Enhancing Heat Transfer from a Porous Plate with Transpiration Cooling (original) (raw)
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A heat transfer analysis from a porous plate with transpiration cooling
Thermal Science, 2019
Present study is focused on improving heat transfer from a porous plate by cooling of air with transpiration cooling. Effects of Reynolds number of the air channel flow and particle diameter on cooling effectiveness of porous plate and efficiency of system were investigated experimentally. It was observed that increasing Reynolds number of 15.2% causes a decrease of 6.9% on cooling efficiency of the system and a decrease of 8.6% on cooling effectiveness of porous plate. Decreasing particle diameter causes a significant decrease on surface temperature and an increase on cooling effectiveness of porous plate. Difference of cooling effectiveness of porous plate from dp = 40-200 ?m is 12%. Verification of this study was also shown by comparing experimental results of this study with literature.
Using Porous Media to Enhancement of Heat Transfer in Heat Exchangers
— According to increasing human needs for energy and to avoid energy waste, researchers are struggling to increase the efficiency of energy production and energy conversion. One of these methods is increasing heat transfer and reducing heat dissipation in heat exchangers. Using porous materials in the fluid flow is one of the passive methods to increase heat transfer in heat exchangers. The existence of porous media in the flow path, improve the matrix of thermal conductivity and effective flow thermal capacity and also matrix of porous-solid increase radiation heat transfer, especially in two phase flow (gas-water) systems. In this paper, recent studies on the effect of using porous media on enhancement the amount of heat transfer in heat exchangers has been investigated via using porous media with difference porosity percentage, material and geometric structure in the flow path in numerical simulations and laboratory studies.
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.
Experimental Analysis of Heat Transfer Enhancement through Porous Medium
Heat transfer is the basic phenomenon in thermal application. It plays a vital role in heating and cooling of the material and system as well as it is very important phenomenon in many of the thermal applications like internal combustion engine for its cooling and lubrication, Heat Exchanger to transmit the heat energy from one system to another in refrigeration, air conditioning etc., Heat transfer enhancement motivate to identify new technique and the material through which it can be improved. Enhancement in heat transfer depends upon the various dimensionless parameters along with porosity of the porous material and its aspect ratio. It has been proven that the porous material can enhance the heat transfer rate. During the experimentation by the researchers it is observed that the to evaluate the heat transfer rate from the system and the result were quiet impressive to extend the study for further research.
A numerical analysis of transpiration cooling as an air cooling mechanism
Heat and Mass Transfer, 2018
The present study is focused on investigation of heat transfer from a porous plate by cooling of air with transpiration cooling. Effects of Reynolds number of hot gas stream, inlet temperature of air and mass flow rate of water on local wall temperature and cooling effectiveness of porous flat plate and efficiency of the system inside a rectangular channel with air as a hot gas stream and water as a coolant were investigated numerically. Increasing Reynolds number causes an increase on surface temperature and a decrease on cooling effectiveness of porous plate and efficiency of the system. Increasing of air inlet temperature does not cause a significant increase on cooling efficiency of the system. An increase of water flow rate causes a decrease on surface temperature and an increase on effectiveness of porous plate and cooling efficiency of the system. Numerical results prepared by RNG k-ε turbulence model have a good approximation and show a similar flow characteristic with experimental results. Keywords Computational fluid dynamics. Heat transfer. Navier-stokes-equation. RNG k-ε model. Structured surface. Transpiration cooling Nomenclature A Surface area of porous plate, m 2 B m Mass transfer driving force, B m ¼ m ev −m s m s −1 B h Heat transfer blowing parameter, B h ¼ m ⋅ ev :Cp hc * F Blowing ratio, F ¼ q c :V c q air:V air
Forced convection cooling enhancement by use of porous materials
International Journal of Heat and Fluid Flow, 1998
Results are presented for laminar forced convection cooling of heat generating blocks mounted on a wall in a parallel plate channel. The eect on heat transfer of insertion of a porous matrix between the blocks is considered. The¯ow in the porous medium is modeled using the Brinkman±Forchheimer extended Darcy model. The mass, momentum and energy equations are solved numerically by a control-volume-based procedure. The local Nusselt number at the walls of the blocks, the mean Nusselt numbers and the maximum temperature in the blocks are examined for a wide range of Darcy number and thermal conductivity ratio. The computations are ®rst conducted for a single block, then for evenly mounted blocks. The results show that the insertion of a porous material between the blocks may enhance the heat transfer rate on the vertical sides of the blocks. Although the porous matrix reduces the heat transfer coecient on the horizontal face, signi®cant increases in the mean Nusselt number (up to 50%) are predicted and the maximum temperatures within the heated blocks are reduced in comparison with the pure¯uid case. Ó 1998 Elsevier Science Inc. All rights reserved.
—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.
An Innovative Cooling System Based on Evaporation from a Porous Tank
2016
The exponential increase of the cooling demand in buildings obliges to find alternatives to the high electricity consumption with air conditioning systems. This work investigates a new cooling system based on evaporation. The key component of this system is a porous tank filled with water. Evaporation process occurs at the outside surface, which cools down water in the tank. Fresh water is then used to meet the cooling demand in the building. To model the impact of this new system, an accurate model of the porous tank is needed. A numerical model is developed, based on the heat and mass transfer balances and compared with experimental results, showing accurate results in terms of energy balance and prediction of water-cooling.
Experimental Investigation of Heat Transfer through Porous Material Heat Exchanger
2017
Latest developments in the manufacturing technology have led to development of advance lightweight materials for thermal applications. Heat transfer through porous materials has gained significance in industrial as well as academic research. In this paper thermal performance including heat transfer and pressure drop through porous material, i.e. metal foam heat exchanger, has been presented. The experimental data has been used to calculate and present graphically various performance parameters such as effectiveness, friction factor, Reynolds number and Nusselt number.The effectiveness of the heat exchangers was compared at u = 0.5–7 m/s fluid velocity, it was found that the best performance is exhibited by heat exchanger at effectiveness (ε = 30%, u = 0.2 m/s). Maximum heat transfer occurs at Reynolds number of 900. For further investigation advance methods such as artificial neural networks, fuzzy logic and genetic algorithm can be used.
Direct evaporative cooling performance of ambient air using a ceramic wet porous layer
Chemical Engineering Research and Design, 2018
Direct evaporative cooling is one of the efficient traditional strategies to provide summer comfort in a building or airconditioning in storage rooms. The present paper concerns a new mathematical approach to analyse the influence of the effective parameters on the performance of direct evaporation from a porous layer. The ambient air flows over a porous material, fed with water. The evaporation of an amount of water into the air reduces its temperature and, at the same time, raises the air's humidity. A mathematical model that accounts for simultaneous heat and mass transfer characteristics in the ambient air and water flow in corporating non-Darcian model in the porous region within vertical parallel walls is presented. The solution of the mathematical model is based on the finite volume method and the velocity-pressure coupling is treated with the SIMPLE algorithm. The results showed that the porous evaporative cooler could satisfy the cooling requirements in arid climates. An average drop of 15 °C of air temperature below the ambient temperature can be reached at the considered conditions. Therefore, the ambient air is satisfactorily cooled. Furthermore, the better cooling performance can be achieved for a high porosity with a thick porous medium and lower air velocity at the entrance.