Studying the Effect of Porosity of Porous Layer Coating on the Performance of the Horizontal Tubular Falling Film Evaporator

2021 ◽  
Author(s):  
Alaa Adel Ibrahim ◽  
Hassan Elgamal ◽  
Ahmed M. Nagib Elmekawy
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Numerical Simulations ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Falling Film ◽  
Film Evaporator ◽  
Porosity Ratio ◽  
Layer Coating

Abstract Through the recent decades, many studies have focused on finding efficient methods to enhance the heat transfer performance in heat exchangers. Therefore, using porous media attracted many researchers, as it is such a simple, efficient, and low-cost technique in enlarging the surface contact area of heat transfer through the fluid pass. Nevertheless, there is little work associated with using porous media to enhance the thermal performance of falling film evaporators. The present study seeks to discuss numerically the liquid flow behaviour over falling film evaporator tubes in the case of bare tubes and tubes with porous layer coating. The two-dimensional multi-phase numerical simulations are also carried out in order to investigate the effect of the porosity ratio of the porous medium added to the tubes in the heat transfer performance. Furthermore, deducing the way to select a decent porosity ratio to be used to get the best thermal performance is demonstrated through the study. Time-averaged results gained from the numerical simulations have been compared to those of bare-tube falling film evaporator to observe much higher heat transfer performance represented in the average surface Nusselt number (Nu) which increased by 3 times.

scholarly journals A comparative study of different heat transfer enhancement mechanisms in a partially porous pipe

2021 ◽  
Vol 3 (10) ◽  
Author(s):  
Nima Fallah Jouybari ◽  
Majid Eshagh Nimvari ◽  
Wennan Zhang
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Porous Material ◽  
Porous Layer ◽  
Heat Transfer Performance ◽  
Pipe Wall ◽  
Critical Role ◽  
Flow In Porous Media ◽  
Turbulent Regime ◽  
Transfer Performance

AbstractThe effect of porous material position on the heat transfer inside a pipe working in a turbulent regime is studied here to obtain a detailed understanding of the heat transfer enchantment mechanisms in different porous substrate positions. To this end, an in-house Fortran code is developed to solve the governing equations using the finite volume method and SIMPLE algorithm. Turbulent flow in porous media is modeled using a modified version of k–ε model. The flow field and heat transfer inside the partially filled pipe are investigated for the two cases of central and boundary configurations. The porous and flow characteristics including Reynolds number, Darcy number, the conductivity ratios of solid to fluid and the thickness of inserted porous layer are varied and the heat transfer performance is studied in different cases. It is observed that two entirely different phenomena enhance the heat transfer in central and boundary configurations. While the channeling of fluid between the porous media and the pipe wall highly affects the heat transfer performance in the former, the thermal conductivity of porous media plays a highly critical role in the latter configuration. It is shown that, for the same filling ratio, inserting the porous layer at the core of the pipe is more effective than placing it at the wall. Investigating porous materials with different solid conductivities revealed that covering the pipe wall with a porous material is justified only for solid matrixes with high thermal conductivities.

Heat Transfer Enhancement With Delta Winglets Vortex Generator for Different Arrangement in a Circular Tube

2018 ◽  
Author(s):  
Md. Islam ◽  
A. Nurizki ◽  
A. Kareem ◽  
A. Baba
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Circular Tube ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Attack Angle ◽  
Transfer Performance ◽  
Pitch Ratio

Various technologies have been developed to enhance the heat transfer. Vortex generator (VG) is one of the passive techniques which can change the flow behavior and ultimately enhances the heat transfer performance. Delta winglet (DW) vortex generator can create longitudinal and horseshoe vortices which do not decay until further downstream and consequently increase heat transfer coefficient with comparatively lower pressure drop. With this vortex generator, it is expected to have higher Nusselt number with some increase of friction factor. Therefore, this study is to study the effect of pitch ratio (PR) and attack angle (B) of DW vortex generator to increase the thermal performance of heat exchanger. Four delta winglets are attached into a ring. Those rings attached with VGs will be used to investigate the influence of different parameters to heat transfer performance. In this study VGs were placed inside a circular copper tube and the heating coil was wrapped up around the outer surface of the copper tube to generate a constant heat flux condition. The experimental setup consists of a blower, orifice meter, flow straightener, calm/flow developing section and test section. The results show the friction factor, Nusselt number, and Thermal Performance Enhancement. It increases the thermal performance due to the formation of longitudinal vortex inside the circular tube. Pitch ratio and attack angle seem to have significant impact on the flow and heat transfer. The Pitch ratio of 1.6 have the highest impact on both (f/f0) and (Nu/Nuo) followed by attack angle. Smoke flow visualization technique was used to study flow behavior and flow structures.

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