N.A. Rahim

Heat Transfer Enhancement of Nanofluids in a Lid-Driven Square Enclosure

A numerical investigation of mixed convection flows through a copper-water nanofluid in a lid-driven square enclosure has been executed here. The two horizontal walls of the enclosure are insulated, while the vertical walls are kept differentially heated by constant temperature with the left wall moving at a constant speed. The physical problem is represented mathematically by a set of governing equations, and the transport equations are solved using the finite element method based on Galerkin-weighted residuals. Comparisons with previously published work are performed and found to be in excellent agreement. Computational results are obtained for a wide range of parameters such as the Richardson number, solid volume fraction, and Reynolds number. Copper-water nanofluids are used with Prandtl number Pr = 6.2, and solid volume fraction φ is varied as 0%, 2%, 4%, and 8%. Reynolds number Re is varied from 50 to 200, while the Richardson number Ri is from 0 to 5 on the flow and thermal fields; heat transfer characteristics are also studied in detail. Results are offered in terms of streamlines, isotherms, average Nusselt number, and fluid temperature for the mentioned parameters. It is found that heat transfer increased by 9.91% as φ increases from 0% to 8% at Ri = 5. On the other hand, at the same convective regime, heat transfer increased by 120.91% as Re increased from 50 to 200.

Global solar energy use and social viability in Malaysia

Along with the enhancement of technology and alarming of global warming, various types of technologies are advanced worldwide nowadays to harness the energy from the sun such as solar thermal energy, ocean thermal energy conversion, solar ponds, solar tower and photovoltaic systems to utilize the energy in the majority of domestic applications and industrial sector to a certain extent. Subsequently, gradual increase usage of solar energy requires creating awareness among public to protect the environment in term of green campaign which is one of the hot topics among the Malaysians where there are many organizations organizing green campaign such as Environmental Protection Society Malaysia (EPSM), Malaysia Environment NGOs (MENGO) and Treat Every Environment Special Sdn. Bhd. (TRESS). Therefore, this study examines solar energy production and consumption worldwide by looking at various existing solar technologies to have the understanding of each technology. This article also intends to catch up specifically the social viability of solar energy production and use, with the availability of the resources for the full scale development.

Finite element simulation of magnetohydrodynamic mixed convection in a double-lid driven enclosure with a square heat-generating block

Magnetohydrodynamic (MHD) mixed-convection flow and heat transfer characteristics inside a square double-lid driven enclosure have been investigated in this study. A heat-generating solid square block is positioned at the centre of the enclosure. Both of its vertical walls are lid-driven and have temperature T-c and uniform velocity V-0. In addition, the top and bottom surfaces are kept adiabatic. Discretization of governing equations is achieved using finite element technique based on Galerkin weighted residuals. The computation is carried out for a wide range of pertinent parameters such as Hartmann number, heat-generating parameter, and Richardson number. Numerical results are reported for the effects of aforesaid parameters on the streamline and isotherm contours. In addition, the heat transfer rate in terms of the average Nusselt number and temperature of the fluid as well as block center are presented for the mentioned parametric values. The obtained results show that the flow and thermal fields are influenced by the above-mentioned parameters.

Analysis of energy, exergy and energy savings of a fire tube boiler

Energy efficiency improvement as well as energy savings is the major concern in most of the development countries all over the world. In this study, the useful concept of energy and exergy utilization is analyzed to investigate the energy and exergy efficiency, energy and exergy losses and energy savings of boilers. The energy and exergy efficiencies of a combustion chamber and stream production chamber of the boiler have been analyzed as well. The exergy efficiency of the combustion chamber is found to be 49.6 %. The energy and exergy efficiencies of the stream production chamber are found to be 55.4 % and 34.6 % respectively. The overall boiler energy and exergy efficiencies are found to be 60.3 % and 19.9 % respectively. It has been found that the combustion chamber is the major contributor for exergy destruction followed by stream production chamber of the boiler. By using heat recovery system, the savings will be 5278 L/year fuel that is about 7917 RM/year.

Present Solar Energy Potential and Strategies in China

Facing great pressure of economic growth and energy crisis, China pays much attention to the renewable energy. Renewable energy development is one of the main targets of the Chinese government on the way to the sustainable development and climate change mitigation. Chinas energy policy target is to reach 15.4% renewable energy share by 2020 and 27.5% by 2050. Chinas total installed electrical power capacity reached 700 GW by the end of 2007 and is predicted to surpass 900 GW in 2010. A similar goal exists for the solar photovoltaic power sector which China intends to increase generating capacity from 0.14 GW as of 2009 to over 1.8 GW by 2020. In order to achieve this target, the Government has implemented many instruments from laws and policies and financial incentives. The paper gives introduction to the present situation of the solar energy development in China and overviews the main policies that China uses to promote and develop the solar energy. Also, the suggestions for the further development of solar energy technologies in China are given.

Thermal performance improvement of solar thermal power generation

Power is the driving tool for modernization of the world. Upraised fossil fuel prices and environmental issue drive the world to searching alternative option for producing power. In such case, solar energy appears as the most attractive option due to its abundancy and clean feature. Today solar thermal technologies are the most popular advanced techniques. The performance of solar thermal technologies depends on some factors. Among these factors, thermo fluids have very crucial role in power producing through effective usage of solar thermal energy. System efficiency depends on temperature of thermo fluids. So, thermo fluids used in power generation is an important concern. This article accumulates latest literatures in terms of thesis, journal articles, reports, etc on thermo fluids for solar power generation. However, this review article shows that performance of solar thermal system can be improved by utilizing appropriate thermo fluid.

Outdoor performance of solar PV/T air system

Major application of PV modules is to convert solar energy into electrical energy. One of the weaknesses of PV module is its efficiency are depends on temperature. In simple way, it can be describe that as temperature increase, the efficiency of PV module decrease. According to that, new area of research called PV/T is given attention to generate more electricity while cooling the PV module by extracting heat using fluid. In this paper, an outdoor testing to investigate the electrical and thermal performance of air based PV/T system with different speed of air has been carried out. The electrical performance of PV/T system is then being compared to electrical performance of PV module without thermal collector. Electrical output of the system can be used for the purpose of lighting and else while heated air is important to provide warm and comfortable environment in the house especially in cold climate country.

Investigation of Waste Heat Recovery in Cement Industry: A Case Study

 Abstract—In recent years, there has been an increasing interest in waste heat recovery in the cement industry. The aim of this work is to determine the waste heat recovery by utilizing the waste exit gases from the pre-heater and grate cooler to generate electricity, furthermore estimation of cost saving. The results based on the operational data which is collected from Al-Muthanna Cement Plant. The net power output of 834.12 kJ/kg was estimated. A 6.673 ×103 MWh/yr electricity generation were achieved. The cost saving was estimated of 467,110.00 USD/yr in addition to 20 months was expected as the simple payback period.

Effectiveness enchancement of heat exchanger by using nanofluids

Heat exchanger is the almost common equipment for the industrial process heating. Heat is transferred from one fluid to other fluids by convection and conduction through the wall of the heat exchanger. Effectiveness of heat exchanger depends on the convection heat transfer coefficient of the fluid. Convective heat transfer coefficient of water, Cu-water, Al-water, Al<inf>2</inf>O<inf>3</inf>-water and TiO<inf>2</inf>-water of 2% nanoparticle concentration has been calculated for counter flow heat exchanger. It is found that convective heat transfer coefficient of Cu-water, Al-water, Al<inf>2</inf>O<inf>3</inf>-water and TiO<inf>2</inf>-water nanofluids are 81%, 63%, 66% and 64% higher compared to pure water respectively. It is found that overall heat transfer coefficient of Cu-water, Al-water, Al<inf>2</inf>O<inf>3</inf>-water and TiO<inf>2</inf>-water nanofluids are 23%, 20%, 21% and 20% higher compared to pure water respectively.

A numerical model for the simulation of double-diffusive natural convection in a triangular solar collector

A numerical model is presented for the simulation of double-diffusive natural convection in a triangular solar collector. This design is encountered in greenhouse solar stills where vertical temperature and concentration gradients between the saline water and transparent cover induce flows in a confined space. This phenomenon plays an important function in the water distillation process and in the biological comfort. In this double-diffusion problem, the ratio Br of the relative magnitude thermal and compositional buoyancy and Rayleigh numbers are key parameters. Finite element technique is used to solve the governing equations. Numerical results are presented for the effect of the above-mentioned parameters on local heat and mass transfer rate. In addition, results for the average heat and mass transfer rate are offered and discussed for the mentioned parametric conditions. Some interesting results are found in this investigation.