In this paper, an exact analytical solution for forced convective heat transfer of nonlinear viscoelastic fluid in isothermal circular micro-channel is presented. The nonlinear Giesekus constitutive equation is used to model the Giesekus fluid heat transfer in micro-channel with constant wall temperature, which is the main innovative aspect of the current study. This constitutive equation is a powerful tool and able to model the fractional viscometric functions, extensional viscosity, and elastic property. The solution of temperature profile and Nusselt number is obtained based on the Frobenius method. The effects of Weissenberg number, mobility factor, slip coefficient, and Navier index on temperature distribution, velocity profile, and Nusselt number are investigated in detail. The results show that the increases in both slip coefficient and Navier index cause the increases in slip velocity and maximum dimensionless temperature at the wall and the micro-channel center, respectively. Moreover, the Nusselt number has an upward trend with increases in slip coefficient and Navier index parameters. The results are indicated that the flow and temperature fields have a complex relation with mobility factor which controls the level of the nonlinearity of the Giesekus model. Additionally, three correlations for Nusselt number of Giesekus flow in micro-channel are presented.

Heat transfer to flowing gas–solid mixtures in pipes is required in many applications including chemical processing, pneumatic transport, and nuclear reactors but no well-verified method for predicting heat transfer is available. A new correlation is presented, which has been validated with a wide range of data that includes a variety of particles (minerals, metals) in several gases. Particle diameters range from 13 to 1130 µm, pipe diameters 5.1 to 77 mm, and the solids loading ratio of 0–520. Flow orientations include horizontal, vertical up, and vertical down. The new correlation has a mean absolute deviation (MAD) of 18.9% with 630 data points from 20 studies. The same data were also compared with six published correlations. Their MAD ranged from 35% to 57%. Hence, the new correlation is likely to help in more accurate design.

In ground air heat exchanger (GAHE) system, the heat transfer between air and underground soil largely depends on soil thermal properties and therefore, any improvement in soil thermal properties will shorten the pipe length required and the land area needed for its installation. The objective of the present study is to investigate the effect of different backfilling materials (low cost and locally available) on the thermal performance of GAHE system using a small-scale laboratory experimental setup. Seven different backfilling materials have been considered for the study and it was observed that after 6 h of continuous operation, the drop in air temperature was 6.2 °C at outlet section of pipe (2.4 m away from inlet) for the native soil. However, for sand–bentonite with graphite as a backfilling material (BFM), the drop in air temperature of 6.2 °C was obtained at a pipe length of 1.15 m only. Therefore, the use of sand–bentonite with graphite as a BFM reduces the pipe length of GAHE system by more than 50%. The study establishes the fact that the length of pipe and land area requirement for GAHE system can be substantially reduced by using thermally enhanced backfilling materials at the close vicinity of GAHE pipes.

The heat exchanger is a device in which heat transfer takes place between two fluids at different temperatures. Among various classifications of heat exchangers, parallel and counter flow types are used widely in many industrial applications. This paper presents two fuzzy logic expert systems (FLES's), one for parallel and another for counter flow double pipe heat exchanger (DPHE). Such FLES's are capable of predicting the exit temperature of heat carrier fluids and its effectiveness in an accurate manner. In total, 96 sets of experiments have conducted for parallel and counter flow under different combinations of mass flow rate. The performance accuracy of the fuzzy logic expert system is measured by comparing fuzzy predicted results with experimental data sets. Such a comparison indicates a good agreement between experimental data sets and fuzzy predicted results. The accuracy of the parallel flow FLES in predicting exit temperature and effectiveness is 92.78% and 95%. The accuracy of the counter flow FLES in predicting exit temperature and effectiveness is 94.28% and 95.5%.

Different-radius of curvature pipes are experimentally investigated using distilled water and Fe 3 O 4 –water nanofluid with two different values of the nanoparticle volume fraction as the working fluids. The mass flow rate is approximately varied from 0.2 to 0.7 kg/min (in the range of laminar flow); the wall heat flux is nearly kept constant. The experimental results reveal that utilizing the nanofluid increases the convection heat transfer coefficient and Nusselt number in comparison to water; these outcomes are also observed when the radius of curvature is decreased and/or the mass flow rate is increased (equivalently, a rise in Dean number). The resultant pressure gradient is, however, intensified by an increase in the volume concentration of nanoparticles and/or by a rise in Dean number. For any particular working fluid, there is an optimum mass flow rate, which maximizes the system efficiency. The overall efficiency can be introduced to include hydrodynamic as well as thermal characteristics of nanofluids in various geometrical conditions. For each radius of curvature, the same overall efficiency may be achieved for two magnitudes of nanofluid volume concentration.

Earth air tunnel heat exchanger (EATHE) is a capable and quite simple passive technique which may be utilized for space cooling/heating using the constant temperature of underground subsoil. However, it could not gain much attraction as a heating/cooling system as it requires larger trench lengths to accommodate longer pipes. Larger trench lengths involve huge excavation cost and a sufficiently large piece of land. The length of the trench needed can be reduced substantially by adopting a proper pipe layout. In the present study, the performance of U-shaped, slinky-coil, and helical-coil pipe layouts of an EATHE system is compared numerically using ANSYS FLUENT 15.0. Results reveal that the temperature drop and heat transfer rate per unit trench length are higher in the slinky-coil pipe layout than in U-shaped and helical-coil pipe layouts. After 12 h of continuous operation, the effectiveness of the EATHE system with U-shaped, slinky-coil, and helical-coil pipe layouts is obtained as 0.60, 0.80, and 0.78, respectively. The study reveals that the selection of pipe layout for the EATHE system mainly depends on temperature drop EATHE is capable of giving, heat transfer rate, pumping power required, and ease of fabrication and installation as all these factors directly affect the initial and recurring capital investment for the EATHE system.

This technical paper presents results of an air-cooled supercritical CO 2 (sCO 2 ) finned-tube sink heat exchanger (HX) performance test comprising wide range of variable parameters (26–166 °C, 7–10 MPa, 0.1–0.32 kg/s). The measurement covered both supercritical and subcritical pressures including transition of pseudocritical region in the last stages of the sink HX. The test was performed in a newly built sCO 2 experimental loop which was constructed within Sustainable Energy (SUSEN) project at Research Centre Rez (CVR). The experimental setup along with the boundary conditions are described in detail; hence, the gained data set can be used for benchmarking of system thermal hydraulic codes. Such benchmarking was performed on the open source Modelica-based code ClaRa. Both steady-state and transient thermal hydraulic analyses were performed using the simulation environment DYMOLA 2018 on a state of the art PC. The results of calculated averaged overall heat transfer coefficients (using Gnielinski correlation for sCO 2 and IPPE or VDI for the air) and experimentally determined values shows reasonably low error of + 25% and – 10%. Hence, using the correlations for the estimation of the heat transfer in the sink HX with a similar design and similar conditions gives a fair error and thus is recommended.

The gradient porous materials (GPMs)-filled pipe structure has been proved to be effective in improving the heat transfer ability and reducing pressure drop of fluid. A GPMs-filled pipe structure in which radial pore-size gradient increased nonlinearly has been proposed. The field synergy theory and tradeoff analysis on the efficiency of integrated heat transfer has been accomplished based on performance evaluation criteria (PEC). It was found that the ability of heat transfer was enhanced considerably, based on the pipe structure, in which the pore-size of porous materials increased as a parabolic opening up. The flow resistance was the lowest and the integrated heat transfer performance was the highest when radial pore-size gradient increasing as a parabolic opening down.

The demand for plastic is eternally growing in urban areas and producing enormous quantity of plastic waste. The management and disposal of plastic waste have become a major concern worldwide. The awareness of waste to energy retrieval is one of the promising modes used for the treatment of the waste plastic. The present investigation evaluates the prospective use of waste plastic oil (WPO) as an alternative fuel for diesel engine. Different blends (WPO0, WPO30, and WPO50) with diesel are prepared on a volume basis and the engine is operated. Experiments are conducted for various injection timings (9 deg, 12 deg, 15 deg, and 18 deg BTDC) and for different exhaust gas recirculation (EGR) rates (0%, 10%, 15%, and 20%) at 100 MPa injection pressure. Combustion, performance, and tail pipe emissions of common rail direct injection (CRDI) engine are studied. The NO x , CO, and Soot emissions for waste plastic oil-diesel blends are found more than neat diesel. To reduce the NO x , EGR is employed, which results in reduction of NO x considerably, whereas other emissions, i.e., CO and Soot, get increased with increase in EGR rates. Soot for WPO-diesel blends is higher because of aromatic compounds present in plastic oils. Brake thermal efficiency (BTE) of blends is found to be higher compared to diesel.

Paint-based protective films (PPFs) are used to protect condenser tubes from corrosion and erosion but have been shown to be susceptible to biofouling. Here, the biocidal properties of copper-oxide fillers incorporated into PPFs are explored in this paper. Specifically, two PPFs filled with 20% and 50% filler (by weight) are tested in parallel with a nonbiocidal ordinary epoxy PPF, and bare stainless steel tube. Using double-pipe co-current flow heat exchangers installed at a thermal power plant, actual cooling water exiting the condenser is evenly distributed between the test tubes. Heat transfer in the condenser is simulated by heated water flowing through each annulus of the double-pipe heat exchangers, thereby maintaining repeatable outer convection conditions. An exposure test of 125 days shows that the 50% biocide-filled PPF has the lowest fouling factor of all the tubes. The nonbiocidal epoxy has the highest fouling factor and the 20% filled PPF behaves similarly. Both of these are greater than the bare stainless steel control tube. The 50% filled PPF is compared to the fouling of an existing admiralty brass tube and the shapes of the fouling curves are similar. This evidence suggests that provided the filler concentration is sufficiently high, there is the potential for the copper-oxide filler to reduce the asymptotic composite fouling factor by virtue of its antibacterial properties.

A clamp-on measurement system for flexible and accurate fluid temperature measurements for turbulent flows with Reynolds numbers higher than 30,000 is presented in this paper. This noninvasive system can be deployed without interference with the fluid flow while delivering the high accuracies necessary for performance and acceptance testing for power plants in terms of measurement accuracy and position. The system is experimentally validated in the fluid flow of a solar thermal parabolic trough collector test bench, equipped with built-in sensors as reference. Its applicability under industrial conditions is demonstrated at the 50 MW el AndaSol-3 parabolic trough solar power plant in Spain. A function based on large experimental data correcting the temperature gradient between the measured clamp-on sensor and actual fluid temperature is developed, achieving an uncertainty below ±0.7 K (2 σ ) for fluid temperatures up to 400 °C. In addition, the experimental results are used to validate a numerical model. Based on the results of this model, a general dimensionless correction function for a wider range of application scenarios is derived. The clamp-on system, together with the dimensionless correction function, supports numerous combinations of fluids, pipe materials, insulations, geometries, and operation conditions and should be useful in a variety of industrial applications of the power and chemical industry where temporal noninvasive fluid temperature measurement is needed with good accuracy. The comparison of the general dimensionless correction function with measurement data indicates a measurement uncertainty below 1 K (2 σ ).

In the production process of large-diameter seamless steel pipes, the blank heating quality before roll piercing has an important effect on whether subsequently conforming piping is produced. Obtaining accurate pipe blank heating temperature fields is the basis for establishing and optimizing a seamless pipe heating schedule. In this paper, the thermal process in a regenerative heating furnace was studied using fluent software, and the distribution laws of the flow field in the furnace and of the temperature field around the pipe blanks were obtained and verified experimentally. The heating furnace for pipe blanks was analyzed from multiple perspectives, including overall flow field, flow fields at different cross sections, and overall temperature field. It was found that the changeover process of the regenerative heating furnace caused the temperature in the upper part of the furnace to fluctuate. Under the pipe blanks, the gas flow was relatively thin, and the flow velocity was relatively low, facilitating the formation of a viscous turbulent layer and thereby inhibiting heat exchange around the pipe blanks. The mutual interference between the gas flow from burners and the return gas from the furnace tail flue led to different flow velocity directions at different positions, and such interference was relatively evident in the middle part of the furnace. A temperature “layering” phenomenon occurred between the upper and lower parts of the pipe blanks. The study in this paper has some significant usefulness for in-depth exploration of the characteristics of regenerative heating furnaces for steel pipes.

In this paper, from the heat transfer mechanisms between perforated horizontal well and formation, the mathematical models for the heat transfer and pressure drops of the horizontal well with different steam injection pipe configurations are developed. All the conventional single-pipe, concentric dual-pipe, and parallel dual-pipe configurations are considered. A correlation is proposed to represent a relationship between the thermophysical properties of the formation and the formation pressure and temperature. Then, using the method of wellbore microcontrol elements and node analysis, the steam injection process in the three different well configurations is numerically investigated. Based on the test data of a parallel dual-pipe horizontal well from an actual oilfield, a steam backflow procedure for the parallel dual-pipe configuration is proposed to confirm the sealed status of a thermal packer. The theoretical investigation plays an important role in the performance evaluation and productivity prediction of horizontal well-based thermal recovery projects. Furthermore, it also sheds some important insights on a steam injection project design with dual-pipe horizontal wells.

Earth air tunnel heat exchanger is a passive cooling device with advantageous feature to reduce energy consumption in buildings. Curtailing the electricity consumption of conventional vapor compression system based air-conditioner is a major concern especially in area with hot and dry weather conditions. The performance of conventional air-conditioners can substantially be enhanced by coupling these active cooling systems with passive cooling systems. In the present research, the thermal performance and energy conservation potential of hybrid cooling system has been investigated experimentally. An attempt has been made to enhance the thermal performance of active cooling system by coupling it with earth air tunnel heat exchanger (EATHE) in two different hybrid modes. The air which comes out of EATHE is relatively cooler than the ambient air and therefore can be used either for cooling the condenser tubes of a conventional window type air-conditioner or supplying it directly to the room being conditioned. The energy consumption of conventional 1.5TR window type air conditioner is found to be reduced by 16.11% when cold air from EATHE is completely used for condenser cooling.

A new 2D numerical model of a single U-tube ground heat exchanger is proposed and a four-thermal-resistance model is adopted to evaluate the effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances. The influence of temperature distributions on both borehole surface and outer diameter of two pipes to these thermal resistances has been thoroughly studied. The best-fit correlations of effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances are proposed and compared with the available equations in the literature. It is found that the present correlations of thermal resistances for ground heat exchanger are more accurate than those of available formulas. Furthermore, based on these obtained thermal resistance correlations, an analytical model is proposed to evaluate the heat transfer performance of the ground heat changer.

Several options exist to collect thermal energy from the sun for domestic use. This study examines a system integrating evacuated tube collectors with heat pipes with a storage unit using melted paraffin wax to store thermal energy. A shell-and-tube heat exchanger is embedded within the paraffin wax storage with a volume of 0.23 m 3 . The heat exchanger includes two loops: one for glycol to transfer heat to the paraffin and one for water to extract heat from the melted paraffin. Although the paraffin has the benefit of being inexpensive and nontoxic, it has low thermal conductivity. Therefore, the heat exchanger has large brazed copper fins to extend areas of high thermal conductivity into the wax reservoir. To determine the benefit of the fins, wax and working fluid temperature data are taken from a constructed thermal energy storage unit and then used to verify a finite-difference one-dimensional analytical model of the unit. The maximum operating temperature of the glycol/water mix heat transfer fluid was approximately 65 °C when the fluid flowed at 3.78 l/min. City water at approximately 11.34 l/min was used to test the water heating capabilities of the unit. The one dimensional model proved useful in predicting the heat storage mode of the system. Due to its form, which was specifically developed for the unit in the study, the model could be adjusted to calculate thermal performance of similarly constructed thermal storage units.

Stationary spiral inserts can effectively enhance heat transfer and temperature blending in the heat convection systems. In this paper, the impact of the segment length on the performance of a stationary insert is studied for flow Re numbers from ∼ 80 to ∼ 7900 through numerical simulation of heat transfer in streams of cold and hot gases flowing across it. The segment length to width ratio is from 1.11 to 2.33. The temperature of the studied gas is from 300 K to 1300 K. It is shown that the insert with variable segment length is more effective in temperature blending for two compressible streams compared with an insert with constant segment length, especially for low-Re-number turbulent flows.

Enhancement of the natural and forced convection heat transfer has been the subject of numerous academic and industrial studies. Air blenders, mechanical agitators, and static mixers have been developed to increase the forced convection heat transfer rate in compressible and incompressible flows. Stationary inserts can be efficiently employed as heat transfer enhancement devices in natural and mixed convection systems with compressible flow. These devices have low maintenance and operating costs, low space requirements, and no moving parts. Through numerical studies, this paper demonstrates how an insert improves heat transfer in buoyancy driven flow. The numerical predictions are validated using experimental data. Using different measurement tools, the global performance of the insert and the impact of the geometrical parameters are studied, leading to identification of the most effective design for a given application.