C#将String默认的字符编码改为UTF-8

有没有简单的将C#中String的字符编码转换成UTF-8的方法；

public static string utf8_gb2312(string text)
    {
        //声明字符集   
        System.Text.Encoding utf8, gb2312;
        //utf8   
        utf8 = System.Text.Encoding.GetEncoding("utf-8");
        //gb2312   
        gb2312 = System.Text.Encoding.GetEncoding("gb2312");
        byte[] utf;
        utf = gb2312.GetBytes(text);
        utf = System.Text.Encoding.Convert(gb2312, utf8, utf);
        //返回转换后的字符   
        return utf8.GetString(utf);
    }