Mechanical engineering info

WHAT IS PATTERN  IN CASTING?  Pattern is an important tool in the casting process. A pattern is the model of the part to be cast, it is considered as the replica of the part to be cast , except for the various allowances. it is slightly larger than the desired casting  the process of making a pattern is known as pattern making It is the first step in making a casting. a pattern may contain core, prints, runners , gates, and risers . casting is considered as the most ancient process of producing metallic component by using pattern PATTERN MATERIALS Quantity to be casted Degree of surface finish Type of moulding finish Design of casting and possibility of its change in future These some factors are considered while selecting material for pattern which material are used for pattern making? generally wood  metal plastics plaster wax these materials are used for pattern making WOOD  Wood is most commonly used material for pattern making because it is  economical, readily available, reasonal

 FOUR STROKE ENGINE WHAT IS ENGINE ?        In the simple language engine is a power plant of vehicle which provides power  to all the unit parts of the vehicle those needs power. it is usually mounted at the front end of the car.   classification of engine   According to strokes  four stroke engine two stroke engine According to combustion  internal combustion external combustion According to ignition spark ignition  compression ignition WORKING OF ENGINE ( PETROL) four stroke engine consist four cycles (stroke) Suction stroke ( intake) compression stroke expansion or power stroke  exhaust stroke SUCTION STROKE Suction stroke starts whens piston is at the top dead centre and moves downwards. during suction stroke inlet valves is open . due to piston moving downwards low pressure region is created inside the cylinder and fresh air fuel mixture inters in cylinder at the same time the exhaust valve will closed. at the end of the suction stroke inlet valve closes COMPRESSION STROKE During

 CONDUCTION, CONVECTION, RADIATION HEAT TRANSFER. MODES OF HEAT TRANSFER  CONDUCTION HEAT TRANSFER CONVECTION HEAT TRANSFER RADIATION HEAT TRANSFER CONDUCTION HEAT TRANSFER  Conduction heat transfer is single phase phenomenon , its tack place due to molecular impact & electrons flow  we know that every substance having molecular structure and molecules are vibrating continuously when molecular impact take place heat transferred form one molecule to another molecule In metals the atomic structure consist of electrons, due to high temperature energy level of electron increases & it leaves its atom carrying excess energy this phenomenon is similar to flow of current for the conduction heat transfer always apply fourier's law of heat conduction CONVECTION HEAT TRANSFER convection heat transfer is a two phase phenomenon, in which at least one substance is fluid  the fluid molecules are free to move so they take heat from surface of the other substance accordingly heat is transfe

 HEAT TRANSFER WHAT IS HEAT TRANSFER ? Heat transfer is a form of energy transmit due to temperature difference . Heat transfer is a transmission of energy from one region to another region as a result of temperature difference Heat is a path function . heat flow from high temperature to lower temperature transfer heat high body to lower body STEADY STATE HEAT TRANSFER There is no change in heat transfer with time at any point in a direction within the medium dQ/dT = 0 ,  here Q is heat transfer In this case of energy transfer the temperature is only function of space-coordinate , not a function of time, mathematically for rectangular coordinate system   T=f(x,y,z) for example of steady state heat transfer Heat exchanger with fluid flow Heat generation due to electric current UNSTEADY STATE HEAT TRANSFER Change in heat transfer at any point with time in direction within the medium is called as unsteady heat transfer Q is heat transfer is not equal to zero In this case of energy transfe

 ENTHALPY WHAT IS ENTHALPY ? Enthalpy is a thermodynamic property of system , it is the sum of the internal energy added to the product of the pressure and volume of the system  H = E +(PV) where , H = enthalpy              E = internal energy               P = pressure              V = volume It reflects the capacity to do no mechanical and capacity to release heat . Enthalpy is denoted by H & the specific enthalpy is denoted by h . Common units are used to express enthalpy are Joule's , colorie , BTU ( british thermal unit) Enthalpy is constant in throatling process Eenthalpy of system measurement is possible to measure the difference between in enthalpy between one state and another IMPORTANCE OF ENTHALPY It is used to calculate the head of reaction of a chemical process measuring the change in enthalpy , to determine wheather a reaction was endothermic ( absorbed heat positive change in enthalpy ) OR exothermic ( released heat , negative change in enthalpy) change in enthal