Experimental analysis and modeling of hydronic radiant ceiling panels using transient-state analysis

The model developed in this investigation considers the hydronic panels as a transient-state heat exchanger connected to a detailed lumped transient model of the building. The behavior of the hydronic ceiling system and the interactions with its environment has been experimentally and numerically evaluated. This article presents the results of a study performed to develop a transient model of hydronic ceiling panels in heating or cooling modes and its environment (window, building structure, internal thermal loads and ventilation).Only the dry regime is considered in this case. Using as inputs the hydronic ceiling and room dimensions, material properties and the transient measurements of the air temperature at the adjacent zones, climatic conditions, supply air and water temperatures and mass flow rates, the model permits to estimate the water exhaust temperature, ceiling average surface temperature, resultant and dry air room temperatures, hydronic ceiling power and internal surface temperatures of the room in order to compare with measurements taken during the commissioning process. Two transient tests in heating and cooling modes are used to the experimental validation.     

Experimental study on cooling enhancement of crushed rock layer with perforated ventilation pipe under air-tight top surface

Under the warm and ice-rich nature of permafrost and the scenarios of climate warming on the Qinghai-Tibet Plateau, it will be necessary to use combinatorial techniques of cooling the ground temperature in the proposed Qinghai-Tibet Express Highway of construction. For the crushed rock highway embankment embedded a perforated ventilation pipe in permafrost regions of the Qinghai-Tibet Plateau, the mechanism of impact on the cooling capability enhanced by a perforated ventilation pipe in the air-tight crushed rock layer was studied using laboratory experiment. All boundary conditions at each edge of the crushed rock sample with dimensions of 100 × 60 × 100 cm except the inlet and outlet of the perforated pipe are air-tight. A ventilation steel pipe with an inner diameter of 8 cm was drilled with many small holes with a diameter of 1 cm and horizontally embedded in the length direction of the crushed rock sample with a depth of 53 cm. The laboratory experiments with a periodically fluctuating air temperature in the inner test tank regulated by program control were performed. The perforated pipe is only ventilated during the negative temperature fluctuation period in the inner test tank. The results show that the heat transfer processes in the crushed rock layer embedded a perforated ventilation pipe with an air-tight surface include pure heat conduction, forced convection that occurs in the crushed rock layer forming directly a pore air circulation in conjunction with the in-duct air by the small holes of perforated pipe wall absorbed from the inner test tank, and convective heat transport between the in-duct air and the inner surface of ventilation pipe wall. When air temperatures in the inner test tank are colder than the pore air temperatures in the crushed rock region around the perforated ventilation pipe, the perforated ventilation pipe can produce a significantly enhanced cooling of the crushed rock layer base due to the direct formation of a complete pore air circulation in the crushed rock layer in conjunction with the in-duct air via the small holes of the perforated pipe wall. When the fluctuating air temperature in the inner test tank rises from a minimum value to a warmer one than the pore air temperature in the crushed rock region around the perforated pipe during the negative temperature ventilating period, a warming process begins to occur in the crushed rock layer due to a warmer in-duct air absorbed from the inner test tank. This stronger warming process in the crushed rock region around the perforated pipe may decrease the cooling capability of the air-tight crushed rock layer. Thus, in order to avoid this warming process at this stage before ventilating end, the ventilating end time of ventilation pipe ought to be brought forward.     

A theoretical study on a novel solar based integrated system for simultaneous production of cooling and heating

An integrated system for simultaneous production of triple-effect cooling and single stage heating is proposed in this paper to harness low grade solar energy. The proposed system combines the heliostat field with a central receiver and the ejector-absorption cycle with the shaft power driven transcritical CO₂ cycle. A parametric study based on first and second laws of thermodynamics is carried out to ascertain the effect of varying the exit temperature of duratherm oil, turbine inlet pressure, and evaporators temperature on the energy and exergy output as well as on the energy and exergy efficiencies of the system. The results obtained indicate that major source of exergy destruction is the central receiver where 52.5% of the inlet solar heat exergy is lost followed by the heliostat where 25% of the inlet exergy is destroyed. The energy and exergy efficiencies of the integrated system vary from 32% to 39% and 2.5%–4.0%, respectively, with a rise in the hot oil outlet temperature from 160 °C–180 °C. It is further shown that increase in evaporator temperature of transcritical CO₂ cycle from −20 °C to 0 °C increases the energy efficiency from 27.45% to 43.27% and exergy efficiency from 2.51% to 2.97%, respectively. The results clearly show how the variation in the values of hot oil outlet temperature, turbine inlet pressure, and the evaporator temperature of transcritical CO2 cycle strongly influences the attainable performance of the integrated system.     

Experimental study on the performance of a simultaneous heating and cooling multi-heat pump with the variation of operation mode

The cooling load in the winter season becomes significant in commercial buildings and hotels because of the wide usage of office equipment and improved wall insulation. In this study, a simultaneous heating and cooling multi-heat pump having four indoor units and an outdoor unit was designed and tested in five operation modes: cooling-only, heating-only, cooling-main, heating-main, and entire heat recovery. The performance of the system with R410a was optimized by adjusting the system's control parameters. In the cooling-main mode, the rate of the bypass flow to the heating-operated indoor unit was optimized by controlling the EEV opening of the outdoor unit. In the heating-main mode, the mass flow rate to the cooling-operated indoor unit was optimized by adjusting the EEV opening in the outdoor unit. In the entire heat recovery mode, the compressor speed was controlled to improve the system COP with appropriate heating and cooling capacities.     

Experimental study on cooling performance of air conditioning system with dual independent evaporative condenser

Evaporative condenser is an energy efficient and environmentally friendly air conditioning equipment. This paper proposed an air conditioning system using dual independent evaporative condenser and investigated the cooling performance. Many factors, such as evaporator water inlet temperature, compressor frequency, air dry-bulb temperature, air velocity and water spray rate, which influenced the cooling performances of air conditioning system with evaporative condenser have been investigated. The results indicated that cooling capacity and coefficient of performance (COP) increased significantly with the increasing of evaporator water inlet temperature (12–25 °C), the air velocity (2.05–3.97 m s⁻¹) and the water spray rate (0.03–0.05 kg m⁻¹ s). However, COP decreased with the increasing ambient air dry-bulb temperature (31.2–35.1 °C) and the compressor frequency (50–90 Hz). Furthermore, the heat transfer coefficient (K₀) was 232–409 W m⁻² K⁻¹ in different air velocity and water spray rate.     

Experimental study of boiling on heating surfaces during the thermal fluidization of a bed of particles

The results of an experimental investigation into the boiling of distilled water, aqueous solutions of NaCl, and sea-water brine on heating surfaces situated in a bed of mutuallydisconnected particles at atmospheric and reduced pressures are presented.     

Optimization of a magnetic refrigerator at room temperature for air cooling systems

The purpose of this study is to understand the optimum operating condition of magnetic refrigerator at room temperature for direct air-cooling. The basic components of the target system are a magnetic circuit including two permanent magnets, a test section, an air blower, and an associated instrumentation. The test section consists of 10 test cells which enclose gadolinium chips as a magnetic working substance in a prescribed packing rate. In order to change the applied magnetic field from 0 to 0.9 T, the magnetic circuit is installed on an electric slider which generates reciprocating motion. The system performances are widely investigated both experimentally and analytically for the variety of conditions such as a volumetric flow rate of air, a packing length of magnetic working substance, and a heat exchange cycle. The results reveal that the present magnetic refrigerator has a maximum value of the cooling rate in an appropriate operating condition.     

Numerical study on cooling characteristics of two-phase closed thermosyphon embankment in permafrost regions

The two-phase closed thermosyphon (TPCT) is an effective heat transfer device decreasing the ground temperature around it in cold season, but not absorbing heat energy in warm season. In this paper, in order to research the efficiency of the TPCT applied to the embankment in permafrost regions, a three-dimension model for the TPCT embankment was presented based on the work characteristics of the TPCT and on the related heat transfer theories. The numerical results showed that 1) the model can reasonably solve the coupled heat transfer problem of air-TPCT-soil for TPCT embankment; 2) the TPCT embankment is effective to protect the underlying permafrost and to ensure the stability of roadway in permafrost regions; furthermore, it could play rapidly a cooling effect and approach a thermal balance state after 5 years of construction; and 3) the TPCT, if combined with other engineering methods such as insulation, crushed rock, etc., can be an more effective engineering measure to ensure the stability of roadway engineering in warm permafrost regions.     

Experimental and numerical study of heavy gas dispersion in a ventilated room

In order to better evaluate the consequences of an accidental release of heavy gas, such as uranium hexafluoride (UF(6)), in some installations in the nuclear fuel cycle, an experimental and numerical study was conducted by IRSN on heavy gas dispersion in a ventilated room. This study was based on about 20 injection configurations of a large quantity of a heavy tracer gas, sulphur hexafluoride (SF(6)), inside two ventilated rooms of different sizes. Stratification of the tracer gas was detected in all the configurations studied, even at low concentrations. Numerical simulations performed with the multidimensional CFX code enabled the stratification and the concentration levels reached in the rooms to be predicted overall, and the higher the air flow rate, the more satisfactory the comparison between simulation and experiment.     

火车站候车厅热舒适性模拟研究

本文利用CFD技术作为辅助工具,运用商用软件Airpak,采用k-ε模型进行求解,对西安北站候车大厅的热舒适性进行模拟计算,通过模拟计算对热舒适性进行预测。计算结果表明PMV以及PPD值均能满足规范要求。通过模拟计算可以利用较低的成本为工程设计提供可靠的理论依据。     

Thermoelectric cooling of microelectronic circuits and waste heat electrical power generation in a desktop personal computer

Thermoelectric cooling and micro-power generation from waste heat within a standard desktop computer has been demonstrated. A thermoelectric test system has been designed and constructed, with typical test results presented for thermoelectric cooling and micro-power generation when the computer is executing a number of different applications. A thermoelectric module, operating as a heat pump, can lower the operating temperature of the computer's microprocessor and graphics processor to temperatures below ambient conditions. A small amount of electrical power, typically in the micro-watt or milli-watt range, can be generated by a thermoelectric module attached to the outside of the computer's standard heat sink assembly, when a secondary heat sink is attached to the other side of the thermoelectric module. Maximum electrical power can be generated by the thermoelectric module when a water cooled heat sink is used as the secondary heat sink, as this produces the greatest temperature difference between both sides of the module.     

Experimental investigation on cold startup characteristics of a rotary compressor in the R290 air-conditioning system under cooling condition

R290 is one of the most alternative refrigerants for the air-conditionings for its negligible environmental impact and high efficiency. This experimental study investigated the cold startup characteristics of the rotary compressor in a R290 air-conditioning system under cooling condition. The characteristics include the pressures and temperatures in the system and the rotary compressor respectively, the mixture of oil and refrigerant viscosity and oil level of the oil sump. The measurements showed that the startup time for the pressures and the temperatures were much longer than that of R410A and R22 systems. A slight liquid slugging happened in the cylinder at the initial time of startup for the pressure during the later exhaust process increasing rapidly to 2.21 MPa in 1.3 seconds. After startup of the system, both the mixture of oil and refrigerant viscosity and oil level of the oil sump in the compressor were within a proper range to guarantee a steady startup of the air-conditioning system.     

Experimental study on the performance of a room temperature magnetic refrigerator using permanent magnets

An investigation of a room temperature active magnetic refrigerator was carried out in this work. An experimental rig was built, in which two reciprocating regenerative beds packed with 1167.4 g of gadolinium were used, helium gas was used as a heat transfer fluid, and an average 1.5 T magnetic field was supplied by permanent magnets. With this apparatus, the influence of the gas pressure, the operating frequency and the temperature range were studied systematically. The lowest no heat load temperature of −2.79 °C at the cold end heat exchanger and a maximum no heat load temperature span of 42.28 °C were obtained. A maximum cooling power of 51.3 W was achieved over a temperature span of 18.16 °C. The results in this study provide useful data for future design and development of room temperature magnetic refrigerators.     

层式通风室内气流组织特性试验研究

针对新型通风方式——层式通风,测量不同换气次数条件下办公室呼吸区位置的气流组织,主要测量温度、速度及浓度,并根据测量结果对呼吸区热舒适度进行研究。结果表明：5次较6次换气次数条件下呼吸区温度、污染物浓度以及风速更优;PMV及PPD的计算结果表明,5次换气次数条件下,呼吸区具有更佳的热舒适度。研究结果对层式通风在工程应用和相关理论研究中具有重要的指导意义。     

Ice formation process by cooling water–oil emulsion with stirring in a vessel

An emulsion, which was a mixture of silanol-aqueous solution and silicone oil, was investigated as a heat storage material for a dynamic type ice storage system. The emulsion was poured into a vessel, which was immersed into a constant temperature bath at a low temperature, and frozen with stirring. Using stainless steel vessels coated with PFA resin and PTFE vessels with different thickness, the experiments were carried out under various conditions of temperature. Measuring the temperature history in the vessel, overall heat transfer coefficients before the start of freezing and during the ice formation were obtained. The effects of the material of the cooling surface and the thermal resistance of the wall on the ice formation process were clarified. If the heat flux of the wall was less than a critical value, slurry ice was formed without adhesion to the cooling surface. The results obtained under the same condition of the thermal resistance proved that it was effective against ice adhesion to coat PFA resin inside the vessel. It was found by the experiments in which the PTFE vessels were used that the critical value of the heat flux was nearly constant regardless of the thermal resistance.     

Laboratory investigation on the cooling effect of the embankment with L-shaped thermosyphon and crushed-rock revetment in permafrost regions

The road construction engineering in permafrost regions and global warming can both induce warming, even thaw permafrost, which exert great influence on the embankment stability. A series of cooling technique, e.g. insulation, crushed-rock revetment and thermosyphon, has been proved to be effective to keep the thermal stability of embankment. However, almost all of the present cooling measures are limited to the embankment of ordinary width. Since the heat intake of the embankment increases greatly due to the width and asphalt pavement for high-grade highways of large width, the traditional cooling measures may be inadequate to protect the underlying permafrost and ensure the stability of the embankment. Because of these factors mentioned above, an L-shaped thermosyphon was presented, and was applied to the wide-width embankment with crushed-rock revetment and insulation. A laboratory test was carried out to investigate the joint cooling effect of this new kind of embankment and the property of the L-shaped thermosyphon. Laboratory test results indicate that the combined measures, presented in the paper, is able to keep the thermal stability of large-width embankment in cold regions.     

Methodology research on solving non-steady state radiation heat transfer in the room with Ceiling Radiant Cooling Panels

Long wave radiation heat transfer is the dominant cooling mode of the Ceiling Radiant Cooling Panels (CRCP). This unique cooling mode makes the calculation of indoor long wave radiation heat transfer extremely important. Actually, indoor radiation heat transfer is usually under non-steady state conditions. General calculation methodology (simplifying radiation heat transfer or using the equivalent network method of steady state) is complex and less accurate when solving this kind of problem. In addition, general methodology fails to solve the situation that the temperatures of some interior surfaces are lacking but the heat flows are known. This paper provides a calculation methodology improving the Gebhart method for modeling the non-steady state radiation heat transfer between indoor surfaces. Given parameter variations (temperature and net radiant heat flow) of the surfaces are transformed into discrete column vectors of unit time, and then matrix equations are established, which can greatly reduce the work. This methodology has been verified experimentally, which can be regarded as a theoretical basis for solving indoor non-steady state radiation heat transfer of CRCP systems.     

Experimental analysis of a novel cooling system driven by liquid refrigerant pump and vapor compressor

This study introduced a novel energy saving cooling system, i.e. a combined cycle coupled with a traditional vapor compression cycle with a pumped liquid two-phase cooling cycle. The system has two operation modes, i.e. the compression cycle mode driven by compressor and the pump cycle mode driven by refrigerant pump. A multi-purpose test bench was constructed to experimentally evaluate the performance of the integrated cycle system under various operation conditions. The effects of cycle working condition and the shift temperature between the two operation modes on the overall cycle performance were investigated in detail. It is found that the novel cycle system has a higher EER compared to the traditional compressor system when the ambient temperature is relatively low. The further experimental results and comparative annual energy saving analysis also indicated that the proper shift temperature is about −5 °C from the system EER and cooling capacity point of view.     

Neural model for forecasting temperature in a distribution network of cooling water supplied to systems producing petroleum products

This article presents the application of a neural model of heat transfer for the purpose of forecasting temperature at selected points of a circulating water ring network. The purpose of a circulating water system is to lower the temperature of petroleum products manufactured on numerous petrochemical lines at a Polish petrochemical plant. Temperature forecasting at 96 nodes of the circulating water system, significant from the point of view of system operation, is carried out using SVM neural networks. Neural networks learn based on archival data recorded in the process parameter monitoring system. Thermal, hydraulic and control parameters of the cooling process, as well as weather variables, constitute crucial input data for the neural model. The temperature forecasting algorithm has been implemented in a computer program that was then applied and remains in use for temperature forecasting in a maintenance department of an industrial plant.