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Energy Basics/Foundation for Understanding
Published in Dale R. Patrick, Stephen W. Fardo, Ray E. Richardson, Brian W. Fardo, Energy Conservation Guidebook, 2020
Dale R. Patrick, Stephen W. Fardo, Ray E. Richardson, Brian W. Fardo
The transfer of heat between objects or areas is determined primarily by temperature. Heat must always flow from a warmer object to a colder object. The transfer rate of heat flow depends on the temperature difference between objects. Consider, for example, what would take place when two objects, one small and one large, are placed in an insulated box of suitable size. We must also assume that the temperature of the smaller object is twice that of the larger object. The heat level of the larger object is much greater than the smaller object, depending on the volume ratio of the two. However, because of the difference in temperature, heat will be transferred from the smaller object to the larger until they have both reached the same temperature. The length of time that heat flow occurs is dependent on the volume ratio of the objects.
Heat Transfer
Published in Arthur J. Kidnay, William R. Parrish, Daniel G. McCartney, Fundamentals of Natural Gas Processing, 2019
Arthur J. Kidnay, William R. Parrish, Daniel G. McCartney
Figure 3.1 depicts heat flowing through a solid media. The rate of heat flow, Q, has units of energy per unit time (e.g., Btu/h or W). The heat flow rate is determined by four factors: Temperature difference, t2 − t1 (°F or °C)Cross-sectional area, A (ft2 or m2)Solid thickness, L (ft or m)Thermal conductivity of the solid, k (Btu/h-ft-°F1 or W/m-°C)
Non-structural physical properties of masonry
Published in Peter Domone, John Illston, Construction Materials, 2018
The rate of heat flow through a given material is controlled by the thermal conductivity. As discussed in Chapter 7, metals generally have higher conductivities and very-low-density porous materials (containing a lot of air or other gas) have lower values. Masonry materials fall in a band between the two extremes. The property is important in that it affects the winter heat loss from a building through the walls and thus the energy efficiency of the structure. Surprisingly, although it is often of lower density and quite porous, normal bedding mortar is frequently a poorer insulator than many bricks and blocks, as shown by Fig. 36.1. This has led to the development of insulating mortars containing low-density aggregate particles and thin-joint mortar. The latter type reduces heat loss because of its much smaller area proportion of the wall face. Because porosity is a key parameter the thermal conductivity (k) is bound to be partially related to material density, and general equations for dry solid porous building materials tend to be a function of density (ρ) with regression equations of the form: k=0.0536+0.000213ρ−0.0000002ρ2
Mechanical and thermo-chemical degradation of concrete exposed to simulated airfield conditions
Published in Road Materials and Pavement Design, 2023
Muhammad Monowar Hossain, Md Kamrul Hassan, Sukanta Kumer Shill, Safat Al-Deen
At ambient temperature, the thermal conductivity of concrete was found to be in the range of 1.4–3.6 W/m K and changes with an increase/decrease in temperature (Kodur & Sultan, 2003). Figure 12(a) shows the thermal conductivity of mortar and original PCC subjected to elevated temperature only and simultaneously exposed to HC fluids and high temperature. Thermal conductivity was measured using the following equation: where Q = rate of heat flow, A = area through which the heat flow, Q = heat flux, λ = thermal conductivity of the sample, ΔT = temperature difference across the sample, Δx = thickness of the sample.