• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.8 no.1
• /
• pp.13-25
• /
• 1996

The purpose of this paper is to study heat transfer characteristics of rotating heat pipe with tapered condensers by numerical analysis and experimental method. An experimental investigation has been carried out on thermal resistance between condenser wall and vapor region fo the rotating heat pipe with various taper 0, 1/11.4, 1/38. Heat transfer characteristics by analytical study were applied to describe various Nu numbers on the base of dimensionless condensate film, Re and Pr numbers in both condensers. Comparison between calculated results and experimental data showed qualitatively good agreement and the numerical analysis of this study can be utilized to predict the performance of a rotating heat pipe. The thermal resistance can be decreased by increasing the revolution per minute. Regardless of various dimensionless condensate film, Nu number was largely influenced by saturation temperatures of working fluid.

• Journal of the Korean Solar Energy Society
• /
• v.22 no.4
• /
• pp.18-25
• /
• 2002

For application to medium temperature solar collerctors $(80\sim120^{\circ}C)$, a heat pipe should be designed properly to efficiently transfer heat to a hotter condenser than common applications. Among many wick structure candidates for heat pipes of this type, a slab wick was selected based on promising performance data reported previously. The thermal performance of slab wick heat pipes, screen wick heat pipes and thermosyphons with enlarged condenser section were experimentally investigated for comparison purpose. The heat pipes were 8.0 mm O.D. (evaporator section) and 25.4 mm O.D. (condenser section) made of copper. The experimental data of the heat pipes were analysed in terms of thermal resistance against thermal load and coolant temperature.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.2
• /
• pp.510-515
• /
• 2012

The objective of this study is to investigate low temperature performance characteristics of the thermosyphon with/without wick. Thermosyphons using water as the working fluid are tested with variations of wick, charge amount of the working fluid, outdoor temperature, and heat load for the evaporator section at a low temperature. As a result, the heat transfer of thermosyphon was optimized at the charge amount of 40% and increased with the rise of the outdoor temperatures.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.9
• /
• pp.557-567
• /
• 2016

In this study, the optimal design of heat exchangers, including the evaporator and condenser of a solar-heating ocean thermal energy conversion (SH-OTEC), is investigated. The power output of the SH-OTEC is assumed to be 100 kW, and the SH-OTEC uses the working fluid of R134a and high-performance commercial tubes. The surface heat transfer area and the pressure drop were strongly dependent on the number of tubes, as well as the number of tube passes. To solve the reciprocal tendency between the heat transfer area and pressure drop with respect to the number of tubes, as well as the number of tube passes, a genetic algorithm (GA) with two objective functions of the heat transfer area (the capital cost) and operating cost (pressure drop) was used. Optimal results delineated the feasible regions of heat transfer area and operating cost with respect to the pertinent number of tubes and tube passes. Pareto fronts of the evaporator and condenser obtained from multi-objective GA provides designers or investors with a wide range of optimal solutions so that they can select projects suitable for their financial resources. In addition, the surface heat transfer area of the condenser took up a much higher percentage of the total heat transfer area of the SH-OTEC than that of the evaporator.

• Korean Journal of Materials Research
• /
• v.13 no.7
• /
• pp.460-464
• /
• 2003

Ni and Ti films were deposited by the thermal evaporator, and then annealed in the N$_2$ ambient at 300-80$0^{\circ}C$ in a RTA(rapid thermal annealing) system. Four point probe, AEM, FESEM, AES, and XPS were used to study the effects of Ti-capping layers on the thermal stability of NiSi thin films. The Ti-capped NiSi was stable up to $700^{\circ}C$ for 100 sec. RTA, while the uncapped NiSi layers showed high sheet resistance after $600^{\circ}C$. These results were due to that the Ni in-diffusion and Si out-diffusion were retarded by the capping layer, resulting in the suppression of the formation of NiSi$_2$and Si grains at the surface.

• Journal of the Korean Society of Visualization
• /
• v.17 no.3
• /
• pp.52-58
• /
• 2019

Thermal performance and flow patterns inside the closed loop pulsating heat pipe (CLPHP) were experimentally investigated. For investigating the effect of working fluids, CLPHP was filled with various working fluids including methanol, acetone and ethanol. The thermal resistance was calculated by temperatures in evaporator and condenser and flow patterns were visualized by a digital camera. The thermal resistances for all fluids were decreased as the heat increases. Flow patterns change from static slug to elongated slug flows, bulk circulation and annular flows as the heat increases. Dry-out occurs after annular flows. For reasonable comparison of thermal performances, normalized CHF, Kutateladze number (K_u), was compared. Even though ethanol has smallest CHF, K_u of ethanol is similar with that of methanol. In addition, acetone has the highest K_u that means CLPHP with acetone provides the higher thermal performance compared with CLPHP with other fluids.

• Proceedings of the SAREK Conference
• /
• 2004.11a
• /
• pp.127-127
• /
• 2004

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.201-201
• /
• 2010

The evaporative desalination system with solar energy would be the efficient and attractive method to get fresh water. This study was described the development of Multi Effect Distillation(MED) with solar energy desalination system. The system was designed and manufactured Multi effect distillation on the capacity of $3m^3$/day. The experimental apparatus consists mainly of ejector pump, Hot water pump, flow meter, demister, cooler, evaporator and condenser. Evaporator and condenser were made Shell&Tube Heat Exchanger type with corrugated tube. The experimental variables were chosen $75^{\circ}C$ for hot water inlet temperature, 40, 60 and $80{\ell}$/min for hot water inlet volume flow rate, 6.0 and $8.0{\ell}$/min for evaporator feed seawater flow rate, $18^{\circ}C$ for sea water inlet temperature to cover the average sea water temperature and the salinity of sea water is measured about 33,000 PPM (parts per million). for a year in Korea. This study was analyzed the results of thermal performance of Multi Effect Distillation. The results are as follows, The experimental Multi effect distillation is required about 40 kW heat source for production of $3m^3$/day fresh water. Various operating flow rate was confirm in the experiments to get the optimum design data and the results showed that the optimum total flow was $8.0{\ell}$/min. Comparison of Single Effect Distillation with Multi Effect Distillation showed MED is at least more than double of SED.

• Journal of Energy Engineering
• /
• v.2 no.2
• /
• pp.179-186
• /
• 1993

Heat pipes. applied to a flat plate solar collector, have a long and slender configuration with relatively low heat flux in the evaporator section. Such a heat pipe has a tendency to build-up a liquid pool at the lower part of the evaporator section. and at this pool occurs such complicated phenomena of evaporation and fluid dynamics as superheat, sudden generation of bubble, its likely explosive growth process and flooding, etc. In the present study. we tried to solve these problems by means of adjusting two principal design parameters, the liquid inventory and the installation region of the wick, using 4 heat pipes and 3 thermospheres. The corresponding results can be summarized as follows$\^$1)/. The effective thermal conductances of the heat pipe was greatly improved by eliminating the wick in the adiabatic and condenser sections$\^$2)/. The liquid inventory should be increased by about 40% larger than what is saturated the wick$\^$3)/. In the evaporator section the wick has a favorable effect to reduce both unstable operation by intermittent occurrence of nucleate boiling and response time at the initial start-up process.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.12
• /
• pp.1646-1654
• /
• 2002

A two-phase closed thermosyphon was one of the most effective devices in the removing heat because of its simple structure, thermal diode characteristics, wide operating temperature range and so on. In this study, a two-phase closed thermosyphon(working fluid PFC(C6F14), container copper(inner grooved surface)) was fabricated with a reservoir which can change the fill charge ratio. The experiments were performed in the range of 50~600W heat flow rate and 10~70% fill charge ratio. The results were compared with some correlations that were presented by Rohsenow and Immura et al. in the evaporator, by Nusselt, Gross and Uehara et al. in the condenser and by Cohen and Bayley, Wallis, Kutateladze and Faghri et al. in heat transfer limitation etc.. The heat transfer coefficient at the evaporator increased with the input power. However the effect of the fill charge ratio was nearly negligible. At the condenser, it showed an opposite trend to the evaporator and with increase of the fill charge ratio, showed some enhancement of heat transfer. The heat transport limitation was occurred by the dry-out limitation for small fill charge ratio(10%) and presented about 100W. For the case of large fill charge ratio(Ψ$\geq$40%), it was occurred by the flooding limitation at about 500W.