Hun Sik Han

Performance measurement and analysis of a thermoelectric power generator

The thermoelectric power generation with various thermal conditions is examined. An analysis model considered the manufacturing factors and the pellet size is presented to predict the performance characteristics of thermoelectric generators. The theoretical analysis shows that the maximum power output is produced when the electrical internal resistance is identical to the external load resistance. The overall performance is significantly increased with the temperature difference between cold and hot sides of thermoelectric generator. Under the fixed temperature difference, the thermoelectric generator produces the identical voltage, current and power outputs regardless of the operating temperature since the assumption of the constant thermoelectric properties is adopted in the analysis model. However, the experimental results obtained disclose that the effect of the operating temperature appears in the overall performance of the thermoelectric generator. Thus, the experimental correction of electrical internal resistance is adopted in the modified analysis model. Considerations are focused on the explicit role of the temperature-dependent electrical internal resistance for a method of accurate performance prediction. The modified analysis model is shown to be consistent with the experimental results in terms of the voltage output, current output and power outputs.

A Study on Performance of Thermoelectric Air-Cooling System in Parallel Flow

Experimental and theoretical studies on cooling performance of two-channel thermoelectric air-cooling system in parallel flow are conducted. The effects of operating temperature to physical properties of thermoelectric module (TEM) are experimentally examined and used in the analysis of an air-cooling system considering thermal network and energy balance. The theoretical predicted temperature variation and cooling capacity are in good agreement with measured data, thereby validating analytic model. The heat absorbed rate increases with increasing the voltage input and decreasing thermal resistance of the system. The power consumption of TEM is linearly proportional to mean temperature differences due to variations of the physical properties on operation temperature of TEM. Furthermore thermal resistance of hot side has greater effects on cooling performance than that of cold side.

Effect of Boundary Temperature Distributions on the Outlet Gas Composition of the Cylindrical Steam Reformer

ABSTRACT:Numerical simulations have been conducted for the cylindrical steam reformer having various boundary temperature distributions. CH 4 , H 2 O, CO, H 2 and CO 2 are often generated or destroyed by the reactions, namely the Steam Reofrming(SR) reaction, the Water-Gas Shift (WGS) reaction and the Direct Steam Reforming(DSR) reaction. The SR and the DSR reactions are endothermic reactions, and the WGS reaction is an exothermic reaction. The rate of reactions can be slightly controlled by artificially given boundary temperature distributions. Therefore, the component ratio of the gases at the outlet are different for various boundary temperature distri-butions, namely the constant, cubic and linear distributions. Among these distributions, the linear temperature distribution is outstanding for efficient hydrogen production of the steam reformer.Keywords:Steam reformer(수증기 개질기), Reaction model(반응 모델), Hydrogen production(수소 생산) †Corresponding author Tel.: +82-2-958-5683; fax: +82-2-568-7853 E-mail address: seoykim@kist.re.kr

Thermal performance of a thermoelectric air-cooling system with heat sinks

Thermal performance of a louver-fin and a plate-fin in a thermoelectric cooling system with a duct-flow type fan arrangement is analytically evaluated. The thermoelectric cooling system consists of a thermoelectric module and two heat exchanger fins. The analytic results show that the optimized louver fin has lower thermal resistance than plate fin. The COP and heat absorbed rate of the thermoelectric cooling system with optimized louver fins are about 10% and 6% higher than optimized plate fins, respectively.

Performance Evaluation of a Cylindrical Steam Reformer with Various Thermal Conditions

Abstract The experimental performance evaluation of a cylindrical steam reformer with various thermal conditions has beenconducted. The bottom space of the cylindrical reactor was packed with Ruthenium (Ru) catalyst. A three-segment furnace was installed to create the axially variable boundary temperature distribution. Six K-type thermocouples were inserted into the catalyst layer, and three exhaust ports were fabricated on the side wall along the flow direction. The exhausted gasesat each port were analyzed by using gas chromatograph (GC) system. The experimental results showed that the reforming reaction occurs intensively in the upstream region and more hydrogen is obtained when the intake gas is sufficiently heatedup through the enhanced steam reforming (SR) reaction. The axially increasing boundary temperature setup provided the maximally accumulated reforming efficiency of 74.8%, when the reactor was placed at the 3rd section of the furnace. Key words Steam reformer(수증기 개질기), Boundary temperature distribution(경계온도 분포), Accumulated reforming efficiency(개질누적효율)†Corresponding author, E-mail:

Development of a 200 W Portable PEM Fuel Cell System

A 200 W portable polymer electrolyte membrane fuel cell (PEMFC) system is developed. The PEMFC system consists of an air-cooled fuel cell stack module, a fuel supply subsystem, a power management subsystem, and a control electronics subsystem. The control logic is designed for the stable system operation. The system-level performance evaluation discloses that the present PEMFC system provides a rated power output of 200.5 W at 13.4 V with the maximum balance-of-plant (BOP) efficiency of 72%, and maximum system efficiency based on lower heating value (LHV) is 37% at 120.7 W system power output.

Effect of chip die bonding on thermal resistance of high power LEDs

Thermal resistance of high power blue Light Emitting Diode (LED) package is experimentally examined. The LED package consists of eight CREE EZ900 chips. The dimension of each chip is 880 μm×880 μm and the metal board area is 30 mm×32 mm with 3 mm thickness. The LED package is operated at the current of 11 A with 10 % duty cycle. To measure junction temperature, the forward voltage method is used. The metal board temperature is measured by attaching K-type thermocouple. Then, the thermal resistance from junction to metal board is calculated. For comparison, six identical LED packages are examined. Each LED package shows different thermal resistance from 0.4 K/W to 10.3 K/W. To investigate how the chips are well attached on the metal board, X-ray computed tomography (CT) images of the LEDs are taken and air gap areas are evaluated. The result shows that the thermal resistance increases with the increase of air gap area.