Ho-Saeng Lee

Thermodynamic design data and performance evaluation of the water + lithium bromide + lithium iodide + lithium nitrate + lithium chloride system for absorption chiller

Abstract Duhring (P–T–X) and enthalpy-concentration (H–X–T) diagrams of the H2O + LiBr + LiNO3 + LiI + LiCl (mole ratio of LiBr : LiNO3 : LiI : LiCl = 5 : 1 : 1 : 2) system were constructed by using the experimental data sets. Thermodynamic design data for a double-effect series-flow absorption chiller were calculated at various operating conditions [ 2≤Te≤14°C, 30≤Ta≤50°C, 30≤Tc≤50°C, T gh COP =0 ≤T gh ≤T gh (crystallization limit)] by a computer simulation. The proposed working fluid was found to be applicable to cycle operation of air-cooled absorption chiller with no crystallization problem at higher absorber temperature.

Investigation of Safety and Design of Mooring Lines for Floating Wave Energy Conversion

A study was performed on the design of a mooring line to maintain the position of a floating WEC (wave energy conversion) system. The procedure to design a mooring line is set up and the safety of the designed mooring system is evaluated using commercial software, Orcaflex. The characteristics curve for one line is analyzed to determine the properties and pretension of a mooring line. While considering the ocean environmental condition and importance of a floating WEC system, a multi-line layout is determined. A 4-point mooring system with 4 lines shows the instability in the yaw motion of the floating WEC system under a designed ocean environmental condition. The redesigned 4-point mooring system with 8 lines is found to be safe on the condition of a harsh ocean environment. The floating WEC system with the redesigned mooring system also shows stable motion in surge and pitch under operating conditions. From a parametric study on the mooring line length, the extreme value of the mooring line tension is found to be very sensitive to the pretension and length of mooring line. The results of this study can contribute to the establishment of a design procedure for mooring lines.

Wireless piezoelectric strain sensing measurement using a frequency modulation technique

A simple wireless strain sensor using a frequency modulation technique is presented. The sensor employs a piezoelectric transducer that produces electric voltage as it is mechanically strained. When the piezoelectric sensor is connected to a single-transistor frequency modulation circuit, the sensor output voltage causes the modulation circuit frequency to shift. This modulated signal is then wirelessly transmitted to a remote station, where a demodulation circuit retrieves the buried strain measurement data in real time. Using this technique, a dynamic strain measurement is possible without any wire connection between the sensing point and the monitoring station. In order to demonstrate the performance of the wireless strain sensor and the measurement system, a wireless measurement of a vibrating cantilevered beam is experimentally conducted. This type of sensor has numerous applications in the strain or vibration measurement of moving or rotating structures such as turbo machinery.

Efficiency enhancement of the ocean thermal energy conversion system with a vapor–vapor ejector

In this article, 20 kW ocean thermal energy conversion with a vapor–vapor ejector is newly proposed. As a vapor–vapor ejector is installed in the system, the pressure difference between the turbine inlet and outlet increases. Therefore, the amount of the working fluid required for the total turbine work of 20 kW is less than when no vapor–vapor ejector is installed. Therefore, installing a vapor–vapor ejector in the system decreases the evaporation capacity and the pump work. The performance analysis considered the outlet pressure of the high-stage turbine, the mass flow ratio of the working fluid at the outlet of a separator just after the high-stage turbine, and the nozzle diameters of the vapor–vapor ejector. As the outlet pressure of high-stage turbine becomes lower, the turbine gross power of high-stage turbine and system efficiency increase although lower outlet pressure of high-stage turbine results in lower ejector performance. Similarly, in terms of mass flow ratio, the highest system efficiency was shown at mass flow ratio of 0.4 at the outlet of a separator just after the high-stage turbine. On the other hand, the performance of the ejector at mass flow ratio of 0.5 at the outlet of a separator was largest. When the nozzle diameters of the vapor–vapor ejector are properly designed, the vapor–vapor ejector shows the highest performance. After the optimization of the operation parameters, system efficiency of the proposed ocean thermal energy conversion power cycle was 2.47%, relatively 15% higher than that of the basic ocean thermal energy conversion power cycle (2.2%).

A novel working fluid for building air-conditioning and ocean thermal energy conversion

An azeotropic mixture of R32/R290 is proposed for both building air-conditioning and ocean thermal energy conversion (OTEC) applications. R32/R290 is an environmentally safe working fluid mixture with no ozone depletion potential (ODP) and low global warming potential (GWP). This mixture can successfully replace R410A used in many residential air-conditioners and heat pumps since its GWP is quite low, about 25% of that of R410A. The same mixture also can be used in OTEC power plants to replace conventional working fluids of medium vapor pressure. Due to the increase in density, a significant reduction in equipment is expected, which consequently will result in an initial cost reduction.

Performance Analysis of Closed-type OTEC Cycle using Waste Heat

The cycle performance of closed ocean thermal energy conversion (OTEC) system with 50 kW gross power was evaluated to obtain the basic data for the optimal design of OTEC using waste heat such as solar power, discharged heat from condenser of power plant. The basic thermodynamic model for OTEC is Rankine cycle, and the surface seawater and deep seawater were used for the heat source of evaporator and condenser, respectively. The cycle performance such as efficiency, heat exchanger capacity, etc. was analyzed on the variation of temperature increase by waste heat. The cycle efficiency increased and necessary capacity of evaporator and condenser decreased under 50kW gross po wer with respect to the temperature increase of working fluid. Also, when the temperature increase is about 13.5o C, the heat which can be used is generated. By generator with 0.9 effectiveness under the simulated condition, the cycle efficiency was improved approximately 3.0% comparing with the basic cycle.

Performance Characteristics of a Closed-Circuit Cooling Tower With Multiple Paths

The performance of a closed-circuit wet cooling tower (CWCT) with multiple paths having a rated capacity of 9 kW has been studied experimentally. When the CWCT has to operate with a partial load, the required quantity of cooling water reduces and thereby the velocity of the process fluid inside the tubes decreases. The velocity of the process fluid can be increased by installing blocking tubes in the heat exchanger. The test section in this experiment has multiple paths that have been used as the inlet for cooling water that flows from the top part of the heat exchanger. The heat exchanger consists of eight rows and 12 columns and the tubes are in a staggered arrangement. Heat and mass transfer coefficients and temperature drops were calculated with several variations including multiple paths. The results obtained from this study were compared with those reported and found to conform well. The investigation indicates that a CWCT operating with two paths has higher heat and mass transfer coefficients than with one path.

Key Technologies for Floating Type Artificial Upwelling System to Strengthen Primary Production

The abundant nutrients contained in deep seawater are delivered by natural upwellings from the deep sea to the surface sea. However, the natural upwelling phenomenon is limited to specific areas of the sea; in other areas, the thermocline separates the surface sea from the lower layer. Thus, the surface layer is often deficient in nutritive salts, causing the deterioration of its primary productivity and ultimately leading to an imbalance in the marine ecosystem. Without a consistent supply of nitrogenous nutritive salts, they are absorbed by phytoplankton, resulting in a considerable problem in primary productivity. To solve this issue, a floating type of artificial upwelling system is suggested to artificially pump up, distribute, and diffuse deep seawater containing rich nutritive salts. The key technologies for developing such a floating artificial upwelling system are a floating offshore structure with a large diameter riser, self-supplying energy system, density current generating system, method for estimating the emission and absorption of CO2, and way to evaluate the primary production variation. Strengthening the primary production of the sea by supplying deep seawater to the sea surface will result in a sea environment with abundant fishery resources.

Mitigation of environmental impact of power-plant discharge by use of Ocean Thermal Energy Conversion system

This study aims to evaluate the mitigation method of environmental impact of power-plant discharges by reducing the temperature difference between effluent and coastal water. To minimize excessive thermal pollution which could cause serious socio-economic problems, Ocean Thermal Energy Conversion (OTEC) system can be applied to control the resultant temperature of combined discharge as well as to produce electricity by reusing the warm discharge from power-plant as a heat source for OTEC. Adaptability analysis of closed cycle OTEC was examined to 350MW fossil fuel power plant. The results show that combined system could mitigate the thermal discharge effectively if suitable size of OTEC is connected with the power-plant. Furthermore, this method gives us marine forest to absorb carbon dioxide which may be altered to green house gas emission credit as well as clean electric power.

Performance Characteristics of 20kW Ocean Thermal Energy Conversion Pilot Plant

To experiment 20kW OTEC, the closed-cycle type of OTEC (Ocean Thermal Energy Conversion) was designed and manufactured. R32 (Difluoromethane, CH2F2) was used as the working fluid and a temperature of heat source and heat sink is 26°C, 5°C, respectively. The semi-welded type heat exchanger is applied for the evaporator and condenser and the cycle was designed for the gross power of 20kW. In the plate arrangement of the semi-welded type heat exchanger, one channel for working fluid is welded, and another channel for seawater is sealed by gasket. In this paper, various performance evaluations and experiments were carried out as constructing subminiature pilot plant of the OTEC and compared with the results of cycle analysis. In results, gross power of the turbine shows 20.1kW and cycle efficiency is 1.91% when heat source and heat sink is 26°C, 5°C. For the variation of temperature difference between the heat source and heat sink, when the temperature difference was 21°C, the gross power increased by about 33.3% from that when the temperature difference was 19 °C.Copyright