For turbulent flow, the heat transfer coefficient increases with increasing mass flux (or Reynolds number) . This is because higher velocity increases turbulence, which in turn provides a more efficient radial transport/mixing of heat.
What affects convection coefficient?
Accordingly, the convection heat transfer coefficient depends on (1) the fluid thermophysical properties and (2) the fluid velocity . These factors should be considered in the analysis and design of energy geostructures.
What factors influence the convective heat transfer coefficient?
The convective heat transfer coefficient h strongly depends on the fluid properties and roughness of the solid surface, and the type of the fluid flow (laminar or turbulent) .
What does convective heat transfer coefficient depend on?
The heat convection coefficient, the most important parameter for the convection process, is dependent on not only the wind velocity (the speed of air convection near the pavement surface) but also the pavement surface characteristics (roughness) [189,190][189][190].
How do you increase heat transfer coefficient?
To increase heat-transfer rates, the velocity through a jacket can be increased by recirculating the cooling or heating liquid . For simple jackets without baffles, heat-transfer will be mainly by natural convection and the heat-transfer coefficient will range from 200 to 400 W/m 2 °C.
Does heat transfer coefficient depend on material?
Heat transfer coefficient is not a thermophysical property of material, while it depends on the surface geometry and the conditions of boundary layer . ... It depends on many factors like geometry, temperature of fluid, other thermo-physical properties like viscosity, thermal conductivity etc.
On what factors heat transfer depends?
The process of heat conduction depends on four basic factors: the temperature gradient, the cross section of the materials involved, their path length, and the properties of those materials .
What is the relation between convection heat transfer coefficient?
The convective heat transfer coefficient, h, can be defined as: The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference . The convective heat transfer coefficient is dependent upon the physical properties of the fluid and the physical situation.
What is convection coefficient a function of?
The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference . The convective heat transfer coefficient is dependent upon the physical properties of the fluid and the physical situation. The convective heat transfer coefficient is not a property of the fluid.
What affects the overall heat transfer coefficient?
Heat transfer coefficient depends on both the thermal properties of a medium , the hydrodynamic characteristics of its flow, and the hydrodynamic and thermal boundary conditions. ...
Does heat transfer coefficient change with flow rate?
The heat transfer coefficient decreases by ̃10% with a threefold increase in the mass flow rate under these conditions, based on the commonly used Dittus-Boelter correlation for estimation of the heat transfer coefficient. ... Doubling the mass flow rate will result in a 92% increase in the heat transfer coefficient.
How is heat transfer coefficient of radiation calculated?
The rate of heat transfer by emitted radiation is determined by the Stefan-Boltzmann law of radiation: Qt=σeAT4 Q t = σ e A T 4 , where σ = 5.67 × 10 − 8 J/s · m 2 · K 4 is the Stefan-Boltzmann constant, A is the surface area of the object, and T is its absolute temperature in kelvin.
Can the overall heat transfer coefficient be negative?
In addition, with traditional definition of convective heat transfer coefficient, which is based on the temperature difference of an interior surface and room air, the coefficient value can be negative .
What is average heat transfer coefficient?
Heat-transfer coefficient equal to the heat flow (Q) across the heat-transfer surface divided by the average temperature (Δt) and the area of the heat-transfer surface (F)
Is laminar or turbulent flow better for heat transfer?
The study of heat transfer can be done either in laminar flow or in turbulent flow. ... Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions. This is due to the increase in the Reynolds number of the flowing fluid in turbulent flow.
Which one has the highest value of overall heat transfer coefficient?
Which one is having highest value of overall heat transfer coefficient? Explanation: Overall heat transfer coefficient for feed water heaters is 8500 W/m 2 K while that of steam, alcohol condensers and ammonia condensers are 5000 W/m 2 K, 630 W/m 2 K and 1400 W/m 2 K.
