• Korean Journal of Food Science and Technology
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• v.16 no.1
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• pp.78-82
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• 1984

Effects of various drying conditions of agar gel on the physico-chemical properties of dried agar were investigated. For drying of the agar gel$(1.0{\times}1.0{\times}34.0cm)$ by means of sun drying, simple solar drying, hot-air drying ($30^{\circ}C$, control, natural convection), hot-air drying ($30^{\circ}C$, pretreatment, natural convection) and freeze drying, it took 96, 75, 67, 50 and 21 hours, respectively. The gel strengths of dried agar gel prepared by sun drying, solar drying, freeze drying and spray drying were320, 370, 270 and $360g/cm^2$, respectively and that of hot air-dried agar gel was influenced by drying temperature, pretreatment an mode of heat transfer. The gel strength, the gelation temperature and other quality index of spray-dried agar were not inferior to those of sun-dried agar, but it was not expected to be economical because of it recovery rate. In case of hot air drying, the gel strength value of agar increased as the drying rate increased. No significant differences among various products were noted in the gelation temperature, the melting temperature, the ash and $SO_3$ content.

• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.204-211
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• 2019

The purpose of this study is to provide basic data for setting environmental design standards for domestic greenhouses. We conducted experiments on thermal environment measurement at two commercial greenhouses where hot water heating system is adopted. We analyzed heat transfer characteristics of hot water heating pipes and heat emission per unit length of heating pipes was presented. The average air temperature in two greenhouses was controlled to $16.3^{\circ}C$ and $14.6^{\circ}C$ during the experiment, respectively. The average water temperature in heating pipes was $52.3^{\circ}C$ and $45.0^{\circ}C$, respectively. Experimental results showed that natural convection heat transfer coefficient of heating pipe surface was in the range of $5.71{\sim}7.49W/m^2^{\circ}C$. When the flow rate in heating pipe was 0.5m/s or more, temperature difference between hot water and pipe surface was not large. Based on this, overall heat transfer coefficient of heating pipe was derived as form of laminar natural convection heat transfer coefficient in the horizontal cylinder. By modifying the equation of overall heat transfer coefficient, a formula for calculating the heat emission per unit length of hot water heating pipe was developed, which uses pipe size and temperature difference between hot water and indoor air as input variables. The results of this study were compared with domestic and foreign data, and it was found to be closest to JGHA data. The data of NAAS, BALLS and ASHRAE were judged to be too large. Therefore, in order to set up environmental design standards for domestic greenhouses, it is necessary to fully examine those data through further experiments.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.302-314
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• 1994

The effects of the inclination of enclosure and partition on natural convective flow and heat transfer were investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was positioned perpendicularly at the mid-height of one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were performed with the variations of the partition length and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). The effects of the inclination angle of enclosure and partition on the heat transfer within an enclosure were also studied. As the results, the increase of the inclination angle of enclosure rapidly raised the heat transfer rate, while the inclination angle for the maximum Nusselt number was retarded with the increase of the partition length and the decrease of the heat transfer rate became larger in proportion to the increase of the partition length. The Nusselt number obtained by the inclination of partition was smaller than that of the inclination of enclosure. However, the difference of the heat transfer rates was considerably decreased at the longer partition lengths and the trends for the variation of the average Nusselt number were more similar with that of the inclination of enclosure. The upward oriented partition increases the convective heat transfer distinctly in contrast to that of the inclination of enclosure as the partition length increases.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.196-202
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• 2005

In cryogenic feeding system of turbo pump fed liquid-propulsion rocket, rise of cryogenic propellant temperature can bring into geysering in pipe or cavitation in turbo pump. In this paper, performance analysis of recirculation line which is one of the method to inhibit these phenomenon is carried out based on the configuration of KSLV-I 1st stage LOX feeding system, and parametric study to find design parameter. Diameter and re-entrance height, initial LOX temperature, ullage pressure, and natural convection heat transfer coefficient are varied to see the effects on performance. Additional He is injected into recirculation line to promote LOX recirculation. 1-dimensional analysis using network-solver, SINDA/FLUINT is carried out.

• Journal of the Korean Solar Energy Society
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• v.27 no.3
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• pp.63-69
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• 2007

The heat transfer characteristics of inorganic salt for high temperature heat storage material of solar power system were examined. The inorganic salts employed in this study was a mixture of $NaNO_3$ and $KNO_3$ and the operating temperature range was determined by measuring the melting temperature with DSC and by measuring the thermal decomposition temperature with TGA. The heat transfer characteristics was qualitatively obtained in terms of temperature profiles of salt in the tanks during the heat storage and heat release process as a function of steam flow rates, steam inlet temperature and the inlet position of steam. The effects of steam flow rates and inlet temperature of steam were experimentally determined and the effect of natural convection was observed due to significant density difference with temperature.

• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.41-46
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• 2003

This study deals with the Benard flow of magnetic fluids in a rectangular cavity. The ratio of height to length of the cavity is 1 : 4 and the bottom of the cavity is assumed to be a heating face while the other sides are to be cooling faces. When magnetic field was equally impressed, considering the internal rotation of the elementary ferromagnetic particle, we found the following result from the numerical analysis of the GSMAC algorithm applied to the equations for the magnetic fluid. Benard flow was controled by the intensity and the direction of magnetic fields, and a critical point was appeared when the magnetic field near H=-7000 was applied.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.1022-1027
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• 2005

An experimental study is conducted to investigate the characteristics of the ion wind generated by the electric field between a needle electrode and the parallel plate electrodes. The ion wind enhances heat and mass transfer between the surface and the surrounding gas. Moreover such enhancement makes no noise or vibration. This study is conducted to develop the electronic cooling device. The measured gas velocities and heat transfer coefficients are proportional to the applied voltage. The heat transfer coefficient can be increased as compared with a natural convection. The maximum enhancement of heat transfer obtained in this system is $47\%$ for 3 W in heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.383-390
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• 2010

In this study, a thermoelectric power generation system was constructed for a waste-heat recovery. Thermoelectric modules were attached to a stainless steel duct, and a hot air blower was set such that it faced the duct inlet. We found that to achieve the maximum power out of the system, the temperature in the hot side of the thermoelectric module should be uniform. The optimum compressive pressure exerted on the module was observed. Further, the thermoelectric power performance was evaluated using the heat sink attached to the cold side of the thermoelectric module. In particular, when using a natural-convection heat sink, the power output difference is approximately five times.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.122.2-122.2
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• 2010

Knowledge of ground thermal properties is most important for the proper design of BHE(borehole heat exchanger) systems. The configure type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for in-situ determination of design data for Standing Column Well apply. The main purpose has been to determine in-situ values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a sub-circulation pump, a boiler, temperature sensors, flow meter and a data logger for recording the temperature and circulation fluid flow data. A constant heating power is injected into the SCW through the test rig and the resulting temperature change in the SCW is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective in-situ values of rock thermal conductivity and thermal resistance of SCW.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.53-61
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• 2010

In the present study, a laminar natural convection flow of $H_2O$-Cu nanofluid in a two dimensional enclosure has been investigated using a thermal lattice Boltzmann approach with the Bhatnagar-Gross-Krook (BGK) model. The effect of suspended nanoparticles on the fluid flow and heat transfer process have been studied for different controlling parameters such as particle volume fraction ($\Phi$), Rayleigh number (Ra). For this investigation the Rayleigh number changes from 104 to 106 and volume fraction varied from 0 to 10% with three different particle diameters (dp), say 10 nm, 20 nm and 40 nm. It is shown that increasing the Rayleigh number (Ra) and the volume fraction of nanofluid causes an increase of the effective heat transfer rate in terms of average Nusselt number (Nu) as well as the thermal conductivity of nanofluid. On the other hand, increasing the particle diameter causes the decrease of the heat transfer rate and thermal conductivity. The result of the analysis are compared with experimental and numerical data both for pure and nanofluids and it is seen a relatively good agreement.