# How is the LMTD calculated?

## How is the LMTD calculated?

Formula for LMTD calculation – For a Parallel Flow Heat Exchanger, Hot fluid entering at temperature 100 degree Celsius and exiting at 90 degree Celsius . Cold fluid Entering at 30 degree Celsius and exiting at 50 degree Celsius. Find the LMTD . LMTD = ((100 – 30)-(90-50)) / ln (100-30/90-50) = 53.6 degree Celsius .

How do you calculate LMTD correction factor?

Hence a correction factor ‘F’ must be introduced in the general heat equation and the equation is modified as Q = UA (F) LMTD. This correction factor ‘F’ depends on the number of shells of the heat exchanger and on the terminal temperatures of the heat exchanger.

What are the expressions of LMTD for parallel flow and counter flow heat exchangers?

LMTD = (θmax—θmin)/ ln( θmax/θmin)

### How do you calculate LMTD for a plate heat exchanger?

Calculation method

1. Heat load, Theta and LMTD calculation. Where: P = heat load (btu/h) m = mass flow rate (lb/h)
2. Heat transfer coefficient and design margin. The total overall heat transfer coefficient k is defined as: α1 = The heat transfer coefficient between the warm medium and the heat transfer surface (btu/ft2 h °F)

What is the unit of LMTD?

The “Logarithmic Mean Temperature Difference“ (LMTD) is a logarithmic average of the temperature difference between the hot and cold feeds at each end of the heat exchanger. The larger the LMTD, the more heat is transferred.

What is UA LMTD?

The equation for the heat load “Q” (Btu/hr) done by a system is Q = U*A*LMTD. “U” would be the overall heat transfer coefficient for the process, “A” would be the surface area, and “LMTD” is the log mean temperature difference.

#### What is LMTD and 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. Log Mean Temperature Difference Correction Factor F is dependent on temperature effectiveness P and heat capacity rate ratio R for a given flow arrangement.

Why we use LMTD correction factor?

Why do we use LMTD Correction factor? Explanation: In a shell and tube heat exchanger we observe both counter current and concurrent flow at different regions of the shell. This phenomenon makes the use of complete countercurrent LMTD unsuitable for calculations.

How is the logarithmic mean temperature difference LMTD calculated for heat exchangers?

by definition given above, LMTD for counter current flow = (60-50) / ln(60/50) = 10 / 0.1823 = 54.850C. For co-current heat exchanger, ΔT1 = TH1 – TC1 = 100 – 30 = 700C (At first end hot and cold fluids enter the heat exchanger.) (At the other end hot and cold fluids exit the heat exchanger.)

## When effectiveness and NTU method is used instead of lmtd method?

In heat exchanger analysis, if the fluid inlet and outlet temperatures are specified or can be determined by simple energy balance, the LMTD method can be used; but when these temperatures are not available The NTU or The Effectiveness method is used.

What is LMTD and NTU?

From Wikipedia, the free encyclopedia. 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).