{"id":20816,"date":"2019-01-19T15:46:50","date_gmt":"2019-01-19T15:46:50","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=20816"},"modified":"2023-02-17T07:44:06","modified_gmt":"2023-02-17T07:44:06","slug":"boiling-modes-types-of-boiling","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/boiling-and-condensation\/boiling-modes-types-of-boiling\/","title":{"rendered":"Boiling Modes \u2013 Types of Boiling"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\">\n<p>From a practical engineering point of view, <strong>boiling<\/strong> can be categorized according to <strong>several criteria<\/strong>.<\/p>\n<p><strong>Categorization by the flow regime:<\/strong><\/p>\n<ul>\n<li><strong>Pool Boiling<\/strong><\/li>\n<li><strong>Flow Boiling<\/strong><\/li>\n<\/ul>\n<p><strong>Categorization by the wall superheat temperature, \u0394T<\/strong><strong><sub>sat<\/sub><\/strong><strong>:<\/strong><\/p>\n<ul>\n<li><strong>Natural Convection Boiling<\/strong><\/li>\n<li><strong>Nucleate Boiling<\/strong><\/li>\n<li><strong>Transition Boiling<\/strong><\/li>\n<li><strong>Film Boiling<\/strong><\/li>\n<\/ul>\n<\/div><\/div>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Pool-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20783\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Pool-Boiling-Boiling-Modes-300x276.png\" alt=\"Pool Boiling - Boiling Modes\" width=\"250\" height=\"230\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Pool-Boiling-Boiling-Modes-300x276.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Pool-Boiling-Boiling-Modes.png 526w\" sizes=\"(max-width: 250px) 100vw, 250px\" \/><\/a>From a practical engineering point of view, <strong>boiling<\/strong> can be categorized according to <strong>several criteria<\/strong>.<\/p>\n<p><strong>Categorization by the flow regime:<\/strong><\/p>\n<ul>\n<li><strong>Pool Boiling<\/strong>. Perhaps the most common configuration, known as <strong>pool boiling,<\/strong> is when a pool of liquid is heated from below through a horizontal surface. In pool boiling, the liquid is quiescent, and its motion near the surface is primarily due to <a title=\"Natural Convection \u2013 Free Convection\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/convection-convective-heat-transfer\/natural-convection-free-convection\/\">natural convection<\/a> and mixing induced by bubble growth and detachment. The pioneering work on pool boiling was done in 1934 by <strong>S. Nukiyama<\/strong>, and he\u00a0was the first to identify four well-known\u00a0<strong>different regimes of pool boiling<\/strong>\u00a0using his apparatus.<\/li>\n<\/ul>\n<ul>\n<li><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Flow-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20784\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Flow-Boiling-Boiling-Modes-117x300.png\" alt=\"Flow Boiling - Boiling Modes\" width=\"59\" height=\"150\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Flow-Boiling-Boiling-Modes-117x300.png 117w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Flow-Boiling-Boiling-Modes.png 367w\" sizes=\"(max-width: 59px) 100vw, 59px\" \/><\/a>Flow Boiling. <\/strong>In <strong>flow boiling<\/strong> (or forced convection boiling), fluid flow is forced over a surface by external means such as a <strong>pump <\/strong>as well as buoyancy effects. Herefore, <strong>flow boiling<\/strong> is always accompanied by other convection effects. Conditions depend strongly on geometry, involving external flow over heated plates and cylinders or internal (duct) flow. In <strong>nuclear reactors<\/strong>, most boiling regimes are just forced convection boiling.<\/li>\n<\/ul>\n<p><strong>Categorization by the wall superheat temperature, \u0394T<\/strong><strong><sub>sat<\/sub><\/strong><strong>:<\/strong><\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Boiling-Curve-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20779\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Boiling-Curve-Boiling-Modes-208x300.png\" alt=\"Boiling Curve - Boiling Modes\" width=\"208\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Boiling-Curve-Boiling-Modes-208x300.png 208w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Boiling-Curve-Boiling-Modes.png 601w\" sizes=\"(max-width: 208px) 100vw, 208px\" \/><\/a>The pioneering work on boiling was done in 1934 by <strong>S. Nukiyama<\/strong>, who used electrically heated nichrome and platinum wires immersed in liquids in his experiments. Nukiyama was the first to identify <strong>different regimes of pool boiling<\/strong> using his apparatus. He noticed that boiling takes different forms, depending on the value of the wall superheat temperature <strong>\u0394T<\/strong><strong><sub>sat<\/sub><\/strong> (also known as the excess temperature)<strong>, <\/strong>defined as the difference between the wall temperature, <strong>T<sub>wall,<\/sub><\/strong> and the saturation temperature,<strong> T<sub>sat<\/sub><\/strong>.<\/p>\n<p>Four different boiling regimes \u00a0of pool boiling (based on the excess temperature) are observed:<\/p>\n<ul>\n<li><strong>Natural Convection Boiling<\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0<strong>\u0394T<\/strong><strong><sub>sat<\/sub><\/strong> &lt; 5\u00b0C<\/li>\n<li><strong>Nucleate Boiling<\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a05\u00b0C &lt; <strong>\u0394T<\/strong><strong><sub>sat<\/sub><\/strong> &lt; 30\u00b0C<\/li>\n<li><strong>Transition Boiling<\/strong> \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a030\u00b0C &lt; <strong>\u0394T<\/strong><strong><sub>sat<\/sub><\/strong> &lt; 200\u00b0C<\/li>\n<li><strong>Film Boiling<\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 200\u00b0C &lt; <strong>\u0394T<\/strong><strong><sub>sat<\/sub><\/strong><\/li>\n<\/ul>\n<p>Description of <strong>Boiling Modes<\/strong>:<\/p>\n<ul>\n<li><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Natural-Convection-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20781\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Natural-Convection-Boiling-Boiling-Modes-300x235.png\" alt=\"Natural Convection Boiling\" width=\"200\" height=\"155\" \/><\/a>Natural Convection Boiling. I<\/strong>n <a title=\"Thermodynamics\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/\">thermodynamics<\/a>, the requirement for <strong>boiling<\/strong> of pure substances to occur is that T<sub>wall<\/sub> = T<sub>sat<\/sub>. But in real experiments, boiling does not occur until the liquid is heated a few degrees above the saturation temperature. The surface temperature must be somewhat above the saturation temperature in order to sustain vapor formation. In this <strong>boiling mode<\/strong>, <strong>vapor will be observed<\/strong> over the water surface, but usually, <strong>no bubbles<\/strong> will be observed. As the superheat temperature increases, bubble inception will eventually occur, but the fluid motion is determined principally by natural convection currents below point A. Point A is usually referred to as the <strong>onset of nucleate boiling &#8211; ONB<\/strong>.<\/li>\n<li><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Nucleate-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20782\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Nucleate-Boiling-Boiling-Modes-300x234.png\" alt=\"Nucleate Boiling - Boiling Modes\" width=\"200\" height=\"155\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Nucleate-Boiling-Boiling-Modes-300x234.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Nucleate-Boiling-Boiling-Modes.png 623w\" sizes=\"(max-width: 200px) 100vw, 200px\" \/><\/a>Nucleate Boiling<\/strong>. The most common type of local boiling encountered in nuclear facilities is<strong> nucleate boiling<\/strong>. In <strong>nucleate boiling<\/strong>, steam bubbles form at the heat transfer surface and then break away and are carried into the mainstream of the fluid. Such movement enhances heat transfer because the heat generated at the surface is carried directly into the fluid stream. Once in the main fluid stream, the bubbles collapse because the bulk temperature of the fluid is not as high as the heat transfer surface temperature where the bubbles were created. This heat transfer process is sometimes desirable because the energy created at the heat transfer surface is quickly and efficiently \u201ccarried\u201d away.<\/li>\n<li><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Transition-Boiling-Partial-Film-Boiling-schema.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20777\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Transition-Boiling-Partial-Film-Boiling-schema-300x225.png\" alt=\"Transition Boiling - Partial Film Boiling\" width=\"200\" height=\"155\" \/><\/a>Transition Boiling<\/strong>. The nucleate boiling heat flux cannot be increased indefinitely. We call it the \u201c<strong>critical heat flux<\/strong>\u201d (<strong>CHF<\/strong>) at some value. The steam produced can form an insulating layer over the surface, which in turn deteriorates the heat transfer coefficient. This is because a large fraction of the surface is covered by a vapor film, which acts as thermal insulation due to the low thermal conductivity of the vapor relative to that of the liquid. Immediately after the critical heat flux has been reached, <strong>boiling becomes unstable,<\/strong> and <strong>transition boiling<\/strong> occurs. The transition from nucleate boiling to film boiling is known as the \u201c<strong>boiling crisis<\/strong>\u201d. Since the heat transfer coefficient decreases beyond the CHF point, the transition to film boiling is usually inevitable.<\/li>\n<li><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Film-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20778\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Film-Boiling-Boiling-Modes-300x231.png\" alt=\"Film Boiling - Boiling Modes\" width=\"200\" height=\"155\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Film-Boiling-Boiling-Modes-300x231.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Film-Boiling-Boiling-Modes.png 634w\" sizes=\"(max-width: 200px) 100vw, 200px\" \/><\/a>Film Boiling<\/strong>. A \u00a0further increase in the heat flux causes a film of vapor to cover the surface. This significantly reduces the convection coefficient since the vapor layer has significantly lower heat transfer ability. As a result, the excess temperature shoots up to a very high value. Beyond the <strong>Leidenfrost point<\/strong>, a continuous vapor film blankets the surface, and there is no contact between the liquid phase and the surface. In this situation, the heat transfer is both by radiation and conduction to the vapor. If the material is not strong enough for withstanding this temperature, the equipment will fail by damage to the material. This phenomenon is also known as <strong>burnout<\/strong>. In pressurized water reactors, one of the key safety requirements (maybe the most important) is that a <strong>departure from nucleate boiling<\/strong> (<strong>DNB<\/strong>) will not occur during steady-state operation, normal operational transients, and anticipated operational occurrences (AOOs). Fuel cladding integrity will be maintained if the minimum DNBR remains above the 95\/95 DNBR limit for PWRs ( a 95% probability at a 95% confidence level). Since this phenomenon deteriorates the heat transfer coefficient and the heat flux remains, heat <strong>accumulates <\/strong>in the fuel rod, causing the <strong>dramatic rise<\/strong> of cladding and fuel <strong>temperature<\/strong>. Simply, a very high-temperature difference is required to transfer the critical heat flux being produced from the surface of the fuel rod to the reactor coolant (through the vapor layer).<\/li>\n<\/ul>\n<p><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Subcooled-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20785\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Subcooled-Boiling-Boiling-Modes-300x231.png\" alt=\"Subcooled Boiling - Boiling Modes\" width=\"300\" height=\"231\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Subcooled-Boiling-Boiling-Modes-300x231.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Subcooled-Boiling-Boiling-Modes-180x138.png 180w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Subcooled-Boiling-Boiling-Modes.png 616w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>Categorization by the subcooling temperature, \u0394T<\/strong><strong><sub>sub<\/sub><\/strong><strong>.<\/strong><\/p>\n<p>Boiling may also be classified according to whether it is subcooled or saturated:<\/p>\n<ul>\n<li><strong>Subcooled boiling. <\/strong>I <strong>\u00a0subcooled boiling<\/strong>, the temperature of most of the liquid is below the saturation temperature, and bubbles formed at the surface may condense in the liquid. T is condensation (collapsing) produces a sound of frequency ~ 100Hz &#8211; 1 KHz. This is why an electric kettle makes the most noise before the water becomes saturated boiling. T e term <strong>subcooling<\/strong> refers to a liquid existing at a temperature <strong>below<\/strong> its normal boiling point.<\/li>\n<li><strong>Saturated Boiling<\/strong>. I\u00a0 <strong>saturated boiling<\/strong> (also known as <strong>bulk boiling<\/strong>), the temperature of the liquid slightly exceeds the saturation temperature. Bulk boiling may occur when system temperature increases or pressure drops to the boiling point. At this point, the bubbles entering the coolant channel will not collapse, and the bubbles will tend to join together and form bigger steam bubbles. Steam bubbles are then propelled through the liquid by buoyancy forces, eventually escaping from a free surface.<\/li>\n<\/ul>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Saturated-Boiling-Boiling-Modes.png\"><img loading=\"lazy\" class=\"aligncenter size-medium wp-image-20780\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Saturated-Boiling-Boiling-Modes-300x232.png\" alt=\"Saturated Boiling\" width=\"300\" height=\"232\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Saturated-Boiling-Boiling-Modes-300x232.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Saturated-Boiling-Boiling-Modes-180x138.png 180w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/01\/Saturated-Boiling-Boiling-Modes.png 629w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Vapor Quality<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/dry-steam-saturated-vapor-min.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-16092\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/dry-steam-saturated-vapor-min-300x256.png\" alt=\"dry-steam-saturated-vapor-min\" width=\"300\" height=\"256\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/dry-steam-saturated-vapor-min-300x256.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/dry-steam-saturated-vapor-min.png 633w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>As can be seen from the\u00a0<strong>phase diagram of water<\/strong>, in the two-phase regions (e.g., on the border of vapor\/liquid phases), specifying temperature alone will set the pressure and specifying pressure will set the temperature. B t these parameters will not define the volume and enthalpy because we will need to know the relative <strong>proportion of the two phases<\/strong>\u00a0present.<\/p>\n<p>The\u00a0<strong>mass fraction<\/strong>\u00a0of the vapor in a two-phase liquid-vapor region is called the\u00a0<a title=\"Vapor Quality \u2013 Dryness Fraction\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/vapor-quality-dryness-fraction\/\"><strong>vapor quality<\/strong><\/a>\u00a0(or dryness fraction),\u00a0<em>x<\/em>, and it is given by the following formula:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/Vapor-quality.png?5a260f\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-16088\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/Vapor-quality.png?5a260f\" alt=\"vapor quality\" width=\"189\" height=\"154\" \/><\/a><\/p>\n<p>The value of the quality ranges from\u00a0<strong>zero to unity<\/strong>. A though defined as a ratio, the quality is frequently given as a percentage. F om this point of view, we distinguish between three basic types of steam. I\u00a0 must be added at x=0, and we are talking about the <a title=\"Saturated and Subcooled Liquid\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturated-and-subcooled-liquid\/\"><strong>saturated liquid state<\/strong><\/a>\u00a0(single-phase).<\/p>\n<ul>\n<li><a title=\"Wet Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/wet-steam\/\"><strong>Wet Steam<\/strong><\/a><\/li>\n<li><a title=\"Dry Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/dry-steam\/\"><strong>Dry Steam<\/strong><\/a><\/li>\n<li><a title=\"Superheated Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/superheated-steam\/\"><strong>Superheated Steam<\/strong><\/a><\/li>\n<\/ul>\n<p>This classification of steam has its limitation. Consider the system\u2019s behavior, which is heated at a pressure that is <strong>higher than the critical pressure<\/strong>. In this case, there would be <strong>no change in phase<\/strong> from liquid to steam, and in all states, there would be only one phase. Vaporization and condensation can occur only when the pressure is less than the critical pressure. T e terms liquid and vapor tend to lose their significance.<\/p>\n<p>See also:\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturation-boiling-point\/\">Saturation<\/a><\/p>\n<p>See also:\u00a0<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-processes\/throttling-process-isenthalpic-process\/\">Throttling\u00a0of Steam<\/a><\/div><\/div><\/div>\n<h2>Boiling<\/h2>\n<figure id=\"attachment_14172\" aria-describedby=\"caption-attachment-14172\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/04\/Boiling-point-of-water.png\"><img loading=\"lazy\" class=\"size-medium wp-image-14172\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/04\/Boiling-point-of-water-300x255.png\" alt=\"Phase diagram of water\" width=\"300\" height=\"255\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/04\/Boiling-point-of-water-300x255.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/04\/Boiling-point-of-water.png 696w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-14172\" class=\"wp-caption-text\">Phase diagram of water.<br \/>Source: wikipedia.org CC BY-SA<\/figcaption><\/figure>\n<p>We have discussed <a title=\"Convection \u2013 Convective Heat Transfer\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/convection-convective-heat-transfer\/\"><strong>convective heat transfer<\/strong><\/a> in the preceding chapters with a very important assumption, and we have assumed a <strong>single-phase convective heat transfer<\/strong> without any phase change. This chapter focuses on convective heat transfer associated with the <strong>change in phase of a fluid<\/strong>. In particular, we consider processes that can occur at a solid-liquid or solid\u2013vapor interface, namely, <strong>boiling<\/strong> (liquid-to-vapor phase change) and <strong>condensation<\/strong> (vapor-to-liquid phase change).<\/p>\n<p><strong>Latent heat effects<\/strong> associated with the phase change are significant for these cases. <strong><a title=\"Enthalpy of Vaporization\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/enthalpy-of-vaporization\/\">Latent heat<\/a><\/strong>, also known as the enthalpy of vaporization, is the amount of heat added to or removed from a substance to produce a change in phase. This energy breaks down the intermolecular attractive forces and also must provide the energy necessary to expand the gas (the <strong>p\u0394V work<\/strong>). When <strong>latent heat<\/strong> is added, no temperature change occurs.<\/p>\n<figure id=\"attachment_16677\" aria-describedby=\"caption-attachment-16677\" style=\"width: 232px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Specific-Enthalpy-Water-and-Steam-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-16677\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Specific-Enthalpy-Water-and-Steam-min-242x300.png\" alt=\"Latent heat of vaporization - water at 0.1 MPa, 3 MPa, 16 MPa\" width=\"242\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Specific-Enthalpy-Water-and-Steam-min-242x300.png 242w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/02\/Specific-Enthalpy-Water-and-Steam-min.png 616w\" sizes=\"(max-width: 242px) 100vw, 242px\" \/><\/a><figcaption id=\"caption-attachment-16677\" class=\"wp-caption-text\">The heat of vaporization diminishes with increasing pressure while the boiling point increases, and it vanishes completely at a certain point called the critical point.<\/figcaption><\/figure>\n<p>The <strong>enthalpy of vaporization<\/strong> is a function of the pressure at which that transformation takes place.<\/p>\n<p>Latent heat of vaporization \u2013 water at 0.1 MPa (atmospheric pressure)<\/p>\n<p><strong>h<\/strong><strong><sub>lg<\/sub><\/strong><strong> = 2257 kJ\/kg<\/strong><\/p>\n<p>Latent heat of vaporization \u2013 water at 3 MPa<\/p>\n<p><strong>h<\/strong><strong><sub>lg<\/sub><\/strong><strong> = 1795 kJ\/kg<\/strong><\/p>\n<p>Latent heat of vaporization \u2013 water at 16 MPa (pressure inside a <a href=\"http:\/\/sitepourvtc.com\/pressurizer\/\">pressurizer<\/a>)<\/p>\n<p><strong>h<\/strong><strong><sub>lg<\/sub><\/strong><strong> = 931 kJ\/kg<\/strong><\/p>\n<p>The <strong>heat of vaporization<\/strong> diminishes with increasing pressure while the <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturation-boiling-point\/\">boiling point<\/a> increases, and it vanishes completely at a certain point called the <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/critical-point-of-water\/\">critical point<\/a>. Above the critical point, the liquid and vapor phases are indistinguishable, and the substance is called a <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/supercritical-fluid-supercritical-water\/\">supercritical fluid<\/a>.<\/p>\n<p><img loading=\"lazy\" class=\"alignright size-medium wp-image-16094\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/Supercritical-phase-critical-point-min-300x256.png\" alt=\"supercritical-phase-critical-point-min\" width=\"300\" height=\"256\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/Supercritical-phase-critical-point-min-300x256.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/12\/Supercritical-phase-critical-point-min.png 633w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/>The change from the liquid to the vapor state due to <strong>boiling<\/strong> is sustained by heat transfer from the solid surface; conversely, <strong>condensation<\/strong> of a vapor to the liquid state results in heat transfer to the solid surface. <strong>Boiling and condensation<\/strong> differ from other forms of convection in that they depend on the <strong>latent heat of vaporization<\/strong>, which is <strong>very high<\/strong> for common <a title=\"What is Pressure \u2013 Physics\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-pressure-physics\/\">pressures<\/a>. Therefore large amounts of heat can be transferred during boiling and condensation essentially at a constant temperature. <a title=\"Convective Heat Transfer Coefficient\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/convection-convective-heat-transfer\/convective-heat-transfer-coefficient\/\">H at transfer coefficients<\/a>, h, associated with <strong>boiling and condensation<\/strong> are typically <strong>much higher<\/strong> than those encountered in other forms of convection processes that involve a single phase.<\/p>\n<p>This is because even in <a title=\"Turbulent Flow\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/fluid-dynamics\/turbulent-flow\/\">turbulent flow<\/a>, there is a stagnant fluid film layer (laminar sublayer) that isolates the surface of the heat exchanger. This <strong>stagnant fluid film layer<\/strong> plays a crucial role in the convective heat transfer coefficient. It is observed that the fluid comes to a <strong>complete stop at the surface<\/strong> and assumes a zero velocity relative to the surface. This phenomenon is known as the no-slip condition, and therefore, <strong>at the surface, <\/strong>energy flow occurs <strong>purely by conduction. <\/strong>But in the next layers, both conduction and diffusion-mass movement occur at the molecular or macroscopic levels. Due to the mass movement, the rate of energy transfer is higher. As was written, <strong>nucleate boiling<\/strong> at the surface effectively disrupts this stagnant layer. Therefore, nucleate boiling significantly increases the ability of a surface to transfer <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/internal-energy-thermal-energy\/\">thermal energy<\/a> to the bulk fluid.<\/p>\n<div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span> Two-phase Fluid Flow<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/06\/two-phase-fluid-flow.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-14768\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/06\/two-phase-fluid-flow-74x300.png\" alt=\"two-phase fluid flow\" width=\"74\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/06\/two-phase-fluid-flow-74x300.png 74w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/06\/two-phase-fluid-flow.png 82w\" sizes=\"(max-width: 74px) 100vw, 74px\" \/><\/a>By definition,\u00a0<a title=\"Two-phase Fluid Flow\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/fluid-dynamics\/two-phase-fluid-flow\/\"><strong>multiphase flow<\/strong><\/a>\u00a0is the interactive flow of\u00a0<strong>two or more\u00a0<\/strong>distinct phases with common interfaces in, say, a conduit. Each phase, representing a volume fraction (or mass fraction) of solid, liquid, or ga搜索引擎优化us matter, has its <strong>own<\/strong>\u00a0properties,\u00a0<strong>velocity<\/strong>, and\u00a0<strong>temperature<\/strong>.<\/p>\n<p>A multiphase flow can be a simultaneous flow of:<\/p>\n<ul>\n<li>Materials with\u00a0<strong>different states or phases<\/strong>\u00a0(e.g., water-steam mixture).<\/li>\n<li>Materials with\u00a0<strong>different chemical properties<\/strong>\u00a0but in the same state or phase (e.g., oil droplets in water).<\/li>\n<\/ul>\n<p>There are\u00a0many combinations in industrial processes, but the\u00a0<strong>most common<\/strong>\u00a0being the simultaneous flow of\u00a0<strong>steam and liquid water<\/strong>\u00a0(as encountered in\u00a0<a title=\"Steam Generator\" href=\"http:\/\/sitepourvtc.com\/steam-generator\/\"><strong>steam generators<\/strong>\u00a0<\/a>and\u00a0<strong>condensers<\/strong>). In reactor engineering, a great deal of study has been performed on the nature of <strong>two-phase flow<\/strong>\u00a0in case of a loss-of-coolant accident (<strong>LOCA<\/strong>), an accident of importance in reactor safety, and all thermal-hydraulic analyses (<strong>DNBR analyses<\/strong>).<\/p>\n<h2><span id=\"Characteristics_of_Two-phase_Fluid_Flow\">Characteristics of Two-phase Fluid Flow<\/span><\/h2>\n<p>All two-phase flow problems have features that are characteristically different from those found in single-phase problems.<\/p>\n<ul>\n<li>In the case of steam and liquid water, the <strong>density<\/strong>\u00a0of the two phases\u00a0<strong>differs by a factor of about 1000<\/strong>. Therefore the influence of gravitational body force on multiphase flows is of much greater importance than in the case of single-phase flows.<\/li>\n<li>The\u00a0<strong>sound speed<\/strong> changes dramatically for materials undergoing a phase change and can be orders of magnitude different. This significantly influences a <strong>flow through an orifice<\/strong>.<\/li>\n<li>The relative\u00a0<strong>concentration<\/strong>\u00a0of different phases is usually a dependent parameter of great importance in multiphase flows, while it is a parameter of no consequence in single-phase flows.<\/li>\n<li>The phase change means flow-induced pressure drops can cause further phase change (e.g., water can evaporate through an orifice), increasing the relative volume of the ga搜索引擎优化us, compressible medium and increasing efflux velocities, unlike single-phase incompressible flow where decreasing of an orifice would decrease efflux velocities.<\/li>\n<li>The spatial distribution of the various phases in the flow channel strongly affects the flow behavior.<\/li>\n<li>There are many types of instabilities in multiphase flow.<\/li>\n<\/ul>\n<\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Boiling Point - Saturation<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">In thermodynamics, the term <a title=\"Saturation \u2013 Boiling Point\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturation-boiling-point\/\"><strong>saturation<\/strong><\/a> defines a condition in which a mixture of vapor and liquid can exist together at a given temperature and pressure. T e temperature at which <strong>vaporization\u00a0<\/strong>(boiling) starts to occur for a given pressure is called the<strong>\u00a0saturation temperature<\/strong>\u00a0or\u00a0<strong>boiling point<\/strong>. T e pressure at which vaporization (boiling) starts to occur for a given temperature is called the saturation pressure.<\/p>\n<p>When the vapor quality is equal to 0, it is referred to as the\u00a0<strong><a title=\"Saturated and Subcooled Liquid\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturated-and-subcooled-liquid\/\">saturated liquid state<\/a>\u00a0<\/strong>(single-phase). On the other hand, when the vapor quality is equal to 1, it is referred to as the<a title=\"Dry Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/dry-steam\/\">\u00a0<strong>saturated vapor state<\/strong><\/a>\u00a0or\u00a0<a title=\"Dry Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/dry-steam\/\"><strong>dry steam<\/strong><\/a> (single-phase). B tween these two states, we talk about <strong>vapor-liquid mixture<\/strong>\u00a0or<a title=\"Wet Steam\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/wet-steam\/\"><strong>\u00a0wet steam<\/strong><\/a> (two-phase mixture). A\u00a0 constant pressure addition of energy does not change the mixture\u2019s temperature, but the <a title=\"Vapor Quality \u2013 Dryness Fraction\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/vapor-quality-dryness-fraction\/\"><strong>vapor quality<\/strong><\/a> and specific volume change.<\/div><\/div><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\u00a0 <div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Heat Transfer:<\/strong>\n<ol>\n<li>Fundamentals of Heat and Mass Transfer, 7th Edition. Theodore L. Bergman, Adrienne S. Lavine, Frank P. Incropera. John Wiley &amp; Sons, Incorporated, 2011. I BN: 9781118137253.<\/li>\n<li>Heat and Mass Transfer. Yunus A. Cengel. McGraw-Hill Education, 2011. I BN: 9780071077866.<\/li>\n<li>U.S. Department of Energy, Thermodynamics, Heat Transfer and Fluid Flow. D E Fundamentals Handbook, Volume 2 of 3. M y 2016.<\/li>\n<\/ol>\n<p><strong>Nuclear and Reactor Physics:<\/strong><\/p>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>W.S.C. Williams. N clear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n<li>Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n<li>U.S. Department of Energy, Nuclear Physics and Reactor Theory. D E Fundamentals Handbook, Volume 1 and 2. January 1993.<\/li>\n<li>Paul Reuss, Neutron Physics. E P Sciences, 2008. I BN: 978-2759800414.<\/li>\n<\/ol>\n<p><strong><\/strong><strong>Advanced Reactor Physics:<\/strong><\/p>\n<ol>\n<li>K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n<li>K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n<li>D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.<\/li>\n<li>E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-default\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Boiling and Condensation<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/boiling-and-condensation\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>From a practical engineering point of view, boiling can be categorized according to several criteria. Categorization by the flow regime: Pool Boiling. Perhaps the most common configuration, known as pool boiling, is when a pool of liquid is heated from below through a horizontal surface. In pool boiling, the liquid is quiescent, and its motion &#8230; <a title=\"Boiling Modes \u2013 Types of Boiling\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/boiling-and-condensation\/boiling-modes-types-of-boiling\/\" aria-label=\"More on Boiling Modes \u2013 Types of Boiling\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":20709,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/20816"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=20816"}],"version-history":[{"count":5,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/20816\/revisions"}],"predecessor-version":[{"id":37347,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/20816\/revisions\/37347"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/20709"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=20816"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}