Jae-Hyeong Seo

Numerical Investigation on Heat and Flow Characteristics of Temperature-Sensitive Ferrofluid in a Square Cavity

The objective of this paper is numerically to study the heat and flow characteristics of temperature-sensitive ferrofluid in the square cavity with and without the magnetic intensity. The numerical model was developed to predict the behavior of the ferrofluid using finite element method (FEM) and showed good agreement with the existing data within 5% at all Rayleigh number ranges from 103 to 106. Natural convection and heat transfer characteristics of the ferrofluids within the tested cavity were found to depend on both magnetic intensity and magnetic volume fractions of magnetite. In addition, the mean Nusselt numbers and mean velocity of the ferrofluid in a square cavity were increased with the rise of the magnetic intensities and increased by 23.2% and 143.7%, respectively, at both magnetic intensity of H = 10000 A/m and the elapsed time of t = 30000 seconds.

Thermophysical Characteristics of the Ferrofluid in a Vertical Rectangle

The article aimed to analytically investigate the thermophysical behaviors of a ferrofluid in a vertical rectangle with the variation of intensity of the magnetic field, viscosity of the ferrofluid and boundary conditions. The governing equations of the ferrofluid include the continuity, momentum and energy equations for describing the thermal-fluidic behaviors of the ferrofluid and the Maxwell equation and magnetization equation are also added to consider rotating effect of the nano-sized particles. The flow behavior and heat transfer characteristics of the ferrofluid with the intensity of the magnetic field, viscosities of the ferrofluid and boundary conditions were analyzed through isotherms, velocity profiles and both mean and local Nusselt numbers. As a result, the isotherms of the ferrofluid in the vertical rectangle increased with the increase of the magnetic volume fractions and magnetic field intensities. In addition, the mean Nusselt numbers increased with the increase of magnetite volume fractions at all magnetic field intensities because of the combined effects of both heat conduction by magnetite and the magnetic volume force.

Study of Natural Convection of Magnetic Fluid in Cubic Cavity

This study aims to numerically investigate the natural convection characteristics of a magnetic fluid in a cubic cavity. The governing equations of the magnetic fluid are solved using the Generalized-Simplified Marker and Cell Method (GSMAC). The natural convection and heat transfer characteristics of the magnetic fluid were analyzed by varying the intensity and direction of the magnetic field. As a result, it was found that the natural convection characteristics were controlled by the intensity and direction of the magnetic field, and the mean Nusselt numbers were minimized at a vertical intensity of H=-4000 and horizontal intensity of H=12000 of the magnetic field. In addition, the mean Nusselt numbers increased with the intensities of the magnetic field, regardless of the direction of the magnetic field.

Numerical analysis on thermal-fluidic characteristics of the magnetic fluid in a cavity using GSMAC

The article is aiming to investigate the thermal-fluidic characteristics of magnetic fluid in a cavity using GSMAC (generalized-simplified marker and cell method). The transport equations of the magnetic fluid are including the continuity equation, momentum equation and energy equation for natural convection and Maxwell equation and magnetization equation of magnetite nano-sized particles motion. In addition, the heat transfer characteristics such as temperatures and Nusselt numbers and flow characteristics such as streamlines and isotherms of the magnetic fluid were analyzed with the intensity and direction of the magnetic fields. As a result, the thermal-fluidic characteristics of the magnetic fluid in a cavity were could be controlled by the intensity and direction of the magnetic fields.

REVIEW OF CONVENTIONAL AIR CONDITIONING SYSTEM FOR INTERNAL COMBUSTION ENGINES

In spite of the increase of the concern on electric vehicles (which is called green cars) and electrically driven automotive air conditioning system, the conventional automotive air conditioning system for internal combustion engines has been still investigated widely due to the realistic consideration. This paper is intended to include many automotive air conditioning system articles published in 1997 to 2013. This review, although extensive cannot include every paper; some selection is necessary. Reviewed papers herein are related to the research and development on effective design and performance improvement for the automotive air conditioning system and components, including theoretical, numerical, analytical and experimental works. Therefore, a number of published articles about the automotive air conditioning system, which contain the belt-driven compressors, heat exchangers and refrigerants, were considered. Many researches have focused on improving the efficiency of automotive air conditioning system to decrease the usage rate of the internal combustion engines.

Experimental Study on the Heating Performances of the Air Heater with Diesel for Passenger Cabin Heating of an Electric Vehicle

The objective of this study is to experimentally investigate the heating performances of the portable air combustion heater using diesel fuel for auxiliary cabin heating of the battery electric vehicle. In order to evaluate the heating performances of the air combustion heater, the heating capacity was calculated by the temperature at inlet and outlet parts of the considered heater and the inner temperature distribution characteristics of the vehicle were measured during 1600 seconds with an interval of 1 second. The theoretical efficiency of the tested heater was calculated by temperature data of the air of supplying and exhausting to the cabin. As the air passed the heat-sink, the air temperature at the end of heat-sink reached to 101.3 o C and the difference of temperature on heat-sink was 67.8%. The average heating capacity of the air combustion heater showed 2.0 kW. After 1800 seconds, the inner temperature of the vehicle cabin was continuously increased. The temperatures of the top side and the bottom side of the car cabin under consideration were increased upto 42.5 o C and 24.3 o C, respectively, and the theoretical efficiency of the tested heater was on average 63.7%.

Thermal-flow Characteristics of Magnetic Fluid for Concentric Annuli Under Fixing Magnetic Field Using Visualization Technique

This article is experimentally to investigate thermal-flow characteristics of the magnetic fluid for concentric annuli under externally fixed magnetic fields using visualization technique. Temperatures of the inner tube and outer tube in the tested concentric annuli were constantly maintained at both and and the middle tube was filled with the magnetic fluid. Magnetic field was uniformly applied using 4 permanent magnets at 4 directions of the concentric annuli. As a result, the thermal-flow characteristics of the magnetic fluid for concentric annuli could be controlled by directions of the external magnetic fields.

Investigation on the Performance of Special Purpose Automotive Air-Conditioning System Using Dual Refrigeration Cycle

C로 증가할수록 냉방용량은 19.1 kW에서 20.5 kW로 7.3% 증가했으나 냉방성능(COP)는 4.67에서 5.1로 7.0%감소하였다. Abstract: The objective of this study is to investigate the cooling performance of an air-conditioning system for a special purpose vehicle under tropical and severe weather conditions. In order to evaluate and compare the cooling performances, the dual refrigeration cycle using R-134a was tested on a special purpose vehicle with various refrigerant charge amounts and indoor temperatures. The cycle was tested considering indoor cooling speed and compression ratio (discharge pressure), and was optimized at the refrigerant charge amount of 1.5 kg and outdoor temperature of 40.0 °C. The time to reach indoor temperature of 15.0 °C increased by 86.5％ and 38.1％, at the indoor temperatures from 25.0 °C to 32.5 °C and from 32.5 °C to 40.0 °C, respectively. In addition, with the increase in indoor temperature from 25.0 °C to 40.0 °C, the cooling capacity increased by 7.3％, from 19.1 kW to 20.5 kW, but decreased by 7.0％ from 4.67 to 5.1.

Numerical Study on Thermal Performances of Multi Heat Source Heating System Using Butane for Electric Vehicle

This study numerically investigates the thermal performance of a 2.0-kW butane-based combustion heating system for an electric vehicle under cold conditions. The system is used for cabin space heating and coolant-based battery thermal management. ANSYS CFX 17 software was used for parametric analysis. The mass flow rates of cold air and coolant were varied, and their effects were compared. The numerical results were validated with theoretical studies, which showed an error of 0.15%. As the outside air mass flow rates were increased to 0.005, 0.01, and 0.015 kg/s, the cabin supply air temperature decreased continuously while the coolant outlet temperature increased. When the coolant mass flow rates were increased to 0.005, 0.01 and 0.015 kg/s, the air temperature increased while the coolant outlet temperatures decreased. The optimal mass flow rates are discussed in a consideration of the requirements for high cabin heating capacity and efficient battery thermal management.

Heat transfer characteristics of the heat pipe using simplified heat transfer model

The objective of this study was to examine numerically the heat transfer and flow characteristics of the heat pipe with a wick using the simplified heat transfer model to enhance the cooling effects of high heat flux devices and minimizing the energy consumption for electric vehicles. The heat pipe with a wick was analyzed using commercial software with COMSOL and water was used as the working fluid. The velocity and temperature characteristics of the heat pipe were simulated numerically along the heat pipe and the local and average Nusselt numbers were calculated. As a result, the driving force occurred because of the temperature difference between the hot side and the cold side. The heat transfer of the heat pipe occurred from the hot side to the cold side and increased toward the center position. In addition, the average Nusselt numbers were 1.88 for the hot side and 0.1 for the cold side, and the maximum Nusselt number was 4.47 for the hot side and 0.7 for the cold side.