Gilbong Lee

Performance Evaluation of Geothermal Heat Pump With Direct Expansion Type Vertical Ground Heat Exchanger

Vertical closed-loop groun-source heat pump systems have been installed widely in Korea since they can extract a moderate temperature level of geothermal heat in a relatively small area. For a ground heat exchanger, a vertical closed-loop type with brine circulation is mostly preferred since it is simpler and less harmful to the ground environment. However, it requires a secondary loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground would be increased, which causes performance degradation. In this paper, performances of direct expansion ground-source heat pump were evaluated mathematically as an alternative to the conventional secondary-loop ground-source heat pump.

Development of the Supercritical Carbon Dioxide Power Cycle Experimental Loop in KIER

Three supercritical carbon dioxide (CO2) power cycle experimental loops have been developed in Korea Institute of Energy Research (KIER) from 2013. As the first step, a 10 kWe-class simple un-recuperated Brayton power cycle experimental loop was designed and manufactured to test its feasibility. A 12.6 kWe hermetic turbine-alternator-compressor (TAC) unit which is composed of a centrifugal compressor, a radial turbine and the gas foil bearings was manufactured. The turbine inlet design temperature and pressure were 180 °C and 130 bar, respectively. Preliminary operation was successful at 30,000 RPM which all states of the cycle existed in the supercritical region. Second, a multi-purpose 1 kW-class test loop which operates as a transcritical cycle at a temperature of 200 °C was developed to concentrate on the characteristics of the cycle, control and stability issues of the cycle. A high-speed turbo-generator was developed which is composed of a radial turbine with a partial admission nozzle and the commercial oil-lubricated angular contact ball bearings. Finally, a 60 kWe-class Brayton cycle is being developed which is composed of two turbines and one compressor to utilize flue-gas waste heat. As the first phase of development, a turbo-generator which is composed of an axial turbine, a mechanical seal and the oil-lubricated tilting-pad bearings was designed and manufactured.Copyright

Analysis of Performance of Heat Pump System with Flue Gas Heat Recovery through Field Test

Abstract A field test of a 70 ㎾ heat pump system with flue gas heat recovery was performed by an experiment at theKorea Institute of Energy Research. The flue gas is exhausted from a 320 RT absorption chiller-heater in the heating season.Using this flue gas, source water of the heat pump is heated by a condensed-type heat exchanger in the chimney. Theoperating characteristics of the heat recovery heat pump system were analyzed. Based on the results of the experiments, operating maps were obtained, and an optimum operating range is suggested, in which the return and heat source watertemperature are 51 ℃ and 31 ℃ , respectively. Additionally, economic analysis of this system was conducted and about 50%energy cost savings can be expected in the heating season. Key words Condensing heat recovery(응축열회수), Flue gas(배가스), Heat recovery system(열회수 시스템), Latent heat(잠열), Condensation(응축)†Corresponding author, E-mail: yslee@kier.re.kr 기호설명COP H ： 난방성능계수 Q cond ： 응축(난방)열량 [ ㎾ ] Q evap ： 증발열량 [ ㎾ ]

Numerical Analysis of Unsymmetric Flatbak Trailing Edge Airfoil to Reduce Turbomachinery Noise in Power Generation Cycle

A turbomachinery is essential part in the power generation cycle. But, it is main noise source to annoy workers and users and to make environmental problem. Thus it is important to reduce this noise for operating the power generation cycle. This noise is created by flow instability on rotor blade trailing edge. An airfoil that becomes a section of a rotor blade of a rotating machine is manufactured as a blunt trailing edge (TE) with a round or flatback shape rather than the ideal sharp TE shape for the purposes of producibility and durability. This increases the tonal noise and flow-induced vibration at low frequency owing to vortex shedding behind TE when compared with a sharp TE. In order to overcome this problem, this study investigates the oblique TE shape using numerical simulation. In order to do so, the flow was simulated using large eddy simulation (LES) and the noise was analysed by acoustic analogy coupled with LES result. Once the simulation results were verified using the flatback airfoil measurements of Sandia National Laboratories, numerical prediction was performed for airfoils modified to have oblique trailing edge angles of 60°, 45°, and 30° to analyse the flow and noise characteristics. From the simulation results for an airfoil having an oblique TE, it could be seen that the vortex shedding frequency moves in accordance with the oblique angle and that the vortex shedding noise characteristics change according to this angle when compared to the flatback TE airfoil. Therefore, it is considered that modifying the flatback TE airfoil to have an appropriate oblique angle can reduce noise and change the tonal frequency to a bandwidth that is suitable for mechanical systems.

Optimization of a CO2-based shipboard waste heat recovery system

Under the resolution adopted at the 62nd Marine Environment Protection Committee (MEPC), carbon emission restrictions have been implemented for large ships since 2013. In order to comply with this, a number of efforts are being made to reduce fuel consumption in ships. In this study, in order to utilize engine exhaust waste heat, a carbon dioxide power cycle, which utilizes a carbon dioxide as a working fluid in contrast to conventional steam power cycle, was investigated. The power cycle was modeled and simulated to investigate its characteristics and performances under the shipboard waste heat recovery condition. The cycle power was maximized by using multivariate optimization method at various cycle minimum temperature conditions. Simulation results show that when the cycles lowest temperature varied in the range of 16-40 degC, the waste heat recovery system increases power by 7.1-3.5%.