{"id":20420,"date":"2018-12-02T10:48:06","date_gmt":"2018-12-02T10:48:06","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=20420"},"modified":"2023-02-15T07:57:18","modified_gmt":"2023-02-15T07:57:18","slug":"convective-heat-transfer-coefficient","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/convection-convective-heat-transfer\/convective-heat-transfer-coefficient\/","title":{"rendered":"Convective Heat Transfer Coefficient"},"content":{"rendered":"
The convective heat transfer coefficient,<\/strong> h, can be defined as:<\/p>\n The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference.<\/em><\/p>\n <\/a><\/p>\n<\/div><\/div>\n Despite the complexity of convection<\/strong>, the rate of convection heat transfer is observed to be proportional<\/strong> to the temperature difference<\/strong>. It is\u00a0conveniently expressed by Newton\u2019s law of cooling<\/strong>, which states that:<\/p>\n The rate of heat loss of a body is directly proportional to the difference in the temperatures between the body, and its surroundings, provided the temperature difference is small, and the nature of radiating surface remains the same.<\/em><\/p>\n <\/a><\/p>\n Note that \u0394T<\/strong> is given by the surface or wall temperature<\/strong>, Twall,<\/sub> <\/strong>and the bulk temperature<\/strong>, T\u221e<\/sub><\/strong>, which is the temperature of the fluid sufficiently far from the surface.<\/p>\n As can be seen, the constant of proportionality<\/strong> will be crucial in calculations, and it is known as the convective heat transfer coefficient<\/strong>, h<\/strong>. The convective heat transfer coefficient,<\/strong> h, can be defined as:<\/p>\n The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference.<\/em><\/p>\n <\/a><\/p>\n <\/a>The convective heat transfer coefficient<\/strong> depends on the fluid\u2019s physical properties and the physical situation. The convective heat transfer coefficient is not a property of the fluid. It is an experimentally determined parameter whose value depends on all the variables influencing convection, such as the surface geometry<\/strong>, the nature of fluid motion<\/strong>, the properties of the fluid<\/strong>, and the bulk fluid velocity<\/strong>.<\/p>\n Typically, the convective heat transfer coefficient<\/strong> for laminar flow<\/strong><\/a> is relatively low compared to the convective heat transfer coefficient<\/strong> for turbulent flow<\/strong><\/a>. This is due to turbulent flow having a thinner stagnant fluid film layer<\/strong> on the heat transfer surface.<\/p>\n It must be noted this stagnant fluid film layer<\/strong> plays a crucial role in the convective heat transfer coefficient. It is observed that the fluid comes to a 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, at the surface, <\/strong>energy flow occurs 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, nucleate boiling<\/strong> at the surface effectively disrupts this stagnant layer. Therefore, nucleate boiling significantly increases the ability of a surface to transfer thermal energy<\/a> to the bulk fluid.<\/p>\n A similar phenomenon occurs for the temperature. It is observed that the fluid\u2019s temperature at the surface and the surface will have the same temperature<\/a> at the point of contact. This phenomenon is known as the no-temperature-jump condition, and it is very important for the theory of nucleate boiling.<\/strong><\/p>\n Values of the heat transfer coefficient<\/strong>, h, have been measured and tabulated for the commonly encountered fluids and flow situations occurring during heat transfer by convection.<\/p>\nNewton\u2019s Law of Cooling<\/h2>\n
Convective Heat Transfer Coefficient<\/h2>\n