Korea''s winter horticulture is done by hot air furnace, and more than 95% is used as a diesel fuel. In order to winter cultivation the soil temperature must be maintain above 16 ~ 18 ℃. Facility horticulture farmers have great difficulty due to sharp increase in international oil price. Thus, the study is needed for reduce oil consumption and improve the productivity of horticulture farmers.
In this study, Bubble Jet Loop Heat Pipe(BJLHP) was applied to the root heating system.
Bubble Jet Loop Heat Pipe generates the forced nucleate boiling by heater in evaporating section, and the boiling heat is transported to condensation section by bubble oscillation and circulation. So it is possible to overcome low efficiency in horizontal condition of heat pipe. I conducted two kinds of fundamental studies to improve the performance of BJLHP. First we changed clearance of annual space in evaporating section as 0.79mm, 2.17mm and 3.76mm. As a result of this study, case of clearance 2.17mm showed good thermal performance of three cases. And then we used enhanced boiling surfaces in evaporation section to improve the thermal performance. We used sinter tube, enhanced boiling tube and compared with smooth tube. Sinter tube BJLHP shows best thermal performance of three types.
In this study BJLHP was designed by length 4m, and heat source is cartridge type electric heater(220V-100W). Heater input capacity was changed by slidacs 25W, 50W, 75W and 100W. And then each case of BJLHP temperature was measured. And I tested on-off system according to controlled deviation using temperature controller.
As a result the temperature difference between evaporating section and condensing section is 1℃ in case of 100W. So the device showed a uniform temperature as a whole. And effective thermal conductivity is 2,721 kW/m·K. It means BJLHP thermal conductivity is 6800 times better compared with copper.
BJLHP was installed in strawberries farm located in gimhae. When BJLHP operating soil temperature was kept at about 18℃.