Heat Exchangers Jorge Seda #84012 José Luis García #69260 Billy Gerena #73656 Robert De Aza #66880 Prof. Eduardo Cabrera ME

Outline Introduction Objective Theory Equipment and Experimental Procedure Conclusion

Introduction A heat exchanger is a device that allows heat from a fluid (liquid or gas) to pass to a second fluid without the two fluids having to mix together or come into direct contact. There are various types of heat exchangers, air-to-liquid cooling, liquid-to-air cooling, liquid-to-liquid cooling, or air-to-air cooling.

Objective The objective of this experiment is to characterize the heat transfer in different types of heat exchangers. Parallel Flow Counter Flow Cross-flow

Objective In this experiment the following points will be put into experimentation. Flow Arrangement Energy Balance Temperature Efficiency Log Mean Temperature Difference Global Heat Transfer Coefficient

Flow Arrangement Parallel Flow Heat Exchanger Similarly a shell and tube heat exchanger can be operated in approximately parallel flow by having both fluids enter at one end and exit at the other end. With parallel flow the temperature difference between the two fluids is large at the entrance end, but it becomes small at the exit end as the two fluid temperatures approach each other.

Correction Factor Parallel Flow

Flow Arrangement Crossflow Heat Exchanger Crossflow heat exchangers are typically used for heat transfer between a gas and a liquid as in these two examples. Shell and tube heat exchangers with two or four tube passes are common. They will have a hybrid flow pattern, condenser where it might be approximately concurrent flow in some part of the heat exchanger and approximately parallel flow or crossflow in another part. A car radiator and an air conditioner evaporator coil are examples of crossflow heat exchangers. In both cases evaporator coil heat transfer is taking place between a liquid flowing inside a tube or tubes and air flowing past the tubes

Correction Factor Cross Flow

Flow Arrangement Counter flow Heat Exchanger A counter flow heat exchanger has the hot fluid entering at one end of the heat exchanger flow path and the double pipe heat exchanger cold fluid entering at the other end of the flow path. Counter flow is the most common type of liquid-liquid heat exchanger, because it is the most efficient.

Energy Balance

Temperature Efficiency

Log Mean Temperature Difference (LMTD)

Global Heat Transfer Coefficient, U

F correction factor depends on the geometry of the heat exchanger and the inlet and outlet temperatures of the hot and cold fluid streams. F for common cross-flow and shell-and- tube heat exchanger configurations is given in the figure versus two temperature ratios P and R defined as: Correction Factor

Effectiveness NTU Method

The heat transfer in a heat exchanger will reach its maximum value when (1) the cold fluid is heated to the inlet temperature of the hot fluid (2) The hot fluid is cooled to the inlet temperature of the cold fluid. These two limiting conditions will not be reached simultaneously unless the heat capacity rates of the hot and cold fluids are identical. When Cc≠Ch, which is usually the case which is usually the case, the fluid with the smaller heat capacity rate will experience a larger temperature change, and thus it will be the first to experience the maximum temperature, at which point the heat transfer will come to a halt. Maximum Heat Transfer