A device intended to measure fouling and to locally heat an electrical insulating medium. At least one electrically resistive heating element (6, 8) is associated with a fouling detection unit. The fouling detection unit includes metallic elements (6, 10) in contact, at at least two points, with the insulating medium. The resistance variation between the two points is measured and is directly linked with the fouling of the medium.

The present invention is a filtering unit providing after-treatment of the gases emited in the exhaust of Diesel engines, comprising a filtering set which includes at least one filtering element (11, 12, 13); at least one resistive element (3) which heats a zone (121, 122, 123) of one of the at least one filtering element; at least one detection device which determines fouling of the filtering set (1); a control (5), responsive to the at least one detection device, which controls independently each of the resistive elements, according to the fouling of the filtering set and electrical power available to the at least one resistive element. The resistive elements (3) can be each wound around a zone of a filtering element. The invention further relates to the associated process.

Thin plate-like electric heaters are disposed among multi-layer cylindrical filters for capturing particulates in positions without contacting with the filters. As the means for more reducing the power supply to the heater as the position of the heater is closer to the central cylinder of the multi-layer filters, the thicknesses of the thin plate-like electric heaters or the geometrical patterns of the electric conduction paths are changed to thereby set the resistance values of the heaters in advance in order to reduce the temperature of the central-side cylinder which is apt to be high to thereby realize the balance with the temperature of the outer-circumferential cylinder, or the electric conduction quantity to the heaters is selectively more reduced as the position of the heater is closer to the central cylinder to realize the balance of temperature distribution with the filter on the outer-circumferential side filter.

A particulate trap which can be used in a medium- or small-sized diesel engine car includes concentrically arranged cylindrical filters made of a three-dimensionally reticulated metallic porous material and a plate-shaped electric heater for regeneration having an output of 400 W or less, and is provided between the filters and spaced therefrom. The filters have a relatively shortened length. The heating amount of the filters by the heater is 0.60 W/cm.sup.2 or more. The filter has an increased thickness to make up for reduction in the filter surface area due to the shortened filter length. With this arrangement, it is possible to achieve a high regeneration efficiency with a low-output heater while suppressing heat loss.

A method for removing a liquid from a gas, comprises passing the gas and the liquid through a network of fibers containing at least one fiber in which a temperature gradient has been induced along at least a portion of the length of the fiber, thereby permitting droplets of the liquid to be captured by the at least one fiber, and wherein the temperature gradient causes migration of the droplets. A method of preventing the fouling of a coalescence filter is also disclosed. The method comprises inducing a temperature gradient along at least a portion of a length of at least one fiber within the filter, wherein the temperature gradient causes migration of liquid droplets captured by the fiber. A coalescence filter medium comprising at least one fiber in which a temperature gradient has been induced along at least a portion of the length of the fiber is also provided.