scholarly journals CFD simulation of natural convection and heat transfer in a flat solar thermal collector with fins on the glazing - horizontal case

2019 ◽  
Vol 3 (2) ◽  
pp. 1
Author(s):  
Adel Laaraba
Keyword(s):  
Heat Transfer ◽  
Solar Collector ◽  
Transfer Rate ◽  
Cfd Simulation ◽  
Solar Thermal ◽  
Heat Transfer Characteristics ◽  
Convection And Heat Transfer ◽  
Flow And Heat Transfer ◽  
Solar Thermal Collector ◽  
Different Temperatures

This study is based on a CFD simulation of a flat horizontal solar thermal collector containing fins on its inner face of the glazing. The walls of the solar collector with insulation are considered adiabatic and the rest of the walls are at constant different temperatures. The principal objective of this work is to study the effects of the number of fins that changed from 0 to 30, as well as their length varied from 0 to 0.8 on the air flow and heat transfer characteristics. It has been observed that the heat transfer rate is strongly affected by the number of fins and the length of the fins. The obtained result showed that the increase of the fins reduces the heat loss by convection by 54 %.

Heat transfer enhancement in microchannels using ribs and secondary flows

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Karthikeyan Paramanandam ◽  
Venkatachalapathy S. ◽  
Balamurugan Srinivasan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

A Numerical Study of Flow and Heat Transfer Between Two Rotating Spheres With Time-Dependent Angular Velocities

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Ali Jabari Moghadam ◽  
Asghar Baradaran Rahimi
Keyword(s):  
Heat Transfer ◽  
Viscous Incompressible Fluid ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Heat Transfer Characteristics ◽  
Coriolis Forces ◽  
Flow And Heat Transfer ◽  
Concentric Spheres ◽  
Different Temperatures ◽  
Angular Velocities

The transient motion and the heat transfer of a viscous incompressible fluid contained between two vertically eccentric spheres maintained at different temperatures and rotating about a common axis with different angular velocities are numerically considered when the angular velocities are arbitrary functions of time. The resulting flow pattern, temperature distribution, and heat transfer characteristics are presented for the various cases including exponential and sinusoidal angular velocities. Long delays in heat transfer of large portions of the fluid in the annulus are observed because of the angular velocities of the corresponding spheres. As the eccentricity increases and the gap between the spheres decreases, the Coriolis forces and convection heat transfer effect in the narrower portion increase. Special results for concentric spheres are obtained by letting eccentricity tends to zero.

Determination of Heat Transfer Characteristics of Solar Thermal Collectors as Heat Source for a Residential Heat Pump

2015 ◽  
Author(s):  
Maarten G. Sourbron ◽  
Nesrin Ozalp
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Low Temperature ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Heat Pump ◽  
Solar Collector ◽  
Solar Thermal ◽  
Heat Transfer Characteristics ◽  
Temperature Heat

One of the best ways of making efficient use of energy in residential units is to use heat pump. Heat pump performance can be further enhanced by integrating a solar thermal unit to provide hot water and subsidize space heating. This paper presents numerically examined energy feasibility study of a solar driven heat pump system for a low energy residence, where a flat plate solar collector served as the sole low temperature heat source. A parametric study on the ambient-to-solar fluid heat transfer coefficient has been conducted to determine the required solar collector heat transfer characteristics in this system. Solar collector area and storage tank volume were varied to investigate their impact on the system performance. A new performance indicator availability was defined to assess the contribution of the solar collector as low temperature energy source of the heat pump. Results showed that the use of a solar collector as low temperature heat source was feasible if its heat transfer rate (UA-value) was 200 W/K or higher. Achievement of this value with a realistic solar collector area (A-value) required an increase of the overall ambient-to-solar fluid heat transfer coefficient (U-value) with a factor of 6 to 8 compared to the base case with only natural convection heat exchange between solar collector cover and ambient.

Effect of Variable Sidewall Temperatures on the Combined Surface Radiation—Convection in a Discretely Heated Enclosure

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
S. Saravanan ◽  
N. Raja
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Surface Radiation ◽  
Computational Results ◽  
Heat Transfer Characteristics ◽  
Total Heat Transfer ◽  
Flow And Heat Transfer ◽  
Volume Method ◽  
Made In

This paper reports the changes made in the flow and heat transfer characteristics of a closed enclosure in the presence of sidewalls with symmetrical linear heating. The flow inside the enclosure is primarily driven by a centrally placed discrete heater with thermal radiation included at all surfaces involved. Finite volume method-based computational results corresponding to the resulting steady-state were obtained. The factors causing augmentation and suppression of heat transfer are discussed for two types of sidewall heating. Moreover, it is found that the role of radiation is well stronger than convection in determining the total heat transfer rate when the sidewall heating is decreasing with height.

The Effect of Asymmetrically Confined Circular Cylinder and Opposing Buoyancy on Fluid Flow and Heat Transfer

2017 ◽  
Vol 374 ◽  
pp. 18-28 ◽  
Author(s):  
Houssem Laidoudi ◽  
Mohamed Bouzit
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Transfer Rate ◽  
Richardson Number ◽  
Convection Heat Transfer ◽  
Heat Transfer Characteristics ◽  
Thermal Buoyancy ◽  
Flow And Heat Transfer ◽  
Mixed Convection Heat Transfer

In this paper, a two-dimensional numerical investigation is carried out to understand the effects of opposing thermal buoyancy and Prandtl number on fluid flow and mixed convection heat transfer characteristics of symmetrically and asymmetrically confined cylinder submerged in Newtonian fluid. The detailed flow and temperature field are illustrated in term of streamlines and isotherm contours to interpret the flow and thermal transport visualization. The numerical results are presented and discussed for the range of conditions as: Ri = 0 to -4, Pr = 0.7 to 50, eccentricity factor ε = 0 to 0.7 at Re = 40 and for a fixed blockage parameter B = 0.2. The effect of opposing buoyancy is brought about by varying Richardson numbers. The overall drag coefficient and average Nusselt number are computed to elucidate the role of Prandt number, eccentricity factor and Richardson number on the flow and heat transfer. At ε = 0, it is found that, when the buoyancy is opposed the flow becomes asymmetrically and some rotating zones appear under and above the cylinder. Moreover, the eccentricity factor has a tendency to decrease the rotating regions and to increase the heat transfer rate. For example an increase in eccentricity factor from 0 to 0.6 increases Nu by 77% at Ri = 4.

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