China
Africa
Explore chapters and articles related to this topic
Aperture and Phased Array Antennas
Published in Habibur Rahman, Fundamental Principles of Radar, 2019
In parabolic reflector antennas the parabola is illuminated by a source of energy called feed placed at the focus of the parabola and directed toward the reflector surface. The basic parabolic contour is used in a variety of configurations. Rotating the parabola about its axis produces what is called a paraboloid. It can be shown by geometrical optics considerations that a spherical wave emerging from the focal point and incident on the paraboloid reflector is transformed after reflection into a plane wave traveling on the direction of the positive axis of the paraboloid.
Concentrating Solar Thermal Power
Published in D. Yogi Goswami, Frank Kreith, Energy Conversion, 2017
Manuel Romero, Jose Gonzalez-Aguilar, Eduardo Zarza
The most practical and simplest primary geometrical concentrator typically used in STP systems is the parabola. Even though there are other concentrating devices like lenses or compound parabolic concentrators (Welford and Winston, 1989), the reflective parabolic concentrators and their analogues are the systems with the greatest potential for scaling up at a reasonable cost. Parabolas are imaging concentrators able to focus all incident paraxial rays onto a focal point located on the optical axis (see Figure 19.7). The paraboloid is a surface generated by rotating a parabola around its axis. The parabolic dish is a truncated portion of a paraboloid. For optimum sizing of the parabolic dish and absorber geometries, the geometrical ratio between the focal distance, f, the aperture diameter of the concentrator, d, and the rim angle, Θ, must be taken into account. The ratio can be deducted from the equation describing the geometry of a truncated paraboloid, x2 + y2 = 4fz, where x and y are the coordinates on the aperture plane, and z is the distance from the plane to the vertex. For small rim angles, the paraboloid tends to be a sphere, and in many cases, spherical facets are used; therefore, in most solar concentrators, the following correlation is valid:
Electromagnetic Diffraction from a Metallic Spherical Cavity.
Published in S. S. Vinogradov, P. D. Smith, E. D. Vinogradova, Canonical Problems in Scattering and Potential theory Part II, 2002
S. S. Vinogradov, P. D. Smith, E. D. Vinogradova
A study of the focal region is essential for the proper design of any focusing system. Theoretically, the best shape of a reflector is parabolic. From a geometric optics perspective, any bundle of parallel rays reflected from the concave surface of a parabolic mirror, collects at the same point of the optical axis, the focus. However, in practice, instead of focusing to a single point, the rays concentrate in a region known as the focal spot. In better designs, the extent of this spot is about a wavelength. However the centre of the spot is usually shifted some distance from the focal point predicted by GO, even for the supposedly ideal parabolic dish (albeit of finite extent).
A comprehensive review on solar assisted cooling system
Published in International Journal of Ambient Energy, 2020
Alka Solanki, Yash Pal, Rajesh Kumar
Parabolic Dish offers higher efficiency and higher operating temperature when used as a solar concentrator. The surface produced by rotating a parabola about its optical axis is called paraboloid or parabolic dish. It presents a point image of a parallel beam of light. The receiver of PD is integrated into high-efficiency external combustion engine and can provide power in the range of 10–25 KW. Its concentration ratio is 500–1500.
Parametric analysis of solar energy conversion system using parabolic concentrator and thermopile
Published in International Journal of Ambient Energy, 2020
Meeta Sharma, Anoop Kumar Shukla, Akash Singh, Sukrit Johri, Harsh Pratap Singh
The proposed model consists of a parabolic mirror reflector, thermopiles and an energy storage device and a sturdy construction on which all the components are mounted. A parabolic mirror is used because, at no matter what angle to the normal a ray of light impinges on the mirror, the reflected ray always passes through the focus of the parabola. To focus the maximum amount of energy, the material required must have a high reflection coefficient. The most significant component of the system is the thermopiles made up of a number of thermocouple junction pairs associated electrically. Generally, these thermopiles are placed either in series or parallel and used to an increased net electromotive force. The combination of thermal energy through one of the thermocouple connections, called the active connection, raises its temperature. The temperature difference between the active connection and a reference connection kept at a fixed/low temperature creates an electromotive force directly proportional to the temperature difference created. The protective covering in which the combination stack of thermopiles will be placed is so designed that the heat loss from the hot face is minimised and the temperature of the cold side is maintained low/refrigerated. The major consideration for the design of the proposed system is energy losses from the faces of thermopile casing which causes a lower temperature gradient. The losses occur mainly due to various ways of heat transfer or combination of conductive, convective and radiative resistances between the major interfaces. The heat losses need to minimise the high temperature difference to generate a high electromotive force. The heat is taken away due to radiation heat transfer due to black body radiation and convection heat transfer. These losses are to be minimised by covering the hot face of the thermopile by a polycarbonate sheet. It is used for the casing due to the fact that its temperature tolerance is very high and they are comparatively cheap. When the hot face is covered with the sheet, convection losses from the hot face are reduced. To reduce the conduction and radiation heat losses, partial vacuum is created between the hot face and the sheet. A frame is used to mount the parabolic concentrator and the thermopile stack; it can be mobile or fixed.
Extraction of water particles from atmospheric air through a Scheffler reflector using different solid desiccants
Published in International Journal of Ambient Energy, 2020
Shobhit Srivastava, Avadhesh Yadav
Reflector dishReceiverDish standTracking systemReflector dish: The reflector dish is the main part of the Scheffler reflector. Currently, 16 and 8 m2 types of the Scheffler reflector are available, but in the present study, a new novel design Scheffler reflector of surface area 1.54 m2 is used. The reflector consists of several flat aluminium reflective sheets which are mounted on a structural frame. The reflector rotates about in the North–South direction parallel to the earth's axis to track the sun's movement. The seasonal tracking is also possible by the movement of the dish in the East–West direction. Focus is fixed at a distance of the focal length of the paraboloid along the axis of the paraboloid.Receiver: The mirrors are arranged to give a paraboloidal shape and reflect the incident solar radiation to a common point called the receiver. The receiver is placed at the focus of the dish so as to capture the incident solar radiation and transfer it to the thermal medium used in the system. The receiver is designed according to the application of the end user and also the size of the receiver depends on the size of the focus and storage requirement. In this experiment, the receiver is rectangular in shape.Dish stand: The basic framework of the dish stand is a steel structure. The structure is designed to withstand wind speed in operating and non-operating conditions.Tracking system: The tracking system allows the reflector dish to concentrate towards the sun to capture maximum possible direct solar radiation during the day. It also tracks the sun’s movement as it changes its position during the season.