• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.12
• /
• pp.782-790
• /
• 2011

Typical temperature control methods of a cooler for machine tools are hot-gas bypass and compressor variable speed control. The hot-gas bypass system has been widely used to control the cooler temperature in many general industrial fields. On the contrary, the compressor variable speed control is focused on special fields such as aerospace and high precision machine tools which need high precision control. The variable speed control system usually has two control variables such as target temperature and superheat. In other words, the variable speed control system is basically multi-input multi-output(MIMO) system. In spite of MIMO system, the proportional integral derivative(PID) feedback control methodology that based on single-input single-output (SISO) system is generally used for designing the variable speed control system. Therefore, it is inevitable to describe transfer functions for dynamic behaviors of every controlled variables and decide the PID gains with tremendous iteration process. Moreover, the designed PID gains do not provide optimum system performances. To solve these problems, high performance controller design method based on a state space model is suggested in this paper. An optimum controller is designed to minimize both control errors and energy inputs. This method was more simple to describe dynamic behaviors and easier to design the cooler controller which is MIMO system.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.7
• /
• pp.252-257
• /
• 2018

In this paper, we propose a mean time to failure (MTTF) to improve the solution for a cryogenic cooler, which is an important part of a cooled thermal device. Common electronic devices have a high possibility of failure due to various environmental factors, such as temperature and humidity. But some special devices (such as thermal devices) are designed to overcome environmental factors. The most affected part of a cooled thermal device's MTTF is the cryogenic cooler. The MTTF of a cryogenic cooler is affected by the device's internal heat. Therefore, if the device's internal heat is reduced, the cryogenic cooler's MTTF increases. From the present device's internal heat simulation, we analyze the improvement method of the device. The proposed improvement method's effectiveness is verified by simulation and MTTF calculation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.22 no.5
• /
• pp.328-335
• /
• 2010

The purpose of this study is to make an analysis of influence on the cooling capacity and COP of a desiccant cooling system with a regenerative evaporative cooler when a direct evaporative cooler was applied to the inlet of regeneration process of this system. We used cycle simulation in order to analyze the performance of this system. From the cycle simulation, we knew that the optimal rotation time of desiccant rotor was between 160s and 220s and hardly ever affected cooling capacity of desiccant cooling system when this system was operated at the outdoor air condition of $35^{\circ}$ and 40% RH and low regeneration temperature of $60^{\circ}$. Also there was optimal area ratio of regeneration to dehumidification between 0.7 and 1.0. Our results showed that it had a small effect on the system’s cooling capacity to install direct evaporative cooler at the inlet of regeneration process.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.8
• /
• pp.7-16
• /
• 1999

To maintain thereasonable temperature in the engines is very important to keep the steady combustion state of engine and to prevent increasing of oil consumption , deteriorating of lubricant, shortening of the life time of engine and decreasing of material strength. The method of energy balance for divided elements of radiator and engine-oil cooler is considered to analyse the performance of radiator and engine-oil cooler. The data obtained by engine test and vehicle cooling tunnel test are applied to program for calculation of radiator outlet temperature. As a result, data obtained by numerical analysis agree well with those by experiments. And thus, it is concluded that this simulation program is available in developing the cooling system for a new car.

• Journal of the Korean housing association
• /
• v.19 no.1
• /
• pp.89-96
• /
• 2008

This study measured the thermal environment and residents' control behaviors of cooing according to 3 groups of household type-families with preschool children, families of middle age and families of senior. The object of this study are to fmd the difference of the actual condition of indoor thermal environment and cooling control behavior by age or household type and to develop user oriented climate control system. The results were summarized as follows. When the age of members at household is younger, the indoor mean temperature and temperature that people turned off the air conditioner became lower. These different indoor thermal environment of each group means that younger generation is familiar with cooler from their early age and these early uses of cooler made them prefer cooler condition than family of senior. Therefore, this results show that different indoor thermal environment is influenced by factors such as household type and metabolism difference and so on.

• Journal of the Korean Institute of Educational Facilities
• /
• v.18 no.3
• /
• pp.35-41
• /
• 2011

Performance of a small-capacity solar absorption cooling system was investigated experimentally. Ten sets of evacuative-tube solar-heat collectors and a 5 kW single-stage absorption cooler were combined to produce a hybrid cooling system. The performance of the cooling system was measured using a tim-coil unit installed in a small plastic storage. It was found from the test on a sunny day of May that when the temperature of the hot water supplied from the solar collectors to the generator of the absorption cooler reached $60^{\circ}C$, the absorption cooler started cooling and the cold water temperature measured from the fan-coil unit reached $18^{\circ}C$. The COP, which is defined as the ratio of the cooling power to the total electrical power input was higher than 1.0.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1459-1462
• /
• 2007

In general a thermoelectric cooler (TEC) consists of a series of P type and N type thermoelectric materials sandwiched between two wafers. When a DC current passes through these materials, three different effects take place; Peltier effect, Joule heating effect and heat transfer by conduction due to temperature difference between hot and cold plates. In this study we have developed a micro TEC using $Bi_2Te_3$ (N type) and $Bi_{0.5}Sb_{1.5}Te_3$ (P type) thin films. In order to improve that performance of a micro TEC, we made 10 um height TE legs using special PR only for lift-off. We measured COP (coefficient of performance) and temperature difference between hot and cold connectors with current.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.3
• /
• pp.333-342
• /
• 1997

An experimental study has been carried out to investigate the effects of the combination of the different wire mesh number in a regenerator and the tube number in a cooler on the cooling performance of a Vuilleumier cycle heat pump. Effects of operating conditions, such as charging pressure, operating speed, and heat input, on the cooling performance are also studied. The experimental results obtained indicate that the cooling performance could be improved with the proper combination of different wire meshes in a regenerator. More tubes in a cooler are desirable for better cooling performance. It is also found that the cooling capacity is enhanced, whereas COP is reduced with an increase in the heater tube temperature and the revolution speed. Both the cooling capacity and COP are incereased with a higher charging pressure.

• Journal of Sensor Science and Technology
• /
• v.22 no.1
• /
• pp.44-48
• /
• 2013

For a successful commercialization of microbolometer, it is required to develop a robust package including thermal stabilizing mechanism. In order to regulate the temperature within some operating range, thermoelectric cooler is generally used but it's not easy to model the whole package due to the coupled physics nature of thermoelectric cooler. In this paper, SPICE-compatible modeling methodology of a microbolometer package is presented, whose steady-state results matched well with FEM results at the maximum difference of 5.95%. Although the time constant difference was considerable as 15.7%, it can be offset by the quite short simulation time compared to FEM simulation. The developed model was also proven to be useful for designing the thermal stabilizer through parametric and transient analyses under the various working conditions.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.1
• /
• pp.1-6
• /
• 2006

The objective of this study is CFD analysis of CPU cooler jacket. The ANSYS code using was for this CFD analysis. In order to analysis of CPU cooler jacket, many variables such as boundary condition, conductivity, mass density, specific heat were considered. This analysis results are compare to small inner size jacket and large inner size Jacket.