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Heat Transfer in Food Processing
Published in Susanta Kumar Das, Madhusweta Das, Fundamentals and Operations in Food Process Engineering, 2019
Susanta Kumar Das, Madhusweta Das
Thus, convective heat transfer takes place from the surface of the solid body to the fluid. Similar to hydrodynamic boundary layer with flow of fluid over a solid body, a thin thermal boundary layer (stagnant fluid film) around the surface is also formed. Heat transfer from the surface to the fluid occurs through this thin film by conduction. Owing to low thermal conductivity of most of the fluids, thickness of this film vis-à-vis its thermal resistance becomes a controlling factor for heat transfer. An increase in velocity of the fluid over the solid causes the thickness of thermal boundary layer to decrease and consequently the magnitude of heat transfer increases. The thermal resistance with the boundary layer thickness (δ), we can write heat transfer equation similar to Eq. 3.14c as q=kAΔTδ=AΔTδ/k
Heat Transfer
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
Similar to the velocity boundary layer, a thermal boundary layer develops due to the temperature gradient that exists between the fluid stream and surface. The thermal boundary layer is a region of a fluid flow near a solid surface, where the fluid temperatures are directly influenced by the heating or cooling from the surface wall. The concept of thermal boundary layer finds application in determining the temperature of the surface, which is in contact with the fluid. The temperature of the surface which is in contact with a liquid food product should not be very high as the product would attain the same temperature as that of the surface, which is detrimental to the product quality.
Heat and Mass Transfer Fundamentals for Flow Visualization
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
Like the development of a velocity boundary layer, a thermal boundary layer must develop if the fluid freestream and surface temperatures differ (see Fig. 1b). The temperature profile at the leading edge is uniform, with T = T∞, while the surface is at a temperature of Ts. The fluid region in which temperature gradients exist is the thermal boundary layer. The thermal boundary layer thickness δt is defined as the value of y for which the ratio (Ts – T)/(Ts – T∞) = 0.99. The local heat flux in the fluid at the surface y = 0 may be obtained by applying Fourier’s conduction law as qkA=−k(∂T∂y)y=0 This amount of heat must be transferred to the freestream. By equating this expression to Newton’s law of cooling, one obtains h=−k(∂T/∂y)y=0Ts−T∞
Multiple slips and double stratification in MHD flow of hybrid nanofluid past a permeable sheet: triple solutions and stability analysis
Published in Waves in Random and Complex Media, 2023
Rusya Iryanti Yahaya, Norihan Md Arifin, Najiyah Safwa Khashi'ie, Fadzilah Md Ali, Siti Suzilliana Putri Mohamed Isa
Next, the effects of solutal stratification parameter, are portrayed in Figure 8(a) with the reduction of temperature profile by . The thinning of the thermal boundary layer raises the temperature gradient and boosts the heat transfer rate. In Figure 8(b), the increase in reduces the concentration profile in the region near the sheet surface. Since the solutal stratification parameter is the ratio of ambient hybrid nanofluid concentration to the surface concentration, the increase in promotes the reduction of mass transfer rate by lowering the concentration gradient. However, the concentration profile shows an enhancement with after some distance away from the surface.
Microstructure and inertial characteristic of a magnetite Ferro fluid over a stretched sheet embedded in a porous medium with viscous dissipation using the spectral quasi-linearisation method
Published in International Journal of Ambient Energy, 2021
K. Gangadhar, P. R. Sobhana Babu, M. Venkata Subba Rao
Figure 14 shows the skin friction coefficient variation for different values of and K. From this it is observed that increase in K causes reduction in the magnitude of wall shear stress, whereas increase in enhances the friction factor. In view of the fact that, permeability strength in flow decreases the flow velocity. Because of this velocity, the boundary layer thickness is reduced and consequently, there is an enhancement in wall shear stress. Finally, from Figure 15, it can be seen that the rate of heat transfer decreased with the increase in and Ec. In view of the fact that the temperature of the flow enhanced for higher values of and Ec. Because of this thickness the thermal boundary layer is enhanced, as a result rate of heat transfer decreased.
Patterns of Natural Convection in an Irregular Arc-Shaped Enclosure
Published in Heat Transfer Engineering, 2020
Mahendra Pratap Singh, Anupam Rajvanshi, Harishchandra Thakur
Figure 6 shows the isotherms and streamlines for the A = 0.1. For Gr = 104, the conductive behavior appears. With increasing Gr value the isotherms appear with waviness, it easily showed in Figure 6c,d. Waviness increases due to an increase of strength of re-circulating pattern. The flow field features single cell recirculation pattern for Figure 6a–d. The strength of the recirculation increases with Gr. In addition, thermal boundary layers are formed along both the arc-shaped and flat walls. In theory, a thinner thermal boundary layer is accompanied by a higher local heat transfer rate. As expected, when the value of Gr is increased, the thickness of the boundary layer is apparently decreased and the heat transfer rate is increased.