Category: Advance Concept Mechanical Eng

Centroid of U-section

The U-section shown in Figure 11.4 can be divided into three parts—lower part of area A1 and two upper parts of area A2. The lengths and widths of all the parts of U-section are shown in Figure 11.4. Let the X and Y coordinates pass through origin O. Figure 11.4 U-section The coordinates for centroid can be calculated using the following formula:

Centre of Gravity, Centre of Mass, and Centroid of an Irregular Shape

In Figure 11.1, an irregular shape is shown for which we want to calculate the centre of gravity, centre of mass, and centroid. Here, our purpose is to differentiate the concepts of these three different terms. It is assumed that the irregular shape, as shown in Figure 11.1, is of uniform thickness, density, and subjected to uniform gravitational field.… Continue reading Centre of Gravity, Centre of Mass, and Centroid of an Irregular Shape

INTRODUCTION

The centroid of an area is the mean position of elements of area. The coordinates of centriod is mean value of coordinates of all the elemental points in the area. The centre of mass is the mean position of elements of mass. In a uniform gravitational field, the gravitational force acts through the centre of… Continue reading INTRODUCTION

AXIAL FLOW COMPRESSORS

In axial flow compressors, the flow proceeds throughout the compressor in a direction essentially parallel to the axis of the machine. The unit consists of adjacent row of rotor blades and stator blades. One stage of the machine comprises a row of rotor blades followed by a row of stator blades. For efficient operation, the… Continue reading AXIAL FLOW COMPRESSORS

CENTRIFUGAL COMPRESSORS

In these compressors the pressure rise takes place due to the continuous conversion of angular momentum imparted to the gas by a high-speed impeller into static pressure. Unlike reciprocating compressors, centrifugal compressors are steady flow devices hence they are subjected to less vibration and noise. Figure 10.9 shows the working principle of a centrifugal compressor. As shown… Continue reading CENTRIFUGAL COMPRESSORS

ROTARY COMPRESSORS

Fixed Vane Type Compressors These compressors belong to the category of positive displacement type as compression is achieved by reducing the volume of the gas. In this type of compressors, the rotating shaft of the roller has its axis of rotation that matches with the centre line of the cylinder; however, it is eccentric with… Continue reading ROTARY COMPRESSORS

Work Done in Multistage Compression

P−V and T−S diagrams for multistage compression are shown in Figure 10.6. Figure 10.6 ρ−V and T−S Diagrams for Multistage Compressor If P1, T1 and delivery pressure P3 are fixed, the optimum value of the intermediate pressure P2 for minimum work can be obtained by setting the derivative dW/dP2 = 0. For perfect cooling,  In general, if there are N stages, the pressure ratio for each stage will be given by, Heat Rejected During… Continue reading Work Done in Multistage Compression

Multistage Compression

Number of stages required depends on the pressure to be developed in compressor. Normally, following relationships are used with pressure and number of stages. Advantages of Multistage Compression Assumption in Multistage Compression: The following assumptions are usually made in calculation of work done in multistage compression:

Volumetric Efficiency

The volumetric efficiency of a compressor is the ratio of actual free air delivered to the displacement of the compressor. Substituting the value of V4 in Eq. (10.1), we get Where ∈ is clearance ratio  and r is pressure ratio  Example 10.1: A single cylinder, single acting air compressor has a cylinder diameter of 150 mm and stroke of 300 mm. It… Continue reading Volumetric Efficiency