Fill Charge Ratio Research Articles

EXPERIMENTAL AND THEORETICAL STUDY OF TWO-PHASE HEAT PIPE

In this study, thermal characteristics of a two-phase closed heat pipe were investigated experimentally and theoretically. A two-phase closed heat pipe (copper container, Fluorocarbon FC-72 (C6F14) working fluid) was fabricated to examine its performance under the effect of input heat flux range of 250–1253 W/m2 , 70% fill charge ratio and various tilt angles. The temperature distribution along the heat pipe, input heat to evaporator section, and output heat from condenser were monitored. A comprehensive mathematical model was developed to investigate the steadystate heat transfer performance of a two-phase closed heat pipe. A steady state analytical model, is presented to determine important parameters on the design of two-phase closed heat pipe, including temperature levels and heat transfer coefficients for condenser and evaporator. The experimental and simulation results of this work are found in good agreement. The experimental boiling heat transfer coefficients were compared with existing previously reported correlations.

EXPERIMENTAL INVESTIGATION OF INDIVIDUAL EVACUATED TUBE HEAT PIPE SOLAR WATER HEATING SYSTEMS

lar water heating systems with heat pipes of three diameter groups of 16, 22 and 28.5 mm. The first and third groups had evaporator lengths of 1150, 1300 and 1550 mm. The second group had an additional length of 1800 mm. all heat pipes were of fixed condenser length of 200 mm. Ethanol at 50% fill charge ratio of the evaporator volume was used as the heat pipes working fluid. Each heat pipe condenser section was inserted in a storage tank and the evaporator section inserted into an evacuated glass tube of the Owens- Illinois type. The combined heat pipe and evacuated glass tube form an active solar collector of a unique design.The resulting ten solar water heating systems were tested outdoors under the meteorological conditions of Baghdad, Iraq. Experiments were carried out with no load, intermittent and continuous load conditions. Some tests, at no load, were carried out with and without reflectors. The overall system efficiency was found to improve with load conditions by a maximum of 55%. The system employing an 1800 mm evaporator length and 22 mm heat pipe (HP7) showed the best performance by higher water temperatures, overall useful energy gain and efficiency at various load conditions. System performance was predicted theoretically using electrical analogy derived from an energy balance. An agreement of within 14% was obtained between theoretical and experimental values.

Comparative experimental investigation of two evacuated tube solar water heaters of different configurations for domestic application of Baghdad- Iraq

Evacuated tube solar water heaters have drawbacks that limit their performance against local habits of hot water consumption, like slow water temperature rise and slow response to loading. A method to enhance their performance is using heat pipes as heat transport tools from the solar collectors to the storage water. The present work investigates the enhancement of thermal performance of evacuated tube solar water heaters subjected to (non- standard) load conditions and weather conditions of Baghdad- Iraq. Two identical evacuated tube solar water heaters (both of 120 l capacity and 20 evacuated tube solar collectors) are investigated experimentally. One system works with thermosyphon (natural convection); the other system incorporates 20 wickless heat pipes (closed thermosyphon tubes), of 16 mm diameter and 1750 mm length and are charged with methanol as working fluid at 50% fill charge ratio, as thermal conductors from the solar collectors to the storage tank. A comparison of performance of the two solar systems has been conducted by subjecting them simultaneously to different load conditions namely; no load, intermittent and continuous loading to simulate the hot water consumption habits in the local community. Extra experiments were conducted at sunny days and various weathers at no load to verify the thermal diode effect of heat pipes and the effect of weather conditions on the systems performance. Experimental results reveal an enhancement in overall daily efficiency of the heat pipe system over the thermosyphon system by 22.5% for no load, 42.5% for intermittent loading and 32.4% for continuous loading. The heat pipe system produced higher temperatures and better response at all load conditions and adverse weather conditions that make it more suitable for local domestic application. The thermosyphon system performs suitably with no load and intermittent load at small removal quantities. Results agree with those in the literature.

Numerical study of flat plate solar collector performance with square shape wicked evaporator

In this work, a system of a heat pipe is implemented to improve the performance of flat plate solar collector. The model is represented by square shape portion of the evaporator section of wicked heat pipe with a constant total length of 510 mm, and the evaporator section inclined by an angle of 30o. In this models the evaporator, adiabatic and condenser lengths are 140mm, 140mm, and 230mm respectively. The omitted energies from sunlight simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 240%. The efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20o C). The numerical result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRAE standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of wicked heat pipe is decreases, where the heat transfer from the evaporator to condenser increases. The numerical results showed the performance of solar collector with square shape evaporator greater than other types of evaporator as a ratio 15 %.

Experimental study of flat plate solar collector performance with twisted heat pipe

In this work, a system of heat pipe is implemented to improve the performance of flat plate solar collector. The experiment rig consists of sun light simulator, flat plate, heat pipe (wickless), heat exchanger, and measurement instruments. The model is represented by twisting portion of the evaporator section and also inclined by an angle of 30° with a constant total length of 1140 mm. In this model the evaporator, adiabatic and condenser lengths are 780mm, 140mm and 230mm respectively. The omitted energies from sun light simulator are 200, 400, 600, 800 and 1000 W/m2 which is close to the normal solar energy in Iraq. The working fluid for all models is water with fill charge ratio of 30% and the efficiency of the solar collector is investigated with three values of condenser inlet water temperatures, namely (12, 16 and 20° C). The experimental result showed an optimum volume flow rate of cooling water in condenser at which the efficiency of collector is a maximum. This optimum agree well with the ASHRA standard volume of flow rate for conventional tasting for flat plate solar collector. When the radiation incident increases the thermal resistance of thermosyphon is decreases, where the heat transfer from the evaporator to condenser increases. The experimental results showed the performance of solar collector with twisted evaporator greater than other types of evaporator as a ratio 13.5 %.

Flow and heat transfer in a rotating heat pipe with a conical condenser

The flow and heat transfer phenomena in a rotating heat pipe (RHP) with a conical condenser were numerically studied by using a comprehensive numerical model based on the full discretized Navier-Stokes equations. The impact of parameters such as the heat transfer rate, rotational speed, fluid fill charge ratio and working fluid property on the performance of the RHP were examined. The operation characteristics of the RHP was captured in detail by using the present model. It is shown that as the heat transfer rate increased, the temperature gradient along the RHP experienced an increase. The overall thermal resistance of the RHP was reduced due to the enhancement of natural convection in the liquid at the evaporator section with larger heat transfer rates. The RHP has better performance at higher rotational speed in virtue of the enhancement of natural convection induced by larger centrifugal acceleration. The charge of fluid has impact on the performance of the RHP since the thermal resistance of the evaporator experienced an increase with the increase in the fluid fill charge ratio. As the working fluid, water has a better performance than ethanol, due to a larger thermal conductivity, a larger latent heat, and a bigger thermal expansion coefficient.

Investigation of a long term passive cooling system using two-phase thermosyphon loops for the nuclear reactor spent fuel pool

Given postulated accidents that go beyond the plant design basis, long term passive cooling for the nuclear reactor spent fuel pool is important to demonstrate. Large amount of heat transport with small temperature difference is required. Two-phase thermosyphon loops are suitable for these cases. Flow and heat transfer characteristics of a two-phase thermosyphon loop were numerically investigated using RELAP5 code. Effects of fill charge ratio on the heat transfer were analyzed. The fill charge ratio should be chosen between 30% and 80%, smaller than 30% or larger than 80% will reduce the heat transfer. Based on the analysis of two-phase thermosyphon loops, a complete design of a passive cooling system for the spent fuel pool was proposed. An analysis method for decoupling of the thermo-hydraulics of the water natural circulation in spent fuel pool, two-phase flow of ammonia in thermosyphon loop and air natural circulation in cooling tower was presented. The results indicate that 1528 two-phase thermosyphon loops can passively remove 16MW decay heat from the spent fuel pool successfully. Finally, the velocity and temperature distributions in the spent fuel pool were numerically simulated using ANSYS FLUENT software. It was proved that natural circulation of water in spent fuel pool can be realized with the present design. The temperature uniformity was fairly well and the maximum water temperature was 81°C.

An Experimental Study on a Sodium Loop-type Heat Pipe for Thermal Transport from a High-temperature Solar Receiver

Abstract A loop-type heat pipe was fabricated and tested to transport high-temperature thermal energy from a solar receiver in a CSP application. The purpose of the heat pipe in this study was to transport an 800-W thermal load at 1000 K to a specific energy conversion device 0.5 m in distance from the solar receiver. The container wall and transport lines of the loop-type heat pipe were made of stainless steel 304, and the working fluid was sodium. The evaporator and condenser were disk-type containers with diameters of 122 and 216 mm, respectively, though bothhad a height of 20 mm. The diameters of the vapor and liquid lines were 12.7 and 9.53 mm, respectively. The total length of the loop was approximately 1.4 m. A pillar structure with a diameter of 43 mm and height of 114 mm was installedin the center region of the condenser to interface with an AMTEC device that had a unique geometry. It was desired that the upper surface of the condenser as well as the whole outer surface of the pillar would have temperatures as close as possible during heat discharge. As one of the unique features in this study, the liquid line was located close to the vapor line for a preheating effect to reduce the frozen-startup time. The influence of the fill charge ratio of the working fluid as well as operating conditions such as the thermal load and the cooling condition in the condenser were analyzed with respect to the performance indices of the heat pipe, including the effective thermal conductance, the thermal resistance, and the maximum temperature difference. The optimum fill charge ratio of the heat pipe was 32% based on the evaporator volume.

루우프형 2상 유동 열사이폰의 응축열전달 특성에 관한 연구

This study concerns the performance of condensation heat transfer in two-phase loop thermosyphons. In the present work, R134a has been used as the working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, heat flux and wind speed of condensation have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The optimum liquid fill charge ratio for the best condensation heat transfer rate was 80%.

Experimental investigation of thermosyphon loop thermal performance

This paper presents the experimental investigation of a two-phase closed loop. The experimental setup consists of an evaporator and a condenser connected by two insulated tubes. Using water as a working fluid, the experiments were conducted to evaluate the performance of a thermosyphon: the effects of fill charge ratio, the condenser jacket coolant inlet temperature and the mass flow rate. Finally, the results show that the optimal fill charge ratio is between 7% and 10%, the cooling system has the optimal performance when controlling the condenser jacket water temperature and flow rate at 5°C and at 0.7l/min respectively. System, loop, evaporator, vapor line, condenser, and liquid line thermal resistances analysis is directed additionally to the pressure and temperature evolutions for the better understand of the main parameters affecting the cooling system performance.

Heat Transfer Performance of a Self-Oscillating Heat Pipe using Pure Water as Working Fluid

Department of Mechanical System Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan (Received 4 January 2012; received in revised form 22 March 2012; accepted 26 April 2012) Abstract This experimental study is performed to investigate heat transfer performance of a new self-oscillating heat pipe in the condition of different fill charge ratios and different heat fluxes. In this experiment, pure water is employed as the working fluid. The heat pipe is composed of a heating section, a cooling section and an adiabatic section. The heating and cooling sections have the same size and are connected by four circular parallel tubes. The corresponding external dimensions are 45mm in length, 45mm in width and 8mm in thickness, and the internal dimensions are 42mm, 42mm and 5mm, respectively. The adiabatic section is consisted of four parallel circular tubes whose dimension is φ6 (external diameter) x φ5 (internal diameter) x 45 (length) mm. A series of experiments with different fill charge ratios and heat fluxes were carried out to measure temperature of the heat pipe. It is found that heat transfer performance as well as effective thermal conductivity of the heat pipe affected by various operating conditions. diameter and is also charged with a fixed amount of Key words Heat Transfer Performance, Self-Oscillating Heat Pipe, Working Fluid, Fill Charge Ratio, Effective Thermal Conductivity transfer characteristics of a self-oscillating heat pipe using 1. Introduction There are a lot of equipment or parts generating high heat amount during their working process – those can be called heating elements. Therefore, in order to maintain their technical features as well as their longevity, they need to be kept cooled and maintained at an appropriate temperature. For the elements that generate a high amount of heat during working process, the conventional cooling methods, e.g., heat sink, fans, cooling fins do not meet the cooling requirements. Direct cooling method using circular water have been proved to be effective, but not always applicable, especially with electrical or electronic devices, since during cooling process, the electric or electrical devices should be insulated from each other or other surrounding devices. Thus, a study to make a corresponding cooling device is essential. Manufacturers now make a number of different devices for cool heating elements. The most common device is a heat pipe. It works base on boiling heat transfer and condensation heat transfer principles. Working fluid inside the heat pipe absorbs heat and boils at a certain pressure value in the heating area. are measured by the digital multi-meter (AC/DC POWER HITESTER 3334). After boiling, working fluid becomes vapor and evaporates to the already cooled area and the vapor releases latent heat to this section and is condensed to working fluid again. After that, working fluid travels back down into the heating area by capillary principle with a wick composed of a porous substance. This device was suggested by Peterson, 1994; Faghri, 1995; Boo, 1998. Despite being widely developed and applied, this type of heat pipe still has some weaknesses. They need a complicated structure – wick to take working fluid back to the heating area. Therefore, its performance will be decreased due to blending between condensed working fluid and evaporating vapor. In addition, with this design, it is difficult to manufacture a fine product. Akachi (1988) suggested “The loop type capillary heat pipe” which is a self- oscillating heat pipe with three sections: a heating section, an adiabatic section and a cooling section. This type of heat pipe is usually made by closed circuit copper tube with calculated internal working fluid, it has no wick at all. With the study of Akachi in 1990 and Koizumi in 1992, this heat pipe is desirable with high performance. Seok Hun Yoon et al (2002) also investigated the heat pure water as a working fluid, the excellent results were obtained in this study but this heat pipe was just applied with low heat fluxes. With the same purpose to develop heat pipe, this study developed and investigated a new heat pipe with a very simple structure. In this research, the heat transfer performance was investigated with different fill charge ratios and different heat fluxes. The maximum heat flux applied for the heat pipe is too high – 250 kW/m

HEAT TRANSFER PERFORMANCE OF A SELFOSCILLATING HEAT PIPE USING PURE WATER AND EFFECT OF INCLINATION TO THIS PERFORMANCE

This experimental study is performed to investigate heat transfer performance and effect ofinclinations to a self-oscillating heat pipe developed. In this experiment, pure water isemployed as the working fluid. The heat pipe is composed of a heating section, a coolingsection and an adiabatic section. The heating and cooling sections have the same size andare connected by four circular parallel pipes. The corresponding external dimensions are45mm in length, 45mm in width and 8mm in thickness, and the internal dimensions are42mm, 42mm and 5mm, respectively. The adiabatic section is consisted of four parallelcircular pipes whose dimension is 6 (external diameter) x 5 (internal diameter) x 45(length) mm. According to the experimental results, the effective thermal conductivity ofthe heat pipe in the case of fill charge ratio at 100% is higher than that of 30%and this effective thermal conductivity is decreased when the angle between the axisof the heat pipes and vertical direction is increased.

A comparison of the heat transfer performance of thermosyphon using a straight groove and a helical groove

This study is focused on the comparison of heat transfer performance of two thermosyphons having 60 straight and helical internal grooves. Distilled water has been used as working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, the inclination angle and operating temperature were used as experimental parameters. The heat flux and heat transfer coefficient are estimated from experimental results. The conclusions of this study may be summarized as follows; Liquid fill charge ratio, inclination angle and geometric shape of grooves were very important factors for the operation of thermosyphon. The optimum liquid fill charge ratio for the best heat flux were 30%. The heat transfer performance of helically grooved tube was higher than that of straight grooved tube in low inclination angle (less than 30°), but the results were opposite in high inclination angle (more than 30°). As far as optimum inclination angle concerns, range of 25°-30° for a helically grooved tube and about 40° for a straight grooved tube are suggested angles for the best results.

내부에 그루브와 스크린 메쉬를 갖는 평판 스트립형 히트파이프의 열성능에 대한 실험적 연구

The thermal performance of a flat-strip heat pipe with inner grooves and the screen mesh cover was investigated experimentally. The heat pipes were made of 2024 aluminum alloy of which the dimensions were 30(W) x 4(T) x 150(L) ㎜. The cross sectional dimensions of inner groove were 0.4 x 0.9㎜ and the space between grooves was 0.6㎜. To enhance the capillary force, fine screen meshes were attached to cover the grooved inner surface. In the grooved heat pipes without screen mesh cover, the maximum thermal load of 180 W (12 W/㎠) was achieved for operating temperature below 130℃ at horizontal position. The beat pipes with screen mesh cover showed the thermal resistances less than one third of those without screen mesh cover, and showed less fluctuation in the thermal resistance values. Furthermore, the thermal performance of the former exhibited less dependence on the tilt angle and the fill charge ratio.

Isothermal characteristics of a rectangular parallelepiped sodium heat pipe

The isothermal characteristics of a rectangular parallelepiped sodium heat pipe were investigated for high-temperature applications. The heat pipes was made of stainless steel of which the dimension was 140 m(L) ×95m(W) ×46m(H) and the thickness of the container was 5 mm. Both inner surfaces of evaporator and condenser were covered with screen meshes to help spread the liquid state working fluid. To provide additional path for the working fluid, a lattice structure covered with screen mesh wick was inserted in the heat pipe. The bottom surface of the heat pipe was heated by an electric heater and the top surface was cooled by circulating coolant. The concern in this study was to enhance the temperature uniformity at the bottom surface of the heat pipe while an uneven heat source up to 900 W was in contact. The temperature distribution over the bottom surface was monitored at more than twenty six locations. It was found that the operating performance of the sodium heat pipe was critically affected by the inner wall temperature of the condenser region where the working fluid may be changed to a solid phase unless the temperature was higher than its melting point. The maximum temperature difference across the bottom surface was observed to be 114°C for 850 W thermal load and 100°C coolant inlet temperature. The effects of fill charge ratio, coolant inlet temperature and operating temperature on thermal performance of heat pipe were analyzed and discussed.

충전율의 변화가 밀폐형 2-상 열사이폰의 열전달 특성에 미치는 영향에 관한 연구

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(C_6,F_14), 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(??≥40%), it was occurred by the flooding limitation at about 500W.

중온 작동 범위에서의 슬랩윅 히트파이프 성능에 관한 실험 연구

A slab-wick heat pipe was fabricated and tested for applications where the condenser temperature is in a range of 80 to 120°C. The pipe material was 9.53 mm 0.0. copper tube and the working fluids were ethanol and water. The total length of the heat pipe was 1.6 m, in which evaporator section was 1.4 m and the condenser was 0.10 m. The slab was a composite wick structure fabricated with STS316 wire screens. Thermal load was varied for a specified fill charge ratio and inclined<br/> angle. The optimum fill charge ratio was identified to be 110% based on a theoretical calculation of<br/> the pore space in the slab wick of the heat pipe. The maximum thennal load was 120W for ethanol and the same was 200W for water with the condenser temperature of 80°C. The thermal performance of the slab wick heat pipe is analysed in terms of temperature characteristics and thermal resistance against thermal load, tilt angle and fill charge ratio.<br/>

A study on the improvement of heat transfer performance in low temperature closed Thermosyphon

The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal grooves. Three different working fluids (distilled water, methanol, ethanol) are used with various volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube. The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum inclination angle for this study is 20°-30° from the horizontal position.

Heat transfer characteristics of a two-phase closed thermosyphon to the fill charge ratio

In this study, the heat transfer characteristics of a two-phase closed thermosyphon were investigated. For the test, a two-phase closed thermosyphon (copper container, FC-72 (C 6F 14) working fluid) was fabricated with a reservoir which could change the fill charge ratio. The experiments were performed in the range of 50–600 W heat flow rate and 10–70% fill charge ratio. Some findings are as follows. The heat transfer coefficients of the evaporator to the fill charge ratio were nearly negligible. These presented about 1–5 kW/m 2 K with the increase of heat flux and compared with those of smooth surface, showed some enhancement by the grooved surface. However at the condenser, the heat transfer coefficients showed some enhancement with the increase of fill charge ratio by the expanded working fluid pool. And the heat transport limitations appeared in different ways to the fill charge ratio. For the relatively small fill charge ratio ( Ψ<20%), it presented about 100 W ( Ψ: 10%) by the dry-out limitation. For the large fill charge ratio, it occurred by the flooding limitation and the maximum heat flow rate was about 500–550 W ( Bo: 26–28), 230 W ( Bo: 18.3) respectively and the Kutateladze number was about 1.9–2.1.

An analytic study on laminar film condensation along the interior surface of a cave-shaped cavity of a flat plate heat pipe

An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical wall, the average heat transfer coefficient in the cave-shaped cavity presented 10-15% lower values due to the fact that the average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about ??? = 3~7%, ???/=0.5-1.3%, respectively, in the range of heat flux ?"=5~90kW/㎡