Experimental study on the condensation of a thermosyphon by electrical capacitance tomography

The study on the condensation and the two-phase flow pattern in the condensation section is important to understand the operating mechanisms in a thermosyphon. In this paper, a new electric capacitance tomography (ECT) sensor was designed for the visualization measurement in a liquid by removing the shielding case and sealing with insulating hydrophobic material. It was successfully used to measure the condensation process in a thermosyphon under different operating temperatures. The thermosyphon was made of silica glass, and alcohol was used as a working fluid. The alcohol vapor was cooled to condense through the heat convection with the cooling water. The operating temperature was controlled by a heater with different power outputs. The experimental results show that the alcohol vapor condensed in stripes and unevenly on the wall surface at a low operating temperature. The liquid bridge will be formed periodically at the operating temperature of 90°C, and the time interval between two liquid bridges will be shorter with the increase of the operating temperature. At 117°C or even higher operating temperatures, the complete liquid bridge cannot be formed sometimes due to the difference of the growth rate of the surface wave around the circumference.     

Thermal convection in a porous toroidal thermosyphon

Stability of natural convection in porous media differs from that in Newtonian fluid due to the changes of the thermal inertia and the friction. This paper aims to investigate the natural convection and its stability in a toroidal thermosyphon filled with porous media. The flow and temperature fields were numerically simulated and compared with that of Newtonian fluid. The results predicted two obvious local reversal flows near the connections of heating and cooling halves. A one-dimensional model was proposed which described qualitatively the occurring and stability of the thermal convection. The model suggested that the flow stability depends largely on the Prandtl number. The global flow can probably be chaotic only if the Prandtl number is finite. Contradictions of the conclusions drawn by different researchers were also discussed.     

Performance of large solar water heating system: Thermosyphon mode

Two large solar water heating systems (non-pressure type), each having 1000-1. capacity, have been installed at IIT New Delhi and their performances have been studied under the thermosyphon mode between the collectors and the storage tank. A simple transient analysis of the system, incorporating the effect of withdrawal of hot water from the storage tank, has been developed. The effect of stratification in the storage tank has been studied experimentally. It is found that the experimental observations are in good agreement with the theoretical results obtained by the present model.     

重力热管的工质选择

作为高效传热方式，重力热管已在太阳能技术、冻土保持等方面获得广泛应用。本文介绍了工质选择的准则，然后讨论工质的热物理特征对热管换热性能的影响。     

Analysing the effect of the laeh in the storage tank on the performance of a tsaeh

When an auxiliary electric heater (AEH) is incorporated in a thermosyphon solar water system, the system performance becomes more complex and it is more difficult to simulate and analyse its operational characteristics. Using a ‘fixed-node, equally-convecting-mixing model’ that they have developed, the authors perform detailed simulations and analysis of the effects of the location of the auxiliary electric heater (LAEH) in the storage tank on the performance of the thermosyphon solar water system with an auxiliary electric heater (TSAEH), and discover for the first time some new laws governing the system operation. The authors believe that their simulations and analysis will be very beneficial for optimal design and practical application of such systems in the future.     

Thermal performance of a closed advanced two-phase thermosyphon loop for cooling of radio base stations at different operating conditions

In this investigation an advanced thermosyphon loop with extended evaporator and condenser surfaces has been tested at high heat fluxes. The thermosyphon investigated is designed for the cooling of three parallel high heat flux electronic components. The tested evaporators were made from small blocks of copper in which five vertical channels with a diameter of 1.5 mm and length of 14.6 mm were drilled. The riser and downcomer connected the evaporators to the condenser, which is an air-cooled roll-bond type with a total surface area of 1.5 m² on the airside. Tests were done with Isobutane (R600a) at heat loads in the range of 10–90 W/cm² to each of the components with forced convection condenser cooling and with natural convection with heat loads of 10–70 W.     

Hybrid photovoltaic and thermal solar-collector designed for natural circulation of water

The electricity conversion-efficiency of a solar cell for commercial application is about 6–15%. More than 85% of the incoming solar energy is either reflected or absorbed as heat energy. Consequently, the working temperature of the solar cells increases considerably after prolonged operations and the cell’s efficiency drops significantly. The hybrid photovoltaic and thermal (PVT) collector technology using water as the coolant has been seen as a solution for improving the energy performance. Through good thermal-contact between the thermal absorber and the PV module, both the electrical efficiency and the thermal efficiency can be raised. Fin performance of the heat exchanger is one crucial factor in achieving a high overall energy yield. In this paper, the design developments of the PVT collectors are briefly reviewed. Our observation is that very few studies have been done on the PVT system adopting a flat-box absorber design. Accordingly, an aluminum-alloy flat-box type hybrid solar collector functioned as a thermosyphon system was constructed. While the system efficiencies did vary with the operating conditions, the test results indicated that the daily thermal efficiency could reach around 40% when the initial water-temperature in the system is the same as the daily mean ambient temperature.     

Modeling and optimization of hybrid solar thermoelectric systems with thermosyphons

We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copper–water, stainless steel–mercury, and nickel–liquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300–1200 K, solar concentrations of 1–100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776 K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as 1.2 W/mK have comparable efficiencies to that of high conductivity material thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems.     

Experimental and analytical performance study of a thermosyphon water heater

The performance of a thermosyphon solar water heater was studied analytically and experimentally. A finite-difference model was used to predict year-round performance. Tests were conducted on an experimental heater subjected to acutal weather conditions in Benghazi, Libya. Satisfactory qualitative and quantitative agreement was found between experimental and predicted results. A storage volume of 60 liters per unit collector area was found to be optimum for Benghazi conditions. The day-end temperature was found to vary between 23° and 51°C for the test period, which occurred in winter, with an average of 41°C.     

Development of a heat exchanger for the cold side of a thermoelectric module

A heat exchanger for the cold side of Peltier pellets in thermoelectric refrigeration, based on the principle of a thermosyphon with phase change and capillary action has been developed. This device improves the thermal resistance between the cold side of a Peltier pellet and the refrigerated ambient by 37% (from 0.513 of the finned heat sink, to 0.323 K/W). Analytic calculations and experimental optimisation of the TPM have been carried out by building and testing several prototypes. It also has been experimentally proved that the COP of thermoelectric refrigerators can be improved up to 32% (from 0.297 to 0.393) by incorporating the developed device.