Hi,
Here’s the [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-15r-n5110_service%20manual_en-us.pdf|service manual] for the laptop.
Go to p.75 to view the necessary pre-requisite steps and then the procedure to remove the thermal cooling assembly. This will give you access to the fan so that you can check if it is OK (clogged with dust?) or if it is faulty and needs to be replaced.
If it is faulty then replacement fans are available online. Just search for ''Dell Inspiron N5110 fan'' or use the information from the label on the fan itself, to find suppliers that suit you.