Heat-transfer characteristics of a closed-loop oscillating heat-pipe with check valves

The heat-transfer characteristics of this system i.e. a CLOHP/CV, depend on the ratio of check valves (Rcv), aspect ratio (Le/di) and the dimensionless parameters of the heat transfer. The CLOHP/CV used employed a copper tube with inner diameters of 1.77 and 2.03 mm. The evaporator, adiabatic and condenser lengths were equal to 50, 100 and 150 mm. The selected working fluids were water (H2O), ethanol (C2H5OH) and R123 (CHCl2CF3) with a filling ratio of 50% of total volume. The number of turns was 40. The Rcv values were 20, 8, 5 and 4. The evaporator was heated by hot water, while the condenser section was cooled by distilled water. The inclination of the CLOHP/CV used in the experiments was 90° to the horizontal, with a controlled working-temperature of 50 °C. When the system reached the steady state, the temperature and the flow rate of the cooling water were measured in order to calculate the heat-transfer rate of the CLOHP/CV. The experimental results showed that the heat-flux increases with an increase of Rcv and decreases with an increased aspect ratio. A correlation for predicting the heat-transfer rate for the heat-pipe in the vertical position has been established.Closed-loop oscillating heat-pipe Check valves Heat -transfer characteristics

Design and construction of an oven for drying palm bunch using glycerine as fuel together with using closed-loop oscillating heat-pipe with check valves (CLOHP/CV) heat exchanger for waste heat recovery

138-143This research addresses design and construction of an oven (2 m x 3 m x 2 m) for effectively drying palm bunch using glycerin as a fuel and a closed-loop oscillating heat-pipe with check valves (CLOHP/CV) as a heat exchanger for waste heat recovery. In each experiment, palm bunches (500 kg) were baked in oven with and without CLOHP/CV heat exchanger. CLOHP/CV (0.2 m x 0.8 m x 0.5 m) is made of copper tubes (inner diam, 2.03 mm). Working fluids were distilled water, ethanol and R134a. Waste heat from oven was recovered by heat exchanger and was beneficial for pre-heating the air in combustion process. Pre-heating was useful in burning glycerine, and distribution of heat inside oven with CLOHP/CV was better than without CLOHP/CV. Consequently, palm bunches received uniform heat that restrained enzyme thus slowing dissolution reactions that would otherwise produce free fatty acids and cause loss of palm oil. Use of a CLOHP/CV also reduced moisture content of palm bunches to 1.2 wt% on dry basis. When using oven with CLOHP/CV as a heat exchanger with R134a as working fluid, the highest thermal efficiency of drying palm bunch was 42.4%, highest effectiveness of CLOHP/CV was 43.0% and highest efficiency of glycerin stove was 45.0%