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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Korean Journal of Air-Conditioning and Refrigeration Engineering
Journal Basic Information
Journal DOI :
The Society of Air-Conditioning and Refrigerating Engineers of Korea
Editor in Chief :
Volume & Issues
Volume 12, Issue 12 - Dec 2000
Volume 12, Issue 11 - Nov 2000
Volume 12, Issue 10 - Oct 2000
Volume 12, Issue 9 - Sep 2000
Volume 12, Issue 8 - Aug 2000
Volume 12, Issue 7 - Jul 2000
Volume 12, Issue 6 - Jun 2000
Volume 12, Issue 5 - May 2000
Volume 12, Issue 4 - Apr 2000
Volume 12, Issue 3 - Mar 2000
Volume 12, Issue 2 - Feb 2000
Volume 12, Issue 1 - Jan 2000
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Enthalpy Flow Loss by Steady Mass Streaming in Pulse Tube Refrigerators
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 623~631
Effects of the taper angle and the angular velocity of a pulse tube on the enthalpy flow loss associated with the steady mass streaming were analysis by two-dimensional analysis of a pulse tube with variable cross-section. It was shown that the steady mass flux can lead to a large steady second-order temperature. The enthalpy flow loss associated with the steady mass streaming increases as the angular velocity increases. For a pulse tube where the viscous penetration depth is far thinner than the inner radius, the enthalpy flow loss can be significantly reduced by tapering the pulse tube since both the steady mass flux and the steady second-order temperature decrease as the taper angle increase.
Simulation of Supply Air Control in a VAV System Using a Stratified Lumped Thermal Model
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 632~641
The present study concerns the simulation of supply-air control in a variable air volume (VAV) system. A stratified lumped thermal model (multi-zone model) is suggested to predict local thermal response of an air-conditioned space. The effects of various thermal parameters such as the cooling system capacity, the thermal mass of air-conditioned space, the time delay of thermal effect, and the building envelope heat transmission are investigated in detail. Further, the influence of control parameters, PI control factor and the sensor location on a VAV system is quantitatively delineated. The results obtained show that the previous homogeneous lumped thermal model (1-zone model) may predict a significantly different thermal response in the air-conditioned space according to the sensor location.
Falling Film Heat Transfer on a Horizontal Single Tube
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 642~648
Falling film heat transfer analyses with aqueous lithium bromide solution were peformed to investigate the transfer characteristics of the copper tubes. Finned(knurled) tube and a smooth tube were selected as test specimens. Averaged generation fluxes of water and the heat transfer performances(heat flux, heat transfer coefficient) were obtained. The results of this work were compared with the data reported previously. As the film flow rate of the solution increased, the generation fluxes of water decreased for both tubes. The reason is estimated by the fact that the heat transfer resistance with the film thickness increased as the film flow rate increased. The effect of the enlarged surface area at the knurled tube was supposed to be dominant at a small flow rate. The generation fluxes of water increased with the increasing degree of tube wall superheat. Nucleate boiling is supposed to occur at a wall superheat of 20 K for a smooth tube, and at 10 K for a knurled tube. The heat transfer performance of the falling film was superior to pool boiling at a low wall superheat below 10 K for both tubes tested. The knurled tube geometry showed good performance than the smooth tube, and the increased performance was mainly came from the effect of the increased heating surface area.
Performance Analysis on the Variable Speed Scroll Compressor with Operating Conditions
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 649~658
Thermodynamic modeling of low-pressure scroll compressor was developed by combining continuity and energy conservation equation. Suction gas heating was considered using energy balance inside the low pressure shell. Pressure, temperature and mass of refrigerant-22 as a function of orbiting angle were calculated by solving the governing equations using fourth order Rung-Kutta scheme. Motor efficiency was taken by experiments with a variation of frequency. The developed model was applied to the analysis of an inverter driven scroll compressor with a variation of frequency, pressure ratio and operating conditions. The model was verified with the experimental results at the same operating conditions. The developed model was adequate to predict performance of the inverter driven scroll compressor as a function of operating conditions. Calculated parameters from the model were discharge temperature, mass flow rate, power input, COP, and thermodynamic properties with respect to orbiting angle. To enhance the performance of a scroll compressor, it is essential to diminish leakage at low frequency level and improve the mechanical efficiency at high frequency level.
Influence of Working Fluids to Heat Transfer Characteristics of the Heat Exchanger using Oscillating Capillary Tube Heat Pipe for Low Temperature Waste Heat Recovery
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 659~666
Heat transfer characteristics of a heat exchanger for low temperature waste heat recovery using oscillating capillary tube heat pipe were evaluated against the charge ratio variation of working fluid and various working fluids. R-l42b, R-22 and R-290 were used as working fluids. The heat exchanger was composed of heat pipe with capillary tube bundles, having a 2.6mm in outer diameter, 1.4mm in inner diameter with 101m long, and 40 turns. Charge ratio of working fluid was 40% and 50%. Water was used as secondary fluid. Inlet temperature and mass velocity for each secondary fluid were 297 K, 280 K and9~27 kg /
, respectively. From experimental results, it was found that heat transfer performance of R-22 was higher than those of R-l42b and R-290 and it was proportional to Figure of merit for thermosyphons. As a result, it was thought that R-22 was the most suitable working fluid of waste heat recovery for low temperature waste heat recovery.
An Experimental Study on Enhancement of Laminar Flow Heat Transfer in a Circular Pipe with Inserts
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 667~673
In order to understand the laminar flow heat transfer enhancement by the swirl flow, the effects of heat transfer in a circular pipe with a twisted tape insert were investigated experimentally. In the present study, the uniform heat flux condition was considered. The laminar heat transfer correlations were developed using the least-square-fit from the surface temperature distribution of an electrically-heated pipe and flow property data. Average Nusselt number correlations with the twisted tape insert were expressed as a function of swirl parameter, Reynolds number and Prandtl number. In the case of the twisted ratio y = 6.05, the mean Nusselt number increased approximately 500% and the friction factor increased approximately 300%, compared to the case of the empty pipe, respectively.
Computational Analysis of the Three-Dimensional Flow Characteristics and the Performance of Sirocco Fan
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 674~679
The Sirocco fan performance and its three-dimensional flow characteristics were numerically predicted by STAR-CD software. Turbulent flow computations were performed using approximately 500,000 mesh points, and the performance results of two computational methods, transient analysis and quasi-static analysis were compared with experimental data. At present, our attention was focused on localizing the three-dimensional flow characteristics of the Sirocco fin, especially the structure of the secondary flow in the scroll and the through-flow characteristics of the Sirocco fan blades. Also, for an optimization, the scroll passage was tilted with 10 degrees to change the flow characteristics and improve the performance of the Sirocco fan.
A Study on the Optimal Control of Ondol System Using Artificial Neural Network
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 680~687
The objective of this study is to improve the control performance of Ondol system which causes overheating and underheating with 2-position on/off control. For this, a predictive control that determines the suitable on/off positions using Artificial Neural Network(ANN) model was proposed Dynamic analyses using computer simulation show that the neural network used in the predictive control is adapted to each room whose loads variation and thermal characteristics are different. To examine the applicability of this predictive control with ANN it was compared with 2-position on/off control through experiments.
Regression Model-Based Fault Detection of an Air-Handling Unit
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 688~696
A scheme for fault detection on the subsystem level is presented. The method uses analytical redundancy and consists in generating residuals by comparing each measurement with an estimate computed from the reference models. In this study regression neural network models are used as reference models. The regression neural network is memory-based feed forward network that provides estimates of continuous variables. The simulation result demonstrated that the proposed method can effectively detect faults in an air handling unit(AHU). The results show that the regression models are accurate and reliable estimators of the highly nonlinear and complex AHU.
The Experimental Study of Water Hammer by Valve Closure in Water Supply Piping System
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 12, issue 7, 2000, Pages 697~702
This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening copper piping system. Experiments were conducted under the following conditions : initial pressure 1~5 bar, flow velocity 0.6~3.0 m/s and water temperature
. Results indicated that the peak pressure generated by quick valve closure reached Joukowsky's value. And we also found that the maximum pressure rise and the pressure history were depended on not only closing time but also flow velocity,