Heat Transfer Performance Factor Research Articles

Investigation and evaluation of heat transfer enhancement for PEMFC under high current density based on a multiphase and non-isothermal electrochemical model

Heat management plays a vital role in the efficient and stable operation of proton exchange membrane fuel cells (PEMFCs), especially at high current densities, which is directly related to the cooling flow field (CFF). In this paper, a non-isothermal electrochemical model coupled with CFF of PEMFC is developed, and the effects of CFF structures on the water and heat transfer performance enhancement of PEMFC at high current densities are studied. In addition, an Evaluation Criteria is expected to be applied to evaluate the heat transfer capacity of CFFs. The results indicate that high temperatures effectively alleviate PEMFC concentration polarization. Due to the twists and turns design within the channel, the heat transfer capability of the Wave CFF performs well, Nusselt number and field synergy angle values respectively 35.7 % higher and 3.34 % lower than those of Parallel CFF. Additionally, the heat transfer performance factor is used to evaluate the heat transfer capability of different cooling flow field structures. The performance factor of the Wave CFF reaches 1.44 at a coolant temperature difference of 1 K.

Heat Transfer and Pressure Loss Simulations of Matrix Cooling Channels for Gas Turbine Airfoils

The paper selected 10 geometrical parameter combinations to numerically investigate the dependencies of heat transfer enhancement, flow resistances and overall thermal performance on three geometrical factors including rib inclination angle, channel blockage ratio and subchannel number. The investigated Reynolds number starts at 5,000 and can be as high as 90,000. The turbulence model selected was Transition SST model. The results show that the matrix cooling channels of 30deg rib angle have greater heat transfer enhancement and much higher pressure loss than that of 60deg rib angle. Moreover, matrix cooling channels of higher channel blockage ratio have greater heat transfer enhancement and higher flow friction, while the relationship between the overall thermal performance and the channel blockage ratio depends on the Reynolds number. It was also concluded that the heat transfer performance factor of matrix cooling channel does not change linearly with the subchannel number and the effect of subchannel number on heat transfer performance is less significant than the other two factors. Besides, matrix cooling channels of higher subchannel number have higher pressure loss and poorer overall thermal performance.

Effect of rib diameter on flow boiling heat transfer with staggered rib arrays in a heat sink

With the integration development of electronic equipment, a more compact and higher efficiency heat dissipation system is required to meet its cooling demands. In this work, the design of ribbed channel heat sink in a limited volume to maximize its heat transfer capacity is analyzed. Two-phase flow boiling performance of rib diameters ranging from D = 1–10 mm is characterized using the Mixture multiphase model. The working fluid is coolant Novec649 and its mass flux is 1527 kg m−2 s−1. The heat fluxes imposed on the channel wall range from 50 to 300 kW m−2. The results show that the average heat transfer coefficient increases and the wall temperature decreases with the increase of the rib diameter, respectively. The heat transfer performance factor increases with the decrease of heat fluxes, and first decreases with the increase of the rib diameters, then keeps constant. The comprehensive heat transfer performance factor is defined by temperature uniformity. It appears two maximum values which are located at D = 5 and 10 mm, one minimum value at D = 7.14 mm. The best comprehensive heat transfer performance of the heat sink is at D = 10 mm.

Optimization of heat transfer and pressure drop of the channel flow with baffle

Abstract In this article, the numerical analysis has been carried out to optimize heat transfer and pressure drop in the horizontal channel in the presence of a rectangular baffle and constant temperature in two-dimension. For this aim, the governing differential equation has been solved by computational fluid dynamics software. The Reynolds numbers are in the range of 2,000 < Re < 10,000 and the working fluid is water. While the periodic boundary condition has been applied at the inlet, outlet, and the channel wall, axisymmetric boundary condition has been used for channel axis. For modeling and optimizing the turbulence, k–ω SST model and genetic algorithm have been applied, respectively. The results illustrate that adding a rectangular baffle to the channel enhances heat transfer and pressure drop. Hence, the heat transfer performance factor along with maximum heat transfer and minimum pressure drop has been investigated and the effective geometrical parameters have been introduced. As can be seen, there is an inverse relationship between baffle step and both heat transfer and pressure drop so that for p/d equal to 0.5, 1, and 1.25, the percentage of increase in Nusselt number is 141, 124, and 120% comparing to a simple channel and the increase in friction factor is 5.5, 5, and 4.25 times, respectively. The results of modeling confirm the increase in heat transfer performance and friction factor in the baffle with more height. For instance, when the Reynolds number and height are 5,000 and 3 mm, the Nusselt number and friction factor have been increased by 35% and 2.5 times, respectively. However, for baffle with 4 mm height, the increase in the Nusselt number and friction factor is 68% and 5.57 times, respectively. It is also demonstrated that by increasing Reynolds number, the maximum heat transfer performance has been decreased which is proportional to the increase in p/d and h/d. Moreover, the maximum heat transfer performance in 2,000 Reynolds number is 1.5 proportional to p/d of 0.61 and h/d of 0.36, while for 10,000 Reynolds number, its value is 1.19 in high p/d of 0.93 and h/d of 0.15. The approaches of the present study can be used for optimizing heat transfer performance where geometrical dimensions are not accessible or the rectangular baffle has been applied for heat transfer enhancement.

Heat transfer enhancement through a rectangular channel by DBD plasma actuators as vortex generators

This paper represents a three-dimensional numerical simulation to figure out the application of the DBD plasma actuators as an active vortex generator system to enhance heat transfer through a smooth rectangular channel. This system as an active flow control device consists of a pair of DBD plasma actuators, which have been implemented asymmetrically on the bottom wall by several angles of attack to induce the cross airflow. The investigation deals with the optimum angle of attack according to different Reynolds number (Re) ranging from 2300 to 3800 and alternating current voltages of 31–37 kV. The heat transfer rate, pressure drop, and overall performance have been assessed. The results show the optimum choice for the angles of attack was 30° among various flow conditions. By this design, at the voltage of 37 kV and Re of 2300, the average Nusselt number (Num) increased about 56% and heat transfer performance factor ( $$\eta$$ ) increased about 111%. Furthermore, at the lowest applied voltage (31 kV) and highest Reynolds number (3800), the value of Num rises to 41% and 59%, respectively. Thereupon, as the next optimum choices, angle of attack of 45° at high Re and angle of attack of 15°at low Re enhanced heat transfer performance.

Comparative study of heat transfer enhancement using different fins in semi-circular absorber tube for large-aperture trough solar concentrator

An improved evacuated absorber tube (AT) design consisting of a semi-circular tube is proposed for large-aperture parabolic trough concentrator. The absorber tube also contains a flat-plate radiation shield in the vacuum part of the tube in the glass cover. To enhance the heat transfer in the AT, different fins geometries added to the bottom of the AT were analyzed here. Compared to an AT without fins, the thermal efficiency of the tube could be increased from 75.7% to 76.9% with a short and thick fin and to 77.3% with a long and thin fin in the flow velocity range of 0.4–1.5 m/s. The long and thin finned AT shows better enhancement of heat transfer, but the heat transfer performance factor also accounting for frictional losses is higher for short and thick fin. Simultaneously, increasing the number of long and thin fins in the AT would not improve much the heat transfer performance.

Heat Transfer Enhancement Analysis of Tube Receiver for Parabolic Trough Solar Collector With Central Corrugated Insert

Abstract Tube receiver with central corrugated insert was introduced as the absorber tube of parabolic trough receiver to increase the overall heat transfer performance of the tube receiver for parabolic trough solar collector (PTC) system. The Monte Carlo ray tracing method (MCRT) coupled with finite volume method (FVM) was adopted to investigate flow characteristics and the heat transfer performance of tube receiver for parabolic trough solar collector system. The numerical results were successfully validated with the empirical correlations existing in the literature. The numerical results indicated that the introduction of the corrugated insert inside the absorber tube of the parabolic trough receiver can effectively enhance the heat transfer performance, where the average Nusselt number can be increased up to 3.7 times compared to the smooth absorber. While the overall heat transfer performance factor can be found to be in the range of 1.3–2.6. The results indicate that the heat transfer increases with increasing corrugated insert twist ratio and increases also with decreasing pitch between two corrugations.

Effect of Actual Gas Turbine Operating Conditions on Mist/Steam Cooling Performance in a Ribbed Passage

This study numerically examines the effect of actual gas turbine operating conditions on heat transfer characteristics in a ribbed passage with mist/steam cooling. A 60° ribbed passage with aspect ratio of 1/1 was investigated at Reynolds number of 300,000, and steam cooling was used to provide a contrast. Three main factors were considered: coolant temperature, operating pressure, and wall heat flux density. The heat transfer enhancement mechanism of mist/steam cooling was explored, and the results showed that the heat transfer performance of mist/steam cooling was superior to steam cooling. When the coolant temperature varied from 300 to 500 °C, the average Nusselt number of mist/steam cooling decreased by 26.6%, and the heat transfer enhancement ratio dropped from 15% to 10%. As operating pressure increased, the heat transfer performance factor of mist/steam firstly increased and then decreased. At an operating pressure of 1.5 MPa, the heat transfer achieved its optimal performance, and the heat transfer enhancement ratio achieved its maximum value of 15.9%. Larger wall heat flux density provided less heat transfer enhancement. When the heat flux density increased from 100,000 to 300,000 W·m−2, the average Nusselt number of mist/steam cooling decreased by 13.8%, while the heat transfer enhancement ratio decreased from 25.3% to 12.6%.

Characteristic analysis and structure optimization of a type of plate heat exchanger

In this work, the single-phase heat transfer and flow characteristics in a type of plate heat exchanger considering water as working medium are numerically simulated and analyzed, which agree well with experimental results. To further optimize the plate structure, eight cases for three exchanger factors including corrugation inclination, corrugation normal pitch and corrugation depth are selected using uniform experimental design method for investigation. Based on the results, the regression equation of comprehensive heat transfer performance factor Ψ is proposed. The Ψ reaches the maximum in the condition of β = 110°, P=5.8mm, b=3.2mm and increases by 31.27% compared with Ψ0 in the initial condition.

Experimental Investigation of Hydro¬dynamics and Heat Transfer Characteristics of Two-Phase Gas/Liquid Mist Flow in Tandem Arranged Heated Spheres

The article presents an experimental investigation, performed to evaluate the hydrodynamics and heat transfer characteristics in tandem arranged heated rows packed inside cylindrical channel, which use air as well as air/water mist flows as operational medium. The average surface temperature has been recorded under various air main flow, water mist rate, surface heat flux and constant pitch ratio ( y / d = constant). The heat transfer rate was found to increase with the water mist rate and decrease with the surface temperature. Heat transfer rate was enhanced over that for the single-phase air flow as a result of water mist evaporation and direct heat conduction by the water film generated on the heated surfaces. Overall, the heat transfer coefficient was enhanced by about 140%, 42%, and 10% respectively for the upper, middle and lower heated rows by suspending (111.68 kg m –2 hr –1 ) water mist rate. The frictional resistance for air/water mist flow is found to exceed that in the single-phase air flow. Compared to each water mist rate over the investigated range, the percentage enhancement in the overall heat transfer performance factor of around 116%, 35%, and 10% respectively for all the heated rows under the highest water mist rate. New experimental results obtained can be used in the development of heat exchanger modules design processes.

Heat transfer enhancement analysis of tube receiver for parabolic trough solar collector with pin fin arrays inserting

Tube receiver with pin fin arrays inserting was introduced as the absorber tube of parabolic trough receiver to increase the overall heat transfer performance of tube receiver for parabolic trough solar collector system. The Monte Carlo ray tracing method (MCRT) coupled with Finite Volume Method (FVM) was adopted to investigate the heat transfer performance and flow characteristics of tube receiver for parabolic trough solar collector system. To validate the feasibility of the developed MCRT and FVM combined method, the numerical results have been compared with experimental results conducted in the DISS test facility in Spain and the max relative error is less than 5%. The numerical results indicated that the introduction of absorber tube with pin fin arrays inserting design for the absorber tube of the parabolic trough receiver can effectively enhance the heat transfer performance. The average Nusselt number can be increased up to 9.0% and the overall heat transfer performance factor can be increased up to 12.0% when the tube receiver with pin fin arrays inserting was used.

Heat transfer performance enhancement and thermal strain restrain of tube receiver for parabolic trough solar collector by using asymmetric outward convex corrugated tube

With the aim to increase the overall heat transfer performance and reliability of tube receiver for parabolic trough solar collector system, asymmetric outward convex corrugated tube is introduced as the metal tube of parabolic trough receiver. An optical-thermal-structural sequential coupled method was developed to study the heat transfer performance and thermal strain of tube receiver for parabolic trough solar collector system. Heat transfer performance and thermal strain comparisons between conventional tube receiver and asymmetric outward convex corrugated tube receiver are conducted. The researches indicated that the usage of asymmetric outward convex corrugated tube as receiver can enhance the heat transfer performance and reduce the thermal strain effectively. By using asymmetric outward convex corrugated tube as receiver, the maximum enhancement of overall heat transfer performance factor is 148% and the maximum restrain of von-Mises thermal strain is 26.8%.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

A Generalized Prediction of Heat Transfer Surfaces

A new way of presenting the heat transfer data is shown. This leads to a dimensionless performance plot between a “heat transfer performance factor” and a “pumping power factor” with a nondimensional “flow length between major boundary layer disturbances” as a varying parameter. This approach leads to the possibility of approximately presenting all surface geometries on a single “idealized” performance plot, the nondimensional “flow length” being a geometrical characteristic of each surface. The method can be used to predict approximately the heat transfer performance characteristics of a new, untested surface. The plot permits the rapid assessment and comparison of various heat transfer geometries for a given application. The performance plot is valid only in the turbulent flow regime. The method will prove invaluable in optimizing a design accounting for space limitations, economic restraints, and system considerations such as pumping power and effectiveness tradeoffs.