Energy Equation Mechanical Energy Forms of energy that

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Energy Equation

Energy Equation

Mechanical Energy? Forms of energy that can be converted to MECHANICAL WORK completely and

Mechanical Energy? Forms of energy that can be converted to MECHANICAL WORK completely and directly by mechanical device(s) Kinetic energy (KE) & Potential energy (PE) are forms of Mechanical energy (emech) Thermal energy is not in the form of emech Chapter 2 Lecture 3 2 Energy Equation

Mechanical Energy? (Contd. ) Pressure can be associated with emech P = P/A =

Mechanical Energy? (Contd. ) Pressure can be associated with emech P = P/A = N/m 2 = (N. m)/m 3 = J/m 3 It’s energy per unit volume! Systems used to transport fluid may exerted or extracted energy Chapter 2 Lecture 3 3 Energy Equation

Flow Work It’s the work effect produced due to pressure acting over the distance

Flow Work It’s the work effect produced due to pressure acting over the distance Stated in the amount of per unit mass (P/ρ) Convenient to be expressed in fluid properties terms as part of the fluid energy It’s called as FLOW ENERGY Chapter 2 Lecture 3 4 Energy Equation

Flow Work & Flow Energy For a flowing fluid, emech can be written; emech

Flow Work & Flow Energy For a flowing fluid, emech can be written; emech = = eflow (P/ρ) + KE + PE + (V 2/2) + (gz) Changes of emech for a flowing fluid turns to; Chapter 2 Lecture 3 5 Energy Equation

Flow Work & Flow Energy (Contd. ) If emech > 0 = work is

Flow Work & Flow Energy (Contd. ) If emech > 0 = work is supplied to the fluid If emech < 0 = work is extracted from the fluid If emech = 0 = flow properties constant Consider; (Cengel & Cimbala, 2006) Chapter 2 Lecture 3 6 Energy Equation

Flow Work & Flow Energy (Contd. ) From previous Figure also; Work generated per

Flow Work & Flow Energy (Contd. ) From previous Figure also; Work generated per unit mass is same for top and bottom generation i. e. ; emech top = emech bottom Chapter 2 Lecture 3 7 Energy Equation

Energy Transfer and Efficiency emech is transferred by rotating devices such as pump and

Energy Transfer and Efficiency emech is transferred by rotating devices such as pump and turbine Pump = Transfer emech from shaft to fluid Turbine = Transfer emech from fluid to shaft Efficiency of emech conversion is ηmech Chapter 2 Lecture 3 8 Energy Equation

Mechanical Efficiency is defined as; Where; Emech, out = Emech, in – Emech, loss

Mechanical Efficiency is defined as; Where; Emech, out = Emech, in – Emech, loss Chapter 2 Lecture 3 9 Energy Equation

Pump & Turbine Efficiency In fluid system, attention is given to increase the pressure,

Pump & Turbine Efficiency In fluid system, attention is given to increase the pressure, velocity and elevation This is done by supplying mechanical energy to the fluid by pump of fan Also, by reversing the process to reduce the pressure, velocity, and elevation of the fluid This is done by extracting mechanical energy from the fluid by turbine Chapter 2 Lecture 3 10 Energy Equation

Pump & Turbine Efficiency (Contd. ) Pump efficiency is defined as; Where; Chapter 2

Pump & Turbine Efficiency (Contd. ) Pump efficiency is defined as; Where; Chapter 2 Lecture 3 11 Energy Equation

Pump & Turbine Efficiency (Contd. ) While turbine efficiency is defined as; Where; Chapter

Pump & Turbine Efficiency (Contd. ) While turbine efficiency is defined as; Where; Chapter 2 Lecture 3 12 Energy Equation

Motor & Generator Efficiency Should not be confused with ηmech Motor Efficiency; Generator Efficiency;

Motor & Generator Efficiency Should not be confused with ηmech Motor Efficiency; Generator Efficiency; Chapter 2 Lecture 3 13 Energy Equation

Motor & Generator Efficiency (Contd. ) Electrical Power Flowing Fluid Chapter 2 Lecture 3

Motor & Generator Efficiency (Contd. ) Electrical Power Flowing Fluid Chapter 2 Lecture 3 ηmotor ηturbine Motor (Pump) ηpump Generator ηgenerator (Turbine) 14 Flowing Fluid Electrical Power Energy Equation

Combined Efficiency Pump-Motor System Ratio of the increase in the mechanical energy of the

Combined Efficiency Pump-Motor System Ratio of the increase in the mechanical energy of the fluid to the electrical power consumption of the motor Turbine-Generator System Ratio of the decrease in the mechanical energy of the fluid to the electrical power generation of the generator Chapter 2 Lecture 3 15 Energy Equation

Combined Efficiency (Contd. ) Mathematically; For pump-motor For turbine-generator Chapter 2 Lecture 3 16

Combined Efficiency (Contd. ) Mathematically; For pump-motor For turbine-generator Chapter 2 Lecture 3 16 Energy Equation

Energy Simplification in term of emech can be written as; emech in – emech

Energy Simplification in term of emech can be written as; emech in – emech out = ∆emech system + emech loss For steady operation, energy balance turns to be; emech in = emech out + emech loss That’s steady flow analysis! Chapter 2 Lecture 3 17 Energy Equation

Examples & Tutorials Consider a river flowing toward a lake at an average velocity

Examples & Tutorials Consider a river flowing toward a lake at an average velocity of 3 m/s at a rate of 500 m 3/s at a location 90 m above the lake surface. Determine the total mechanical energy of the river water per unit mass and the power generation potential of the entire river at that location Chapter 2 Lecture 3 18 Energy Equation

Examples & Tutorials (Contd. ) Electric power is to be generated by installing a

Examples & Tutorials (Contd. ) Electric power is to be generated by installing a hydraulic turbine-generator at a site 70 m below the free surface of a large water reservoir that can supply water at a rate of 1500 kg/s steadily. If the mechanical power output of the turbine is 800 k. W and the electric power generation is 750 k. W, determine the turbine efficiency and the combine turbine-generator efficiency of this plant. Neglect losses in the pipes Chapter 2 Lecture 3 19 Energy Equation

Examples & Tutorials (Contd. ) At a certain location, wind is blowing steadily at

Examples & Tutorials (Contd. ) At a certain location, wind is blowing steadily at 12 m/s. Determine the mechanical energy of air per unit mass and the power generation potential of a wind turbine with a 50 m diameter blades at that location. Also determine the actual electric power generation assuming an overall efficiency of 30 percent. Take air density to be 1. 25 kg/m 3 Chapter 2 Lecture 3 20 Energy Equation

Next Lecture? Bernoulli’s Equation Chapter 2 Lecture 3 21 Energy Equation

Next Lecture? Bernoulli’s Equation Chapter 2 Lecture 3 21 Energy Equation

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