• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.11
• /
• pp.2196-2202
• /
• 1992

The optimum size combination of heat exchangers in a Joule-Thomson(J-T) circuit for small cryogenic systems has been sought analytically, when the circuit is combined with a two-stage Gifford-McMahon(GM) cooler. Full thermodynamic cycle analysis was carried out to predict the performance of the combined refrigeration system. Relevant convective heat transfer coefficients, the computerized properties of helium, and the refrigeration capacity curve of a typical GM cooler have been used in the analysis. The result showed that, by changing the configuration(heat exchanger area ratio) of the system, the performance of the commonly-used GM/J-T refrigerators could be optimized. For the maximum refrigeration performance, the optimum mass flow rate of the refrigerant and the relative size between the heat exchangers have been obtained, when the cooling load was 0.1W at 3.995K with the total heat exchanger area being given.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.3
• /
• pp.59-70
• /
• 2020

Obtaining external forced convection heat transfer from bubble boiling and validating it with experimental results using cryogenic liquids are suggested to derive total heat transfer coefficient with pool boiling condition in the case of coil type heat exchanger with a bundle of tubes and to overcome the limitation of using the empirical correlation. Experiment is conducted with pool boiling heat transfer of saturate liquid nitrogen with helical coil type heat exchanger using liquid oxygen as hot stream fluid. Experimentally measured heat transfer coefficient is well-agreed with the estimated curve considering nucleate boiling and forced convection induced by bubble rise.

• Journal of the Korean Wood Science and Technology
• /
• v.37 no.1
• /
• pp.94-104
• /
• 2009

It is urgently required to develop the production of fermentation-heat energy from the waste agricultural and forest biomass and its effective heat exchanging system for the supply of warm water to rural households and greenhouses. In this study 3 helical-type and 1 plate-type heat exchangers using 3 different waste biomasses [e.g. hardwood (HW) sawdust (100%), softwood (SW) sawdust : HW sawdust (50 : 50) and HW sawdust : grass (90 : 10)] were applied in order to find out the best heat recovery system. The heat exchanger was basically considered to improve the overall heat recovery efficiency, to minimize heat loss and to simplify manufacturing, assembling and breaking up the fermenting beds. The helical-type heat exchanger (HX-H3) installed in fermenting bed of HW sawdust : grass (90 : 10) showed relatively higher temperature profiles, in particular mid- and upper-parts than lower and surface parts during 45-day fermentation process. The maximum temperature was ranged from $40^{\circ}C$ to $65^{\circ}C$ with average $60^{\circ}C$. The water temperature of tank outlet was ranged to $33{\sim}48^{\circ}C$ during whole measuring periods. By the way plate-type one (HX-P) installed in same biomass compositional fermenting bed showed $64.5{\sim}76.5^{\circ}C$ at center part, and $43{\sim}56^{\circ}C$ and $42{\sim}58^{\circ}C$, water tank and tank outlet temperatures, respectively, during 100 day measurement. It could be concluded that the plate-type heat exchanger (HX-P) provides not only the effective heating for the rural households and greenhouses, but also having the best heat recovery performance, easy manufacturing, assembling and breaking up the systems.

• Journal of Advanced Marine Engineering and Technology
• /
• v.40 no.3
• /
• pp.174-179
• /
• 2016

To protect the ocean environment, the use of liquefied natural gas (LNG) carriers, bunkering ships, and fueled ships is increasing. Recently, Korean shipbuilders have developed and supplied a partial reliquefaction facility for boil-off-gas (BOG). Despite reasonable insulation, heat leakage in vessel storage tanks causes LNG to be continuously evaporated as BOG. This research analyzed the maximum liquid yield rate for various partial reliquefaction systems (PRS) and considered related factors affecting yields. The results showed a liquid yield of 48.7% from an indirect PRS system (heat exchanges between cold flash gas and compressed natural gas), and 41% from a direct PRS system (BOG is mixed with flash gas and discharged from a liquid-vapor separator). The primary factor affecting liquid yield was heat exchanger effectiveness; the exchanger's efficiency and insulation characteristics directly affect the performance of BOG reliquefaction systems.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.14 no.6
• /
• pp.1215-1220
• /
• 2019

Currently, each farm bears both the outbreak of foot-and-mouth disease and the damage caused by AI. In addition, complaints about odors in the livestock industry are constantly being recovered and are expected to occur in the future. The purpose of this study is to improve the indoor air quality of enclosed facilities such as barns, houses, pigsty, and etc. This paper develops low-temperature plasma waste heat ventilation system to be installed in ventilation unit location and standardizes heat exchange element, low-temperature plasma lamp, and ballast for enhanced air cleaning function. In addition, this study intends to develop a new control system so that the farmers can connect with existing weather systems, flow fans, and other facility equipment by incorporating ICT.

• Applied Chemistry for Engineering
• /
• v.8 no.5
• /
• pp.729-736
• /
• 1997

For the recovery of industrial waste heat, a chemical heat transformer based on the reversible reaction between metal chlorides and ammonia gas was designed and a pilot scale unit of 1 kW-1hr was developed. A static calculation, which determined the amount of reacting materials and operating condition of system, and dynamic simulations were performed for the optimal design. The temperature and output power of generator in the system were varying with the amount of salt and heat exchange area. Optimum conditions such as the amount of salt-graphite, apparent density and size of mechanical unit were determined by the dynamic simulation for the system. According to the operating cycle of 4 stages, experimental results of temperature and output power were well agreed with the simulation values. This chemical heat transformer is turned out to be a very promising system for recovery of industrial waste heat because of its effective feature of lifting temperature.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.11
• /
• pp.2189-2195
• /
• 1992

The performance of heat exchanger as an energy conversion device can be described by the available energy output and efficiency. The efficiency is defined as the ratio of the available energy output and the exergy of the heat source flow. In present study, a counterflow heat exchanger is analyzed and the conditions to obtain maximum output is numerically determined. As a result, the avilable energy obtained by the cold flow can be determined as functions of the heat capacity flow, the cold flow inlet temperature and the heat transfer capacity of heat exchanger. At the maximum output condition the heat capacity flow of the cold fluid is larger than that of the heat source, and the heat capacity flow ratio is equal to the ratio of the cold flow inlet temperature and the atmospheric temperature. And the avilable energy output increases as the heat transfer capacity of the heat exchanger become larger, but in the economic point of view there is also an optimum heat transfer capacity for a given heat source flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.247-253
• /
• 2011

An experimental study on performance characteristics of an evaporative heat exchanger based on tests for various operating conditions was presented. The heat exchanger maximizes the heat transfer rate per unit volume by applying mini-channels for both the air and coolant flow paths, and minimizes the amount of the coolant by using its latent heat of evaporation. The heat exchanger was manufactured by etching the flow paths, brazing the heat exchange plates, and welding the in/out ports of the media. The basic performance test has confirmed that the heat exchanger met its design requirements, and the results of the map test were analyzed to produce the performance characteristics quantitatively depending on the air inlet temperature, the air flow rate, and the coolant flow rate.

• Korean Journal of Computational Design and Engineering
• /
• v.17 no.1
• /
• pp.54-61
• /
• 2012

In this paper, we performed numerical analysis to improve the heat exchange efficiency of wasted heat recovery ventilator which has a delivery and a exhaustion fan. One of the most important design factors that affect the efficiency of heat exchange is uniform counter-flow between inbound and outbound air flows. We had simulated several types of porous plates which were installed at air intake area. With plate having 45 degrees of installation angle and 15 mm diameter holes which are uniformly arranged, we can generate a uniform air flows at the area of porous media where inbound and outbound air flows are cross over. In addition, we installed a duct to reduce vortex flows at the outlet and to discharge exhaust airs rapidly. By using the proposed numerical assessment, we expect the improvement of the heat exchange efficiency of ventilator.

• Korean Chemical Engineering Research
• /
• v.59 no.1
• /
• pp.60-67
• /
• 2021

This study presented techno-economic analysis of a 500 MWe oxy-coal power plant with CO2 capture. The power plant included a circulating fluidized-bed (CFB), ultra-supercritical steam turbine, flue gas conditioning (FGC), air separation unit (ASU), and CO2 processing unit (CPU). The dry flue gas recirculation (FGR) was used to control the combustion temperature of CFB. One FGR heat exchanger, one heat exchanger for N2 stream exiting ASU, and a heat recovery from CPU compressor were considered to enhance heat efficiency. The decrease in the temperature difference (ΔT) of the FGR heat exchanger that means the increase in heat recovery from flue gas enhanced the electricity and exergy efficiencies. The annual cost including the FGR heat exchanger and FGC cooling water was minimized at ΔT = 10 ℃, where the electricity efficiency, total capital cost, total production cost, and return on investment were 39%, 1371 M$, 90 M$, and 7%/y, respectively.