scholarly journals Modeling and Analysis of a Coated Tube Adsorber for Adsorption Heat Pumps

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6878
Author(s):  
João M. S. Dias ◽  
Vítor A. F. Costa
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Working Conditions ◽  
Fluid Velocity ◽  
Heat Pumps ◽  
Heating Power ◽  
Adsorption Heat ◽  
Coefficient Of Performance ◽  
Water Heating

This work investigates the effects of several parameters on the coefficient of performance (COP) and the specific heating power (SHP) of a coated-tube adsorber for adsorption heat pumps (AHP) suitable for water heating (space and/or domestic water heating). The COP and SHP are obtained based on physical models that have already been proven to adequately describe this type of adsorber. Several parameters are tested, namely, the regeneration, condenser and evaporator temperatures, the heat transfer fluid velocity, the tube diameter, the adsorbent coating thickness, the metal–adsorbent heat transfer coefficient, and the cycle time. Two different scenarios were tested, corresponding to distinct working conditions. The working conditions for Scenario A are suitable for pre-heating water in mild climates. Scenario B’s working conditions are based on the European standard EN16147. The maximum COP is obtained for regeneration temperatures of 75 °C and 95 °C for Scenarios A and B, respectively. The COP increases for longer cycle times (more complete adsorption and desorption processes) whilst the SHP decreases (less complete cycles by unit time). Hence, the right balance between the COP and the SHP must be found for each particular scenario to have the best whole performance of the AHP. A metal–adsorbent heat transfer coefficient lower than 200 W·m−2·K−1 leads to reduced SHP. Lower adsorbent coating thicknesses lead to higher SHP and can still provide reasonably high COP. However, low coating thicknesses would require a too-high number of tubes to achieve the desired adsorbent mass to deliver the required useful heating power, resulting in too-large systems. Due to this, the best relationship between the SHP and the size of the system must be selected for each specific application.

Experimental Study of Flow Boiling Heat Transfer Coefficient of FC-72 Over Micro-Pin-Finned Surfaces

2010 ◽  
Author(s):  
Y. F. Xue ◽  
M. Z. Yuan ◽  
J. J. Wei
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Experiments of flow boiling heat transfer coefficient of FC-72 were carried out over simulated silicon chip of 10×10×0.5 mm3 for electronic cooling. Four kinds of micro-pin-fins with the dimensions of 30×60, 30×120, 50×60, 50×120 μm2 (thickness, t × height, h) respectively, were fabricated on the chip surfaces by the dry etching technique to enhance boiling heat transfer. A smooth chip was also tested for comparison. The experiments were conducted at three different fluid velocities (0.5, 1 and 2m/s) and three different liquid subcoolings (15, 25 and 35K). All micro-pin-finned surfaces show a considerable heat transfer enhancement compared to the smooth surface. Both the forced convection and nucleate boiling heat transfer contribute to the total heat transfer performance. The contribution of each factor to the total heat transfer has been clearly presented in the flow boiling heat transfer coefficient curves. In a lower heat flux region, the heat transfer coefficient increases greatly with increasing fluid velocity, but increases slightly with increasing heat flux, indicating that the single-phase forced convection dominates the heat transfer process. With further increasing heat flux to the onset of nucleate boiling, the heat transfer coefficient increases remarkably. For a given liquid subcooling, the curves of flow boiling heat transfer coefficient at fluid velocities of 0.5 and 1 m/s almost follow one line for each surface, showing insensitivity of nucleate boiling heat transfer to fluid velocity. However, at the largest fluid velocity of 2 m/s, the slope of the flow boiling heat transfer coefficient curves for micro-pin-finned surfaces becomes smaller, indicating that the forced convection also plays an important role besides the nucleate boiling heat transfer. The curves of the flow boiling heat transfer coefficient can be used to determine the boiling incipience at different fluid velocities, which provides a basis for the suitable fluid velocity selection in designing highly efficient cooling scheme for electronic devices.

scholarly journals Numerical Study on Regenerative Cooling Characteristics of Kerosene Scramjets

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Xuan Jin ◽  
Chibing Shen ◽  
Xianyu Wu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Fluid Velocity ◽  
Regenerative Cooling ◽  
Outlet Pressure

The use of kerosene-based regenerative cooling for scramjet has been found widespread attention due to its inherent nature of high energy utilization efficiency and good thermal protection performance. In order to provide a reference for the later design and experiments, three-dimensional turbulence simulations and sensitivity analysis were performed to determine the effects of three operating mode parameters, heat flux, mass flow rate, and outlet pressure, on the regenerative cooling characteristics of kerosene scramjets. A single rectangular-shaped channel for regenerative cooling was assumed. The RNG k-ε turbulence model and kerosene cracking mechanism with single-step global reaction were applied for the supercritical-pressure heat transfer of kerosene flows in the channel. Conclusions can be drawn that as the kerosene temperature rises along the channel, the decrease of fluid density and viscosity contributes to increasing the fluid velocity and heat transfer. When the kerosene temperature is close to the pseudocritical temperature, the pyrolysis reaction results into the rapid increase of fluid velocity. However, the heat transfer deterioration occurs as the specific heat and thermal conductivity experience their turning points. The higher heat flux leads to lower heat transfer coefficient, and the latter stops rising when the wall temperature reaches the pseudocritical temperature. The same rising trend of the heat transfer coefficient is observed under different outlet pressures, but the heat transfer deterioration occurs earlier at smaller outlet pressure for the reason that the corresponding pseudocritical temperature decreases. The heat transfer coefficient increases significantly along with the rise of the mass flow rate, which is mainly attributable to the increase of Reynolds number. Quantitative results indicate that as the main influence factors, the heat flux and mass flow rate are respectively negatively and positively relative to the intensification of heat transfer, but outlet pressure always has little effects on cooling performance.

Computer 2D modelling of a micro-grip fluid cooling system

2021 ◽  
pp. 4-20
Author(s):  
Ильдар Шамилевич Насибуллаев ◽  
Олег Владимирович Даринцев
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Fluid Velocity ◽  
Physical Parameters ◽  
Peltier Element ◽  
Fluid Cooling ◽  
Flow Frequency

Представлено компьютерное численное моделирование системы жидкостного охлаждения камеры микрозахвата. Построены математические модели течения жидкости, переноса тепла жидкостью, теплообмена между жидкостью и радиатором, теплообмена между радиатором и элементом Пельтье. Определено влияние геометрических и физических параметров камеры микрозахвата на эффективность системы охлаждения, а также найдена зависимость максимальной температуры, установившейся на радиаторе, от скорости течения охлаждающей жидкости и коэффициента теплопередачи между радиатором и жидкостью для стационарного течения. Проведено исследование влияния нестационарного течения жидкости на колебания температуры радиатора. На основе результатов численного моделирования предложены простые аналитические формулы, которые можно использовать в программном обеспечении системы управления микрозахватом Numerical simulation of a micro-grip chamber fluid cooling system is presented. The mathematical models for mass and heat transfer in a fluid, heat exchange between the fluid and the radiator as well as the heat exchange between the radiator and the Peltier element are constructed in a variational form. The equations of hydrodynamics and heat equations were simulated by the finite element method in the FreeFem++ software. The influence of the geometric and physical parameters of the cooling system chamber on the efficiency of the device is determined. It is shown that as the heat transfer coefficient between the radiator and the fluid and the velocity of the coolant increases, the maximum steady-state temperature on the radiator nonlinearly decreases with saturation. When flow of coolant oscillates then the temperature on the radiator so does with the flow frequency. As the flow frequency increases, the amplitude of temperature fluctuations decreases. The increasing amplitude of flow oscillations leads to the amplification of the temperature amplitude. Using orthogonal central compositional method, the influence of the parameters (heat transfer coefficient, fluid velocity) on the efficiency of the cooling system is found, and the contribution of pairwise interaction is determined. Based on the results of numerical modelling, simple analytical formulas are proposed that can be used in the software module of the micro-grip cooling control system.

Electrohydrodynamic Microfabricated Ionic Wind Pumps for Thermal Management Applications

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Andojo Ongkodjojo Ong ◽  
Alexis R. Abramson ◽  
Norman C. Tien
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Management ◽  
High Reliability ◽  
Semiconductor Industry ◽  
Heat Removal ◽  
Coefficient Of Performance ◽  
Air Cooling ◽  
Ionic Wind

This work demonstrates an innovative microfabricated air-cooling technology that employs an electrohydrodynamic (EHD) corona discharge (i.e., ionic wind pump) for electronics cooling applications. A single, microfabricated ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. A grid structure on the collector electrodes can enhance the overall heat-transfer coefficient and facilitate an IC compatible batch process. The optimized devices studied exhibit an overall device area of 5.4 mm × 3.6 mm, an emitter-to-collector gap of ∼0.5 mm, and an emitter curvature radius of ∼12.5 μm. The manufacturing process developed for the device uses glass wafers, a single mask-based photolithography process, and a low-cost copper-based electroplating process. Various design configurations were explored and modeled computationally to investigate their influence on the cooling phenomenon. The single devices provide a high heat-transfer coefficient of up to ∼3200 W/m2 K and a coefficient of performance (COP) of up to ∼47. The COP was obtained by dividing the heat removal enhancement, ΔQ by the power consumed by the ionic wind pump device. A maximum applied voltage of 1.9 kV, which is equivalent to approximately 38 mW of power input, is required for operation, which is significantly lower than the power required for the previously reported devices. Furthermore, the microfabricated single device exhibits a flexible and small form factor, no noise generation, high efficiency, large heat removal over a small dimension and at low power, and high reliability (no moving parts); these are characteristics required by the semiconductor industry for next generation thermal management solutions.

scholarly journals Modeling the Performance of Water-Zeolite 13X Adsorption Heat Pump

2017 ◽  
Vol 38 (4) ◽  
pp. 191-207 ◽  
Author(s):  
Kinga Kowalska ◽  
Bogdan Ambrożek
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Pump ◽  
Heat Pumps ◽  
Adsorption Heat ◽  
Coefficient Of Performance ◽  
Desorption Kinetics ◽  
Zeolite 13X ◽  
Adsorption Heat Pump

Abstract The dynamic performance of cylindrical double-tube adsorption heat pump is numerically analysed using a non-equilibrium model, which takes into account both heat and mass transfer processes. The model includes conservation equations for: heat transfer in heating/cooling fluids, heat transfer in the metal tube, and heat and mass transfer in the adsorbent. The mathematical model is numerically solved using the method of lines. Numerical simulations are performed for the system water-zeolite 13X, chosen as the working pair. The effect of the evaporator and condenser temperatures on the adsorption and desorption kinetics is examined. The results of the numerical investigation show that both of these parameters have a significant effect on the adsorption heat pump performance. Based on computer simulation results, the values of the coefficients of performance for heating and cooling are calculated. The results show that adsorption heat pumps have relatively low efficiency compared to other heat pumps. The value of the coefficient of performance for heating is higher than for cooling

Simulation and validation of air flow and heat transfer in an autoclave process for definition of thermal boundary conditions during curing of composite parts

2017 ◽  
Vol 52 (12) ◽  
pp. 1677-1687 ◽  
Author(s):  
Tobias Bohne ◽  
Tim Frerich ◽  
Jörg Jendrny ◽  
Jan-Patrick Jürgens ◽  
Vasily Ploshikhin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Fluid Dynamic ◽  
Fluid Velocity ◽  
Computational Effort ◽  
Autoclave Process ◽  
Thermal Boundary Conditions ◽  
The Heat Transfer Coefficient

Aerospace carbon fibre-reinforced components are cured under high pressure (7 bar) and temperature in an autoclave. As in an industrial environment, the loading of an autoclave usually changes from cycle to cycle causing different thermal masses and airflow pattern which leads to an inhomogeneous temperature distribution inside the carbon fiber-reinforced plastic part. Finally, the overall process can be delayed and the part quality can be compromised. In this paper, the heat transfer in a small laboratory autoclave has been investigated using calorimeter measurements and a fluid dynamic model. A complex turbulent flow pattern with locally varying heat transfer coefficient has been observed. Especially, the pressure and the inlet fluid velocity have been identified as sensitive process parameters. Further finite element simulations with adjusted boundary conditions provide accurate results of the curing process inside of the components for selective process control. The heat transfer coefficient has been found to be almost stationary during the observed constant pressure autoclave process allowing a separated investigation of the heat transfer coefficient and the curing of the components. The presented method promises therefore a detailed observation of the autoclave process with reduced computational effort.

Multi-Factors Analysis of Condenser Vacuum under Overall Working Conditions

2014 ◽  
Vol 654 ◽  
pp. 109-112
Author(s):  
Ning Ling Wang ◽  
Feng Ming Chu ◽  
Peng Fu ◽  
Zhi Ping Yang ◽  
Yong Ping Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Energy Saving ◽  
Water Flow ◽  
Working Conditions ◽  
Thermal Power ◽  
Maximum Output Power ◽  
Maximum Output ◽  
Circulating Water

It is of great significance to determine an optimal condenser vacuum for energy-saving diagnosis, for the vacuum means a lot to the safe and economic operation of thermal power units. The key parameters were calculated by the practical data, such as the cleanliness factor. The condenser heat transfer coefficient is affected by both the dirty of condenser water side and other factors on the basis of the method of adjusting the circulating-water flow unilaterally to get the optimal vacuum of condenser in this paper. The impacts of the exhausting steam resistance, the oxygen content of condensate caused by the change of the circulating-water flow were considered in this paper. The practical operation data was analysed with the results from HEI. The simulations were examined in the comparison of heat transfer coefficient. The impacts of unit energy consumption characteristics under overall working conditions caused by condenser vacuum were obtained in the approach based on the theory of energy specific fuel consumption (ESFC). The variation of auxiliary specific consumption as the temperature of circulating-water changing was obtained. The results indicated that the optimal condenser vacuum determined by the method aiming at maximum output power and many factors under overall working conditions accounted for played an important role in the energy saving diagnosis of thermal power units.

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