Thanks for the information sir. This helps me a lot.
In our school the server rack are close but not all. Do you have any idea about the temperature range?
Not sure whether you mean close or closed, but I'd be very surprised that even if there is a solid glass front door on the cabinet, the back will be open or nearly so. Often the cooling air is brought in from below with a false-floor arrangement. Proper racks will be designed to facilitate proper airflow even when they are right next to each other. There may be specs on aisle space.
I do not know any temperature ranges, I will again have to direct you to the equipment manufacturer. There may be some standard, or if not a formal standard, then a typical industry rule of thumb. I've spent a fair amount of time in data centers, usually knew the environmental guys but did not get into that part myself. It can get pretty involved, measuring, adjusting temperatures and airflows. I wouldn't be surprised if the racks have specifications regarding airflow (CFM) and maximum heat (BTUs) that can be exhausted. Equipment specs should also include BTUs.