Heat absorption properties of ground material for solar chimney power plants

One of the major challenges to the widespread application of the solar chimney power plant is its low-power conversion efficiency because of the three technological processes involved. The chimney efficiency is difficult to improve, and thus enhancing the collector or turbine performance can considerably improve the total plant efficiency. This work focused on enhancing the energy conversion efficiency of the collector and also extending the operation time using a heat storage medium. The solar to thermal conversion and thermal storage capabilities of six ground materials that are potentially available in Malaysia were studied experimentally and numerically. The experimental model was designed such that the six materials were exposed to the same operation boundary conditions. The numerical studies were conducted using ANSYS software, where the geometrical models were developed and simulated using FLUENT for the fluid flow and energy/thermal field studies. The selected ground materials were ceramic, black stones, sawdust, dark-green painted wood, sand, and pebbles. The simulation and experimental results are in good agreement in terms of air stream velocity and energy conversion efficiency. The results showed that the different materials have different heat storage capacities, and that ceramics extend the operation with improved efficiency until nighttime. The results also showed that ceramic and black stones have better performance than the other materials. However, black stones are recommended as the absorbing material for solar chimney power plants in Malaysia and regional countries because they are readily available

Transonic airfoil design for helicopter rotor applications

Despite the fact that the flow over a rotor blade is strongly influenced by locally three-dimensional and unsteady effects, practical experience has always demonstrated that substantial improvements in the aerodynamic performance can be gained by improving the steady two-dimensional charateristics of the airfoil(s) employed. The two phenomena known to have great impact on the overall rotor performance are: (1) retreating blade stall with the associated large pressure drag, and (2) compressibility effects on the advancing blade leading to shock formation and the associated wave drag and boundary-layer separation losses. It was concluded that: optimization routines are a powerful tool for finding solutions to multiple design point problems; the optimization process must be guided by the judicious choice of geometric and aerodynamic constraints; optimization routines should be appropriately coupled to viscous, not inviscid, transonic flow solvers; hybrid design procedures in conjunction with optimization routines represent the most efficient approach for rotor airfroil design; unsteady effects resulting in the delay of lift and moment stall should be modeled using simple empirical relations; and inflight optimization of aerodynamic loads (e.g., use of variable rate blowing, flaps, etc.) can satisfy any number of requirements at design and off-design conditions

How to Increase the Long Run Growth Rate of Bangladesh?

This paper develops a framework to analyse the determinants of the long term growth rate of Bangladesh. It is based on the Solow (1956) growth model and its extension by Mankiw, Romer and Weil (1992) and follows Senhadji’s (2000) growth accounting procedure to estimate total factor productivity (TFP). Our growth accounting exercise showed that growth rate in Bangladesh, until 1990, was due to factor accumulation. Since then, however, TFP made a small positive contribution to growth. An analysis of the determinants of TFP showed that remittances by emigrant workers have negative effects which seem to be due to the loss of skilled labour force. Using these results policy options, to double per capita income of Bangladesh in about 15 years, are discussed.Solow Growth Model, Endogenous Growth, Total Factor Productivity, Growth Accounting, Remittances, Bangladesh

Are the Direct and Indirect Growth Effects of Remittances Significant?

Development economists believe that migrant workers’ remittances are an important source of funds for long run growth. Therefore, recent studies have investigated the growth effects of remittances and reached different conclusions. In many such studies the growth of output is simply regressed on both remittances and the channels through which remittances affect growth. Thus there is no distinction between the indirect and direct growth effects of remittances and such specifications may give unreliable estimates because of the correlation between the channels and remittances. In this paper we make a distinction between the indirect and direct effects of remittances. Our model is estimated with panel data of 40 high remittance recipient countries and a system GMM panel data estimation method.Remittances, Growth, Panel Data, System GMM

Stochastic maize production technology and production risk analysis in Dadar district, East Ethiopia

A stochastic production technology that allows risk effects of factor inputs was estimated for maize farmers in Ethiopia. The results suggested that the promoted improved maize technology exhibits constant returns to scale whereas non-adopters use decreasing returns to scale technology. The study showed that timely planting is critical for maize yield stability among both adopters and non-adopters and suggests the importance of using oxen and higher efforts to achieve that. Nevertheless, the results showed that most of the factors under the control of the farmers do not offer powerful explanation to maize yield variability compared to natural factors such as rainfall, frost, pests and diseases.Crop Production/Industries,