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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 13, Issue 12 - Dec 2001
Volume 13, Issue 11 - Nov 2001
Volume 13, Issue 10 - Oct 2001
Volume 13, Issue 9 - Sep 2001
Volume 13, Issue 8 - Aug 2001
Volume 13, Issue 7 - Jul 2001
Volume 13, Issue 6 - Jun 2001
Volume 13, Issue 5 - May 2001
Volume 13, Issue 4 - Apr 2001
Volume 13, Issue 3 - Mar 2001
Volume 13, Issue 2 - Feb 2001
Volume 13, Issue 1 - Jan 2001
Selecting the target year
Low Rayleigh Number Thermal Convection Between Two Horizontal Plates with Sinusoidal Temperature Distributions
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 145~152
Low Rayleigh number thermal convection in a fluid layer confined between two-infinite horizontal walls kept at spatially sinusoidal temperature distributions,
, is theoretically investigated by a regular perturbation expansion method. For small wave numbers, an upright cell is formed between the two walls at
=0. The cell is tilted, as the phase difference increases, and a flow with tow counter-rotating eddies occurs at
. when the wave number is large, isolated eddies are formed near the lower and upper walls, for all the phase differences. There exists a wave number at which maximum heat transfer rate at the walls occurs, at each of the phase differences. And the wave number increases with increase of the phase difference. for a fixed wave number, the heat transfer rate decrease with increase of the phase difference.
Performance Analysis of a Multi-type Inverter Heat Pump
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 153~159
A system simulation program was developed for a multi-type inverter heat pump. Electronic expansion valve(EEV) was used to extend the capacity modulating range of the heat pump as expansion device. The program was also developed to calculate actual system performance with the building load variation with climate during a year. The performance variation of a multi-type hat pump with two EEV and an inverter compressor was simulated with compressor speed, capacity, and flow area of the EEV. As a result, the optimum operating frequency of the compressor and openings of the expansion device were decided at a given load. As compressor speed increased, he capacity of heat pump increased, the capacity of heat pump increased. Therefore flow area of EEV should be adjusted to have wide openness. Thus the coefficient of performance(COP) of the heat pump decreased due to increasement of compressor power input. The maximum COP point at a given load was decided according to the compressor speed. And under the given specific compressor speed and the load, the optimum openings point of EEV was also decided. Although the total load of indoor units was constant, the operating frequency increased as the fraction of load in a room increased. Finally ad the compressor power input increased, the coefficient of performance decreased.
The Effect of Flow Rate into Room by Natural Convection in Air Conditioner Duct
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 160~166
A numerical analysis has been performed for natural convection in an air conditioner duct system. The governing equations were solved a finite volume method using a SIMPLE algorithm. In the calculation mode of duct, the room temperature was preserved at
and duct wall temperature had a temperature of 15, 20.0, 22.5, 23.75, 26.25, 27.5 30 and
. The results of velocity vectors and contours have been represented for various parameters. Based on the numerical data, the relationships between temperature difference and flow rate into room was represented. In the case of $T_\gamma>T_\omega$, the equation for temperature difference and flow rate was
, and in the case of $T_\gamma>T_\omega$, the equation was
. The duct system has an important relation to room temperature and duct wall temperature.
Study on the Numerical Analysis for Microenvironments in Bed Mattress
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 167~173
This paper represents the numerical analysis for microenvironments various temperature and humidity in bed mattress. He purpose of this study is for healthful bed mattress by controling a bacteria with a prediction of the vapor and temperature distributions in the bed mattress. The numerical model is one dimensional unsteady state and the governing equations were discretized by fully implicit scheme. The numerical results were compared with experimental data, and showed a good agreement with them. Specially, the excess-relative humidity shows a lower distribution near the surface of mattress, meaning that the optimum living condition for bacteria will be caused.
Study on Pressure Drop and Condensation Heat Transfer Characteristics of R-404A in Brazed Plate Heat Exchanger
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 174~183
Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-404A. Data are presented for the following range of variables: the mass flux (
), chevron angle(
) and inlet pressure of he refrigerant (1.4 and 1.6 MPa). for both subcooled and tow-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation hat transfer coefficient and pressure drop was compared with the previously proposed correlations. Among them, Traviss correlation agreed with experimental results within -35~82% for heat transfer coefficient and -73~93% for pressure drop.
A Study on the Control Method of Ventilating System for High Speed Train in a Tunnel
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 184~193
The present study develops programs simulating the internal pressure change of cars due to the change of external pressure when trains run into or passing each other in a tunnel. A new continuous ventilating system control method has been developed in order to alleviate the aural discomfort of passengers riding a high speed train. This method is based on the change of the charged and discharged flow rate by detecting the air pressures generated outside and inside of the train. When the outside and inside pressure are detected, the speed of the charge or exhaust fans and also the valve opening ratios are changed. The elementary performance of the system is checked using dta of the TGV-K high speed train at a speed of 300km/h. Moreover, applicability of the system to the Koran high speed train at a speed of 350 km/h is ascertained by simulation and its effectiveness as a means to alleviate the ear pains is confirmed. This application of the system to the Korean high speed vehicles running in the speed range of 350km/h is considered to have good prospect.
The Study on Drag Reduction Rates and Degradation Effects in Synthetic Polymer Solution with Surfactant Additives
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 194~199
The turbulent flow resistance of water solution with polymer is reduced as compared with that of pure water. This effects is named th drag reduction and offers the significant reduction of the pumping power and the energy consumption. But the intense shear forces and the high temperature experienced by the polymer solution when passing through the pipes cause the degradation a loss of drag reduction effectiveness. Especially, the degradation behavior is found to be strongly dependent on temperature. This mechanical and thermal degradation can be avoided by adding materials such as surfactant to the polymer solution, which enhance the bonding force between molecules. In the present study, Copolymer and SDS were utilized and they were mixed in 10 different mixture ratios, while total concentration was fixed as 100wppm. Degradation of Copolymer-SDS mixture solutions was investigated experimentally in closed loop at the temperature of
with various flow average velocities of 1.5 m/sec, 3.0m/sec, and 4.5m/sec. Degradation characteristics of polymer solution without surfactant show a radical loss of drag reduction effectiveness at high temperature. Degradation alleviation ability of surfactant is especially effective at high temperature. Consequently, this results show that the addition of surfactant to the polymer solution can control unfavorable degradation phenomena for high temperature systems.
Indoor Temperature Control of a Heat Pump Based on Model Predictive Control Considering Energy Efficiency
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 200~208
In indoor temperature control of a heat pump, a reduction in energy consumption is very important. However, most control schemes for heat pumps have focused only on control performance such s settling time and steady-state error. In this paper, the model predictive control (MPC) which includes the energy-related variable in this cost function is proposed. By computing the control signal minimizing this cost function, the trade-off between energy reduction and temperature control performance can be obtained. Since the MPC required the process model, the dynamic mode of a heat pump is also obtained by the system identification technique. Performance of the proposed MPC considering energy efficiency is compared with the two other control schemes. It si shown that the proposed scheme can consume less energy thant hte others in achieving similar control performance.
Effect of Circumferential Velocity from Guide Vane on the Nozzle Flow of a Jet Fan
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 209~216
A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.
A Numerical Analysis on Forced Ventilation using Indoor Air Cleaner in an Apartment House
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 13, issue 3, 2001, Pages 217~223
There exist a number of approaches which can evaluate ventilation and indoor air quality. The measurement and analysis of indoor carbon dioxide concentrations can be useful for evaluating indoor air quality and ventilation. This paper describes a numerical analysis of carbon dioxide concentrations for evaluating indoor air quality and ventilation and the factors the need to be considered in their use. The conditions of this numerical analysis are tow types of positions and inlet velocities of ventilation system in a two-dimensional model of an apartment house. The simulation results could be used as a base data for further analysis for ventilation design of other industrial processes producing a proper ventilation system for a healthier and more comfortable environment in a building.