Sajjad Ahmed Memon S.S./ Health Physicist NIMRA 1 Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Applications of First Law of Thermodynamics Sajjad Ahmed Memon Senior Scientist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Heat can be supplied to a thermodynamic system under the following conditions: Isobaric Process Isochoric Process Isothermal Process Adiabatic Process Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Isobaric Process A thermodynamic process in which pressure of the system remains constant during the supply of heat. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Consider a cylinder fitted with a frictionless piston. The piston is free to move in the cylinder. An ideal gas is enclosed in the cylinder. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA DQ = DU + DW But DW = PDV Thus DQP = DU + PDV As DV = (V2 - V1) DQP = DU + P (V2 - V1) Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Isochoric Process A thermodynamic process in which the volume of the system remains constant during the supply of heat. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Consider a cylinder fitted with a frictionless piston. An ideal gas is enclosed in the cylinder. The piston is fixed at a particular position so that the volume of cylinder remains constant during the supply of heat. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Let DQ amount of heat is added to the system. Addition of heat causes the following changes in the system: DQ = DU + DW But DW = PDV Thus DQ = DU + PDV As DV = 0 DQ = DU + P (0) = DU Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA This expression indicates that the heat supplied under isochoric process is consumed in increasing the internal energy of the system but no work is performed. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Isothermal Process A thermodynamic process in which the temperature of the system remains constant during the supply of heat. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Isothermal Compression Consider a cylinder of non-conducting walls and good heat conducting base. The cylinder is fitted with a frictionless piston. An ideal gas is enclosed in the cylinder. In the first stage pressure on the piston is increased and the cylinder is placed on a cold body. Due to compression, the temperature of the system increases but at the same time DQ amount of heat is removed from the system and the temperature of the system is maintained. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA DQ = DU + DW Since temperature is constant, therefore, there is no change in internal energy of the system. i.e. DU = 0 As the work is done on the system, therefore, DW is negative DQ = 0 + (-DW) DQ = -DW Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Isothermal Expansion In another situation the cylinder is placed over a hot body and the pressure on the system is decreased. Due to expansion, the temperature of the system is decreased but at the same time DQ amount of heat is absorbed from the hot body and the temperature of the system is again maintained. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA DQ = DU + DW Since temperature is constant, therefore, there is no change in internal energy of the system. i.e. DU = 0 As the work is done by the system, therefore, DW is positive DQ = 0 + (DW) DQ = +DW Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Adiabatic Process A thermodynamic process in which there is no heat transfer into or out of the system takes place. In other words DQ = 0. An adiabatic process is generally obtained by surrounding the entire system with a strongly insulating material or by carrying out the process so quickly that there is no time for a significant heat transfer to take place. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA DQ = DU + DW Since there is no heat transfer into or out of the system. i.e. DQ = 0. 0 = DU + DW DU = - DW Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA Since DU is the change in internal energy and DW is the work done by the system, therefore the possible outcomes: 1. A system that expands under adiabatic conditions does positive work, so the internal energy decreases. 2. A system that contracts under adiabatic conditions does negative work, so the internal energy increases. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

Sajjad Ahmed Memon S.S./ Health Physicist NIMRA