What if LMTD is negative?

According to the definition modeled above, LMTD cannot be negative. According to the definition modeled above, LMTD cannot be negative. The short answer to the question is “NO”, which is in agreement with Raida Innab’s answer to Can LMTD be negative?.

What is the significance of NTU?

NTU means number of transfer units. It signifies that the heat transfer capacity of a given heat exchanger. NTU signifies how much number of units of heat, the given heat exchanger is capable of transferring from one fluid to other.

Which assumptions are made to derive LMTD logarithmic mean temperature difference?

Assumptions made for calculation of logarithmic mean temperature difference are. (i) Constant overall heat transfer coefficient. (ii) The kinetic and potential energy changes are negligible. (iii) There is no conduction of heat along the tubes of heat exchanger.

What is the purpose of using LMTD correction factor?

here F (< 1) is interpreted as a geometric correction factor, that when applied to the LMTD (Log Mean Temperature Difference) of a counter flow heat exchanger, provides the effective temperature difference of the heat exchanger under consideration.

What is LMTD in heat exchanger?

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 difference between NTU and LMTD method?

The LMTD method is convenient for determining the overall heat transfer coefficient based on the measured inlet and outlet fluid temperatures. The ε-NTU method is more convenient for prediction of the outlet fluid temperatures if the heat transfer coefficient and the inlet temperatures are known.

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.)

What are the assumptions made in LMTD?

One of the fundamental assumptions adopted in the derivation of the LMTD method is that the fluid specific heats are constant and the fluid temperature variations only result from heat exchange.

What is physical significance of LMTD?

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.

What is the importance of LMTD in heat exchanger?

Significance of the LMTD. The LMTD is the driven force for the heat exchange between the two fluids. As the LMTD value increases, the amounts of heat transfer between the two fluids also increase. The LMTD value is used for calculating the heat duty of the heat exchanger.

What is LMTD (log mean temperature difference)?

Log Mean Temperature Difference or LMTD is the driving force for the amount of exchanged heat by a heat exchanger. LMTD approach is quite straight forward and simple.

Can I use a single LMTD for evaporation?

Because evaporation is taking place at constant temperature, it cannot be used a single LMTD. In this case the heat exchanger has to be treated as a combination of two or three (when superheat occurs) heat exchangers. Consider a parallel-flow heat exchanger, which is used to cool oil from 70°C to 40°C using water available at 30°C.

What does LMTD stand for?

Engineers often use a logarithmic mean temperature difference (LMTD), which is used to determine the temperature driving force for heat transfer in heat exchangers. Thermal Engineering