Heat Exchanger Geometry Research Articles

Design and testing of vertical tubular baffle heat exchanger as an internal reboiler in the distillation device

Reboiler in the distillation device is a heat exchanger to heat or boil liquid material in the distillation column. In this research vertical tubular baffle heat exchanger was designed and used as an internal reboiler in the distillation device. The aim of the study was to observe the temperature distribution during the liquid heating process in the vertical tubular baffle heat exchanger with different dimensions. The study was conducted by designing heat exchangers (HE) with different dimensions in height, diameter, and surface area (number) of tubes. Times and fuels needed to heat the liquid to a temperature of 78 °C were calculated. Based on observations it was found that the different geometry of the vertical tubular baffle heat exchanger gives different performance. Height, diameter, and the number of tubes (surface area) affect the value of the overall heat transfer coefficient, times and fuels needed for heating liquids at a temperature of 78 °C. In the same surface area but different in height and diameter of the heat exchanger, give a different result in overall heat transfer coefficient (U). HE with the number of tubes 3 and 7 obtained a higher value of U with a tube height of 4 cm and a diameter of 4 cm, compared with the value of U in HE with a tube 8 cm in high and 2 cm in diameter, but the opposite occurs in HE with a number of tubes 5.

Thermal Design of a Shell and Tube Heat Exchanger with Internal Fins

To alleviate the severe challenge of energy depletion, it’s extremely urgent to improve the available heat recovery technology. Heat exchangers play a key role in waste heat recovery and have attracted much attention. To recover waste heat, a shell and tube heat exchanger with sinusoidal wavy fins and blocked-core tube inside the tube, and with bare surfaces outside was designed by segmented log-mean temperature difference (LMTD) method. In the shell and tube heat exchanger, liquid water outside the tube was heated by compressed air inside. The effect of air-side inlet pressure on the geometry of heat exchanger was investigated under identical temperature conditions (Ta,i, Ta,o, Tw,i, Tw,o) and water-side inlet pressure. The results show that air-side inlet pressure has little effect on the structure parameters of heat exchanger, but greatly affect the pressure drop of air side.

Heat Transfer Characteristics of Heat Exchangers for Waste Heat Recovery from a Billet Casting Process

The application of the thermoelectric generator (TEG) system to various industrial facilities has been explored to reduce greenhouse gas emissions and improve the efficiency of such industrial facilities. In this study, numerical analysis was conducted according to the types and geometry of heat exchangers and manufacture process conditions to recover waste heat from a billet casting process using the TEG system. The total heat absorption increased by up to 10.0% depending on the geometry of the heat exchanger. Under natural convection conditions, the total heat absorption increased by up to 45.5%. As the minimum temperature increased, the effective area increased by five times. When a copper heat exchanger of direct conduction type was used, the difference between the maximum and minimum temperatures was significantly reduced compared to when a stainless steel heat exchanger was used. This confirmed that the copper heat exchanger is more favorable for securing a uniform heat exchanger temperature. A prototype TEG system, including a thermosyphon heat exchanger, was installed and a maximum power of 8.0 W and power density of 740 W/m2 was achieved at a hot side temperature of 130 °C. The results suggest the possibility of recovering waste heat from billet casting processes.

Use of Heat from Wastewater

There are increasing demands on energy efficiency at all areas of life e.g. heating, cooling and hot water supply. Using waste water is meeting requirements of sustainability and environmental protection. Waste water has great energy potential. The article deals with the optimization of sewer heat exchanger and economic efficiency. Heat exchanger effect is depending on shape and geometry of heat exchanger. Also temperature of waste water affects heat exchanger effect. Usual temperature of sewage is about 20 degrees Celsius in summer and about 10 degrees Celsius in winter. Cooling for a maximum about 1 degrees Celsius and flow at least 10 litters per second is required for seamless operation. To pass requirement of minimum flow is this system suitable for bigger buildings. It is also necessary for positive economic effect. For proper design and optimization it is necessary to use three basic methods: diagnostics, heat balance calculations and modelling. Numeric simulations are made for selection of the best sewer heat recovery. Recovered heat energy was used for heating, cooling also for hot water supply. Positive economic effect is provided in case study of administrative building.

Investigation on local convection heat transfer of supercritical CO2 during cooling in horizontal semicircular channels of printed circuit heat exchanger

The local heat transfer characteristics of supercritical CO2 flowing in horizontal semicircular straight channel of the printed circuit heat exchanger (PCHE) geometries during cooling under forced and mixed convection conditions have been numerically investigated in the present study. A new local heat transfer correlation accounting for the thermophysical property variations and the buoyancy effects has been developed based on analysis of the thermophysical property variations and the buoyancy effects on the local heat transfer performance. It predicts 93% of the data with errors of less than ±15%. The developed correlation is further adopted to a preliminary design calculation of typical PCHE channels based on a generalized mean temperature difference (GMTD) method instead of the conventional logarithmic mean temperature difference (LMTD) method. The design calculation results agree fairly well with the CFD results. Moreover, a dimensionless parameter, Cvp, is developed to evaluate the deviations induced by the constant property assumptions on which the conventional LMTD method is based. Results show that the deviation is generally between −15% and 15% when Cvp is in the range of 0.6 to 1.6.

Thermodynamic assessment of downhole heat exchangers for geothermal power generation

Downhole heat exchanger is a device to extract heat from geothermal fluid. While it is widely used for heating purposes, its use for power generation has not been reported. The aim of this study is to examine the feasibility of power generation from a 2500 m deep existing geothermal well with high temperature gradient and insufficient flowrate by using a downhole heat exchanger. For this purpose, a thermodynamic and an economic evaluation model are developed by the use of Engineering Equation Solver software. Additionally, the parametric studies have been carried out to identify the effects of insulation, geothermal well conditions, geometry of downhole heat exchanger, mass flowrate and type of working fluids on the performance of downhole heat exchanger system. Consequently, work output of the best alternative is computed as 2511 kWe with 64 kg/s mass flowrate of R-134a for 2500 m-deep downhole heat exchanger having inner pipe diameter of 0.127 m. Electricity generation cost and simple payback time are calculated as 46 $/MWh and 2.25 years, respectively. The obtained results showed that the downhole heat exchanger system can be a feasible alternative for wells with very low geothermal flowrate to generate power.

Optimal heat rejection pressure of CO2 heat pump water heaters based on pinch point analysis

The control of heat rejection pressure is of great importance for transcritical CO2 heat pump water heaters. However, almost all the existing correlations of optimal heat rejection pressure are based on an assumption of constant CO2 exit temperature from gas cooler when changing the high-side pressure. Actually, pinch effect occurring in CO2 gas cooler would have great impacts on CO2 exit temperature as the high-side pressure varies, which in turn affects overall system performance. A cycle simulation model was developed in the present study incorporating pinch point analysis for gas cooling process. The model is independent on heat exchanger geometry parameters, which guarantees the generality of the model. Sensitivity analyses of main impact factors were conducted in detail including inlet and outlet water temperature, refrigerant evaporation temperature and superheat degree, pinch temperature difference and isentropic efficiency of compressor. Furthermore, a new correlation of optimal heat rejection pressure was proposed.

Latent Heat Storage: Container Geometry, Enhancement Techniques, and Applications—A Review

Energy storage helps in waste management, environmental protection, saving of fossil fuels, cost effectiveness, and sustainable growth. Phase change material (PCM) is a substance which undergoes simultaneous melting and solidification at certain temperature and pressure and can thereby absorb and release thermal energy. Phase change materials are also called thermal batteries which have the ability to store large amount of heat at fixed temperature. Effective integration of the latent heat thermal energy storage system with solar thermal collectors depends on heat storage materials and heat exchangers. The practical limitation of the latent heat thermal energy system for successful implementation in various applications is mainly from its low thermal conductivity. Low thermal conductivity leads to low heat transfer coefficient, and thereby, the phase change process is prolonged which signifies the requirement of heat transfer enhancement techniques. Typically, for salt hydrates and organic PCMs, the thermal conductivity range varies between 0.4–0.7 W/m K and 0.15–0.3 W/m K which increases the thermal resistance within phase change materials during operation, seriously affecting efficiency and thermal response. This paper reviews the different geometry of commercial heat exchangers that can be used to address the problem of low thermal conductivity, like use of fins, additives with high thermal conductivity materials like metal strips, microencapsulated PCM, composite PCM, porous metals, porous metal foam matrix, carbon nanofibers and nanotubes, etc. Finally, different solar thermal applications and potential PCMs for low-temperature thermal energy storage were also discussed.

Experimental study on single phase operation of microjet augmented heat exchanger with enhanced heat transfer surface

The article presents experimental investigations on a prototype heat exchanger. Presented research is focused on combined active and passive enhancement techniques of surface modification and microjet impingement. The results were compared to reference plate heat exchanger without microjet impingement.The Wilson plot method was applied to determine the heat transfer coefficients in the single phase operation. The heat exchanger was capable of exchanging 300 W of thermal energy at LMTD of 40 K. The obtained overall heat transfer rates reach 600 W/m2.Introducing knurled surface resulted in ∼10% increase heat transfer area, and similar enhancement in transferred heat in reference to plate heat exchanger geometry. Knurled surface decreased heat transfer in combination with a multi-jet impingement in comparison to a smooth surface. A possible explanation of that effect is that the flow in wall jet region is disrupted by the knurled surface and directed in the bulk of the fluid. Initiating mixing with colder fluid, thicker thermal boundary layer, and affecting local temperature distribution.

Shell-and-Tube Heat Exchanger Geometry Modification: An Efficient Way to Mitigate Fouling

Crude oil fouling of a shell-and-tube heat exchanger sized according to TEMA standard is compared to a No-Foul design under industrial operating conditions. For similar operating conditions, TEMA and No-Foul heat exchangers have the same behavior regarding fouling. Since the No-Foul one has less tubes by design for the same heat duty, shear stress is increased. Consequently, the No-Foul heat exchanger is less prone to fouling at the same throughput. Impact of tube bundle geometry is then investigated. Helically finned tubes are compared to plain tubes in the No-Foul heat exchanger. Under similar operating conditions, fouling rates measured are up to an order of magnitude lower than plain tubes (respectively 10−11 and 10−10 m2 K/J). However, pressure drop across the tube-side in both No-Foul plain and finned setup are increased in comparison to the TEMA heat-exchanger.

Computational Analysis of Heat Transfer Effect on Liquid–Vapor Phase Change and Boiling-Induced Phase Instabilities

Liquid–vapor phase change (boiling/evaporation and condensation) is one of the most important phenomena in thermal management and many other applications of flow and heat transfer. Numerically, it poses challenge due to disparate densities of the phases, resulting in a stiff matrix. The presence of a third phase increases the numerical challenge. In the case of a primary domestic heater, water is heated by hot flue gas in a plate heat exchanger. It is important to avoid boiling of water in this heat exchanger and ensure a steady flow. In the present study, simplified plate heat exchanger geometry is used to predict the flow, heat transfer, and boiling in the heat exchanger in the given condition through CFD. Physically meaningful flow and phase change behavior could be predicted with moderate computational cost. Although it should be a steady process in absence of boiling, the formation of water vapor induces oscillation in the flow. It is observed that dead zones in the heat exchangers initiate local boiling and the vapor is periodically flushed out by the liquid. An oscillatory pattern is observed with a single dominant frequency, which is supported by experimental observations.

Numerical investigation of dense granular flow around horizontal tubes: Qualification of CFD model with validated DEM model

Granular material offer many advantages which qualify them for use as heat transfer medium and heat storage material in solar thermal power plants and industrial processes. Moving bed heat exchangers (MBHE) with horizontal tubes are favorable to extract thermal energy from hot granular materials. However, due to the complex flow phenomena and heat transport mechanisms in granular materials precise design tools for MBHE are lacking.In previous studies we introduced a discrete particle model (DEM) to calculate the granular flow in MBHE and validated it by experiments. In this study we use this precise but computationally expensive DEM model to qualify a more efficient continuum model (CFD) which is being introduced in this work.We compare the two models with regard to the granular flow speed along the tube surface and find deviations of |Δu/uref| < 20% in the upper part of the tubes. Both models coherently predict the formation of a static area at the top of the tubes. The formation of the void area below the tubes is less accurately predicted, calling for further adaptations of the CFD model. The thus qualified CFD allows to study large heat exchanger geometries with substantially reduced computational effort.

An analytical design tool for sorber bed heat exchangers of sorption cooling systems

A new 2-D analytical solution is presented and validated using the data collected from our custom-built gravimetric large pressure jump test bed and two-sorber bed sorption test bed. The proposed closed-form 2-D transient solution includes all salient thermophysical and sorption properties, heat exchanger geometry, and operational conditions as well as the thermal contact resistance at the interface in sorber beds. It is shown that the optimum amount of thermally conductive additive in the sorbent depends on the geometrical and heat transfer characteristics of the sorber bed and the cycle time. Furthermore, it is shown that the sorber bed geometry, heat transfer characteristics, sorption composite composition and cycle time can have conflicting effects on specific cooling power and coefficient of performance and should be optimized simultaneously to establish an optimal design.

Comparative analysis of U-pipe location on the sizing of borehole heat exchangers

The geometry of borehole heat exchangers (BHEs) is important for their sizing. In practice, a U-pipe can be located anywhere inside a borehole. To simplify the BHE modeling, ASHRAE has two standardized borehole geometries (the B type and BC type borehole geometry). In general, the B type is hard to achieve, although it is widely used in current BHE sizing. The BC type is the one that most likely occurs in practice, but there is a lack of detailed studies. This study presents a comparative analysis of the effects of U-pipe locations on BHE sizing. As current models are only feasible for the B type, a model for the BC type is first developed and verified using the well-known Sandbox experiment developed by Beier. Then, a comparative study of the B and BC types is conducted using the borehole depth and investment costs of a real office building. Finally, the factors influencing the borehole depth differences of the B or BC types are discussed, and guidelines for future BHE sizing are suggested.

Numerical analysis of heat transfer in air-water heat exchanger with microchannel coil

This paper presents numerical analysis of fluid flow and heat transfer in the heat exchanger with microchannel coil (MCHX). In accordance with previously published experimental results, 3D mathematical model has been defined and appropriate numerical simulation of heat transfer has been performed. Geometry and working parameters of cross-flow air-water heat exchanger with microchannel coil, installed in an open circuit wind tunnel and used in experimental investigations, have been applied in numerical analysis in order to validate the mathematical model. 3D model with air and water fluid flow and heat transfer domains has been used, as it gives more precise results compared to models that assume constant temperatures or constant heat fluxes on the pipe walls. Developed model comprised full length of air and water flows in the heat exchanger. Due to limitations of computational capacity, domain has been divided in multiple computational blocks in the water flow direction and then solved successively using CFD solver Fluent. Good agreement between experimentally measured and numerically calculated results has been obtained. The influence of various working parameters on heat transfer in air-water heat exchanger has been studied numerically, followed with discussion and final conclusions.

Optimisation of a Quasi-Steady Model of a Free-Piston Stirling Engine

Energy from waste heat recovery is receiving considerable attention due to the demand for power systems that are less polluting. This has led to the investigation of external combustion engines such as the free-piston Stirling engine (FPSE) due to its ability to generate power from any source of heat and, especially, waste heat. However, there are still some limitations in the modelling, design and practical utilisation of this type of engine. Modelling of the FPSE has proved to be a difficult task due to the lack of mechanical linkages in its configuration, which poses problems for achieving stability. Also, a number of studies have been reported that attempt to optimise the output performance considering the characteristics of the engine configuration. In this study the optimisation of the second-order quasi-steady model of the gamma-type FPSE is carried out using the genetic algorithm (GA) to maximise the performance in terms of power output, and considering the design parameters of components such as piston and displacer damper, geometry of heat exchangers, and regenerator porosity. This present study shows that the GA optimisation of the RE-1000 FPSE design parameters improved its performance from work done and output power of 33.2 J and 996 W, respectively, with thermal efficiency of 23%, to 44.2 J and 1326 W with thermal efficiency of 27%.

Design and operating considerations for a shell-and-plate, moving packed-bed, particle-to-sCO2 heat exchanger

An efficient modeling methodology for simulating moving packed-bed heat exchangers for the application of particle-to-sCO2 heat transfer in next-generation concentrating solar power (CSP) plants is presented. Moving packed-bed heat exchangers have application to power-cycle heat addition for particle-based CSP plants and indirect energy storage for direct sCO2 CSP receivers. Further development of moving packed-bed heat exchangers for application to commercial CSP systems requires numerical simulation tools for the design and evaluation of particle-to-sCO2 heat transfer. In this paper, a steady-state reduced-order model of a shell-and-plate moving packed-bed heat exchanger is presented and used to investigate design considerations and performance limitations. The model appropriately captures the flow configuration of a multi-bank shell-and-plate design where the local cross-flow and global counter-flow configurations are addressed. This allows for the design tradeoffs in heat exchanger geometry and particle properties to be explored on the heat exchanger conductance and sCO2 pressure drop. Overall heat transfer coefficients for the particle-to-sCO2 heat exchanger at CSP operating temperature (500–800 °C) can approach 400 W m−2 K−1 using particle channel dimensions of 4 mm with particle diameters of 200 µm. The sensitivity of particle thermophysical properties was also explored to identify important parameters for improving the overall heat transfer coefficient that can be leveraged in the development of alternative particles. Packed bed void fraction and solid thermal conductivity were identified to be areas for potential improvement of sintered bauxite particles, which could increase the overall heat transfer coefficient by up to 60 W m−2 K−1. To achieve DOE cost targets (<$150 kWt−1) for sCO2 power cycle heat addition, diffusion bonded plates containing sCO2 microchannels must be produced at less than $2400 m−2 for the moving packed-bed heat exchanger to become commercially viable.

Modeling of solidification including supercooling effects in a fin-tube heat exchanger based latent heat storage

Latent heat storages are a promising technology to increase both the efficiency of thermal energy systems and the penetration of renewable energy sources such as solar energy. A major challenge regarding latent storage technology is the relatively high costs resulting from expensive heat exchangers concepts required to transfer thermal energy from the storage material to the heat transfer fluid. Within the presented study, a new modeling method which allows for the optimization of complex heat exchanger designs such as fin-tube concepts in latent storages units is proposed. The mathematical model of the heat transfer in latent heat storages during the solidification process can account for the effects resulting from the supercooling of the phase change material. In order to achieve a low computational effort, the model is composed of two subparts. The first is a 3-dimensional model describing the thermal behavior of the phase change material surrounding the fin structure of the heat exchanger. The second is a 1-dimensional model of the tube coil which allows obtaining the overall heat flow rate in the entire storage unit based on the 3-dimensional phase change material model.The developed model is calibrated and validated using experimental data of a commercial sodium acetate trihydrate based storage unit of manufacturer Sunamp with a phase change temperature of 58 °C. A good agreement between experimental and simulated heat flow rates and heat transfer fluid outlet temperatures could be observed. Moreover, the model is capable of predicting supercooling effects with high accuracy. Due to the acceptable computational effort achieved, the developed model may be used for a heat exchanger geometry optimization in future studies.

The effect of heat exchanger geometry on adsorption chiller performance

The adsorption technology applied to cooling production is one of the possible means of waste heat utilization and it therefore contributes to a reduction of power consumption in air-conditioning and desalination facilities. Increasing the performance of the adsorption chiller can be achieved by the intensification of heat transfer in the sorption bed which in turn is directly influenced by heat exchanger geometry. The carried out research utilized numerical methods to define the correlation between the fin-tube heat exchanger design and the main factors influencing adsorption chiller performance such as gradient of heating water temperature, logarithmic mean temperature difference, effective mass factor of silica gel, silica gel average temperature and spatial temperature distribution in the sorption bed. The obtained correlations can be used by sorption bed designers to balance the thermal effectiveness of the device and its overall dimensions and mass.

Experimental investigation of counter flow heat exchangers for energy recovery ventilation in cooling mode

Ventilation heat recovery is a system that requires low power to operate and has a high capacity to reduce the energy consumption and increase the overall efficiency for air conditioning. This paper reports the experimental investigation of air-to-air heat exchangers employed for heat recovery ventilation in cooling mode. The two main objective of this research are to design, fabricate and testing two polymers heat exchangers of different plate geometries and to evaluate and compare the thermal performance two quasi-counter flow plate heat exchangers. The key aims were to evaluate the effect of the surface geometry of the plates heat exchanger on the performance parameters specified in ANSI/ASHRAE Standard 84 and ANSI/AHRI Standard 1060 and narrow the gap of the limited experimental comparison of polymers sensible heat exchanger in cooling mode. The experiments were conducted on two polymer heat exchangers, one with a flat plate and the other with a dimpled surface plate.The experimental results showed that the cooling capacity of the dimpled surface heat exchanger as ventilation heat recovery system in cooling mode was 50–60% better than that of the flat surface plate heat exchanger. In addition, the sensible efficiency of the dimpled surface heat exchanger was higher than that of the flat surface plates heat exchanger at lower air velocities and higher air initial temperatures. The highest COP was 6.6 achieved with dimpled surface heat exchanger under primary air operating temperature of 32.6 °C.