Analytical Study of Heat Transfer When Heating or Cooling a Limited Volume of Liquid

The paper shows the results of analytical studies of heat transfer when heating or cooling a limited volume of liquid. The purpose of the research was to determine the size of the heat transfer surface, with the initial parameters of the coolants, the final temperature in the reactor and its thermal equivalent, as well as the flow rate of the second coolant through the heat exchanger corresponding to the water equivalent at a given cooling time τo. Moreover, if intensive mixing is carried out in the vessel, i.e., if the temperature of the second heat carrier practically does not change along the length of the heat transfer surface, then W2 → ∞. The solution was based on the Laplace --- Carson integral transform. The exact solution was converted for special cases of heat transfer. In particular, it should be noted that in many practical cases formulas give a fairly good approximation to the exact solution. Only at low values of the heat transfer coefficient, as well as when the volume occupied by the coolant inside the heat exchanger is commensurate with the volume of the liquid contained in the vessel, it is necessary to apply the given exact solution

Variations of nanoparticle layer properties during nucleate pool boiling

The nanoparticle layer detachment during nucleate pool boiling and its influences on heat transfer surface properties were explored experimentally. The material of the heat transfer surface was copper and the nanoparticle layer was formed on the heat transfer surface by nucleate boiling in the water-based TiO2 nanofluid. It was found that the detachment of the nanoparticle layer during nucleate boiling in pure water is significant. In the present experiment, more than half of nanoparticles deposited on the heated surface were detached before the CHF condition was reached. The thickness and roughness decreased accordingly. However, the wettability and wickability that are the influential parameters on the CHF value were maintained even after the occurrence of nanoparticle layer detachment and deteriorated only after the CHF condition was reached. It is therefore considered that the onset of CHF brings qualitative change to the capillary suction performance of the layer of nanoparticles. In exploring the effect of the nanoparticle layer properties on the nucleate boiling heat transfer, sufficient attention should be paid to the variation of the nanoparticle layer properties during nucleate boiling.

The influence of anionic surfactant in water on the quenching process

Understanding the patterns of heat transfer during quenching is important for many technical applications. Of particular interest is the boiling regime, which is characterized by high intensity and occurs at surface temperatures exceeding the temperature of attainable liquid superheat. This work is aimed at studying the effect of surfactants on the onset of intense heat transfer during quenching. For this, experiments were carried out on quenching spheres made of different metals (nickel, stainless steel and zirconium) in water with different concentrations of surfactants. The surfactant was alkylbenzene sulfonate, the concentration of which varied from 0.1 to 2%. The analysis of the obtained cooling thermograms revealed the influence of not only the surfactant concentration on the beginning of the intensive cooling mode, but also the state of the heat transfer surface.

CFD Numerical Investigation of a New Solar Flat Air-Collector Having Different Obstacles with Various Configurations and Arrangements

This work deals with a numerical parametric optimization study of a new Solar Flat Air Collector (SFAC) configuration. The CFD numerical parametric study investigates various SFAC structures inside the air cavity without obstacles and with spherical, cubic, cylindrical, and pyramidal obstacles. The study optimizes the most convenient configuration and arrangement that allow for the increase of the heat-transfer surface and to make the flow homogeneous in order to generate turbulence zones inside the SFAC air cavity. The result shows that the thermal performances of the cubic form are close to those of the spherical obstacles. Another set of simulations was performed to evaluate the performances of the cubic shape baffles for three orientation angles equal to 0°, 22.5°, and 45°, respectively. Each configuration has three forms of arrangement with a relative roughness pitch (b/a) varying between 2, 4, and 6. The results of the simulation study showed that the relative roughness pitch, the Reynolds number, as well as the angle of orientation influence the performance and the operation of the SFAC. The results of the simulations showed that the combination of an orientation of 45° with a roughness pitch of b/a = 2 increases the SFAC thermal performances, which can reach 85%.

Failure Analysis of Heat Exchangers

Heat exchangers are devices used to transfer thermal energy between two or more fluids, between a solid surface and a fluid, or between a solid particulate and a fluid at different temperatures. This article first addresses the causes of failures in heat exchangers. It then provides a description of heat-transfer surface area, discussing the design of the tubular heat exchanger. Next, the article discusses the processes involved in the examination of failed parts. Finally, it describes the most important types of corrosion, including uniform, galvanic, pitting, stress, and erosion corrosion.

ANALYSIS OF HEAT TRANSFER MECHANISMS IN THE SOLIDIFICATION OF PCM WITH DIFFERENT PASSIVE ENHANCEMENT TECHNIQUES FOR FREE COOLING APPLICATIONS

The continuous increase in the level of green-house gas emissions and the depletion of fossil fuels are identified as the major driving forces behind efforts to effectively utilize different sources of renewable energy. Free cooling concept is gaining importance in building cooling applications. The medium which is used to store energy is Phase Change Material. Among the phase change materials available commercial PCM is of great use. The only drawback with the PCM is its thermal conductivity is very low. Various heat-transfer enhancement techniques between the phase change material (PCM) and the heat transfer fluid (HTF) were tried by researchers. Passive enhancement techniques are very simple and gives good heat transfer enhancement which decreases the solidification time and increases the solidification rate. In the present work two types of passive enhancement techniques like increasing the roughness of the heat transfer surface and dimples over the heat transfer surface were tried and it has been observed that the dimpled surface will provide better results compared to rough surface over normal surface. Overall there is decrease in solidification time of 37 min. and increase in solidification rate of 19.37% with dimpled surface over normal surface.

Comparison between Heat Pipes based condenser and Conventional condenser of Power Plant

This paper explores the feasibility of using heat pipes for steam condensation and heat pipe based condenser. The concept of heat pipes for steam condensation is newly proposed and studied herewith. . CFD analysis and Experimental studies carried on the single heat pipe for steam condensation. Experimental setup and results of heat pipes based steam condenser presented. Properties like Effectiveness, heat transfer surface area, exergy analysis for the conventional condenser made of simple copper tubes and heat pipe based condenser are compared