{"id":2541,"date":"2016-03-14T15:07:40","date_gmt":"2016-03-14T15:07:40","guid":{"rendered":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/?p=2541"},"modified":"2016-03-14T15:07:40","modified_gmt":"2016-03-14T15:07:40","slug":"summary-of-power-and-refriger-a-tion-cycles","status":"publish","type":"post","link":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/summary-of-power-and-refriger-a-tion-cycles\/","title":{"rendered":"SUMMARY OF POWER AND REFRIGER A TION CYCLES"},"content":{"rendered":"<div class=\"nfkgt6a0dcc392a82c\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '61e5902552e2353963d8d2f1bd1f4a8f',\n\t\t'format' : 'iframe',\n\t\t'height' : 250,\n\t\t'width' : 300,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/61e5902552e2353963d8d2f1bd1f4a8f\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.nfkgt6a0dcc392a82c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.nfkgt6a0dcc392a82c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.nfkgt6a0dcc392a82c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.nfkgt6a0dcc392a82c {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.nfkgt6a0dcc392a82c {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<p align=\"justify\"><font size=\"5\"><b>SUMMA<\/b><b>R<\/b><b>Y<\/b><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The most efficient cycle operating between a heat source at temperature <i>T<\/i><i>H <\/i>and a sink at temperature <i>T<\/i><i>L <\/i>is the Carnot cycle, and its thermal efficiency is given by<\/font><\/p>\n<p align=\"justify\"><i><font size=\"5\"><\/font><\/i> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0373.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0373\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0373\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0373_thumb.jpg\" width=\"96\" height=\"41\"><\/a><\/font><\/p>\n<p align=\"justify\"><font size=\"5\">The actual gas cycles are rather complex. The approximations used to simplify the analysis are known as the <i>ai<\/i><i>r<\/i><i>-standa<\/i><i>r<\/i><i>d assumptions. <\/i>Under these assumptions, all the processes are assumed to be internally reversible; the working fluid is assumed to be air, which behaves as an ideal gas; and the combustion and exhaust processes are replaced by heat-addition and heat- rejection processes, respectively. The air-standard assumptions <\/font><font size=\"5\">are called <i>cold-air-standard assumptions <\/i>if, in addition, air is assumed to have constant specific heats at room temperature.<\/font><\/p>\n<p align=\"justify\"><font size=\"5\">In reciprocating engines, the <i>compression ratio r <\/i>and the <\/font><font size=\"5\"><i>mean effective pressure <\/i>MEP are defined as<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0374.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0374\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0374\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0374_thumb.jpg\" width=\"179\" height=\"54\"><\/a><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">where <i>r<\/i><i>c <\/i>is the <i>cutoff ratio, <\/i>defined as the ratio of the cylinder volumes after and before the combustion process.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The ideal cycle for modern gas-turbine engines is the <i>Bray- ton cycle, <\/i>which is made up of four internally reversible processes: isentropic compression, constant-pressure heat addition, isentropic expansion, and constant-pressure heat rejection.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">Under cold-air-standard assumptions, its thermal efficiency is<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0375.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0375\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0375\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0375_thumb.jpg\" width=\"105\" height=\"31\"><\/a><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">where <i>r<\/i><i>p <\/i>= <i>P<\/i>max\/<i>P<\/i>min is the pressure ratio and <i>k <\/i>is the specific heat ratio. The thermal efficiency of the simple Brayton cycle increases with the pressure ratio.<\/font> <\/p><div class=\"jgvrl6a0dcc392aa51\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '0c1eb4c533eaedb7b996f49a5a4983a9',\n\t\t'format' : 'iframe',\n\t\t'height' : 300,\n\t\t'width' : 160,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/0c1eb4c533eaedb7b996f49a5a4983a9\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.jgvrl6a0dcc392aa51 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.jgvrl6a0dcc392aa51 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.jgvrl6a0dcc392aa51 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.jgvrl6a0dcc392aa51 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.jgvrl6a0dcc392aa51 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<div class=\"glkdn6a0dcc392a936\" ><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-0778475562755157\"\n     crossorigin=\"anonymous\"><\/script>\n<!-- 300x600 hydraulics-and-pneumatics -->\n<ins class=\"adsbygoogle\"\n     style=\"display:inline-block;width:300px;height:600px\"\n     data-ad-client=\"ca-pub-0778475562755157\"\n     data-ad-slot=\"3735577695\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.glkdn6a0dcc392a936 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.glkdn6a0dcc392a936 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.glkdn6a0dcc392a936 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.glkdn6a0dcc392a936 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.glkdn6a0dcc392a936 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n\n<p align=\"justify\"><font size=\"5\">The deviation of the actual compressor and the turbine from the idealized isentropic ones can be accurately accounted for by utilizing their isentropic efficiencies, defined as<\/font><\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0376.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0376\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0376\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0376_thumb.jpg\" width=\"193\" height=\"57\"><\/a><\/font><\/p>\n<p align=\"justify\"><font size=\"5\">where states 1 and 3 are the inlet states, 2<i>a <\/i>and 4<i>a <\/i>are the ac<font size=\"5\">tual exit states, and 2<i>s <\/i>and 4<i>s <\/i>are the isentropic exit states.<\/font><\/font><\/p>\n<p align=\"justify\"><font size=\"5\">The <i>Otto cycle <\/i>is the ideal cycle for the spark-ignition reciprocating engines, and it consists of four internally reversible processes: isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection. Under cold-air-standard assumptions, the thermal efficiency of the ideal Otto cycle is<\/font><\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0381.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0381\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0381\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0381_thumb.jpg\" width=\"266\" height=\"118\"><\/a><\/font><\/p>\n<p align=\"justify\"><font size=\"5\">The <i>Carno<\/i><i>t cycle <\/i>is not a suitable model for vapor power cycles because it cannot be approximated in practice. The model cycle for vapor power cycles is the <i>Rankine cycle, <\/i>which is composed of four internally reversible processes: constant- pressure heat addition in a boiler, isentropic expansion in a turbine, constant-pressure heat rejection in a condenser, and isentropic compression in a pump. Steam leaves the condenser as a saturated liquid at the condenser pressure.<\/font><\/p>\n<p align=\"justify\"><font size=\"5\">The thermal efficiency of the Rankine cycle can be increased by increasing the average temperature at which heat is added to the working fluid and\/or by decreasing the average temperature at which heat is rejected to the cooling medium. The average <\/font><font size=\"5\">increased, the expansion and reheat processes approach an isothermal process of expansion at maximum temperature. Re- heating also decreases the moisture content at the turbine exit. The transfer of heat from lower-temperature regions to higher-temperature ones is called <i>r<\/i><i>efrigeration. <\/i>Devices that produce refrigeration are called <i>r<\/i><i>efrigerators<\/i><i>, <\/i>and the cycles on which they operate are called <i>r<\/i><i>efrigeration cycles. <\/i>The working fluids used in refrigerators are called <i>r<\/i><i>efrigerants. <\/i>Refrigerators used for the purpose of heating a space by transferring <\/font><font size=\"5\">heat from a cooler medium are called <i>heat pumps.<\/i><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The performance of refrigerators and heat pumps is expressed in terms of <i>coefficient of performance <\/i>(COP), defined as <\/font><font size=\"5\">temperature during heat rejection can be decreased by lowering the turbine exit pressure. Consequently, the condenser pressure of most vapor power plants is well below the atmospheric pressure. The average temperature during heat addition can be in<\/font><font size=\"5\">creased by raising the boiler pressure or by superheating the fluid to high temperatures. There is a limit to the degree of su<\/font><font size=\"5\">perheating, however, since the fluid temperature is not allowed to exceed a metallurgically safe value.<\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">Superheating has the added advantage of decreasing the moisture content of the steam at the turbine exit. Lowering the exhaust pressure or raising the boiler pressure, however, in-<font size=\"5\">creases the moisture content. To take advantage of the im<\/font><font size=\"5\">proved efficiencies at higher boiler pressures and lower <font size=\"5\">condenser pressures, steam is usually <i>r<\/i><i>eheated <\/i>after expanding partially in the high-pressure turbine. This is done by extract<font size=\"5\">ing the steam after partial expansion in the high-pressure tur<\/font><font size=\"5\">bine, sending it back to the boiler where it is reheated at constant pressure, and returning it to the low-pressure turbine for complete expansion to the condenser pressure. The average temperature during the reheat process, and thus the thermal efficiency of the cycle, can be increased by increasing the number of expansion and reheat stages. As the number of stages is<\/font><\/font><\/font><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\"><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0382.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"POWER AND REFRIGERATION CYCLES-0382\" border=\"0\" alt=\"POWER AND REFRIGERATION CYCLES-0382\" src=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-content\/uploads\/2016\/03\/POWER-AND-REFRIGERATION-CYCLES-0382_thumb.jpg\" width=\"255\" height=\"168\"><\/a><\/font> <\/p>\n<p align=\"justify\"><font size=\"5\">The most widely used refrigeration cycle is the <i>vapor-com<\/i><\/font><font size=\"5\"><i>pression refrigeration cycle. <\/i>In an ideal vapor-compression refrigeration cycle, the refrigerant enters the compressor as a saturated vapor and is cooled to the saturated liquid state in the condenser. It is then throttled to the evaporator pressure and vaporizes as it absorbs heat from the refrigerated space.<\/font><\/p>\n","protected":false},"excerpt":{"rendered":"<p>SUMMARY The most efficient cycle operating between a heat source at temperature TH and a sink at temperature TL is the Carnot cycle, and its thermal efficiency is given by The actual gas cycles are rather complex. The approximations used to simplify the analysis are known as the air-standard assumptions. Under these assumptions, all the [&hellip;]<br \/><a href=\"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/summary-of-power-and-refriger-a-tion-cycles\/\" class=\"more-link\" >Continue reading&#8230;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2541"}],"collection":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/comments?post=2541"}],"version-history":[{"count":1,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2541\/revisions"}],"predecessor-version":[{"id":2542,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/posts\/2541\/revisions\/2542"}],"wp:attachment":[{"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/media?parent=2541"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/categories?post=2541"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/hydraulics-and-pneumatics\/wp-json\/wp\/v2\/tags?post=2541"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}