-channel was larger about 90% and 75% than those of the tube. But the pressure drop of the micro-channel was more larger, compared with that of the tube.

Effects on Performance of an Internal Heat Exchanger According to Charge Amount and Operating Condition in $CO_2$ Cooling Mode (이산화탄소 냉방운전 시 냉매충전량 및 운전조건에 따라 내부열교환기가 성능에 미치는 영향)

  • Kwak, Myoung-Seok;Cho, Hong-Hyung
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.8 no.1
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    • pp.13-20
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    • 2012
  • This is an experimental study on the performance characteristics of effective heat pump in the cooling mode using a single-stage compression $CO_2$ cycle with an IHX(internal heat exchanger). The performance of a single-stage compression with IHX was investigated according to charge amount and operating condition. Moreover, the performance characteristic of cooling operating was analyzed with the length of IHX. As a result, the optimum refrigerant charge amount was 2.2 kg. The optimal system COP for compressor frequency of 30, 40, 50, and 60 Hz was 3.493, 3.228, 2.978, and 2.659, respectively. Since the system with IHX can maintain large cooling capacity regardless of operating condition, the system performance doesn't reduce considerably under unfavorable condition. When the compressor frequency was 40 Hz, the COP for a system with IHX length of 3 m and 5 m was 3.361 and 3.51, respectively. By using the IHX into a $CO_2$ cooling system, the performance and reliability improves simultaneously.

Experimental Study on the Cooling Performance Improvement of a Two-stage Compression $CO_2$ Cycle (2단압축 이산화탄소 사이클의 냉방성능 향상 특성에 대한 실험적 연구)

  • Cho Hong-Hyun;Lee Ho-Seong;Kim Yong-Chan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.10
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    • pp.835-841
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    • 2006
  • A $CO_2$ system using the two-stage compression cycle was tested by varying $1^{st}-2^{nd}$ compressor frequencies in the cooling mode. To improve the cooling performance of the two-stage compression $CO_2$ cycle, the following cycle options were applied: a basic cycle, a cycle with an intercooler, a cycle with an IHX (internal heat exchanger), and a cycle with an intercooler and IHX. The cycle with the intercooler-IHX showed the highest cooling capacity improvement among the cycle options at all compressor frequencies. The cycle with the intercooler, the cycle with the IHX, and the cycle with the intercooler-IHX improved the cooling COP by 7, 12, and 15%, respectively, over the basic $CO_2$ cycle when the compressor frequencies for the first and second compressors were 50 Hz and 30 Hz, respectively. In addition, the applications of the selected cycle options enhanced system reliability.

Performance Characteristics of Vehicle Air Conditioning System Using Internal Heat Exchanger with Inner Fin (휜 타입 내부열교환기 적용에 따른 차량용 냉방시스템 성능 특성)

  • Kim, Sung Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.1
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    • pp.69-73
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    • 2013
  • Internal heat exchanger (IHX) apparatus using the temperature difference between high and low pressure lines in vehicle air conditioning system is a good method to enhance the cooling performance. In this study, we designed various double-pipe internal heat exchangers which have inner fins between the internal pipe and external pipe. We also measured the performance characteristic (pressure drop, cooling capacity, compressor work and coefficient of performance (COP)) of the modified internal heat exchangers that had the change of the fin height and the inside shape of the internal pipe. This experimental results indicated that the liner and serration type internal heat exchanger was the best cooling performance. In addition, the air conditioning system with the liner and serration type internal heat exchanger showed the improved performances of about 6.4% and 9.2%, respectively, for the cooling capacity and COP.

Experimental Study on the Cooling Performance of a Variable Speed $CO_2$ Cycle with Internal Heat Exchanger and Electronic Expansion Valve (내부열교환기 및 전자팽창장치를 적용한 가변속 이산화탄소 사이클의 냉방성능에 관한 실험적 연구)

  • Cho Honghyun;Ryu Changgi;Kim Yongchan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.3
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    • pp.209-215
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    • 2005
  • Since a transcritical $CO_2$ cycle shows lower performance than conventional air conditioners in the cooling mode operation, it is required to enhance the performance of the $CO_2$ cycle by applying advanced technologies and optimizing components. In this study, the cooling performance of a $CO_2$ system measured by varying refrigerant charge amount, compressor frequency, EEV opening and length of internal heat exchanger. As a result, the cooling COP of the basic system without internal heat exchanger was 2.1. The cooling performance of the modified cycle applying internal heat exchanger improved by $4-9\%$ over the basic cycle.

Performance Variation with Length of Internal Heat Exchanger in CO2 Cooling Cycle Using an Ejector (이젝터를 적용한 이산화탄소 냉동사이클의 내부열교환기 길이에 따른 성능 변화)

  • Kang, Byun;Cho, Hong-Hyun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.24 no.2
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    • pp.147-154
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    • 2012
  • Recently, many researchers have studied the performance of the transcritical $CO_2$ refrigeration cycle in order to improve the system efficiency. In this study, the length of IHX in the $CO_2$ ejector cycle was varied so as to evaluate the performance improvement. As a result, compressor work and cooling capacity was increased by 3% and 5% as the length of internal heat exchanger was changed from 3 m to 15 m. The best COP was appeared at internal heat exchanger length of 12 m, and it was 3.01. Besides, the length of internal heat exchanger has a big effect to pressure lift ratio and entrainment ratio in the ejector $CO_2$ cycle and it may be changed with operating conditions and system specifications.

Study on Heat Transfer Characteristics of Internal Heat Exchanger for $CO_2$ Heat Pump under Heating Operating Condition (난방운전 조건하에서 $CO_2$ 열펌프용 내부 열교환기의 열전달 특성에 대한 연구)

  • Kim, Dae-Hoon;Lee, Sang-Jae;Choi, Jun-Young;Lee, Jae-Heon;Kwon, Young-Chul
    • Journal of Energy Engineering
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    • v.17 no.2
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    • pp.116-123
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    • 2008
  • In order to study the heat transfer, effectiveness and pressure drop of an internal heat exchanger (IHX) for $CO_2$, heat pump under heating condition, the experiment and numerical analysis were performed. Four kinds of IHXs were used. The section-by-section method and Hardy-Cross method were used for the numerical analysis. The effects of IHX on the flow rate of refrigerant, the IHX length, the operating condition of a gas-cooler and an evaporator and the type of IHXs were investigated. With increasing the flow rate, the heat transfer rate increased about 25%. The heat transfer of the micro-channel tube was larger about 100% than that of the coaxial tube. With increasing the IHX length, the heat transfer rate decreased. The low-side pressure drop was larger compared with that of the high-side. And the pressure drop of the microchannel tube was larger about 100% than that of the coaxial tube. With increasing the high-side temperature and decreasing the low-side temperature, the heat transfer rate increased about 3%. From this study, we can see that new correlation on $CO_2$ heat transfer characteristics and tube type is necessary.

Study on the Performance Improvement for an Automobile Air Conditioning System Using Alternative Refrigerant R1234yf (대체냉매 R1234yf를 적용한 자동차용 에어컨 시스템의 성능 향상에 관한 연구)

  • Cho, Honghyun;Lee, Hoseong;Park, Chasik
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.25 no.4
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    • pp.201-207
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    • 2013
  • The performance of automobile air conditioning systems of R1234yf was evaluated and compared with that of R134a. In particular, the performance evaluation was carried out by installing an internal heat exchanger in order to improve the performance of the system used in R1234yf. A performance comparison between the R1234yf and R134a for automotive air conditioning revealed that the cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively.