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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 10, Issue 6 - Nov 1998
Volume 10, Issue 5 - Sep 1998
Volume 10, Issue 4 - Jul 1998
Volume 10, Issue 3 - May 1998
Volume 10, Issue 2 - Mar 1998
Volume 10, Issue 1 - Jan 1998
Selecting the target year
Heat transfer characteristics between a rotating flat plate and an impinging water jet
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 509~522
An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.
Conjugated heat transfer on convection heat transfer from a circular tube in cross flow
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 523~534
The convection heat transfer on horizontal circular tube is studied as a conjugated heat transfer problem. With uniform heat generation in a cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer are investigated for the case of forced convection around horizontal circular tube in cross flow of air and water. Non-dimensional conjugation parameter
which can be deduced from the governing energy differential equation should be used to express the effect of circumferential wall heat conduction. Two-dimensional temperature distribution
is presented. The influence of circumferential wall heat conduction is demonstrated on graph of local Nusselt number.
Numerical study for performance analysis and design of a counterflow type cooling tower
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 535~549
A numerical study for performance analysis of a counterflow type forced draft tower and natural draft cooling tower has been performed based on the method using the finite volume method with non-orthogonal body fitted and non-staggered grid system. For solving the coupling problem between water and air, air enthalpy balance, moisture fraction balance, water enthalpy balance, and water mass balance equations are solved with Navier-Stoke’s equations simultaneously. For the effect of turbulence, the standard k-
turbulent model is implied in this analysis. The predicted result of the present analysis is compared with the experimental data and the commercial software result to validate the present study, The predicted results show good agreement with the experimental data and the commercial software result. To investigate the influence of the cooling tower design parameters such as approach, range and wet bulb temperature, parametric studies are also peformed.
A new type of saturated vapor density correlation for refrigerants
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 550~557
The saturated vapor density correlation proposed here relates logarithmic density to the inverse of temperature. Its performance is examined correlating the date listed in the ASHTAE tables for 40 refrigerants. The correlation equation is valid over the entire range where data point exist and gives better results than a conventional equation with the same number of adjustable coefficients. Number of terms in the equation is a variable so that great flexibility can be given to the representation of data.
The effect of forced convection on boiling heat transfer from a horizontal tube
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 558~568
This paper presents the results of experiments involving external forced convection on boiling heat transfer from electrically heated horizontal tube to water in cross flow. In these experiments, all of the following primary variables were varied: heat flux, cross flow velocity, pressure and degree of subcooling. Local surface temperatures were measured at nine peripheral positions. Surface temperature distributions are classified into four groups as a function of heat flux. The characteristics of the boiling curve at different velocity, degree of subcooling and pressure are examined.
Condensation heat transfer characteristics of alternative refrigerants for CFC-11, CFC-12 for enhanced tubes
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 569~580
In this study, condensation heat transfer coefficients(HTCs) of a plain tube, low fin tube, and Turbo-C enhanced tube for CFC-11, HCFC-123, CFC-12, HFC-l34a are measured and compared against each other. All data are taken at the vapor temperature of 39
with a wall subcooling temperature 3~8
. Test results show that HTCs of a low vapor pressure refrigerant, HFC-123, for a plain, low fin, and Turbo-C tubes are 10.5~20.5%, 8.2~12.2%, 16.5~19.2% lower than those of CFC-11, respectively. On the other hand, HTCs of a medium vapor refrigerant, HFC-l34a, for a plain, low fin, and Turbo-C tubes are 20.6~31.8%, 0.0~8.0%, 13.2~20.9% higher than those of CFC-12, respectively. For all refrigerants tested, HTCs of Turbo-C tube are the highest among the three tubes showing almost 8 times increase in HTCs as compared to those of a plain tube. Nusselt's prediction equation for a plain tube yielded 12% deviation for all plain tube data while Realty and Katz's prediction equation for a low fin tube yielded 20% deviation for all low tube data.
Experimental investigation of enhanced heat and mass transfer toy LiBr/
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 581~588
An experimental study of the absorption process of water vapor into Lithium Bromide solution was performed. For the purpose of development of high performance absorption chiller-heater utilizing Lithium Bromide solution as working fluid, the absorber is the most effective to improve the performance of an absorber because it requires the largest heat transfer area in an absorption chiller-heater system. This paper introduces bare tube and floral tube for the absorber of absorption chiller-heaters. floral tube has higher heat and mass transfer performance than bare tube conventionally used in absorbers and the it is expected to perform high heat and mass transfer. This paper will provide important information on the selection of absorber tubes in commercial absorption chiller -heaters.
Experimental study of air side pressure drop and heat transfer characteristics of wave and wave-slit fin-tube heat exchangers
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 589~599
Air side heat transfer and pressure drop for fin-tube heat exchanger with wave and wave-slit fins were measured for various fin spacings and number of tube rows. Outer diameter of the tube including fin collar is 10.07mm, and experiments were done with dry surface condition. Longitudinal and transverse tube spacings of the heat exchangers are 21.65mm and 25mm respectively, and wave depth of the wave fin is 2mm. Experiments were conducted for 1, 2 and 3 rows and 3 different fin spacings, 1.3, 1.5 and 1.7mm. An attempt was made to demonstrate advantage of the enhanced fins over the plane fin by introducing the concept of fan power, Effect of the number of tube rows on heat transfer was discussed in connection with general mechanisms of heat transfer enhancement for fin-tube heat exchanger. Also the effect of hydrophilic coating was investigated. Lastly, correlations for Colburn j-factor and friction factor were developed.
Thermal response of porous media cooled by a forced convective flow
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 600~609
The experimental investigation of thermal response characteristics by the air flow through the porous media has been carried out. The packed spheres of steel or glass were considered as the porous media in the present study. Temperature distributions of the fluid in the porous media as well as pressure drops through the porous media were measured. The transient temperature variations in the porous media are compared favorably with the analytical results in the high Reynolds number ranges. However, in the low Reynolds number ranges, the experimental data deviate from the analytical results, due to the dominant heat conduction penetration to the upstream direction, which is not considered in the analytical model. The cool-down response of porous media is found to be dependent upon the specific dimensionless time considering the material property and air velocity. The heat discharge process is recommended to be operated until a certain time, considering the cost efficiency.
Ventilation effectiveness measurements utilizing a tracer gas in an under floor air-conditioning space
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 610~618
In this study, a tracer gas technique was used to measure ventilation effectiveness in a thermal environmental chamber simulating an under-floor air conditioning system. A tracer gas of
was injected in a supply duct using step-up and step-down methods. Local mean ages and room mean ages were calculated from the measured concentrations under isothermal and cooling conditions with and without diffusers. Ventilation effectiveness is found to be higher in cooling ventilation operations than in isothermal operations. Results also show that ventilation effectiveness is not significantly affected by a diffuser.
Development of a 9as-liquid two-phase flowmeter using double orifice plates
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 619~629
An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.
Study on optimization technique for the design of ventilation system of subway
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 630~639
The present research aimed at development of a computer code for the optimal design of ventilation system based on one-dimensional analysis of the air flow. Model experiment and three-dimensional flow analysis have been implemented to determine loss coefficients that were needed for the optimization technique. A research on optimum shape of ventilation shaft has been also carried out through the three-dimensional analysis of the flow.
Effect of supply air temperature and airflow rate on ventilation effectiveness in an underfloor air conditioning space
Korean Journal of Air-Conditioning and Refrigeration Engineering, volume 10, issue 5, 1998, Pages 640~648
A numerical study has been conducted to investigate the effect of inflow supply air temperature and velocity on ventilation effectiveness in an underfloor air conditioning space. A low Reynolds number k-
model is implemented to calculate steady state turbulent velocity distributions. A step-down injection method is used to calculate local and room mean ages from transient concentrations based on the concept of the age of air. Results show that there is a significant effect of Archimedes number on ventilation effectiveness especially for cooling conditions. Reynolds number shows relatively minor effect on velocity distribution and ventilation effectiveness especially for isothermal and heating conditions. It can be concluded that underfloor air conditioning system provides good ventilation characteristics for cooling conditions because of temperature stratification in the space.