BigPatents India

Apparatus 2 comprises a chamber 4 to which a gas in question, for example natural gas is supplied through inlet 6 and leaves through outlet 8. The speed of sound SoS at ambient temperature is measured using any suitable method such as electronic control and calculating means 14 and an ultra-sound emitter 10 and an ultra-sound receiver 12. The ambient temperatures Tais observed by temperature sensor 22, and a thermal conductivity sensor measures the thermal conductivity of the gas at two different temperatures above ambient temperature. One value ThCH of the thermal conductivity is measured at 70 °C above ambient and the other value ThCL of the thermal conductivity is measured at 50°C above ambient. The control means 14 calculates the calorific value CV of the gas according to the formula CV= a.ThCH + b.ThCL + c.SoS + d.Ta+ e.Ta2+ f. where a,b,c,d,e and f are constants.