Heat exchanger with heilical flights and tubes

A heat exchanger comprising:

• a shell having a first inlet and a first outlet for a first fluid (H) and a second inlet and a second outlet for a second fluid (C);
• a screw element having a core and first and second nested helical flights mounted to the core and arranged within the shell and defining first and second helical primary fluid passages along the shell between the first and second helical flights, the first primary fluid passage being in fluid communication with the first inlet and the first outlet and the second primary fluid passage being in fluid communication with the second inlet and the second outlet;
• a first plurality of tubes mounted between adjacent turns of the first helical fluid passage and extending across the second helical fluid flow passage formed between the adjacent turns of the first helical fluid passage, the first plurality of tubes providing a first secondary fluid passage for conducting the first fluid (H) from one turn of the first fluid passages to the adjacent turn of the first helical fluid passage;
• and
• a second plurality of tubes mounted between adjacent turns of the second helical fluid passage and extending across the first helical fluid flow passage formed between the adjacent turns of the second helical fluid passage, the second plurality of tubes providing a second secondary fluid passage for conducting the second fluid (C) from one turn of the second fluid passage to the adjacent turn of the second helical fluid passage.