HT2008-56233 Slip-flow and Conjugate Heat Transfer in Rectangular Microchannels

ABSTRACT Slip-flow and conjugate heat transfer in rectangular microchannels are studied numerically for thermally developing laminar flow subjected to constant wall temperature (T) and constant wall heat flux (H2) boundary conditions. A three-dimensional numerical code based on finite volume method is developed to solve the coupled energy equations in the wall and fluid regions together with temperature jump at the wall-fluid boundary. A modified convection-diffusion coefficient at the wall-fluid interface is defined to incorporate the temperature-jump boundary condition. The numerical code is validated by comparing the present results with the published data. The effect of rarefaction and wall conduction on the heat transfer in the entrance region is analyzed in detail. Results show that the wall conduction has a considerable influence on the developing Nusselt number along the channel for the H2 boundary condition, particularly at low Knudsen numbers. In the case of the T thermal boundary condition, negligible influence of wall conduction on the Nusselt number is observed for all Knudsen numbers considered

Hardware-in-the-loop testing of control of a precooled desiccant air-cooling system

Increasing the energy efficiency of cooling in buildings is an important component of the management of global energy consumption. A super-efficient cooling system based on the evaporation concept has been developed, and initial simulation results using the MATLAB/Simulink software tool have already been published by our team. In this paper, we present the results of hardware-in-the-loop (HIL) testing of the real-time controller for the cooler. HIL testing is an engineering process in which the actual controller hardware and software are implemented and interfaced with a real-time simulated model of the controlled system. Using HIL testing, many real-world problems can be fixed before testing on the actual prototype. The controller design is implemented on a small-footprint industrial PC with CODESYS RTE and application code, while control software is implemented using IEC 61131-3 programming languages. Similarly, a real-time thermodynamic and input–output variable-based model of the room, environment, and cooler and its mechanical components (sensors and actuators) are modeled using another industrial PC with the same software tools. HIL test results show very good agreement with the offline simulations

Energy-efficient indirect evaporative cooler design framework: An experimental and numerical study

A remarkable surge in cooling demand is observed in the last decades. Currently, the cooling market is dominated by mechanical vapor compression chillers which are energy intensive and use harmful chemical refrigerants. Therefore, the current focus of the current research in cooling is the development of unconventional, sustainable cooling systems. In this regard, indirect evaporative coolers have shown significant potential (particularly under hot-dry climates) with high energy efficiency, low cost, water-based sustainable operation, and benign emissions. However, these systems are in the development stage and have not yet been fully commercialized because of certain design challenges. An innovative indirect evaporative cooler is proposed, fabricated, and experimentally tested in this study. Particularly, the study is focused on the development of heat transfer coefficient correlation for the system for commercial-scale design and expansion. This is because the earlier available correlation is based on simple airflow between parallel plates assumption and does not incorporate the effect of the evaporative potential of the system resulting in under/over-estimation of the heat transfer characteristics. The results showed that the proposed system achieved a temperature drop of 20 °C, a cooling capacity of around 180 W, and an overall heat transfer coefficient of up to 30 W/m2K. Moreover, the study presents an experiment-regression-based heat transfer coefficient correlation that satisfactorily captures the effect of outdoor air temperature and airflow rate ratio which are critical in the design of evaporative coolers. The proposed correlation showed a high (±5%) with experimental data thus making it suitable for the future design of IEC systems over assorted operating scenarios

Recommendations for effective documentation in regional anesthesia: an expert panel Delphi consensus project

Background and objectives: Documentation is important for quality improvement, education, and research. There is currently a lack of recommendations regarding key aspects of documentation in regional anesthesia. The aim of this study was to establish recommendations for documentation in regional anesthesia. Methods: Following the formation of the executive committee and a directed literature review, a long list of potential documentation components was created. A modified Delphi process was then employed to achieve consensus amongst a group of international experts in regional anesthesia. This consisted of 2 rounds of anonymous electronic voting and a final virtual round table discussion with live polling on items not yet excluded or accepted from previous rounds. Progression or exclusion of potential components through the rounds was based on the achievement of strong consensus. Strong consensus was defined as ≥75% agreement and weak consensus as 50%-74% agreement. Results: Seventy-seven collaborators participated in both rounds 1 and 2, while 50 collaborators took part in round 3. In total, experts voted on 83 items and achieved a strong consensus on 51 items, weak consensus on 3 and rejected 29. Conclusion: By means of a modified Delphi process, we have established expert consensus on documentation in regional anesthesia

Review of Dew Point Evaporative Cooling Technology for Air Conditioning Applications

Indirect evaporative cooling has the potential to significantly improve the natural environment. It follows from a significant reduction in electricity consumption in the hot period, and hence lower operating costs for cooling systems. This paper presents the current state of knowledge and research directions on dew point indirect evaporative cooling. It was found that researchers focus on the development of dew point indirect evaporative coolers (DPIEC) by improving its design, geometry, water distribution, and new porous materials implementation. To evaluate the performance of new types of DPIEC, different methods are used by the scientists. Finally, optimized devices are studied in terms of their performance in different systems, like hybrid and desiccant systems, considering different climate conditions. Potential directions of development of evaporative technologies were indicated, such as increasing the coefficient of performance of solid desiccant evaporative cooling systems, developing novel geometry, and efficient water distribution, including development of porous materials

Development of Low Cost Total Energy Exchange Devices for Reducing Building Energy Consumption

The primary goal of this program is to develop a commercially viable enthalpy exchangers that exhibits performance comparable to state-of-the-art exchangers, meets flammability test standards, supports no biological growth, maintains mechanical integrity for a 10 year life (typical of competitive warrantees) and exhibits a total media raw material cost of approximately 1/5 of that of the competition. The first three program tasks were devoted to: (1) gathering background information on competitors and their methods of manufacturing; (2) establishing experimental and evaluation procedures for the program; (3) identifying potential desiccants, supports and binders to be tested; (4) preparing matrix combinations on a laboratory scale; (5) testing component combinations for equilibrium moisture uptakes at different relative humidities (isotherms) and dynamic moisture adsorption rates; (6) using media adsorption properties to models to predict exchanger performance; (7) estimating ease of manufacture and finished wheel costs; and (8) calculating raw material, wheel and cassette costs based on the best media formulations. Since the rotary enthalpy exchangers have high rotational speeds, uptake rate is at least as important as equilibrium moisture uptake. Therefore, a procedure and apparatus were developed to determine adsorption rate so that the Lewis number (the ratio of mass transfer resistance to heat transfer resistance) could be calculated. The calculated values for different media materials could then be used for performance model predictions. Based on the results achieved, three systems have been selected as enthalpy exchange media candidates for the next phase of work. All materials are expected to give at least the same level of sensible and latent performance as the competitive media

Analytical Investigation of a Novel System for Combined Dew Point Cooling and Water Recovery

This paper presents the analytical investigation of a novel system for combined Dew Point Cooling and Water Recovery (DPC-WR system). The operating principle of the presented system is to utilize the dew point cooling phenomenon implemented in two stages in order to obtain both air cooling and water recovery. The system performance is described by different indicators, including the coefficient of performance (COP), gained output ratio (GOR), energy utilization factor (EUF), specific energy consumption (SEC) and specific daily water production (SDWP). The performance indicators are calculated for various climatic zones using a validated analytical model based on the convective heat transfer coefficient. By utilizing the dew point cooling phenomenon, it is possible to minimize the heat and electric energy consumption from external sources, which results in the COP and GOR values being an order of magnitude higher than for other cooling and water recovery technologies. The EUF value of the DPC-WR system ranges from 0.76 to 0.96, with an average of 0.90. The SEC value ranges from 0.5 to 2.0 kWh/m3 and the SDWP value ranges from 100 to 600 L/day/(kg/s). In addition, the DPC-WR system is modular, i.e., it can be multiplied as needed to achieve the required cooling or water recovery capacity

Solid State Microchp Based On Thermophotovoltaic And Thermoelectric Conversion

MicroCHP involves the coproduction of both heat and electric power in (typically) residential heating systems. A range of different energy conversion technologies are currently receiving attention for this application including Stirling engines, internal combustion engines, fuel cells, and Rankine cycles with steam or organic compounds as working fluids. In this work the use of ThermoPhotoVoltaic (TPV) and ThermoElectric (TE) conversion devices either alone or in combination for power production in an oil-fired heating system have been explored. The focus of this work to date has been on sufficient electric power output to achieve self-powering of the appliance with the consideration that reliability of the heating system during power outages may provide the greatest value to the consumer. Also explored is the potential for producing larger power output levels, to 1 kW. Low cost, currently available TE devices, based on bismuth telluride, have very low thermal to electric power conversion efficiencies. The use of these in self-powered heating appliances for other applications is established art. Further for simply self-powering, a low conversion efficiency is all that is required to produce the 100 watts needed to power the system. Advanced TE materials under development offer strong potential for increased efficiency in the future. TPV, while currently at an earlier state of development offers the potential for higher conversion efficiencies. This work will report the production of power with both TE and TPV integrated with a residential boiler. A hydronic system was selected relative to a forced air system because of the lower electric power requirements. Using a novel pressure atomized oil burner in combination with very low power circulating pumps, the total running power demand has been reduced to 72 watts. In consideration of cycling, it is estimated that a minimum steady state power output level of 120 watts is required. Experimental results on power production with both TE and TPV in this system are presented. The potential for integration of both TE and TPV devices in a hybrid system are discussed