As @Sahil says you cannot ban the installation of your application if you have an apk file.
but, AFAIK, you say that you have an IMEI number of 50 mobile phones. Therefore, I think it can be 70% possible with Stratergy.
I think I can help you solve your problem to a certain level (not completely).
As I said, it will not solve your problem completely, but you can limit your application, which will not be installed in the "Other devices" section, which are not included in the list of names of mobile brands 50.
You can prevent the application from being installed in all other Brands / Models that are not included in the list of 50 mobile phones.
What you can do is filter out the application for a specific device using the names of your devices.
Using below, you do not have to filter your application based on programming.
nut you can do it from the developer console of the Android developer - Here , when you publish your application.
The developer console has a section "Supported devices", which shows a list of all devices that can access the android market. You can then filter out devices or manufacturers that are not compatible with your application.
This is the section in the main developer console:

Here you can prevent devices and / or manufacturers from seeing your application

For more information, see the Device Availability man page that says:
The Device Availability dialog can help developers in two powerful ways:
Understand which devices can find your application in the Android Market
Device Availability provides a dynamic list of compatible devices based on your manifest settings. For example, if your apks manifest indicates a large screen size, the console will display supported devices that your application can find in the Market.
You can also use dynamic search to see devices that will not be available to your application. j. You can search the manufacturer for the name of the project (for example, “Passion”), or the actual name of the public device (for example, “Nexus One”) to find out if manifest parameters filtered the device. Filter problem or incompatible devices This feature provides a device-specific administrative option for developers. When you add a device to the "Manually Excluded Devices" list, your application will not be available for that device in the Market. This is primarily intended to help developers provide the best user experience by helping developers filter devices that are known to have compatibility issues.
As I said, it will not solve your problem completely, but you can limit your application, which will not be installed in the "Other devices" section, which are not on your list of mobile brand names 50.
Hope this helps you.