Height equivalent to a theoretical plate

As the value of N is proportional to column length, L, the other parameter H or HETP, the so-called height equivalent to a theoretical plate, is Introduced as 

The value of H gives the height of one plate in the longitudinal direction of a column i.e., the column length per one theoretical plate. A small value of H means that the column is more efficient and has a large number of theoretl- 

The HETP is given approximately by the van Deemter equation which is derived from the rate theory. 

The plate height equation that incorporates the coupling theory introduced by Giddings [ref. 5] is expressed as 

Eg = Cgdf /Dg (sts11 ouaTy-pha3e mass transfer) 

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In the case of a plate column the performance of a real plate is related to the performance of a theoretical one by the plate efficiency. In the case of a packed column the height equivalent to a theoretical plate HETP) gives a measure of the contacting efficiency of the packing. 

Sometimes the height equivalent to a theoretical plate (HETP) is employed rather than and to characterize the performance of packed towers. The number of heights equivalent to one theoretical plate required for a specified absorption job is equal to the number of theoretical plates,... 

An alternative to determining packed height is through the use of an empirical term, height equivalent to a theoretical plate (HETP). This term can be measured in a fashion similar to that used for the overall plate efficiency of a column (eq. 44) ... 

Height equivalent to a theoretical plate (HETP) plate tower data ... 

Column efficiency (number of theoretical plates) As in batch chromatography, one needs to determine the efficiency of the column in order to evaluate the dispersion of the fronts due to hydrodynamics dispersion or kinetics limitations. The relationship of N proportional to L can be expressed in terms of the equation for height equivalent to a theoretical plate (HETP) as ... 

HETP = height equivalent to a theoretical plate, ft HTU = height of a transfer unit, ft L = liquid mass velocity, Ib/hr-ft m = exponent a 1.0 n = exponent 0.44 Pr = Prandtl number, dimensionless Sc = Schmidt number dimensionless U, = linear velocity of gas based on total column cross-sectional area, ft/sec... 

The HETP (Height Equivalent to a Theoretical Plate (stage or plate)) is the tray spacing divided by the fractional overall tray efficiency [82]. The transfer unit concept has been useful for generalized correlations [89]. Because packed towers operate with continuously changing compositions through the packed height, the concept... 

Height equivalent to a theoretical plate (HETP) A measure of the efficiency of a column usually expressed in millimeters. HETP — LIN, where L is the length of a column and N is the number of theoretical plates. The reciprocal of HETP is also used to describe efficiency and is often expressed by the terms plates per meter. 

Van Deemter equation An equation relating efficiency (HEPT in mm) to linear flow velocity in a chromatographic column. The efficiency is expressed as the height equivalent to a theoretical plate HEPT = A + BIV + Cv), where A, B, and Cv are constants and V is the linear velocity of the carrier gas. This equation tells us that to obtain maximum efficiency, the carrier gas flow must be optimized. 

Consequently, (ax) the variance per unit length of a column is numerically equal to the height equivalent to a theoretical plate (H) and thus, equation (9) becomes... 

Golay equation 21, 611 gradient (LC) 490 height equivalent to a theoretical plate 11 longitudinal diffusion 16 mass transfer resistance 17 nonlinear chromatography SOS plate model 14 rate theory IS reduced parameters 78, 361, 611... 

Time-dominated processes inherently govern chromatography. The horizontal axis of a chromatogram is time (and not energy as in spectroscopy). To describe the quality of a chromatographic system the concepts of the height equivalent to a theoretical plate, HETP or H, and the number of theoretical plates N are used (Equation 4.1) ... 

HETP = height equivalent to a theoretical plate. It is derived from the plate theory of distillation which is a confusing concept having no basis in fact in the context of modem chromatographic separations. Nevertheless the terms plate number and plate height are still very widely used. 

Now you have a column with one-point-six theoretical plates. Is that good you ask. Relative to what, I say. If that column is six feet high, that s terrible. The Height Equivalent to a Theoretical Plate (HETP) is 3.7feet/ plate. Suppose another column also had 1.6 theoretical plates, but was only 6 inches (0.5 ft) high. The HETP for this column is 3.7in/plate, and if it were 6 feet high, it would have 19 plates. The smaller the HETP, the more efficient the column is. There are more plates for the same length. 

Here, A is the random path, B the longitudinal molecular diffusion and C the RTMT contributions with the velocity of the mobile phase u shown separately. H is referred to as the Height Equivalent to a Theoretical Plate and is terminology borrowed from distillation. While the distillation HETP is not truly applicable, the terminology has persisted. It can be shown that the H in this expression is the equivalent to variance/unit length. This is the expression introduced by Van Deemter and co-workers in 1956 in a discussion of band broadening. 

The height equivalent to a theoretical plate, H, is that length of column that represents one theoretical plate, or one equilibration step. Obviously, the smaller the value of this parameter, the more efficient the column. The more theoretical plates packed into a length of column, the better the resolution. It is calculated by dividing the column length by N ... 

The retention time of a certain component on a particular 2.0-m gas chromatography column is 3.1 min. The width at the base for the peak is 0.39 min. How many theoretical plates are in this column and what is the height equivalent to a theoretical plate ... 

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