Abstract: An evaporator includes an enclosure with a lateral confinement shell with a substantially horizontal axis, which internally accommodates a dispenser of a coolant fluid and at least one tube bundle, which is arranged below the dispenser. The evaporator further includes exchanger tubes, which are passed through by a fluid to be cooled. At least one first group of exchanger tubes is arranged along rows which extend on substantially horizontal and mutually superimposed planes. The exchanger tubes of each row are arranged in at least one respective tray for collecting and distributing the liquid coolant fluid. Each tray has, along at least one first longitudinal edge, at least one first containment sidewall which is adapted to allow the liquid coolant fluid contained therein to fall by overflowing into an underlying tray and is provided in its bottom with openings for draining the liquid coolant fluid.