Hi Arun,
You can use expression #{userName} as actorid where you are currently passing krisv and pass the userName as parameter at the time of creation of the process. For that you have to create the process variable named userName. And also it is essential that you add that user name to the taskSession.
Or the other way you can use local task server and you do not need to add that user to taskSession. for that you have to use jbpm5.2 local task server.
You can study the example https://community.jboss.org/people/bpmn2user/blog/2011/12/18/jbpm5-web-example--local-human-task for local task server.