Length Of Heat Exchanger Research Articles

Determining Design Parameters and an Optimal Design Method for Coaxial Geothermal Heat Exchangers Using Verification Experiments and GLHEPro Numerical Analysis

In this study, we investigated the effects that are dependent on the characteristics (length, diameter, type, and flow direction in a pipe) of a coaxial ground heat exchanger, via head loss and pressure drop measurement experiments. We identified that an increase in the length, a decrease in the diameter, and counter-flow generation inside the coaxial ground heat exchanger are the main factors responsible for increases in head loss. To optimize the design of a heat exchanger via numerical analysis using GLHEPro, we performed a sensitivity analysis considering the range of EWT, the number of heat exchangers, and the interval for installation. Based on these results, we calculated a 'Pareto solution' of 3 for the number of heat exchangers, taking into consideration the total heat exchanger length and power consumption conditions. Keywords: Coaxial Ground Heat Exchanger, Head Loss, Pressure Drop, GLHEPro, Sensitivity Analysis, Pareto Solution

Performance optimization of common plate-type thermoelectric generator in vehicle exhaust power generation systems

A plate-type thermoelectric generation (TEG) system is typically used in engine exhaust waste heat recovery systems because of its appropriate structure. To obtain an effective design of these TEG systems, this study focuses primarily on optimal matching performance analysis, by building a complete numerical TEG model with the finite element method using FORTRAN. A commercial-type thermoelectric material is used in the numerical calculation. Moreover, all types of work conditions with different exhaust parameters (mf = 10–50 g s−1 and Tfin = 300–600 °C) and cooler’s heat transfer processes are included. When peak net power is achieved, all corresponding optimal features are analyzed, where both air-cooling and water-cooling methods are considered. The results indicate that, for any type of work condition, the optimal height remains the same (Bopt = 7.0 mm for the air-cooling method and Bopt = 4.0 mm for the water-cooling method) and the other optimal parameters can be expressed by fitting correlations, which can deduce the optimal length (Lopt) and width (wopt) of an exhaust heat exchanger (for example, they are Lopt = 1.55 m and wopt = 0.78 m when mf = 50 g s−1, Tfin = 500 °C, and hc = 80 W m−2 K−1 for the air-cooling method). The introduced fitting correlations are verified to have a high accuracy.

An experimental study on the offset-strip fin geometry optimization of a plate-fin heat exchanger based on the heat current model

The compact heat exchanger is significant for hybrid and electric/fuel cell vehicles with high energy utilization efficiency. This contribution introduces the heat current method to propose a new solution for the design and optimization of heat exchanger structure by combining the empirical correlations of heat transfer and flow resistance. On the premise of decreasing the air flow length of a plate-fin heat exchanger, the tree traversal method is utilized to optimize the offset strip fins on both the hot and the cold fluid sides of a plate-fin cross-flow heat exchanger. Moreover, an experimental setup is built for testing the thermal-hydraulic performances of the original and improved heat exchangers. The results show that the difference between the experimental and the theoretical results is less than 3.23% which represents the heat current method is feasible for heat exchanger analysis and optimization. Meanwhile, the total heat transfer coefficient increases by 7.43% and the pressure loss on the air side reduces by 29.7% for the improved heat exchanger, which is more suitable and high-efficient for the limited space in a high-power vehicle. Finally, the corresponding functions of the total heat transfer coefficient and pressure loss with different air mass flow rates are constructed for future practical applications of the improved heat exchanger.

Analytical investigation and performance optimization of a three fluid heat exchanger with helical coil insertion for simultaneous space heating and water heating

In this paper, a three fluid heat exchanger is analytically modeled in order to predict the effects of different design parameters on its thermal performances. The optimum values of these parameters relating to maximum heat transfer and minimum pressure drop are assessed using Taguchi based optimization technique. The present heat exchanger is an improvement of double tube heat exchanger, where a helical coil is inserted in the annular space occupied in between two straight tubes. It is different from other three fluid heat exchangers with respect to construction, flow arrangement and thermal communication point of view, where the hot water is flowing through the helical coil as the heating fluid and continuously transferring thermal energy to normal water and air, which are flowing, in outer annulus and innermost straight tube. The results of the analytical approach are compared and validated against literature and good conformity between them is observed. The temperature distributions of three different fluids along the length of the present heat exchanger are assessed analytically for different flow configurations. Three different non-dimensional design parameters i.e. curvature ratio, non dimensional coil pitch and coil side Reynolds number are selected and their effect on heat transfer and pressure drop characteristics i.e. coil side Nusselt number, effectiveness and friction factor respectively are assessed. It is found that, for tube size 0.0045 m, coil pitch 0.013 m, coil diameter 0.04253 m and hot water flow rate 5 liters per minute, present heat exchanger will perform optimum. It is also resulted that, volumetric flow rate of hot water is the most effective parameter affecting heat transfer with a contribution ratio of 66.82% and tube size is the most effective parameters affecting pressure drop with a contribution ratio of 71.07%.

Geothermal power based ULTDH for cooling and heating purposes

Ultra-low temperature district heating systems facilitate use of waste and renewable heat sources. The article presents a possible scheme of operation and optimisation of small ultra-low temperature district heating system consisting of waste heat source, a number of heated individual dwellings and borehole thermal energy storage plant. Optimisation performed for typical meteorological year for Kraków indicate significant potential of decreasing energy amount discharged to the environment and total length of borehole heat exchangers, compared to individual heat/cold production from low-temperature geothermal resources. Meanwhile, satisfied is a set of constrains providing borehole thermal energy storage sustainability and fulfilling entire heating and cooling demands.

Heat transfer enhancement from power transformer immersed in oil by earth air heat exchanger

In this study, the modelling of power transformer with (250 kVA) by using (ANSYS17.1/FLUENT) code program was done. The power transformer was connected with earth air heat exchanger to decrease the temperature of (oil, core, and coils) of transformer which will increase its efficiency for preventing the damage and/or failure. The case study used the weather conditions of Nasiriya city, Iraq, at July 1st with 50?C as maximum ambient temperature and full electrical load of the power transformer. In addition to different pipe diameter, length of earth air heat exchanger and different air velocity entering to pipe. The results showed the temperature of (oil, core, and coils) for power transformer decreased with increase the pipe length and earth air heat exchanger depth underground. The air velocities inlet to earth air heat exchanger that used in the study were (2, 4 , and 6 m/s, respectively) and the results showed the increasing of air velocity inlet to earth air heat exchanger should decrease the temperature of (oil, core, and coils) for power transformer and increase the thermal conductivity of oil. The study concluded when using earth air heat exchanger in the power transformer and performance of power transformer will be increasing and led to decrease the temperature of oil about (18.5?C).The results showed a significant convergence with previous researches.

Analysis of Air Heating in Winter in Underground Heat Exchangers and in Water Bodies During Water Freezing on Submerged Pipes

Background. Air heating in winter in the ambient temperatures range below -5 °С is possible both by the heat of the soil and by the heat of the phase transition of water to ice. Heated air reduces energy consumption in ventilation systems and heat pumps such as air–water and air–air during peak loads on the heating system, which reduces the installed capacity of the heat-generating equipment.Objective. The aim of the paper is determination of the influence of air velocity (flow rate) on the desired length of pipes at a constant value of the diameter of the channel with air, as well as determination of thermal resistances and linear heat flux density with a comparison of the processes of soil cooling and water crystallization.Methods. Air with a temperature below -5 °С is passed through elements of the natural environment for use in ventilation systems, heat pumps, and in the buffer zones of buildings during the frost period. The lower the air temperature, the greater the economic and energy efficiency.Results. The calculated analysis of the effect of air velocity (flow rate) on the required length of pipes embedded in the ground and submerged in water subject to a phase transition of water to ice was carried out. It is shown that the required length of the ground heat exchanger is strongly influenced by the mode of operation (continuous operation without interruptions or operation with interruptions). To heat the air from -10 to -3 °С, depending on the air speed in the ground heat exchangers, the needed length of the pipes should be 1.5–2 times longer because the thermal resistance of the soil is greater than that of ice and the ice thickness is lower than that of the cooled soil, due to the high heat value of water crystallization. At high speeds, the linear density of the heat flux reaches 40–60 W/m2.Conclusions. When placing a channel in the form of a pipe in the ground or in water, it is possible to pre-heat the frosty air during peak loads on heating systems, which makes it possible to reduce the installed power of the heat-generating equipment. The technology of water freezing during air heating has significant advantages, especially when operating in annual mode.

SYSTEMATIC REVIEW OF RESEARCH AND UTILIZATION OF SHALLOW GEOTHERMAL ENERGY IN CROATIA

The utilization of shallow geothermal energy is well known in several European countries. Even though large parts of the Republic of Croatia show signifi cant potential for its use, the installation of ground source heat pump systems (heat pump and heat exchangers) is slowly progressing. Therefore, a short overview of research published thus far concerning the utilization and assessments of shallow geothermal potential for Croatia was done. In Croatia, there is no agency or government department in charge of collecting and publishing data concerning installations of heat exchangers. Therefore, a study was done to collect the available data on installed closed-loop heat exchangers either from scientifi c research or from personal contacts with drilling companies. Based on the collected data, a map was produced that shows general locations of installed heat exchangers. From the obtained data of installed heat exchanger length, a fi rst assessment of utilizing shallow geothermal potential in Croatia was given.

Life-cycle-cost based analysis of borehole heat exchanger lengths considering groundwater flow effects in a residence as a case study

Life-cycle-cost based analysis of borehole heat exchanger lengths considering groundwater flow effects in a residence as a case study

Simulation for evaporative cooling in partially wetted plate heat mass exchanger

The thermal characteristics of a M-cycle counter flow type plate heat exchanger (PHE), intended for use as a cooler, has been investigated numerically as an indirect evaporative cooler. For a fixed heat exchanger length (L = 50d) and the space between plates (d = 6 mm), the investigation included a numerical simulation for the PHE and the study of its performance with the variation in the number of the wetted zone (n) from 1 to 16 for inlet Reynolds number Re = 200. The computational results indicate that the heat exchanger performs better with the number of the wetted zone, high inlet air temperature and low relative humidity. Results show that the cooler consumes less water and it is an environmentally friendly cooler for dry areas.

Investigating the Effect of Soil Type and Moisture on the Performance of a Ground Source Heat Pump System Used for a Greenhouse in Iran

Abstract We investigate the effect of soil type and moisture on the operation of a ground source heat pump (GSHP) system in supplying the energy needs of a greenhouse in Karaj, Alborz province, Iran, in terms of the required length of ground heat exchanger, the working hours, the electricity consumption, as well as the coefficient of performance (COP) of heat pumps. In order to predict the capacity of heat pumps, we use the numerical heat transfer model of Noorollahi et al. (2016, “Numerical Modeling and Economic Analysis of a Ground Source Heat Pump for Supplying Energy for a Greenhouse in Alborz Province, Iran,” J. Cleaner Prod., 131, pp. 145–154) in which the governing equations of heat transfer in the ground heat exchanger are numerically solved through a novel finite difference method. Thermal properties of various soil types, namely sandy soil, sand, silty loam, and silty clay, with three different levels of moisture content referred to as dry, damp, and saturated, are considered as the main inputs for the computer code. The simulations indicate that when moisture is increased from dampness to saturation, the annual working hours of heat pumps decrease by 1.1%, 5.1%, 6.1%, and 4.6%, and their annual electricity consumption is reduced by 2.2%, 10.6%, 12.6%, and 9.7% for sandy soil, sand, silty loam, and silty clay, respectively. Moreover, the average COP of heat pumps increase by 0.9%, 4.0%, 5.2%, and 3.7% in heating mode and 2.4%, 13.0%, 16.5%, and 11.7% in cooling mode for the mentioned soils, respectively.

Study on accurate identification of soil thermal properties under different experimental parameters

The thermal properties of soil are vital in designing the length of buried heat exchangers. Based on a matured experimental technique commonly used for thermal response test in situ, a simulation model was built in this paper to determine the thermal properties of soil. Several sets of thermal response tests were carried out using the simulation model under different experimental conditions. The line heat source model (LHSM) and the column heat source model (CHSM) were applied to identify the thermal properties of soil. In order to analyze the variation of the identification error of the thermal properties under different experimental conditions, the identification results were then compared with the original setting values. The results showed that both identification methods could produce some errors in the identification of soil thermal and physical parameters under different experimental parameters. However, the accuracy of identification could be improved by selecting an appropriate test time. The best test time was duration to determine the thermal properties of soil was defined as an optimum length of time when the identification error was minimized. The best test time duration varied with different experimental parameters and different identification models. It is found that the best test time duration of the column heat source model was shorter than the one of the line source model. Giving longer lead time before counting the test time duration, increasing the thermal conductivity of the backfill material and heat injection, or reducing the circulating fluid flow rate, could effectively shorten the best test time duration.

Numerical simulation of two phase refrigerant flow through non-adiabatic capillary tubes using drift flux model

This research presents a drift flux model to simulate steady state refrigerant flow through horizontal lateral straight capillary tube-suction line heat exchangers with refrigerant R134a as a working fluid. The geometry of capillary tube is divided into two regions: An entrance length and lateral heat exchanger length. Metastable flow phenomenon is neglected in this work. To better study of fluid behavior in non-adiabatic capillary tube, according to the refrigerant state at the entrance of heat exchanger region, three modes were studied and the fundamental equations were solved for all three modes, then the results were analyzed. The present data using a drift flux model were validated with previous numerical work with a homogeneous model with obtaining reasonable agreement. By considering the slip ratio effects in drift flux model, therefore, this model could able to predict refrigerant flow behavior more accurately than other two-phase flow models in non-adiabatic flow condition through capillary tube.

CFD modelling and parametric study of small scale Alpha type Stirling Cryocooler

In this paper, a small-scale Stirling Cryocooler is developed using computational fluid dynamics through COMSOL Multiphysics 5.3. The model has been validated using experimental data from an Alpha type Stirling engine reported in the literature. Extensive parametric study was carried out to investigate the effect of various parameters such as operating speed and phase angle with the aim of optimizing the Cryocooler design parameters and operating conditions. Results showed that there exists an optimal value for the regenerator porosity 50%, phase angle 900 and heat exchanger lengths 142mm where 455W cooling power was obtained at heat sink temperature of 193K.Whereas increasing the speed and pressure resulted in an increase in cooling power at the heat sink.

SIMULATION STUDY OF FINNED DOUBLE PIPE HEAT EXCHANGER

Double pipe heat exchangers are extensively used in process industries. Increasing the surface area of heat exchanger results in enhanced heat transfer. In the current study double pipe heat exchanger was simulated using ANSYS Fluent simulator program. The fins were added to the outer surface of the inner pipe and the geometries studied were, rectangular, triangular and leaf shaped. Water outlet temperature of the heat exchanger was studied with mass flow rates of 0.20 kg/s, 0.24 kg/s and 0.28 kg/s. It was determined that with increase in mass flow rate the outlet temperature of cold water decreased. Higher outlet temperature of cold water was obtained with leaf fins as compared to rectangular, triangular and without-fin cases at mass flow rates of 0.20 kg/s and 0.24 kg/s. The percentage differences in temperature gradient seem to vary with change in mass flow rate. It is shown from the study that the length of heat exchanger with fins could be reduced to half to achieve about 90% of the temperature gradient.

Experimental and analytical investigation on pipe sizes for a coaxial borehole heat exchanger

This paper investigates the use of a vertical coaxial borehole heat exchanger (BHE), focusing on those consisting of standard geothermal piping material, as a component in a ground-source heat pump system. The results of a lab-scale experiment are used to verify the trends exhibited by a recent semi-analytical model, referred to as the composite coaxial (CCx) model, considering short-term behavior when laminar flow is experienced in the annular space of a coaxial heat exchanger. The discussion on pipe sizes is then expanded upon using the suggested model along with a modified design procedure to compare the performances realized by an example heat pump. A comparison is made here between configurations having various nominal inner pipe diameters while maintaining the same outer pipe. The results of the analysis show that increasing the inner pipe diameter, within the verified limit of the composite coaxial model, will reduce the required length of heat exchanger and increase the overall coefficient of performance realized by the heat pump.

Key parameters effects and design on performances of hydrogen/helium heat exchanger for SABRE

Hydrogen/helium heat exchanger is a kind of heat exchanger dedicated to SABRE (Synergetic Air-breathing and Rocket Engine). Its special working environment and operating condition have brought a great challenge to its design. Hydrogen/helium heat exchanger with micro-channel/plate heat exchanger as its configuration is taken as the research object in this paper. Mathematical model of the heat exchanger is set up based on logarithmic mean temperature difference method, and the parameters that affect the heat transfer performance of heat exchanger is analyzed. The results showed that, reducing the thickness of fin or plate can help reduce the pressure loss of working fluids, the length and weight of hydrogen/helium heat exchanger. Reducing the width of micro-channel can reduce the length of heat exchanger and increase the height of heat exchanger. Reducing the height of micro-channel can reduce the length and height of heat exchanger. As a whole, the pressure loss of working fluids shows a trend of decreasing at first and then rising with the height or width of micro-channel rising. The pressure loss of helium is much greater than that of hydrogen, which means the pressure loss of helium is more sensitive to geometric parameters of heat exchanger and should be well controlled. In order to gain the best performance of the heat exchanger, the geometric parameters of heat exchanger is designed by Artificial Fish Swarm Algorithm.

Thermodynamic design optimisation of an open air recuperative twin-shaft solar thermal Brayton cycle with combined or exclusive reheating and intercooling

The present work applies the method of entropy generation minimisation to investigate the effects of reheating and intercooling on the optimal design and maximum net power output of an open recuperative solar thermal Brayton cycle. Three cases are considered. The intercooled cycle demonstrates both the greatest net power output per unit collector area and the highest ratio of total irreversibility to heat input, followed by the combined and reheated cycles, respectively. Temperature differences across the components are identified as the primary cause of entropy generation. The receivers are found to be the primary site of entropy generation in all cases, and entropy generation in the intercoolers found to constitute the smallest proportion of the total entropy production rate. The optimised heat exchanger lengths are shown to lie on the maximum constraints, and the channel cross-sections found to constrict with increasing mass flow rate such that the total plate surface area is increased to promote heat transfer. The receiver and reheater geometric parameters are found to vary such that the absorber tube surface temperatures are kept below the maximum constraint, and the trends in the optimal parameters for receivers and reheaters comprising circular cross-section absorber tubes found to fluctuate considerably.

A Comprehensive Empirical Correlation for Finned Heat Exchangers with Parallel Plates Working in Oscillating Flow

The oscillating-flow heat transfer performance in finned heat exchangers is one of the main factors affecting the working efficiency of regenerative heat engines and refrigerators. In addition to the working parameters, the geometrical parameters of finned heat exchangers are also major influencing factors. In the present study, the ratio of the heat exchanger length and hydraulic diameter is applied as an independent similarity criterion. An experimental study has been carried out with six different geometrical dimensions of finned heat exchangers with parallel plates, in order to analyze the impacts of fin length, plate spacing, and corresponding relative fluid displacement amplitude, under various working conditions. Based on 298 tested points, a comprehensive empirical correlation for the finned heat exchangers with parallel plates working in oscillating flow has been proposed, providing a relatively accurate prediction, with 98.6% of data in the ±20% deviation and 83.9% of data in the ±10% deviation, within the range discussed.

A generic solar-thermochemical reactor model with internal heat diffusion for counter-flow solid heat exchange

For nonstoichiometric redox reactions that produce CO and H2 from CO2 and H2O, heat recuperation from the solid phase is a promising mechanism to improve the cycle efficiency. Many different approaches to heat recuperation and gas separation have been presented in solar thermochemical reactor concepts recently. To describe the many possible degrees of freedom in the reactor design, a generic reactor model is described for two-step redox reactions of solid pieces of reactant moving in counter flow between reduction and oxidation chambers. The reactive material is assumed to be porous ceria, where heat recuperation from the solid phase is achieved through radiation heat exchange between reduced and oxidized elements moving in opposite directions. A separation wall prevents gas cross-over and provides structural support. Heat transfer by radiation in the porous material is modeled with the Rosseland diffusion approximation and by conduction with the three resistor model. The model can be adapted to a wide range of reactor concepts.A study of crucial design parameters shows that heat diffusion in the reactive material can have a significant influence on the performance of the heat exchanger. If the time required for heat diffusion is large with respect to the total residence time in the heat exchanger, the material thickness can be decreased to enhance the share of the material actively participating in the heat exchange process. Furthermore, at the relevant temperatures, radiation dominates the heat exchange within the porous structure, thus the overall heat exchange can be enhanced through an increase of porosity. Heat exchanger length and residence time are correlated, allowing different combinations of these two variables at constant heat exchanger efficiency. In general, efficiencies close to 70% are possible with an adequate parameter combination. However, the achievement of the maximum heat exchanger efficiency requires a minimum number of chambers and thus physical length, as irreversibilities are reduced for a larger number of intermediate temperature levels.The presented generic model includes the description of heat diffusion within the reactive material, is a valuable tool for the design of heat exchangers, and can be used to identify technically interesting reactor concepts for the achievement of high energy conversion efficiencies.