scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Heat Transfer Enhancement in a Flat-Plate Solar Water Heater Through Longitudinal Vortex Generator

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
F. A. S. Silva ◽  
L. O. Salviano
Keyword(s):  
Heat Transfer ◽  
Solar Energy ◽  
Flat Plate ◽  
Thermal Energy ◽  
Vortex Generator ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water ◽  
Delta Winglet

The solar energy is a renewable source that has a great potential for conversion into thermal energy or for generation of electric power through photovoltaic panels in Brazil. Concerns about environmental impacts and the fossil resources scarcity have motivated the technological development of renewable alternatives to fill out the energy matrix. The flat-plate solar water heater is an equipment used for domestic or commercial applications to heat fluids, which can minimize the demand for electric energy and, consequently, decrease the electrical bill. However, the development of technologies to increase the conversion of solar energy into thermal energy remains a challenge in order to increase the efficiency of these devices. Thus, passive techniques to enhance heat transfer have been applied and those results seem to be promissory. Among them, delta-winglet longitudinal vortex generator (VG) is a consolidated passive technique currently applied on compact heat exchangers, although few works have been applied this technique on the solar water heater. By a computational fluid dynamics approach, in this work, we analyze the augmentation of heat transfer through delta-winglet longitudinal vortex generator inside a tube of a flat-plate solar water heater. For the Reynolds numbers 300, 600, and 900, the better ratio between the heat transfer and the pressure drop penalty is found for the attack angle of the delta-winglet of 30 deg, while the highest heat transfer was to the attack angle of 45 deg. Moreover, the first vortex generators showed significant impact only on the friction factor and could be eliminated of the solar water heater with no penalty to the heat transfer.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Second-Law Analysis of a Two-Phase Self-Pumping Solar Water Heater

1992 ◽  
Vol 114 (3) ◽  
pp. 188-193 ◽  
Author(s):  
H. A. Walker ◽  
J. H. Davidson
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Hot Water ◽  
Solar Water Heater ◽  
Total Entropy ◽  
Water Heating ◽  
Water Heater ◽  
Two Phase ◽  
Solar Water ◽  
Order Of Magnitude

Entropy generated by operation of a two-phase self-pumping solar water heater under Solar Rating and Certification Corporation rating conditions is computed numerically in a methodology based on an exergy cascade. An order of magnitude analysis shows that entropy generation is dominated by heat transfer across temperature differences. Conversion of radiant solar energy incident on the collector to thermal energy within the collector accounts for 87.1 percent of total entropy generation. Thermal losses are responsible for 9.9 percent of total entropy generation, and heat transfer across the condenser accounts for 2.4 percent of the total entropy generation. Mixing in the tempering valve is responsible for 0.7 percent of the total entropy generation. Approximately one half of the entropy generated by thermal losses is attributable to the self-pumping process. The procedure to determine total entropy generation can be used in a parametric study to evaluate the performance of two-phase hot water heating systems relative to other solar water heating options.

Experiment of a Flat Plate Solar Water Heater Collector with Modified Design and Thermal Performance Analysis

2014 ◽  
Vol 624 ◽  
pp. 332-338 ◽  
Author(s):  
Shouquat Hossain ◽  
Ali Wadi Abbas ◽  
Jeyraj Selvaraj ◽  
Ferdous Ahmed ◽  
Nasrudin Bin Abd Rahim
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Flat Plate ◽  
Thermal Performance ◽  
Solar Water Heater ◽  
Water Heater ◽  
Pipe Surface ◽  
Solar Water ◽  
Useful Heat ◽  
Absorber Surface

An investigation is reported of the thermal performance of a flat plate solar water heater with a circulating absorber pipe surface. The thermal performance of the 2-side parallel serpentine flow solar water heater depends significantly on the heat transfer rate between the absorber surface and the water, and on the amount of solar radiation incident on the absorber surface. The modified pipe arrangement has a higher characteristic length for convective heat transfer from the absorber to the water, in addition to having more surface area exposed to solar radiation. It means during the operation of water heater, more solar energy is converted into useful heat. However, this modification has reduced the efficiency of the system marginally.

Sign in / Sign up

Export Citation Format

Share Document