THERMODYNAMICS FLUIDS AND DEVICES CLASS NOTES

THERMODYNAMIC  FLUIDS

 AND DEVICES CLASS NOTES

 

 In thermodynamics, meaning of ‘thermo’ is heat energy.

Dynamics means the motion of molecules or atoms.

Thermodynamic fluids are heat with fluids in motion.

Fluids are liquids, vapors & gases. Pressure, temperature,

specific volume, density, internal energy & specific weight

are important thermodynamic properties of fluids.

Thermodynamic properties which cannot be directly

measured are internal energy, entropy, enthalpy,

Helmholtz free energy and Gibbs free energy.

They are concepts to make the subject easy.

Calculate these from experimentally measurable properties.

Thermodynamics devices involve mass transfer,

energy transfer and both mass & energy transfer

Their study involves chemical reactions &

phase transformations, power consumption and power production.

Their use exists in heat transfer, combustion, fluid mechanics.

It uses laws of thermodynamics, Newton’s laws of motion,

laws of conservation of mass and steady flow energy equation.

Heat transfer deals with transfer of heat from

 by conduction, convection & radiation.

Temperature gradient causes heat transfer. It deals

with heating, cooling, phase transformations and heat treatments.

Combustion deals with conversion of chemical

energy of fuels to heat energy. Energy gives

 motion and work.

Fluid mechanics studies forces and their

effect on fluids. Study of fluids at rest

lies under fluid statics. Fluid dynamics include

 kinematics and fluid kinetics. Fluid

kinematics deals with motion

of fluids. Fluid kinetics deals with motion

of fluids under forces acting on it.

Thermodynamics mainly dears with heat

and work conversions with fluids flow in various

thermodynamic devices. It considers a thermodynamic

system with boundary and surroundings.

 Thermo-fluids
  1. Water
 Boilers, pumps and water turbines use water
  1. Vapor
 Nozzles, steam engines, steam turbines & refrigerators use vapors.
  1. Air
 Compressors and air conditioners use air
  1. Refrigerants
Different refrigeration systems use different refrigerants like R-22, R-134 a and R-717.
  1. Fuel and air
 Petrol, diesel, gas engines and gas turbines use fuel & air.
        6. Steam
 Steam engines, steam turbines & refrigeration system use steam as the working substance.
          7. Other fluids
 Heat exchangers use other fluids.

Thermodynamics

 

Fig. Simple vapor compression refrigeration cycle

(Fluid = refrigerant , device= refrigeration system)

 Thermodynamic Devices
  1. Pump increases pressure of liquids using electrical energy.
  2. Nozzles increase velocity at the expense of pressure energy.
  3. Combustion chamber exists in internal combustion engines and gas turbines. This converts chemical energy of the fuels into heat energy.
  4. Piston cylinder arrangement used in internal & external combustion engines. It produces mechanical and electrical power.
  5. Pistons used in pumps and compressors consume electrical power to increase pressure.
  6. Pressure vessels convert heat energy into pressure energy as in boilers.
  7. Furnace converts chemical energy into heat energy.
  8. Turbines convert kinetic energy into mechanical and electrical energies.
  9. Turbo-compressors convert mechanical energy into pressure energy.
  10. Diffusers convert kinetic energy into pressure energy. Turbo-compressors, jet engines and steam jet refrigeration system use diffusers.
  11. Fans and blowers convert electrical energy into kinetic energy.
  12. Wind mill coverts kinetic energy into mechanical and electrical energy.
  13. Photo voltaic cells convert solar energy into electrical energy.
  14. Human body converts chemical energy of foods into many other forms of energy. These energies are sound energy, mechanical energy, light energy and kinetic energy.
  15. Throttle valve is constriction in a pipe to decrease pressure
  16. Heat exchanger helps heat transfer from a hot fluid to a cold fluid.
  17. Boiler converts liquid into vapors using heat.
  18. Condenser converts vapors into liquid by losing heat.
  19. Heat pump pumps heat from cold to hot regions.