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- P - heat power
- Heat energy in the unit of time exchanged in the device.
- q - volume flow
- Volume flow rate of the fluid at actual pressure and temperature.
- ṁ - mass flow rate
- Fluid flow rate in terms of units of mass per unit of time
- T
_{1}- inlet temperature - Fluid temperature in front of the heat exchanger
- T
_{2}- outlet temperature - Fluid temperature after the heat exchanger
- ΔT - temperature change
- Fluid temperature difference before and after the heat exchanger. Gained or lost temperature depending if the device is a heater or a chiller
- ρ - fluid density
- Actual fluid density in terms of mass per unit of volume on real pressure and the temperature
- C - specific heat
- Heat capacity (specific heat) of the fluid; Specific heat at constant pressure for a gas, in terms of energy per unit of mass and temperature.
- D - diameter of tube
- Internal pipe diameter
- V - flow velocity
- Fluid flow velocity in the pipe of the heat exchanger

- Select calculation type
- P
- Calculate heat power for known flow rate
- q / ṁ
- Calculate flow rate for known heat power

- Select value to input. You should enter selected one. The other one will be calculated
- q
- volume flow rate
- ṁ
- mass flow rate

- Select value to input. You should enter selected one. The other one will be calculated
- T2
- temperature after the heater/chiller
- ΔT
- temperature difference in the device

- Select value to input. You should enter selected one. The other one will be calculated
- D
- internal pipe diameter
- V
- fluid velocity

- Select device type
- Heater
- Device that has outlet temperature lower then inlet one, due to heat energy released from the fluid to the surrounding one
- Chiller
- Device that has outlet temperature higher then inlet one, due to heat energy of the fluid increased and surrounding fluid chilled

HeaterWaterQ, T_{1}, T_{2}, dP

Task: Calculate the heat output of the heat exchanger if the water flow is 2 l/s, the temperature in front of the exchanger is 25 C, and behind the exchanger is 60 C. The diameter of the connecting pipes is 60 mm.

Solution: Heat output: 292.43 kW

HeaterWaterP, T_{1}, T_{2}, dQ

Task: Calculate the flow of water through the heat exchanger if the heat output of the exchanger is 2000 kW. The temperature in front and behind the exchanger is 70 C and 90 C. The diameter of the connecting pipes is 150 mm.

Solution: Flow rate: 86.173 m3/h

ChillerWaterP, T_{1}, T_{2}, dQ

Task: Calculate the flow of water through the chiller if the output of the chiller is 2000 kW. The temperature in front and behind the chiller is 12 C and 7 C. Calculate also the diameter of the connecting pipes for a known water flow rate of 1 m/s.

Solution: Flow rate: 344.96 m3/h