Microbial Lethality
Compute the lethality rate (L-value) of a thermal process, L = 10^((T − Tref)/z), the factor indicating how many times faster (or slower) microbial destruction at a temperature T is than at the reference temperature. Integrated over time, the lethality gives the process F-value. It is the basis of the general-method sterilization calculation, which sums the lethality over the product's actual thermal history. Enter the temperature, the reference temperature and the z-value.
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Microbial lethality
The lethal rate (L value) answers one question: at temperature T, how many times faster (or slower) is microbial destruction than at the reference temperature? L = 10^((T − Tref)/z). For example, with Tref = 121.1 °C and z = 10 °C, sitting at 131.1 °C (10 °C above) gives L = 10 — killing runs ten times faster; at 111.1 °C, L = 0.1 — ten times slower. Lethality is the working tool of the general method for computing thermal processes: since the temperature at the cold spot of a can varies throughout heating and cooling, L is evaluated at each instant and integrated over time (∫L dt) to obtain the total accumulated F value of the process. This captures real sterilization, including the lethality delivered during the come-up and cool-down phases — not only at the holding plateau. It is more accurate than the simplified formula methods. Enter the temperature, the reference temperature and the z value.
Related Tools
F₀ Sterilization Value
Compute the F₀ value of a thermal process, F₀ = t·10^((T − 121.1)/z), the equivalent sterilization time at 121.1 °C (250 °F) with z = 10 °C, the reference for Clostridium botulinum. It is the universal 'currency' that compares thermal processes at different temperatures: an F₀ of 3 minutes is the minimum safety for low-acid canned foods (botulinum cook). Enter the time, the process temperature and the z-value.
Pasteurization Units (PU)
Compute the pasteurization units (PU) of a process, PU = t·10^((T − Tref)/z), the lethal time equivalent at a reference temperature. Widely used for beer and juice (Tref = 60 °C, z = 7 °C): a beer needs ~15 PU for microbiological stability. It lets you compare and control pasteurizers operating at different time-temperature combinations. Enter the time, the process temperature, the reference temperature and the z-value.
Decimal Reduction Time (D-Value)
Compute the decimal reduction time (D-value) of a microorganism, D = t/(log N₀ − log N), the time needed, at a given temperature, to destroy 90% of the population (a one-log reduction). It is the fundamental parameter of thermal death kinetics in food processing: the larger the D, the more heat-resistant the microorganism. Enter the heating time and the initial and final populations.
Photo Paper Chemicals Liters
Estimates liters of chemicals needed to process photo paper.
Brake Power Dissipated
Calculate the power dissipated by a brake under torque, P = T·(2π·n/60), from the braking torque T (N·m) and the rotation n (rpm). Dissipated power is the rate at which the brake converts mechanical energy to heat — the product of braking torque and angular velocity. It differs from total braking ENERGY: energy is the total heat generated (joules), while power is the INTENSITY of that heat generation (watts), and it determines the brake's steady-state temperature. A brake dissipating much energy but slowly (low power) heats little; one dissipating the same energy fast (high power) heats much more. Dissipated power is critical in brakes working CONTINUOUSLY or repetitively: retention brakes on long descents, industrial equipment brakes (hoists, cranes, conveyors holding load), and dynamometers (which measure engine power precisely by dissipating it in a brake). There, the steady-state dissipated power sets the COOLING capacity needed (ventilation, water cooling) to keep temperature stable. Equating dissipated power to cooling capacity gives the equilibrium temperature. Enter the braking torque and the rotation.
Martensite Fraction (Koistinen-Marburger)
Computes the fraction of austenite already transformed into martensite when quenching stops at a given temperature, using the Koistinen-Marburger equation, f = 1 − e^(−0.011·(Ms − Tq)), where Ms is the martensite start temperature and Tq the temperature at which the part stopped cooling. The result is the percentage of martensite formed — whatever is missing from 100 % stays as retained austenite, which is soft, dimensionally unstable and able to transform later in service, distorting the part. Because the exponent is linear in the temperature difference, 63 °C below Ms already converts half the austenite, but 209 °C are needed to reach 90 % and the end of the transformation is asymptotic, never exact — which is precisely why precision parts get a cryogenic treatment after quenching. Enter the steel Ms temperature and the quench stop temperature.
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