Thursday, November 27, 2014

A2 70 bolt naming

Photo: SS A2-70 Bolt
SS bolt A2-70: The meaning of A2-70 in top of the SS bolt- When we see A2 Steel then we can say it SS 304 grade, also can be said 18/8 because it approximately consists of 18-20% chromium and 8-10% Nickel. 
This A2 (304) is Austenitic Steel (Primary Phase Face Centered Cubic Crystal). It has commonly three Property Classes: 50 (soft) , 70 (cold-worked) Tensile strength 700 N/mm2 & 80 (high-strength) – the most common of which is the 70 class which is cold drawn” from bar stock.
So, In a nut-shell The meaning of A2-70 is Grade 304 Stainless Steel having 700 N/mm2 tensile Strength.
Uses : used extensively for sinks, tabletops, stoves, refrigerators , pots, pans dairy equipment, brewing industry, fruit industry, food processing plants, dye tanks, pipelines,  and more plants/industry.

Tuesday, November 11, 2014

DPDC exam questions

common mechanical engineering topics

Some common Mechanical Engineering Topics
Net Positive suction Head: It is the difference between the net inlet head to the head corresponding to the vapor pressure of the fluid.
slip of Reciprocating pump: It is the difference between the theoretical discharge to the actual discharge of the pump.
Impulse Turbine: It is used in High head, low discharge.
Reaction Turbine: It is used in Low head, High Discharge.
Centrifugal Pump: High Discharge, Low Head
Reciprocating Pump: Low Discharge, High Head

Saturday, November 8, 2014

major and minor loss in pipes

Major and minor loss in pipes/duct system
Head loss of a pipe is equal to Major loss and the minor loss in the pipe. The major loss is due to friction in the pipe or duct system.  The Minor loss is due to the components in the system.
hloss = Σ hmajor_losses + Σ hminor_losses      
hloss = total head loss in the pipe or duct system
hmajor_losses = major loss due to friction in the pipe or duct system
hminor_losses = minor loss due to the components in the system
  • Major Head Loss - head loss or pressure loss - due to friction in pipes and ducts.
  • Minor Head Loss - head loss or pressure loss - due to components as valves, bends, tees and sudden enlargement , sudden contraction, exit of the pipe, inlet of the pipes and the like in the pipe or duct system.

Sunday, November 2, 2014

draft tube of turbine

What is draft tube?
Draft Tube: The draft tube is a pipe gradually increasing area used for discharging water from the exit of a reaction turbine. It is an integral part of mixed and axial flow turbine. Because of the draft tube, it is possible to have the pressure at runner outlet much below the atmospheric pressure.
Efficiency of a draft tube is defined as the ratio of net gain in pressure head to the velocity head at entrance of draft tube.
What is the calorific value of Bituminous coal?
Answer: The calorific value of Bituminous coal is 33,500 Kj/Kg