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Turbulent Flows with Chemical Reaction
Published in Bart Merci, Tarek Beji, Fluid Mechanics Aspects of Fire and Smoke Dynamics in Enclosures, 2023
Two types of convection exist: forced convection and natural convection. Forced convection refers to conditions where the motion in the fluid is not caused by the heat transfer itself, but rather by a device such as a fan or a pump. In such conditions, a characteristic velocity, v, can be defined, and thus also a characteristic Reynolds number can be defined: Re=ρvLμ=vLν.
Plants and Equipment
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
The last means, convective heat transfer, uses a transport mechanism to get the heat from one spot to another. In a house, the furnace or boiler heats air or water, which is then moved (blown or pumped) to the rooms in the house and heats the air in the rooms. There are two types of convection heating: natural and forced. Forced convection is the result of a fan, pump, or blower forcing the movement of the fluid over a heated surface, where it picks up the heat and then moves on to another surface where it gives up that heat. In a house with a radiator next to the wall, that radiator is heating the air around it. That air gets lighter (less dense) as it expands from the heating. It rises up in the room like a lighter-than-air balloon. When it reaches the ceiling, it starts to cool because it is giving up heat to the ceiling. It is pushed aside by hot air following it. When the air reaches a cooler outside wall, it gives up more heat, shrinks to become denser, and drops to the floor. It then travels back to the radiator. That is natural convection heat transfer. All these methods of heat transfer occur in a boiler.
Thermal Modeling of Solar Drying Systems
Published in Om Prakash, Anil Kumar, Solar Drying Systems, 2020
In the forced convection mode of heat transfer, the Nusselt number (Nu) is the function of the Reynolds number (Re) and Prandtl number (Pr). Mathematically, it is expressed as follows:Nu=hcXlKV=C′RePrn′ From Equations (5.11) and (5.16): mvZ=C′RePrn′Equation (5.17) is equivalent to Equation (5.11).
Effect of thermal radiation and nth order chemical reaction on non-Darcian mixed convective MHD nanofluid flow with non-uniform heat source/sink
Published in International Journal of Ambient Energy, 2023
Arindam Sarkar, Hiranmoy Mondal, Raj Nandkeolyar
Convection is an important property during the investigation of fluid flow. Convection is of two types, natural convection and forced convection. Natural convection happens due to gravity, whereas forced convection causes by external forces. Convection is significant in the manufacturing of many electronic devices, heat exchangers, solar cells and so many engineering implementations. Chamkha and Khaled (2000) investigated the hydromagnetic mixed convective nanofluid flow passing a porous media. Sadr et al. (2022) studied the mixed convective nanofluid flow contained in a rotating heated cylinder. Bafakeeh et al. (2022) scrutinised both the free and forced convective nanofluid flow considering the slip velocity. They conclude that enhancement of the thermal profile is growing for the suspension of silver nanosised particles in kerosine oil. 2D mixed convective thermal property analysed by Abderrahmane et al. (2022). In addition, the inspection of the Peclet number and Reynolds number over 2-dimensional micropolar fluid passing through a horizontal channel has been investigated by Shamshuddin et al. (2023). Mandal et al. (2023) examined the effect of mixed convection on hybrid nanofluid flow. On the other hand, the analysis of entropy generation through mixed convective nanofluid flow was scrutinised by Raja et al. (2022).
Entropy generation and thermohydraulics of mixed convection of hybrid-nanofluid in a vertical tube fitted with elliptical‑cut twisted tape inserts - a computational study
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Amir Mohamad Khfagi, Graeme Hunt, Manosh C Paul, Nader Karimi
Mixed convection flow occurs when natural (free) and forced convection mechanisms contribute comparably to heat transfer (Galvez et al. 2008). In natural convection, fluid motion is the result of fluctuating gravitational body forces and fluid density. Forced convection induces fluid mobility by the application of an external force (Bergman et al. 2011). Different parameters such as flow direction, arrangement geometries, and flow regimes, type of working fluid and magnitude of the temperature difference that drives heat transfer characterize the contributions of natural and forced convection (Joye, Bushinsky, and Saylor 1989; Oni and Paul 2015). Buoyancy forces are responsible for the formation of natural convection currents, and their direction depends on whether the forced flow is upward, downward, horizontal, or any mix of the three. The natural convection currents are said to be “assisting” when they move in the same direction as the forced flow and “opposing” when they move in the opposite direction (Bergman et al. 2011). Several engineering applications employ mixed convection heat transfer in tubes. These include heat exchangers for cooling electrical equipment and solar collectors. Pipelines used to carry oil, and boilers are further examples (Kakaç, Shah, and Aung 1987; Mohammed 2008). The significance of mixed convection heat transmission in pipes has sparked various research projects in order to increase the efficiency of many industrial applications (Ozsunar, Baskaya, and Sivrioglu 2001).
Effect of selected geometric parameters on natural convection in concentric square annulus
Published in Australian Journal of Mechanical Engineering, 2022
I. K. Adegun, S. E. Ibitoye, A. Bala
The convection heat transfer coefficient is not a property of the fluid, it is an experimentally determined parameter and its value depends on all the variables influencing convection heat transfer. The variables include surface geometry, nature of fluid motion, properties of fluid and bulk fluid velocity (Moutaouakil, Zrikem, and Abdelbaki 2017; Fattahi, Farhadi, and Sedighi 2010). Since the convective mode of heat transfer involves fluid flow along with conduction, it is generally categorised into natural or free convention and forced convection. If the motion of the fluid arises from an external agent such as fan, blower, wind, or the motion of the heated object itself, which imparts pressure to drive the flow, the process is termed forced convection (Bejan and Kraus 2013; Wang et al. 2019; Mahmoodi, Hemmat, and Akbari 2015). However, if no such externally induced flow exists and the flow arises naturally from the effect of density difference, resulting from a temperature or concentration difference in a body force field such as gravity, the process is termed natural convection (Bejan and Kraus 2013; Masoud and Hijazi 2008; Basant and Oni 2018; Chen, Tölke, and Krafczyk 2010). The density difference gives rise to buoyancy forces due to which the flow is generated.