Page 59 - MASHRAE 35th Anniversary

15th Asia Pacific Conference on the Built Environment 5R Technology for Building Environment Copyright © 2019 by ASHRAE Region XIII
Experimental Investigation of Two Phase Loop Thermosyphon Solar Drying System
WenBin Ng1, Aloysuis Decruz2, Yeong Jin King3
1HeatingVentilating Air Conditioning and Refrigeration Section, Universiti Kuala Lumpur Malaysia France Institute, Bandar Baru Bangi, Malaysia; ngwenbin@unikl.edu.my
2HeatingVentilating Air Conditioning and Refrigeration Section, Universiti Kuala Lumpur Malaysia France Institute, Bandar Baru Bangi, Malaysia; aloysius@unikl.edu.my
3Department of Mechanical and Material Engineering, Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Malaysia; kingyj@utar.edy.my
Abstract
Solar drying systems are extensively used in Malaysia because of high solar irradiance. Most of the developed solar drying systems employed air-based solar collector in generating hot drying air. Therefore, the solar drying system proposed in this work employs a liquid-based solar collector with a thermosyphon close loop whereby a phase change working fluid is used to transfer the heat energy from solar collector. This system is used evacuated tube collector to generate heat from the sun. The effects of different working fluid with different quantity of collectors are used to identify performance of two phases close loop thermosyphon solar drying system. The performances of water, ethanol, R134a and R600a as the phase change working fluid are also tested with different quantity of collectors. The results show R600a has better efficiency with two collectors at 27.6%, water at 16.28%, ethanol at 10.19% and R134a at 2.4%. For mass flow rate result is, R600a also has better result with using eight collectors at 0.55564 kg/s, water at 0.10301 kg/s, ethanol at 0.10216 kg/s and R134a at 0.09190 kg/s. For temperature outlet collector is, water get the highest result using eight collectors at 110.2°C, ethanol at 94°C, R134a at 80.8°C and R600a at 80.2°C.
Keywords: Closed loop thermosyphon, drying system, efficiency.
INTRODUCTION
Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, the fluid in the system circulates without pumping fluid using a mechanical pump. This means that the fluid is circulated by using gravity feed. The circulation of liquids and volatile gases is used in thermosyphon system in heating and cooling
applications such as boilers, water heaters, heat pumps and furnaces (Vasiliev et al. 2017).
Thermosyphon contain of two main sections, evaporator and condenser. Where the function of evaporator part is to absorb the heat by the working fluid and the condenser part is to reject heat. By the evaporation and condensation of vapour, heat also can transfer in this system. However, the system is properly classified as a heat pipe thermosyphon. If the system also consists other fluids, such as air, then the heat flux density will be less than in a real heat pipe, which only contains a single fluid.(Danielewicz et al. 2014) Thermosyphons are used in some liquid-based solar heating systems to heat a liquid such as water, acetone, chloroform or other fluids. The water is heated passively by solar energy and the part of quandary can condensate or transform to the hot vapour phase. Convection permits for the movement of the heated liquid out of the solar collector to get replaced by warm liquid that is successively heated. Because of this principle, it's necessary for the water to be keep in an exceedingly tank on top of the collector.
Many researchers study the performance of working fluid in thermosyphon system without using evacuated tube collector (ETC) (Leong et al. 2012; Ma et al. 2017; 􏰀􏰁􏰂􏰃􏰄􏰅􏰆􏰇􏰄􏰈 􏰊􏰅􏰋􏰈 􏰁􏰌􏰍 􏰎􏰅􏰁􏰏 􏰐􏰑􏰒􏰓􏰔 􏰕􏰁􏰌􏰖􏰇􏰗􏰘 􏰅􏰙 􏰁􏰚􏰛 􏰐􏰑􏰒􏰜􏰔 Kuznetsov et al. 2016). One of the studies was investigated on performance of nanofluids as working fluid in a thermosyphon air-preheater by Leong et al, (2017). Leong et al., (2017) concluded that when hot air velocity increases from 2.0 m/s to 4.75 m/s, the overall heat transfer is increase to 23% for water based, 7% for alumina and 4% for titanium dioxide nanofluids respectively. Ersoz, Mustafa Ali (2016) and 􏰕􏰁􏰌􏰖􏰇􏰗􏰘 􏰅􏰙 􏰁􏰚􏰛 􏰝􏰐􏰑􏰒􏰜􏰞 obtained the same result for acetone which has the highest performance in their studies. From the result obtained by 􏰕􏰁􏰌􏰖􏰇􏰗􏰘 􏰅􏰙 􏰁􏰚􏰛 􏰝􏰐􏰑􏰒􏰜􏰞 shown that the best cooling effect is acetone, second is fluorinert FC-72 and third is ethyl alcohol. Acetone has the lowest value of thermal resistance, that is the best for heat transfer