## What do you mean by LMTD?

logarithmic mean temperature difference
The logarithmic mean temperature difference (also known as log mean temperature difference, LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers.

What is LMTD formula?

LMTD = dT1 – dT2 /ln (dT1/dT2) For parallel flow – dT1 = Temperature of the hot fluid entering – Temperature of the cold fluid entering. dT2 = Temperature of the hot fluid exit – Temperature of the cold fluid exit. For counter flow –

What is LMTD correction factor?

It is a measure of the heat exchanger’s departure from the ideal behavior of a counter flow heat exchanger having the same terminal temperatures.

### What are the assumptions in the LMTD?

Assumptions made in LMTD method: The specific heats (Cp) and mass flow rates of both fluids is constant. The flow conditions are steady. There is no change of phase either of the fluid during the heat transfer. There is no loss of heat to the surroundings, due to heat exchanger being perfectly insulated.

Why is LMTD used?

The log mean temperature difference (LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. The LMTD is a logarithmic average of the temperature difference between the hot and cold streams at each end of the exchanger.

What is LMTD and NTU?

The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD).

#### What happens when LMTD is zero?

Zero LMTD means no further heat transfer is possible and if heat transfer is to be done than infinite area is required, which is not possible.

What is the fouling factor?

The fouling factor represents the theoretical resistance to heat flow due to the buildup of a fouling layer on the tube surfaces of the heat exchanger. In practice, fouling factors are often overstated by the end user in an attempt to minimize the frequency of cleaning.

What is meant by fouling factor?

The fouling factor represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger, but they are often overstated by the end user in an attempt to minimise the frequency of cleaning.

## Why LMTD is used instead of mean temperature?

We use LMTD instead of average temperature in heat exchanger because we concern about both inlet and outlet temperature of both hot and cold fluids . Because of which, LMTD came into use. In LMTD, we include all the inlet and outlet temperature of both hot and cold fluids.

What is meant by NTU method?

The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the LogMean Temperature Difference (LMTD).