Study of Circuit Number on the Evaporator in CO2 Heat Pump Water Heater

2011 ◽  
Vol 71-78 ◽  
pp. 2266-2270 ◽  
Author(s):  
Kang Liu ◽  
Jing Lv ◽  
Song Bo Zhang ◽  
Jie Yang
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pump ◽  
Temperature Difference ◽  
Water Heater ◽  
Overall Heat Transfer Coefficient ◽  
Heat Pump Water Heater ◽  
Simulation Package

In the design of a carbon dioxide heat pump water heater evaporator, the effect of the circuit number on the evaporator is investigated numerically by EVAP-COND 3.0 version simulation package of American National Institute of Standards and Technology. It is found that as the circuit number increases the temperature difference between the air and the refrigerant increases, but it reduces the overall heat transfer coefficient. The evaporator capacity will rise firstly, and then drop with the circuit number and achieve the maximum in the optimum circuit number. Therefore, selecting the appropriate circuit number of the evaporator can significantly improve the efficiency and optimize the design.

scholarly journals Error Analysis of QUB Method in Non-Ideal Conditions during the Experiment

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3398
Author(s):  
Naveed Ahmad ◽  
Christian Ghiaus ◽  
Moomal Qureshi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Difference ◽  
Temperature Response ◽  
Weather Conditions ◽  
Outdoor Temperature ◽  
Overall Heat Transfer Coefficient ◽  
Median Error ◽  
Indoor And Outdoor

Overall heat transfer coefficient, also known as the intrinsic performance measurement of the building, determines the amount of heat lost by a building due to temperature difference between indoor and outdoor. QUB (Quick U-value of Buildings) is a short-term method for measuring the overall heat transfer coefficient of buildings. The test involves heating and cooling the house with a power step and measuring the indoor temperature response in a single night. Ideally, the outdoor temperature during QUB experiment should remain constant. To compare the influence of variable outdoor temperature, the QUB experiments are simulated on a well-calibrated model with real weather conditions. The experiments at varying outdoor temperature and constant outdoor temperature during the night show that the results in both conditions are nearly similar. A ±2 °C increase or decrease in the outdoor temperature during the QUB experiment can change the results in the measured overall heat transfer coefficient by ±5%. QUB experiments simulated during the months of winter show that the majority of results are ±15% of the steady-state overall heat transfer coefficient. The QUB results during the months of summer show relatively large variation. The large errors coincide with the small temperature difference between indoor and outdoor temperatures before the start of QUB experiment. The median error of multiple QUB experiments during summer can be reduced by increasing the setpoint temperature before the start of QUB experiment.

Diagnostic Method Research on the Dirty Level of the Water Side Tube and the Tightness of Vacuum System of Condenser

2012 ◽  
Vol 614-615 ◽  
pp. 212-215
Author(s):  
Yong Li ◽  
Kai Fu Deng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Difference ◽  
Curve Analysis ◽  
Vacuum System ◽  
Operating Personnel ◽  
Overall Heat Transfer Coefficient ◽  
Side Tube ◽  
Water Side

The condenser vacuum influences the steam turbine’s safety and economy. The dirty level of the water side tube and the air accumulation of the steam side affect overall heat transfer coefficient .That make the condenser vacuum low and terminal temperature difference increase. It is a generally interested problem that making a distinction between fouling loss and air accumulation loss for the operating personnel and maintenance person. In this article, we judged the vacuum system work normal or not by comprehensive cleaning curve, and further calculation and curve analysis were done so as to distinguish the affection of the dirty level of the water side tube and the air accumulation of the steam side to overall heat transfer coefficient and terminal temperature difference.

Utilization of a Graphite Foam Radiator on a Natural Gas Engine-Driven Heat Pump

2002 ◽  
Author(s):  
R. D. Ott ◽  
A. Zaltash ◽  
J. W. Klett
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pump ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Overall Heat Transfer Coefficient ◽  
Bulk Thermal Conductivity ◽  
Graphite Foam

A natural gas engine-driven heat pump was outfitted with a graphite foam radiator to demonstrate its thermal efficiency and compare it with that of a conventional radiator. A sequence of tests was performed with the graphite foam radiator operating in series with the standard aluminum radiator. Most aluminum air-to-water radiators exhibit an overall heat transfer coefficient up to 100 W/(m2·K). Laboratory experiments have demonstrated that a graphite foam radiator can achieve an overall heat transfer coefficient up to an order of magnitude larger. The mesophase pitch derived graphite foam is a material that offers excellent thermal management capability. The foam has an accessible surface area of 4 m2/g and an open cell structure with graphitic ligaments aligned parallel to the cell walls, giving it an overall bulk thermal conductivity of up to 175 W/(m·K). The bulk thermal conductivity of aluminum is 180 W/(m·K). The density of the graphite foam is a fifth of that of aluminum and its thermal diffusivity is three times greater than aluminum. These properties allow the graphite foam to be utilized in radiator, or any other heat exchanger, designs that are more efficient than conventional radiators. A graphite foam radiator designed to reject a given amount of heat will be smaller in size, weigh less, require less cooling air, and be quicker at removing heat than a conventional aluminum radiator.

Heat Transfer Coefficient in Falling Film Evaporators With Different Tube Arrangements

2012 ◽  
Author(s):  
Shengqiang Shen ◽  
Gangtao Liang ◽  
Yali Guo ◽  
Xingsen Mu ◽  
Rui Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Difference ◽  
Saturation Temperature ◽  
Horizontal Tube ◽  
Falling Film ◽  
Overall Heat Transfer Coefficient ◽  
Spray Density ◽  
Total Temperature

A set of experimental facilities were set up to measure overall heat transfer coefficient of horizontal-tube falling film evaporators with triangular, rotated square and square-pitch bundles. Effect of spray density, saturation temperature, total temperature difference and inlet steam velocity on the overall heat transfer coefficient K is studied respectively. The tubes are made of HAL77-2A aluminium brass with an outer diameter of 25.4 mm. Fluids inside and outside the tubes are steam and fresh water respectively. The results indicate that growth of spray density and saturation temperature helps to increase the K. The K could also be increased by reducing the total temperature difference. However, the impact of the inlet steam velocity on the K is less significant. The K in the evaporator with rotated square-pitch arrangement is supreme. Furthermore, space distribution of local overall heat transfer coefficient K̃ in the evaporators is also discussed. Based on this investigation, basic engineering design information will be provided to establish the governing parameters for horizontal-tube falling film evaporator in the field of seawater desalination.

scholarly journals A numerical model and validation of phase change material integrated thermoelectric radiant cooling panel

2019 ◽  
Vol 111 ◽  
pp. 01001
Author(s):  
Hansol Lim ◽  
Hye-Jin Cho ◽  
Seong-Yong Cheon ◽  
Soo-Jin Lee ◽  
Jae-Weon Jeong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Numerical Model ◽  
Surface Temperature ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Phase Change Material ◽  
Overall Heat Transfer Coefficient ◽  
Radiant Cooling ◽  
Change Material

A phase change material based radiant cooling panel with thermoelectric module (PCM-TERCP) is proposed in this study. It consists of two aluminium panels, and phase change materials (PCMs) sandwiched between the two panels. Thermoelectric modules (TEMs) are attached to one of the aluminium panels, and heat sinks are attached to the top side of TEMs. PCM-TERCP is a thermal energy storage concept equipment, in which TEMs freeze the PCM during the night whose melting temperature is 16○C. Therefore, the radiant cooling panel can maintain a surface temperature of 16◦C without the operation of TEM during the day. Furthermore, it is necessary to design the PCM-TERCP in a way that it can maintain the panel surface temperature during the targeted operating time. Therefore, the numerical model was developed using finite difference method to evaluate the thermal behaviour of PCM-TERCP. Experiments were also conducted to validate the performance of the developed model. Using the developed model, the possible operation time was investigated to determine the overall heat transfer coefficient required between radiant cooling panel and TEM. Consequently, the results showed that a overall heat transfer coefficient of 394 W/m2K is required to maintain the surface temperature between 16○C to 18○C for a 3 hours operation.

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