Heat Transfer In Thermosyphon Research Articles

Experimental study of closed‐loop thermosyphon with a different evaporator geometry

AbstractIn this study, the effect of evaporator geometry on the loop thermosyphon's heat transfer coefficient is experimentally verified by using water as a working fluid with three filling ratios (50%, 70%, 90%), constant heat input (185 W), and condenser cooling water flow rate remaining constant at 2 Lpm. Three evaporator pipes are used (I: straight; II: helical coil evaporator with a diameter of 100‐mm coil and two turns; III: helical coil evaporator with a diameter of 50‐mm coil and four turns). From the experimental results, it can be observed that the performance of evaporator III is higher than the two other forms. A greater heat transfer coefficient value is found in case of type III evaporator and is equivalent to 2456 W/m2·°C. The maximum thermal resistance reduction occurs in the type III evaporator (37.32%), and the highest effective thermal conductivity for the same type is 6.123e + 05 W/m·°C. The experimental results demonstrate good agreement with the empirical equations.

Effect of SiO2 super-hydrophobic coating and self-rewetting fluid on two phase closed thermosyphon heat transfer characteristics: An experimental and numerical study

The realization of the importance of high-performance heat transfer units, in this case a two-phase closed thermosyphon (TPCT), has gained a foothold in recent years. To this end, the super-hydrophobic coating has been applied in the TPCT condenser surface and 1-Butanol is added as a self-rewetting aqueous solution in the working fluid. The super-hydrophobic coating has been created by using surface engineering and synthesis super-hydrophobic SiO2 nanoparticles. In this work, in a bid to measure some well-established parameters (heat input, filling ratio, and coolant mass flow rate) which are capable of getting thermal efficiency and resistance surging toward desirable numbers, experimentally considered TPCT implement. In order to illustrate boiling and condensation phenomena, the numerically simulation have been conducted assists by volume of fluid (VOF) multiphase model and user-define function (UDF) house code. Results indicate that in the heat input of 250 watts, the condenser convective heat transfer coefficient of TPCT with super-hydrophobic coating is 13.34% higher than the TPCT with non-modified condenser. Also, increasing heat input, filling ratio and 1-Butanol mass concentration decreases the TPCT thermal resistance opposite of the coolant mass flow rate. The numerical simulation illustrates that the boiling in a TPCT with 1-Butanol-water working fluid has occurred faster than TPCT with water working fluid. Also, the condensation has been appeared droplet due to high contact angle in the condenser with super-hydrophobic coating.

Confinement and vapour production rate influences in closed two-phase reflux thermosyphons Part B: Heat transfer

This work investigates boiling heat transfer for a small scale thermosyphon. Heat transfer results were analysed for three fluids; water, ethanol and HFE-7000. The influence of confinement and vapour mass flux on thermosyphon heat transfer was studied using a fully transparent two-phase closed thermosyphon. By considering the thermal performance of the thermosyphon together with the observed flow regimes, diabatic flow maps were developed. Of particular importance is the reduced pressure of the system which influences the size of the generated vapour bubbles in the evaporator. At low reduced pressures, bubble diameters may be large enough to span the tube diameter and the thermosyphon exhibits confined flow behaviour similar to that of micro-scale convective two-phase flows. Flows of this nature result in oscillatory behaviour and the boiling heat transfer is less effective. The phenomenon can be avoided by increasing the reduced pressure or tube diameter of the system. The most favourable flow regime in the context of thermosyphon heat transfer was found to be churn-type flow. It was found that slug/plug-type flow was not conducive to heat transfer where vapour production rates, and thus latent heat transfer, were relatively low. The flow regime maps relating phase superficial momentum flux the heat transfer coefficient may be used as an aid to the design of thermosyphons for specific applications.

An experimental investigation on the evaporation and condensation heat transfer of two-phase closed thermosyphons

Two-phase closed thermosyphons (TPCTs) are excellent thermal transfer devices that their integration into heat exchangers has been shown a strong potential for energy savings. The scope of this study is an experimental evaluation of the evaporation and condensation heat transfer of a TPCT for uniformly heated evaporator surface. Water as the working fluid is charged in a TPCT with a length of 500mm and an inner diameter of 33mm at different filling ratios (8–100%). The Thermosyphon heat transfer performances are compared with some predictive correlations of suppress the pool boiling insert uniquely and suppress the pool boiling combined with film evaporation for the evaporator section at different filling ratios. The experimentally obtained condensation heat transfer is also evaluated by available filmwise condensation model. Results show an agreement with the most of the selected correlations with tolerance ±30% and the appropriate set of correlations are introduced giving an accuracy within ±10%.

Numerical investigation of heat transfer in thermosyphon under the emergency mode of operation of lithium-ion batteries of aircraft

Numerical study of heat transfer in a closed two-phase thermosyphon using the software package ANSYS FLUENT is carried out. Characteristic temperature distributions, current lines and velocity vectors are obtained at critical thermal loads. The temperature difference in the investigated region decreases with increasing heat load was obtained.

Analysis of Influence of Heat Transfer Conditions on the Upper Cover to Heat Transfer in Thermosyphon

Numerical analysis of thermal conditions of a two-phase closed thermosyphon using the software package ANSYS FLUENT has been carried out. Temperature distributions at various heat transfer conditions on upper cover and different heat flow on bottom cover of thermosyphon have been obtained.

Numerical Analysis of Influence of Thickness of Liquid Film on Bottom Cover to Heat Transfer in Thermosyphon in Conditions Emergency Modes of Work the Rechargeable Batteries of Aircrafts

Numerical analysis of thermal conditions of a two-phase closed thermosyphon using the software package ANSYS FLUENT has been carried out. Dynamics of change of thickness of the liquid film depending on time impact of heat load are obtained.

Thermal and hydrodynamic characteristics of supercritical CO2 natural circulation in closed loops

Natural convective flow of supercritical fluids has become a hot topic in engineering applications. Natural circulation thermosyphon using supercritical/trans-critical CO2 can be a potential choice for effectively transportation of heat and mass without pumping devices. This paper presents a series of numerical investigations into the fundamental features in a supercritical/trans-critical CO2 based natural circulation loop. New heat transport model aiming at trans-critical thermosyphon heat transfer and stability is proposed with supercritical/trans-critical turbulence model incorporated. In this study, the fundamentals include the basic flow and heat transfer behavior of the above loop, the effect of heat source temperature on system stability, the effect of loop diameter on natural convection supercritical CO2 loop and its coupling effect with heat source temperature and the effect of constant changing heat input condition and system behavior evolution during unsteady input or failure conditions. The fundamental potentials of supercritical/trans-critical CO2 based natural convection system are confirmed. Basic supercritical CO2 closed loop flow and heat transfer behaviors are clarified. During this study, the CO2 loop stability map are also put forward and introduced as an important feature of supercritical CO2 system. Stability factors of natural convective trans-critical CO2 flow and its implications on real system control are also discussed in this paper.

저온작동 조건에서 자동차용 써모사이폰의 성능특성에 관한 연구

The objective of this study is to investigate low temperature performance characteristics of the thermosyphon with/without wick. Thermosyphons using water as the working fluid are tested with variations of wick, charge amount of the working fluid, outdoor temperature, and heat load for the evaporator section at a low temperature. As a result, the heat transfer of thermosyphon was optimized at the charge amount of 40% and increased with the rise of the outdoor temperatures.

Simulation of Heat Transfer and System Behavior in a Supercritical CO2 Based Thermosyphon: Effect of Pipe Diameter

This paper deals with the natural convective circulation thermosyphon with supercritical CO2 flow. New heat transport model aiming at supercritical thermosyphon heat transfer and stability is proposed and numerically studied. Two-dimensional rectangular natural circulation loop model is set up and the effect of pipe diameter is systematically analyzed. Finite volume method is used to solve the conservative equations with supercritical turbulence model incorporated. It is found that supercritical CO2 thermosyphon can achieve high Reynolds flow as 104–105 even temperature differences between source and sink is small. Stabilized flow is found for larger pipe diameter group due to the developed flow field and enhanced heat transfer. Heat transport at cooler side can be enhanced at higher operating temperature and be critical for the stabilization of the supercritical thermosyphon. Correlations of flow and heat transfer are reexamined and good agreements with classical reports are also obtained in the present study.

Phase change heat transfer device for process heat applications

The next generation nuclear plant (NGNP) will most likely produce electricity and process heat, with both being considered for hydrogen production. To capture nuclear process heat, and transport it to a distant industrial facility requires a high temperature system of heat exchangers, pumps and/or compressors. The heat transfer system is particularly challenging not only due to the elevated temperatures (up to ∼1300 K) and industrial scale power transport (≥50 MW), but also due to a potentially large separation distance between the nuclear and industrial plants (100+ m) dictated by safety and licensing mandates. The work reported here is the preliminary analysis of two-phase thermosyphon heat transfer performance with alkali metals. A thermosyphon is a thermal device for transporting heat from one point to another with quite extraordinary properties. In contrast to single-phased forced convective heat transfer via ‘pumping a fluid’, a thermosyphon (also called a wickless heat pipe) transfers heat through the vaporization/condensing process. The condensate is further returned to the hot source by gravity, i.e., without any requirement of pumps or compressors. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. Two-phase heat transfer by a thermosyphon has the advantage of high enthalpy transport that includes the sensible heat of the liquid, the latent heat of vaporization, and vapor superheat. In contrast, single-phase forced convection transports only the sensible heat of the fluid. Additionally, vapor-phase velocities within a thermosyphon are much greater than single-phase liquid velocities within a forced convective loop. Thermosyphon performance can be limited by the sonic limit (choking) of vapor flow and/or by condensate entrainment. Proper thermosyphon requires analysis of both.

Natural-Convection Thermosyphon Heat Transfer from a Stack of Horizontal Plates

Steady laminar natural convection of water about vertically stacked, two-sided, horizontal heated plates was studied experimentally over a range of plate gap to plate half-width ratio, H/a, from 0.078 to 0.94. Measurements were made of power input per plate, plate temperatures, and inlet and outlet bulk fluid temperatures. From these data were determined average Nusselt and Rayleigh numbers for each plate, which were correlated with a power law Nu = C Ran for each gap height. The Nusselt numbers increased with gap height up to H/a 0.47 (from 8 to 48), and then became independent of H/a. The exponent n increased from n 0.2 at the lowest gap height tested (H/a 0.078), to a high value of n approximately equal to 0.4 at H/a = 0.24 and then decreased back to n = 0.2 for H/a greater than or equal to 0.47.