• Journal of the Korean Society for Railway
• /
• v.3 no.4
• /
• pp.177-184
• /
• 2000

In this paper, a HVAC controller which has a bilinear system is designed to control the air temperature in building room and a saving of energy on the HVAC system. For modeling of the HVAC bilinear system, AHU(Air Handling Unit) is modeled on the control of inside-outside air flow using three dampers in a duct. A heat exchanger and the single room are also modeled by the energy conservation law. Under the modeling of the HVAC bilinear system, the control's law of the bilinear HVAC system is derived by Lyapunov's non-linear theory and Deress's the linear feedback laws for bilinear system. In this paper it was proved that the controller of the HVAC bilinear system is able to control the air temperature with a disturbance in order to get a target of temperature in the building room by the computer simulation when the control inputs regulate the air flow rate and a capacity of the heat exchanger.

• Nuclear Engineering and Technology
• /
• v.39 no.2
• /
• pp.95-102
• /
• 2007

The conceptual design of the MIT modular pebble bed reactor is described. This reactor plant is a 250 Mwth, 120 Mwe indirect cycle plant that is designed to be deployed in the near term using demonstrated helium system components. The primary system is a conventional pebble bed reactor with a dynamic central column with an outlet temperature of 900 C providing helium to an intermediate helium to helium heat exchanger (IHX). The outlet of the IHX is input to a three shaft horizontal Brayton Cycle power conversion system. The design constraint used in sizing the plant is based on a factory modularity principle which allows the plant to be assembled 'Lego' style instead of constructed piece by piece. This principle employs space frames which contain the power conversion system that permits the Lego-like modules to be shipped by truck or train to sites. This paper also describes the research that has been conducted at MIT since 1998 on fuel modeling, silver leakage from coated fuel particles, dynamic simulation, MCNP reactor physics modeling and air ingress analysis.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.2
• /
• pp.136-142
• /
• 2015

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-${\epsilon}$ are adopted. The path line and local axial velocities are calculated between two baffles using this program.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.8
• /
• pp.563-568
• /
• 2007

The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performances of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. An empirical modeling equation has been derived from the experimental results using accelerated tests and it showed good predictions of the fouling characteristics of the slitted finned tube heat exchangers. However the modeling equation predicts only the fouling characteristics of new heat exchangers and it can not predicts fouling characteristics obtained from actual field data which contains the effect of hydrophilicity deterioration. Therefore an modified modeling equation is proposed and it shows good predictions of the actual fouling characteristics of finned-tube heat exchangers.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.16 no.1
• /
• pp.64-71
• /
• 2012

While a conventional ECS mainly consisted of an air cycle machine and heat exchangers, a new concept of a phase change heat exchanger was added to improve the transient performance of the ECS. As a result, an ECS modeling program including the phase change heat exchanger is newly developed to estimate its effect in various flight conditions such as take-off, maneuver, cruise, and landing. The simulation result regarding a virtual flight profile has confirmed the new ECS fulfilled the requirement by showing the temperature of the cooling air returned from the bay was always kept below $80^{\circ}C$. Through this study, the new ECS concept with PCHE was verified successfully.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2003.10a
• /
• pp.401-411
• /
• 2003

Tube expanding process is for combining a heat-sink plate with hair-pins (Cu-tube) through plastic deformation. The two parts, i. e. , heat-sink plate and hair-pins are they components of a heat-exchanger for an air conditioner. This paper presents the analysis and dynamic modeling of a high-speed tube expander which integrates transfer of parts, fixing of parts, and tube expanding into one process. The 3-dimensional modeling of all the parts for the tube-expander was constructed using CATIA$\circledR$. then the CATIA$\circledR$ models are transferred into visuaINastran$\circledR$ to execute the 3-dimensional animation for checking prescribed cycle-time. The technique presented in this paper has been shown to be effective as a priori tool for verifying the design of a high-speed tube expander.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.6 no.1
• /
• pp.57-64
• /
• 2010

PHE(Process Heat Exchanger) is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR(Very High Temperature Reactor) to the chemical reaction that yields a large quantity of hydrogen. Korea Atomic Energy Research Institute established the gas loop for the performance test of components, which are used in the VHTR, and they manufactured a PHE prototype to be tested in the loop. In this study, as part of the high-temperature structural-integrity evaluation of the PHE prototype, which is scheduled to be tested in the gas loop, we carried out high-temperature structural-analysis modeling, thermal analysis, and thermal expansion analysis of the PHE prototype. The results obtained in this study will be used to design the performance test setup for the PHE prototype.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.9
• /
• pp.1189-1194
• /
• 2013

The Intermediate Heat Exchanger (IHX) of a Very High Temperature Reactor (VHTR) is a core component that transfers the high heat of $950^{\circ}C$ generated in the VHTR to a hydrogen production plant. The Korea Atomic Energy Research Institute manufactured a lab-scale prototype of a Printed Circuit Heat Exchanger (PCHE) as a candidate for an IHX. In this study, as a part of a high-temperature structural integrity evaluation of the lab-scale PCHE prototype made of SUS316L, we carried out high temperature structural analysis modeling and macroscopic thermal and elastic structural analysis for the lab-scale PCHE prototype under helium experimental loop (HELP) test conditions as a precedent study prior to the performance test in HELP.

• Journal of Hydrogen and New Energy
• /
• v.33 no.4
• /
• pp.430-436
• /
• 2022

This paper presents the numerical model development of a microchannel heat exchanger in mobile air-conditioning and heat pump applications. The model has been developed based on the effectiveness-NTU method using a segment-by-segment modeling approach. State-of-art correlations are used for refrigerant- and air-side heat transfer coefficients and pressure drops. The calculated heat condenser capacities are in good agreement with experimental data, with an average difference of 1.86%. The current model can be used for microchannel condenser simulations under various operating conditions. It is anticipated to improve productivity in designing and optimizing microchannel heat exchangers with folded louver fin geometry.

• Nuclear Engineering and Technology
• /
• v.56 no.4
• /
• pp.1135-1144
• /
• 2024

With the increasing ratio of renewables in the grid, a low-carbon and stable base load source that also is capable of load tracking is in demand. Sodium cooled fast reactors (SFRs) coupled to thermal heat storage system (THS) is a strong candidate for the need. This research focuses on the designing and performance validation of a two-tank THS based on molten salt to integrate with a 280 MW_th sodium cooled fast reactor. Designing of the THS includes the vital component, sodium-to-salt heat exchanger which is a technology gap that needs to be filled, and designing and parameter selection of the tanks and related pumps. Modeling of the designed THS is conducted followed by the description of operation strategies and control logics of the THS. Finally, the dynamic simulation of the designed THS is conducted based on Fortran. Results show, the proposed power system meets the need of the design requirements to store heat for 18 h during a day and provide 500 MW_th for peak demand for the rest of the day.