LMTD log mean temperature difference

Us = overall heat transfer coefficient, Btu/hr-ft -°F LMTD = log mean temperature difference corrected by Figures 3-17 and 3-18, °F... 

LMTD = log mean temperature difference, °F M = mass flow rate, Ib/hr Ntu = number of heat transfer units, dimensionless N = number tubes/row in direction of air flow n = number tubes/row, per ft of exchanger width, 1 /ft Q = total exchanger heat load (duty), Btu/hr R = = heat capacity ratio, dimensionless... 

LMTD = log mean temperature difference, °F = number of rows N, = number of tubes per row APj, = air-side pressure drop, inch HjO Q = exchanger duty, Btu/hr R = number of tube rows T, = outlet process fluid temperature, °F T2 = inlet process fluid temperature, °F t, = estimated air outlet temperature, °F t, = calculated outlet air temperature, °F t2 = inlet air temperature, °F At = temperature difference, °F... 

LMTD = log mean temperature difference. See glossary and pp. 126-128 of reference 51.)... 

Ihv = lower heating value = net heating value. Whereas gross or higher heating value (fihv) is the total heat release, net or lower hv is hhv minus the latent heat of vaporization of the water vapor formed by the combustion of hydrogen in the fuel. In the United States, hv is assumed to be hhv unless otherwise specified. In European practice, nhv or Ihv is normally used, lintel = a horizontal beam support for refractory wall or roof may be water cooled. LMTD = log mean temperature difference, which see. See reference 51, p. 128. LNI = low NOx injection. 

Because of high column pressure, the column bottom temperature increases, which will have some impact on the reboiler heat input. In case steam or hot oil is used as the heat source, the LMTD (log mean temperature difference) of the reboiler is reestimated. Because of the increase in bottom temperature, the LMTD and reboiler heat duty would reduce. In case of a fired heater, reboiler heat duty is assumed to be the same. 

There are two basic approaches to heat-exchanger design for low temperatures (1) the effec tiveness-NTU approach and (2) the log-mean-temperature-difference (LMTD) approach. The LMTD approach is used most frequently when all the required mass flows are known and the area of the exchanger is to be determined. The effec-... 

In the basic heat transfer equation it is necessary to use the log mean temperature difference. In Equation 2-4 it was assumed that the two fluids are flowing counter-current to each other. Depending upon the configuration of the exchanger, this may not be true. That is, the way in which the fluid flows through the exchanger affects LMTD. The correction factor is a function of the number of tube passes and the number of shell passes. 

Note that the Log Mean Temperature Difference (LMTD) is somewhat less than the arithmetic mean, represented by the following ... 

AT = Log Mean Temperature difference = LMTD here Atj = Temperature difference at one end of exchanger (smaller value), see Figure 10-29. 

A further advantage of the plate heat exchanger is that the effective mean temperature difference is usually higher than with the tubular unit. Since the tubular is always a mixture of cross and contra-flow in multi-pass arrangements, substantial correction factors have to be applied to the log mean temperature difference (LMTD). In the plate... 

Logarithmic-mean driving force, packed column absorbers, 1 53 Logarithmic mean temperature difference (LMTD), 13 251, 252 Logic circuits, CMOS, 22 251-253 Logic gates, molecular-based, 17 61 Log-mean temperature difference (LMTD), 26 64... 

LMTD The natural log-mean temperature difference that promotes heat transfer. 

Ft Log-mean temperature-difference (LMTD) correction factor. Fw Correction factor for window leakage. 

The log mean temperature difference LMTD is simply the average or weighted temperature difference between the hot side and the cold side of the exchanger. Use Eq. (5.10) to determine this mean average temperature. It is simply, as the term indicates, the average temperature difference between the tube and shell sides of the exchanger. 

The process conditions in the FEHE (counter-current flow with no phase change and constant physical properties) lend themselves naturally to calculating the duty on the basis of the log mean temperature difference (LMTD) ... 

This temperature difference is called the log mean temperature difference (LMTD). Stated verbally, it is the temperature difference at one end of the heat exchanger less the temperature difference at the other end of the exchanger... 

Estimate the log-mean temperature temperature-difference driving force. The formula is LMTD = (tg — ti)/ln(tg — ti), where LMTD is log-mean temperature difference, tg is the maximum temperature difference between steam and cooling water, and is the minimum temperature difference between them. The maximum difference is (212 — 80), or 132 the minimum is (212 — 115), or 97. Accordingly, LMTD = (132 - 97)/ln( 132/97) = 113.6°F. 

Tn upcoming sections, we discuss the two methods used in the analysis of heat exchangers. Of these, the log mean temperature difference (or LMTD) method is best suited for the first task and the ffecliveness-NTlJ method for the second task. But first we present some general considerations. 

When heat is exchanged between a surface and a fluid, or between two fluids flowing through a heat exchanger, the local temperature driving force, AT, varies with the flow path. For this condition, the concept of the log-mean temperature difference (LMTD) may be applied when the overall heat-transfer coefficient, U, is given. In this case. 

For multipass and cross-flow exchangers, the log-mean temperature difference (LMTD) method is still applicable, i.e., the heat transfer rate is... 

In the majority of industrial operations, higher velocities, shorter tubes, and a more economical exchanger can be achieved with a multipass flow design as shown in Figure 8-1. The flow pattern is however part countercurrent and part co-current. Therefore, the mean temperature difference lies between the countercurrent and co-current log mean temperature differences (LMTD). The mean temperature differences for the... 

The computer program PROGS 1 calculates the required number of shell passes, the F-factor, the Log Mean Temperature Difference (LMTD), and the Corrected Mean Temperature Difference (CMTD). Table 8-21 shows the input data and computer output of the problem. The number of shells required is 1, the F-factor is 0.8917, the LMTD is 152.2°F and the corrected LMTD is 135.7°F. 

CALCULATE THE CORRECTED LOG MEAN TEMPERATURE DIFFERENCE CLMTD = F LMTD... 

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