Refrigerant 134a enters a horizontal pipe operating at steady state at 40°C, 300 kPa, and a velocity of 25 m/s. At the exit, the temperature is 90°C and the pressure is 240 kPa. The pipe diameter is 0.1 m. Determine: (a) the mass flow rate of the refrigerant, in kg/s, (b) the velocity at the exit, in m/s, and (c) the rate of heat transfer between the pipe and its surroundings, in kW.

a) 2.42

b) 37.20 m/s

c) 120.56 kW

Explanation:

Given that:

The fluid in the Refrigerant = R-134a

Diameter (d) = 0.1 m

In the Inlet:

Temperature

Pressure

Velocity = 25 m/s

At the exit:

Temperature

Pressure

From the  Table A-12 for Refrigerant R-134a at and

Specific Volume

From the  Table A-12 for Refrigerant R-134a at and

Specific Volume

Their corresponding Enthalpy and are as follows:

Enthalpy  =284.05 kJ/kg

Enthalpy = 333 kJ/kg

a) The mass flow rate of the refrigerant can be calculated as :

b) The velocity at the exit point:

we knew that:

∴

c) Expression for calculating heat transfer (as long as there is no work that is said to be done and the pipe is horizontal) can be represented as: