week 2 Flashcards
what is a heat exchanger
a device used to facilitate heat transfer between 2 streams of fluid at different temperatures without mixing
how does the heat exchanger not have any heat loss
it is well insulated preventing heat loss (no heat loss through boundary)
what are the 3 categories of heat exchangers
flow arrangement
types of construction
function
what are the 3 types of ‘flow arrangements’
parallel flow
counterflow
crossflow
what is a parallel flow in ‘flow arrangements’
both streams of fluid follow in the same direction
what is a counter flow in ‘flow arrangements’
two streams of fluid flow in opposite direction
what is a cross-flow in ‘flow arrangements’
one stream crosses another stream
what are the 3 different types of ‘construction’
concentric tube
shell and tube
plate heat exchangers
what are the different functions of heat exchangers, name 4
evaporators
condensers
boilers
regenerators
what analysis of heat exchangers are used
Log-Mean Temperature Difference (LMTD)
how do you work out ‘the amount of heat exchangerd between 2 streams of fluid’
q = mC {↓p} (T {↓o} - T {↓i})
= mass flow rate X specific heat capacity X (temperture difference) eg: outlet - inlet
how do you work out ‘the heat lost from the hot fluid to the cold fluid’ 2 equations
For hot and cold fluids
1) q = M {hot} X C {p, hot} (T {IN} - T {OUT}) FOR HOT FLUID
2) M {cold} X C {p, cold} (T {OUT} - T {IN}) FOR COLD FLUID
equation for mean fluid temperature
(change in) *T = T {hot} - T {cold}
equation for mean temperature difference
q = U (heat transfer coefficient) X A (surface area) X *T {mean}
what is heat flux and what is the equation for it
Heat Flux is the rate of heat energy that passes through a surface
q = U (heat transfer coefficient) X A (surface area) *T {log mean}
