• Title/Summary/Keyword: Heat exchanger performance

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A Study on Selection of Pipe Materials Considering EWT (EWT를 고려한 지중열교환기 파이프 선정에 관한 연구)

  • Ryu, Hyung-Kyou;Chung, Min-Ho;Lee, Byung-Seok;Choi, Hyun-Jun;Choi, Hang-Seok
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.10 no.2
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    • pp.13-18
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    • 2014
  • This paper proposes an optimum pipe material (PVC vs. PE) design & selection for open loop ground heat exchangers. Heat exchange efficiency and/or workability, and the need for trench insulation were investigated by comparing EWT (cooling mode) of each system. CFD simulations for the PVC and PE pipe with the same inner diameter show similar EWT. This is because the PVC pipe has a small thickness but a low thermal conductivity as compared to the PE pipe, and thus these two properties tend to offset each other. However, a hypothetically insulated pipe led to a meaningful drop of EWT. This means pipe insulation is of importance in performance of ground heat exchangers. From analyzing climate data and system operation, it is not advantageous to insulate trench pipes due to construction difficulties and ground temperature characteristics that are seasonally varied.

Investigation of condensation with non-condensable gas in natural circulation loop for passive safety system

  • Jin-Hwa Yang;Tae-Hwan Ahn;Hwang Bae;Hyun-Sik Park
    • Nuclear Engineering and Technology
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    • v.55 no.3
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    • pp.1125-1139
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    • 2023
  • The system-integrated modular advanced reactor 100 (SMART100), an integral-type pressurized water small modular reactor, is based on a novel design concept for containment cooling and radioactive material reduction; it is known as the containment pressure and radioactivity suppression system (CPRSS). There is a passive cooling system using a condensation with non-condensable gas in the SMART CPRSS. When a design basis accident such as a small break loss of coolant accident (SBLOCA) occurs, the pressurized low containment area (LCA) of the SMART CPRSS leads to steam condensation in an incontainment refuelling water storage tank (IRWST). Additionally, the steam and non-condensable gas mixture passes through the CPRSS heat exchanger (CHX) submerged in the emergency cooldown tank (ECT) that can partially remove the residual heat. When the steam and non-condensable gas mixture passes through the CHX, the non-condensable gas can interrupt the condensation heat transfer in the CHX and it degrades CHX performance. In this study, condensation heat transfer experiments of steam and non-condensable gas mixture in the natural circulation loop were conducted. The pressure, temperature, and effects of the non-condensable gas were investigated according to the constant inlet steam flow rate with non-condensable gas injections in the loop.

Evaluation of Heat Exchange Efficiency and Applicability for Parallel U-type Cast-in-place Energy Pile (병렬 U형 현장타설 에너지파일의 열교환 효율 및 적용성 평가)

  • Park, Sangwoo;Kim, Byeongyeon;Sung, Chihun;Choi, Hangseok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.2
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    • pp.361-375
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    • 2015
  • An energy pile is one of the novel ground heat exchangers (GHEX's) that is a economical alternative to the conventional closed-loop vertical GHEX. The combined system of both a structural foundation and a GHEX contains a heat exchange pipe inside the pile foundation and allows a working fluid circulating through the pipe, inducing heat exchange with the ground formation. In this paper, a group of energy piles equipped with parallel U-type (5, 8 and 10 pairs) heat exchange pipes was constructed in a test-bed by fabricating in large-diameter cast-in-place concrete piles. In addition, a closed-loop vertical GHEX with 30m depth was constructed nearby to conduct in-situ thermal response tests (TRTs) and to compare with the thermal performance of the cast-in-place energy piles. A series of thermal performance tests was carried out with application of an artificial cooling and heating load to evaluate the heat exchange rate of energy piles. The applicability of cast-in-place energy piles was evaluated by comparing the relative heat exchange efficiency and heat exchange rate with preceding studies. Finally, it is concluded that the cast-in-place energy piles constructed in the test-bed demonstrate effective and stable thermal performance compared with the other types of GHEX.

The Performance Improvement of a Gas Injection Heat Pump with a Flash Tank (기액분리기를 적용한 가스 인젝션 히트펌프의 성능 향상에 관한 실험적 연구)

  • Son, Kilsoo;Kim, Dongwoo;Choi, Sungkyung;Kim, Yongchan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.6
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    • pp.297-305
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    • 2017
  • Air-source heat pumps are widely used in residential heating systems. However, the decrease in the capacity of the heat pump is unavoidable when operating at very low and high ambient temperatures. The vapor injection technique is considered a promising technology to overcome this problem. Recent research on vapor injection cycles have mainly adopted a scroll compressor with an internal heat exchanger at severe operating conditions. This study measured the COP and EER of a gas injection heat pump using a flash tank with an inverter-driven rotary compressor at severe operating conditions. Compared to non-injection heat pumps, the heating capacity and COP of the gas injection heat pump improved up to 15% and 2.9%, respectively, at outdoor temperatures of $-10^{\circ}C$ to $7^{\circ}C$. The cooling capacity of the gas injection heat pump was 11% higher than the non-injection heat pump at an outdoor temperature of $35^{\circ}C$. At the same time, the EER of the gas injection heat pump was similar to that of the non-injection heat pump.

Analysis of Performance of Heat Pump System with Flue Gas Heat Recovery through Field Test (실증운전을 통한 배가스 열회수 히트펌프 시스템의 성능 분석)

  • Lee, Seung-Ho;Lee, Gil-Bong;Lee, Young-Soo;Park, Sang-Il;Ko, Chang-Bok;Baik, Young-Jin;Lee, Kwan-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.1
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    • pp.1-7
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    • 2014
  • A field test of a 70 kW heat pump system with flue gas heat recovery was performed by an experiment at the Korea Institute of Energy Research. The flue gas is exhausted from a 320 RT absorption chiller-heater in the heating season. Using this flue gas, source water of the heat pump is heated by a condensed-type heat exchanger in the chimney. The operating characteristics of the heat recovery heat pump system were analyzed. Based on the results of the experiments, operating maps were obtained, and an optimum operating range is suggested, in which the return and heat source water temperature are $51^{\circ}C$ and $31^{\circ}C$, respectively. Additionally, economic analysis of this system was conducted and about 50% energy cost savings can be expected in the heating season.

Analysis of Heat Transfer Performance for Mini-Channel Tube Bundles in Cross flow using CFD (전산유체역학을 이용한 직교류 미세관 관군의 전열 성능 해석)

  • Nam, Ki-Won;Min, Jun-Kee;Jeong, Ji-Hwan
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.4
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    • pp.491-499
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    • 2010
  • Heat transfer performance of tube bundles have long been investigated since they were widely used. Most of previous experimental and numerical works for tube bundles were performed with tube diameter in the range of 25~51mm and Reynolds number of $8.000{\leq}Re{\leq}30.000$. Recently, tube bundles with small diameter tube collects interests since the mini-channel tube provides higher compactness. The present work aims to investigate the applicability of previous correlations available in the open literature to the tube bundles with small diameter of 1.5mm and $3.000{\leq}Re{\leq}7.000$. A commercial CFD package was used to analyze the thermal-hydraulic performance of them. The results show that the Zukauskas correlation developed for larger diameter tube and higher Reynolds number are still in good agreement with them within the discrepancy of 4.7%. The analyses also show that the Nuselt number increases with a decrease in the longitudinal pitch.

Study on the Heat Transfer Characteristic of Metallic Foam (발포금속의 열전달 특성에 관한 실험적 연구)

  • Kim, Pil-Hwan;Jin, Mei-Hua;Kim, Young-Jin;Jeong, Hyo-Min;Chung, Han-Shik
    • Proceedings of the SAREK Conference
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    • 2008.11a
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    • pp.618-623
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    • 2008
  • To enhancement heat transfer performance, the metallic foam as heat exchanger was studied rapidly. This was attributed to its high surface area to volume ratio as well as intensive flow mixing by tortuous flow passages. So the experimental study about the heat transfer characteristic of metallic foam is presented in this paper. The material in this experiment was used as FeCrAl which has density of 10 ppi, 20 ppi and 30 ppi respectively. And the results show the heat transfer is rise with permeability Reynolds number increase and the pressure drop metallic foam was increased with the ppi increase.

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Recent Progress in Air Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2007 (설비공학 분야의 최근 연구 동향 : 2007년 학회지 논문에 대한 종합적 고찰)

  • Han, Hwa-Taik;Shin, Dong-Sin;Choi, Chang-Ho;Lee, Dae-Young;Kim, Seo-Young;Kwon, Yong-Il
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.12
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    • pp.844-861
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    • 2008
  • The papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during the year of 2007 have been reviewed. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environments. The conclusions are as follows. (1) The research trends of fluid engineering have been surveyed as groups of general fluid flow, fluid machinery and piping, etc. New research topics include micro nano fluid, micropump and fuel cell. Traditional CFD was still popular and widely used in research and development. Studies about fans and pumps were performed in the field of fluid machinery. Characteristics of flow and fin shape optimization are studied in the field of piping system. (2) The research works on heat transfer have been reviewed in the field of heat transfer characteristics, heat exchangers, and desiccant cooling systems. The research on heat transfer characteristics includes thermal transport in pulse tubes, high temperature superconductors, ground heat exchangers, fuel cell stacks and ice slurry systems. For the heat 'exchangers, the research on pin-tube heat exchanger, plate heat exchanger, condensers and gas coolers has been cordially implemented. The research works on heat transfer augmenting tubes have been also reported. For the desiccant cooling systems, the studies on the design and operating conditions for desiccant rotors as well as performance index are noticeable. (3) In the field of refrigeration, many papers were presented on the air conditioning system using CO2 as a refrigerant. The issues on the two-stage compression, the oil selection, and the appropriate oil charge were treated. The subjects of alternative refrigerants were also studied steadily. Hydrocarbons, DME and their mixtures were considered and various heat transfer correlations were proposed. (4) Research papers have been reviewed in the field of building facilities by grouping into the researches on heat and cold sources, air conditioning and air cleaning, ventilation and fire research including tunnel ventilation, flow control of piping system, and sound research with drain system. Main focuses have been addressed to the promotion of efficient or effective use of energy, which helps to save energy and results in reduced environmental pollution and operating cost. (5) Studies were mostly focused on analyzing the indoor environment in various spaces like cars, old tombs, machine rooms, and etc. in an architectural environmental field. Moreover, subjects of various fields such as the evaluation of noise, thermal environment, indoor air quality and development of energy analysis program were researched by various methods of survey, simulation, and field experiment.

The performance of solar heat pump with non-freon refrigerant $CF_3CH_2F$(R-134a) for school classroom heating[II] (태양열 이용 비프레온계 $CF_3CH_2F$(R-134a)적용 열펌프시스템에 의한 학교교실 난방에 관한 연구(II))

  • Sun, Kyung-Ho;Jung, Hyun-Chai;Kim, Ki-Sun
    • Solar Energy
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    • v.17 no.1
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    • pp.3-15
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    • 1997
  • The goal of this paper is to measure and compare the performance of solar heat pump for school classroom heating. To accomplish the goal, solar heat pump with alumium roll bond type evaporator and indoor heat exchanger(condenser) was built and fully instrumented with thermocouples and pressure transducers etc. The test results showed that the COP and capacity of R-134a($CF_3CH_2F$) were higher than those of R-12($CF_2Cl_2$). The solar heat pump system for room heating was designed to show the best efficiency that the room temperature make $18{\sim}20^{\circ}C\;and\;23{\sim}25^{\circ}C$ in Seoul during November, December, and January.

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Development of Optimum Design Method for Geothermal Performance based on Energy Simulation (지열 성능해석 시뮬레이션에 기반한 최적 설계 수법 개발)

  • Moon, Hyeongjin;Kim, Hongkyo;Nam, Yujin
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.35 no.3
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    • pp.43-48
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    • 2019
  • Since the revision of the Rationalization of Energy Use Law, the spread of new and renewable energy in buildings has been promoted. In addition, the production of electric power and thermal energy is an important issue in the change of energy paradigm centered on the use of distributed energy. Among them, geothermal energy is attracting attention as a high-performance energy-saving technology capable of coping with heating / cooling and hot water load by utilizing the constant temperature zone of the earth. However, there is a disadvantage that the initial investment cost is high as a method of calculating the capacity of a geothermal facility by calculating the maximum load. The disadvantages of these disadvantages are that the geothermal energy supply is getting stagnant and the design of the geothermal system needs to be supplemented. In this study, optimization design of geothermal system was carried out using optimization tool. As a result of the optimization, the ground heat exchanger decreased by 30.8%, the capacity of the heat pump decreased by 7.7%, and the capacity of the heat storage tank decreased by about 40%. The simulation was performed by applying the optimized value to the program and confirmed that it corresponds to the load of the building. We also confirmed that all of the constraints used in the optimization design were satisfied. The initial investment cost of the optimized geothermal system is about 18.6% lower than the initial investment cost.