Packing Height (HTU·NTU)
Compute the packing height of an absorption or distillation column, Z = HTU·NTU, multiplying the height of a transfer unit (HTU, which depends on hydrodynamics and packing type) by the number of transfer units (NTU, which depends on the desired separation). It is the HTU-NTU method of sizing packed columns — it separates the 'kinetic' part (HTU) from the 'thermodynamic' (NTU). Enter the HTU and the NTU.
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Packing height (HTU · NTU)
Sizing a packed column for absorption or distillation comes down to one elegant multiplication: Z = HTU · NTU. The strength of the method lies in separating two aspects that depend on entirely different things. The NTU (number of transfer units) is purely thermodynamic, a matter of process: it depends only on how much separation is required (inlet and outlet concentrations) and on the equilibrium. The HTU (height of a transfer unit), on the other hand, is kinetic and hydrodynamic: it depends on the type and size of the packing (Raschig rings, saddles, structured packing), on the gas and liquid flow rates, on the fluid properties and on the mass transfer coefficients. More efficient packings have a smaller HTU, meaning more separation per metre of column. So the engineer works out the NTU from the separation specification and the HTU from the hydraulics, and the height of the bed falls out of the product of the two. It is one of the most widely used methods in tower design across the chemical industry. Enter the HTU and the NTU.
Related Tools
Number of Transfer Units (NTU)
Compute the number of transfer units (NTU) of an absorption or stripping column (dilute case), NTU = ln(C_in/C_out), from the inlet and outlet concentrations. NTU measures the 'difficulty' of the separation: the greater the removal desired, the more transfer units are needed. Together with the height of a unit (HTU), it defines the total packing height. Enter the inlet and outlet concentrations.
Metallostatic Pressure
Calculate the metallostatic pressure exerted by molten metal at the bottom of a mold, P = ρ × g × h, from the molten metal density ρ (kg/m³), gravity g and the metal column height h (m). The result, in pascals, is the pressure the molten metal exerts on the mold walls and bottom due to its own weight — analogous to hydrostatic pressure, but with the high density of metals. It is essential to size the mold strength (which can 'burst' or deform under pressure), predict core flotation and metal penetration into gaps. Dense metals (iron, ~7000 kg/m³) generate high pressures. Enter the metal density and the column height.
Overall Plate Efficiency (O'Connell Correlation)
Estimates the overall plate efficiency of a distillation column by the O'Connell correlation, the step that converts theoretical stages into actual trays in preliminary design. The correlation uses a single combined variable, the product of liquid viscosity and mean relative volatility, and reads efficiency = 0.492 × (viscosity × relative volatility) raised to −0.245, with viscosity in centipoise. What governs it is the product μ·α: a low-viscosity liquid with relative volatility near 1 lands in the 70 to 80% band, and efficiency falls to 40% or less once the liquid is viscous or the relative volatility is high. Note that a difficult separation, with α close to 1, gives the highest efficiency per tray — that column is tall because of the theoretical stage count, not the efficiency, which there actually dampens the height. The analytical fit 0.492 × (μ·α)^−0.245 was adopted, the usual form for hand calculation; the Kessler and Wankat polynomial on the logarithm of the product differs by a few percentage points at the ends of the range. Enter the liquid viscosity at the mean column temperature and the mean relative volatility.
Actual Plates (Efficiency)
Compute the number of actual plates of a distillation column, N_actual = N_theoretical / (efficiency/100), from the number of theoretical (equilibrium) plates and the column's overall efficiency (%). Since no real plate reaches perfect equilibrium, more actual plates than theoretical are needed: a 50% efficiency doubles the plate count. It is the step that turns the theoretical design into the physical column. Enter the theoretical plates and the overall efficiency.
Minimum Reflux (Underwood)
Estimate the minimum reflux ratio of a binary distillation by Underwood's equation (saturated-liquid feed), Rmin = [xD/xF − α·(1−xD)/(1−xF)]/(α − 1), from the relative volatility (α) and the light-component mole fractions in the distillate (xD) and feed (xF). At minimum reflux, the column would need infinite plates; the operating reflux is a multiple of it (1.1–1.5×). It is a key number in column design. Enter α, xD and xF.
WHtR Waist-to-Height Ratio
Enter waist and height in centimetres for the waist-to-height ratio and its band: under 0.5 healthy, 0.5 to 0.6 raised, 0.6 and up high cardiometabolic risk.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.