Liter per Hour
Symbol: L/hWorldwide
¿Qué es un/una Liter per Hour (L/h)?
Formal Definition
The liter per hour (symbol: L/h) is a metric unit of volumetric flow rate equal to one liter of fluid passing through a given point in one hour. In SI base units, 1 L/h equals approximately 2.7778 × 10⁻⁷ cubic meters per second (m³/s). The liter per hour is used for low and moderate flow rates, particularly in applications where flow is sustained over long periods.
The L/h is the natural unit for applications where consumption or delivery is measured over hours rather than minutes or seconds: fuel consumption, drip irrigation, chemical dosing, and slow infusions. It provides manageable numerical values for these relatively slow but sustained flows.
Relationship to Other Units
1 L/h = 1/60 L/min ≈ 0.01667 L/min; 1 L/h = 1/3600 L/s ≈ 0.000278 L/s; 1 L/h ≈ 0.001 m³/h; 1 L/h ≈ 0.00441 US GPM. For conversion to the more common L/min, simply divide by 60.
Etymology
Component Terms
The name "liter per hour" combines the metric volume unit "liter" (from French "litron," ultimately Greek "litra") with "hour" (from Old French "hore," Latin "hora," Greek "hora" meaning season or time of day). The division indicated by "per" expresses the rate concept: a volume divided by a time period.
Notation
The standard notation is L/h, though l/h and LPH are also used. In automotive contexts, fuel consumption is often written as "L/100km" (liters per 100 kilometers) rather than L/h, since the relevant variable is distance rather than time.
Precise Definition
SI Conversion
One liter per hour equals exactly 1/3,600,000 cubic meters per second: 1 L/h = 0.001 m³ / 3600 s = 2.7778 × 10⁻⁷ m³/s.
Key Conversions
1 L/h ≈ 0.01667 L/min; 1 L/h ≈ 0.000278 L/s; 1 L/h = 0.001 m³/h; 1 L/h ≈ 0.00441 US GPM; 1 L/h ≈ 0.03531 ft³/h. For practical purposes, multiplying L/h by 0.01667 gives L/min, and multiplying by 0.001 gives m³/h.
Measurement Instruments
Low flow rates in the L/h range are measured using precision rotameters, Coriolis mass flow meters, positive displacement meters, and thermal mass flow meters. For drip irrigation, inline flow meters calibrated in L/h are standard equipment. Medical infusion pumps display rates in mL/h (where 1,000 mL/h = 1 L/h).
Historia
Agricultural Irrigation
The liter per hour became a key unit with the development of modern drip irrigation in the 1960s. Simcha Blass, an Israeli engineer, developed the first practical drip emitter in 1965, and the technology was commercialized by Netafim starting in 1966. Drip emitters were rated in L/h because they deliver small, steady flows over extended periods. A typical emitter delivers 1–8 L/h, making L/h the natural unit for this revolutionary agricultural technology.
Chemical Process Engineering
Chemical dosing and metering pumps have used L/h since the widespread adoption of automated chemical treatment in the mid-20th century. Water treatment plants dose chlorine, fluoride, and coagulants at rates measured in L/h. The unit provides practical values for the small but continuous flows required for precise chemical dosing.
Fuel Consumption
Although fuel consumption in most countries is expressed as L/100km (fuel economy per distance), the actual fuel flow rate through an engine is measured in L/h. Engine fuel consumption at various RPM and load conditions is plotted as L/h on brake-specific fuel consumption (BSFC) maps, which are essential tools for engine calibration and efficiency optimization.
Medical Infusion
Intravenous fluid administration in medicine uses mL/h, which is the sub-unit of L/h. IV pumps precisely control fluid delivery at rates from 1 mL/h to 999 mL/h (0.001 to 0.999 L/h). This application demands extreme accuracy because medication dosing errors can have life-threatening consequences.
Uso actual
Drip Irrigation
Drip irrigation systems worldwide specify emitter flow rates in L/h. Standard emitters are available at 1, 2, 4, and 8 L/h. Pressure-compensating emitters maintain a constant L/h output despite variations in water pressure. For a vineyard with 2,000 vines per hectare, each with a 4 L/h emitter, total flow is 8,000 L/h (8 m³/h) per hectare.
Fuel Flow Rates
Marine engines display fuel consumption in L/h on multifunction displays, helping captains optimize cruising speed for fuel economy. A small outboard motor may consume 5–15 L/h, a medium diesel auxiliary 10–30 L/h, and a large cargo ship engine 5,000–15,000 L/h. Aircraft fuel flow is also monitored in L/h (or kg/h) during flight.
Chemical Dosing
Water treatment plants dose chemicals at rates of 0.1–100 L/h depending on the chemical and treatment stage. Chlorine dosing for drinking water typically ranges from 0.5–5 L/h of sodium hypochlorite solution. Pool chlorinators dose at 1–10 L/h.
Laboratory and Industrial
Precision metering pumps in laboratories and manufacturing deliver reagents at rates from 0.01 to 100 L/h. Continuous flow chemistry, pharmaceutical manufacturing, and analytical instruments all use flow rates expressed in L/h or mL/h.
Everyday Use
Garden Irrigation
Home gardeners using drip irrigation systems encounter L/h on every emitter and dripper they purchase. Planning a drip system requires calculating total L/h demand and ensuring the water supply can meet it. A typical home garden drip system with 20 emitters at 4 L/h requires 80 L/h of supply.
Vehicle Fuel Consumption
Some vehicle dashboards display instantaneous fuel consumption in L/h, particularly when idling. A typical passenger car consumes 0.6–1.0 L/h at idle, while a truck may consume 2–4 L/h. This reading helps drivers understand fuel waste during prolonged idling.
Coffee and Beverages
A commercial coffee brewer dispenses hot water at about 30–60 L/h. A home coffee maker processes about 4–8 L/h. Beverage dispensing systems in restaurants and bars are rated in L/h for carbonated water, beer, and other drinks.
Dehumidifiers
Residential dehumidifiers are rated by their water extraction rate in L/h or L/day. A typical household dehumidifier extracts 0.4–1.0 L/h (10–24 L/day) of moisture from the air.
Interesting Facts
A single drip irrigation emitter delivering 4 L/h can sustain a mature grapevine through hot summer weather. Israel's adoption of drip irrigation — using precisely calibrated L/h emitters — transformed the Negev Desert into productive farmland and launched a global agricultural revolution.
A Boeing 747-400 at cruising altitude burns approximately 12,000 L/h of jet fuel — about 200 liters per minute, or 3.3 liters per second. Over a 12-hour flight, this totals about 144,000 liters.
IV fluid administration in hospitals runs at rates as low as 1 mL/h (0.001 L/h) for concentrated medications. Modern IV pumps can control flow with an accuracy of ±5% at these tiny rates, delivering a single droplet every few seconds.
An adult human produces about 1.5 L of saliva per day (approximately 0.0625 L/h), 1.5 L of gastric juice per day, and 0.5 L of bile per day. The total digestive fluid production is about 7 L/day (0.29 L/h).
The world's largest desalination plant (Ras Al Khair, Saudi Arabia) produces about 43.2 million L/h of fresh water — enough to supply a city of over one million people.
A standard residential water softener regenerates at a flow rate of about 100–200 L/h during the backwash cycle, using about 150–300 liters of water per regeneration event.