Q = U.A.LMTD .
U= Heat Transfer Co-efficient
A= Heat Transfer Surface Area
LMTD= Mean Temperature Difference
LMTD is the logarithmic temperature deviation betwixt the hot in addition to mutual coldness fluids passing through the each ends of oestrus exchanger pipes.
Formula for LMTD calculation -
LMTD or Logarithmic Mean Temperature Difference is calculated past times keeping roughly factors inward mind
- The type of the oestrus exchanger
- temperature of the fluids at the 4 destination positions
These are -
- Inlet temperature of the hot fluid
- Inlet temperature of the mutual coldness fluid
- Outlet temperature of the mutual coldness fluid
- Outlet temperature of the hot fluid
LMTD = dT1 - dT2 /ln (dT1/dT2)
For parallel menstruum -
dT1 = Temperature of the hot fluid entering - Temperature of the mutual coldness fluid entering
dT2 = Temperature of the hot fluid piece of occupation out - Temperature of the mutual coldness fluid exit
For counter menstruum -
dT1 = Temperature of the hot fluid entering - Temperature of the mutual coldness fluid exiting
dT2 = Temperature of the hot fluid piece of occupation out - Temperature of the mutual coldness fluid entering
Mathematical Example :
1. For a Parallel Flow Heat Exchanger, Hot fluid entering at temperature 100 score Celsius in addition to exiting at xc score Celsius . Cold fluid Entering at xxx score Celsius in addition to exiting at fifty score Celsius. Find the LMTD .
For Parallel or co - electrical flow menstruum ,
According to the to a higher house mentioned formulas -
LMTD = ((100 - 30)-(90-50)) / ln (100-30/90-50) = 53.6 score Celsius .
2. For a Counter Flow Heat Exchanger for same information calculate the LMTD .
For Counter Current HE ,
LMTD = ((100-50)-(90-30))/ln(100-50/90-30) = 54.85 score Celsius .
So Heat transfer charge per unit of measurement for Counter Flow is higher .
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