Dil a torne tri c and ultrasonic meas urem e nt s we re mad e o n m ixtures of pe ntan e a nd 2-m eth ylbutane to give density, re la tive vo lum e , isoth e rm a l bu lk modu lu s, ve loc it y of sou nd , a nd ad iabati c b ulk modulu s to press ure of 24 kilobars (2.4 X l Q9N/m' ).K e y word s : Bulk mod ulu s; co mpre ss ibility; den s it y; dil ato me tri c me as uremen ts; hi gh pressure ; liquid s ; 2-me th ylbuta ne ; pentan e ; ultras oni cs _ . IntroductionThi s r e port s upple me nts a prev ious r eport [IP whi c h gave th e r es ults of measure me nts of mixtures of 2-methylbutane and aviatio n in strum e nt oil to 20 kilobars.2 Mixtures of pe ntan e and 2-methylbutane are used as hydrostati c pressure fluid s to 50 kilobars [2]. Th ese press ures are well above th e freezing pressures of th e individual fluid s. A s tud y was undertaken to de termin e th e properties of th e mixtures as a fun c ti on of pressure at room te mpe rature . Th e freezing press ure at room te mpe rature, give n b y R eeves e t al [4] , is 15 kbar for pe ntan e and is 21 kb ar for 2-methylbutan e . The freezin g press ure of pe ntane was meas ured to be 17.55 ± 0.67 kbar by Gelles [5]. Our ex perim e nts show the press ure r eq uire d at 22°C for initiation of freezing to be 25 kbar for pentane and 29 kbar for 2-m eth ylbutan e with equilibrium fr eezing I press ures of 18.2 ± 0.5 kbar and 22.5 ± 0.5 kbar res pectively.The equilibrium freezin g press ures were d ete rmined by over-pressurizin g th e fluid sufficiently to initiate freezing, then r educin g th e pressure to partially m elt th e solid, and then in creasing the press ure to partially refreeze the liquid in contact with th e solid. The ave rage of the meltin g press ure and thi s refreezing press ure is take n as e quilibrium freezin g press ure. Attempts to determin e freezin g press ures of various mixtures of th e pe ntan es we re un s uccessful. One 1 Fi gures in brac ket s indi cat e th e lit e rature refe re nces at th e e nd of thi s pape r. 2 I kilobar = 108 N/ m2, mixture of 90 per ce nt pentane-lO per ce nt 2-methylbutan e a ppeare d to freeze at 27 kba r but fiv e other attempts to freeze simila r mixtures were un s uccessful at press ures of 30 to 39 kbar. One mixture of 75 perce nt pe ntane-25 percent 2-meth ylbutane ap peared to freeze at 33 kbar but a seco nd mixture failed to freeze at 39 kbar. Oth er mixtures s howe d no freezin g at 39 to 44 kbar. While no sati sfac tory freezing determ in ation s were made for th e mixtures th e pro perti es de te rmin e d for th e mixtures as well as th e pure s ubs tan ces to 24 kbar are prese nted. Th e pure pe ntan es are in the s upe rcoole d (s uperpress urized) state above their equilibrium freezin g press ures. Low-Pressure Measurements (AtmosphericPressure)The densities of the mixtures were dete rmin ed by weighing known volumes of the fluid s . Th e same 10 MHz transducer and electroni c equipm e nt whi c h are used for the high press ure ultrasoni c meas ure me nts, described in refere nce [3], wer...
The mercury melting line has been determined for pressures up to 1200 MPa. The change of electrical resistance in the mercury sample was used for detecting the equilibrium between the solid and liquid phases. Pressure measurements were made with highly stable manganin gages calibrated against two controlled clearance piston gages. Temperature measurements were made in the constant temperature bath by means of platinum resistance thermometry. Systematic errors in pressure and temperature were evaluated for all the measurements as well as the scatter due to the resolution of the equilibrium determination between the two hases of mercury. The mercury melting point at 0 C is 756.84 k 0.16 MPa which is in close agreement with the value obtained by Dadson and Greig. The experimental results are compared with previous melting lines. There are systematic differences when compared to Bogdanov's equation up to 1200 MPa but there is very close agreement with recent data obtained by Houck and Morris over the pressure range they covered. The experimental data were fitted to a third order polynomial; this equation fits the melting line data much more closely than the Simon type heretofore recommended and can be used up to 1200 MPa to increase the accuracy of a practical pressure scale based on the melting line of mercury.
Primary pressure standards in the atmospheric pressure range are often established using mercury manometers. To a lesser extent, controlled-clearance dead-weight testers, in which one component (normally the piston) has been dimensionally measured, have also been used. The recent advances in technology on two fronts: (i) the fabrication of large-diameter pistons and cylinders with good geometries; and (ii) the dimensional metrology capability of these components, have allowed some dead-weight testers at the National Institute of Standards and Technology (NIST) to achieve total relative uncertainties (2 ) in generated pressure near 10 ϫ 10 -6 (10 ppm). This paper describes recent developments at the NIST in which accurate dimensional measurements have been translated into effective areas. It is anticipated that total relative uncertainties in generated pressure may decrease to 5 ppm (2 ) when recent dimensional measurements are incorporated in the newest gauges.
A variety of primary measurement techniques is now available for the measurement of pressure to 1 MPa and above. To ascertain the systematic uncertainty, if any, which exists in the measured pressure using the individual techniques, it is best to perform direct intercomparisons of primary instruments, However, when direct intercomparison is not possible, the next best alternative is to use a highly stable, reproducible transfer artifact such as a simple piston gauge. Such intercomparisons are described here, utilizing a piston gauge calibrated by a mercury manometer (with 0.1 MPa full-scale pressure), four large diameter 'dimensional' piston gauges from two different manufacturen (all with 1 MPa fullscale pressure), and a controlled clearance piston gauge (with 7 MPa full-scale pressure). The area ratio derived from dimensional measuremenk on two of the large diameter gauges, when compared with the ratio obtained from measuremenk traceable to a manometer, agrees within 1 part per million (ppm). For one of the large diameter piston gauges, t h e area value obtained from the manometer agrees within 3 ppm with its dimensional area, and within 10 ppm with the value obtained by its direct calibration against the controlled clearance piston gauge.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.