Delta Log Mean Temperature Calculator

Point	Hot Fluid (°C)	Cold Fluid (°C)	ΔT (Hot-Cold) (°C)	ΔT (Cold-Hot) (°C)	ln(ΔT1/ΔT2)
Inlet	100	20	80	-80	N/A
Outlet	60	50	10	-10	N/A
ΔT1/ΔT2	–	–	80/10 = 8	-80/-10 = 8	N/A
ΔTm (ΔT1-ΔT2)/ln(ΔT1/ΔT2)	–	–	(80-10)/ln(8) ≈ 16.77	(-80-(-10))/ln(8) ≈ -16.77	0

In this table:

• “ΔT (Hot-Cold)” represents the temperature difference between the hot fluid and cold fluid at each point.
• “ΔT (Cold-Hot)” represents the temperature difference between the cold fluid and hot fluid at each point (negative because it’s in the opposite direction).
• “ln(ΔT1/ΔT2)” calculates the natural logarithm of the ratio of temperature differences at each point.
• “ΔTm” calculates the local LMTD for each section of the heat exchanger.

FAQs

How do you find the temperature of LMTD? LMTD itself is not a temperature; it’s a temperature difference. You calculate it using the temperature differences between the hot and cold fluids at different points along a heat exchanger.

How do you calculate log mean temperature difference? The formula for calculating LMTD is:

LMTD = (ΔT1 – ΔT2) / ln(ΔT1 / ΔT2)

Where ΔT1 is the temperature difference at the hot fluid inlet and outlet, and ΔT2 is the temperature difference at the cold fluid inlet and outlet.

What is the logarithmic mean temperature? The logarithmic mean temperature is another term for the LMTD (Logarithmic Mean Temperature Difference). It’s a way to represent the average temperature difference between two fluids in a heat exchanger.

Why is LMTD calculated? LMTD is calculated to determine the overall temperature difference between the hot and cold fluids in a heat exchanger. It is used in the design and analysis of heat exchangers to estimate heat transfer rates.

What is the formula for the mean temperature? There isn’t a single formula for “mean temperature” without specifying the context. In the context of LMTD, the formula for LMTD itself is used to find the average temperature difference.

Why LMTD is used instead of mean temperature? LMTD is used in heat exchanger calculations because it provides a more accurate representation of the temperature difference between the hot and cold fluids, considering their changing temperatures along the heat exchanger length.

What is the difference between LMTD and AMTD? LMTD (Logarithmic Mean Temperature Difference) considers the logarithmic average of temperature differences between the hot and cold fluids, while AMTD (Arithmetic Mean Temperature Difference) calculates a simple arithmetic average. LMTD is more accurate for heat exchanger design and analysis.

What does mean mean in temperature? In the context of temperature, “mean” typically refers to an average value. It represents the middle point or average of a set of temperature values.

What does MC Delta T mean? MCΔT is often used in heat transfer calculations and stands for “mass flow rate (M) times the change in temperature (ΔT).” It is used to calculate heat transfer rates in systems involving fluids.

How do you find the logarithmic mean? The logarithmic mean is found using the formula for LMTD: LMTD = (ΔT1 – ΔT2) / ln(ΔT1 / ΔT2), where ΔT1 and ΔT2 are temperature differences.

What is the unit of log mean temperature difference? LMTD is dimensionless; it does not have units because it represents a ratio of temperature differences.

What are the log mean temperature difference assumptions? Some common assumptions in LMTD calculations include steady-state conditions, constant fluid properties, and no phase change within the heat exchanger.

Is LMTD always positive? No, LMTD can be positive or negative depending on the temperature profiles of the hot and cold fluids.

What to do when LMTD is zero? If LMTD is zero, it means that there is no temperature difference between the hot and cold fluids at any point in the heat exchanger. In practical terms, this indicates that the heat exchanger is not operating as expected, and you should investigate the cause.

What is the log mean temperature difference on a cooling coil? The LMTD on a cooling coil is used to determine the temperature difference between the inlet and outlet of the cooling coil in HVAC systems. It helps in estimating the cooling capacity of the coil.

What is the arithmetic mean temperature difference? Arithmetic Mean Temperature Difference (AMTD) is a simpler method for calculating the average temperature difference between hot and cold fluids. It calculates the arithmetic average of the temperature differences at the inlet and outlet of the heat exchanger.

What is the mean temperature range? The mean temperature range is the difference between the average temperature of a system or process at two different points or states.

What does mean temperature mean in math? In mathematics, “mean temperature” refers to the average temperature calculated from a set of temperature values. It is the sum of the temperatures divided by the number of data points.

What are the advantages of LMTD? The advantages of using LMTD in heat exchanger analysis include its accuracy in representing variable temperature profiles, which makes it more suitable for design and performance evaluation compared to simpler methods like AMTD.

Can LMTD be negative? Yes, LMTD can be negative if the temperature difference at one end of the heat exchanger is greater than at the other end. It reflects the direction of heat transfer.

What should the value of LMTD be in a heat exchanger? The value of LMTD depends on the specific heat exchanger design and the temperature profiles of the fluids. There is no fixed value for LMTD; it is calculated based on the given conditions.

Why is LMTD higher in counterflow? LMTD is typically higher in counterflow heat exchangers because the temperature difference between the hot and cold fluids remains more consistent along the length of the heat exchanger, resulting in better heat transfer efficiency.

How does LMTD change with flow rate? LMTD can change with flow rate because variations in flow rate can affect the temperature profiles of the hot and cold fluids within the heat exchanger. Higher flow rates may lead to different LMTD values.

Is the logarithmic mean temperature difference the same as the arithmetic mean temperature difference? No, they are not the same. LMTD (logarithmic mean temperature difference) considers the logarithmic average of temperature differences, while AMTD (arithmetic mean temperature difference) calculates a simple arithmetic average.

Which is the correct procedure to determine the daily mean temperature? The daily mean temperature is usually determined by taking the average of the maximum and minimum temperatures recorded over a 24-hour period.

How to calculate the mean? To calculate the mean (average) of a set of values, you sum all the values and divide by the number of values in the set.

What is the true mean temperature? The “true mean temperature” is not a standard term. It generally refers to the actual average temperature of a given system or environment based on accurate measurements.

What is Delta T value? Delta T (ΔT) represents a temperature difference or change. It is often used in heat transfer calculations to indicate the temperature change between two points.

How do you calculate the change in temperature? To calculate the change in temperature (ΔT), subtract the initial temperature from the final temperature: ΔT = Final Temperature – Initial Temperature.

What is Delta T in heat loss? In heat loss calculations, ΔT represents the temperature difference between the indoor and outdoor environments. It is used to estimate the rate of heat loss from a building.

What is the purpose of the logarithmic mean? The purpose of the logarithmic mean is to provide a more accurate representation of the average temperature difference between two fluids in a heat exchanger, accounting for variable temperature profiles.

Is the log of the mean the mean of the log? No, the log of the mean is not necessarily equal to the mean of the log. These are different mathematical operations and may yield different results.

What do the numbers in log mean? The numbers in the logarithmic mean (LMTD) represent temperature differences between the hot and cold fluids at various points along a heat exchanger. The logarithmic calculation accounts for the changing temperature profiles.

What are the limitations of LMTD? Limitations of LMTD include its assumption of constant fluid properties and steady-state conditions, which may not always hold in real-world applications. It may also provide less accuracy in non-uniform temperature profiles.

What is the mean metal temperature? Mean metal temperature refers to the average temperature experienced by a material, typically in engineering or material science contexts.

What is weighted mean temperature difference? Weighted mean temperature difference is a variation of LMTD that takes into account variations in heat transfer coefficients and fluid properties along the length of a heat exchanger.

Which assumptions are made to derive LMTD logarithmic mean temperature difference? Assumptions for LMTD calculations include constant fluid properties, steady-state conditions, and no phase change within the heat exchanger.

What is the log mean area? Log mean area is not a standard term in heat exchanger calculations. However, it might refer to using a logarithmic approach to calculate the average heat transfer surface area in some specialized cases.

What does fouling factor mean? Fouling factor represents the additional thermal resistance caused by the accumulation of deposits or fouling on the surfaces of heat exchangers or other heat transfer equipment.

What happens with LMTD if there is the same temperature difference at the inlet and outlet in case of a counterflow heat exchanger? If the temperature difference at the inlet and outlet of a counterflow heat exchanger is the same, the LMTD will be zero.

What is always the LMTD for counterflow? In counterflow heat exchangers, LMTD is typically greater than zero, and it varies depending on the temperature profiles of the hot and cold fluids. It is usually higher than in parallel flow heat exchangers.

What should my AC coil temp be? The temperature of an air conditioning coil depends on various factors, including the design specifications and operating conditions. It can vary significantly, but it’s typically below room temperature to facilitate cooling.

What is normal AC coil temperature? Normal AC coil temperatures can vary, but they are generally within a range that allows the air conditioning system to effectively remove heat from the indoor air.

What is the difference between on coil and off coil temperature? “On coil” and “off coil” temperatures likely refer to temperatures measured at different points in an HVAC system. “On coil” would typically be the temperature at the coil’s inlet, while “off coil” would be the temperature at the coil’s outlet.

What is the log mean temperature? The log mean temperature is another term for LMTD (Logarithmic Mean Temperature Difference), which represents the average temperature difference between two fluids in a heat exchanger.

How do you find the average and mean temperature? To find the average or mean temperature, sum the temperatures at various points and divide by the number of points.

Is mean temperature the same as average temperature? Yes, in most contexts, “mean temperature” and “average temperature” are synonymous, both referring to the temperature that represents the average of a set of temperature values.

What is high mean temperature? A high mean temperature refers to an average temperature that is relatively warm or elevated compared to other measurements or contexts.

What is a low mean temperature? A low mean temperature refers to an average temperature that is relatively cool or below average compared to other measurements or contexts.

What are the 4 types of temperature? The four types of temperature scales commonly used are Celsius (Centigrade), Fahrenheit, Kelvin, and Rankine. These scales represent temperature in different units and have different zero points and increments.