Bryan S. Wang 3S103 Chew 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 Factors Temperature difference Density of fluids Conductivity fluids Viscosity and velocity of the fluid Pressure within heat exchanger Specific heat capacity

Temperature difference The temperature difference affects the rate of energy transfer As 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 transfer Rate of heat transfer is directly proportional to the efficiency of the heat exchanger Higher rate of heat transfer = higher efficiency Lower rate of heat transfer = lower efficiency Rate of heat transfer is calculated using the heat transfer coefficient: ΔQ = heat input or heat lost, J h = heat transfer coefficient, W/(m 2 K) A = heat transfer surface area, m 2 ΔT = difference in temperature between the solid surface and surrounding fluid area, K Δt = time period, s

Effectiveness Formula As mentioned earlier, E: efficiency q: heat transfer rate C c : mass flow rate x heat capacity of cool substance T: Temperature of hot/cool substance

Mass flow rate? ρ is the density v is the velocity A is the flow area

References 5/ex5.html 5/ex5.html lab/me372b5.htm lab/me372b5.htm HeatExchangersApril2005.pdf HeatExchangersApril2005.pdf /lectures/HeatExchangers1-16pages.pdf /lectures/HeatExchangers1-16pages.pdf

References ummaries/thermal_cond.htm ummaries/thermal_cond.htm online.com/catalog/fine_chemicalhttp:// online.com/catalog/fine_chemical