Watirweb chrome - unable to find chromedriver executable

I have kept files from
(http://code.google.com/p/chromium/downloads/list) in Browser_drivers
directory inside present directory.

here is the code:

browser_drivers = "#{Dir.pwd}/Browser_drivers"
browser_drivers.gsub!("/", "\\") if

Selenium::WebDriver::Platform.windows?
profile = Selenium::WebDriver::Chrome::Profile.new
profile[‘download.prompt_for_download’] = false
profile[‘download.default_directory’] = browser_drivers
browser=Watir::Browser.new :chrome, :profile => profile # here I
am getting the error

the error is:
“Unable to find the chromedriver executable. Please download the server
from http://code.google.com/p/chromedriver/downloads/list and place it
somewhere on your PATH. More info at
GitHub - SeleniumHQ/selenium-google-code-issue-archive: Archive, please see main selenium repo

I am now in ubuntu, what changes I need for windows?