TY - JOUR N2 - The performance of ten wickless heat pipes without adiabatic sections is investigated experimentally at low heat inputs 120 to 2000 W/m2 for use in solar water heaters. Three heat pipe diameter groups were tested, namely 16, 22, and 28.5 mm. Each group had evaporator lengths of 1150, 1300, and 1550 mm, respectively, with an extra evaporator length of 1800 mm added to the second group. The condenser section length of all heat pipes was 200 mm. Ethanol, methanol, and acetone were utilized as working fluids, at inventory of 25%, 50%, 70%, and 90% by evaporator volume respectively. The 22 mm diameter pipes were tested at inclination angles 30◦, 45◦, and 60◦. Other diameter groups were tested at 45◦ only. Experiments revealed increased surface temperatures and heat transfer coefficients with increased pipe diameter and evaporator length, and that increased working fluid inventory caused pronounced reduction in evaporator surface temperature accompanied by improved heat transfer coefficient to reach maximum values at 50% inventory for the selected fluids. Violent noisy shocks were observed with 70% and 90% inventories with the tested heat pipes and the selected working fluids with heat flux inputs from 320–1900 W/m2. These shocks significantly affected the heat pipes heat transfer capability and operation stability. Experiments revealed a 45◦ and 50% optimum inclination angle of fill charge ratio respectively, and that wickless heat pipes can be satisfactorily used in solar applications. The effect of evaporator length and heat pipe diameter on the performance was included in data correlations. L1 - http://www.czasopisma.pan.pl/Content/116762/PDF/13_paper.pdf L2 - http://www.czasopisma.pan.pl/Content/116762 PY - 2020 IS - No 2 EP - 276 DO - 10.24425/ather.2020.133632 KW - Wickless heat pipe KW - Adiabatic section KW - Solar heat pipe KW - Fill charge ratio KW - Working fluid inventory KW - Inclination angle A1 - Al-Joboory, Hassan Naji Salman PB - The Committee of Thermodynamics and Combustion of the Polish Academy of Sciences and The Institute of Fluid-Flow Machinery Polish Academy of Sciences VL - vol. 41 DA - 2020.06.25 T1 - Experimental investigation of gravity-assisted wickless heat pipes (thermosyphons) at low heat inputs for solar application SP - 257 UR - http://www.czasopisma.pan.pl/dlibra/publication/edition/116762 T2 - Archives of Thermodynamics ER -