DIFFERENCE BETWEEN HEAT AND WORK

ENGINEERING THERMODYNEMICS

By Kaushal Patel

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•Work and heat are two most important concepts in thermodynamics. Work and heat are highly interrelated but they are not quite the same. Both heat and work are concepts of energy. We are going to discuss definitions, similarities, and difference between heat and work.

WORK AND HEAT

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• In the physics work is defined as “The amount of energy transferred by a force acting though a distance.”

• It can be proved that work is dependent on path taken, which means work is function of path.

WORK

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•But in thermodynamics, work is referred as displacement work(pressure work) which is produced by presser of gas acting on piston.

•Assume that piston moves dx to out word due to pressure acting on it and consider p is constant. The work done by system is

δW = F × d = (p × A) × dx = pdV (dV = Adx)

WORK(Continue…)

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•Heat is defined as “Form of energy that is transferred between system and surrounding or two systems due to temperature difference.”

•Heat can be converted into work and work can be converted into heat.

•When temperature difference exist between two bodies it is cause of heat flow.

•Amount of heat in the system is depends on the state of system. Therefore, heat is a function of the state.

HEAT

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WORK AND HEATTRANSFER IS PATH FUNCTION

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• Heat is energy interaction due to temperature difference. Work is energy interaction by reasons other than temperature difference.

• Heat is low grade energy while work is high grade energy.

• Heat is function of state because it is depend on state of system while work is function of path because it is depend on path taken by system while changing state.

• Efficiency of transfer of work to heat is higher but efficiency of transfer of heat to work.

DIFFERENCE BETWEEN HEAT AND WORK

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• Both heat and work are not properties of system.

• Both are boundary phenomena because they are energies which are crossing the system boundary.

• Both are transient quantities. These energies interaction occurs only when a system undergoes change of state.

• The heat and work is form of energy. Units of both are joule.

• Both heat and work cannot be stored by system.

SIMILARITANDIES BETWEEN HEAT WORK

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