Cold Fluid Flow Rate Research Articles

Energy and exergy analysis and optimization of helically grooved shell and tube heat exchangers by using Taguchi experimental design

In this paper, for improvement of the performance of shell and tube heat exchanger, the effect of adding circular grooves on the shell of heat exchanger is considered numerically. The grooves are created in different heights but with the same pitch of the coil. The obtained results consist of both qualitative and quantitative data affected by geometrical parameters. According to the numerical results, the groove increases the heat transfer rate up to 5% and does not affect the pressure drop dramatically. By use of Taguchi experimental design and exergy analysis, the performance of the heat exchanger is examined in different working conditions, such as different level of cold inlet temperature, cold fluid flow rate, and groove height (roughness value). The results of this consideration revealed that the heat exchanger thermal efficiency varies from 23 to 49% in various conditions and also both the flow rate and the inlet temperature have the same effect on the exergy losses. The optimum groove height is presented equally to 10 mm.

Experimental and numerical study on heat transfer enhancement using ultrasonic vibration in a double-pipe heat exchanger

Heat transfer enhancement of double-pipe heat exchanger in the presence of ultrasonic vibrations is experimentally and numerically studied. A novel experimental setup made of two concentric pipes is constructed and a bolted Langevin ultrasonic transducer is used for applying the ultrasonic vibrations to the inner pipe with a frequency of 26.7 kHz. The numerical simulation is carried out by OpenFOAM software to clarify the reason for heat transfer enhancement. The effects of hot and cold fluid flow rates and acoustic power on heat transfer and pressure drop are studied in this work. The performance of heat exchanger is investigated by comparing the overall heat transfer coefficient and pressure drop with and without the influence of ultrasonic vibrations. Results show that using ultrasonic vibration is more effective at low fluid flow rates. As a result, heat transfer enhances about 60% for both cold and hot fluid flow rates of 0.5 L/min, while heat transfer enhancement is equal to 20% for cold and hot fluid flow rates of 1 and 1.5 L/min, respectively, at the transmitted acoustic power of 120 W. Numerical results demonstrate that the cross-stream flows generated by propagation of ultrasonic waves into the cold fluid are responsible for heat transfer enhancement.

Irreversibility Analysis of a Recuperative Heater during Undergoing the Flowrate Impulsive Disturbance Transient Processes

The recuperative heater is widely used in the industrial production processes, and the irreversibility analysis on the heater during transients is scarce but necessary. Numerical method was adopted to model the recuperative heat exchanger to exhibit its dynamic behaviors during transient processes. The difference between the transient and stationary irreversibility can be called additional irreversibility. In this paper, the dynamic behaviors of the recuperative heater during transients are presented. With these thermal parameters, the irreversibility of a recuperative heater during hot and cold fluid flow rates impulsive disturbance transient processes was calculated and analyzed in detail. The calculation results show that: compared with steady-state corresponding value, the real-time irreversibility rate of the heater during transients is different. The total additional irreversibility values with impulsive disturbance in hot and cold fluid flow rates are obtained separately.

Experimental investigation on heat transfer in double pipe heat exchanger employing triangular fins

Various experiments were carried out for this dissertation to investigate and compare the heat transfer in a DPHE for counter flow arrangement studying with and without usage of longitudinal triangular fins. The test section is a horizontal annular passage formed by copper tube with an inner diameter 15 mm to outer diameter 19 mm with a length of 1000 mm. Triangular fin with dimensions of 9 mm base, 8 mm height and 2 mm thickness are used in the present study. In the beginning we conducted the experiment with the traditional DPHE to analyze the effectiveness parameter for plane heat exchanger and then with 4 longitudinal triangular fins with difference in spacing of fins angle 90 degrees of length 1000 mm. The effects of the fins spacing and mass flow rate of fluid is examined on the thermal performance of heat exchanger. Increase in flow rate of cold fluid results in increase of heat transfer and effectiveness increases to 0.505 in longitudinal triangular finned tube from the value 0.405 in the traditional DPHE of counter flow respectively. Another performance parameter like overall heat transfer coefficient increases and LMTD throughout the experiment decreases respectively.

Entropy generation analysis on a heat exchanger with different design and operation factors during transient processes

Entropy generation analyses on the transient processes of heat exchangers can guide their designs and operations. A dynamic model of a typical recuperative heater is developed based on mass, energy, and momentum conservation equations. Dynamic behaviors of the heater during transient processes are analyzed based on the second law of thermodynamics. The real-time entropy generation rate due to the heat transfer between the work medium and metal surfaces, and the heat conduction in metals are presented and discussed. A cold fluid flow rate with 20% step increase is adopted as the boundary disturbance, and dynamic performances are obtained. Additional entropy is generated in the heater during the transient processes compared with stationary work conditions. Several design and operation factors of the heater are discussed. Calculation results show that the additional total entropy generation diminishes during the transient processes with the increase in the thermal diffusivity of metal. This rule is also suitable for the influence of thermal transfer resistance between the fluid and metal. By contrast, the metal thickness and specific heat capacity of hot work fluid have opposite influences on the total additional entropy generation of the heater during the transient processes.

Numerical Analysis of Heat transfer Enhancement in a double pipe heat exchanger with a holed twisted tape

In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape.The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus.Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number, overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normaltwisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.

Numerical Analysis of Heat transfer Enhancement in a double pipe heat exchanger with a holed twisted tape

In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape.The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus.Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number, overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normaltwisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.

Experimental evaluation of heat transfer efficiency of nanofluid in a double pipe heat exchanger and prediction of experimental results using artificial neural networks

In this study, heat transfer efficiency of water and iron oxide nanofluid in a double pipe heat exchanger equipped with a typical twisted tape is experimentally investigated and impacts of the concentration of nanofluid and twisted tape on the heat transfer efficiency are also studied. Experiments were conducted under the laminar and turbulent flow for Reynolds numbers in the range of 1000 to 6000 and the concentration of nanofluid was 0.01, 0.02 and 0.03 wt%. In order to model and predict the heat transfer efficiency, an artificial neural network was used. The temperature of the hot fluid (nanofluid), the temperature of the cold fluid (water), mass flow rate of hot fluid (nanofluid), mass flow rate of cold fluid (water), the concentration of nanofluid and twist ratio are input data in artificial neural network and heat transfer is output or target. Heat transfer efficiency in the presence of 0.03 wt% nanofluid increases by 30% while using both the 0.03 wt% nanofluid and twisted tape with twist ratio 2 increases the heat transfer efficiency by 60%. Implementation of various structures of neural network with different number of neurons in the middle layer showed that 1–10-6 arrangement with the correlation coefficient 0.99181 and normal root mean square error 0.001621 is suggested as a desirable arrangement. The above structure has been successful in predicting 72% to 97%of variation in heat transfer efficiency characteristics based on the independent variables changes. In total, comparing the predicted results in this study with other studies and also the statistical measures shows the efficiency of artificial neural network.

Design and experimental investigation of a thermoelectric self-powered heating system

In this paper, a combustion-driven thermoelectric residential heating system, which uses Bi2Te3-based thermoelectric modules, is designed, constructed, and tested. The thermoelectric modules are integrated into a heat cell of a natural gas-fired heating boiler. The experiments are carried out to examine the influences of the main operating conditions, cold fluid flow rate, temperature difference between the inlet and outlet at the heat cell and different boiler powers, on output power, voltage, current and efficiency of boiler. The two operating parameters such as the cold fluid flow rate and temperature difference are found to significantly affect the output power, and the efficiency of the boiler. The thermoelectric generator unit has a power generation capacity of approximately 36W. This amount corresponds to about one-third of boiler’s requirement. The study shows that if the combi boiler is redesigned, and its efficiency is enhanced, it can generate sufficient electrical power for electrical components of the combi boiler, such as pump, valves, blower, fan, and control panel. The self-powered heating system provides advantages commercially, and can decrease the electrical power consumption. Also, and economical analysis was conducted for the self-powered heating system and the conventional system, and it was seen that the proposed system is economically applicable.

Experimental simulation of a liquid-metal heat-transfer fluid flow in a T-shaped mixer

The structure of the temperature field in a liquid-metal heat-transfer fluid flowing through a T-shaped mixer is studied experimentally. The experiments are carried out using Rose’s alloy as a working fluid. To find the temperature distribution over the wall of a working section, IR thermography is applied. It is shown that the wall temperature distribution in the zone where fluid flows with different temperatures mix is heavily nonuniform. The temperature distribution substantially depends on the ratio between the hot and cold fluid flow rates. The results can be used to verify the thermal hydraulic computational codes for fluid metal flows.

Experimental Investigation of Thermal Behavior of Cross Flow Plate-fin Heat Exchanger with Offset Strip Fin

The Present work is carried out to investigate the thermal behavior of cross flow plate fin heat exchanger having offset strip fin. An experimental set up has been built in the laboratory to test the Plate fin Heat exchanger. Sets of experiments had conducted to determine the thermal performance of the given heat exchanger. Mass flow rate of cold fluid, mass flow rate of hot fluid, hot fluid inlet temperature, cold fluid inlet temperature, hot fluid and cold fluid inlet pressure are considered as input parameters. The values of the heat transfer co-efficient, effectiveness and pressure drops are obtained for the different value of the input parameters. The experimental results are compared with the correlations developed by Maiti and Sarangi, Manglik and Bergles and Joshi and Webb. Finally, based on the experimental results coluburn factor (j) correlation is developed to predict the value of heat transfer co-efficient.

Parametric investigations on compressor-driven metal hydride based cooling system

In this article, the development of a compressor-driven metal hydride based cooling system (CDMHCS) employing two identical metal hydride reactors each embedded with 60 cooling tubes, filled with 2.75 kg of LmNi4.91Sn0.15 hydride alloy for quasi-continuous cold generation is presented. Performances of the CDMHCS in terms Coefficient of Performance (COP) and Specific Cooling Power (SCP) along with the amount of hydrogen (H2) transferred in each cycle have been investigated at different refrigeration and sink temperatures, cold fluid flow rates and cycle times. The maximum COP and SCP of 2.2 and 53.5 W/kg respectively were observed for a cycle time of 8 min at cold fluid flow rate of 8 lpm, refrigeration and sink temperatures of 20 °C and 25 °C respectively. It was observed that COP and SCP of the system improved significantly with increase in refrigeration temperature; however, they decreased with increase in sink temperature.

Application of CNT nanofluids in a turbulent flow heat exchanger

Nanofluids have received much attention since its discovery owing to its enhanced thermal conductivity and heat transfer characteristics which makes them a promising coolant in heat transfer application. In this study, the enhancement in heat transfer of carbon nanotube (CNT) nanofluids under turbulent flow conditions is investigated experimentally. The CNT concentration was varied from 0.051 to 0.085 wt%, respectively. The nanofluid suspension was stabilised by gum arabic through a process of homogenisation and water bath sonication at 25 °C. The flow rate of cold fluid (water) is varied from 1.7 to 3 L/min, while flow rate of the hot fluid is varied between 2 and 3.5 L/min. Thermal conductivity, density, and viscosity of the nanofluids are also measured as a function of temperature and CNT concentration. The experimental results were validated with theoretical correlations for turbulent flow available in the literature. Results showed an enhancement in heat transfer between 9% and 67% as a function of temperature and CNT concentration.

Study of Plate and Frame Heat Exchanger Performance : The Effects of Mass Flow Rate, Inlet Temperature and Type of Flow Againts The Overall Heat Transfer Coefficient

The purpose of this study is to know the effects of mass flow rate, inlet temperature and type of flow againts overall heat transfer coefficient (U). Heat exchanger used in this study was plate and frame type of TRIMGS 10. Mass flow rate of hot fluida was variated into 0.3 and 0.253 kg/s; mass flow rate of cold fluida was variated into 0.276 and 0.22 kg/s; inlet temperature of hot fluida was variated into 40, 45, 50 o C; type of flow was variated into co-current and counter current. The results show that the faster mass flow rate hot and cold fluida, the bigger overall heat transfer coefficient obtained. Also, the higher inlet temperature, the the bigger overall heat transfer coefficient obtained. In this study, the biggest of U value was obtained with variable of inlet temperatur 50°C, mass flow rate of cold fluid 0.276 kg/s, mass flow rate of hot fluid 0.3 kg/s, which were 140.6532 W/m 2 °C using type of counter-current flow and 135.4576 W/m 2 °C using type of co-current flow. Type of counter-current flow gave more satisfactory result of U value than type of co-current flow

EXPERIMENTAL INVESTIGATION OF DOUBLE-PIPE HEAT EXCHANGER WITH HELICAL FINS ON THE INNER ROTATING TUBE

Heat exchanger is an important device in all the thermal systems. The heat exchanger is widely used equipment in different industries such as process, petroleum refining, chemicals and paper etc. Energy and material saving considerations as well as environmental challenges in the industry have stimulated the demand for high efficiency heat exchanger. To improve the efficiency of heat exchanger one must think of heat transfer enhancement in heat exchanger. Moreover heat transfer enhancement enables the size of heat exchanger to be considerably decreased. A high rate of heat transfer with minimum space requirement is necessity for compact heat exchanger. In present work, to improve the heat transfer characteristic of the double pipe heat exchanger, the helical fins were installed on the outer surface of the inner tube and the level of turbulence increased by the rotating the inner tube. The length of heat exchanger was 1m and the pitch of helical fins kept constant equal to 17 mm. The convective heat transfer coefficients were obtained for the stationary as well as rotating inner tube for the counter flow mode using water as cold fluid in the tube side and glycerol as hot fluid in the shell side. The flow rate of cold fluid was kept constant and that of hot fluid was varied. The Nusselt number was calculated for the each speed of the rotation and compared with standard values obtained from Dittus-Boelter equation. The helical fins increases heat transfer area and rotation of the inner tube increases the mixing of fluid particles which is necessary for the convection mode of heat transfer. The Nusselt number increased up to 64 % at 100 rpm compared to stationary inner tube with helical fins.

Application of Entransy Optimization to One-Stream Series-Wound and Parallel Heat Exchanger Networks

Entransy theory has developed in recent years to describe heat transfer behavior from another point of view. Entransy dissipation is proposed to evaluate the irreversibility of heat transfer and is used to optimize heat transfer processes. We apply this theory to the one-stream series-wound and parallel heat exchanger (HE) networks. The heat transfer optimization for the HE networks includes the distribution of the heat transfer area or heat load. The distribution of the cold fluid flow rate in parallel HE networks can also be optimized. For these problems, physical and mathematical models are set up, analyzed, and discussed with the entransy theory. It is found that the optimization objectives of these problems and the optimization directions of the extremum entransy dissipation principle are consistent. The optimized results for the distribution optimization problem with given heat load are in agreement with the uniformity principle of temperature difference field. Examples of simple one-stream HE networks are given; the distributions of the heat transfer area or heat load are optimized by the extremum entransy dissipation method.

ANFIS Modeling For a Water-Methanol System in a Spiral Plate Heat Exchanger

In this paper, an experimental investigation of Water- Methanol system in a Spiral plate Heat Exchanger (SHE) is presented. Experiments have been conducted by varying the mass flow rate of cold fluid (Methanol), the mass flow rate of hot fluid (Water) and inlet temperature of the hot fluid, by keeping inlet temperature of the cold fluid constant. The effects of relevant parameters on the performance of spiral plate heat exchanger are studied. Also, in this paper, an attempt is made to propose Adaptive Network based Fuzzy Inference System (ANFIS) and Artificial Neural Network (ANN) models for the analysis of SHE. The data required to train the models are obtained from the experimental data based on Response Surface Methodology (RSM). The ANN models are developed using Back Propagation Network (BPN) algorithm, incorporating Levenberg-Marquardt (L-M) training method. The ANFIS models are developed based on advanced neural- fuzzy technology. The ANFIS model possesses the robustness of fuzzy system, the learning ability of neural networks and can adapt to various situations. The accuracy of the trained networks are verified according to their ability to predict unseen data by minimizing root mean square error (RMSE), average percentage error (APE) and correlation coefficient (%R 2 ) value. The prediction of the parameters can be obtained without using charts and complicated equations. The data obtained from ANFIS and ANN models for overall heat transfer coefficient (U) and pumping power (Wp) are compared with those of experimental data. It is observed that the accuracy between the ANFIS model's predictions, NN model's predictions and experimental values are achieved with minimum % error, APE, RMSE and Correlation coefficient (%R 2 ). Also it is proved that ANFIS models give better performance

Experimental and numerical investigation of heat transfer in CNT nanofluids

Nanofluids with their enhanced thermal conductivity are believed to be a promising coolant in heat transfer applications. In this study, carbon nanotube (CNT) nanofluids of 0.01 wt%, stabilised by 1.0 wt% gum arabic were used as a cooling liquid in a concentric tube laminar flow heat exchanger. The flow rate of cold fluid varied from 10 to 50 g/s. Both experimental and numerical simulations were carried out to determine the heat transfer enhancement using CNT nanofluids. Computational fluid dynamics (CFD) simulations were carried out using Fluent v 6.3 by assuming single-phase approximation. Thermal conductivity, density and rheology of the nanofluid were also measured as a function of temperature. The results showed thermal conductivity enhancement from 4% to 125% and nearly 70% enhancement in heat transfer with increase in flow rate. Numerical results exhibited good agreement with the experimental results with a deviation of . CNT nanofluids at 0.01 wt% CNTs showed Newtonian behaviour with no significant increase in the density.

The Influence of Core Capacitance on the Dynamic Performance of a Single-Phase Natural Circulation Loop With End Heat Exchangers

The effect of wall-core capacitance of heat exchangers on the dynamic behavior of a natural circulation loop (NCL) with end heat exchangers is studied under various excitations such as step, ramp, exponential, and sinusoidal. The transient one-dimensional conservation equations are derived for loop fluid, hot and cold fluid streams, and wall core of both heat exchangers. The solution of a set of transient partial differential equations and one integro-differential equation for loop fluid circulation rate is achieved through a finite-element technique. Imposing the excitations to the inlet temperature of hot fluid, the effects of wall-core capacitance on the responses of outlet temperatures of both hot and cold fluid streams and flow rate of loop fluid are studied. Wall-core capacitance diminishes the initial transients and delays the inception of hot and cold fluids outlet temperature profiles as well as loop fluid flow profile. Further, it has the ability to bring even unstable system behavior with reverse flows into a stable system with steady loop flow rate through quickly decaying oscillations. System responses are also greatly influenced by boundary conditions such as hot and cold fluids flow rates and their inlet temperature excitations such as step, ramp, and exponential. As flow stability is an important subject for single-phase NCLs, a stability map is constructed and compared with zero wall-core capacitance. Inclusion of wall-core capacitance in the present study reveals the important fact that the stable state operating zone widens with the wall-core capacitance.

Application of entransy to optimization design of parallel thermal network of thermal control system in spacecraft

For distribution optimization of the flow rate of cold fluid and heat transfer area in the parallel thermal network of the thermal control system in spacecraft, a physical and mathematical model is set up, analyzed and discussed with the entransy theory. It is found that the optimization objective of this problem and the optimization direction of the extremum entransy dissipation principle are consistent in theory. For a two-branch thermal network system, the distributions of the flow rate of the cold fluid and the heat transfer area are optimized by calculating the extremum entransy dissipation with the Newton method. The influential factors of the optimized distributions are also analyzed and discussed. The results show that the main influence factors are the heat transfer rate of the branches and the total heat transfer area. The total flow rate of the cold fluid has a threshold, beyond which further increasing its value brings very little influence on the optimization results. Moreover, the difference between the extremum entransy dissipation principle and the minimum entropy generation principle is also discussed when they are used to analyze the problem in this paper, and the extremum entransy dissipation principle is found to be more suitable. In addition, the Newton method is mathematically efficient to solve the problem, which could accomplish the optimized distribution in a very short time for a ten-branch thermal network system.