{"id":66714,"date":"2026-10-13T08:41:57","date_gmt":"2026-10-13T05:41:57","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66714"},"modified":"2026-10-13T08:41:57","modified_gmt":"2026-10-13T05:41:57","slug":"log-mean-temperature-difference","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/log-mean-temperature-difference\/","title":{"rendered":"Log Mean Temperature Difference"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Find the Temperature Driving Force of a Heat Exchanger<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66714\" data-favorite-title=\"LMTD\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/log-mean-temperature-difference\/\" data-favorite-excerpt=\"Calculate the log mean temperature difference (LMTD) of a heat exchanger from the four terminal temperatures. Choose counterflow or parallel flow and enter the hot and cold inlet\/outlet temperatures in \u00b0C, \u00b0F or K.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-ventilation\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/engineering\/log-mean-temperature-difference\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66714\" data-post=\"66714\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field is-single\" id=\"input-1\"><label for=\"field-1\">Flow arrangement<\/label><div class=\"grid grid-cols-1\"><select id=\"field-1\" name=\"flow_arrangement\"><option value=\"counter\" selected>Counterflow (fluids flow in opposite directions)<\/option><option value=\"parallel\">Parallel flow (fluids flow in the same direction)<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><div class=\"field is-single has-term\" id=\"input-2\"><label for=\"field-2\">Hot fluid inlet temperature (T\u2095\u1d62)<\/label><div class=\"term\">T\u2095\u1d62<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"number\" name=\"hot_fluid_inlet_temperature_t\" id=\"field-2\" placeholder=\"e.g. 150\" step=\"any\" value=\"150\"\/><div class=\"grid grid-cols-1\"><select id=\"field-3\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"f\">\u00b0F<\/option><option value=\"k\">K<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><\/div><div class=\"field is-single has-term\" id=\"input-3\"><label for=\"field-4\">Hot fluid outlet temperature (T\u2095\u2092)<\/label><div class=\"term\">T\u2095\u2092<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"number\" name=\"hot_fluid_outlet_temperature_t\" id=\"field-4\" placeholder=\"e.g. 100\" step=\"any\" value=\"100\"\/><div class=\"grid grid-cols-1\"><select id=\"field-5\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"f\">\u00b0F<\/option><option value=\"k\">K<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><\/div><div class=\"field is-single has-term\" id=\"input-4\"><label for=\"field-6\">Cold fluid inlet temperature (T\u1d9c\u1d62)<\/label><div class=\"term\">T\u1d9c\u1d62<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"number\" name=\"cold_fluid_inlet_temperature_t\" id=\"field-6\" placeholder=\"e.g. 40\" step=\"any\" value=\"40\"\/><div class=\"grid grid-cols-1\"><select id=\"field-7\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"f\">\u00b0F<\/option><option value=\"k\">K<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><\/div><div class=\"field is-single has-term\" id=\"input-5\"><label for=\"field-8\">Cold fluid outlet temperature (T\u1d9c\u2092)<\/label><div class=\"term\">T\u1d9c\u2092<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"number\" name=\"cold_fluid_outlet_temperature_t\" id=\"field-8\" placeholder=\"e.g. 80\" step=\"any\" value=\"80\"\/><div class=\"grid grid-cols-1\"><select id=\"field-9\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"f\">\u00b0F<\/option><option value=\"k\">K<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66714\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> LMTD Results<\/h3><div class=\"result-box\"><div class=\"field-result is-column\" id=\"output-1\"><span class=\"field-title\"><span>Log mean temperature difference (LMTD \/ \u0394T\u2097\u2098)<\/span><span class=\"result-term\">\u0394T\u2097\u2098<\/span><\/span><span class=\"field-value\" id=\"result-1\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result is-column\" id=\"output-2\"><span class=\"field-title\"><span>Temperature differences at the exchanger ends and arrangement comparison<\/span><\/span><span class=\"field-value\" id=\"result-2\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"66714\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>LMTD Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ \\Delta T_{lm} = \\frac{\\Delta T_1 - \\Delta T_2}{\\ln \\left( \\dfrac{\\Delta T_1}{\\Delta T_2} \\right)} \\]<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(\\Delta T_{lm}\\) \u2014 log mean temperature difference (K or \u00b0C)<\/li>\n<li>\\(\\Delta T_1\\) \u2014 temperature difference between the two fluids at one end of the exchanger<\/li>\n<li>\\(\\Delta T_2\\) \u2014 temperature difference between the two fluids at the other end<\/li>\n<li>\\(\\ln\\) \u2014 natural logarithm<\/li>\n<\/ul>\n<p>The end differences depend on the flow arrangement. In <strong>counterflow<\/strong>, \\(\\Delta T_1 = T_{h,i} - T_{c,o}\\) at the hot inlet end and \\(\\Delta T_2 = T_{h,o} - T_{c,i}\\) at the hot outlet end. In <strong>parallel flow<\/strong>, \\(\\Delta T_1 = T_{h,i} - T_{c,i}\\) at the common inlet end and \\(\\Delta T_2 = T_{h,o} - T_{c,o}\\) at the common outlet end.<\/p>\n<p>Because the temperature difference between the fluids varies along the exchanger, a simple average would misrepresent the true driving force. The logarithmic mean weights the smaller end difference more heavily, which is exactly what the heat-transfer equations require. When \\(\\Delta T_1 = \\Delta T_2\\), the formula reduces to \\(\\Delta T_{lm} = \\Delta T_1\\).<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>LMTD \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a counterflow heat exchanger cools a hot stream from 150 \u00b0C to 100 \u00b0C while a cold stream is heated from 40 \u00b0C to 80 \u00b0C.<\/p>\n<p>\\[ \\Delta T_1 = T_{h,i} - T_{c,o} = 150 - 80 = 70\\ \\text{K} \\]<\/p>\n<p>\\[ \\Delta T_2 = T_{h,o} - T_{c,i} = 100 - 40 = 60\\ \\text{K} \\]<\/p>\n<p>\\[ \\Delta T_{lm} = \\frac{70 - 60}{\\ln (70 \/ 60)} = \\frac{10}{\\ln 1.1667} = 64.86\\ \\text{K} \\]<\/p>\n<p><strong>Result:<\/strong> \\(\\Delta T_{lm} \\approx 64.86\\) \u00b0C (identical in K, or 116.75 \u00b0F). Note that the logarithmic mean, 64.86, is slightly below the arithmetic mean of 65 K.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Select the <strong>Flow arrangement<\/strong>: counterflow (fluids flow in opposite directions) or parallel flow (fluids flow in the same direction). The arrangement determines which end temperatures are paired.<\/li>\n<li>Enter the <strong>Hot fluid inlet temperature (T\u2095\u1d62)<\/strong> and pick its unit (\u00b0C, \u00b0F or K).<\/li>\n<li>Enter the <strong>Hot fluid outlet temperature (T\u2095\u2092)<\/strong> with its unit.<\/li>\n<li>Enter the <strong>Cold fluid inlet temperature (T\u1d9c\u1d62)<\/strong> with its unit.<\/li>\n<li>Enter the <strong>Cold fluid outlet temperature (T\u1d9c\u1d52)<\/strong> with its unit.<\/li>\n<li>Read the <strong>log mean temperature difference (\u0394T\u2097\u2098)<\/strong> together with the end differences \u0394T\u2081 and \u0394T\u2082, shown in \u00b0C, K and \u00b0F so you can compare the two arrangements directly.<\/li>\n<\/ol>\n<p>Mixed units are allowed: each temperature can be entered in a different unit, because only temperature <em>differences<\/em> enter the LMTD. A difference of 1 K equals a difference of 1 \u00b0C and equals 9\/5 \u00b0F.<\/p>\n<h2>What Is the Log Mean Temperature Difference?<\/h2>\n<p>The LMTD is the effective temperature driving force for heat transfer in a heat exchanger. The basic heat-transfer rate equation is \\(Q = U \\cdot A \\cdot \\Delta T_{lm}\\), where \\(Q\\) is the heat duty, \\(U\\) the overall heat-transfer coefficient and \\(A\\) the heat-transfer area. The temperature difference between the hot and cold fluid is not constant along the exchanger \u2014 it is largest at one end and smallest at the other \u2014 so the LMTD replaces it with a single, physically correct average.<\/p>\n<p>The reason a logarithmic (rather than arithmetic) mean is needed comes from integrating the local heat-transfer equation along the exchanger length. Where the two fluids run nearly parallel in temperature, the difference changes slowly and the two means nearly coincide. Where the difference changes rapidly \u2014 for example, in parallel flow near the inlet \u2014 the logarithmic mean correctly captures the fact that the heat transfer is dominated by the region where the temperature difference is small.<\/p>\n<p>The flow arrangement matters a great deal. In counterflow the hot inlet meets the cold outlet, so the temperature difference stays relatively uniform and can even remain large over the whole length; in parallel flow the largest difference occurs at the common inlet and decays toward the outlet. For the same terminal temperatures, counterflow always gives a larger LMTD than parallel flow \u2014 in the example above, 64.86 \u00b0C versus 52.80 \u00b0C \u2014 which means a counterflow exchanger needs less heat-transfer area for the same duty.<\/p>\n<p>The LMTD is central to exchanger sizing and rating. Designers use it, together with a correction factor for multi-pass and cross-flow shells, to determine the required area for a given duty. Once the LMTD is known, the analysis often continues with flow-side calculations: check the flow regime with our <a href=\"https:\/\/wpcalc.com\/en\/engineering\/reynolds-number\/\">Reynolds Number<\/a> calculator, estimate <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pipe-pressure-drop\/\">pipe pressure drop<\/a>, or size the pump with the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pump-power\/\">Pump Power<\/a> calculator.<\/p>\n<h2>Assumptions, Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>Constant properties:<\/strong> the classical LMTD assumes constant specific heats, constant overall heat-transfer coefficient \\(U\\), and no phase change along the exchanger. Condensers and evaporators, where one fluid stays at a nearly constant temperature, still work with the formula but need care.<\/li>\n<li><strong>No heat loss:<\/strong> the exchanger is assumed adiabatic with respect to the surroundings, and both fluids are assumed perfectly mixed across each cross-section.<\/li>\n<li><strong>Positive end differences:<\/strong> both \\(\\Delta T_1\\) and \\(\\Delta T_2\\) must be positive. A zero or negative difference means a temperature cross, which cannot occur in a single-pass exchanger \u2014 the calculator flags this rather than returning a misleading number.<\/li>\n<li><strong>Equal end differences:<\/strong> when \\(\\Delta T_1 = \\Delta T_2\\) the logarithm diverges, but the mathematical limit is simply \\(\\Delta T_{lm} = \\Delta T_1\\). The calculator applies this limit automatically.<\/li>\n<li><strong>Correction factors:<\/strong> for multi-pass shell-and-tube and cross-flow arrangements, the true driving force is \\(F \\cdot \\Delta T_{lm}\\) with a correction factor \\(F &lt; 1\\) taken from exchanger design charts. This calculator covers the ideal single-pass counterflow and parallel-flow cases.<\/li>\n<li><strong>Special case \u2014 one fluid condensing or evaporating:<\/strong> its inlet and outlet temperatures are equal (e.g. \\(T_{h,i} = T_{h,o}\\)), and the formula still applies directly.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the log mean temperature difference (LMTD) of a heat exchanger from the four terminal temperatures. Choose counterflow or parallel flow and enter the hot and cold inlet\/outlet temperatures in \u00b0C, \u00b0F or K.<\/p>\n","protected":false},"author":3168,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[4],"tags":[39],"class_list":["post-66714","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-ventilation"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66714","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/3168"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=66714"}],"version-history":[{"count":2,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66714\/revisions"}],"predecessor-version":[{"id":67044,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66714\/revisions\/67044"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66714"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66714"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66714"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}