Base pressure fluctuations on typical missile configuration in presence of base cavity.

Pressure fluctuations in the base region of a typical missile configuration at a freestream Mach number of 0.7 are examined experimentally in the presence and absence of a base cavity. The objective was to characterize the pressure fluctuations and explain the influence of base cavities on their behavior. Experiments include unsteady pressure measurements at six azimuthal locations. Substantial variation in the characteristics of pressure fluctuations is noticed along the azimuthal direction due to the asymmetry of the model. The base cavities are seen to enhance the base pressure and reduce the root mean square of the pressure fluctuations. Higher-order moments show diminishing trend as the length of the base cavity is increased. Spectra in the absence of cavity exhibit three types of narrow-band tones based on the Strouhal number. Type I tones disapper from the spectra for small-length cavities, whereas type II tones get suppressed. On the other hand, for the large-length cavities, type I tones get enhanced, whereas type II tones disappear. Autocorrelation and cross-correlation plots exhibit a large-amplitude, low-frequency oscillation that exists even after large separation times for the larger-length cavities, and virtually no such oscillations are visible for the small-length-cavity models

Use of artificial roughness to enhance heat transfer in solar air heaters – a review

Improvement in the thermo hydraulic performance of a solar air heater can be done by enhancing the heat transfer. In general, heat transfer enhancement techniques are divided into two groups: active and passive techniques. Providing an artificial roughness on a heat transferring surface is an effective passive heat transfer technique to enhance the rate of heat transfer to fluid flow. In this paper, reviews of various artificial roughness elements used as passive heat transfer techniques, in order to improve thermo hydraulic performance of a solar air heater, is done. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts. The objective is to provide a detailed review on heat transfer enhancement by using an artificial roughness technique. This paper will be very helpful for the researchers who are researching new artificial roughness for solar air heater ducts to enhance the heat transfer rate and comparing with artificial roughness already studied by various researchers

Use of artificial roughness to enhance heat transfer in solar air heaters – a review

Improvement in the thermo hydraulic performance of a solar air heater can be done by enhancing the heat transfer. In general, heat transfer enhancement techniques are divided into two groups: active and passive techniques. Providing an artificial roughness on a heat transferring surface is an effective passive heat transfer technique to enhance the rate of heat transfer to fluid flow. In this paper, reviews of various artificial roughness elements used as passive heat transfer techniques, in order to improve thermo hydraulic performance of a solar air heater, is done. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts. The objective is to provide a detailed review on heat transfer enhancement by using an artificial roughness technique. This paper will be very helpful for the researchers who are researching new artificial roughness for solar air heater ducts to enhance the heat transfer rate and comparing with artificial roughness already studied by various researchers

Analyze the factors effecting the development of hydro power projects in hydro rich regions of India

Power is considered as the major back bone for all the nations throughout the world including India on the basis of which development of the country depends. If a country has the resources to generate the power at competitive price in that case the people of the country get the benefits in terms of improvement in their social and economical life. When we talk about India, various locations in the country where still there is no electricity people are living in dark without having the access of the modern technology. The total hydro power potential of India is 1, 50,000 MW out of this total hydro potential only 40,195 MW is exploited till 2014. More than 80% of the total hydro potential of the country is lying in the western Himalayan states (Jammu and Kashmir, Himachal Pradesh, Uttrakhand and Arunachal Pradesh). Small hydro projects are also playing a very important role in the modern world for the development of the remote areas which are not main grid connected specially in western Himalayan region of India. India has a total potential 19,749 MW of small hydro projects and of this total potential only 3990.9 MW harnessed till 2014. Ministry of new and renewable energy in India is also providing special incentives to hydro rich states of India. In this research article we are taken the case study of the small hydro projects in the western Himalayan region because theses states are having vast small hydro potential which is still needed to be harnessed. So, it is very important to identify the factors which are effecting the development of these small ventures especially in western Himalayan region in India

Exergy based modeling and optimization of solar thermal collector provided with impinging air jets

The irreversible absorption of solar energy accompanied by emission for conversion into thermal energy takes place at the cost of exergy losses from the collector and the effectiveness of this conversion is evaluated in terms of exergy efficiency based upon second law of thermodynamics. Presented in this paper is the exergetic efficiency of impinging jet solar thermal collector and its comparison with that of conventional solar collector. The effect of flow Reynolds number, jet diameter, streamwise and spanwise pitch between the jets on exergetic efficiency of impinging jet solar air collector during conversion of solar energy into thermal energy has been studied based upon the correlations developed for heat transfer coefficient and friction factor in the range of investigated flow and geometric parameters. The results reveal that the impinging air jets extract the absorbed exergy from the absorber to the air flowing beneath with higher efficiency than that of the conventional solar air collector. Also, the design plots have been prepared for jet plate parameters with temperature rise parameter in order to obtain an optimum parameter values that would deliver maximum exergetic efficiency for desired value of temperature rise. Design procedure has also been discussed to evaluate the optimum parameters with respect to operating conditions. Keywords: Solar thermal collector, Jet impingement, Exergy, Heat transfer, Optimizatio

Biotechnological tools in the propagation and conservation of threatened species: An overview

217-235Plant diversity is crucial for the balanced functioning of the environment, as humans are highly dependent on them since plants provide sustenance and services like regulation of climate and protection from natural hazards. At present, 20,360 plant species are threatened (critically endangered, endangered and vulnerable), 165 species are extinct and extinct in the wild, due to several factors as per International Union for Conservation of Nature (IUCN) data and their conservation is of utmost importance. The in vitro methodology has become one of the promising tools of biotechnology in the conservation of threatened plants. The technique ensures propagation of taxa with limited explant source, seed dormancy, self-incompatibility, inbreeding depression, etc. resulting in lower seed production. In vitro methods along with the ex situ and in situ methods have been extensively used in the conservation of plants. This review highlights a compilation of several biotechnological tools i.e., micropropagation, somatic embryogenesis, callus induction, organogenesis, cryopreservation, micrografting, employed in the conservation of over a hundred threatened species. Furthermore, the present review sheds light on the importance of genetic homogeneity assessment based on frequently used molecular markers amongst in vitro raised and the donor mother plants. The review will help other researchers to employ various tissue culture methods in conservation programs of threatened and rare plants

An analytical model to predict the thermal performance of a novel parallel flow packed bed solar air heater

A design of a parallel flow solar air heater with packed material in its upper channel and capable of providing a higher heat flux compared to the conventional non-porous bed double flow systems is presented. An analytical model describing the various temperatures and heat transfer characteristics of such a parallel flow packed bed solar air heater (PFPBSAH) has been developed and employed to study the effects of the mass flow rate and varying porosities of the packed material on its thermal performance. The model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass exchanges involved. To validate the proposed analytical model, comparisons between theoretical and experimental results showed that good agreement is achieved with reasonable accuracy. Also, PFPBSAH is found to perform more efficiently than the conventional non-porous double flow solar air heaters with 10-20% increase in its thermal efficiency. Furthermore, the effect of the fraction of mass flow rate in the upper or lower flow channel of PFPBSAH device on its performance, has also investigated theoretically. The fraction of the mass flow rate in the respective channels of the PFPBSAH is shown to be dominant parameter in determining the effective thermal efficiency of the heater.Packed bed Parallel flow Porosity Thermal power Effective efficiency

Characteristics of base pressure fluctuations of a typical missile configuration with a propulsive jet.

Experiments were carried out to investigate the pressure fluctuations in the base region of a typical missile configuration at a freestream Mach number of 0.7 in the presence and absence of a propulsive jet. The objective was to characterize these pressure fluctuations and identify the underlying mechanisms responsible for their origin. Experiments included unsteady pressure measurements at six azimuthal locations and schlieren visualization. Substantial variation in the characteristics of pressure fluctuations is noticed along the azimuthal direction due to the asymmetry of the model. The probability density function (PDF) of pressure fluctuations indicates a significant drop in the peak PDF value and a substantial broadening at the highest nozzle pressure ratio (NPR). With an increase in NPR, the skewness decreases and approaches a Gaussian value while the kurtosis decreases and is seen to go below that of a Gaussian. Spectra of the pressure fluctuations indicate that the narrowband tones can be classified into three types based on the Strouhal number. Two types of tones among the three aforementioned are seen to be suppressed in the presence of the jet. Cross-correlation plots in the absence of the jet exhibit a large amplitude, low frequency oscillation which exists even after large separation times. On the other hand, in the presence of the jet, the oscillations dampen rapidly and vanish as the separation time increases. Finally, an attempt has been made to identify the possible primary mechanisms that are driving the base pressure fluctuations based on the observed characteristics of the acquired unsteady pressure signal