Papers by Keyword: Thermosyphon

Abstract: This paper presents the results of mathematical modelling of three–dimensional heat transfer in a closed two-phase thermosyphon taking into account phase transitions. Three-dimensional conduction equation was solved by means of the finite difference method (FDM). Locally one-dimensional scheme of Samarskiy was used to approximate the differential equations. The effect of the thermosyphon height and temperature of its bottom lid on the temperature difference in the vapor section was shown.

Abstract: The objective of the present study is to investigate the performance of solar collector with serpentine shape of heat pipe and water-ethanol as a working fluid. Serpentine shape is easy of manufacturing and also to reduce cost of manufacturing. In this work, heat pipe is made from copper tube having ID 10mm and OD 12mm.The tube is bent in serpentine manner and filled with Water-ethanol as a working fluid with 70% filling ratio. The length of evaporator, adiabatic and condenser section was 480mm, 50mm and 65mm respectively. The test is conducted for coolant flow rate 4.5 kg/hr different angle of collector 20°, 31.5°, 40°, 50°, 60°. Result shows that water-ethanol collector gives better performance than collector with water as a working fluid. Maximum efficiency is observed at 31.5° inclination.

Abstract: Now a day’s different types of solar flat plate collectors are in use. Out of which only few type of collectors proved their performance by producing better results of expected level. In this paper a new set of collectors are combined as mean to improve performance of series SFPC collectors available in market now a days. In such new combination a collector with reduced overall loss coefficient was used to improve the efficiency of the existing system. New collector with zig-zag flow pattern gives a slight change in flow path. Thus the objective of this experimental analysis is to improve efficiency with new set of series FPC by comparing with existing series FPC. Experimental results obtained give better and higher results suggested by theoretical analysis.

Abstract: Heating of water for domestic purpose by making use of solar energy is essential and it is one of the effective ways of utilizing solar energy. Initial cost of solar water heating (SWH) system is high, but the operation cost is zero. This paper discusses on improving the performance of a flat plate solar energy collector by changing the design parameters of the number of riser tubes and the arrangement of riser tubes in zig-zag pattern from the existing flat plate collector system (FPC) and using the different working nanoparticles with base fluids like aluminium oxide mixed with water. Experiments were conducted using copper tube in headers and risers with two different configurations and maintain the same dimensions. The performance comparison was made for all the two types of collectors in closed loop. The performance shows that the efficiency of FPC with zig-zag arrangement of tubes (Z-Configuration) is higher than that of conventional FPC. Thus the newly presented FPCs system produces higher efficiency than the existing conventional flat plate collector system.

Abstract: In the present study, TiO₂-nanofluid with different volume ratio was used as working fluids of thermosyphon and grooved heat pipe to investigate working stability. The stability behavior of system was studied with various parameters such as volume concentration of nanoparticle, orientation, heat flux, and cooling media were investigated. Specially, the present experimental unstable working behaviors between TiO₂-nanofluid and pure water were compared. In the present study, the TiO₂-nanoparticles were dispersed into pure water with each of cross blended concentrations of 0.05%, 0.1%, 0.5%, and 1%. In the present study, the rate of growth of unstable disturbances is expressed in terms of temperature perturbation. The best stable operation was observed with thermosyphon of 0.5 % TiO₂-nanofluid. The best operation state with nanofluidic TS was observed in the 90° inclination and α = 0.5. In the present study, the enhancement of heat pipe performance with TiO₂-nanofluid is presented. The both heat pipes were fabricated from the straight stainless pipe with the inner diameter and length of 10, 500 mm, respectively.

Abstract: Natural circulation cooling systems, such as the thermosyphon loops are preferred as effective heat dissipation methods where a silent and vibration-free operation is desired in thermal control of devices and processes. Though anomalous enhancement in forced convection heat transfer coefficients have been reported for nanofluids, the effect of addition of nanoparticles to base fluids in natural convection circulation loops is not clearly understood. An experimental study is reported in this work, using aluminum oxide and copper oxide nanofluids with varying concentrations, in a thermosyphon loop. The flow velocity is arrived at from the measured pressure drop. At a nanoparticle concentration of 0.01% by volume Al2O3-water and CuO-water nanofluids shows 88.37% and 42.89% improvement in flow, respectively.

Abstract: Thermal transfer behavior of small diameter thermosyphons with different fill ratio, the inner and outer temperature response at start-up, and the calculated vapor-liquid two-phase vertical flow regimes were studied. The thermosyphons were fabricated by different diameter glass tubes. The present study suggests that the best thermal conductive performance is obtained with 26% fill ratio. Inner and outer thermal behaviors were experimentally studied with innovative methods of attaching thermocouples on thermosyphon walls from both inside and outside. Experimental results indicated a very good temperature uniformity of thermosyphons. Furthermore, a 2D, planar CFD modeling using explicit Multi-Fluid VOF model in the Eulerian multiphase model was carried out to model the interaction/interface between gas and liquid as well as fluid flow movement inside the tube. Real-time vapor bubble generation, combination and vapor slug maps were derived from the simulation. A good agreement was observed between CFD acquired data and experimental observations. It is evidenced that CFD is a powerful tool to model and examine the complex flow and heat transfer in a thermosyphon.

Abstract: Heat pipes are devices capable of very high heat transfer and have been widely used in many thermal management applications. An experimental investigation and CFD simulation of thermal characteristics of heat pipe was presented in this paper. It can be found that UDF in FLUENT can simulate the evaporation and condensation in heat pipe. The pressure difference between evaporation section and condenser ensure the vapor can flow successfully from the evaporation section to condenser. In steady state, the fluctuation of axial velocity is very small in the most area in heat pipe. In general, the magnitudes of velocity vary from 0 to maximum from the end of both evaporation section and condenser, and the maximum value was maintained in the adiabatic section.

Abstract: Thermoelectric module (TEM) systems proposed in this study adopts loop thermosyphon with TiO2-nanofluid as working fluid. The present experimental study is focused on the opt_{SubscrSubscript textipt text}imum operating condition of the TE system proposed to improve energy output and to obtain stable power generation to be used in future hybrid vehicles. The results of the present study indicate a possibility to use such loop thermosyphon TEMs for future thermoelectric hybrid automotive vehicles. The system showed the optimum performance with acetone with 50% charged amount as the working fluid for the TLT. The system with the new working fluid, nanofluids, neither improved its performance nor its stability.

Abstract: This paper investigates the condensation performance of a novel type of two-phase closed thermosyphon with internal helical microfin. The length of the thermosyphon is 1500 mm, with the filling ratio of 60%. A series of experiments were conducted for the novel and conventional thermosyphons. The results show that the internal helical microfins could not only ameliorate the thermal response characteristic but also improve the condensation heat transfer coefficient by 116.87% for the higher heat input. A correlation was developed to predict the condensation heat transfer coefficient of the novel thermosyphon.