Mets pitcher Jacob Rhame pitches against the Phillies at Citi...

Mets pitcher Jacob Rhame pitches against the Phillies at Citi Field on Tuesday, Sept. 5, 2017. Credit: Jim McIsaac

CHICAGO — As the Mets begin their efforts to retool for 2018, the bullpen appears to be an area of focus, with a source saying Tuesday that adding another experienced arm will be part of the plans.

General manager Sandy Alderson has already gone to work to improve on a leaky relief corps that began the day with a 4.52 ERA, which ranks 22nd in baseball. On Tuesday, the Mets announced that 23-year-old righty Eric Hanhold was the player to be named in the Aug. 12 deal that sent Neil Walker to the Brewers.

Hanhold became the seventh relief prospect acquired in trades this summer by the Mets. A sixth-rounder in 2015, Hanhold went 5-1 with a 1.53 ERA in 29 1⁄3 innings in the second half for high Class A Carolina, with his performance improving when he went from pitching as a tandem starter to being used as a traditional one-inning reliever.

But Alderson hasn’t confined his additions to unproven arms, a trend that could continue in the offseason.

Just before the trade deadline, the Mets sent a pair of prospects to the Marlins for an established closer in AJ Ramos. The move was a form of early holiday shopping, as acquiring a reliever of Ramos’ caliber in the open market could require a costly multiyear deal.

Ramos, 30, has pitched well since joining the Mets, with seven saves in 16 appearances with a 3.00 ERA. He remains under team control next year when he’s eligible for arbitration and a raise from his $6.5-million salary for this season.

Manager Terry Collins said Ramos will fit into a veteran core anchored by Jeurys Familia and lefty specialist Jerry Blevins, whose $7-million option will be picked up next season.

Familia, 27, saved a franchise-record 51 games last year. This season, he has a 5.71 ERA as he continues to work his way back from surgery to address a blood clot, which wiped out much of his year. Blevins, 34, has a 2.89 ERA in 67 appearances

“You look at the other side where you go out and get AJ Ramos, you’ve brought yourself in a quality closer,” Collins said. “You combine him with a healthy Jeurys Familia, those are nice pieces.”

Now, it appears the Mets will explore a free-agent market that includes righty Addison Reed, who posted a 2.09 ERA in parts of three seasons with the Mets. Reed was traded to the Red Sox for three relievers at the trade deadline

One of those relievers, Jamie Callahan, has a 3.38 ERA in three appearances since joining the Mets as a September call-up. Righty Jacob Rhame, acquired from the Dodgers in the Aug. 19 deal for Curtis Granderson, allowed his first run Tuesday night in his third outing for the Mets and has a 2.70 ERA.

Both are expected to compete for spots in the bullpen come spring training.

“I think Sandy did an outstanding job with the two guys he’s obtained in those deals,” Collins said. “Rhame and Callahan, they’ve both got outstanding arms. I’m really impressed with the way they’ve gone about things here. They’ve come in and thrown the ball over the plate. I think those are two very good pieces.”