CFD study to investigate heat transfer enhancement using internal fins in the absorber tube of parabolic trough solar collector

As the most widely distributed and typical renewable energy, solar energy has been utilized worldwide to meet the growing energy demand and to mitigate the deteriorating ecological environment. Concentrated solar power (CSP) technology, including parabolic trough collector (PTC), parabolic dish coll

Project Title

CFD study to investigate heat transfer enhancement using internal fins in the absorber tube of parabolic trough solar collector

Project Area of Specialization

Mechanical Engineering

Project Summary

As the most widely distributed and typical renewable energy, solar energy has been utilized worldwide to meet the growing energy demand and to mitigate the deteriorating ecological environment. Concentrated solar power (CSP) technology, including parabolic trough collector (PTC), parabolic dish collector (PDC), linear Fresnel collector and heliostat field concentrator (HFC) are one of the promising and developed technologies in utilization of solar energy. Among the four main CSP technologies, the parabolic trough collector (PTC) technology is the most cost-effective one. Apart from power generation, PTCs have also been applied in many other fields, such as industrial process heat production, desalination, refrigeration and air-conditioning showing great development prospects.

A PTC consists mainly of a parabolic reflector and a receiver tube which is composed of a glass envelope and a metal absorber tube. The annulus between the glass envelope and the absorber tube contains vacuum to reduce heat loss and avoid oxidation of the coating (for example cermet). Due to the sunlight-concentration of the reflector, the reflected rays are mainly focused on the arc of the absorber tube’s circumference facing the reflector, leading to extremely uneven heat flux distribution, which results in a large temperature difference around the absorber. The circumferential temperature difference leads to thermal strain,causing thermal deformation of the absorber, which is the main cause of the receiver tube breaking. Moreover, the peak temperature on parts of the absorber surface may cause local overheating, threatening the stability and reducing the service life of the thermal oil and the coating. Thus, the thermal performance of the receiver tube is of great significance to the PTC’s safety and stability.

Enhancing the heat transfer in the parabolic trough receiver (PTR) can not only improve the thermal efficiency but also reduce the circumferential temperature difference effectively. Numerous heat transfer enhancement methods for the PTR have be proposed and investigated in previous studies.

Project Objectives

It can be seen from the literature review that installing inserts or modifying the tube structure are effective ways to enhance the thermal performance of the PTR.

The circumferential heat flux distribution calculated by the MCRT was loaded to the FLUENT code as the boundary condition using the User Defined Functions (UDF). The UDF was developed using the Fourier formula of the non-uniform heat flux distribution.

Multiple geometries which involve the “Unilateral Spiral Ribbed (USR)”, “Simple Rib”, “Inclined Rib” and “Dimpled tube” will be developed and their thermal and hydraulic performance will be compared to the conventional absorber tube.

Furthermore the project also aims to combine the effects of structural modification of the absorber tube with the use of different nano – fluids.

Four different types of the nanofluid (Al2O3/thermal oil, Cu/thermal oil, SiO2/thermal oil, and TiO2/thermal oil) will be used to further enhance the performance of the solar collector.

Project Implementation Method

1. Electricity Generation Plants

Commercial Plants use solar parabolic trough collector for electricity production but they have an alternative also like natural gas and some have Hybrid system for night shift .In the United States the amount of fossil fuel used in order for the plant to qualify as a renewable energy source is limited to a maximum 27% of electricity production. As of 2014, the largest solar thermal power systems using parabolic trough technology include the 354 MW SEGS plants in California, the 280 MW Solana Generating Station with molten salt heat storage, the 250 MW Genesis Solar Energy Project, the Spanish 200 MW Solaben Solar Power Station, and the Andasol 1 solar power station.

2. Sea Water Desalination:

Water scarcity is a serious problem for human health like as many countries in the world. Further, the demand for water in 2050 is projected to be fifty five percent higher than the world’s current needs. More than 20,000 desalination plants exist today but few are using renewable energy. Jennings and the JennSolar team are developing a solution to desalinate water using solar energy on a large scale. Using solar energy to create clean drinking water is a great goal, a great mix of service engineering and sustainability.

3. Enhanced oil Recovery

Enhanced Oil Recovery (EOR) is a term for techniques used to increase the amount of crude oil that can be extracted from an oil field. Solar EOR uses concentrated solar power to concentrate the sun’s energy to heat water. Solar Enhanced Oil Recovery (EOR) can supply up to 80% of a field’s annual steam requirements, by injecting solar-generated steam during the sunny hours, and a reduced amount of gas-fired steam at night or in less sunny weather or climates.

Benefits of the Project

Solar energy systems have been around for years but their efficiencies are low due to heat loss and inefficient collection of the day’s solar energy. The most efficient shape for a solar collector is the parabolic shape since it can focus the suns energy on a small heat exchanger. By concentrating the sun’s energy onto a focal point, less collection surface area is required and that lowers costs. In addition, parabolic solar collectors can have dual tracking capabilities. Traditional technologies are placed in a static, south-facing position to capture as much of the sun’s radiation as they can. These systems hit their peak efficiencies for about two hours per day. However parabolic solar collectors can track the sun throughout the day which makes them 220% more efficient than flat panels.

The other benefits, of parabolic solar systems is that they do not suffer from stagnated heat conditions, as flat panel and evacuated tube systems do. Flat panels and evacuated tubes are, by their very nature, susceptible to heat stagnation. This occurs when the heat collected cannot be extracted from the collectors because the application has all the heat it requires. The tubes and panels cannot move out of the sun and as a result continue to collect energy which can be damaging and dangerous.

The parabolic solar system used a well documented technology called “Concentrated Solar Power” which uses mirrors and tracking system to focus a large area of sunlight onto a small area. The concentrated light is then used as a heat source for a conventional power plant or is concentrated onto photovoltaic surfaces. A study done by Greenpeace International, the European Solar Thermal Electricity Association, and the International Energy Agency's SolarPACES group investigated the potential and future of concentrated solar power. The study found that concentrated solar power could account for up to 25% of the world's energy needs by 2050. Thermal energy is an excellent source of green energy since it can be used in its raw form to provide heating or cooling for commercial applications like hotels, wineries, hospitals, schools, stores etc. The parabolic solar can create enough thermal heat for use with absorption chillers to provide air conditioning. This optional is not available with standard flat panels and evacuated tube technology.

Technical Details of Final Deliverable

Not Applicalble in our case since our study comprises of CFD study only, leading to the publication of research paper.

Final Deliverable of the Project

Software System

Core Industry

Energy

Other Industries

Others

Core Technology

Clean Tech

Other Technologies

Others

Sustainable Development Goals

Affordable and Clean Energy

Required Resources

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