Lubrication-type analysis of thermo-hydraulic transport in a model grooved heat pipe (original) (raw)
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Heat Pipe Science and Technology, An International Journal, 2010
Axially grooved heat pipes are the devices mainly used to dissipate the heat flow arising due to latent heat of fluid phase change at the state of saturation. Part of the heat injected at the evaporator flows through a microregion where a meniscus remains hung at the top of each groove. This paper presents a 1D steady-state model constructed to study the heat and mass transfers in this zone. It allows one to show an important result concerning the respective behavior of the meniscus in the microregion and in the macroscopic one. Then, the paper compares the performances of various metal/fluid couples relative to the flux evacuated through the microregion and contact angle. Thus, the present study completes the characterization of the microregion and will directly participate in the heat pipe design improvement.
International Journal of Heat and Mass Transfer, 1999
This paper presents a two-dimensional analytical model for low-temperature cylindrical heat pipes. A closed-form solution which incorporates liquid±vapor interfacial hydrodynamic coupling and non-Darcian transport through the porous wick for the ®rst time, is obtained for predicting the vapor and liquid velocity and pressure distributions. In addition, the steady-state vapor and wall temperatures for a given input heat load in the evaporator region and a convective boundary condition in the condenser region, are obtained. The eects of liquid±vapor interfacial hydrodynamic coupling and non-Darcian transport through the porous wick on the vapor and liquid velocity and pressure distributions as well as the heat pipe capillary limit are discussed and assessed. The analytical solutions of the axial vapor and wall temperature distributions, the vapor and liquid pressure distributions, and the centerline vapor velocities compare very well with both experimental and numerical results. This work constitutes for the ®rst time a comprehensive analytical solution which provides closed form solutions for the vapor and liquid¯ow as well as the operating temperature and the maximum heat removal capability of the heat pipe. #
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences
Heat pipes are heat transfer device that do not need external power; as a result, they are used in various thermal systems. Enhancing the performance of heat transfer device is a continues effort. Thus, this study investigates the effect of copper nanofluid on the thermal performance of cylindrical heat pipe (HP) that has screen mesh wick for heat transfer applications. The copper HP consists of 350 mm length and 12.7 mm outside diameter. To investigate its thermal performance mathematical model is developed. Demineralized water based 20 nm copper nanofluids with 0 to 4% particle concentrations were considered in the study. Simulation was done at 100 W heat input and results showed that when the particle concentration increases the evaporator wall temperature drops. At 4% particle concentration nanofluid the HP thermal resistance reduced by 17.5% compared to when the HP uses demineralized water. Furthermore, for a given particle concentration as the heat input increases the temperature change between the evaporator and the condenser increases. The outcome of the investigation can be input to the design of solar heat exchangers that use HPs filled with nanofluids.
HEAT TRANSFER IN GROOVED HEAT PIPES: VISUALISATION AND EXPERIMENTAL ANALYSE OF FLUID BEHAVIOUR
High performances heat pipes modelling needs an increased knowledge of flow behaviour inside grooves. Thus, even if this flow is usually laminar, a free surface governed by capillarity leads to many difficulties to calculate the mean friction factor of the groove. In this study, an experimental bench has been developed in order to visualize the liquid-vapour interface channels of five different axially grooved heat pipes. This experimentation, associated with image processing programs, allows the measurement of height of liquid and meniscus radius and so the determination of the friction factor.
Modelling of Heat Transfer in the Evaporator and Condenser of the Working Fluid in the Heat Pipe
Heat Transfer Engineering, 2018
The aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard method that helps to reduce the economic costs of research and development of new and innovative devices. The article describes the procedures for using numerical simulation in phase-change heat transfer that occurs due to evaporation and condensation of the working fluid. The suggested procedure enables modelling of gravitational heat pipe under different changes in its geometry or under changes in the working fluid. From the simulation results we can find out how the heat pipe behaves under different geometric changes and how much heat output it transfers. The paper presents results obtained from modelling of heat pipes, such as classical gravitational heat pipe, heat pipe with capillary geometry and closed loop pulsating heat pipe. The results gathered from numerical simulation of heat pipes were compared with measurement results.
Heat Transfer, Fluid Mechanics and Thermodynamics—HEFAT2011
Heat Transfer Engineering, 2013
This editorial provides an overview of a special issue dedicated to the 9 th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics -HEFAT2012hosted on Malta. All papers for this conference were peer-reviewed and 270 papers were accepted. Of these, 10 of the best papers were selected for this issue and peer-reviewed for a second time according to journal standards. The 10 papers focus on the characteristics of oxyfuel and airfuel combustion in an industrial water tube boiler, numerical and optical analysis of a weatheradaptable solar reactor, the mitigation of crystallization fouling using projectiles in tubular heat exchangers, the mitigation of crystallization fouling in a single heated tube using projectiles of different sizes and hardness, a framework for the analysis of thermal losses in reciprocating compressors and expanders, an annular impinging jet controlled by radial synthetic jets, multieffect plants and ionic liquids for improved absorption chillers, the effect of climatic parameters on the heat transfer mechanisms in a solar distillation still, empirical correlations for slightly decaying grid turbulence, and pool boiling on modified surfaces using R-123. The current issue of Heat Transfer Engineering is the ninth special journal issue dedicated to selected papers from the HEFAT conferences.
On the radial heat transfer coefficient in grooved heat pipe
2009
It is well known that microscopic effects are important in the evaluation of the radial heat transfer within a grooved heat pipe evaporator. We develop a multi-scale model which is composed of two parts, macroscopic and microscopic, which cannot be decoupled from each other. In our study, we include various effects such as the disjoining pressure, the influence of the interfacial curvature, the variation of the saturation temperature, the interfacial resistance and the thermal conduction. The macroscopic part consists in a heat conduction problem with a mixed boundary condition at the meniscus, while the microscopic part is based on a classical lubrication type theory which allows to determine, thanks to a correlation, the apparent contact angle. This last quantity is essentially in order to couple the two scales. We also underline in particular the variation of the heat transfer coefficient with, on the one hand, the apparent contact angle and, on the other hand, the geometry of th...
Heat transfer and flow pattern in vertical liquid–solids flow
Powder Technology, 2004
Wall-to-bed heat transfer in hydraulic transport of spherical glass particles of diameter 1.20, 1.94 and 2.98 mm and in single-phase flow regime was studied. Experiments were performed by transporting the spherical glass particles with water in a 25.4 mm I.D. copper tube equipped with a steam jacket. In the runs without particles, the tube Reynolds number varied between 2280 and 21,300, while in hydraulic transport runs, the tube Reynolds number varied between 3300 and 20,150. The loading ratio (G p /G f) was between 0.07 and 0.328, and the fluid superficial velocity was between 0.29d U t and 2.86d U t , where U t represents the single particle terminal velocity. For these ratios, the voidage ranged from 0.715 to 0.895. The data for the heat transfer factor (j H) in single-phase flow are correlated using a general form j H =f(Re). The data for wall-to-bed heat transfer in the hydraulic transport of particles show that an analogy between heat and momentum transfer exists. The data were correlated by treating the flowing fluid-particle suspension as a pseudofluid, by introducing a modified suspension-wall friction coefficient (f w) and a modified Reynolds number (Re m).