Phase Change Heat Exchanger Research Articles

Numerical Simulation of Ammonia Phase Change Heat Exchanger Which Used for Composite Air-cooling Circulatory System

Direct air cooling system has some problems. Such as, exhaust steam pressure increased with ambient temperature (dry bulb temperature) rising, furthermore cause the high coal consumption of power supply, heavy pollution, the weak environmental adaptability. To solve above problems, the literature [1] puts forward a new indirect air cooling system. In this system, water cooling steam-condenser is transformed into ammonia phase change heat exchanger whose structure is similar to shell-and-tube heat exchanger. In the tube, ammonia-liquid displaces cooling water of water cooling steam-condenser. Latent heat of ammonia-liquid can improve steam condensation effect. Ammonia phase change heat exchanger is simplified as a single horizontal tube. Simulate ammonia-liquid flowing in it by FLUENT. Shah's heat transfer model for boiling region is used to predict heat transfer coefficient. Compare the predicted with numerical value what calculated by FLUENT. Prove the feasibility of composite air-cooling circulatory system.

Chaotic property analysis of pressure fluctuation for oxygen phase change heat exchanger

Pressure fluctuation signals at the inlet/outlet of an oxygen phase-change heat exchanger are analyzed using non-linear method. Chaotic characteristic parameters such as correlation dimension, Kolomogrov entropy and the largest singular value decomposition (SVD) for the covariance matrix of an established 10-dimensional phase space are analyzed. Results prove that the heat exchanger is a non-linear system with chaotic characteristics. Correlations between these parameters and Prantl Number are also examined for the thermal behavior of oxygen in the critical region. The strong dependence of these characteristic parameters on Pr indicates that they can be used to investigate effectively the phase change behavior of pure substance.

Preliminary experimental study of a bio-inspired, phase-change particle capillary heat exchanger

In this study a new cooling concept using encapsulated phase-change particles flowing with water in a parallel-plate mini-channel is presented. This novel concept is inspired by the gas exchange process in alveolar capillaries, where red blood cells (RBCs) flow with blood plasma, yielding very high gas transfer efficiency. Another important characteristic of alveolar capillary blood flow, which is related to the high efficiency of the lungs, is the snug fitting of the RBCs into the capillaries. Hence, preliminary results of experimental tests using particles with diameter similar to the flow channel spacing flowing with water through a heated parallel-plate channel test module are presented and analyzed. The particles are octadecane paraffin (C 18H 38), a phase-change material, encapsulated in a thin melamine shell. The temperature distribution along the heated surface of the channel is measured for various water flow rates, with and without particles, and with different number of particles. Results are reported in terms of the channel heated surface average temperature and the average heat transfer coefficient, showing a sensible increase (over 20%) in the latter as compared to a clear (of particles) flow. There is strong evidence the increase in heat transfer efficiency to result from a combination of the extra mixing flow effect caused by the presence of particles in the flow and the phase-change effect caused by the EPCM inside the particles.

Dimensionless Numbers in Phase-Change Thermosyphon and Heat-Pipe Heat Exchangers

Heat pipes and thermosyphons can be very effective heat transport devices for transferring the thermal energy of the Next Generation Nuclear Plant to a hydrogen production plant and/or other process heat applications. These devices operate nearly isothermally, transporting large amounts of thermal energy with little or no temperature drop. A dimensional analysis of the thermosyphon and the heat pipe is presented in this paper. Dimensional analysis is a valuable mathematical technique useful in research work for design and conducting model tests. This analysis yielded two terms - Er and EM - particular to the operation of these devices in addition to those commonly used in many heat transfer applications. The Er term relates the latent heat of vaporization to the pressure drop across the device, while the EM term relates the latent heat of vaporization to the capillary pressure. The significance of these two terms is discussed. The universal nature of these numbers should be useful in increasing the fundamental understanding of both the thermosyphon and the heat pipe.

Design of Liquid Metal Phase Change Heat Exchanger for Next-Generation Nuclear Plant Process Heat Application

The Next Generation Nuclear Plant will most likely produce electricity and its reactor heat will be further utilized for the production of hydrogen, oil recovery from tar sands and oil shales, and other process heat applications, that will further the nation's pursuit of energy independence. An intermediate heat exchanger is required to transfer heat from the Next-Generation Nuclear Plant to the hydrogen plant (or other processes) in the most efficient way possible. Phase change heat exchangers are quite attractive in this regard, as they can transfer process heat more efficiently than for the single phase due to the advantage of high-enthalpy transport that includes the sensible heat of liquid, the latent heat of vaporization, and possible vapor superheat. This paper explores the overall heat transfer characteristics and pressure drop of the phase change heat exchanger with helium as the primary and sodium as the secondary heat exchanger coolant. For a two-phase boiling regime, the convective heat transfer coefficient is based on the concept of an additive, interacting mechanism of micro- and macroconvective heat transfer. In this analysis an improved design is proposed for given conditions, so as to obtain a lower overall pressure drop and a moderate/high overall heat transfer coefficient. The analysis presented in this paper will be useful as a guide for future experimental work for Next Generation Nuclear Plant process heat transfer.

Design of Liquid Metal Phase Change Heat Exchanger for Next-Generation Nuclear Plant Process Heat Application

The Next Generation Nuclear Plant will most likely produce electricity and its reactor heat will be further utilized for the production of hydrogen, oil recovery from tar sands and oil shales, and other process heat applications, that will further the nation's pursuit of energy independence. An intermediate heat exchanger is required to transfer heat from the Next-Generation Nuclear Plant to the hydrogen plant (or other processes) in the most efficient way possible. Phase change heat exchangers are quite attractive in this regard, as they can transfer process heat more efficiently than for the single phase due to the advantage of high-enthalpy transport that includes the sensible heat of liquid, the latent heat of vaporization, and possible vapor superheat. This paper explores the overall heat transfer characteristics and pressure drop of the phase change heat exchanger with helium as the primary and sodium as the secondary heat exchanger coolant. For a two-phase boiling regime, the convective heat transf...

A Local Heat Flux Measurement Technique for Inclined Heat Exchanger Tubes

This article presents the design, fabrication, and calibration of thermocouple pairs for local heat flux measurement. The intended application of the thermocouple pairs is on the tubes of phase-change heat exchangers experiencing heat fluxes on the order of 105 W/m2. Particular advantages of this technique are that it is accurate even for thin-wall tubes, there are no restrictions on the tube inclination, and it is economical. A thermocouple pair consists of a sheathed thermocouple which measures the tube outer surface temperature and a novel plug-type thermocouple which measures the tube inner surface temperature without interrupting the heat transfer phenomena. A calibration was performed by imposing a series of known heat fluxes on a condenser tube that had been outfitted with a number of thermocouple pairs and measuring the temperature difference between the thermocouples. The maximum uncertainty associated with the calibration constants was ±9.5%. This tube was then used as the condenser tube of a double-pipe heat exchanger to obtain local heat flux data that had previously been unattainable around a horizontal tube.

A modular phase change heat exchanger for a solar oven

A modular energy storing heat exchanger designed to use pentaerythritol for thermal storage (solid-solid phase change at 182°C) is tested in an oven by circulating heat transfer oil which is electrically heated in a manner to simulate a concentrating solar collector. Three efficiencies for heating the system under controlled and measured power input are determined—the heat exchanger efficiency, the efficiency of the heater with distribution lines, and the total system efficiency. Thermal energy retention times and cooking extraction times are determined, and along with the efficiencies, are compared with the results previously reported for a nonmodular heat exchanger. The modular configuration provides a highly improved extraction rate for cooking due to its wrap-around character and its increased surface-to-volume ratio. A full scale glass model of the copper tubing of the system is described and flow observations reported demonstrating how uniformly the parallel pumping branches perform and how trapped air pockets affect pumping power. A technique for measuring pumping power is described and its application to our system is quantified to show that less than 1 watt is required to circulate the heat transfer oil even when the system includes the solar collector and its longer connecting tubes.

New low-cost storage in air conditioning

SYNOPSIS This paper describes the development of a new low-cost phase-change material packaging concept for air conditioning systems. The realization of the promise of storage assisted air conditioning for saving oil and money is dependent upon the successful development of a low-cost storage subsystem and the adoption of time-of-day electricity rates. Time-of-day rates are currently under consideration or have been adopted in 27 different states and consideration of these rates has been required by federal legislation. The adoption of this low-cost thermal energy storage technology for storage assisted air conditioning and other storage assisted heat pump applications has the potential of saving 100 million barrels of oil over the next ten years and 12 million barrels of oil per year by 1985. These savings would accrue from a change in the summer air conditioning peak electricity load from oil and gas-fired peak electrical generators to the base load electrical generators fired by coal, nuclear and hydroelectric. This low-cost air conditioning storage concept is based on hydrated salt phase change material, specifically a mixture based on sodium sulphate decahydrate and a new low-cost packaging technology which uses a film laminate as the phase change material mixture's package and heat exchanger. In this paper. the relative economics of various technological options for air conditioning storage are compared. It is demonstrated that this economic analysis leads to the necessity to develop a low-cost film package and heat exchanger. An analysis of savings to homeowners based on current and planned off-peak rates is included. Since this is the first product developed utilizing this new low-cost material as a packaging film, it is anticipated that major improvements in both cost and performance specifically related to individual systems will be developed and implemented over the next ten years, with significant improvements coming in the next several years.