volkov Flashcards
what are the thermodynamic categories (2)
power cycle and refrigeration cycles
application of thermodynamic devices
engine
refrigerators, air conditioning heat pumps
why does conduction occur
occurs due to molecular activity in
the heat transfer
where does convection occur and what mechanisms does it have
occurs in fluids, gases and liquids. It
comprises two mechanisms, diffusion (conductions) and bulk motion (transfer of energy in direction of motion)
plane wall insulation
insulation in wall, reducing heat transfer rate
cylindrical wall insulation
for pipes or shells, increasing surface area for insulation, increasing convection heat transfer
extended surfaces
a solid which transfers
heat by conduction within its boundaries and by
convection and/or radiation between its
boundaries
extended surfaces
a solid which transfers heat by conduction within its boundaries and by convection and/or radiation between its boundaries fins
Fin performance
the ratio of the fin heat transfer rate to the heat transfer rate that would
exist without the fin
case D
what is a fin surface efficiency
characterises an array of fins and the base surface to which they
are attached
fin surface efficiency
characterises an array of fins and the base surface to which they
are attached
Velocity boundary layer
region at which velocity gradient exists
thermal boundary layer
region at which temperature gradient exists
what is external flow
Boundary layers develop freely, without
constraints imposed by adjacent surfaces.
what is internal flow
boundary layers are confined to a limited space
and are not, therefore, allowed to continue to
develop unhindered.
what 2 cases occur in fully developed conditions
- Uniform surface temperature
* 2. Uniform surface heat flux
what is a heat exchanger
Devices used to facilitate heat transfer between
two streams of fluid at different temperatures
without mixing
what does LMTD stand for and mean
Log-Mean Temperature Difference (LMTD)
method
The amount of heat exchanged between two
streams of fluid in a heat exchanger
5 assumptions for parallel flow heat exchanger
- heat exchanger insulated from surrounding, only exchanging between hot and cold
- axial conduction along the tubes are negligible
- fluid specific heat is constant
- heat transfer coefficient is constant
