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.
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Potência dissipada no freio
A potência dissipada por um freio em regime de torque é P = T·(2π·n/60), a partir do torque de frenagem T e da rotação n. É a taxa com que o freio converte energia mecânica em calor — o produto do torque de frenagem pela velocidade angular. É um parâmetro distinto da energia total de frenagem: a energia é o total de calor gerado (em joules), enquanto a potência é a intensidade com que esse calor é gerado (em watts), e é ela que determina a temperatura de regime do freio. Um freio que dissipa muita energia, mas lentamente (baixa potência), aquece pouco; um que dissipa a mesma energia rapidamente (alta potência) aquece muito mais. A potência dissipada é crítica em freios que trabalham de forma contínua ou repetitiva: freios de retenção em descidas longas, freios de equipamentos industriais (guinchos, pontes rolantes, esteiras que precisam segurar carga), e dinamômetros (que medem a potência de motores justamente dissipando-a em um freio). Nesses casos, a potência dissipada em regime define a capacidade de refrigeração necessária (ventilação, refrigeração a água) para manter a temperatura estável. Igualar a potência dissipada à capacidade de resfriamento dá a temperatura de equilíbrio. Informe o torque de frenagem e a rotação.
Related Tools
Bearing Power Loss
Calculate the power dissipated by friction in a bearing, P = T × ω, multiplying the friction torque T by the angular velocity ω (rad/s). The result, in watts, is the mechanical energy converted to heat per unit time by friction — a loss that reduces efficiency and heats the lubricant and components. This heat must be dissipated (by convection or oil circulation) to keep a safe operating temperature, since overheating degrades the lubricant and can cause seizure. Estimating the dissipated power is essential to size the cooling and the oil flow. Enter the friction torque and the angular velocity.
Braking Energy
Calculate the energy dissipated in braking, E = ½·m·(v₁² − v₂²), from the mass m (kg), the initial velocity v₁ and the final velocity v₂ (m/s). When a vehicle or machine brakes, its KINETIC energy is converted — by brake friction — into HEAT. The dissipated energy is the kinetic-energy change: braking to a stop (v₂ = 0) dissipates all the initial kinetic energy; partial braking, the difference. This heat must be ABSORBED and DISSIPATED by the brake without overheating beyond the limit (above which the friction material loses effectiveness — fading — and may even burn or glaze). That is why brakes for heavy vehicles, long descents (mountain trucks) and severe duty need large thermal capacity (big, vented discs, or auxiliary brakes like engine braking and retarders, dissipating energy by other means without overloading the service brakes). Braking energy grows with the SQUARE of velocity: braking from 100 km/h dissipates FOUR times more energy than from 50 km/h — so high-speed braking is so much more demanding. This is the basis of brake thermal design and overheating checks in repeated or prolonged braking. Enter the mass and the initial and final velocities.
Brake Temperature Rise
Estimate a brake's temperature rise from one braking, ΔT = E ÷ (m·c), from the braking dissipated energy E (J), the mass of the heat-absorbing component m (kg, the disc or drum) and the material specific heat c (J/(kg·°C), ~460 for steel, ~900 for aluminum). When a brake dissipates a braking's kinetic energy (converting it to heat), this heat is initially ABSORBED by the disc or drum mass, raising its temperature. This formula estimates that rise assuming ALL the heat goes into the component mass, with no loss to the environment (a conservative assumption, valid for a quick, isolated braking — in prolonged braking, part of the heat is dissipated by convection and radiation simultaneously). The temperature rise is critical because friction materials have a thermal limit: above a certain temperature (300-500°C for organic materials, more for metallic/ceramic), friction drops sharply (the FADING phenomenon, which has caused many mountain-descent accidents), the material degrades, and the disc can warp or crack from thermal shock. So severe-duty brakes use large discs (more mass, more heat-absorbing capacity), vented (more dissipation) and high-melting-point materials. This calculation is the heart of brake THERMAL design. Enter the dissipated energy, the mass and the specific heat.
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.