Experimental Investigation of Natural convective flow in Aluminium Open Cell heat exchanger (original) (raw)
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Experimental Thermal and Fluid Science, 2012
A horizontal two-phase loop thermosiphon (HLTS) has been developed as a potential receiver for parabolic trough collectors (PTCs). The design consists of an evaporator (which is horizontally arranged), a condenser, a riser, and a downcomer with a U-turn. This HLTS was designed to push to higher temperatures than previous HLTS studies (200e400 C) by using Dowtherm A as the working fluid. An indoor experimental prototype was built to investigate its heat transfer performance. Three regimes: start-up, transition and steady operation were analyzed. A unique feature of this design, the U-turn compensation tube, was shown be helpful during the transition and steady operation regimes since it forms a liquid seal to avoid bidirectional flow in the loop. However, solidification of the working fluid in the Uturn section was found to adversely impact the start-up regime in the case of cold (e.g. frozen) initial conditions. The system was tested up to a heat flux value 11.22 kW/m 2. The thermal resistance and the two-phase heat transfer coefficient were demonstrated to be considerably better than prior literature. Moreover, the present HLTS was shown to be theoretically limited to 85.6 kW/m 2 , thus demonstrating that this type of system can meet the needs of intermediate temperature PTC receivers.
2016
In this paper an experimental investigation on forced convection in a compact heat exchanger made up with an aluminum foam plate of 212.5mm x 212.5mm with a thickness of 40 mm and a single array with five circular tubes is presented. The foam has a porosity of 0.93 with 10, 20 and 30 pores per inch and the tubes in aluminum have internal and external diameters equal to 9.5 mm and 12.5 mm. The test rig consists of an open air channel and a closed water cycle and the aluminum foam plate is placed inside the channel. The performances of the compact heat exchanger are evaluated for assigned hot water mass flow rate and different hot water inlet temperatures and air mass flow rate. Results are given in terms of heat transfer rates and pressure drops as a function of air velocity and Reynolds numbers. The evaluation of dimensionless, Colburn factor and Nusselt number is performed for different air mass flow rates and hot water inlet temperatures.
In this paper an experimental investigation on forced convection in a compact heat exchanger made up with an aluminum foam plate of 212.5mm x 212.5mm with a thickness of 40 mm and a single array with five circular tubes is presented. The foam has a porosity of 0.93 with 10, 20 and 30 pores per inch and the tubes in aluminum have internal and external diameters equal to 9.5 mm and 12.5 mm. The test rig consists of an open air channel and a closed water cycle and the aluminum foam plate is placed inside the channel. The performances of the compact heat exchanger are evaluated for assigned hot water mass flow rate and different hot water inlet temperatures and air mass flow rate. Results are given in terms of heat transfer rates and pressure drops as a function of air velocity and Reynolds numbers. The evaluation of dimensionless, Colburn factor and Nusselt number is performed for different air mass flow rates and hot water inlet temperatures.
Al-Nahrain Journal for Engineering Sciences NJES, 2023
Natural convection air heat transfer and fluid movement currents around a hot circular cylinder inside an inclined triangular enclosure has been analyzed experimentally. Three different sizes of an enclosure with a long side of 20, 25, and 30 cm, the thickness of 1 mm, and depth of 50 cm were used in the present work to give three radius ratios. The effect of Rayleigh number, radius ratio, the rotation angle of triangle enclosure, and the inclination angle of the apparatus with horizontal axis θ on the heat transfer process was investigated. The ranges of these parameters were: Rayleigh number from 5×106 to 2.5×108 , radius ratio (0.345, 0.455, and 0.618), rotation angle (0o, 45o, and 90o), and inclination angle (0o, 45o and 90o). The results show that the heat transfer rates increase with increase in Rayleigh number and as the rotation angle of enclosure is changed from 0o to 90o. Moreover, the heat transfer rate increases linearly with Rayleigh number at higher radius at rotation angle 0o, 90o only. While, it increases slightly with Rayleigh number at rotation angle 45o. Additionally, the higher heat transfer rates occur at vertical position of enclosure inclination angle 90o and rotation angle 0o (the base of triangle at the bottom) and it decreases as inclination angle deviates from 90o to 0o. This behavior is reverse completely at higher radius ratio 0.618. Empirical correlations for the average Nusselt number has been found to depend on Rayleigh number., radius ratio, rotation angle and inclination angle.
Experimental and numerical analysis of one dimensional heat transfer on open cell aluminum foams
Gazi University Journal of Science
In this study, one dimensional heat transfer of open cell aluminum metal foams is investigated both experimentally and by using numerical methods as well. Open cell aluminum foams with pore densities of 10, 20 and 30 (Number of Pores Per Inch) PPI were shaped into heat exchangers. The foams having sizes of 200 × 100 × 20 mm were insulated on their three faces. Steady heat flux was maintained on the base section of the foam by heating a plate shaped coil electrically. Temperature distributions on the vertical sections and mostly on locations near heaters were measured with the thermocouples located on the aluminum foams. With the help of the recorded temperatures from the tests the graphs of open cell aluminum foams with pore densities of 10, 20 and 30 were plotted. First of all, one dimensional heat transfer equations were derived for the numerical solution of the system. The governing equations obtained were then discretized by using the Central Difference Method and finally solved...
Heat Transfer Improvement in Heat Exchanger using Porous Medium: a Review
1. ABSTRACT The present study is to investigate the heat transfer enhancement in a cylindrical heat exchanger using porous media. The heat exchanger is modeled by a cylindrical cavity (Shell) with inlet and outlet thermally insulated ports and five tubes which contain hot water and cold water flows in the shell. The effect of porosity on heat transfer enhancement is studied at the different mass flow rate. The study about the effect of porosity on heat transfer enhancement is done by both experimentally and CFD based and the results are compared with the simple heat exchanger. By decreasing the porosity, the heat transfer rate increases and the mean outlet temperature of the fluid increases for different mass flow rate.
Numerical Investigation on Thermal and Fluid Dynamic Behaviors of Heat Exchanger in Aluminium Foam
International Heat Transfer Conference 16, 2018
Designers of heat exchangers are regularly searching for new methods that enhance the heat transfer efficiency. A possible substitute of the conventional fins is the use of open-cell metal foams. Low density, good rigidity, high thermal conductivity and huge value of surface/volume ratio represent the best characteristics of porous media. For these features, metal foams are used in several applications such as heat exchangers, fuel cells, heat sinks and solar thermal plants. The need to create new systems in reduced volumes led to the adoption of the aluminum foams for their great specific area surface that allows to have compact heat exchanger characterized by a high thermal performance. A numerical investigation has been accomplished to analyze the thermal and fluid dynamic behavior of a tubular heat exchanger partially filled with aluminum foam. The Darcy-Brinkman-Forchheimer flow model and the thermal non-equilibrium model (LTNE) for the energy are applied to carry out two-dimensional simulations on the metal foam heat exchanger. The foam has a porosity and (number) pores per inch respectively equal to 0.935 and 20. The heat exchanger is analyzed for different air flow rates and a fixed surface tube temperature. The results are given as average and local heat transfer coefficient evaluated on the external surface of the tubes. Furthermore, the local air temperature profiles in the smaller cross section, between two consecutive tubes are given. Finally, the Energy Performance Ratio (EPR) is evaluated in order to demonstrate the thickness of metal foam that improve the system performances.
Italian Association of Chemical Engineering, 2018
The present work studies numerically natural convective flow between a circular adiabatic cylinder located in a square porous enclosure using finite element method. Darcy-Forchheimer model is used in solving the dimensionless governing equations including; continuity, energy and momentum of the fluid along with Bousseinesq approximation. The enclosure is heated from bottom and cooled at isothermal temperature for the vertical walls. The top wall and obstacle are assumed adiabatic. The considered parameters are 10 3 ≤ Ra ≤ 10 6 , 10-5 ≤ Da ≤ 10-3 , obstacle vertical location 0.25 ≤ h ≤ 0.75 and cylinder radius 0.1 ≤ D ≤ 0.9 with Pr = 0.7. It is obtained that as the Rayleigh and Darcy numbers increase, both streamlines; Nusselt numbers will increase leading to increase the rate of heat transfer. The results show that the heat transfer rate is significantly dependent on the diameter of the circular cylinder and the location of the cylinder. It is found the maximum heat transfer rate obtained at D=0.1 and when the cylinder moves vertically upward at h=0.3
Effect of Porous Medium and Copper Heat Sink on Cooling of Heat-Generating Element
Energies, 2020
Cooling of heat-generating elements is a challenging problem in engineering. In this article, the transient free convection of a temperature-dependent viscosity liquid inside the porous cavity with copper radiator and the heat-generating element is studied using mathematical modeling techniques. The vertical and top walls of the chamber are kept at low constant temperature, while the bottom wall is kept adiabatic. The working fluid is a heat-conducting liquid with temperature-dependent viscosity. A mathematical model is developed based on dimensionless stream function, vorticity, and temperature variables. The governing properties are the variable viscosity, geometric parameters of the radiator, and size of thermally insulated strip on vertical surfaces of the cavity. The effect of these parameters on the energy transport and circulation patterns are analyzed numerically. Based on the numerical results obtained, recommendations are given on the optimal values of the governing parame...
—The present study is to investigate the heat transfer enhancement in a cylindrical heat exchanger using porous media. The heat exchanger is modelled by a cylindrical cavity (Shell) with inlet and outlet thermally insulated ports and five tubes which contain hot water and cold water flows in shell. The effect of porosity on heat transfer enhancement is studied at different mass flow rate 0.15, 0.2, 0.25 and 0.30 Kg/sec. The study about effect of porosity on heat transfer enhancement is done by both experimentally and CFD based and the results are compared with simple heat exchanger. In present study, two different types of porous materials are used and Porosity is taken as 80%. The effect of varying mass flow rate on outlet temperature, heat transfer coefficient, Reynolds number and Nusselt number has been investigated.