• Transactions of the Korean hydrogen and new energy society
• /
• v.26 no.6
• /
• pp.590-599
• /
• 2015

In this paper a performance analysis is carried out based on the first and second laws of thermodynamics for heat exchanger in organic Rankine cycle (ORC) for the recovery of low-temperature finite thermal energy source. In the analysis, effects of the selection of working fluid and pinch temperature difference are investigated on the performance of the heat exchanger including the effectiveness of the heat exchanger, exergy destruction, second-law efficiency, number of transfer unit (NTU), and pinch point. The temperature distribution are shown depending on the working fluids and the pinch temperature difference. The results show that the performance of the heat exchanger depends on the pinch temperature difference sensitively. As the pinch temperature increases, the exergy destruction in the evaporator increases but the effectiveness, second law efficiency and NTU decreases.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.6
• /
• pp.621-628
• /
• 2019

The use of the ammonia-water zeotropic mixture as a working fluid in the power generating system has been considered as a proven technology for efficient recovery of low-grade heat sources. This paper presents a thermodynamic performance analysis for ammonia-water evaporator using low-grade heat source, based on the exergy and entransy which has been recently introduced as a physical quantity to describe the heat transfer ability of an object. In the analysis, effects of the ammonia mass fraction and source temperature of the binary mixture are investigated on the system performance such as heat transfer, effectiveness, exergy destruction, entransy dissipation, and entransy dissipation based thermal resistance. The results show that the ammonia mass concentration and the source temperature have significant effects on the thermodynamic system performance of the ammonia-water evaporator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.3
• /
• pp.244-250
• /
• 2000

An air source heat pump using liquid injection technique, which can be applied for very low temperature climate, has been simulated to examine the design options. Comparison between the simulation and experiment has been carried out to validate the simulation method. Effects of various design parameters such as liquid injection rate and injection pressure are Investigated to optimize the performance of the heat pump. Finally, optimal liquid infection rate and injection pressure to maintain sufficient heating capacity and moderate discharge refrigerant temperature are suggested when the heat pump was operated at very low outdoor temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.8
• /
• pp.634-640
• /
• 2002

The purpose of this study is to investigate the propriety of TMA clathrate as a cold storage medium. Particularly, this is to examine the extent of subcooling improvement when the additives is added to the TMA clathrate, because water used for cold storage ma terial has low phase change temperature and subcooling. This study has been analyzed and compared pure water with TMA 30 wt% clathrate how phase change temperature, subcooling and specific heat in the various concentrations are changed. This results prove low phase change temperature and subcooling control effect when the ethanol is added to the TMA 30 wt% clathrate than the TMA 30 wt% clathrate. In addition, it results low specific heat when there is added to the TMA 30 wt% clathrate over 0.5 wt% ethanol in the cold heat source temperature under $-7^{\circ}C$. The other side, it results high specific heat when the ethanol is added in it at the cold heat source temperature under $-5^{\circ}C$. Therefore, it is found that the additive must be controlled by available solution limit and study for new additive must be lasted to know its effect.

• Transactions of the Korean hydrogen and new energy society
• /
• v.25 no.2
• /
• pp.200-208
• /
• 2014

This paper presents thermodynamic performance analysis of organic Rankine cycle (ORC) using low temperature heat source in the form of sensible energy and using liquefied natural gas (LNG) as heat sink to recover the cryogenic energy of LNG. LNG is able to condense the working fluid at a very low condensing temperature in a heat exchanger, which leads to an increased power output. Based on the mathematical model, a parametric analysis is conducted to examine the effects of eight different working fluids, the turbine inlet pressure and the condensation temperature on the system performance. The results indicate that the thermodynamic performance of ORC such as net work production or thermal efficiency can be significantly improved by the LNG cold energy.

• Journal of Biosystems Engineering
• /
• v.24 no.4
• /
• pp.343-350
• /
• 1999

The ambient air is commonly used as low-temperature heat source for heat pump operation. However, the coefficient of performance(COP) of the air to water heat pump is decreased with the ambient air temperature drop. In this study to solve this problem, the AVACTHE(Automatic Variable Area Capillary Type Heat Exchanger) with 3 levels of heat exchange area(0, 1,495.4, 1,794.5$\textrm{cm}^2$)was installed in the refrigerant circuit of the heat pump. The AVACTHE effect on the performance of heat pump was tested with the ambient air temperature variation. The COP improvement of the heat pump could be achieved by the AVACTHE installation when below -5$^{\circ}C$ of the ambient air temperature.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.11
• /
• pp.699-707
• /
• 2017

This study presents a comparative thermodynamic analysis of subcritical and transcritical organic Rankine cycles for the recovery of low-temperature heat sources considering nine substances as the working fluids. The effects of the turbine inlet pressure, source temperature, and working fluid on system performance were all investigated with respect to metrics such as the temperature distribution of the fluids and pinch point in the heat exchanger, mass flow rate, and net power production, as well as the thermal efficiency. Results show that as the turbine inlet pressure increases from the subcritical to the supercritical range, the mismatch between hot and cold streams in the heat exchanger decreases, and the net power production and thermal efficiency increase; however, the turbine size per unit power production decreases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.1
• /
• pp.65-74
• /
• 2008

In Korea, air source heat pump system is less efficient than conventional heat source facilities, such as ground source, river water, because the air temperature in winter season is so low that COP of air source heat pump system drops below 3.0. Therefore, the study on the application of heat pump heating and cooling systems is crucial for the efficient popularization of heat pump. In this work, we present the dynamic analysis of energy consumption for the large resident building by heat resistance-capacitance method. The system simulation of water storage air source heat pump is additionally performed by changing of sizes and locations of the hospital building. The computed results show that energy cost of water storage air source heat pump is low, so it is more economical than absorption chiller & heater.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.513-514
• /
• 2006

Recently intradiscal electrothermal therapy is introduced, which is a new and minimally invasive technique fer the treatment of discogenic low back pain. This procedure involves the percutaneous threading of a flexible catheter into the disc under fluoroscopic guidance. The catheter, composed of thermal resistive coil, heats the posterior annulus of the disc, causing contraction of collagen fibers and destruction of afferent nociceptors. This study tries to investigate the effects of the important factors of this procedure such as heat source temperature and heat applying time on the temperature distribution within the intervertebral disc. This study utilized both computer simulation and the experiment for the verification of finite element analysis. FE analysis was carried out with ANSYS v7.0 (ANSYS Inc, USA) using 10,980 number of brick element and 12,551 number of node. The functional spinal units of 5 month old swine were used for the experiment and the temperature was monitored using 10 channel temperature measurement device MV200. Through this study, it was able to analyze the temperature range of inner intervertebral disc by two mechanisms which are known to alleviate pain clinically. The results showed that when the heat source temperature was kept up 80 degree for 1,020 seconds, the temperature of inner annulus reached at 45 degree up to the distance of 15.6mm from heat source, which explains coagulation of inner annulus by heat. When the same heat source was used, the temperature of inner nucleus reached at 60 degree up to the distance of 9mm from heat source, which explains contraction of inner nucleus by heat.

• Transactions of the Korean hydrogen and new energy society
• /
• v.24 no.6
• /
• pp.510-517
• /
• 2013

The ammonia-water based power generation cycle utilizing liquefied natural gas (LNG) as its heat sink has attracted much attention, since the ammonia-water cycle has many thermodynamic advantages in conversion of low-grade heat source in the form of sensible energy and LNG has a great cold energy. In this paper, we carry out thermodynamic performance analysis of a combined power generation cycle which is consisted of an ammonia-water regenerative Rankine cycle and LNG power generation cycle. LNG is able to condense the ammonia-water mixture at a very low condensing temperature in a heat exchanger, which leads to an increased power output. Based on the thermodynamic models, the effects of the key parameters such as source temperature, ammonia concentration and turbine inlet pressure on the characteristics of system are throughly investigated. The results show that the thermodynamic performance of the ammonia-water power generation cycle can be improved by the LNG cold energy and there exist an optimum ammonia concentration to reach the maximum system net work production.