Pool boiling on horizontal tube, evaluation of ten correlations

The heat transfer coefficient during the pool boiling on the outside of a horizontal tube can be predicted by correlations. Our choice was based on ten correlations known from the literature. The experimental data were recovered from the recent work, for different fluids used. An evaluation was made of agreement between each of the correlations and the experimental data. The results of the present study firstly showed a good reliability for the correlations of Labuntsov [10], Stephan and Abdeslam [11] with deviations of 20% and 27%, respectively. Also, the results revealed acceptable agreements for the correlations of Kruzhlin [6], Mc Nelly [7] and Touhami [15] with deviations of 26%, 29% and 29% respectively. The remaining correlations showed very high deviations from the experimental data. Finally, improvements have been made in the correlations of Shekriladze [12] and Mostinski [9], and a new correlation was proposed giving convincing results

The Effect of Operating Parameters on Total Cross-membrane Flux in a PVDF Flat Sheet Membrane

Membrane distillation (MD) is an emerging thermal membrane technology that involves water vapor driven by a vapor pressure gradient over a hydrophobic membrane. MD faces several challenges, one of which is the flux of water vapor. The total cross-membrane flux in membrane distillation was investigated in this paper using the co-current PVDF flat sheet for direct contact. membrane distillation applications. The goal of this research is to improve total cross-membrane flux. The effect of various operational parameters is studied, including feed inlet temperature (333.15–358.15 K), feed flow rate (1–2.5 kg/s), permeate inlet temperature (288.15–313.15 K), and feed inlet NaCl concentration (0.035 to 0.485 kg/kg). To acquire a good value of total cross-membrane flux, their interactions with the total cross-membrane flux are studied in this work. The obtained results were computed during MATLAB-Simulations under several scenarios adopting the Trial-&-Error approach. This last inputs various parameters' values and thus draws the required curves to be discussed and analyzed. The results indicated that the PVDF flat sheet membranes provide a significantly higher total cross-membrane flux at higher feed input temperatures, producing a 73.2075 kg/(m2 h) at a feed inlet temperature of 358.15 K, a permeate inlet temperature of 293.15 K, and a flow rate of 2.5 kg/s, with a feed inlet NaCl concentration of 0.035 kg/kg. Feed inlet temperature significantly affected the total flux through the membrane; however, flow rate, permeate inlet temperature, and feed inlet NaCl concentration had a less significant effect

Survey on the nucleate pool boiling of hydrogen and its limits

Nucleate pool boiling is a very efficient transfer regime with low temperature gradients, bounded between two heat flux values and which border transitions to other regimes, this phenomenon is well framed with correlations. Our study aims to clarify the applicability of this regime to liquid hydrogen and to develop reliable correlations for a useful and qualitative agreement. An exhaustive review on the nucleate pool boiling of hydrogen and the limits of this regime, whether are the onset nucleate boiling (ONB) and the critical heat flux (CHF) was made, allowing the collection of more than 1400 points from experimental setups, highlighting a variety of parameters. Five predictive correlations were drawn from the literature, graphical and statistical comparisons were made, two in five reveal acceptable results. After analysis of the experimental data, new correlations were developed and compared with the data collected, convincing results were obtained and discussed. A simple form was expressed for the heat flux (…) = 550 . , shows better predicted values; convincing results of the (CHF) have been found on modified correlation, and the CHF value reaches a maximum of 148×103 W/m² for a reduced pressure at 0.35. A nucleate boiling correlation suitable for hydrogen has been developed

Effect of Thermal Barriers on the Martensitic Transformation in a Bar Jominy

The shape and geometry of a part influence the cooling behavior during a martensitic transformation; an experimental study carried out on a control Jominy bar was compared with other bars fitted with one, two, and three slots; the results show differences in hardness along the specimen, the hardness with a slit and more is greater than the hardness on a sample without a slit, this is valid on the cooled side of the specimen, the further away from the side cooled plus the difference is minimal; the study was completed with a simulation on bars with and without slits, the results of the temperature contours show an acceleration of the cooling on the cooled side of the bars provided with slits; far from the cooled face the influence of the slits is weak

Investigations on pool boiling of refrigerant R141b outside a horizontal tube

Boiling produces vapor with a phase change by absorbing a consistent amount of heat. Experimentation and modeling can help us better understand this phenomenon. The present study is focused on the heat transfer during the nucleate pool boiling of refrigerant R141b on the surface of a horizontal copper tube. The results of the experiment were compared with four correlations drawn from the literature, and the critical heat flux was examined for different pressures and also compared with the predicted values. Simulating boiling with two-phase models allowed us to infer the plot of the temperature distribution around the tube and compared it to results from other work

New analysis of experimental data of the hydrodynamic liquid film around jet zone on horizontal plate

Optimization of cooling systems is of major importance due to the economy of cooling water and energy in thermal installations in the industry. The hydrodynamic study of the film is a prerequisite for the study of the intensity of the heat transfer during the cooling of a horizontal plate by a liquid film. This experimental work made it possible to quantify the hydrodynamic parameters by a new approach, a relation linking the thickness of the film to the velocity was found as a function of the geometrical and hydrodynamic characteristics of the sprayer. A new statistical approach has been developed for the measurement of the velocity, the liquid fluid arriving at the edge of the plate and having velocity V is spilled out like a projectile. The recovering of the liquid in tubes allowed us to quantify flow rates for different heights positions relative to the plate, statistical processing permitted us to assess the probable velocity with a margin of error