Heat Exchanger Structure Research Articles

Feasibility study on a novel heat exchanger network for cryogenic liquid regasification with cooling capacity recovery: Theoretical and experimental assessments

There is an increasing research interest in the recovery of cooling capacity stored in cryogenic liquids (CLs) for industrial applications, especially for LNG regasification systems. In this study, a novel heat exchanger network (HEN) has been designed for cryogenic liquid regasification process to recover the released cooling capacity and develop a frozen-free heat transfer system with compact structure and high efficiency. Firstly, the specific design concept is proposed to employ the gasified CL as multiple cyclic streams to vaporize its own liquid in the evaporator, which allows a large temperature difference and a compact structure for the vaporization of the CL. Then, according to the optimization design of the flow arrangement, heat exchanger structure and flow rate control, the temperature of the heat medium can always be kept above its freezing point in the superheater and recuperator. Finally, the heat medium as the coolant extracts and transports the cryogenic cooling capacity from the CL to other refrigerated spaces, which can achieve various discharge temperatures to meet the requirements of different kinds of applications by adjusting the circulation number of the cyclic streams and the flow rates of the fluids. In the process calculation, the specific design parameters and energy balance relation of the HEN are obtained, and the cooling capacity recovery efficiency of the HEN system is analyzed using the pinch technique. A prototype of the heat exchanger network is designed and corresponding experiments are carried out for the regasification process of liquid nitrogen. The results indicate that the recovered cooling capacity and recovery efficiency of the prototype can, respectively, reach up to 17.5 kW and 90% within a 7.5% error range, which proves the feasibility of the novel HEN proposed in this paper.

Optimal Design of Double Pipe Heat Exchanger Structures

This paper investigates the design optimization of double pipe heat exchanger using mathematical programming. The heat exchanger area is minimized and the thermo-fluid dynamic conditions are considered for the use of the right transport correlations, together with design specifications, such as, maximum pressure drops and minimum excess area. The modular nature of this kind of heat exchanger and the allocation of the streams (inside the inner tube or in the annulus) are also contemplated. Two mixed-integer nonlinear programming (MINLP) approaches are proposed. One approach relates the binary variables to the nonlinear constraints directly. In the second, the resulting nonlinearities involving binary variables are formally linearized, without loss of rigor (e.g., no use of truncated Taylor series). The proposed methodology can get better solutions than traditional trial and error procedures. The flexibility of the model is illustrated, together with a comparison between the performances of both MINLP formulations. Additionally, computational time and local optimality issues are discussed.

Entropy Generation of Forced Convection during Melting of Ice Slurry.

This paper looks at entropy generation during ice slurry flow in straight pipes and typical heat exchanger structures used in refrigeration and air-conditioning technology. A dimensionless relationship was proposed to determine the interdependency between flow velocity and the volume fraction of ice, for which the entropy generation rates were at the minimum level in the case of non-adiabatic ice slurry flow. For pipe flow, the correlation between the minimum entropy generation rate and the overall enhancement efficiency was analyzed. As regards heat exchange processes in heat exchangers, the authors analyzed the relationship between the minimum entropy generation rate and the heat exchange surface area and exchanger efficiency.

Influence of Oceanic Climate on Flow and Heat-transfer Capability of R410A Cooling Medium Finned Tubular Heat Ex-changer

ABSTRACT Luo, Q. and Li, J., 2018. Influence of oceanic climate on flow and heat-transfer capability of R410A cooling medium finned tubular heat ex-changer. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 409–413. Coconut Creek (Florida), ISSN 0749-0208. The research method combining numerical simulation with experimental research was proposed. The shell structure of heat exchanger was simplified reasonably, the method of numerical simulation was used to build the flow and heat-transfer model of exchanger through ANASY CFX software. The mesh adaptivity method was used to improve the accuracy of numerical simulation and calculate velocity of shell characteristics and Res. Then the influence of temperature, the humidity, the wind speed on flow and heat-transfer performance of R410A cooling medium finned tubular heat exchanger was experimented. Experimental results show that the proposed method can accurately describe...

Direct contact heat transfer enhancement between two stratified immiscible fluids by artificial interface oscillations

Direct contact heat transfer between stratified immiscible fluids is commonly encountered in solar salt industry, desalination, petrochemical engineering, etc. Usually, the mutual mixing and penetration between stratified flows are weak, and hence the heat and mass transfer rates are quite limited and act as an obstacle in their wider applications. Considering the fact there is always clear surface (interface) between immiscible fluids, this study proposes to stimulate interface oscillations artificially to reinforce the mixing between fluids and thus enhance the transfer processes. The artificial oscillations employed in this paper are sinusoidal wave and their amplitude, period and wave length on the direct contact heat transfer between stratified airstream and water surface are investigated respectively. Heat transfer was found to be enhanced to a great extent by artificial oscillations, ranging from one to three times higher than that without oscillations. With the amplitude, period and wave length covered in this study ranging from 1 mm to 4 mm, 0.1 s to 2 s, and 40 mm to 100 mm, respectively, the heat transfer enhancement effect was found to increase with increase of oscillation amplitude and decrease of wave length, and this effect became more distinct at higher airstream velocity. However, the change of oscillation periods covered in this study shows minor difference on the heat transfer enhancement. Without using special solid inserts or alternation to the heat exchanger structure, artificial oscillation of phasic interface can be a simple and efficient technique to enhance transfer process between stratified flows.

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.

Optimization of ground heat exchanger using microencapsulated phase change material slurry based on tree-shaped structure

Taking into account the potential of the tree-shaped ground heat exchanger to reduce pressure losses and microencapsulated phase change material slurry to enhance heat transfer performance, a new attempt combining microencapsulated phase change material slurry with tree-shaped structure is proposed in this paper. Firstly, to obtain the optimal structure of tree-shaped ground heat exchanger, influences of structure parameters on thermo-fluidic performance of ground heat exchanger are explored. Based on this optimal structure, numerical simulations adopting Eulerian-Eulerian approach are conducted to study hydraulic and heat transfer performance of microencapsulated phase change material slurry flowing through horizontal tree-shaped structure under constant flux. Comparison studies between different working fluid: water and microencapsulated phase change material slurry and different types of tube: horizontal straight tube and Y tube (tree-shaped tube) are studied. The results indicate that the numerical results accordwellwith experimental results. For tree-shaped ground heat exchanger with bifurcation level of 1, the optimal pipe diameter ratio meets D0/D1=23/7, D1/D2=1 and the optimal length ratio is L0/L1=1. Furthermore, the combination of microencapsulated phase change material slurry and tree-shaped structure can efficiently enhance thermal performance and reduce pressure losses. Considering comprehensive performance of microencapsulated phase change material slurry, the optimal volume fraction is 12% for Y tube, whose overall performance is 38.9% higher than that of pure water flowing through straight tube.

Investigating the Effect of Medium Liquid Layer Circulation on Temperature Distribution in a Thermoelectric Generator Heat Exchanger Assembly

Thermoelectric generators (TEGs) are used to produce electricity utilizing two energy reservoirs. Despite the extensive research conducted on thermoelectric (TE) modules, their efficiencies are still low; therefore, any contribution to increase the efficiency of TE modules is valuable. It is known that the efficiency of individual TE modules depends on the temperature difference between their hot and cold faces. In practical applications employing an array of TE modules, the temperature distribution along the flow direction varies, which adversely affects system's efficiency. In this study, it is aimed to attain a homogeneous temperature distribution along a number of TE pieces by focusing on the structure of TEG heat exchanger. The proposed design includes an intermediate layer of liquid that plays a key role in keeping the temperature distribution homogeneous and at the desired temperature difference level. A three-dimensional (3D) computational fluid dynamics (CFD) model was developed for analyzing the circulation of liquid layer and the thermal behavior in the system. Results show decrease in temperature deviation both on cold and hot sides of TE modules, while the decrease is more on the latter. With more homogeneous temperature distribution along the TE surfaces, it is possible to tune the system to operate TE modules in their optimum temperature differences. It is illustrated that the heat transfer rate is increased by 11.71% and the electric power generation is enhanced by 19.95% with the proposed heat exchanger design. The consumption of pumping power has taken into account in the efficiency calculations.

Optimizing dimension of heat sink’s plate fin with the effect of wind velocity in site router tecommunication system

Nowadays, heat dissipation for electronic chips, microprocessors in electrical and electronic equipment, especially in Site Router telecommunication equipment when operating at high intensity is an urgent process to increase life expectancy, productivity and performance. Many telecom providers such as Huawei, Ericsson, Cisco etc have offered solutions for liquid cooling, cold air, heat pipes. However, the complexity, the cost and the effect are not high. Furthermore, there is shortage in optimal parameters of design and operation [1-5]. Derived from the above fact, the author has calculated and modeled a Site Router equipment using extruded blast heat exchanger with a large heat exchanger structure which withstands pressure when falling, combining airflow from fans to speed up the dissipation of heat. In this paper, the author presents the optimal calculation and control process of the size of the heat sink and the contact plate under the influence of actual operation conditions at the specified velocity of the air flow from which the model is built directly to determine the number and the size of the heat sink’s plate fins.

CFD simulation different inner structure of air heat exchanger

Air heat exchanger is the key equipment to fresh air ventilation system, which is helpful for energy recovery. Hence, how to promote the heat exchanger performance are commonly studied. In the present paper, air heat exchanger thermal efficiency was investigated in an office room in summer and four kinds of difference structure of air heat exchanger performances were simulated by computational fluent dynamics (CFD), and showed the air heat exchanger internal temperature distributions and thermal efficiencies. It was found that inner temperature distributions of difference structure of air heat exchanger were difference. The results showed that increasing inlet velocity from 1.2 m/s to 2.5 m/s, thermal efficiencies declined 25 % and energy recovery decreased, and pressure dropped no more than 20 Pa. The study provided that the thermal efficiency of the heat exchanger was affected by the inner structure of air heat exchanger, and inlet velocity was the most important factor.

Simulation of the Deformational Cutting and the Geometric Parameters of Pin Structures to Analyze the Thermohydraulic Characteristics of Heat-Removal Plates

A principle is proposed to form a heat-exchange developed structure with the required thermohydraulic characteristics by deformational cutting using end-to-end computer simulation. Several simulation stages, including the finite element simulation of deformational cutting, are considered using the formation of an acicular pin as an example. The discrepancy between the main geometric parameters of the pin model and a real sample does not exceed 10%.

Thermal-exergetic behavior of a vertical double-tube heat exchanger with bubble injection

ABSTRACTThe use of air bubbles as a heat transfer improvement technique for heat exchangers has been proposed by some researchers. The vertical motion of tiny bubbles because of density difference with liquid provides extra vibration, eddies, turbulences, and consequently further heat transfer rate. The variety of affected parameters, such as injection method, air mass flow rate, bubbles size, number of perforations that forms bubbles, etc., has added to the complexity of this phenomena so that any change in the said parameters significantly influences the thermal-exergetic behavior of the heat exchanger. The quality and quantity of the impact of bubbles on the thermal performance of heat exchangers are different for any type of them. Moreover, each type of heat exchanger requires a specific injection method depending on the heat exchanger structure. In the present research, an injection way is proposed for vertical double-tube heat exchangers, and the effect of bubbles on thermal-exergetic characteristics is experimentally studied and discussed, which have not been performed before. Nondimensional exergy destruction, number of heat transfer units, and effectiveness are the main evaluated parameters in the present paper. Results showed a significant thermal improvement of the heat exchanger under the bubble injection.

A previously unnoticed vascular trait of the middle ear suggests that a cranial heat-exchange structure contributed to the radiation of cold-adapted songbirds

Passeriform birds exhibit previously unreported differences in the course of the arteria ophthalmica externa in the middle ear, which can easily be traced through examination of the involved osseous structures. In the Suboscines and most of the Oscines outside the clade Passerida, the arteria ophthalmica externa runs in the same osseous canal as the vena ophthalmica externa, which is the plesiomorphic condition that is also found in non-passeriform birds. In all Muscicapoidea, Passeroidea, and Certhioidea, as well as in several other taxa of the Passerida and a few songbirds outside this clade, however, the arteria ophthalmica externa is enclosed in its own canal and is widely separated from the vena ophthalmica externa. This derived vascular trait constitutes the first morphological apomorphy of a major subclade of the Passerida and is likely to be of physiological significance. The ophthalmic artery supplies the rete ophthalmicum, which serves as a heat-exchange structure and regulates the brain and eye temperature. The derived course of the arteria ophthalmica externa is here interpreted as an adaptation towards the minimization of heat loss of the arterial blood before it reaches the eye and the brain. The derived state predominantly occurs in taxa that occur in cool climates and may constitute a critical trait enabling the all-season occurrence of songbirds in far northern latitudes.

A New Phase Transition Heat Exchanger for Gas Water Heaters

Gas water heaters take a major part in the Chinese water heater market, while the existing water heater have either low efficiency because of the single utilization of energy or the high failure rate that is caused by low temperature corrosion. A new structure of heat exchanger in the gas water heater is proposed is this article, the heat transfer method of which is not only forced convection, but also phase change heat transfer, which provides a higher heat transfer coefficient in condition of the same heat exchange area, and consequently promote the efficiency of the heat exchanger. An experimental study is carried out to compare the difference between the new water heater and the existing one on efficiency, and result shows that the new water heater is 6% higher in efficiency. Besides, this kind of water heater has a gentle temperature change when a sudden decrease or increase of gas flow rate occurs. An economic analysis is produced in order to predict the economic efficiency of the new heat exchanger. As a result, the new heat exchanger of the water heater can significantly promote the heat transfer efficiency and decrease the failure rate, and it is more economic efficient than the existing one.

Experimental investigation on using the electric vehicle air conditioning system for lithium-ion battery thermal management

It is investigated a lithium-ion battery thermal management (BTM) system using the electric vehicle (EV) air conditioning refrigerant to cool the battery pack directly. In the system, basic finned-tube heat exchanger structure and a special aluminum frame are adopted to design the battery pack thermal management module with lithium-ion batteries of cylindrical shape. The module is then integrated into the electric vehicle air conditioning system using two electronic expansion valves for the automatic control of the pack's temperature with self-programmed control software. Experimental results show that the BTM system can control the battery pack's temperature in an appropriate preset value easily under extreme ambient temperature, as high as 40 °C. In addition, through the refrigerant circuit optimization it can reduce the temperature non-uniformity inside the battery pack. The temperature difference within the pack is less than 4 °C in the constant discharge rate of 0.5 C, 1 C, 1.5 C laboratory tests, and 1.5 °C in road drive tests.

Numerical calculation of wall-to-bed heat transfer coefficients in Geldart B bubbling fluidized beds with immersed horizontal tubes

In dense solid-gas fluidized beds the knowledge of the wall-to-bed heat transfer is of great importance, since it often dominates reactor design and dimensioning. This heat transfer is strongly coupled to the hydrodynamic behavior of the bed material around the immersed objects. In this study the heat transfer coefficient at horizontal tubes in a Geldart B bubbling fluidized bed is determined experimentally and compared to the numerically predicted flow fields. The objective is to improve the understanding and quantify the coupling between hydrodynamics and heat transfer. The findings are applied to derive and verify a numerical-correlative approach for predicting the angle-dependent heat transfer coefficient. Experimental data are obtained from a pilot scale test-rig with different tubular heat transfer probes. Corundum is used as the solid bed material and air as the fluidization gas, entering the cylindrical geometry through a Tuyere nozzle type distributor. The angle-dependent heat transfer coefficient is measured at different superficial gas velocities and probe positions in the bed and compared to three dimensional numerical simulations. The applied CFD model of the fluidized bed treats both gas and powder as Eulerian phases. The size distribution and the shape of the particles is described by two granular phases with corresponding mean diameters and a sphericity factor. The Kinetic Theory of Granular Flow and a sphericity-adapted drag model are incorporated to consider the fluid-solid and solid-solid interactions. The hydrodynamics at the tube surface resulting from the numerical simulations (solid volume fraction, gas velocity and particle velocity fluctuation) are used for correlative calculations of the angle-dependent heat transfer coefficient between the bed material and the immersed tube. Results show that the CFD model is able to predict the magnitude and the tendency of the heat transfer around horizontal tubes correctly and therefore can be used as a valuable tool for designing heat exchanger structures in fluidized bed reactors.

Numerical investigation on paraffin/expanded graphite composite phase change material based latent thermal energy storage system with double spiral coil tube

Latent thermal energy storage (LTES) by using phase change material (PCM) is a promising technology which can solve the temporal and geographical mismatch problems between energy supply and demand in utilization of solar thermal energy and industrial waste heat. However, until now, it is still challenging to provide LTES systems with high energy storage efficiency because of the low thermal conductivity of the PCM and suboptimum structure of heat exchanger. In this work, a novel LTES system with paraffin/expanded graphite (EG) composite PCM and double spiral coil tube as heat-exchange tube was constructed. The radius of the double spiral coil-shaped tube was determined by means of the quasi steady state method. And the effects of heat transfer fluid (HTF) inlet position and the ratio of the heat-exchange area between the inner and outer coil tube on the latent heat storage performance of this system were investigated. Compared with single coil tube, LTES system with double spiral coil tube could reduce the time to finish latent heat storage.

Study on a Battery Thermal Management System Based on a Thermoelectric Effect

As is known to all, a battery pack is significantly important for electric vehicles. However, its performance is easily affected by temperature. In order to address this problem, an enhanced battery thermal management system is proposed, which includes two parts: a modified cooling structure and a control unit. In this paper, more attention has been paid to the structure part. According to the heat generation mechanism of a battery and a thermoelectric chip, a simplified heat generation model for a single cell and a special cooling model were created in ANSYS 17.0. The effects of inlet velocity on the performance of different heat exchanger structures were studied. The results show that the U loop structure is more reasonable and the flow field distribution is the most uniform at the inlet velocity of 1.0 m/s. Then, on the basis of the above heat exchanger and the liquid flow velocity, the cooling effect of the improved battery temperature adjustment structure and the traditional liquid temperature regulating structure were analyzed. It can be seen that the liquid cooling structure combined with thermoelectric cooling demonstrates a better performance. With respect to the control system, the corresponding hardware and software were also developed. In general, the design process for this enhanced battery thermal management system can provide a wealth of guidelines for solving similar problems. The H commutation circuit, matrix switch circuit, temperature measurement circuit, and wireless communication modules were designed in the control system and the temperature control strategy was also developed.

Development and validation of a direct passage arrangement method for multistream plate fin heat exchangers

Passage arrangement quality significantly affects the performance of multistream plate fin heat exchanger (MPFHEs) because a bad arrangement may result in uneven temperature difference field and pressure field between passages and thus reduce the thermal efficiency. However, it is very difficult to design an effective passage arrangement owing to large numbers of possible passage arrangement patterns and complex heat transfer processes between the passages in a MPFHE. This work develops a direct passage arrangement method for MPFHEs to address this problem. In this method, an improvement of passage arrangement with good synergistic heat transfer effect is first proposed. The determination of passage quantity for each fluid is suggested to be proportional to its design heat load. Next, based on the results of the checking calculation, the fin and heat exchanger structure parameters should be adjusted until the constraints including thermal effectiveness, length deviation and pressure drops have been satisfied. Afterwards, the passages are arranged directly by a symmetry arrangement method. To evaluate the effectiveness of this method, three different industrial cases are performed and compared with the existing optimization designs by three evaluation means. The validation results indicate that this method performs better than the complex optimization methods.

Analytical solution of hydrodynamics and heat exchange problem in a porous rectangular channel for thermal boundary conditions of the second kind

In a three-dimensional formulation, an analytical solution of the Darcy-Brinkman equation is obtained together with the two-temperature Schumann model equations for the unidirectional flow of a Newtonian medium in a laminar regime through a horizontal porous channel of a constant rectangular cross-section with known thermal flows at the boundary for small Darcy numbers. The analysis of the specific structure of a compact porous heat exchanger is presented, where the possibilities of the obtained solution for justification its geometrical dimensions during the cooling process of the surface with a heat release of 100 W/cm2 are demonstrated.