LHSV is the liquid hourly space velocity, which is the ratio of liquid volume flow per hour to catalyst volume. LHSV is inversely proportional to residence time. As the flow rate increases, the LHSV increases. In most systems with a fixed catalyst volume & activity, temperature is increased to offset the negative reaction consequences of increasing LHSV. In systems that can replace catalyst and/or regenerate it online, an increase in catalyst make up rate can also be used to offset an increase in LHSV.
It signifies the residence time of feed in the reactor. Higher the value lower the reaction rate. It is dependent on the reaction kinetics.