Hot Fluid Temperature Research Articles

Empirical modeling and experimental validation of gas-to-liquid heat pipe heat exchanger with baffles

Empirical modeling of heat pipe heat exchangers (HPHX) is the most economical and appropriate method for predicting its performance and estimating long-term economic benefits in the industrial field. Unfortunately, no models can predict the performance of HPHX with baffles that show complex flow characteristics, such as a combined flow arrangement of parallel flow and counterflow. This study presents the empirical model for HPHX with baffles, which predicts thermal performance and pressure drop based on empirical correlations and theoretical relations. It fabricated the HPHX with baffles composed of 95 copper two-phase closed thermosyphons (TPCTs) and measured its effectiveness, heat transfer rate, and pressure drop. We validated the presented model based on our experimental results and literature data. The validation results confirm that it can predict the HPHX performance with high accuracy, not only for the presence of baffles but also for various HPHX geometries (heat exchanger dimensions, number of baffles, etc.) and operating conditions (temperature and flow rate of hot and cold fluids). Finally, we analyzed and discussed the composition of HPHX performance, and as a result, enhancing forced convection between the working fluid and the TPCT bundle is a vital key to improving thermal performance, especially for HPHX that utilize gas (or air) as the working fluid. It was also found that the wall material had a negligible impact on thermal performance, so it was reasonable to consider stainless steel, which is more resistant to corrosion and erosion than copper. Our results are expected to be a great reference for engineers designing and manufacturing HPHX in the industrial field.

Experimental investigation and optimization of heat pipe heat exchanger performance under two distinct heat transport mediums through TOPSIS approach

This paper presents a comprehensive thermal performance analysis of the heat pipe heat exchanger by varying the input process parameters and optimizing the best condition for waste heat recovery through the TOPSIS technique. In this work, the heat pipe is constructed with a copper tube and segmented into evaporator and condenser sections carrying hot and cold fluids with a half-fill ratio. The heat pipe is oriented in 0° horizontally with the wick material made from stainless steel and works based on the capillary principle. The efficiency of the HPHE is evaluated by varying the input operational parameters, namely heat input, mass flow rate of hot fluid, inlet temperature of hot fluid, and mass flow rate of cold fluid, on response variables, specifically thermal resistance, energy balance ratio, universal heat transfer coefficient, and effectiveness. The experiment was designed for four factors at three levels as per Taguchi’s L27 orthogonal array, and the best optimising condition was determined by employing the multi-objective technique for order preference by similarity to ideal solution (TOPSIS) approach. The best input condition found was A3B1C1D3, in which the heat input was at 90 W, the mass flow rate of hot fluid was at 0.2 kg min−1, the mass flow rate of cold fluid was at 0.1 kg min−1, and the inlet temperature was at 60 °C. The effect of process parameters and their significance on output responses was analysed by executing an analysis of variance (ANOVA) statistical method. The mathematical regression model was generated, and validation was made to investigate the prediction error percentage.

Feasibility Study and Heat Transfer Analysis of Testbed Shell and Tube Heat Exchanger at Tube Side Fluid Discharge of 5 Lpm and Hot Fluid Temperature of 60 C

Feasibility Study and Heat Transfer Analysis of Testbed Shell and Tube Heat Exchanger at Tube Side Fluid Discharge of 5 Lpm and Hot Fluid Temperature of 60 C

Titanium foil-sealed thermoelectric generator for seafloor hydrothermal vent

The seafloor hydrothermal activity observation equipment needs a stable electric power supply; this study explored the thermoelectric generator (TEG) as the in-situ power supply method. The TEG can utilize the considerable temperature difference of the hydrothermal vent to supply electricity for the observation system. We use the titanium foil combined with the O-ring as the sealing component, thus can decrease the cold side thermal resistance and obtain a compact structure. The pressure test result shows the TEG can withstand pressure up to 20 MPa without leakage. Furthermore, a simulation is conducted to evaluate the temperature distribution of the TEG. To reduce heat loss, Polyetheretherketone (PEEK) material is used as the heat insulation layer at the surface of TEG. The simulation shows that adding the heat insulation layer can increase the hot side temperature by 4.9–7 K. The pool power generation results show that the novel structure TEG can realize 22 W output at the hot fluid temperature of 467 K. This study provides a novel sealing method for seafloor equipment with corrosion-resisting and low thermal resistance features.

Numerical simulation of safety injection and natural circulation in two containers by smoothed particle hydrodynamics on the effects of filling levels and thermal diffusivities

Natural circulation is an important process in reactor thermal-hydraulics study. This process is simulated by Smoothed particle hydrodynamics method for a modeled system of circulation. A new kernel function of (−1, 5) power components has been proposed here and validated by the dam-break case. The modeled circulation system is composed of two containers of different heights. Three filling levels (Case A) and four thermal diffusivities (Case B) have been utilized to analyze their effects. Six vortex-criteria have been utilized to visualize the representative vortical motion of fluids inside the containers. Circulations of velocity and velocity–temperature, heat transfer amount, mean temperature and mean material derivative have been defined here to quantify the feature of natural circulations for the two cases. The results show that the filling levels affect mainly the process of setup, rather than the steady level of natural circulation. A high filling level has a considerable larger amount of heat transfer between the hot and cool fluids. The thermal diffusivity does not affect the process of the circulation level, whereas it has great effects on the mean as well material derivative of the temperature of fluids. For example, comparing the mean temperature of the fluid at the thermal diffusivity α = 0.02 to that at α = 2.79 (in Case B at t=600 s), the mean temperature of cool fluids is about 15 °C lower at α=0.02 than that at α=2.79, whereas the mean temperature of hot fluids is about 7 °C higher at α=0.02 than that at α=2.79. In addition, the difference in the initial temperature of fluids and the difference in heights between two containers affect the natural circulation levels.

Effect of NH4Cl fouling on heat transfer process of heat exchange tube under forced convection condition

The crystallization fouling of ammonium chloride (NH4Cl) often occurs on heat exchange tube bundles in petroleum refining equipment, which seriously reduces the heat transfer and operational efficiency of the equipment. In this paper, the heat transfer characteristics of heat exchange tube (HET) with NH4Cl crystallization fouling was studied experimentally. The effects of velocity, temperature and mass flow rate of hot and cold fluids on the overall and local heat transfer characteristics were analyzed. The results indicate that the local heat transfer coefficient around the tube wall decreases first and then increases with the increase of the circumferential angle (θ) under clean condition. At the position of 0°-45°, the local heat transfer coefficient is the largest. At 90°-135°, the local heat transfer coefficient is the smallest. Under fouling condition, the local heat transfer coefficient increases with the increase of circumferential angle. In the region of 0°-45°, the local heat transfer coefficient is the smallest. The region with the largest local heat transfer coefficient is 135°-180° The heat transfer coefficient (h), fouling resistance (Rf) and average fouling thickness increase with the increase of Reynolds number (Re), temperature of hot fluid (Th) and mass flow rate of cold fluid (qm,c), but decrease with the increase of temperature of cold fluid (Tc).

Experimental and numerical investigation of heat transfer and flow of water-based graphene oxide nanofluid in a double pipe heat exchanger using different artificial neural network models

In this study, a water-based graphene oxide nanofluid was utilized in a counter-current flow double pipe heat exchanger (DPHE). The inner pipe carried the hot fluid (deionized water-based fluid). In the outer pipe, the cold fluid was flown, in which the experiments were performed once for deionized water-based fluid and once for graphene oxide nanofluid. These experiments were conducted at various inlet hot fluid temperatures of 35, 45, and 55 °C, volumetric concentrations of 0.01, 0.055, and 0.1% for nanofluid, and cold fluid flow rates of 14.4, 18.9, and 23.4 ml/s to evaluate the thermohydraulics of the DPHE. The results demonstrated that an increase in the flow rate and concentration of nanoparticles led to an improvement in the heat transfer coefficient (HTC) . It is also observed that inlet hot fluid temperature had a negligible effect on this coefficient compared to the concentration and flow rate. Additionally, the results showed that the friction factor and pressure drop of nanofluid were higher than those of the basefluid and their values were increased by increasing the concentration. The maximum increase compared to the basefluid was 72% for the friction factor and 111%, for the pressure drop. Besides, radial basis function neural network (RBFNN) and multi-layer perceptron neural network (MLPNN) models were designed for estimating the HTC. Both models accurately predicted the coefficient, but the RBFNN model exhibited higher accuracy than the MLPNN model. The results further indicated that the nanofluid outperformed the basefluid in terms of HTC. Due to the exceptionally high thermal conductivity of graphene nanoparticles, the HTC of the nanofluid was improved by up to 85% compared to the basefluid. The optimum value of HTC was achieved at a temperature of 55 °C, a volume concentration of 0.1%, and a flow rate of 23.4 ml/s.

Thermal performance and flow analysis in a brazed plate heat exchanger using MWCNT@water/EG nanofluid

In recent years, the growth of energy consumption and the need to optimize it have drawn the attention of researchers to technologies that can increase the performance of heat transfer devices such as plate heat exchangers. One of these solutions is the use of nanoparticles in common fluids. Despite the many advantages of MWCNT, not enough attention has been paid to its application in plate heat exchangers. The purpose of this study is to investigate the thermal performance and flow of a brazed plate heat exchanger using MWCNT nanoparticles in the cooling fluid of water/Ethylene glycol. The results of the UV spectrum showed that the concentration of 0.05 wt% nanofluid has the most stability. Therefore, the tests required for the two factors of the volume flow rate of cold fluid and temperature of hot fluid were performed at three levels using the response surface method. The results show that at 55 ̊C temperature of hot fluid and volume flow rate of 23.4 l/min of cold fluid, the convection heat transfer coefficient and the heat transfer rate are increased by 20.97% and 34.3% compared with the base fluid. Also, The Nusselt number, pressure drop, friction factor, and pumping power increased by enhancement of the hot fluid temperature and volume flow rate of cold fluid. These parameters of nanofluid at 23.4 l/min and 55 ̊C compared to base fluid increased by 94.45%, 11.25%, 12.87%, and 11.36%, respectively. This study shows better performance at high temperatures compared to similar studies.

Experimental and CFD analysis of fluid flow in rectangular strip based micro channel with nano fluid

Comparative analysis is conducted between nano fluid Al2O3 + CuO + H2O and water as basic fluid through simulation technique and validate it through experimental result. The effect of nano fluid (NF) and water were acknowledge which were flowing inside rectangular shape micro channel (RSMC) internally and externally time to time as per decided experiment sets with or without rectangular-strip micro-insert (RSMI), for observing the fluid flow behaviour, heat transfer attributes and performance characteristics. During preparation of nano fluid 0.05% − 0.1% volume fraction (vol.%), 10–20 nm size nano particles (NP) were taken with 0.5–0.75 ml CTAB as surfactant. Experimentation were conducted for diverse operating condition/parameters under counter-flow conditions, where NF is moving inside micro channel of less than 1 mm diameter having flow rate 0.0001562 to 0.006255 kg/sec. Hot fluid as water is moving inside the concentric-tube of 3.6 cm diameter with flow rate of 0.000782 kg/sec. The operating temperature of NF and hot fluid as water were 308 K and 323 K. As per observation, the results of proposed samples of NF with 0.1 vol% showed better performance than 0.05 vol% NF and water. It happens due to higher rate of thermal-conductivity achieved because NF gain extra molecular area with an addition of diverse NP with base fluid, where as better optimum results were observed with an enhancement of 8%-9% in case of RSMC with micro insert (M.I.) compared with other geometric model because high turbulency received due to extra-exposed area of M.I.. A close error percentage near about 4–5% was developed between experimental and simulation work. Thus it validates the present investigation.

Performance Prediction of a Model Rotary Air Preheater Through Porous Media Approach

Abstract Rotary regenerative heat exchangers or rotary regenerators are used for various heat recovery applications in order to fulfill the energy requirements. Rotary air preheater is a rotary regenerative heat exchanger which is widely used in thermal power plants to recover heat energy from exhaust flue gases. Several numerical works are being carried out to improve the performance and reduce the cost of the rotary air preheater. However, the accurate modeling of the internal structure of the matrix demands a lot of CPU power and is a big challenge for researchers. To overcome this problem, the rotary matrix of the preheater can be modeled using a porous media approach. But a thorough investigation is required to evaluate its performance. In this work, rotary air preheater simulations were carried out by applying a porous media approach. The effects of different operating conditions, such as speed of rotor, the mass flowrate of incoming fluids, material of matrix, and inlet temperature of hot fluid on the performance of rotary air preheater were investigated. Simulation results were validated with the results obtained from the experimentation performed in-house. The effect of fluid flowrates on pressure drop was also studied. It has been observed that the rotational speed of the rotor significantly affects the performance of the preheater, while the inlet temperature of hot fluid has a negligible effect on performance.

Study on the heat transfer characteristics of a plate-fin-typed precooler considering cooling fluid phase change

A quasi-two-dimensional calculation method has been proposed to design a plate-fin-typed precooler with high efficiency and low resistance. This method considers the variation of fluid properties during the heat transfer process, particularly for cryogenics with phase change. The precooler heat transfer characteristics are comprehensively investigated based on the proposed method and calculation models. The calculation results demonstrate that the proposed method effectively explores the fluid properties distribution, such as the temperature distribution and steam quality distribution inside the precooler. Besides, the hot fluid temperature drop exceeds 1200 K, while the pressure drop remains below 15% of the inlet pressure above all cases. Moreover, the heat transfer performance between cooling fluid and hot fluid is compared. It is worth noting that the cooling fluid heat transfer coefficient is10∼102 magnitude higher than that of the hot fluid, especially when the cooling fluid steam quality is below 0.60. Therefore, it is critical to improve the heat transfer performance of the hot fluid for the precooler. Additionally, the first heat exchanger inside the precooler plays a more important role in heat transfer than heat exchangers at other locations because the temperature drop and pressure drop inside the precooler account for the largest proportion, with a value up to 50%.

Computational analysis for temperature separation and correlations prediction for dual-inlet-sections vortex tube

This article intends to examine the cooling capacity enhancement for the Ranque-Hilsch vortex tube when two inlet sections are introduced compared to a single inlet section along with the optimum distance between the intake sections by computational fluid dynamics (CFD) approach. Air is taken as working fluid in a steady-state, 3-D, axisymmetric, Ranque-Hilsch vortex tube. ANSYS FLUENT software has been used to simulate flow using standard k-ɛ turbulent model. The numerical analysis is accomplished with variable intake pressure and validated with the experimental results. The numerical investigation shows that using the two inlet sections decreases the fluid temperature at the cold outlet as compared to single inlet section, but the cold and hot exit fluid temperature increases by increasing the distance between the two sections. The optimum cold outlet temperature value occurs at a dimensionless distance between intake sections of ζ/L = 0.075 and a temperature difference of 19.27 K at cold exit between single and double inlet section of vortex tube has been found from the present study. A correlation has been developed for the hot temperature gradient (ΔTh) and cold temperature gradient (ΔTc) by considering the operating parameters such as mass fraction and inlet pressure.

Evaluation of Fluid Flow Velocity Variations on the Plate Heat Exchanger Performance

Heat exchanger expected to high effectiveness of heat transfer. Type of plate heat exchanger was more efficient compare to another heat exchangers in industrial applications with pressure less than 30 bar. The increased velocity of cold fluid flow has an impact to increase the performance of heat exchanger by heat transfer rate (Q), heat transfer coefficient (U), and the effectiveness of heat exchanger (ε). The increased velocity of cold fluid flow also incresing the heat transfer rate. The study carried out by variation of the cold fluid velocity at 0.03 m/s, 0.037 m/s, 0.045 m/s, 0.051 m/s and 0.059 m/s. Inlet hot fluid temperature (Th,i) at 45°C and cold fluid temperature (Tc,i) at 27°C constant. The results shows Q value from the original 1570.71 Watt to 1916.16 Watt on the hot side and 1751.89 Watt to 2187.01 Watt on the cold side. The U value from the original 1180.46 W/m2.°C becomes 1408,75 W/m2. °C. The ε value increased from 60.33% to 75.69%. The increasing of cold fluid velocity directly proportional to the the heat transfer rate (Q) and performance of the plate heat exchanger. This Phenomenon due to the faster circulation of the cold fluid, which causes the cold fluid to quickly return to its initial temperature (Th,i), an than increasing the plate heat exchanger's performance.

Cogeneration system based on large temperature difference heat transfer with stepwise utilization

Organic Rankine cycle (ORC) plays a critical role in systems such as waste heat recovery, cogeneration, renewable energy generation and energy storage. No matter which field ORC is applied in, the evaporator side of ORC has an extremely poor utilization of the thermal energy from heat source, resulting in the outlet temperature of hot side fluid being much higher than the inlet temperature of cold side fluid. In order to fully capitalize on the thermal energy, this study introduces the two-stage absorption heat exchanger (AHE) and integrates it into ORC to obtain an original high-efficiency cogeneration system (AHEORC-CHP), which is parametrically analyzed by constructing and operating thermo-economic model in terms of the expansion pressure ratio and working fluid of ORC, the type and flow rate of heat source, and the inlet temperature of generator in AHE. Due to the existence of pinch point temperature difference, conventional ORC design can only reduce the outlet temperature of the heat source with an inlet temperature of 130 °C to about 70 °C under the condition of ideal heat transfer. The AHEORC-CHP configuration proposed in this work can achieve a significant reduction in the final outlet temperature of waste heat source (as low as 24.69 °C) and realize heat exchange with large temperature difference and efficient utilization of the heat source. Besides, the thermoelectric efficiency and temperature effectiveness can reach 90.9% and 1.2 respectively, while the profit ratio of investment rises to 8.46. Further improving the performance of AHEORC-CHP system requires optimizing the design of the pressure in absorption heat pump (AHP) cycle as well as the concentration and flow rate of LiBr-H2O solution. This study can provide a simulation pathway for the application of two-stage AHE in ORC, and likewise for future experimental investigations.

Al-Biruni Earth Radius Optimization Based Algorithm for Improving Prediction of Hybrid Solar Desalination System

The performance of a hybrid solar desalination system is predicted in this work using an enhanced prediction method based on a supervised machine-learning algorithm. A humidification–dehumidification (HDH) unit and a single-stage flashing evaporation (SSF) unit make up the hybrid solar desalination system. The Al-Biruni Earth Radius (BER) and Particle Swarm Optimization (PSO) algorithms serve as the foundation for the suggested algorithm. Using experimental data, the BER–PSO algorithm is trained and evaluated. The cold fluid and injected air volume flow rates were the algorithms’ inputs, and their outputs were the hot and cold fluids’ outlet temperatures as well as the pressure drop across the heat exchanger. Both the volume mass flow rate of hot fluid and the input temperatures of hot and cold fluids are regarded as constants. The results obtained show the great ability of the proposed BER–PSO method to identify the nonlinear link between operating circumstances and process responses. In addition, compared to the other analyzed models, it offers better statistical performance measures for the prediction of the outlet temperature of hot and cold fluids and pressure drop values.

Effective waste heat recovery from engine exhaust using fin prolonged heat exchanger with graphene oxide nanoparticles

Waste heat recovery is an important alternative to reduce the energy consumption in industrial processes. Heat Exchangers are used effectively for heat recovery. Thus, the role of heat exchangers for waste heat recovery system is crucial. The exclusive of heat transmission of a heat exchanger can be improved by many methods such as by modifying the geometries and using nano-additives of different concentration. In this continuation, a modified geometry of finned heat exchanger is developed with CFD analysis. Modified heat exchanger includes the fins in the internal pipe to improve heat transfer. Nanoparticles of graphene oxide with various concentrations are introduced in working fluid. A steady numerical study is performed by using ANSYS Fluent with k-omega turbulence model for exhaust flow. Variation at inlet velocities of exhaust gas and water, particles concentration and internal fin geometry are considered. The reduction in hot fluid temperature from 6 m/s to 2 m/s enhanced the effectiveness by approximately 33.3%. The decrease in hot fluid velocity to 2 m/s and 6 m/s can reduce its outlet temperature by 100 K and 14 K at 0.03 m/s cold fluid temperature. The inclusion of nanoparticles at 0.1% can enhance the effectiveness by maximum of 7%.

Preliminary experimental assessment of a vertical shell and tube heat exchanger based on phase change materials

The paper presents an experimental setup developed for phase change materials (PCM) testing inside a vertical shell and tube heat exchanger (VSATHE). The work presented part of a more complex one focusing on designing a PCM heat exchanger that could be used in the defrosting process of commercial and refrigeration systems. The phase change materials (PCM) were commercial paraffin RT54HC, while water was used as heat transfer fluid (HTF). This work was presented The impact of changing the temperature of the inlet water (70 °C, 75 °C, and 80 °C) and the change of flow rate (0.012kg/sec, 0.014kg/sec and 0.016kg/sec) in the solidification and melting of the PCM. The results of the experiments showed that when the inlet hot fluid temperature increases at the same flow rate, the melting time in VSATHE units decreases. At the same time, during the charging process, the increase of flow rate with the difference in inlet temperature has no effect on the total melting time.

Minimizing entransy dissipation for heat transfer processes withq∝Δ(Tn)and heat leakage

Heat transfer process with heat leakage and generalized radiative heat transfer law (HTL) [q∝Δ(Tn)] is investigated. Optimality condition for the minimum entransy dissipation (MED) is derived by applying average optimal control theory. On the basis of the general optimization result, the results for four special cases of Newtonian [q∝Δ(T)], linear phenomenological [q∝Δ(T−1)], radiative [q∝Δ(T4)], and mixed [q∝Δ(T4) with q∝Δ(T)] HTLs are further obtained. Optimal paths are compared with the common strategies of constant heat flux rate and constant hot fluid temperature operation. Numerical examples are presented, and influences of heat transferred amount and heat leakage on optimization performances are analyzed.

Experimental investigation on thermo-hydraulic performance of a helical plate heat exchanger

ABSTRACT The current research presents an experimental study on heat transfer and fluid flow characteristics of a helical plate heat exchanger (HP-HEx). Helical plate with different pitches and cross sectional area of the flow channel was investigated for various fluid mass flow rates and inlet temperatures. The results show that the proposed heat exchanger performed an overall heat transfer coefficient (U) and exergy efficiency (ηex ) about 279.77 W/m2.K and 60.87% respectively. Also, the HP-HEx showed effectiveness (ε) and number of transfer unit (NTU) reach about 0.694 and 1.79 respectively with pressure loss reached 202 kPa, for hot and cold fluids flow rate 0.083 kg/s and 0.07 kg/s at inlet hot and cold fluid temperature 45°C and 28°C respectively, and pitch = 56 mm. The pitch and cross sectional area of the flow channel variation can augment heat transfer rate and decrease the pressure loss. For pitch decreasing from 76 mm to 46 mm, the U, ε, NTU, ηex , and pressure loss increase by 50.60%, 22.39%, 50.60%, 10.35%, and 20.87% respectively. Empirical general correlations were obtained from the experimental data of the present study with maximum deviations about ±16.81%, ±13.33%, ±17.73%, ±16.60% and ±15.60% for U, ε, NTU, ηex , and pressure loss, respectively.

Investigation of Performance on Photovoltaic/Thermal (PV/T) System Using Magnetic Nanofluids

Photovoltaic/Thermal (PV/T) systems provide hot fluid (usually water) production as well as electrical energy production. In addition, since the overheating of the PV systems is prevented by the heat drawn by the thermal system, the electricity production performance of the PVs increases. Nanofluids are offered as a solution to increase the heat absorbed in the thermal system. The main physical events that lead to a significant improvement in the heat transfer performance of nanofluids can be summarized as follows: (i) The thermal conductivity of the prepared nanofluid increases at certain rates because the thermal conductivity of the solid metal is higher than that of the basic fluid, (ii) The heat transfer surface area increases due to the increase in the thermal conductivity of the fluid, (iii) Increase in the effective thermal capacity of the fluid, (iv) Increase in the thermal conductivity of the fluid and turbulent volume due to high fluid activity. In this study, by using nanofluids obtained by adding 1% Fe2O3, Fe3O4 and NiFe2O4 magnetic nanoparticles by weight to the basic fluid water, a bidirectional performance increase was achieved by increasing the thermal heat transfer of the PV/T system while providing more cooling of the PV system. In the experimental study, a 14% improvement in electricity production was achieved in NiFe2O4 nanofluid by drawing more heat from the heated PV panels by utilizing the high thermal conductivity of nanofluids. Since the amount of heat absorbed in the thermal system is high, an average of 104% temperature (∆T) increase in the hot fluid temperature compared to the base fluid water was obtained in the NiFe2O4 nanofluid.