A Convenient Method for the Accurate Calculation of Fin Efficiency of H-Type Fins Based on Linear Nomograms and Fitting Formulae

Fin efficiency, as a measure of the effectiveness of the heat transfer enhancement, is of great importance in studying the heat transfer performance of H-type finned tube banks. The fin efficiency of square fins is adopted by most researchers as an alternative to that of H-type fins, which can create certain errors in the fin efficiency of H-type fins. For this paper, the linear nomograms and fitting formulae of fin efficiency of H-type fins are obtained by the definition method of fin efficiency based on numerous numerical simulations, and the results calculated by this method are verified by experimental data. On this basis, the effects of three geometric parameters (slit width, fin height, and fin thickness) and two thermal parameters (surface heat transfer coefficient and fin thermal conductivity) on the fin efficiency of H-type fins are also investigated and compared to those of square fins. The results indicate that the fin efficiency of H-type fins increases with the increment of fin thickness and thermal conductivity, and decreases with the increase of slit width, fin height, and surface heat transfer coefficient. Accordingly, the linear nomograms and fitting formulae for the fin efficiency of H-type fins, which are well compatible with experimental data, can help to facilitate further theoretical research and engineering application.

Thermal behavior of a flat-plate direct absorption with water-nanohorn mixture

A numerical analysis on a two-dimensional steady state forced convection inside a solar collector with direct absorption due to a nanofluid composed of water and nanoparticles of carbon nanohorns is carried out. The analysis allows to provide the main fluid flow and thermal characteristics of a simple flat solar collector with a distance between the glass and the collecting plate of 1.2 mm and a length of 1.0 m. The solar collector presents heat losses from the upper wall towards the ambient by an external surface heat transfer coefficient. The governing flow equations for the nanofluid are written assuming the single-phase flow and the heat transfer due to the radiation, for the local absorption of nanoparticles, is evaluated by the non-grey discrete ordinates method. The carbon nanohorns optical and thermal properties are estimated by the data available in literature. The finite volume method is used to solve the problem and the results are carried out employing the ANSYS-FLUENT code. The results are given in terms of temperature and velocity fields and transversal profiles inside the channel for different values of mass flow rates, solar irradiance, volumetric nanoparticle concentrations and assigned values of external surface heat transfer coefficient and temperature.

Laboratory observation of interior surface heat transfer at balcony door

This paper informs about laboratory experiments studying heat transfer phenomena at the interior side of balcony doors. A well-insulated testing space representing a typical room with a balcony door equipped with floor heating and warm air heating was used. In the first step, an opaque panel with similar thermal transmittance as a triple glazed balcony door was installed in the opening for reference. A combination of temperature measurements and particle imaging velocimetry (PIV) was used here to study the surface heat transfer in detail for both types of space heat distribution and obstacles by curtains. From the measured data, the surface heat transfer coefficient along the height of the door was evaluated and discussed.

Quality Dahi Preparation in Automated Controlled Ambient Conditions

This automated controlled system eliminates the need of two separate places for incubation of the curd at higher temperature in the range of 39 to 43°C and then shifting the set curd cups into cold rooms for storage purpose and kept at about 4 to 5°C.The transient cooling process of dahi, set in cups and also in steel containers placed in cold air flow was conducted in this experimental study. Recording of the temperature of dahi-cups and of the supplied air were done at regular intervals until the temperature reached below 4°C to 5°C. The exponential curves of cooling by forced convection process for the dimensionless temperature of curd were obtained for the trials conducted at the different velocities of cooling air flow. It was found that the surface heat transfer coefficient increased and duration of cooling decreased by increasing the air velocities from 0.5 m/s by evaluating the Biot number and surface heat transfer coefficient. In the initial period of cooling this pattern was more effective and reduced for higher velocities of air from 3.5 to 4.5 m/s. The method of incubation and storing dahi-cups at the same place and changing the ambient temperature of the whole environment instead of changing the place of dahi-cups for cooling purpose have been applied in this research work to control the problem of whey-off in set-curd.

A Combined Experimental and Numerical Characterization of the Flowfield and Heat Transfer Around a Multiperforated Plate With Compound Angle Injection

The aerodynamic and thermal behaviour of multiperforated zones in combustors is essential to the development of future combustion chambers. Detailed databases are therefore essential for the validation of RANS/LES solvers, but also regarding the derivation of heat transfer correlations used in 0D/1D in-house codes developed by engine manufacturers. In the framework of FP7 EU SOPRANO Program, the test-rig used in a previous study is modified to be compatible with anisothermal conditions. The plate studied is a 12:1 model with a 90° compound angle injection. A heating system is used to generate a moderate temperature gradient of about 20 K between the secondary hot flow and the main cold flow. The aerodynamic field is acquired by a PIV 2D-3C (Particle Image Velocimetry) system. The surface heat transfer coefficient is derived based on surface temperature distribution acquisitions. Several heating power levels are tested, which allows to evaluate the convective heat transfer coefficient and reference temperature through a linear regression. Measurements are conducted on both sides of the plate, which also gives access to those quantities on the injection/suction sides. From a numerical point of view, the configuration is studied using the unstructured ONERA in-house CEDRE solver. A systematic comparison is presented between the experimental and numerical database.

Heat Transfer Parameterization towards Enhancing Shelf Life of Vegetables in Low Cost Cold Chain with FACCC

India is the second-largest vegetable producing country after China. It is observed that there is a huge loss of vegetables due to the lack of low-cost cold chain for its storage & transportation after harvesting from agriculture land to vegetable market. The shelf life of these vegetables is less due to poor temperature control during transportation and storage. If vegetables are not maintained at their prudent temperature, then they will lose their potency, which will lead to enormous economic loss. Therefore, it is observed that temperature control of vegetables and their heat transfer characteristics are a major factor to maintain potency and increase their shelf life. This paper proposed a low-cost design of FACCC for temperature control of vegetables during transportation and storage with the help of Chillers. Further, the effect of air velocity on heat transfer rate and Nusselt number of various vegetables was evaluated to predict the performance of FACCC for enhancing the shelf life of vegetables.Thermophysical characteristics of these vegetables have been calculated at different air flow rate with the help of Reynolds analogy as a function of Stanton Number, Reynold’s Number and Prandtl Number.The airflow rate was maintained between 0.2065 m/s - 0.413 m/s inside FACCC. Experimental study reveals that the average Nusselt Number of these vegetables lies in the range of 57.9 - 115.74 and the range of Surface heat transfer coefficient is 54.48-108.96 W/m2K. Validation of FACCC performance has been done by comparing the heat transfer rate and Nusselt number from published literature. These results are obtained by temperature control of vegetables by varying air flow rate through four fans fitted inside FACCC. It results in higher shelf life due to favourable maintenance of thermodynamic parameters such as surface heat transfer coefficient, Nusselt number, Reynold number and preferable temperature for specific commodities.Thus, the proposed FACCC model can be an effective tool for enhancement of low-cost cold chain for vegetables in future.

Numerical Simulation Analysis of Unsteady Temperature in Thermal Insulation Supporting Roadway

High geothermal hazard is a basic problem that must be solved in deep mining; thereby the research on thermal insulation supporting for high temperature control of deep roadway is increasing. However, the quantitative analysis of its thermal insulation effect is yet to be carried out. By building the physical model and control equations of the thermal insulation supporting roadway and considering heat-humidity transfer at wall, the temperature field distribution of surrounding rock and airflow is numerically calculated. Based on numerical simulation results, the evolution law of temperature with ventilation time is analyzed at airflow inlet, outlet, and different sections, then the variation law of surface heat transfer coefficient with position and time is obtained. For heat insulation support structure, the results show that it is not obvious to change the distribution law of temperature field, but it is effective to weaken the convection heat transfer between surrounding rock and airflow. In the main airflow area, the rate of heat exchange gradually decreases with the heat exchange becoming more and more sufficient; in boundary layer, the airflow temperature quickly transits from the wall temperature to that of the main airflow area because of intense collisions of airflow masses, so the mechanism of temperature change is different. The surface heat transfer coefficient well reflected the unstable heat-humidity transfer, especially in the beginning of ventilation or at airflow inlet. Therefore, the heat insulation supporting structure is helpful to the auxiliary cooling of high temperature mine.