Category: Introduction To Heat Transfer

To increase the necessary surface area with a simple tube and annulus arrangement, the length of the tube may be too large for practical purposes. In order to make the heat exchanger more compact, which is desirable from space considerations, and also to reduce the heat loss from the outside surface, it is necessary to… Continue reading Multi-pass and Mixed Flow Recuperators

A simple cross flow recuperator is shown in Figure 7.12. The calculation of the mean temperature difference is much more difficult in this case. Θm depends on the ratio of the product of the mass flow and specific heat of fluids A and B, as well as on the ratio of the temperature difference between the fluids at… Continue reading Cross flow Recuperator

Consider the case of a fluid flowing through a pipe and exchanging heat with a second fluid flowing through an annulus surrounding the pipe. When the fluids flow in the same direction along the pipe the system is known as parallel flow, and when the fluids flow in opposite directions to each other the system… Continue reading Parallel and Counter Flow Heat Exchangers

Heat exchanger is used to exchange the heat from one fluid to another. In heat exchangers the temperature of each fluid changes as it passes through the exchanger, and hence the temperature of the dividing wall between the fluids also changes along the length of exchanger. Heat exchangers have many applications in engineering such as… Continue reading HEAT EXCHANGER

Consider a hollow sphere of internal radius r1 and external radius r2 as shown in Figure 7.8. Let the inside and outside surface temperature be t1 and t2; and let the thermal conductivity be k. Consider a small element of thickness dr at any radius r. It can be shown that the surface area of this spherical element is given by 4πr2. The heat transfer rate Figure 7.8 Heat… Continue reading Heat Transfer Through Sphere

Consider a cylinder of internal radius r1 and external radius r2 as shown in Figure 7.7. Let the inside and outside temperatures be t1 and t2, respectively. Consider the heat flow through a small element of thickness dr at any radius r, where the temperature is t. Let the thermal conductivity of the material be k, temperature of fluid flow inside the cylinder be tf1, heat transfer coefficient be hf1, temperature… Continue reading Heat Transfer Through Hollow Cylinder

Plane Walls with Convection on Sides There are many cases in practice when different materials are constructed in layers to form a composite wall. This wall may be composed of plaster layer, brick layer, tiles layer, etc. as shown in Figure 7.3. In Figure 7.3 there are three layers A, B, C, of thickness LA, LB, and LC, respectively. The thermal… Continue reading Combined Heat Transfer

The law states that the rate of radiation heat transfer per unit area from a black surface is directly proportional to fourth power of the absolute temperature of the surface and is given by, where Ts is absolute temperature in K; and σ is proportionality constant and called as Stefan–Boltzman constant equal to 5.67 × 10− 8 W/m2K4. The heat… Continue reading Stefan–Boltzmann Law of Thermal Radiation

The law states that the rate of radiation heat transfer per unit area from a black surface is directly proportional to fourth power of the absolute temperature of the surface and is given by, where Ts is absolute temperature in K; and σ is proportionality constant and called as Stefan–Boltzman constant equal to 5.67 × 10− 8 W/m2K4. The heat… Continue reading Stefan–Boltzmann Law of Thermal Radiation

All matter continuously radiates electromagnetic radiation unless its temperature is absolute zero. It is observed that the higher the temperature then the greater amount of energy is radiated. If two bodies at different temperatures are so placed that the radiation from each body is intercepted by the other, then the body at the lower temperature… Continue reading Radiation