A fill sheet arrangement for use in a direct heat exchanger, wherein a first fill sheet comprises a generally rectangular structure having a first side edge, a second side edge, a top edge, and a bottom edge, a front surface and a rear surface, and wherein a second fill sheet comprises a generally rectangular structure having a first side edge, a second side edge, a top edge and a bottom edge, a front surface and a rear surface, and the second fill sheet is adjacent the first fill sheet, the first fill sheet including a plurality of ridges and grooves, the second fill sheet including a plurality of ridges and grooves, characterised in that the first fill sheet and the second fill sheet are configured to be arranged in a direct heat exchanger such that: the first fill sheet and the second fill sheet are adjacent in the direct heat exchanger, a ridge on the rear surface of the first fill sheet is adjacent a ridge on the front surface of the second fill sheet to form a minor air path therebetween, and a groove on the rear surface of the first fill sheet is adjacent a groove in the front surface of the second fill sheet to form a major air path therebetween, wherein a first male separator extends from a ridge on the rear surface of the first fill sheet into the minor air path, and a first female separator is present on a ridge on the front surface of the second fill sheet, and the first male separator on the rear surface of first fill sheet contacts the first female separator on the front surface of the second fill sheet. wherein a first fill sheet comprises a generally rectangular structure having a first side edge, a second side edge, a top edge, and a bottom edge, a front surface and a rear surface, and wherein a second fill sheet comprises a generally rectangular structure having a first side edge, a second side edge, a top edge and a bottom edge, a front surface and a rear surface, and the second fill sheet is adjacent the first fill sheet, the first fill sheet including a plurality of ridges and grooves, the second fill sheet including a plurality of ridges and grooves, characterised in that the first fill sheet and the second fill sheet are configured to be arranged in a direct heat exchanger such that: the first fill sheet and the second fill sheet are adjacent in the direct heat exchanger, a ridge on the rear surface of the first fill sheet is adjacent a ridge on the front surface of the second fill sheet to form a minor air path therebetween, and a groove on the rear surface of the first fill sheet is adjacent a groove in the front surface of the second fill sheet to form a major air path therebetween, wherein a first male separator extends from a ridge on the rear surface of the first fill sheet into the minor air path, and a first female separator is present on a ridge on the front surface of the second fill sheet, and the first male separator on the rear surface of first fill sheet contacts the first female separator on the front surface of the second fill sheet. characterised in that the first fill sheet and the second fill sheet are configured to be arranged in a direct heat exchanger such that: the first fill sheet and the second fill sheet are adjacent in the direct heat exchanger, a ridge on the rear surface of the first fill sheet is adjacent a ridge on the front surface of the second fill sheet to form a minor air path therebetween, and a groove on the rear surface of the first fill sheet is adjacent a groove in the front surface of the second fill sheet to form a major air path therebetween, wherein a first male separator extends from a ridge on the rear surface of the first fill sheet into the minor air path, and a first female separator is present on a ridge on the front surface of the second fill sheet, and the first male separator on the rear surface of first fill sheet contacts the first female separator on the front surface of the second fill sheet.