PROJECT: Laser RamanSpectroscopy
DATE: 03/6/01
ANALYST: M.Brown
HEAT TRANSFER CALCULATIONS:
ASSUMPTIONS:
REF: Fundamentals of Heat & Mass Transfer pp 595
The CCD camera in the Laser Raman Spectrometer requires 25W of heat to be removed from the device. Two cooling ports exist for this purpose the CCD specification requires cooling water to be pumped at .75 lpm and a temperature of 10 degrees celsius.
Potential & kinetic energy changes are negligible.
Negligible tube thermal resistance & fouling.
Constant properties.
Fully developed conditions exist.
PROPERTIES :
Tube Material:Aluminum
thermal conductivity = 177 W/m * K
Flow rate = .75 LPM @ 10 degrees C
Celsius = 273.15 Kelvin
Viscosity Seawater
Seawater
Specific Heat @ Constant pressure
Pure water
Specific Heat @ Constant pressure
Viscosity
Cooling water
Thermal Conductivity
Cooling water
Thermal Conductivity
Seawater
Assume seawater 4degC
For a tube heat exchanger dissipating 25W of heat through a .25 ID X .50 OD tube that is cooled by seawater at 4 deg celsius, what is the length of tube required to cool the return water to 10 deg celsiuis (283 K)
Mass flow rate of hot fluid given .75 lpm @ 10 deg celsius =
Assume sewater flow over outside of tube.
Required Heat transfer rate
Assume Cooling water
Cooling water return temp
Energy Balance equation
Equation 11.7b
HEAT TRANSFER
q = UA D
Where U = Overall convection coeficient
Where A = p
D = Log Mean temperature difference
Overall Heat Transfer Coefficien t
Tube ID=.25in = .00635m
Laminar or Turbulent flow:
Laminar flow ReD < 2300
(Hydraulic Diameter)
Circular Tube:
Nusselt numbers
From Table 8.3
For uniform heat flux
at both surfaces
Where Di/Do = 0.50
= Convection coefficient (outer)
= Convection coefficient (inner)
Overall Heat Transfer Coefficient
Units check: =
Length of tube required: