eChapters

So far we studied direct stress (Tensile or compressive) and tangential stress (shear stress) acting on plane individually. But in many engineering problems these both stresses are acts on a plane at a same time. In such cases resultant stress on that plane will be neither pure normal nor purely shear but there will be combined effect of normal and shear stress.

When any beam is loaded, stresses are induced and so to calculate those stresses, shear force and bending moment acting at load or support location must be required to calculate.

Thermal stress arises whenever there is some increase or decrease in temperature of a body which causes either expansion or contraction in the dimension of body. If body is free to expand or contract, with the rise or fall of temperature, there exist no stress in the body. But if deformation of the body is partially or completely resisted then stresses are set up in the body which is known as Thermal Stress. However amount of stress induced in partially prevented deformation will be small than in case deformation is totally prevented.

Whenever a thin hanging wire is loaded, it elongates and the load moves downwards. Increase in length of wire is governed by the magnitude of the load and nature of wire material. Experimentally it is found that the cohesive force between the molecules of hanging wire offers resistance against the deformation.

Mechanical power is usually transmitted from one shaft to another by using belts, ropes, chains, gears and clutches.

1. Belts and ropes are utilized if distance between the shafts is large. Belts and ropes are flexible and bend easily. But slip occurs between the belt and the pulley.

Machine: It is a device capable to doing work on application of some effort. Work done by machine is to raise load or to lower load or to do some other types of work like rotation of shaft.

Hydraulic pumps are the devices utilized to transfer pressure energy to liquids at the expense of electrical energy. The electrical energy is transferred to a motor which converts it into mechanical work and a pump is coupled to the shaft. The pump converts the mechanical energy to hydraulic or potential energy. 

Hydraulic turbines is a device which transforms the hydraulic energy or potential energy existing with the working medium to mechanical energy. The working medium is normally water which run the hydraulic turbine. The hydraulic energy is available with water by virtue of its height or altitude. The water which flow through the mountains is stored by constructing a dam or reservoir.

The internal combustion (I.C) engines are functioning on open cycle wherin the air is taken from the atmosphere and the exhaust gases are sent back in the atmosphere. The sequence of operation in a 4-stroke petrol and diesel engine involves Suction compression expansion and exhaust. The precise investigation of I.C engines are very complex due to open cycle system, the working fluid enter and leaves at different condition, quality of fuel and its combustion which make the task more difficult.

Heat engines - A device which change heat received by fuel combustion into mechanical work is called a heat engine. It may be classified into two broad categories viz. are Internal and external combustion engines.[8]

The application of (VCRS) Vapour compressor refrigeration system is in the air conditioners (window, split, central or precision), car air conditioners, domestic refrigerator etc. The different parts of a domestic refrigerator are: in the hermetical sealed compressor, air cooled condenser, capillary tube, thermo expansion device, filter, rotameter, solenoid valve, temperature control sensor.

A refrigerant is heat transfer medium through which phase change occurs from liquid to vapour i.e. evaporation at low temperature and pressure in the evaporator and then the phase change occurs from gas to liquid i.e. condensation at high pressure and high temperature in the condenser. The cycle of phase change of refrigerant, continues in the refrigeration system.

Refrigeration mean cooling i.e. lower the temperature by artificial means. It is a process of attaining lower temperature of the space or product below the surrounding temperature. It further involves maintaining the lower temperature achieved.

“Steam generator or boiler is, usually, a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel (solid, liquid or gaseous) to water, and ultimately to generate steam” [4] . The American Society of Mechanical Engineers (ASME) [5] gives the following definition of the steam generating unit:

Steam is utilized in steam power plants, steam engines, atomic power plant, and food industry for pasteurization, sterilization, textile industry, paper industry and in railway to generate power. Steam is also utilized in process type industries like sugar industries, textile industries, chemical industries for sizing and bleaching. Steam is also employed to store energy and transported through pipes.

Thermodynamics is defined as the “branch of science which deals with the interaction between the heat and work”[1]. Thermodynamics is also sometimes stated as the science of energy. Thermodynamic deals with the principles of energy and energy conversion in engineering. It also considers the thermodynamic properties of substances. Thermodynamics deals with the conversion of heat into work and vice-versa.

Integrated farming system is a multidisciplinary whole farm approach, which enables the farmers to identify opportunities and threats and act accordingly. It is a dynamic approach which can be applied to any farming system around the world. It is very effective in solving the problems of small and marginal farmers.

Conservation agriculture is an approach to managing agroecosystems for improved and sustained productivity, increased profits and food security while preserving and enhancing the resource base and the environment. Food and Agriculture Organisation of the United Nations defines conservation agriculture as a farming system that promotes maintenance of a permanent soil cover, minimum soil disturbance (i.e. no tillage), and diversification of plant species.

Low external input agriculture developed as a response to the criticisms surrounding Green Revolution technology being neither sustainable nor feasible for many small-scale farmers around the world. The concept aimed to redesign the agricultural system by optimising the use of biological resources, keeping changes to the natural ecosystem as well as the use of external inputs at a minimum (Pimentel et al., 1989).

The Green Revolution started in the early 1960s that led to the attainment of self-sufficiency in food grain production. This has been considered as the greatest agricultural transformation in the history of humankind. The Green Revolution contributed to widespread poverty reduction, averted hunger for millions of people, and avoided the conversion of thousands of hectares of land into agricultural cultivation.