Hossein Shokouhmand; Hafez Bahrami
Abstract
In this study an analytical model for open loop pulsating heat pipes (PHPs) is presented. The model predicts the effect of different parameters such as evaporator temperature, length of evaporator, filling ratio, number of turn and tube diameter on PHP's performance.
The governing equations in two phase ...
Read More
In this study an analytical model for open loop pulsating heat pipes (PHPs) is presented. The model predicts the effect of different parameters such as evaporator temperature, length of evaporator, filling ratio, number of turn and tube diameter on PHP's performance.
The governing equations in two phase flow including mass, momentum and energy equations are solved for both one dimensional liquid slugs and lumped vapor plugs numerically. The model includes the thin film layer concept which contributes to heat transfer in evaporator and condenser section. A proper model is also investigated to describe the steady oscillatory behavior of device. The results show that this model predicts well the oscillatory behavior of the phenomena. The obtained results are in good agreement with available data and can be properly used for predicting the trend of effective parameters on PHP's performance. It is found that sensible heat transfer has extremely more important role in increasing total heat transfer of PHP . The thermal resistance decreases due to increasing of the latent heat transfer. It can be seen that increasing of the evaporator temperature, while the temperature of the condenser is constant,will increase the total evacuated heat by PHP in specific filling ratio limits. The results show that the PHP's performance increases when the tube diameter increases. In this case, by using a specific non-dimensionalized model, a unique curve for arbitrary number of turn and FR can be obtained. Also it is found that PHP's performance reaches its maximum at filling ratio around 0.6 for different tube diameters.
Mehdi Ashjaee; Hossein Shokouhmand; Mehdi Amiri; Touraj Yousefi
Abstract
Laminar free convection heat transfer from vertical and inclined arrays of horizontal isothermal cylinders in air was investigated experimentally and numerically. Experiments were carried out using Mach-Zehnder interferometer and the FLUENT code was used for numerical study. Investigation was performed ...
Read More
Laminar free convection heat transfer from vertical and inclined arrays of horizontal isothermal cylinders in air was investigated experimentally and numerically. Experiments were carried out using Mach-Zehnder interferometer and the FLUENT code was used for numerical study. Investigation was performed for vertical and horizontal cylinder spacing from 2 to 5 and 0 to 2 cylinder diameters respectively. The Rayleigh number based on the cylinder diameter varied between 103and 3×103.The effect of vertical and horizontal cylinder spacing and Rayleigh number on the local heat transfer from each individual cylinder was investigated. It was seen that the local heat transfer coefficient of each cylinder strongly depends on its position relative to the others. This variation of the local heat transfer coefficient was explained by the interaction of plume's temperature and velocity profiles.
Mohammad Ali Akhavan Behabadi; Hossein Shokouhmand; Masoud Jamali Ashtiani; Amir Mohammadpour
Abstract
The pressure drop of refrigerant R-134a flow boiling inside a horizontal tube has been investigated experimentally. The test set-up which was used in this investigation is a well instrumented vapor compression refrigeration system. These instruments are thermocouples, flow meter, pressure gauges and ...
Read More
The pressure drop of refrigerant R-134a flow boiling inside a horizontal tube has been investigated experimentally. The test set-up which was used in this investigation is a well instrumented vapor compression refrigeration system. These instruments are thermocouples, flow meter, pressure gauges and the pressure drop measuring apparatus. This system consisted of three electrically heated evaporators called as pre-evaporator, test evaporator and after evaporator, respectively. The empirical pressure drop data for two phase flow boiling of R-134a inside a horizontal tube of 7.5mm internal diameter has been collected. The ranges of mass velocities and vapor qualities are 54-136 kg/m2s and 0.2-1, respectively. The collected data were compared with the predicted pressure drop values by seven different correlations. Finally, a new correlation was developed to predict the pressure drop of two phase flow inside evaporators.
Hossein Shokouhmand; Javad Rostami
Abstract
In this paper conjugated heat transfer in thermal entrance region through the sinusoidal wavy channel has been investigated. The fluid flow is assumed to be laminar, steady state, incompressible, and hydrodynamically fully developed. A constant heat flux is assumed to be applied on the outer edge of ...
Read More
In this paper conjugated heat transfer in thermal entrance region through the sinusoidal wavy channel has been investigated. The fluid flow is assumed to be laminar, steady state, incompressible, and hydrodynamically fully developed. A constant heat flux is assumed to be applied on the outer edge of the channel wall. In this study the governing equations including continuity, momentum and energy are solved numerically by a finite volume method (SIMPLE). The flow field for different Reynolds numbers has been obtained using this flow field, pressure loss and skin friction coefficient have been calculated. Also temperature field in both solid and fluid for wide range of effective parameters in conjugated heat transfer such as Peclet number, solid-fluid conductivity ratio and solid thicknesses have been investigated. From the obtained numerical results for thermal field effects of conjugated heat transfer characteristics on fluid mean bulk temperature, solid-fluid interface temperature, solid-fluid interface heat flux and Nusselt number have been calculated. The obtained results have been compared with available numerical and experimental data and a good agreement is achieved.
Mehdi Ashja'ee; Touraj Yousefi; Hossein Shokouhmand
Abstract
An experimental and numerical study of free convection heat transfer from a channel consisting of a vertical sinusoidal wavy surface and a vertical flat plate has been carried out. The vertical wavy surface was maintained at a constant temperature, while the flat plate is adiabatic. A Mach-Zehnder Interferometer ...
Read More
An experimental and numerical study of free convection heat transfer from a channel consisting of a vertical sinusoidal wavy surface and a vertical flat plate has been carried out. The vertical wavy surface was maintained at a constant temperature, while the flat plate is adiabatic. A Mach-Zehnder Interferometer was used to determine the local heat transfer coefficients of sinusoidal wavy surface. FLUENT code was used for numerical simulation. The numerical results are in good agreement with experimental data. The amplitude-wavelength ratio, , in this investigation is kept constant at .The effects of Rayleigh number and wall spacing are investigated as well. Experiments were carried out for eight different Rayleigh numbers and thirteen different wall spacing. Results indicate that the frequency of the local heat transfer rate is the same as that of the wavy surface. The average heat transfer coefficient increases as the Rayleigh number, increases. For each Rayleigh number there is an optimum wall spacing where the heat transfer rate from the wavy sinusoidal surface reaches its maximum value. This optimum wall spacing depends on Rayleigh number and decreases with increasing Rayleigh number.
