Majid Ali

Performance analysis of phase-change material storage unit for both heating and cooling of buildings

Utilisation of solar energy and the night ambient (cool) temperatures are the passive ways of heating and cooling of buildings. Intermittent and time-dependent nature of these sources makes thermal energy storage vital for efficient and continuous operation of these heating and cooling techniques. Latent heat thermal energy storage by phase-change materials (PCMs) is preferred over other storage techniques due to its high-energy storage density and isothermal storage process. The current study was aimed to evaluate the performance of the air-based PCM storage unit utilising solar energy and cool ambient night temperatures for comfort heating and cooling of a building in dry-cold and dry-hot climates. The performance of the studied PCM storage unit was maximised when the melting point of the PCM was ∼29°C in summer and 21°C during winter season. The appropriate melting point was ∼27.5°C for all-the-year-round performance. At lower melting points than 27.5°C, declination in the cooling capacity of the storage unit was more profound as compared to the improvement in the heating capacity. Also, it was concluded that the melting point of the PCM that provided maximum cooling during summer season could be used for winter heating also but not vice versa.

A novel method for analytical solution of transient heat conduction and Stefan problem in cylindrical coordinate

It has been found numerical methods are very tiring and time consuming and so much dependent upon computational calculations, so in order to reduce the computational time a new eigenfunction expansion method is presented for a two dimensional case with heat generation source. This method is applicable to any combination of inhomogeneous first and second kind boundary conditions in the angular and axial direction of cylinder and can be very useful for latent heat energy based storage systems analytical analysis. Analytical problem of one phase melting/solidification of Phase Change Material was also studied with the use of dimensionless parameters using the eigenfunction expansion method. Effect of Dimensionless parameter Stefan number on the melting/solidification of PCM was studied. Results showed increase in the transition time at low Stefan value.

Effectiveness of the phase change material-based thermal energy storage integrated with the conventional cooling systems of the buildings – A review:

A significant portion of energy is consumed by the buildings to provide thermal comfort for its occupants. Energy consumed by the conventional cooling machines is expected to increase substantially around the globe. Cooling systems coupled with phase change materials offer a high potential to minimize the cooling energy demand and shifting peak time cooling load to off-peak time period without compromising the indoor comfort conditions. The interest in phase change material utilization for cooling applications has been increasing significantly over the last decade because of their energy saving benefits in building sector. Therefore, in this work, effectiveness of the phase change material storage coupled with free cooling, evaporative cooling, and compressor-based cooling techniques in reducing the energy consumption or shifting the peak cooling load have been discussed and analyzed in detail. Different types of phase change materials used for active cooling systems along with their selection criteria for a particular application have been elaborated and discussed. Techniques to estimate the thermophysical properties of phase change material have also been explained. Phase change material capsulation techniques along with their merits and demerits are also described. Challenges and issues that may arise during integrating of phase change material storage with the active cooling system have also been explained. Finally, this review also presents some current problems that needed further research in this area. Current review will be a useful guide for the research community working or intending to work in the field of phase change material-based cooling system.

Analytical analysis of latent heat thermal energy storage model for solar thermal power plants

In this paper latent heat thermal energy storage system was studied using analytical method for solar thermal power plant applications. The working fluid circulating in circular tube by forced convection charges and discharge phase change material based on energy storage unit. Temperature distribution and parametric study was performed in order to study the effects of convection on the melting/solidification of KNO3 and NaNO3 salts. In order to provide the guidelines for system analysis and design optimization, temperature distribution along the axial and radial direction has been obtained and represented in 3d graphs.

An analytical method for the solution of two phase Stefan problem in cylindrical geometry

Two phase Stefan problem was solved using analytical method in cylindrical domain. To solve governing equations Eigen conditions were formulated by using separation of variable technique. Eigenvalues of the eigencondition were obtained by applying corresponding boundary conditions for liquid and solid phase. Eigenvalues are graphically validated by using window size method in Mathematica. It is noted radial eigenvalues are free from imaginary values. Interface equation obtained from this method were solved and analyzed by varying the Stefan number and introducing the forced and natural convection. Conduction and convection heat transfer mechanism was studied and results obtained by varying thermal diffusivity, thermal conductivity and Stefan number were discussed. Natural convection effects were studied by introducing Rayleigh number and results showed Stefan number has significant effect than Rayleigh number during Phase transition process. Furthermore, eigen function expansion Method was compared with exact solution of Exponential Integral function method and results showed good agreement for Q = 1.

Modelling of a solar energy driven water desalination system using TRNSYS

The overall broad purpose of this paper is to develop and evaluate a small scale solar humidification dehumidification water desalination system using a graphical tool TRNSYS and assess its thermal behavior. Considering the intense need for the development of alternate technologies for energy deficient and impoverished countries of the world like Pakistan, this model is in particular anticipated for underprivileged communities where pure and uncontaminated drinking water as well as modern technologies are not accessible. The system consists of isolated components for heating, evaporation and condensation, in order to lower the thermal losses. The weather file used was in standard TMY 2 format for Asian data. A flat plate solar collector, humidifier and dehumidifier are to be integrated in an open air open water configuration. The simulations for a water heated cycle revealed that the output water temperature be reliant strongly on the incident solar radiations and inlet water temperature. Collector area and inlet water flow rate also had a considerable impact on productivity. A significant increase in efficiency was observed by using a water storage tank and pre heating the feed water favorably influenced the output.

Simulation, design and fabrication of an efficient single phase transformer

Transformer is a vital component of electric power systems for transmission and distribution. Robust design for the efficiency enhancement is the main stress in the fabrication of a transformer. Efficiency of a practical transformer is limited by the losses which are accounted for the design and manufacturing imperfections. This paper deals with the simulation, design and fabrication of a 0.30 KVA, Single phase, Shell type, tapped transformer. Design and fabrication of this transformer has been made possible by the special calculations and design procedure. Simulation has been performed in MATLAB. Open circuit test and short-circuit tests have been performed to investigate the losses and efficiency of the designed transformer. Simulation results and experimental results have been compared which are closely matching.

Kinetic Study of Containment Retention Factor (CRF) for Large Dry Containment Under Radiation Load

The Nuclear Power Plants (NPPs) have been built on the concept of Defense in depth. The severe accident causes the failure of fission product barriers and let the fission products to escape into environment. The containment is the last barrier to the fission products. Thus, the containment is installed with engineering safety features (ESFs) i.e. spray system, heat removal system, recirculation filtration system; containment filtered venting system (CFVS), and containment exhaust filtration system. In this work, kinetic study of the containment retention factor (CRF) has been carried out for a large dry PWR containment considering 1000 MWe PWR. The computational modeling and simulation have been carried out by developing a kinetic code in MATLAB, which uses the fractions of activity airborne into the containment after the accident. The Kinetic dependency of CRF on containment filtration systems, spray system with caustic and boric acid spray has been carried out. For noble gases, iodine and aerosols, the CRF increases with the increase in exhaust rate. While, CRF for iodine first increases then start reducing with containment spray flow rate. The Kinetic dependency of CRF has also been studied for boric and caustic spray.Copyright

REMOVAL EFFICIENCY OF IODINE AT SATURATED STEAM IN SUBMERGED VENTURI SCRUBBER

Sever accident due to molten core of Nuclear Power Plant causes the production of steam which carries the radioactive iodine. It is important to retain the radioactive iodine from contaminated gas and steam before it is released into the environment. The purpose of this research is to investigate the removal efficiency of iodine in a submerged venturi scrubber for saturated steam at 100°C. Venturi Scrubber is submerged in a venturi tank filled with liquid which is alkaline by adding sodium hydroxide (NaOH) and sodium thiosulphate (Na2S2O3) in scrubbing water. Saturated Steam of 100 °C is injected into an experimental loop. Iodine removal efficiency is investigated for saturated steam at various compressed gas flow rate 330, 420, and 510 kg/s. Inlet and outlet concentration are measured at the sampling points of an experimental loop to calculate the iodine removal efficiency. The maximum removal efficiency of 99.4% is achieved at gas mass flow rate of 510 kg/s.Copyright