• Title/Summary/Keyword: NTU-effectiveness method

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A theoretical Analysis and CFD Simulation on the Ceramic Heat Exchanger (세라믹 열교환기의 이론해석 및 CFD 시뮬레이션)

  • Paeng, Jin-Gi;Yoon, Young-Hwan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.21 no.5
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    • pp.282-290
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    • 2009
  • A ceramic monolith heat exchanger is studied to find the performance of heat transfer and pressure drop by numerical computation and $\xi$-NTU method. The numerical computation was performed throughout the domain including fluid region in exhaust gas-side rectangular ducts, ceramic core and fluid region in air-side rectangular duct with the air and exhaust in cross flow direction. In addition, the heat exchanger was also analyzed to estimate the performance by conventional $\xi$-NTU method with several Nusselt number correlations for flow in rectangular duct from literature. By comparisons of both performances by the numerical computation and the $\xi$-NTU method, the effectiveness by $\xi$-NTU method was closest to the result by numerical computation within a relative error of 2.14% when Stephan's Nusselt number correlation was adopted to the $\xi$-NTU method among the several correlations.

A Numerical Study on the Performance Analysis of the Plume Abatement NWD Cooling Tower (백연 방지를 위한 NWD냉각탑의 성능해석에 관한 수치해석적 연구)

  • 최창혁;최영기;소헌영
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.11
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    • pp.1049-1058
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    • 2001
  • The performance and design analysis for a NWD cooling tower using a combined wet and dry type fill are numerically investigated and compared with the experimental results. The Stoecker's method is applied to the wet section and LMTD or NTU-Effectiveness method to the wet and dry sections. The efficiency ratio of the NWD cooling tower to a wet type crossflow cooling tower is 59.34%. The predicted result shows a good agreement with the experimental data within 1.4% error. Plume abatement is far better with a NWD cooling tower than a counterflow cooling tower. It costs less than a conventional wet/dry tower because the finned exchanger is eliminated. This method also leaves out complexity in structure and Intricacy in operation.

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A Numerical Study on the Performance Analysis of Plume Abatement Cooling Tower with Dry Type Heat Exchanger (건식 열교환기를 이용한 백연방지 냉각탑 성능의 수치해석적 연구)

  • 김병조;최영기
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.12
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    • pp.1018-1027
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    • 2003
  • This study treats the analysis of the performance and the design of plume abatement wet/dry cooling tower with dry type heat exchanger using a numerical method. A two-dimensional analysis is performed using the finite volume method for mechanical draft counterflow and crossflow tower. For a coupling problem between water and air system, a turbulent two phase flow is considered. Effectiveness-NTU method is used for modeling of the dry type heat exchanger. The parameter change simulations of the outer wall shape, the relative flowrate of air, and attachment of an air mixer are performed to examine the effect on plume abatement. It is found that if the relative air flowrate ratio and the adequate air mixer type are chosen well in addition to the ratio of water to air flowrate, the loss of the cooling capacity and the additional cost are reduced and the plume is abated.

Numerical Study on the Performance Analysis of Plume Abatement Cooling Tower with Dry Type Heat Exchanger

  • Kim, Byung-Jo;Choi, Young-Ki
    • International Journal of Air-Conditioning and Refrigeration
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    • v.13 no.2
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    • pp.61-70
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    • 2005
  • This study treats the numerical analysis of performance and design for plume abatement wet/dry cooling tower with a dry type heat exchanger. A two-dimensional analysis is performed using the finite volume method for mechanical draft counterflow and crossflow tower. For a coupling problem between water and air system, a turbulent two phase flow is considered. The Effectiveness-NTU method is used for modeling of the dry type heat exchanger. The parametric simulations such as the relative flowrate of air and attachment length of an air mixer are performed to examine the effect on plume abatement. It is found that if the relative air flowrate ratio and the adequate air mixer type are chosen well in addition to the ratio of water to air flowrate, the loss of cooling capacity and the additional cost are reduced and the plume is abated.

NUMERICAL STUDY FOR THE FULL-SCALE ANALYSIS OF PLATE-TYPE HEAT EXCHANGER USING ONE-DIMENSIONAL FLOW NETWORK MODEL and ε-NTU METHOD (판형 열교환기 Full-scale 해석을 위한 1차원 유동 네트워크 모델 및 ε-NTU 모델의 수치적 연구)

  • Kim, Minsung;Min, June Kee;Ha, Man Yeong
    • Journal of computational fluids engineering
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    • v.19 no.1
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    • pp.47-56
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    • 2014
  • Since a typical plate heat exchanger is made up of a huge number of unitary cells, it may be impossible to predict the aero-thermal performance of the full scale heat exchanger through three-dimensional numerical simulation due to the enormous amount of computing resources and time required. In the present study, a simple flow-network model using the friction factor correlation and a thermal-network model based on the effectiveness-number of transfer units (${\varepsilon}$-NTU) method has been developed. The complicated flow pattern inside the cross-corrugated heat exchanger has been modeled into flow and thermal networks. Using this model, the heat transfer between neighboring streams can be considered, and the pressure drop and the heat transfer rate of full-scale heat exchanger matrix are calculated. In the calculation, the aero-thermal performance of each unitary cell of the heat exchanger matrix was evaluated using correlations of the Fanning friction factor f and the Nusselt number Nu, which were calculated by unitary-cell CFD model.

Evaluation on Thermal Energy Performance of a Plate Heat Exchanger (판형열교환기의 열에너지 성능평가)

  • Kang, Byung-Ha;Kim, Do-Kyu
    • Transactions of the Korean hydrogen and new energy society
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    • v.14 no.1
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    • pp.53-60
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    • 2003
  • Performance evaluation on thermal transport of a plate heat exchanger has been carried out. The $\varepsilon$-Ntu method is employed to evaluate the performance of a brazed type of plate heat exchanger. This problem is of particular interest in the design of a plate heat exchanger. The characteristics of heat transfer as well as pressure drop are studied in the wide range of Reynolds numbers in the cold side while that of hot side is fixed at 620. f-factor correlation in a plate heat exchanger is obtained from the pressure drop data. It is also found that the effectiveness of the plate heat exchanger is increased as the Ntu is increased.

An Experimental Study on the Heat Exchanger for the Engine Waste Heat Recovery Using Serrated Fins and Bayonet Tube (톱니형휜이 부착된 2중 열교환관을 이용한 엔진 배열회수기에 관한 실험적 연구)

  • Yang Tae-Jin;Kim Jong-Soo;Im Yong-Bin
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.6
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    • pp.685-691
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    • 2005
  • In this study, high performance waste heat recovery heat exchanger was developed using the bayonet tube with spiral serrated fins. Especially, heat exchanger of the bayonet tube type was operated well because of double water passes mechanism and characteristics. A cooling water Passes down inner tubes to thimble-form tubes, then flows back up as it boils. The heat exchanger of bayonet tube type was composed of steel tube with 7channels$(I.D_1\;14mm.\;I.D_2\;31.6mm)$ and spiral serrated fins. The performance tests were conducted under the following conditions A cooling water flow rate was 273kg/h and engine l·pm was varied from 750rpm to 3500 rpm. From the experimental result. waste heat recovery was 9.21kW when engine rpm was 3500. and pressure drop was $15\~260mmHg/m^3$ The effectiveness of heat exchanger was about /$0.7\~0.9$. The performance of heat exchanger was evaluated by using the $\varepsilon-NTU$ method. In the study the NTU of the heat exchanger was $1.57\~2.33$.

Heat Exchanger Ranking Program Using Genetic Algorithm and ε-NTU Method for Optimal Design (유전알고리즘과 ε-NTU 모델을 이용한 다양한 열교환기의 최적설계 및 성능해석)

  • Lee, Soon Ho;Kim, Minsung;Ha, Man Yeong;Park, Sang-Hu;Min, June Kee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.11
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    • pp.925-933
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    • 2014
  • Today, computational fluid dynamics (CFD) is widely used in industry because of the availability of high-performance computers. However, full-scale analysis poses problems owing to the limited resources and time. In this study, the performance and optimal size of a heat exchanger were calculated using the effectiveness-number of transfer units (${\varepsilon}-NTU$) method and a database of characteristics heat exchanger. Information about the geometry and performance of various heat exchangers is collected, and the performance of the heat exchanger is calculated under the given operating conditions. To determine the optimal size of the heat exchanger, a Genetic Algorithm (GA) is used, and MATLAB and REFPROP are used for the calculation.

Study on Performance Evaluation of Oscillating Heat Pipe Heat Exchanger for Low Temperature Waste Heat Recovery

  • Bui, Ngoc-Hung;Kim, Ju-Won;Jang, In-Seung;Kang, Jeong-Kil;Kim, Jong-Soo
    • International Journal of Air-Conditioning and Refrigeration
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    • v.11 no.2
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    • pp.73-81
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    • 2003
  • The performance of heat exchanger using oscillating heat pipe (OHP) for low temperature waste heat recovery was evaluated. OHP used in this study was made from low finned copper tubes connected by many turns to become the closed loop of serpentine structure. The OHP heat exchanger was formed into shell and tube type. R-22 and R-141b were used as the working fluids of OHP with a fill ratio of 40 vol.%. Water was used as the working fluid of shell side. As the experimental parameters, the inlet temperature difference between heating and cooling water and the mass velocity of water were changed. The mass velocity of water was changed from 30 kg/$m^2$s to 92 kg/$m^2$s. The experimental results showed that the heat recovery rate linearly increased as the mass velocity and the inlet temperature difference of water increased. Finally, the performance of OHP heat exchanger was evaluated by $\varepsilon$-NTU method. It was found that the effectiveness would be 80% if NTU were about 1.5.

Study on Performance Evaluation of Oscillating Heat Pipe Heat Exchanger for Low Temperature Waste Heat Recovery (저온 폐열 회수용 진동형 히트 파이프 열교환기의 성능 평가에 관한 연구)

  • 안영태;이욱현;김정훈;김종수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.5
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    • pp.368-376
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    • 2001
  • Performance of heat exchanger was evaluated to heat exchanger using oscillating heat pipe for waste heat recovery of low temperature. Oscillating heat pipe used in this study was formed to the closed loop of serpentine shapes using copper tubes. Heat exchanger was formed to shell and tube type and composed of low finned tube. R-22 and R-141b were used to the working fluids of tube side and their charging ratio was 40%. And, water was used to the working fluid of shell side. As the experimental parameters, the inlet temperature difference of heating and cooling part of secondary fluid and the mass velocity of secondary fluid were used. The mass velocity of secondary fluid was changed from 90 kg/$m^2s\; to\;190 kg/m^2$s from the experimental results, heat recovery rate was linearly increased to the increment of the mass velocity of secondary fluid and the inlet temperature difference of secondary fluid. Finally, the performance of heat exchanger was evaluated by using $\varepsilon$-NTU method. It was found that NTU was about 1.5 when effectiveness was decided to 80%.

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