The performance of a thermosyphon loop in a double – cycle distillation heat pump system, utilizing water as a working fluid and finned tube heat exchangers for evaporator and condenser, has been investigated. A mathematical model is set for the whole system and a simulating program is developed to simulate the double – cycle processes during the steady – state operation. A complete steam tables subroutine developed and incorporated with the main program to calculate the water and steam properties in the range of (60 – 120)o C and (0.199 – 1.985)bar.
The experimental results show good agreement with the results obtained from the computer program (Quick Basic). During steady – state operation of the system, it found that the thermosyphon loop performance (loop conductance) increase when the working mass flow rate increase and also it increase when the working fluid pressure increase and has a maximum value (493.022 W/m2. K) At working mass flow rate of 5.5 kg/hr, working fluid pressure of 0.8 bar and process fluid pressure of 1.01825 bar.