Emmanuel College has unveiled plans to expand its campus, including construction of a new dormitory and a library addition. To help pay for the projects, the Fenway college would lease a parcel for development. Emmanuel officials outlined the proposal at a Longwood Medical Area forum Monday night. College officials said they do not yet have cost estimates. Sarah Welsh, Emmanuel’s vice president for government and community relations, said the dorm would be called Julie Hall North, a new 183,000-square-foot residence hall with 425 to 475 beds and a 300-to-400-seat dining hall. The college also plans to renovate the Cardinal Cushing Library, adding about 58,000 square feet. The Boston Redevelopment Authority is accepting public comments on the project through July 25.