Mechanical Engineering Interview Questions & Answers

What is the difference between petrol engine and diesel engine? The Diesel Engine is an IC Engine in which the ignition of the fuel is caused by the elevated temperature of the air which gets mechanically compressed in the cylinder. Petrol Engines, however, employ a spark plug for the ignition. How will you define the calorific value of a fuel? The calorific value of a fuel is the quantity of heat produced by its combustion – at constant pressure and under “normal” (standard) conditions (i.e. to 0°C and under a pressure of 1,013 mbar). What is the meaning of auto-ignition temperature? The Auto-ignition Temperature of a substance is the lowest temperature at which it spontaneously ignites in a standard atmosphere without an external source of ignition, such as a flame or spark. Could you explain why LMTD is introduced in a heat exchanger? LMTD stands for Logarithmic Mean Temperature Difference and is formulated as, LMTD = {(∆T - ∆t) / ln(∆T/∆t)}, where ∆T and ∆t amount to the temperature difference between the fluids at both the ends of the Heat Exchanger. The temperature change that takes place across the Heat Exchanger is not linear - it is exponential. LMTD is also a parameter used to determine the heat transfer rate through the Heat Exchanger. As the LMTD increases, the heat transfer speeds up. What are the heats called, whose sum amounts to the heat required to convert 1 kg of water into 1 kg of steam? Sensible Heat & Latent Heat What's generally the velocity of superheated and saturated steam? The velocity of superheated steam is around 70 m/s, while that of saturated steam is approximately 50 m/s. Where could superheated steam be used? Superheated steam was widely used in steam engines. It can also be used in drying and cleaning, in layering, reaction engineering, epoxy drying, and film use. ' Superheated steam can also be used in pest control. It has wide utilizations in energy systems and nanotechnology as well. Are air compressors efficient? How does the efficiency of air compressors relate to the electrical input provided? Air compressors are highly inefficient because only about 10% of the electrical input gets converted into an output - the remaining 90% amounts to sheer waste. If you suck some cranberry juice in a glass using a straw, the juice would always rise inside the straw. What established principle do you think would get violated if it doesn't? What is the principle? Pascal's Law will be violated if the juice doesn't rise when sucked. The Pascal's Law states that a pressure change at any point in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. What is cavitation in pumps? Cavitation is the formation of bubbles, or cavities, in a liquid, developed in areas of relatively low pressure around an impeller. The implosion or collapse of these bubbles triggers intense shockwaves inside the pump, resulting in significant damage to the impeller as well as the pump housing. What is NPSH in pumps? NPSH stands for Net Positive Suction Head. The margin of pressure over vapour pressure at the pump suction nozzle is defined to be the NPSH. It is the difference between stagnation suction pressure at the pump inlet, with the pump running, and the vapour pressure of the pumpage at the inlet temperature. Which furnace is used for heating metals? Induction Furnace (Electrical) is used for heating metals. How will you define the coefficient of performance? Coefficient of Performance (COP) is defined as the efficiency ratio of the amount of heating or cooling provided by a heating or cooling unit to the energy consumed by the system. The higher the COP of the system, the higher is its efficiency. What does the thickness of insulation usually depend on? What objective is the economic thickness of insulation founded on? The thickness of insulation usually depends on the characteristics of the insulating material and the purpose of the equipment. The economic thickness of insulation is founded on the objective of bearing a minimum, rather an optimum, total cost. How are pipe diameters and pressure drop related? The pipe diameters and pressure loss are inversely related. How do you calculate the volume flow rate of a liquid flowing through a pipe? The volume flow rate of a liquid flowing through a pipe is the product of the cross-section area of the pipe and the speed of flow. Q = A.v What are orthotropic materials? They are a particular class of anisotropic materials which can be described by mentioning their properties in three perpendicular directions. Wood and composites are orthotropic materials. Explain the effect of alloying chromium and nickel in stainless steel? The addition of nickel and chromium increases the tensile strength and increases in resistance to corrosion are assured. What is the curie point? Curie point is the temperature at which outside forces can no longer magnetize ferromagnetic materials. Define buckling factor? Buckling Factor is defined as the ratio of the equivalent length of the column to the minimum radius of gyration. What do you understand by catenary cable? A cable that is attached to the support and carries its weight is referred to as the catenary cable. What is a pyranometer used for? A Pyranometer is a type of Acidometer used for measuring solar irradiance on a planar surface and it is designed to measure solar radiation flux (in Watts per square meter) density from the hemisphere above within a wavelength range of 0.3 to 3 micrometers.