Capillary rise

Surface tension of a liquid can be determined by this method. Capillary tube which is cleaned by ultrasonic rays is mounted vertically through a hole in a cork fitted to a stand. The capillary tube should be uniform throughout its length. Liquid whose surface tension is to be measured is taken in a beaker. The lower end of the tube is kept immersed in thios liquid. The a vertical pointer is passed through the cork. The beaker now raised so that the liquid wets the inside of the tube. The pointer is now adjusted so that its tip just touches the liquid surface in the beaker.

Static torsion

Here we determine the rigidity modulus of the material of the given rod using Searle’s static torsion apparatus. This apparatus consists of a stout metal frame with a cylindrical rod arranged horizontally, the end of which is firmly fixed to a frame. The other end is tightly held by a chuck at the edge of a smooth pulley. One end of the tape is fixed on the rim point with winding over pulley through the groove. A weight hanger is designed at the free end of the tape. Twist produced on the rod is measured using a scale and telescope arrangement.

Compound pendulum

This device is used to determine the acceleration due to gravity at a place. It consists of a uniform rectangular bar, some one meter long, with some equidistant holes drilled on it. It is suspended by a parallel knife edge passing through any of these holes. A vertical pointer is arranged in front of the pendulum to mark its exact equilibrium position. The pendulum is then made to oscillate. The oscillations should be of small amplitudes in a perfectly vertical plane. From the time for some limited number of oscillations, we can determine the acceleration due to gravity at one location.

Screw gauge

This device is used to determine the diameter of a piece of wire. It consists of a U-shaped frame. This frame is attached to a hollow cylinder. A scale graduated in millimeters is marked on the cylinder along its length. This is called pitch scale. A screw is working through the hollow cylinder. The tip of the screw is plane. The other end of the screw is attached to a fine sleeve with a beveled edge. This is called head scale. The pitch of the screw is the distance moved by the tip of the screw for one complete rotation of the screw head.

Vernier calipers

This device is used to measure length of some blocks. It consists of a metallic scale with a jaw fixed at right angles to it at one end. Another jaw which is movable carrying a vernier scale slides over the metallic scale. One precaution is that the inner surfaces of the jaws are plane. When both the jaws are presses together, the zero of the vernier should coincide with the zero of the main scale. If it is not coinciding, zero error exists. Then we have to incorporate zero correction term. The least count of the vernier is the smallest length that can be measured accurately with it.

Wind turbines

Wind turbines usually operate with their axes directed along the wind or at right angles to it. In both the cases, the blade profile is always parallel to the wind direction. If the turbines are with axes inclined to the wind direction of other than zero or 90 degrees, efficiency will be lower. Employing horizontal axis turbines, with two or more blades or propellers we can minimize stresses impressed on supporting structures. Latest blades and propellers have a twist which is given to them which varies from hub to tip. V.Daniel Hunt, Director of the energy institute, made a classification of wind turbines based on their function. The categories included in Wind energy conversion systems (WECS) are Water-pumping wind mills and electricity producing WECS.

Magneto hydro dynamic (MHD) technology

MHD power generation is very expensive. We have to deal with very difficult concepts here. The origin of this type of power generation is Faraday’s theory of electromagnetic induction. The fields of both MHD and nuclear fusion depend on harnessing high temperatures and man has not yet shown progress in these fields. Now the MHD power generator is used as the aid for nuclear power generation, thanks to LMFBR. Modern MHD systems use dried and pulverized coal, with minimal ash content (below 20%). This coal is carefully injected at the input end through coal-injection equipment. Air is compressed and heated before being fed to the combustor utilizing heat in the exhaust gases of the MHD generator. MHD research oriented systems prefer argon and helium gases. But for large scale power production, this is not sufficient.

Fuel cells and batteries

Fuel cells and batteries convert chemical energy to electrical energy. These are the devices which possess greater efficiency comparing with other energy converters. The importance of devices like these is of prime when we discuss coupling of energy conversion devices such as wind mills and solar cells. Fuel cells employ hydrogen fuel and oxygen oxidant. These two gases are pumped into a cell which contains cathode and an anode with an electrolyte. An external electrical load will draw electric current. Here electric current is due to the electrons which are separated from the hydrogen nucleus at the anode flow. These electrons get absorbed at the cathode by the hydrogen and oxygen ions forming H2O. The electrolyte is necessary which is responsible for the continuity of the circuit. At the initial stage fuel cells were used for manned space missions.

Three level and four level laser systems

In three level laser, the laser emission occurs when the atoms in the metastable state are stimulated to undergo transition to the ground state. Very high pump power required here because the terminal level of the laser transition is the ground state. Thus efficiency is lower. Continuous wave mode operation is not possible here. Eg:- Ruby laser.In four level laser, laser transition occurs between two intermediate levels rather than the ground state and higher excited state. Here population inversion can easily achieved with lower pumping requirements. Thus efficiency is greater. Continuous wave mode operation is possible here Eg:- He-Ne laser

Aluminum-Characteristics

This has light weight but when we prepare alloys using this, strengths generated. It is highly ductile, resistant to corrosion and non toxic. Change in color not occurs while heating. Thermal conductivity is greater and when exposed to air, oxide films are produced on the surface. Heat treatable aluminum alloys acquire properties which are very unique by solution heat treating, quenching, aging etc. Additional strength by cold working may also be employed. Ductility can be enhanced by annealing.

Filler Metal

Aluminum alloy filler metal is an important alloy material. While selecting the material, we have to take extra care for the end product and its use. A number of base metal alloys and their combination can be used. While choosing consider the optimum conditions and specific applications. Material should be free from cracks, tensile strength should be more, it should be ductile, wide temperature range characteristic should be there, it should be corrosion resistant and color should match after anodizing.

Cast alloys

Comparing with wrought alloys, casting alloys consists of larger amounts of alloy components like silicon and copper which results in a heterogeneous structure. Thus it contains phase impurities. This may lead to notches and cracks. To block this metallurgical and foundry environment should keep in optimum condition. In fatigue, the elongation, strength, brittleness, ductility etc. of most cast products is relatively poor in comparison with their wrought counterparts. The strongest of the common casting alloys is heat treated 201.0/AlCu4Ti.

Pre-weld cleaning

This is an essential process just before welding. This is employed to assure weld quality. Here conditions are more stringent and before direct current electrode negative GTAW, arc exerts no cleaning action. But before welding, surface contamination is to be removed. Washing and scrubbing with a detergent solution is one way for this. Oily contaminations can be removed by swabbing with cloths or cotton which is soaked in an approved nontoxic solvent. Removal oxide layers are possible by wire brushing, by steel wool, mill filer, portable milling tool or a scraper. Chemical treatment using butyl alcohol-phosphoric acid can also be employed

Joint design and edge preparation

This process is similar to both steel and aluminum. Direct current electrode negative GTAW is employed, root face become thicker and grooves very much narrow. It is avoidable in any case, the welding a lap joint. Small continuous filler suitably weld on both sides of the joint is preferable in this case. About 10mm thick materials which can be sheared to a well defined and cut square edge is used. It is cleaned well. Design ambiguities will lead to lapping of material on prepared edges that can trap lubricant. But this may result in weld porosity.

Fixtures

We expect severe dimensional changes in welding aluminum base alloys. This can be twice as great as in the welding of steel. These parameters do influence the design of fixtures. It is a fact that coefficient of expansion of aluminum is twice that of steel and melting point is about half that of steel. But the rate of expansion is inversely proportional to the speed of welding. To reduce distortion, rigid clamping can be employed. This may induce residual stress even comparable to yield strength of the base metal resulting in cracking. Hold-down fingers design will help to tackle these problems.

Arc welding power sources

Shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and gas tungsten arc welding (GTAW) are the main arc welding processes. We are not using line voltage as such since it is very large. Here in between an electrode and work piece, usually low voltage high current arcs are preferred. Rated terminal voltage or open circuit voltage required for arc welding is generated by a transformer or a solid state inverter. Motor-generator set also can be used. In the latest category of solid-state arc sources, pulses over a broad range of frequencies are possible and this is termed as pulsed power sources.

Pulsed mode power source

This is used to minimize the power of arc during the spray transfer. The basic principle employed is that the metal transfer from the electrode wire takes place either by spray transfer or globular transfer. The critical current at which globular to spray transition taking place is known as transition current. In this mode, the current is raised above the transition current for some time to allow transfer of a few droplets. This current is called pulse current. Major disadvantage of this system is that it is difficult to set the variables for a given welding requirements.