bryan s. wang 3s103 chew hanson 3s109 lim han xin 3s119
TRANSCRIPT
Bryan S. Wang 3S103Chew Hanson 3S109
Lim Han Xin 3S119
Effectiveness ?Definition:
Ratio between the actual heat energy transferred to the maximum possible heat energy that can be transferred.
Calculating the effectiveness allows us to predict how a heat exchanger will perform its job.
The FactorsTemperature differenceDensity of fluidsConductivity fluidsViscosity and velocity of the fluidPressure within heat exchangerSpecific heat capacity
Temperature differenceThe temperature difference affects the rate of
energy transferAs heat energy tends to transfer from a
region of higher temperature of a region of lower temperature, increasing the temperature difference of the two substances would increase the rate of heat transfer.
Density of fluid↑Density, ↑Conduction↓Density, ↓Conduction
This is due to the distance between each molecule is increased as its density is decreased.
Hence, the fluids should ideally be denser to increase rate of heat transferred through conduction
Conductivity of fluid↑Conductivity of fluid, ↑Rate of heat
transfer, ↑Heat conducted away
Therefore, we should choose a cooling fluid with high thermal energy conductivity
Viscosity and Velocity↑Viscosity, ↓Velocity Type of flow is determined
↑Viscosity , ↓Velocity = Laminar flow↓ Viscosity, ↑ Velocity=Turbulent flow
Hence, we should use liquids of less viscosity
Pressure within heat exchanger↑ Pressure, ↑Viscosity of substance
Viscosity leads to the creation of laminar flow which decreases heat exchanger efficiency
Specific Heat Capacity↑Specific heat capacity, ↑Energy required to
heat Substance can absorb more heat energy
without changing it’s temperature by a lot
This helps to maintain the high temperature difference between the two fluids
Conclusion
Rate of heat
transfer
Temperature difference
in substances
Density of fluids
Viscosity and
velocity of fluid
Pressure within heat
exchanger
Specific heat
capacity
Conductivity of fluids
Heat transferRate of heat transfer is directly proportional
to the efficiency of the heat exchangerHigher rate of heat transfer = higher efficiencyLower rate of heat transfer = lower efficiency
Rate of heat transfer is calculated using the heat transfer coefficient:
ΔQ = heat input or heat lost, Jh = heat transfer coefficient, W/(m2K)A = heat transfer surface area, m2
ΔT = difference in temperature between the solid surface and surrounding fluid area, KΔt = time period, s
Effectiveness FormulaAs mentioned earlier,
E: efficiencyq: heat transfer rateCc: mass flow rate x heat capacity of cool
substanceT: Temperature of hot/cool substance
Mass flow rate?
ρ is the densityv is the velocityA is the flow area
Referenceshttp://www.cheresources.com/hteffzz.shtmlhttp://granular.che.pitt.edu/~mccarthy/che10
11/Ex/Ex5/ex5.htmlhttp://classes.engineering.wustl.edu/mase-the
rmal-lab/me372b5.htmhttp://www.unene.ca/un702-2005/lectures/CA
-HeatExchangersApril2005.pdfhttp://www.unene.ca/un702-2009/lectures/
HeatExchangers1-16pages.pdf
Referenceshttp://www.velocityreviews.com/http://physics.csustan.edu/Marvin/
HeatLightSound/Summaries/thermal_cond.htm
http://www.linkinghub.elsevier.com/retrieve/pii/S0017931007004358
http://www.achilles-online.com/catalog/fine_chemical