Mechanical engineer interviews questions

What is effluent? Liquid waste flowing out of a factory, farm, commercial establishment, or a household into a water body such as a river, lake or a sewer system or reservoir. Waste discharged into air is called emission. What is industrial waste water? Industries use water that obtained from the water treatment system for a variety of purposes, such as - For manufacturing goods. - For cooling. - For heating. - As carrier of waste matter. - As carrier of raw material. - As a solvent. The resulting water is then classified as a waste water.

Types of waste water treatment process are as follows: 1. Effluent Treatment Plants (ETP) 2. Sewage Treatment Plants (STP) 3. Common and Combined Effluent Treatment Plants (CETP).  Effluent Treatment Plants (ETP) Physical Unit Operations Treatment methods in which the application of physical forces predominates. Screening, mixing, flocculation, sedimentation, flotation, filtration, and gas transfer are typical unit operations. Biological Unit Processes Treatment methods in which the removal of contaminants is brought about by biological activity. Biological treatment is used primarily to remove the biodegradable organic substances (colloidal or dissolved) and nutrients (nitrogen & phosphorus) from waste water.Basically, these substances are converted into gases that can escape to the atmosphere and into biological cell tissue that can be removed by settling.  Chemical Unit Processes Treatment methods in which the removal or conversion of contamin...

Method of corrosion A metal in contact with an aqueous solution functions as an electrode. The potential of this electrode is a measure of the tendency of the metal to act as an anode and become oxidized when coupled with some other material or with localized portions of the same metal which can act as cathodes. The anodic or corrosive half reaction can be represented as Where, M1 is metal corroded. The e.m.f. of the galvanic corrosion cell formed is given by Ecell = -Eanode + Ecathode This gives a driving force behind the process under equilibrium conditions. The values of e in the above expression for both anode and cathode are considered as reduction potentials which explain the negative sign for anode.

How to cool water in cooling tower? Consider the surface of a warm water droplet or film in contact with an air stream. Assuming that the water is hotter than the air, it will be cooled. By radiation –  This effect is likely to be very small under normal condition, and may be neglected. By conduction and convection –  This will depend on the temperature difference, the surface area, air velocity, etc.

Method of Measuring Dry-bulb temperature Dry-bulb temperature can simply and inexpensively be measured by an alcohol-in-glass or a common mercury thermometer. It is the temperature recorded by using a conventional thermometer. The thermometer without muslin cloth in the psychrometer records dry-bulb temperature. It just reads the ordinary temperature of the air and is a measure of sensible heat content of the air. Its unit is degree C or kelvin (K). When taking readings, the thermometer should be shielded from radiant heat sources such as motors, lights, external walls, and people. The reading must be taken in an area protected from these sources of radiation or thermometers must be shielded from radiant energy.

Method of Measuring Dew point Measurements It is defined as the temperature at which air attains saturation and a further addition of water vapour leads to dew formation because of condensation of water vapour. It is rarely used to indicate the moisture content of the air. The temperature recorded in this case is dry bulb temperature. At dew point, dry bulb and wet bulb temperature are same.  Dew point products use chilled mirror hygrometers. These can measure dew/frost points from -80 degree C to 85 degree C that is obtained by cooling a solid surface usually a mirror, until condensation occurs on the surface. High accuracy (±0.15 degree C) platinum RTD is embedded in the mirror surface to measure the reading. Various methods used to cool the mirror include ice, refrigerants (freon), thermoelectric cooling etc. These are often used as a secondary standard to calibrate other humidity transducers.

Wet bulb temperature (WBT) is usually measured with a sling or aspirated psychrometer consisting of two mercury thermometers, one of which is wrapped with a wick around the mercury bulb. The other is used to measure dry bulb temperature. To use this instrument, the wick is saturated with clean water and the psychrometer is whirled for approximately 10 to 15 seconds. The process is repeated two or three times until there is no further temperature drop on the wicked thermometer.  It is recorded by thermometer having wet muslin cloth on its bulb. The temperature recorded is in general lower than dry-bulb temperature because of cooling effect of the evaporating water of wet muslin cloth. They are equal only when air is in saturation and no net evaporation of water from wet muslin cloth takes place. Wet-bulb temperature can never be higher than dry-bulb temperature.

ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers ASHRAE 14- Methods of Testing for Rating Positive Displacement Condensing Units ASHRAE 15- Safety Code for Mechanical Refrigeration ASHRAE 20- Methods of Testing for Rating Mechanical-Draft Air-Cooled Refrigerant Condensers ASHRAE 34- Number designation and Safety Classification of Refrigerants ASHRAE Standard 55: This standard provides the thermal environmental conditions for human occupancy ASHRAE Standard 62: This standard provides guidelines to the ventilation for acceptable Indoor Air Quality ASHRAE 70- Method of Testing for Rating the Airflow Performance of Outlets and Inlets ASHRAE Standard 90.1: This standard provides guidelines to the energy efficient design of new buildings intended for human occupancy.

Allowable equipment parameters Shaft run out: 0.08 mm maximum. Pad plate squareness: 0.08 mm maximum. Concentricity of pad plate bore: 0.13 mm maximum. End play: 0.10 mm maximum. Precautions prior to fitting of seal Do not remove the seal from package till you are ready to install on the shaft. All working surfaces should be cleaned thoroughly before you start & throughout installation. Do not uses hammer while fitting the seal.