Normal emissivity of an isothermal, diffusely reflecting cylindrical cavity (with top) as a function of inside radius

The norm a l e mi ss ivit y of an isothe rm al cylindri cal ca vit y (with top), with a diffu se ly re fl ecting inte rior of re fl ec ti vit y mu c h less th a n 1, is calcul ate d a' pprox im ate ly as a fun cti on of th e in sid e radiu s of th e cylind er b y th e DeVos method. Th e c alc ul a tio n is a na lyti ca l, a nd co nside rs th e sin gly and doubl y r e fl ec ted radi ati on escapin g fro m the cavity aperture, Th e res ults of th e a na lysis indi cate th at , for cylind ers wh ose le ngth-t o -lid a pe rture ra ti o is mu c h la rger th a n]: (a), for a gi ve n cylind e r length a nd lid ape rture, the co nfig ura ti on with th e inside diam ete r a pproxim a te ly 0 ,64 th e le ngth has t he smaLLest no rmal em iss ivity; (b), as th e in sid e di amete r in c reases or dec reases fro m th e confi gura tion of s ma ll es t norm al e miss ivit y, th e nor ma l e mi ss ivit y increases monotoni ca ll y,