Search results
Results from the WOW.Com Content Network
The macroscopic energy equation for infinitesimal volume used in heat transfer analysis is [6] = +, ˙, where q is heat flux vector, −ρc p (∂T/∂t) is temporal change of internal energy (ρ is density, c p is specific heat capacity at constant pressure, T is temperature and t is time), and ˙ is the energy conversion to and from thermal ...
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
In controlled experiments, the effect can entirely be explained by undercooling and the time of freezing was determined by what container was used. [12] Experimental results confirming the Mpemba effect have been criticized for being flawed, not accounting for dissolved solids and gasses, and other confounding factors.
Thermal conduction is the diffusion of thermal energy (heat) within one material or between materials in contact. The higher temperature object has molecules with more kinetic energy; collisions between molecules distributes this kinetic energy until an object has the same kinetic energy throughout.
Convection (or convective heat transfer) is the 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 diffusion) and advection (heat transfer by bulk fluid flow ).
In most cases this leads to natural circulation: the ability of a fluid in a system to circulate continuously under gravity, with transfer of heat energy. The driving force for natural convection is gravity. In a column of fluid, pressure increases with depth from the weight of the overlying fluid.
Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time. [37] The statement by Clausius uses the concept of 'passage of heat'. As is usual in thermodynamic discussions, this means 'net transfer of energy as heat', and does not refer to contributory transfers one way and the ...
The parameter of importance in forced convection is the Péclet number, which is the ratio of advection (movement by currents) and diffusion (movement from high to low concentrations) of heat. = When the Peclet number is much greater than unity (1), advection dominates diffusion. Similarly, much smaller ratios indicate a higher rate of ...