Effect of solar heat flux and thermal loading on the flow distribution within the riser pipes of a closed-loop solar thermo-syphon hot water system

Solar energy is one of the main sources of renewable energy that is abundantly available throughout the world. Solar energy can be used for useful purposes through a number of mechanical artefacts. One such artefact is known as Thermo-syphon, which typically contains water as its working fluid. One of the major applications of Thermo-syphon is within the residential and industrial units, where a constant supply of hot water is required. The use of Computational Fluid Dynamics (CFD) based solvers has recently been proven capable of predicting the flow behaviour within thermo-syphons with reasonable accuracy. Hence, the present study focuses on using a commercial CFD based solver to predict the flow behaviour within the riser pipes of a thermo-syphon with varying solar heat flux and thermal loading conditions. In order to qualitatively and quantitatively analyse the flow structure within the riser pipes of the thermo-syphon, velocity magnitude and static temperature distributions within these pipes is analysed in detail. The results depict that the solar heat flux has a significant impact on the velocity magnitude and static temperature profiles within the riser pipes. Furthermore, it has been observed that the thermal loading has negligible effects on the velocity magnitude and static temperature profiles within the riser pipes. The data has also been used to develop novel design correlations

Design, development and optimisation of a novel thermo-syphon system for domestic applications

In order to decrease reliance on fossil fuels, renewable energy has become an important topic of research in recent years. The development in the renewable energy source will help in meeting the requirements of limiting greenhouse-gas effects, and conserve the environment from pollution, global warming, ozone layer depletion, etc. There are various naturally available renewable energy sources. One of these sources is solar energy. Solar energy is available in abundance throughout the world and is the cleanest of all known energy sources. There are various devices that can be used to harness solar energy. One of such devices is a thermo-syphon. Thermo-syphon converts the solar energy obtained from the Sun into thermal energy of a working fluid. This thermal energy in the working fluid can be used for various industrial and household activities. In a closed loop thermo-syphon system, the working fluid circulates within the thermo-syphon loop via natural convection phenomenon and does not need any external devices, such as a pump. Therefore, it is considered to be one of the most efficient devices for the heat transfer. Moreover, the absence of a pumping device reduces the manufacturing and maintenance costs of a thermo-syphon system. The heat exchange process in the thermo-syphon is a complicated process, which considers the heat convection phenomenon. Therefore, to understand the natural convection process in the thermo-syphon and their effect on the thermal performance of the system a Computational Fluid Dynamics (CFD) based techniques have been used. Numerical results obtained have been verified against the experimental results, and they match closely with each other. The comparison between the CFD and experimental result, suggest that CFD can be used as an effective tool to analyse the performance of a thermo-syphon with reasonable accuracy. In order to investigate the flow structure within the thermo-syphon system, detailed qualitative and quantitative analyses have been carried out in the present study. The qualitative analysis of the flow field includes descriptions of the velocity magnitude and the static temperature distributions contours within the closed loop thermo-syphon system. Furthermore, the variation in the temperature of water within the storage tank, temperature of the working fluid, heat transfer coefficient, wall shear stress, and local velocity and temperature distribution of the working fluid within thermo-syphon loop have been quantified as a function of time. In addition, numerical studies have been conducted to identify the effects of various geometrical parameters, which include the number of the riser pipes, length-to-diameter ratio of the riser pipe on the thermal performance of a closed loop thermo-syphon system. Moreover, a further investigation has been carried out to analyse the effect of various heat flux conditions and different transient thermal loadings on the thermal performance of a closed loop thermo-syphon system. Based on these analyses some novel semi-empirical relations have been developed to predict the thermal performance of the thermo-syphon, which is one of the focal points of this research. Another goal of the current study is to improve the thermal performance characteristic of thermo-syphon solar water heating system using an enhancement device to improve the heat transfer. This aspect of the work focuses on the increasing energy conversion from the riser pipes to the working fluid within the thermo-syphon loop. This is accomplished by increasing the surface area of riser pipes by employing several design modifications, such as straight, wavy and helical pipes, within the riser pipes, while maintaining the amount of the working fluid constant within the closed loop thermo-syphon system. In this study, a comparative analysis has been carried out for these new design modifications to identify the best in terms of heat transfer coefficient, heat gain in collector etc., as an indication of thermal performance. According to the findings of this analysis, the model comprising of pipe inside the riser pipe depict better thermal performance as compared to other models. After defining the best design modification, a further detailed investigation has been carried out between the traditional and modified design (straight pipe inside the riser pipe) using experimental and numerical method. Established methods regarding the design process of thermo-syphons are very limited, and they are severely limited in estimating important design parameters, such as useful heat gain and heat transfer coefficient, which have a significant impact on the thermal performance of thermo-syphon system/loop. A design methodology has been developed to enrich the design process of a closed loop thermo-syphon solar water heating system. The developed methodology is more efficient and reliable since it is capable of estimating various geometrical and thermal parameters, such as collector area, diameter and length of the riser pipes, distance between the centers of the riser pipes, heat transfer coefficient, temperature of the working fluid and the mass flow rate. This design methodology is user friendly and robust

Numerical Investigations on the Effects of Transient Heat Input and Loading Conditions on the Performance of a Single-phase Closed-loop Thermo-syphon

One of the most important sources of renewable energy is solar energy, which is readily available throughout the world. There is a requirement to make the solar energy affordable for everyday use in order to minimise the present reliance on fossil fuels. This would also assist in meeting the requirements of limiting greenhouse-gas effects, and hence conserve the environment from pollution, global warming, ozone layer depletion, etc. Thermo-syphons are systems that capture solar energy using a working fluid. In the present study, Computational Fluid Dynamics based solver has been employed to carry out an extensive investigation on the performance analysis of a thermo-syphon operating under transient conditions. There has been limited research conducted on the transient performance of thermo-syphons. This study focuses on the effects of various heat flux inputs and thermal loading conditions on the performance of a closed-loop solar hot water thermo-syphon system. The study reveals that the effect of heat flux input on heat transfer coefficient is dominant as compared to thermal loading. The results provided here can be used to optimally design thermo-syphon systems. Furthermore, it has been demonstrated that Computational Fluid Dynamics can be used as an effective tool to analyse the performance of a thermo-syphon with reasonable accuracy

Effect of solar heat flux and thermal loading on the flow distribution within the riser pipes of a closed-loop solar thermo-syphon hot water system.

Solar energy is one of the main sources of renewable energy that is abundantly available throughout the world. Solar energy can be used for useful purposes through a number of mechanical artefacts. One such artefact is known as Thermo-syphon, which typically contains water as its working fluid. One of the major applications of Thermo-syphon is within the residential and industrial units, where a constant supply of hot water is required. The use of Computational Fluid Dynamics (CFD) based solvers has recently been proven capable of predicting the flow behaviour within thermo-syphons with reasonable accuracy. Hence, the present study focuses on using a commercial CFD based solver to predict the flow behaviour within the riser pipes of a thermo-syphon with varying solar heat flux and thermal loading conditions. In order to qualitatively and quantitatively analyse the flow structure within the riser pipes of the thermo-syphon, velocity magnitude and static temperature distributions within these pipes is analysed in detail. The results depict that the solar heat flux has a significant impact on the velocity magnitude and static temperature profiles within the riser pipes. Furthermore, it has been observed that the thermal loading has negligible effects on the velocity magnitude and static temperature profiles within the riser pipes. The data has also been used to develop novel design correlations

Computational fluid dynamics based analysis of a closed thermo-siphon hot water solar system.

One of the alternative sources of energy is solar energy which is available in abundance throughout the world. The energy contained within the solar rays is capable of starting natural convection within closed mechanical systems containing a suitable working fluid. One such system is commonly known as a Thermo-Siphon which transfers solar energy into internal energy of the working fluid, commonly water. In the present study, an attempt has been made towards better understanding of the flow structure within a thermo-siphon by analysing the natural convection phenomenon using Computational Fluid Dynamics techniques. A commercial CFD package has been used to create a virtual domain of the working fluid within the thermo-siphon, operating under no-load condition. The effects of the length to diameter ratio of the pipes connecting the condenser and the evaporator, number of connecting pipes, angle of inclination of the thermo-siphon and the heat flux from the solar rays to the working fluid, on the performance of the thermo-siphon, have been critically analysed in this study. The results depict that the heat flux and the length to diameter ratio of the pipes have significant effects on the performance of a thermo-siphon, whereas, the angle of inclination has negligibly small effect. Furthermore, an increase in the number of connecting pipes increases the temperature of the working fluid by absorbing more solar energy. Hence, CFD can be used as a tool to analyse, design and optimise the performance output of a thermo-siphon with reasonable accuracy

Effect of the shape of connecting pipes on the performance output of a closed-loop hot water solar Thermo-syphon

In order to conserve the environment from pollution, which is caused by the use of the fossil fuels, numerous research works have been carried out in renewable energy area to minimize the dependency on the fossil fuels. There are several energy sources naturally available, and solar energy is considered to be the best amongst them. Therefore it became a motivating area for the researchers in recent years. Thermo-syphon is one of many devices that use solar energy for power generation. Thermo-syphon converts solar energy into internal energy of the working fluid; mainly water. In this work, a computational fluid dynamics (CFD) code has been used to analyse the natural convection phenomenon in a thermo-syphon. The thermo-syphon model consist of steel pipes with an internal diameter of 25mm, along with a condenser having diameter equal to five times the pipe’s diameter, has been considered. The study has been carried out under no-loading conditions, for two thermo-syphon models comprising of straight and helical shaped pipes of 10, 20 and 30. A practical solar heat flux of 500W/m2 has been applied on the pipes. The numerical results depict that the working fluid within the condenser, in case of helical pipes, gains higher temperature as compared to the straight pipes. Furthermore, increase in the number of helical pipes has negligibly small effect on the temperature of the fluid within the condenser, and hence on the performance output of the thermo-syphon

HEAT TRANSFER INSIDE BUILDING- CLADDING SOLAR COLLECTOR

In this work numerical and experimental investigation have been adopted to collect and store solar energy in exterior-wall cladding, Various improvements have been investigated inside and outside the duct to increase the efficiency of thermal heating. ANSYS software has been used to simulate current case. Results show that there is a good agreement between experimental and numerical results and this agreement increases as air velocity increases. The average percentage error for air inside duct at velocity of air 1 m/s, 3 m/s and 5 m/s is 8%, 16.5% and 5% respectively. Several vertical cooper cylinders with 12 mm diameter were added inside basin to increase the surface area. It has been found that the enhancement in temperature of air between this case and Smooth Duct, Smooth Cover base model for air velocity of 1,3and 5 m/s is 3, 4 and 11 % respectively. The effect of increasing surface area by using granular (corrugated) duct on the air temperature distribution along the duct. Have been also investigated the percentage enhancement in temperature of air between this case and previous base smooth duct case for velocities of 1, 3 and 5 m/s is 19.4, 28.6 and 16.5 % respectively. The enhancement in heat transfer when using both granular hollow sphere duct with vertical metal cylinders for air velocity of 1, 3 and 5 m/s is 27.5, 33 and 35.2 % respectively

Computational Fluid Dynamics based Analysis of a Closed Thermo-Siphon Hot Water Solar System

One of the alternative sources of energy is solar energy which is available in abundance throughout the world. The energy contained within the solar rays is capable of starting natural convection within closed mechanical systems containing a suitable working fluid. One such system is commonly known as a Thermo-Siphon which transfers solar energy into internal energy of the working fluid, commonly water. In the present study, an attempt has been made towards better understanding of the flow structure within a thermo-siphon by analysing the natural convection phenomenon using Computational Fluid Dynamics techniques. A commercial CFD package has been used to create a virtual domain of the working fluid within the thermo-siphon, operating under no-load condition. The effects of the length to diameter ratio of the pipes connecting the condenser and the evaporator, number of connecting pipes, angle of inclination of the thermo-siphon and the heat flux from the solar rays to the working fluid, on the performance of the thermo-siphon, have been critically analysed in this study. The results depict that the heat flux and the length to diameter ratio of the pipes have significant effects on the performance of a thermo-siphon, whereas, the angle of inclination has negligibly small effect. Furthermore, an increase in the number of connecting pipes increases the temperature of the working fluid by absorbing more solar energy. Hence, CFD can be used as a tool to analyse, design and optimise the performance output of a thermo-siphon with reasonable accuracy

Effects of condenser volume on the performance of a solar thermo-syphon

One of the alternative sources of energy is solar energy which is available in abundance throughout the world. The energy contained within the solar rays is capable of starting natural convection within closed mechanical systems containing a suitable working fluid. One such system is commonly known as a Thermo-syphon which transfers solar energy into internal energy of the working fluid, commonly water. In the present study, an attempt has been made towards better understanding of the flow structure within a thermo-syphon by analysing the natural convection phenomenon using Computational Fluid Dynamics based techniques. A commercial CFD package has been used to create a virtual domain of the working fluid within the thermo-syphon, operating under no-load condition. The effects of the condenser volume, on the performance of the thermo-syphon, have been critically analysed in this study. The results depict that as the condenser volume increases, the average temperature of water within the condenser decreases. Hence, CFD can be used as a tool to design, analyse and optimize the performance of a thermo-syphon with reasonable accurac