Thermosyphon Research Articles

Performance of copper oxide/distilled water nanofluid in evacuated tube solar collector (ETSC) water heater with internal coil under thermosyphon system circulations

In this study, the effect of CuO/distilled water nanofluid on the performance of evacuated tube solar collector (ETSC) water heater with internal coil under thermosyphon system circulations was experimentally investigated. The volume fraction of nanoparticles was considered at 0.03–0.06%. The mass flow rate of water passing through the coil was varied from 20 to 60L/h. ASHRAE standard 86–93 was considered to calculate the efficiency of the collector. From the study, we found that the efficiency of ETSC increase when the nanofluid was used as an absorption medium. CuO nanofluids at 0.03% volume fraction in ETSC gave enhancement up to 14%, when compared to water.

Modeling of natural convection and radiative heat transfer in inclined thermosyphon system installed in the roof of a building

AbstractSome construction laws require the integration of an open thermosyphon system having multiple functions to the building roof. In order to analyze the efficiency of this system, a numerical model was developed. This model is based on the study of the natural convection coupled with radiative heat transfer in an inclined air channel. Two configurations are studied, the first one is a simple channel formed by two parallel plates and the second one is equipped with fin blades joined to the upper plate. The air flow in the channel which is due to the buoyancy forces is fully turbulent and the turbulence was modeled using the k‐ε model. Some numerical results obtained were validated using the experimental ones of Khedari et al. (2002) and those of Nouanégué and Bilgen (2009). The effect of the radiative heat transfer on the mean Nusselt number was shown. Correlations for Nusselt numbers were obtained for the two configurations as functions of the geometric parameters and the Rayleigh number. The main objective of this study is to use these correlations in other models to facilitate the operation of this system

Performance enhancement of air conditioning using thermosyphon system’s energy storage unit for cooling refrigerant before entering the condenser

This research focused on application of a heat transfer device, a Thermosyphon system energy storage unit (TSES unit), to air conditioning systems. The aim was to experimentally investigate use of the TSES unit to provide energy savings and enhance the heat transfer of the refrigerant. The TSES unit was installed between the compressor and the condenser. R-22, R-410A and R-134a refrigerants were used as working fluids in the thermosyphon heat pipe. Comparison of a conventional air conditioning system with the TSES unit-based air conditioning system shows that R-134a provides the best performance enhancement of the investigated refrigerants. The results show that the TSES unit-based system with R-134a reduced the refrigerant temperature at the condenser inlet to 11.67 °C, had the highest coefficient of performance with an increase of 22.75 %, increased the system’s cooling by 19.62 % and reduced power consumption by up to 3.76 %. This confirms that the device can lead to real energy savings.

Вычисление распределений температуры в грунте, охлаждаемом системой “ГЕТ”, методом стохастического прогнозирования

Вычисление распределений температуры в грунте, охлаждаемом системой “ГЕТ”, методом стохастического прогнозирования

Heating Performance Study on a Passive Solar Heater

A passive thermosyphon heating system was designed, fabricated and tested for its thermal performance in semi-arid and four-season climate of Pakistan. The heating system design was based on a two-stage storage and natural thermosyphon circulation of the water. The objective of the study was to enhance the heating performance of the thermosyphon systems by using a semicircular steel pot collector, water carrying copper coil cover, two step water storage, and side mirror reflectors. The experiments were conducted during April to July 2014 when ambient temperature was reported to vary between 32°C and 44°C. In continuous flow mode operation, the hot water temperature remained between 46°C and 78°C. Since water temperature in the range of 45°C to 50°C is considered suitable for the domestic use, the presented design can easily reach the temperatures even higher than those acceptable for the domestic use.

Temperature distribution in soil cooled by a HET thermosyphon system: prediction by stochastic analysis.

Temperature distribution in soil cooled by a HET thermosyphon system: prediction by stochastic analysis.

THE INFLUENCE FACTORS ON HEAT TRANSFER PERFORMANCE OF LOOP THERMOSYPHON SYSTEM

The influence factors on the heat transfer performance of a loop thermosyphon system, a passive cooling device, are studied systematically. The parameters investigated include types of enhanced boiling structure, the depth to width ratio of enhanced boiling structures, the gap of evaporator, the condenser height and the inclination of evaporator. The results show the depth to width ratio and the condenser height has positive influences on the heat transfer performance. An optimal channel gap of evaporator exists and possesses better heat transfer performance. The inclination effect of evaporator may not be favorable to heat transfer. Among those, the horizontal and 90° inclination of evaporator has better cooling performance.

Thermosyphon-assisted cooling system for refrigeration applications

Residential refrigeration is one of the largest contributors to home appliance energy consumption in the U.S. This energy use is nearly doubled if commercial refrigeration is included. By using cold outside temperatures for cooling, however, energy savings can be realized. In this work, a thermosyphon-assisted cooling system for a household refrigerator is presented. A single finned copper-tube thermosyphon with methanol as the working fluid is used. An environmental chamber that can reproduce outside ambient temperatures to −5 °C is located above the refrigerator. Results are presented for different outside temperatures, fan speeds, and filling ratios in the thermosyphon. The electricity use for both the original equipment refrigeration and the thermosyphon system is reported. The interior temperature is found to vary depending on the number of fans that are used to blow air over the thermosyphon evaporator in the refrigerated space. This can be used to produce localized micro-climates within the refrigerated space for further energy savings.

Experimental investigations of heat transfer from an internally finned two phase closed thermosyphon

This paper reports the results of an experimental investigation of heat transfer from an internally finned thermosyphon charged with either water or acetone. Six constant area fins with a rectangular cross section are placed internally along the length at the condenser section. The ratio of initial liquid pool volume to the evaporator volume, known as the filling ratio in a thermosyphon system, has been varied in this study. Experiments are carried out for filling ratios of 20, 50, and 80% for two working fluids (i) water and (ii) acetone. Results show that a fill ratio of 50% gives better heat transfer performance. Providing internal fins at the condenser produces additional condensation which improves the thermal performance of the thermosyphon by 17% in terms of the temperature reduction at the source and sink and 35.48% in terms of reduction in thermal resistance at lower heat inputs. The thermosyphon is tested between power levels of 50 and 275W.

Investigation of solar hybrid system with concentrating Fresnel lens, photovoltaic and thermoelectric generators

Summary An experimental model of a solar hybrid system including photovoltaic (PV) module, concentrating Fresnel lens, thermoelectric generator (TEG), and running water heat extracting unit was created and studied. The PV module used was of c-Si and TEG of Bi2Te3; the Fresnel lens (solar concentrator) and TEG share an optical train, whereas PV module was illuminated separately with non-concentrated light. Heat extracting unit operated in thermo siphon mode. In climatic conditions of Mexico (Queretaro, 20o of North latitude, summer time), the Fresnel lens accepted 120 W of solar radiation power, and the system generated 7.0 W of electric power and 30 W of thermal one. The discussion is made of the possible characteristics of a hypothetical hybrid system where all its elements share the same optical train. Copyright © 2016 John Wiley & Sons, Ltd.

Flow instabilities in a horizontal thermosyphon reboiler loop

Thermosyphon systems have been the subject of several studies due to instability issues negating their attractive high heat fluxes, low temperature gradients requirement, reduced weight and simple, pump-less system. There is a dearth of design data for horizontal thermosyphons hence the transient behaviour of a horizontal thermosyphon reboiler loop has been studied experimentally here. Most studies here have explored and defined geysering instability in single and parallel vertical columns with closed bottom end. This study presents geysering detected in 51mm riser of a horizontal thermosyphon reboiler.Experiments were undertaken with water as the process fluid and steam as the heating medium, using 6–20kW/m2 heat flux, 1.165–1.265m static head and a range of recycle flow restrictions. Pressure, temperature and flow rate data were continuously logged at 100Hz. Flow rate was examined as a significant indicator of instability since it is the parameter with highest and varied amplitude of oscillation. Heat flux is most significant for stability: above 20kW/m2, the system is stable; between 11 and 20kW/m2 there are varying degrees of sustained oscillations and below 11kW/m2 flow rate is low. Reboiler inlet flow restriction also stabilises the system by reducing the flow rate to such a level that heat transfer rate can maintain a consistent vapour product rate. Static head influences the recirculation rate and subcooling at the reboiler inlet, but has a secondary effect on stability. Churn flow pattern is detected in the riser as a characteristic aftereffect of the cyclic instability.

Investigation on the Optimum Volume-Filling Ratio of a Loop Thermosyphon Solar Water-Heating System

Volume-filling ratio of the working fluid has a predominant effect on the system performance of a closed two-phase solar water-heating (SWH) system. To study this effect, a prototype of a loop thermosyphon SWH system, which uses remolded flat-plate solar collector as the evaporator and the coil pipe in the water tank as the condenser, was set up. A set of long-term outdoor experiments under 10%, 20%, 30%, 50%, and 70% volume-filling ratios were conducted in this paper. R600a was used as working fluid. Loop thermosyphon solar collector thermal performance and system thermal performance under different volume-filling ratios, including the temperature distribution of loop thermosyphon evaporator, were presented. It is shown that the loop thermosyphon solar collector and the system had a better thermal performance than the conventional ones under 30% and 50% volume-filling ratio, and the loop thermosyphon evaporator had an even temperature distribution when the volume-filling ratio was higher than 30%. The optimum volume filing ratio lies in between 30% and 50% of the whole system volume.

A two-phase closed thermosyphon with an adiabatic section using a flexible hose and R-134a filling

This research aimed to investigate the effects of bending and tilting in a flexible hose thermosyphon (TS) on thermal performance. The adiabatic section of the TS was constructed of a Teflon hose with an inner diameter of 12.7mm, while the evaporator and condenser were made of straight copper tubing with an identical diameter of 17.4mm. The proposed TS was charged with R-134a refrigerant. The effects of bending positions and tilt angles on evaporator temperature, flow resistance, overall thermal resistance and heat transfer characteristics (Q/Q90) were tested in comparison with a TS that is vertically oriented. At the same tilt angle, bending at the upper end of the flexible hose would decrease TS performance more than bending at the lower end. Bending at both ends would result in the lowest TS performance. The optimum tilt angle for most cases was 45°, except for the case with bending at both ends, which was 60°.

Study of HTS Machine System Cooling With a Closed-Loop Thermosyphon: Stability of Unsteady Heat Load and Transient Conduction

Thermosyphoning (TS) is a heat exchange mechanism that uses a circulating refrigerant based on natural convection with no need for a mechanical pump. This cooling technique has been employed to circulate liquid coolant and gaseous coolant for high-temperature superconductor (HTS) rotating machine systems. These machines operate with an HTS field pole in the temperature range from 25 to 40 K, which are suitable temperatures for the survivability of HTS wires. The cryomechanical components are simple; there are a condenser, an evaporator, and adiabatic tubes located between the condenser and the evaporator. For applications to ship propulsion motors or generators of the radial gap type, the liquid/gas coolant flow along the adiabatic tube inside the rotating shaft may be considerably affected by the ship's rolling and/or pitching motion. In this work, we studied the temperature stability and heat load survivability of cryogenic TS, by constructing a 100 W @ 30 K-grade model. We investigated the temperature, thermal resistance, and heat flux, with a maximum load up to 60 W, of ground and onboard tests. The observed TS behavior indicates that there is sufficient survivability to assemble megawatt-class ship propulsion systems.

Numerical Analysis on the Fluid Flow and Heat Transfer in Corrugated Channel

The present work concerns the study of Numerical analysis on the fluid flow and heat transfer in corrugated channel with various geometry configurations, under constant heat flux conditions is considered. This is largely studied both experimentally and numerically due to their wide industrial application in various fields such as nuclear reactor urgency, solar boiler, heat exchangers and thermo siphon solar capturers, etc. A great deal of relevant research work consists of numerical simulations of forced convection mechanisms with turbulent flows in corrugated channel. We are interested in determining the flow for various amplitudes and periods. The influence of geometry on several factors such as: temperature, the local Nusselt number, friction number, turbulent kinetic energy k and its dissipation e are considered. Based on the Navier-Stokes equations, these equations were solved by a CFD technique using the Finite Volume Method. The results show that when we gradually increase the amplitudes of the protuberance part (say a=0.03, a=0.06) the maximal temperature increases with the increase of amplitude. This is due to the rise of the heat transfer surface of the modified wall. Regarding heat transfer parameters, the results show that the number of local Nusselt varies accordingly with the amplitudes and number of periods. This explains that the modified wall is affected locally by a pure conduction. The results of this study are expected to lead to guidelines which will allow the selected wavy channel geometry configuration for designing heat exchanger that increase thermal performance.

Experimental and Cfd Studies On Heat Transfer and Friction Factor Characteristics of A V-Trough Solar Water Heater

Experimental investigation of heat transfer and friction factor of a modified V-trough solar water heater using thermo siphon has been conducted and the results are compared with flat plate collector for same operating conditions. CFD analyses for the experimental conditions are also made. Results conclude that, heat transfer and friction factor are higher in modified V-trough solar water heating system.

Numerical Analysis of Thermosyphon Solar Water Heaters

This paper presents the modeling and simulation as well as validation of a natural circulation closed thermosyphon glass tube solar collector water heater. Energy conservation equations for the heat transfer fluid flow and the storage tank were written in finite-difference form, integrated and solved to yield the characteristics of the thermosyphon system at different solar insolations and water mass flow rate conditions as well as water temperatures. Comparison between experimental data and numerical prediction of the proposed showed that the model predicted fairly the evacuation of storage tank temperature at various initial temperature of the water at the storage tank.

Effect of receiver diameter ratio on thermal performance of natural circulation steam generation system as applied to parabolic trough collector using water as working fluid

Flow boiling heat transfer of water in a thermosyphon loop based natural circulation solar steam generation system with a horizontally-arranged receiver towards parabolic trough collector (PTC) applications was studied experimentally. The diameter ratio (Rd) of the receiver was varied over a range from 1.0 to 2.0 to explore its effect on flow boiling heat transfer, especially the stratified flow boiling characteristics in the receiver tube, and thermal performance of the thermosyphon system. The results show that flow boiling heat transfer in the receiver was improved since Rd was increased to 1.2 due to a flow pattern transition which eliminated the effect of gas–liquid stratification on surface wettability deterioration in the receiver. An optimal tube diameter ratio was found to be 1.4 with a heat transfer coefficient enhancement by 12.2% in comparison to the baseline case. Simultaneously, the rise of Rd resulted in an enhancement of backflow in the inlet of receiver. The effect of backflow on isothermal improvement in the falling tube of thermosyphon, however, was found to be irrelevant to the total heat pipe thermal resistance (RHP).

Investigation of a Novel Combination for Both Solar Chimney and Solar Tower Systems

The aim of this work was to propose a novel system combines both solar chimney and thermo siphon solar tower systems. To this end, theoretical study to the proposed system was conducted. In this new system, the solar tower was installed at the exit of the solar chimney. The results of the theoretical study showed that, the new system generates more power compared with the conventional system. It was found that the maximum power extracted from the new system was about two times that obtained from the conventional system at the same height, for the specified range studied in this work. In addition, it was found that the new system has higher overall efficiency and generates higher speeds of air at the chimney inlet. This increase in both maximum power and air speed at the chimney inlet from the new system is enhanced with the rise in solar irradiance, radius of collector, and ratio of solar tower height to solar chimney height. Moreover, the results indicated that there is a certain ratio between solar tower length and width at which the maximum extracted mechanical power reached a maximum value for the specified parameters of solar irradiance, collector radius, height of chimney, and height of solar tower.

Comparison of the effects of Al 2 O 3 and CuO nanoparticles on the performance of a solar flat-plate collector

Abstract To improve the efficiency of solar flat-plate collectors further, a study had been carried out wherein the conventional working fluid was replaced by nanofluids. A 25-L/day solar flat-plate water heater with collector area of 0.5 m 2 $\text{m}^2$ has been designed and fabricated. The thermosyphon system of the solar water heater was monitored at 15 locations using T-type thermocouples. Alumina and CuO nanoparticles were synthesized and characterized using Brunauer–Emmett–Teller and X-ray diffraction techniques and dispersed using ultrasonic mechanism. To stabilize the system at an optimum level, the collector is operated with volume fractions of 0.2% and 0.4% of synthesized Al 2 O 3 and CuO nanoparticles mixed with distilled water and used in the solar flat-plate collector. The temperature profile was compared with different volume fractions of the nanoparticles in the flowing medium. Enhanced heat transfer was observed in the solar flat-plate collector using nanoparticles, and hence, it is inferred that addition of nanoparticles improves the efficiency of the solar water heaters. This paper details the temperature profile observed in the collectors, variation of insolation over the day, and change in efficiency both on the primary side (collector) and on the secondary side (storage tank) of the solar water heater.