Method of monitoring an air operated heat exchanger and an air operated heat exchanger

An air operated heat exchanger comprising:

• a plurality of process tubes for process fluid;
• a plurality of rotating fans to move ambient air along one or more air stream paths past the plurality of process tubes, each of the plurality of rotating fans corresponding to a segment of the plurality of process tubes;
• an optical sensing system comprising at least two optical fibres configured within the one or more air stream paths, the at least two optical fibres comprising a first optical fibre located in a first layer in the air stream path downstream of the process tubes and a second optical fibre located in a second layer in the air stream path upstream of the process tubes, the first layer and the second layer being within the air operated heat exchanger, and a measurement unit comprising an active light source to pass at least one light pulse to the at least one of the two optical fibres, an optical receiver to detect an optical signal from the at least one of the two optical fibres to provide a signal profile, and
• a programmable computing device programmed to:
• (i) determine from the signal profile one or more air temperatures in the one or more air stream paths at a plurality of locations along the at least one of the two optical fibres, (ii) correlate said one or more air temperatures to monitor the operation of at least one of the plurality of rotating fans and the cooling provided to the corresponding segment of the plurality of process tubes, and (iii) evaluate at least one of the one or more air temperatures from at least one of the plurality of locations against one or more comparison operational conditions.