• 한국분무공학회지
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• 제29권3호
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• pp.124-133
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• 2024

Heat pumps play a crucial role in achieving the 2050 Net-Zero targets in many countries worldwide. This study addresses this issue by modifying simulation conditions and selecting relevant cases to determine optimal COP conditions using Simulink. By analyzing the efficiency of heat pump heating, utilizing Simulink models provided by MATLAB, and evaluating economic feasibility, we aim to identify the key factors influencing heat pump performance, including the heat source type, refrigerant, heating set temperature, and piping. Our goal is to establish optimal conditions for maximizing the efficiency of these eco-friendly systems while considering economic factors. In this study, it was confirmed that the heat exchanger flow arrangement of the air-source heat pump using R407c was set to cross-flow, and the diameter of the heat exchanger inner tube was set to 0.95 times the existing size, which was found to be optimal for maximizing efficiency. The COP was approximately 4.07 under these conditions.

• 대한기계학회논문집B
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• 제33권2호
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• pp.124-132
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• 2009

Experiments have been performed to investigate fluid-elastic instability of tube bundles, subjected to twophase cross flow. Fluid-elastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and the threshold flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

• 설비공학논문집
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• 제17권11호
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• pp.1014-1021
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• 2005

Flow channels with non-circular cross-sections are encountered in a wide variety of heat exchangers. Accurate friction factor and Colburn j factor data are essential for the design and viable applications of such heat exchangers. In this study, an analysis is con ducted on heat transfer and pressure drop characteristics for tube-bundle heat exchanger with various arrangements of tubes, of which their geometry could easily be modified from a circular one in a harsh environment. The parameters investigated are aspect ratio, pitch, and inclined angle of tubes. The results obtained are: (1) Aspect ratio has larger influence on the j and f factor than pitch; (2) As aspect ratio increases, both j and f factors decrease; (3) The high performance is achieved when the pitch and aspect ratio are in the range of 1.5${\~}$2.5 and 1.25${\~}$2.0, respectively; and (4) the inclined arrangements of tubes show unfavorable results for both heat transfer and pressure drop characteristics in spite of the positive possibility of condensate removals in a latent heat recovery system.

• 대한기계학회논문집B
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• 제22권11호
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• pp.1555-1563
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• 1998

Heat transfer and pressure drop for ${\phi}10.07$ dry surface fin-tube heat exchanger with wave and wave-slit fins were measured for different fin spacings and number of tube rows. Longitudinal and transverse tube spacings of the heat exchangers are 21.65mm and 25mm respectively, and wave depth of wave fin is 1.5mm. The experiments were performed for 4 different fin spacings, 1.3, 1.5, 1.7 and 2.0mm, and the number of tube rows were 1,2 and 3 rows. The present results were compared with the previous results for the wave depth of 2mm. Also hydrophilic coated and bare fins were tested. Correlations for Colburn j-factor and friction factor were developed.

• 설비공학논문집
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• 제21권11호
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• pp.613-620
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• 2009

The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from $8\times2$ to $4\times2$, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of $4\times2$ bolt joining halls. Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1129-1134
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• 2009

A numerical study has been conducted to investigate the effect of tube arrangement on the heat transfer and the pressure loss for cross flow heat exchangers. By defining a transverse deviation factor, ${\varepsilon}_t=l_T/S_T$, the flow pattern and the heat transfer characteristics are compared for selected ${\varepsilon}_t$ values of 0.0(in-lined), 0.1, 0.2, 0.3, 0.4, 0.5(staggered) by using a commercial software. Computational domain includes 1 pitch in the transverse direction and 5 pitches in the flow direction with due periodic boundary conditions.

• 대한설비공학회지:설비저널
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• 제25권2호
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• pp.151-160
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• 1996

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.851-856
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• 2003

A cross-flow fan consists of an impeller, a stabilizer and a rearguider. When it applied for an air conditioner, an evaporator should be added. It relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice and blades have a forward curved shape. Therefore, the performance of a cross-flow fan is influenced 25% by the impeller, 60% by the rearguider and the stabilizer, 15% by the heat exchanger. At the low flow rate, there are a rapid pressure head reduction, a noise increase and an unsteady flow against a stabilizer and a rearguider. Moreover, the reciprocal relation between the impeller and the flow passage is the important factor for performance improvement of the cross-flow tan because each parameter is independent. The performance characteristics in the cross-flow fan are graphically depicted with various impeller outlet angles and rearguiders.

• 소음진동
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• 제4권2호
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• pp.199-208
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• 1994

Two-phase cross-flow exists in many shell-tube heat exchangers such as nuclear steam generators, condensers and reboilers. An understanding of damping and of flow-induced vibration excitation mechanisms in necessary to avoid problems due to excessive tube vibration. In this paper, we present the results of experiments on normal-triangular tube bundles of pitch to tube diameter ratio, p/d, 1.22, 1.32 and 1.47. The bundle were subjected to air-water mixtures to simulate realistic mass fluxes and vapour qualities corresponding to void fractions from 5 to 99%. Damping, fluidelastic instability and turbulence- induced excitation are discussed. The behaivior of damping and two vibration mechanisms are different for intermittent flows from for bubbly flows. The effect of pitch to tube diameter ratio and void fraction is dominant on damping and fluidelastic instability.

• 한국압력기기공학회 논문집
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• 제14권1호
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• pp.8-14
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• 2018

Printed circuit heat exchangers (PCHEs) are widely used with an increasing demand for industrial applications. PCHEs are capable of operating at high temperatures and pressure. We consider a PCHE as a candidate intermediate heat exchanger type for a high temperature gas-cooled reactor (HTGR). For conventional application using stainless steels, design and manufacturing of PCHEs are well established. For applications to HTGR, knowledge of longitudinal conduction and deformation of channel is required to estimate design margin. This paper analyzes the effects of longitudinal conduction and deformation of channel on thermal performance using a code internally developed for design and analysis of PCHEs. The code has a capability of two dimensional simulations. Longitudinal conduction is estimated using the code. In HTGR operating condition, about ten percent of design margin is required to compensate thermal performance. The cross-sectional images of PCHE channels are obtained using an optical microscope. The images are processed with computer image process technique. We quantify the deformation of channel with dimensional parameters. It is found that the deformation has negative effect on structural integrity. The deformation enhances thermal performance when the shape of channel is straight in laminar flow regime. It reduces thermal performance in cases of a zigzag channel and turbulent flow regime.