Effect of the Heat Pipe Adiabatic Region

International Journal of Heat and Mass Transfer, 2020

In this article, two-phase flow in a double-pipe porous heat exchanger and associated phase change processes has been numerically analysed to investigate the impacts of the relative permeabilities. The modified h -formulation along with the assumption of Local Thermal Equilibrium condition has been employed. Finite Volume Method (FVM) has been used to discretise the governing equations. The solutions of incomplete evaporation process have been validated with the experiments and they show an excellent agreement between them. The pertinent parameters have been systematically investigated to demonstrate the importance of the above mentioned influences on the complete evaporation process. It has been observed that the power index of the relative permeabilities for either liquid or vapour region has a significant effects on the beginning and ending of phase change operation, especially when the steam is formed inside the pipe. Comparison between results obtained with maximum and minimum values of the power index indicated that the latter value must be used while simulating the complete evaporation process, particularly for very low inlet Reynolds number and very high wall temperature. It is also evident that the operating conditions and geometric parameters of the heat exchanger have been substantially changed the location of the beginning and ending of the phase change process. On the other hand, the properties of porous media have only minor influence.

Scientia Iranica, 2017

This paper developed a new mathematical model to investigate the heat transfer as well as wick's thickness of a heat pipe. The model was established by conservative equations of continuity, momentum, and energy in the thermal boundary layer. Using a similarity variable, the governing equations were changed to a set of ordinary di erential equations and were solved numerically by the forth-order Runge-Kutta method. The ow variables, such as velocity components, wick's thickness, and Nusselt number, were obtained. The results show that the Nusselt number is proportional to the square root of the Darcy-modi ed Rayleigh number and to the distance from the edge of the condenser surface. Furthermore, the thickness of the wick material depends on the Jakob number and is proportional to the heat transfer between the wall and liquid lm.

Applied Thermal Engineering, 2005

Heat pipes are two-phase heat transfer devices with extremely high effective thermal conductivity. They can be cylindrical or planar in structure. Heat pipes can be embedded in a metal cooling plate, which is attached to the heat source, and can also be assembled with a fin stack for fluid heat transfer. Due to the high heat transport capacity, heat exchangers with heat pipes have become much smaller than traditional heat exchangers in handling high heat fluxes. With the working fluid in a heat pipe, heat can be absorbed on the evaporator region and transported to the condenser region where the vapour condenses releasing the heat to the cooling media. Heat pipe technology has found increasing applications in enhancing the thermal performance of heat exchangers in microelectronics, energy and other industrial sectors. Utilisation of a heat pipe fin stack in the drying cycle of domestic appliances for heat recovery may lead to a significant energy saving in the domestic sector. However, the design of the heat pipe heat exchanger will meet a number of challenges. This paper presents a design method by using CFD simulation of the dehumidification process with heat pipe heat exchangers. The strategies of simulating the process with heat pipes are presented. The calculated results show that the method can be further used to optimise the design of the heat pipe fin stack. The study suggests that CFD modelling is able to predict thermal performance of the dehumidification solution with heat pipe heat exchangers.

Energy Conversion and Management, 2008

A numerical study of flow and heat transfer characteristics is made in a double pipe heat exchanger with porous structures inserted in the annular gap in two configurations: on the inner cylinder (A) and on both the cylinders in a staggered fashion (B). The flow field in the porous regions is modelled by the Darcy-Brinkman-Forchheimer model and the finite volume method is used to solve the governing equations. The effects of several parameters such as Darcy number, porous structures thickness and spacing and thermal conductivity ratio are considered in order to look for the most appropriate properties of the porous structures that allow optimal heat transfer enhancement. It is found that the highest heat transfer rates are obtained when the porous structures are attached in configuration B especially at small spacing and high thicknesses.

Foundation of Computer Applications, 2019

Gas-solid flows in vertical pipes are found in many industries for heat transfer applications. Some of them are chemical industries, food and process industries, pharmaceutical industries, etc. In the present paper, the two-fluid model (the Eulerian-Eulerian approach) of ANSYS FLUENT 15.0 is used to model the heat transfer in gas-solid flows in an adiabatic, vertical pipe. The variable gas properties with respect to temperature are considered in the current study. The computational results are well validated with the benchmark experimental data. The effect of particle diameter on heat transfer and pressure drop is studied. It is noticed that the gas temperature increases and the solid temperature decreases with increasing the particle diameter. Again, increasing the particle diameter increases the logarithmic mean temperature difference and pressure drop; however, it decreases the average gas-solid Nusselt number.

Journal of Fluids Engineering, 2004

A numerical method based on the SIMPLE algorithm has been developed for the analysis of vapor flow in a concentric annular heat pipe. The steady-state response of a concentric annular heat pipe to various heat fluxes in the evaporator and condenser sections are studied. The fluid flow and heat transfer in the annular vapor space are simulated using Navier-Stokes equations. The governing equations are solved numerically, using finite volume approach. The vapor pressure and temperature distributions along a concentric annular heat pipe are predicted for a number of symmetric test cases. The vapor flow reversal and transition to turbulence phenomena are also predicted. The results are compared with the available numerical data and have shown good agreement in all cases. Therefore, the vapor flow model developed in this paper has shown good accuracy and convergence behavior in the range of low to moderate radial Reynolds numbers.

The size of electronic devices are decreasing day by day and throwing challenges on thermal engineers to find and invent better means to challenge heat dissipation rates. This led to give rise to my idea of getting this work on Heat pipe. Heat pipes are promising means to drive the heat from the electronic devise to the environment without using mechanical devices to operate the flow in it. The factors effects the performance of Heat pipe are geometry design, number of evaporators and condensers, working fluid selection, by coating different coatings to increase adhesive nature between inner wall of pipe and working fluid etc.,In this thesis, Heat Pipe System with multiple evaporators will be designed and modelled in 3D modelling software Pro/Engineer. Heat transfer characteristics will be determined by CFD and transient thermal analysis. CFD analysis will be done to determine the heat transfer rate, pressure drop, mass flow rate, heat transfer coefficient with R134 and R410 as the working fluid. Transient thermal analysis will be done to determine heat transfer rate and temperature distribution

Applied Thermal Engineering, 2016

Heat and mass transfer with phase change in an evaporator unit cell is analysed using a mixed pore network model. Two different kind of wick are investigated: a monoporous capillary structure characterised by a monomodal pore size distribution and a bidispersed capillary structure characterised by a bimodal pore size distribution. The evaporator thermal performance, i.e. the conductance, and the overheating of the casing are compared at different heat loads with experimental results and show a good agreement. For a large range of flux, the bidispersed wick has higher thermal performance than the monoporous wick. A bidispersed wick prevents the overheating of the casing which is the most encountered limit in LHP application. The liquid-vapour phase distribution, as well as the vapour saturation and the vapour mass flow rate are investigated to explain these behaviours.

2014

Interest in the use of heat pipe technology for heat recovery and energy saving in a vast range of engineering applications has been on the rise in recent years. Heat pipes are playing a more important role in many industrial applications, particularly in improving the thermal performance of heat exchangers and increasing energy savings in applications with commercial use. In this paper, a comprehensive CFD modelling was built to simulate the details of the two-phase flow and heat transfer phenomena during the operation of a wickless heat pipe or thermosyphon, that otherwise could not be visualised by empirical or experimental work. Water was used as the working fluid. The volume of the fluid (VOF) model in ANSYS FLUENT was used for the simulation. The evaporation, condensation and phase change processes in a thermosyphon were dealt with by adding a user-defined function (UDF) to the FLUENT code. The simulation results were compared with experimental measurements at the same condition. The simulation was successful in reproducing the heat and mass transfer processes in a thermosyphon. Good agreement was observed between CFD predicted temperature profiles and experimental temperature data.

2007 Proceedings of the ASME InterPack Conference, IPACK 2007, 2007

A mathematical model predicting the oscillating motion in an oscillating heat pipe is developed. The model considers the vapor bubble as the gas spring for the oscillating motions including effects of operating temperature, non-linear vapor bulk modulus, and temperature difference between the evaporator and the condenser. Combining the oscillating motion predicted by the model, a mathematical model predicting the temperature drop between the evaporator and the condenser is developed including the effects of the forced convection heat transfer due to the oscillating motion, the confined evaporating heat transfer in the evaporating section, and the thin film condensation in the condensing section. In order to verify the mathematical model, an experimental investigation was conducted. Experimental results indicate that there exists an onset power input for the excitation of oscillating motions in an oscillating heat pipe, i.e., when the input power or the temperature difference from the evaporating section to the condensing section was higher than this onset value the oscillating motion started, resulting in an enhancement of the heat transfer in the pulsating heat pipe. Results of the investigation will assist in optimizing the heat transfer performance and provide a better understanding of heat transfer mechanisms occurring in the oscillating heat pipe.