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Convection (heat Transfer)
Convection (or convective heat transfer) is the heat transfer, transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of Conduction (heat), conduction (heat diffusion) and advection (heat transfer by bulk fluid flow). Convection is usually the dominant form of heat transfer in liquids and gases. Note that this definition of convection is only applicable in Heat transfer and Thermodynamics, thermodynamic contexts. It should not be confused with the Fluid dynamics, dynamic fluid phenomenon of Convection#Terminology, convection, which is typically referred to as ''Natural Convection'' in thermodynamic contexts in order to distinguish the two. Overview Convection can be "forced" by movement of a fluid by means other than buoyancy forces (for example, a water pump in an automobile engine). Thermal expansion of fluids may also force convection. In o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecules
A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and ''molecule'' is often used when referring to polyatomic ions. A molecule may be homonuclear, that is, it consists of atoms of one chemical element, e.g. two atoms in the oxygen molecule (O2); or it may be heteronuclear, a chemical compound composed of more than one element, e.g. water (two hydrogen atoms and one oxygen atom; H2O). In the kinetic theory of gases, the term ''molecule'' is often used for any gaseous particle regardless of its composition. This relaxes the requirement that a molecule contains two or more atoms, since the noble gases are individual atoms. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Conductivity
The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials such as mineral wool or Styrofoam. Metals have this high thermal conductivity due to free electrons facilitating heat transfer. Correspondingly, materials of high thermal conductivity are widely used in heat sink applications, and materials of low thermal conductivity are used as thermal insulation. The reciprocal of thermal conductivity is called thermal resistivity. The defining equation for thermal conductivity is \mathbf = - k \nabla T, where \mathbf is the heat flux, k is the thermal conductivity, and \nabla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Transfer Enhancement
Heat transfer enhancement is the process of increasing the effectiveness of Heat exchanger, heat exchangers. This can be achieved when the heat transfer power of a given device is increased or when the pressure losses generated by the device are reduced. A variety of techniques can be applied to this effect, including generating strong Secondary flow, secondary flows or increasing boundary layer turbulence. Principle During the earliest attempts to enhance heat transfer, plain (or smooth) surfaces were used. This surface requires a special surface geometry able to provide higher values per unit surface area in comparison with a plain surface. The ratio of of an enhanced heat transfer surface to the plain surface is called Enhancement Ratio " E_h ". Thus, E_h= The heat transfer rate for a two-fluid counterflow heat exchanger is given by In order to better illustrate the benefits of enhancement, the total length 'L' of the tube is multiplied and divided in the eq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Transfer Coefficient
In thermodynamics, the heat transfer coefficient or film coefficient, or film effectiveness, is the Proportional (mathematics), proportionality constant between the heat flux and the thermodynamic driving force for the Heat transfer, flow of heat (i.e., the Temperature gradient, temperature difference, ). It is used to calculate heat transfer between components of a system; such as by convection between a fluid and a solid. The heat transfer coefficient has SI units in Watt, watts per square meter per kelvin (W/(m2K)). The overall heat transfer rate for combined modes is usually expressed in terms of an overall Thermal conduction, conductance or heat transfer coefficient, . Upon reaching a steady state of flow, the heat transfer rate is: :\dot=hA(T_2-T_1) where (in SI units): : \dot: Heat transfer rate (W) : h: Heat transfer coefficient (W/m2K) : A: surface area where the heat transfer takes place (m2) : T_2: temperature of the surrounding fluid (K) : T_1: temperature of the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mixed Convection
In fluid thermodynamics, combined forced convection and natural convection, or mixed convection, occurs when natural convection and forced convection mechanisms act together to transfer heat. This is also defined as situations where both pressure forces and buoyant forces interact. How much each form of convection contributes to the heat transfer is largely determined by the flow, temperature, geometry, and orientation. The nature of the fluid is also influential, since the Grashof number increases in a fluid as temperature increases, but is maximized at some point for a gas. Characterization Mixed convection problems are characterized by the Grashof number (for the natural convection) and the Reynolds number (for the forced convection). The relative effect of buoyancy on mixed convection can be expressed through the Richardson number: : \mathrm=\frac The respective length scales for each dimensionless number must be chosen depending on the problem, e.g. a vertical length f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conjugate Convective Heat Transfer
The contemporary conjugate convective heat transfer model was developed after computers came into wide use in order to substitute the empirical relation of proportionality of heat flux to temperature difference with heat transfer coefficient which was the only tool in theoretical heat convection since the times of Newton. This model, based on a strictly mathematically stated problem, describes the heat transfer between a body and a fluid flowing over or inside it as a result of the interaction of two objects. The physical processes and solutions of the governing equations are considered separately for each object in two subdomains. Matching conditions for these solutions at the interface provide the distributions of temperature and heat flux along the body–flow interface, eliminating the need for a heat transfer coefficient. Moreover, it may be calculated using these data. History The problem of heat transfer in the presence of liquid flowing around the body was first formulate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Transfer Coefficient
In thermodynamics, the heat transfer coefficient or film coefficient, or film effectiveness, is the Proportional (mathematics), proportionality constant between the heat flux and the thermodynamic driving force for the Heat transfer, flow of heat (i.e., the Temperature gradient, temperature difference, ). It is used to calculate heat transfer between components of a system; such as by convection between a fluid and a solid. The heat transfer coefficient has SI units in Watt, watts per square meter per kelvin (W/(m2K)). The overall heat transfer rate for combined modes is usually expressed in terms of an overall Thermal conduction, conductance or heat transfer coefficient, . Upon reaching a steady state of flow, the heat transfer rate is: :\dot=hA(T_2-T_1) where (in SI units): : \dot: Heat transfer rate (W) : h: Heat transfer coefficient (W/m2K) : A: surface area where the heat transfer takes place (m2) : T_2: temperature of the surrounding fluid (K) : T_1: temperature of the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulk Temperature
In thermofluids dynamics, the bulk temperature, or the average bulk temperature in the thermal fluid, is a convenient reference point for evaluating properties related to convective heat transfer, particularly in applications related to flow in pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circu ... and ducts. The concept of the bulk temperature is that adiabatic mixing of the fluid from a given cross section of the duct will result in some equilibrium temperature that accurately reflects the average temperature of the moving fluid, more so than a simple average like the film temperature. Kreith, Frank, and Bohn, Mark S. ''Principles of Heat Transfer, Sixth Edition.'' Brooks/Cole: Pacific Grove, CA, 2001. References Continuum mechanics Heat transfer Temperature {{the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RWTH Aachen University
RWTH Aachen University (), in German ''Rheinisch-Westfälische Technische Hochschule Aachen'', is a German public research university located in Aachen, North Rhine-Westphalia, Germany. With more than 47,000 students enrolled in 144 study programs, it is the second largest technical university in Germany. RWTH Aachen in 2019 emerged from the final of the third federal and state excellence strategy. The university will be funded as a university of excellence for the next seven years. RWTH Aachen was already part of the federal and state excellence initiative in 2007 and 2012. Since 2007, RWTH Aachen has been continuously funded by the Deutsche Forschungsgemeinschaft, DFG and the German Council of Science and Humanities as one of eleven (previously nine) German German Universities Excellence Initiative, Universities of Excellence for its future concept ''RWTH 2020: Meeting Global Challenges'' and the follow-up concept ''The Integrated Interdisciplinary University of Science and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mixed Convection
In fluid thermodynamics, combined forced convection and natural convection, or mixed convection, occurs when natural convection and forced convection mechanisms act together to transfer heat. This is also defined as situations where both pressure forces and buoyant forces interact. How much each form of convection contributes to the heat transfer is largely determined by the flow, temperature, geometry, and orientation. The nature of the fluid is also influential, since the Grashof number increases in a fluid as temperature increases, but is maximized at some point for a gas. Characterization Mixed convection problems are characterized by the Grashof number (for the natural convection) and the Reynolds number (for the forced convection). The relative effect of buoyancy on mixed convection can be expressed through the Richardson number: : \mathrm=\frac The respective length scales for each dimensionless number must be chosen depending on the problem, e.g. a vertical length f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
