# ChE 230

## 9 terms · Fluid & Heat Dynamics

qx=-k(dT/dX)

### Equation for Newton's Law of Cooling

q=h*(Tsurface-Tfluid)

### Define Conduction

The process by which heat is directly transmitted through a substance when there is a difference of temperature between adjoining regions, without movement of the material.

### Define Convection

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

### Define NTU

The Number of Transfer Unit method is one method of characterizing heat-exchanger performance by using the change in temperature of one stream divided by the average temperature difference or driving force in the heat exchanger

### Equation for logarithmic mean temperature difference

LMTD=(Delta T1-Delta T2)/(ln(Delta T1/Delta T2))

### Equation Used to predict the performance of certain heat exchangers

U=(qt)/(At*Log Mean T)

### Restrictions on the Logarithmic Mean Temperature Difference

Should not be used when U changes significantly; Should not be used when the temperature difference is not a linear function of heat transfer; Heat transfer occurs in a jacketed reactor; Any one of the four assumptions for the LMTD is not met

### Assumptions for Logarithmic Mean Temperature Difference

1. Overall coefficient U is constant;
2. The specific heats of the hot and cold fluids are constant.
3. Heat Exchange with the ambient air is negligible.
4. The flow is steady and either parallel or counter current.