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