scholarly journals Analysis of the possibility of applications for a two-phase reverse thermosyphon in passive heat transport systems

2018 ◽  
Vol 49 ◽  
pp. 00020 ◽  
Author(s):  
Michal Duda ◽  
Jurij Dobrianski ◽  
Daniel Chludzinski
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Transport ◽  
Heat Load ◽  
Experimental Studies ◽  
Hot Water ◽  
Transport Systems ◽  
Working Fluid ◽  
Two Phase

Devices called reverse thermosyphon enable passive heat transfer when the heat source is above the place of its receipt. This is often the case in solar installations for the preparation of hot water. The article concerns the determination of the possibility of using a two-phase inverted thermosyphon with two working factors in a passive downwards heat transport installation. The analysis was carried out on the basis of previous experimental studies. The height of the tested installation in one case was 1.5 m, in the second 18 m, at a heat load of 300, 600 and 900 W. Water and pentane was used as a working fluid inside the loop. Initial conclusions from the analysis confirm the possibility of using reverse thermosyphon with two working factors in the construction of a passive heat transport system.

Experimental Study of Linear and Radial Two-Phase Heat Transport Devices Driven by Electrohydrodynamic Conduction Pumping

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Source ◽  
Capillary Pressure ◽  
Heat Transport ◽  
Radial Direction ◽  
Heat Pipes ◽  
Working Fluid ◽  
Phase Flow ◽  
Transport Capacity ◽  
Two Phase ◽  
Capillary Phenomenon

Heat pipes are well known as simple and effective heat transport devices, utilizing two-phase flow and the capillary phenomenon to remove heat. However, the generation of capillary pressure requires a wicking structure and the overall heat transport capacity of the heat pipe is generally limited by the amount of capillary pressure generation that the wicking structure can achieve. Therefore, to increase the heat transport capacity, the capillary phenomenon must be either augmented or replaced by some other pumping technique. Electrohydrodynamic (EHD) conduction pumping can be readily used to pump a thin film of a dielectric liquid along a surface, using electrodes that are embedded into the surface. In this study, two two-phase heat transport devices are created. The first device transports the heat in a linear direction. The second device transports the heat in a radial direction from a central heat source. The radial pumping configuration provides several advantages. Most notably, the heat source is wetted with fresh liquid from all directions, thereby reducing the amount of distance that must be travelled by the working fluid. The power required to operate the EHD conduction pumps is a trivial amount relative to the heat that is transported.

Experimental Studies on the Gas-Stack Heat Transfer in a Thermoacoustic Refrigeration System

2003 ◽  
Author(s):  
Phani R. Gurijala ◽  
Emmanuel C. Nsofor
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Experimental Studies ◽  
Heat Losses ◽  
Inert Gases ◽  
Working Fluid ◽  
Sound Waves ◽  
Thermoplastic Material ◽  
Pressure Transducers ◽  
Thermoacoustic Refrigeration

Thermoacoustic refrigeration employs inert gases as the working fluid and uses high intensity sound waves to pump heat energy. The major components of the system are the resonator, the acoustic driver, the heat exchangers and the stack. The useful thermoacoustic process for cooling in the system takes place between the gas particles and the stack. The system was designed and constructed. Experimental studies on the gas-stack heat transport and the Streaming Reynolds Number, which play crucial roles in the heat transport behavior, were studied. Input signals for the experiments, for the data acquisition system was from thermocouples and pressure transducers. Results from the study were used to make recommendations for the system. It was observed that for a given frequency, the heat transfer increases with drive ratio. Results from the comparison of the heat losses for a stainless steel stack and a stack built of thermoplastic material show that the plate heat losses can be significantly reduced if the stack with thermoplastic material is used for the system.

Water-Ammonia Cycles for the Utilization of Low Temperature Geothermal Resources

2015 ◽  
Author(s):  
Daniele Fiaschi ◽  
Giampaolo Manfrida ◽  
Lorenzo Talluri
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Heat Source ◽  
Unit Cost ◽  
Heat Capacities ◽  
Hot Water ◽  
Saturated Steam ◽  
Working Fluid ◽  
Evaporator Temperature ◽  
Power Cycle

The research deals with the possibility of effective exploitation of low temperature geothermal energy resources, which are generally much more widespread worldwide compared to conventional high temperature ones, typically available only in limited areas of the Earth. The basic idea is the application of an advanced binary cycle, only thermally coupled to the primary endogen heat source. The selected reference-power cycle is the well-known Kalina, which gives the possibility of optimizing the matching between heat capacities of the geothermal fluid (i.e. typically hot water or saturated steam) and the cycle working fluid, which is a non azeotropic NH3-H2O mixture with variable vaporization temperature at a fixed pressure. The heat transfer diagrams of the main Kalina heat exchangers, namely the condenser and the evaporator, are analysed with the aim of minimizing the irreversibilities related to the heat transfer. At different fixed NH3-H2O composition and condenser pressures, the evaporator pressure shows an efficiency optimizing value between 40 and 55 bar, generally increasing at higher condenser pressure. At fixed geothermal heat source temperature, condenser/evaporator pressures and working mixture composition, the cycle efficiency increases with increasing evaporator temperature, because of the reduction in the approach temperature difference between the geothermal and the working fluid. Higher efficiencies are found at higher NH3 concentrations. The proposed Water-Ammonia power cycle is further enhanced introducing a chiller (thus making the power cycle a CCP unit), thanks to the properties of the fluid mixture downstream the absorber, through an intermediate heat exchanger between the condenser and the evaporator. Mainly due to the better matching of heat capacities between the geothermal and the working fluid, the proposed power cycle offers the possibility of interesting improvements in electrical efficiency compared to traditionally proposed binary cycles using ORCs, at fixed temperature level of the heat source. In the investigated proposal, values of electric efficiency between 15 and 20% are found. An economic analysis is presented, demonstrating that the CCP system is able to produce electricity at decreased unit cost with respect to the power-only unit.

Experimental studies on thermosyphon using low global warming potential refrigerant HFE7000 and nanorefrigerant HFE7000/Al2O3

2020 ◽  
pp. 095440891989669
Author(s):  
R S Anand ◽  
C P Jawahar ◽  
A Brusly Solomon ◽  
Varghese Benson ◽  
Ashie Alan K ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Volume Concentration ◽  
Experimental Studies ◽  
Bond Number ◽  
Considerable Effect ◽  
Economic Feasibility ◽  
Working Fluid ◽  
Two Phase ◽  
Technology Advancement ◽  
Natural Refrigerant

Thermosyphon is used in numerous applications such as permafrost, cooling building and structures, Alaska pipeline, electronic cooling, and other applications. Improving the performance of thermosyphon is essential for technology advancement. Therefore, experimentation is conducted to improve the efficiency of thermosyphon with the natural refrigerant hydrofluoroether (HFE) and Al2O3/HFE7000 nanorefrigerant. The Al2O3 nanoparticle is chosen based on its economic feasibility and better thermo-physical properties with the refrigerants. Firstly, the preparation of Al2O3/HFE7000 nanorefrigerant is carried out specifically at different volume concentrations of the nanoparticle to check the long-term stability. Secondly, the heat transfer characteristics of the thermosyphon charged Al2O3/HFE7000 nanorefrigerant of 0.025%, 0.05%, and 0.075% volume concentration and pure HFE7000 is investigated experimentally. The nanorefrigerant charged thermosyphon experimented for different inclinations and different volume concentrations as the working fluid. It was observed that the two-phase closed thermosyphon charged with Al2O3/HFE7000 nanorefrigerant enhanced its evaporator heat transfer performance also decreased the thermal resistance of 57.5% compared with the pure HFE7000 and was at its peak for 0.05% volume concentration. The heat transfer of nanorefrigerant Al2O3/HFE7000 0.025%, 0.05%, and 0.075% volume concentration is increases 41.61%, 88.414%, and 74.362% than HFE7000. In conclusion, the results of the experiments suggest that the use of Al2O3/HFE7000 nanofluid produce a significant thermal enhancement in thermosyphon. This research also discloses the effect of dimensionless parameters such as the Bond number of the boiling phenomenon, Prandtl and condensation number of conduction phenomenon, and Ohensorge number of buoyancy phenomenon in thermosyphon with Al2O3/HFE7000 nanorefrigerant. It is identified that the volume concentration of 0.05% Al2O3/HFE7000 has a considerable effect on nondimensional parameters.

Radial, Two-Phase Heat Transport Device Driven by Electrohydrodynamic Conduction Pumping

2011 ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Thin Film ◽  
Heat Flux ◽  
Heat Source ◽  
Liquid Film ◽  
Heat Pipe ◽  
Heat Transport ◽  
Working Fluid ◽  
Bottom Surface ◽  
Two Phase ◽  
Transport Device

Electrohydrodynamic (EHD) conduction pumping can be readily used to pump a thin film of a dielectric liquid along a surface, using electrodes that are embedded into the surface. This effect has been demonstrated under adiabatic conditions and has also been used to create a two-phase heat transport device that is similar to a heat pipe, but with the wicking structure replaced by an EHD conduction pump. In this study, a circular two-phase heat transport device is created. The device features circular electrodes that are arranged concentrically on the bottom surface and that pump a liquid film towards a heat source located at the center of the device. This heat source evaporates the liquid, and a large annular condenser at the periphery of the bottom surface provides a continuous supply of fresh liquid. This radial pumping configuration provides several advantages. Most notably, the heat source is wetted with fresh liquid from all 360 degrees, thereby reducing the amount of distance that must be travelled compared to a linear device. Consequently, the heat flux that can be removed from the central heat source far exceeds the normal critical heat flux of the working fluid. Electrodes are embedded in the condenser, adiabatic, and evaporator sections to maximize the amount of pumping head that can be generated and thereby maximize the heat flux removal.

scholarly journals Utilisation of bleed steam heat to increase the upper heat source temperature in low-temperature ORC

2011 ◽  
Vol 32 (3) ◽  
pp. 57-70 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Jarosław Mikielewicz
Keyword(s):  
Power Plant ◽  
Low Temperature ◽  
Heat Source ◽  
Silicone Oil ◽  
Hot Water ◽  
Working Fluid ◽  
Preliminary Heating ◽  
Source Temperature ◽  
Heat Source Temperature ◽  
Steam Heat

Utilisation of bleed steam heat to increase the upper heat source temperature in low-temperature ORC In the paper presented is a novel concept to utilize the heat from the turbine bleed to improve the quality of working fluid vapour in the bottoming organic Rankine cycle (ORC). That is a completely novel solution in the literature, which contributes to the increase of ORC efficiency and the overall efficiency of the combined system of the power plant and ORC plant. Calculations have been accomplished for the case when available is a flow rate of low enthalpy hot water at a temperature of 90 °C, which is used for preliminary heating of the working fluid. That hot water is obtained as a result of conversion of exhaust gases in the power plant to the energy of hot water. Then the working fluid is further heated by the bleed steam to reach 120 °C. Such vapour is subsequently directed to the turbine. In the paper 5 possible working fluids were examined, namely R134a, MM, MDM, toluene and ethanol. Only under conditions of 120 °C/40 °C the silicone oil MM showed the best performance, in all other cases the ethanol proved to be best performing fluid of all. Results are compared with the "stand alone" ORC module showing its superiority.

A Loop Thermosyphon With Hydrophobic Spots Evaporator Surface

2018 ◽  
Author(s):  
Hongbin He ◽  
Biao Shen ◽  
Sumitomo Hidaka ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Immersion Method ◽  
Two Phase ◽  
Coating Materials ◽  
High Heat Transfer ◽  
Coated Surface

Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circle spots (non-electroplating Ni-PTFE, 0.5∼2 mm in diameter and 1.5–3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) reveals the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation sites density. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. The comparison of three evaporator surfaces with same spot parameters but different coating materials is carried out experimentally. Ni-PTFE coated surface with immersion method performs the optimal performance of the thermosyphon.

Modeling and Analysis of Power Conversion System for High Temperature Gas Cooled Reactor With Cogeneration

2008 ◽  
Author(s):  
Ali Afrazeh ◽  
Hiwa Khaledi ◽  
Mohammad Bagher Ghofrani
Keyword(s):  
High Temperature ◽  
Heat Source ◽  
Gas Turbine ◽  
Power Conversion ◽  
Hot Water ◽  
Working Fluid ◽  
Closed Cycle ◽  
Nuclear Heat ◽  
Conversion System ◽  
High Temperature Gas

A gas turbine in combination with a nuclear heat source has been subject of study for some years. This paper describes the advantages of a gas turbine combined with an inherently safe and well-proven nuclear heat source. The design of the power conversion system is based on a regenerative, non-intercooled, closed, direct Brayton cycle with high temperature gas-cooled reactor (HTGR), as heat source and helium gas as the working fluid. The plant produces electricity and hot water for district heating (DH). Variation of specific heat, enthalpy and entropy of working fluid with pressure and temperature are included in this model. Advanced blade cooling technology is used in order to allow for a high turbine inlet temperature. The paper starts with an overview of the main characteristics of the nuclear heat source, Then presents a study to determine the specifications of a closed-cycle gas turbine for the HTGR installation. Attention is given to the way such a closed-cycle gas turbine can be modeled. Subsequently the sensitivity of the efficiency to several design choices is investigated. This model is developed in Fortran.

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