LMTD Method Research Articles

Explicit Calculation Method for Heat Exchanger Considering Variable Physical Property Treatment

AbstractThis work presents a heat exchanger calculation method characterized by the explicit temperature solution (ETS) for the working medium. This method is derived for both parallel-flow and counter-flow patterns based on the traditional LMTD method. As the temperature distribution is given in an explicit form related to the mixing temperature, the heat transfer performance of heat exchangers can be solved without iterations, improving the efficiency of heat exchanger design. Considering the practical engineering application, the influence of variable physical property is discussed. The temperature distributions of the reference temperature method and the integral method (whole length) are compared with the accurate distribution of the adaptive-grid method (segmented). Results indicate that the temperature distribution obtained by the integral method highly coincides with the accurate one, showing a relative error of only 0.36 %. The proposed ETS method with integral physical property treatment is an efficient and accurate way for heat exchanger design.

Unleashing novel configurations of gravitational water vortex thermal energy exchanger

This study presents thermal and hydrodynamics investigations for novel configurations of gravitational water vortex heat exchanger (GWVHE). The proposed novel configurations of GWVHE include SWB (shell with baffles), CSFH (circular spiral flow helix) and RSFC (rectangular spiral flow channel). The thermal energy balance between two fluid domains has been calculated numerically for various operational conditions. An analytical model is developed using the Kern's approach, the effectiveness-NTU method, and the LMTD method for heat exchangers to calculate the heat transfer characteristics of two fluids to validate numerical results. Moreover, a transient two-phase flow numerical model has been solved to investigate the volume fraction of air and water during the development of the vortex at the center of the basin. The results show that a convincing thermal energy balance is present between both fluid streams for all the proposed configurations of GWVHE. However, the heat exchange rate for the RSFC configuration of GWVHE is higher than the SWB and CSFH of GWVHE. Because it has maximum heat exchange surface area of 1.08 m2 and thermal losses in RSFC are significantly lower than those computed in CSFH and SWB at different operating conditions. The thermal losses reported for RSFC are just 1 % compared to CSFH and SWB thermal losses of 2 % and 5 %, respectively. Moreover, the maximum volume fraction of air obtained at the center of basin during vortex formation is 18 %, indicating an effective vortex air core.

Experimental analysis of a tri-partite brazed plate gas cooler for CO2 heat pump water heaters

Gas cooler is a crucial component in CO2 systems, and its performance significantly influences the overall efficiency of the CO2-based heat pump system. Brazed plate heat exchangers feature a compact design, reduced refrigerant charge, enhanced heat transfer coefficient, and lower pressure drop, resulting in space savings and improved system performance. This experimental study investigates a water-cooled tri-partite brazed plate gas cooler in a CO2 heat pump. The tri-partite brazed plate gas cooler has a double effect: it allows matching the temperature glide of CO2 with that of water and meeting the requirements for both domestic hot water and space heating simultaneously. The experiments are conducted in only domestic hot water and combined space and domestic hot water operative modes. The effects of different operating parameters on heat duty, supply temperature, temperature approach, and pinch point location are evaluated. The actual conductance of gas coolers is calculated, and a new definition is adopted to determine the ϵ−NTU of gas coolers. Results show that preheating gas cooler (GC3) has a higher heat duty at pressures near the critical pressure. As the inlet pressure increases, the domestic hot water supply temperature increases, the pinch point moves to the cold end of GC3, and the temperature approach decreases. The LMTD method may result in an undersized or oversized CO2 gas cooler by up to ±50% for different pressures. The errors reach their maximum values when the temperature difference is low at the cold end and high at the hot end. The effectiveness ranges from 0.56 to 0.94 and the NTU ranges from 2.64 to 5.41. The gas cooler shows promising performance. The outcomes of this research are anticipated to serve as a valuable reference for enhancing the design and optimization of transcritical CO2 systems.

Cooling Design Analysis of The Use of Land Engine On Ship

Based on the survey, the majority of fishermen in Indonesia choose to use land engines as propulsion for the main engine and auxiliary engine on ships because in terms of the price of land engines, they are much cheaper than ship engines produced by marine engine factories. Therefore, not a few workshops that often serve land engine modifications for further use as ship propulsion. Regulations regarding the use of land engines as ship’s main engines in Indonesia are currently not widely regulated in the Classification Agency regulations. Heat exchanger that supports the cooling system for optimal use of land engines on ships. Furthermore, the heat exchanger design process with a heat transfer load of 17,416 Watt was carried out using the LMTD method and obtained a heat transfer area value of 1,204 m2 with a staggered arrangement configuration. From the results of the CFD simulation, the temperature value at the hot water outlet is 51.39 C.

Development and optimization on separated structure steam generator based on a new thermal design model

• A new thermal design model with the micro-element superposition was proposed. • The effect of operation on the thermal performance of the SS-SG was discussed. • The optimization design has been conducted using a hybrid intelligent algorithm. • The total cost can be greatly reduced with precise structural design for the SS-SG. Adopting the traditional LMTD method to design the SS-SG (Separated Structure Steam Generator) usually leads to a larger deviation due to drastically change in physical properties of flue gas with changing temperature. This makes the consumption of steel tubes and power energy during both the manufacturing and operation processes increase. As an exploratory investigation, a novel thermal design model was developed with the idea of micro-element superposition and validated against the experiment herein. It revealed that the maximum absolute deviation between prediction and experiment was less than 2.5%, which outperformed a lot compared to the traditional method. As an application case, this model was used to design an actual steam generator in this study. The design results showed that the steel tube consumption can be reduced by 27.19%, while the power energy consumption can be saved by 11.45% for long-term operation. Using the proposed model, the effect of operating conditions on thermal performance of the steam generator was discussed. It indicated that the increase in the inlet temperature and mass flow rate of flue gas, as well as the operating pressure, generally weakens the comprehensive thermal performance indexes PE A and PE B . Besides, this novel model can also be combined with an intelligent algorithm to perform structure optimization. For this case, compared to the original structure, the total cost can be further decreased by 17.57% with the obtained optimal structure from an economic point of view. It is of great significance to improve the economics of recovering flue gas waste heat.

An Explicit Design Method for Heat Exchanger Based on Logarithmic Mean Temperature Difference (Lmtd) Method

An Explicit Design Method for Heat Exchanger Based on Logarithmic Mean Temperature Difference (Lmtd) Method

Heat Transfer Analysis of Recuperator for Waste Heat Recovery Purpose Using LMTD & NTU Method

The dumped heat from captive industry like power generation plant, steel plant, refineries, etc. has tremendous potential for multiple energy effect like cooling, power and heating effect. The novel thermodynamic system has been invented for waste heat recovery (WHR) purpose as organic Rankine cycle, kalian thermal system, etc. The recuperator type heat exchanger (HEx) can support for WHR at category of medium and high-grade heat discharge. The design and operating parameters of recuperator is essential for complete development and its thermodynamic analysis. The proposed title of research deals with the heat transfer modeling using LMTD & NTU approach with the help of MATLAB R2017 analytical tool. And ANSYS is used for design work of mentioned heat exchanger. The major outcomes of this paper are maximizing the heat transfer rate, improve overall efficiency by operating parameters, and HEx effectiveness. The shell and tube material, diameter, number of turns of tubes.

Simulation and Study of Shell and Tube Type Heat Exchangers

Design of the shell and tube heat exchanger using comsol multipyhiscs application. The calculation of the dimensions of the heat exchanger aims to determine the quality of the heat exchanger based on the overall heat transfer coefficient, impurity factor, and the pressure drop that will occur. The heat exchanger that is made and designed is a shell and tube type heat exchanger 1 (one) pass shell and 1 (one) pass tube made of stainless steel 304 and copper with fluid flow in the form of air and water. The analysis results obtained that the heat exchanger that is designed already meets the requirements of the effectiveness coefficient of the baffle, understands the factors that exist in the shell and tube type of heat exchanger and understands the factors that affect efficiency and effectiveness.Calculations using the LMTD method, obtained that receive heat released has a large unity with time Q, then the heat received by cold fluid is Q = 4565.16 W, LMTD produced also shows the number 20, with a proven factor (F) is 1. Reynolds Number of the tube side is greater than shell side.

Analysis of Shell and Tube Heat Exchanger Type

The stationary-head prototypes unusually are designed using low cost manufacture and simple construction, without bolt or nut to join both the stationary-head and shell. The shell has four holes to supply hot/cold fluid, and next to the tube-sheet hole to supply cold/hot fluid, the position both of them are inside the stationary-head. The calculation of the dimensions of the heat exchanger aims to determine the quality of the heat exchanger based on the overall heat transfer coefficient, impurity factor, and the pressure drop that will occur.Calculations using the LMTD method, obtained that receive heat released has a large unity with time Q, then the heat received by cold fluid is Q = 4565.16 W, LMTD produced also shows the number 20, with a proven factor (F) is 1. Comparison obtained from the calculation of the tube side and shell side is the value of Re generated is greater than the value of Re on the shell side.

Design and experimental analysis of solar-powered water desalination system using humidification–dehumidification

ABSTRACT Desalination with solar-powered air heating and packed bed humidification is designed and fabricated using locally available materials. The system with fined type dehumidifier is designed using the LMTD method. There are different solar desalination techniques such as solar still, solar air humidification dehumidification and solar water flash evaporation. Among these desalination techniques, solar air humidification dehumidification was already successfully used in very large-scale desalination but, not effectively tried for small-scale desalination. Desalination system with HDH was designed and fabricated during this research project for small-scale output. There are three main components of the system: Solar air heater, humidifier and dehumidifier. The packed bed was used in the design of humidifier for increasing the surface contact area of air with water. Psychrometric properties are recorded with the use of sensors DHT11 and ESP8266 micro-controller Wi-Fi board. The water temperatures are recorded with PT100 sensors and 8 channels data logger.

Numerical analysis on thermal–hydraulic performances of staggered tube bundles for an aero-engine compact precooler

The deeply precooled air-breathing technique is an effective approach to cool down the extreme hot incoming air for hypersonic engine. This paper investigates the thermal performance of staggered mini-tube bundle as the compact precooler for aero-engine application. The coupling heat exchange between the hot air and in-tube coolant is explored. Two methods (i.e., surface temperature method and LMTD method) are used to evaluate the airside heat transfer characteristics. Comparison of predicted Nusselt number and empirical correlations shows that both methods have acceptable discrepancies, especially for surface temperature method. In addition, Nusselt number predicted by the surface temperature method almost keeps identical at different coolant velocities, while the LMTD method is sensitive to the flow velocity of in-tube coolant. In order to better understand the influences of boundary conditions, the detailed analysis for parameters such as inlet pressure, inlet temperature, transverse pitch, coolant velocity and property variation on thermal performance of the tube bundle is carried out.

Experimental Examination over heat Exchanging Capacity on the Hollow Pipe Incorporated with Corrugated Copper Plate Dividend and Baffles

Heat exchanging devices produce an outstanding part in numerous engineering applications. Because of this, a varied sort of researches are undertaking to decrease the size and cost of the heat transfer equipment with high performance by indulging in diverse invaluable works similar to changing its design, incorporating corrugated structures with different dimension with different flow configurations. In this work, the design of double pipe heat exchanger had been modified similar to the plate type model with the incorporation of a corrugated copper plate which separates the hot and cold fluid inside the SS304 material tube. Three baffles at the top and two baffles at the bottom of the plate have been placed to reduce the velocity and heat interaction timing of the fluids. This could enhance the surface area of the plate and point of contact between the plate surface and fluid particle flowing over the plate surface. The experiment had been undergone with the parameters like engendering the flow arrangements of hot and cold fluid in counter current direction, hot fluid in the three sided baffle at the top and cold fluid at the two sided baffle at the bottom. This allowed liquids of differing thermodynamic equilibrium to interact, bringing about thermal transfer to calculate its maximum efficiency. In addition to these factors, the heat exchanging performance has been estimated with the heat transfer coefficient using LMTD method gave 8-10% enhancement in the overall heat transfer coefficient with respect to the mass flow rate.

Compact heat exchangers – Design and optimization with CFD

Heat transfer is one of the key aspects of machineries, devices and industrial processes for maintaining their functionality and also for achieving better product quality. Hence, heat exchangers of different types and sizes are used in these applications with the purpose of removing the extra process/device heat to maintain the desirable working temperatures. However, the size of a heat exchanger is a major consideration for any type of process/device as it decides the space requirements (i.e., the size) of the machine/device or the processing plant. At first, this study aims to investigate the design procedure of a heat exchanger theoretically and then its performance will be analyzed and optimized using computational fluid dynamics. For the design purposes, a counter flow heat exchanger was considered and its length was theoretically calculated with the LMTD method while the pressure drop and energy consumption were also calculated with the Kern method. Afterwards, a computational model of the same heat exchanger was implemented with ANSYS and then this model was extended to six different models by altering its key design parameters for the optimization purposes. Eventually, these models were used to analyze the heat transfer behavior, mass flow rates, pressures drops, flow velocities and vortices of shell and tube flows inside the heat exchanger. Theoretical and CFD results showed only a 1.05% difference in terms of the cooling performance of the hot fluid. The axial pressure drops showed positive correlations with both the overall heat transfer coefficient and pumping power demand. Overall, the results of this study confirms that CFD modelling can be promising for design and optimization of heat exchangers and it allows testing of numerous design options without fabricating physical prototypes.

3D design and optimization of heat exchanger network for solid oxide fuel cell-gas turbine in hybrid electric vehicles

The development of electric vehicles is considered as one of the sustainable way in the automotive industry to reduce greenhouse gases emissions and to allow transportation sector to comply with environmental targets required in present and future years. Due to the limited range of autonomy of the electric vehicles and the induced cost and environmental impacts of large capacity batteries, hybrid electric vehicles have been deeply investigated and developed over the last years. In this study, a Solid Oxide Fuel Cell combined with Gas Turbines (SOFC-GT) is used as a range extender in hybrid electric vehicle. The SOFC-GT system increases the autonomy of the electric vehicle and has high electric efficiency of 77%. In this work, the Heat Exchanger Network (HEN) to recover thermal energy in the SOFC-GT system has been studied. The HEN has to meet the targets of limited volume and mass to be compatible with the installation on the hybrid vehicle. This study is basically divided into three steps. In the first step, the HEN synthesis is performed with a mathematical model developed in AMPL, stating the optimal matches between hot and cold streams. In the second step, a model is developed to size the heat exchangers with the LMTD method. In the final step, an optimization problem is solved to minimize the volume or mass of the HEN, by sizing the heat exchangers with a global view of HEN, considering their assembly in a limited space and defining the paths of flow streams. Finally, some heat exchangers have been printed using plastic with a SLA 3D printer, with presentation purpose.

Heat transfer characteristics of deionized water-based graphene nanofluids in helical coiled heat exchanger for waste heat recovery of combustion stack gas

Heat transfer phenomena of a fully developed laminar flow of deionized water-based graphene nanofluids (DI-water/GNPs) in vertical helical coils for heat recovery of combustion stack gas was carried out with different helical coil dimensions. The GNPs particle concentrations were 0.05 and 0.08% by weight and the calculation of experimental heat transfer data was based on countercurrent flow LMTD method under condition of constant wall heat flux. With higher thermal conductivity and lower specific heat capacity, the graphene nanofluids provided better heat transfer performance compared to pure DI-water. The increase of the thermal conductivity was found to be 13.36% at particle fraction of 0.05% by weight which resulted in the increase of heat transfer coefficient by 21–25% compared to that of the DI-water. The better heat transfer characteristics could be obtained at more particle concentration. The effect of coil dimensions on heat transfer phenomena of helical coils had been discussed and a new correlation of heat transfer data for the nanofluids was created. The overall heat transfer coefficient between the hot exhaust gas and the heat transfer fluid in the helical coil was also considered.

Heat transfer phenomena on waste heat recovery of combustion stack gas with deionized water in helical coiled heat exchanger

Theoretical and experimental studies on waste heat recovery of combustion stack gas and heat transfer phenomena of a fully developed laminar flow of deionized water in vertical helical coils were carried out with coil dimensions: tube diameter to coil diameter ,di/D=0.04−0.06 and pitch to coil diameter, p/D=0.1−0.25. The calculation of heat transfer data was based on countercurrent flow LMTD method. The result showed that deionized water (DI-water) possessed better heat transfer than that of normal water. The effect of coil pitch, coil diameter, and coiled tube diameter on heat transfer phenomena of helical coils had been discussed and a new set of correlation of heat transfer data was created and it could be found that the results from the correlation agreed well with the experimental data. In addition, the overall heat transfer coefficient between the hot exhaust gas and the heat transfer fluid in the helical coil was also considered. Smaller tube diameter gave better overall heat transfer coefficient at low water-side Reynolds number and when the Reynolds number was over 3500 the bigger tube diameter showed the advantage. Smaller coil diameter seemed to get better overall heat transfer coefficient at low water-side Reynolds number.

Pinch point analysis and design considerations of CO2 gas cooler for heat pump water heaters

Due to strong nonlinear variation of supercritical CO2 specific heat capacity with temperature, pinch point would occur in water-cooled CO2 gas cooler, which has great impacts on the heat transfer characteristics of gas cooler and overall system performance. Pinch point analysis was conducted for CO2 gas cooler in the present study. The effects of refrigerant pressure, mass flow ratio (mw/mc), inlet water temperature and heat transfer area on pinch point location, approach temperature difference and heat transfer rate were analyzed in detail. Based on the analysis of pinch point location in CO2 gas cooler, the critical flow ratios were proposed to effectively control the approach temperature difference. Furthermore, the actual conductance of gas cooler was calculated and compared with that estimated by LMTD method. The results showed that CO2 gas cooler may be undersized by as much as a factor of 30–60% for different pressures if LMTD method is used. However, the UA value evaluated by LMTD method also may be overestimated under high refrigerant pressures when the approach temperature difference tends to be zero. Results of the present study are helpful to practical designs of CO2 gas cooler and heat pump water heaters.

Thermal analysis of shell and tube heat exchangers using artificial neural networks

The shell and tube heat exchangers are most commonly used industrial equipment to transfer heat from one fluid to another. The design process is specified by Tubular Exchanger Manufacturers Association (TEMA). The initial design has to be iteratively optimized for increasing the heat transfer, minimize the pressure drop and reduce the fluid pumping power. LMTD method is chosen for its simplicity and quick analysis. The design procedure if approached by Finite element method, needs high computing power and tedious to converge. A feed-forward artificial neural network is set up to simplify the iterative nature of the design process. This also gives the necessary quick design iteration cycles to reach the optimized design. A design space is created with heat exchanger parameters, and the feed forward network is trained with semi-empirical data. The trained network is used in the design performance evaluation. This approach shows promise of quick design changes and can accommodate variable thermo-physical properties of fluids, and can be trained for different fouling patterns in the heat exchangers from real time data. The neural network can predict the steady state performance within the design space and results match well with LMTD calculations. Subsequent to the steady state analysis, dynamic modeling is attempted. A neural network method is used to reduce the complication of the model. Simplified mathematical model is used initially to train the network. It is found that the feed forward networks can predict the dynamic behavior, but it needs additional parameters to improve its predictions.Keywords: Shell and tube heat exchanger, feed forward, artificial neural network

Simulation study of a two-stage adsorber system

The present study simulates a two-stage silica gel + water adsorption desalination (AD) and chiller system. The adsorber system thermally compresses the low pressure steam generated in the evaporator to the condenser pressure in two stages. Unlike a standalone adsorption chiller unit which operates in a closed cycle the present system is an open cycle wherein the condensed desalinated water is not fed back to the evaporator. The mathematical relations formulated in the current study are based on conservation of mass and energy along with isotherm relation and kinetics for RD-type silica gel + water pair. Various constitutive relations for each component namely the evaporator, adsorber and condenser are integrated in the model. The dynamics of heat exchanger are modeled using LMTD method, and LDF model is used to predict the dynamic characteristic of the adsorber bed. The system performance indicators namely, specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP) are used as objective functions to optimize the system. The novelty of the present work is in introduction of inter-stage pressure as a new parameter for optimizing the two-stage operation of AD chiller system.

Performance Assessment of a Shell Tube Evaporator for a Model Organic Rankine Cycle for Use in Geothermal Power Plant

The global energy demand increases with development and population rise. Most electrical power is currently generated by conventional methods from fossil fuels. Despite the high energy demand, the conventional energy resources such as fossil fuels have been declining and harmful combustion byproducts are causing global warming. The Organic Rankine Cycle power plant is a very effective option for utilization of low grade heat sources for power generation. In the Organic Rankine Cycle heat exchangers such as evaporators and condensers are key components that determine its performance. Researches indicated that shell tube heat exchangers are effectively utilized in this cycle. The design of the heat exchanger involves establishing the right flow pattern of the interacting fluids. The performance of these exchangers can be optimized by inserting baffles in the shell to direct the flow of fluid across the tubes on shell side. In this work heat exchangers have been developed to improve heat recovery from geothermal brine for additional power generation. The design involved sizing of heat exchanger (evaporator) using the LMTD method based on an expected heat transfer rate. The heat exchanger of the model power plant was tested in which hot water simulated brine. The results indicated that the heat exchanger is thermally suitable for the evaporator of the model power plant.