Thermal and Hydraulic Performance of Heat Exchangers for Low Temperature Lift Heat Pump Systems

The work presented in this dissertation focused on investigating and understanding the hydraulic and thermal design space and tradeoffs for low temperature difference high performance heat exchangers for a low temperature lift heat pump (LTLHP) system, which benefits from a small difference between the condensing and evaporating temperatures of a working fluid. The heat exchangers for the LTLHP application require a larger heat transfer area, a higher volume flow rate, and a higher temperature of heat source fluid, as compared to the typical high temperature lift heat pump system. Therefore, heat exchanger research is critical, and it needs to be balanced between the heat transfer and pressure drop performance of both fluids in the heat exchanger. A plate heat exchanger (PHX) was selected to establish a baseline of a low temperature lift heat exchanger and was investigated experimentally and numerically. The traditional PHX is designed to have the identical surface area and enhancements on both fluid sides for ease of production. However, fluid side heat transfer coefficients and heat transfer capacities can be drastically different, for example, single-phase water versus two-phase refrigerant. Moreover, the PHX needs to have a large cross sectional flow area in order to reduce the heat-source fluid-side pressure drop. In the experimental test, the PHX showed a relatively low overall heat transfer performance and a large pressure drop of the heat source fluid side under LTLHP operating conditions. The CFD simulation was carried out to further improve the potential of the PHX performance. However, there were limitations in the PHX. It was concluded that the PHX was restricted by two main factors: one was a large pressure drop on the heat source fluid-side due to corrugated shape, and the other was low overall heat transfer performance due to the low refrigerant-side mass flux and resulting low heat transfer performance. A concept of a novel low temperature lift heat exchanger (LTLHX) has been developed based on the lessons learned from the PHX performance investigation for the application to the LTLHP. Geometries were newly defined such as a channel width, channel height, channel pitch, and plate flow gap. Two design strategies were applied to the novel heat exchanger development: the flow area ratio was regulated, and plates were offset. The design parameters of the novel heat exchanger were optimized with multi scale approaches. After developing the laboratory heat exchanger test facility and the prototype of the novel LTLHX, its performance was experimentally measured. Then the thermal and hydraulic performance of the novel LTLHX was validated with experimental data. The heat transfer coefficient correlations and the pressure drop correlations of both the water-side and refrigerant-side were newly developed for the novel LTLHX. The overall heat transfer performance of the novel LTLHX was more than doubled as compared to that of the PHX. Moreover, the pressure drop of the novel heat exchanger was drastically lower than that of the PHX. Lastly, the novel heat exchangers were applied to a water source heat pump system, and its performance was investigated with parametric studies

A Comprehensive in Depth Study of Domestic Refrigerating Systems

Refrigeration systems are essential in everyday life, especially when it comes to food storage and preparation, as well as safety and convenience. The primary function of a home refrigerator is to preserve the quality of perishable goods. The efficiency of the refrigerator, which is largely determined by temperature distribution and air flow in the compartments, is critical to this quality. Thus, in this paper, we are attempting to shed light on the work of investigators by experimenting on various geometries of the refrigerating system in order to improve their efficiency. In addition, we have attempted to provide an overview of the DAR cycle as well as the components of the refrigeration system, which will aid scholars in understanding the fundamental operation of cooling systems

Modelling, Design, and Optimization of Membrane based Heat Exchangers for Low-grade Heat and Water Recovery

Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations. By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit

Feasibility Study of Jet-Ejector Refrigeration Systems as a Mechanism for Harnessing Low-Grade Thermal Energy from Different Sources

[ES] Los sistemas de refrigeración por eyección activados por calor de origen renovable o fuentes de calor residual tienen el potencial de alcanzar ahorros energéticos significativos al sustituir o asistir a los sistemas de refrigeración tradicionales. Su campo de aplicabilidad es muy amplio y el presente trabajo se ha centrado en un estudio detallado de dos aplicaciones con gran potencial siguiendo un enfoque computacional: (i) generación de aire acondicionado activado por energía solar térmica y (ii) refrigeración de la admisión de un motor de combustión reutilizando la energía térmica disponible en la línea de escape de este. Las actividades de investigación han estado dirigidas a mitigar dos de los principales puntos débiles que caracterizan a los ciclos de refrigeración por eyección: su eficiencia relativamente baja y la incapacidad mostrada por la configuración base del ciclo de eyección para operar de forma robusta en condiciones de operación alejadas de las de diseño. La primera cuestión ha sido abordada principalmente diseñando geometrías de eyector altamente optimizadas usando técnicas de mecánica de fluidos computacional y optimizando la integración del eyector en el conjunto del sistema de refrigeración. La segunda cuestión se ha abordado caracterizando el comportamiento del sistema en condiciones de diseño y fuera de diseño. Se han propuesto dos estrategias avanzadas para hacer frente a la caída de prestaciones que sufre el sistema al operar en condiciones fuera de diseño, como son la utilización de eyectores de geometría ajustable o la implementación de tanques de almacenamiento térmico. La respuesta del sistema se ha analizado en condiciones fuera de diseño con dos aproximaciones temporales complementarias. Los modelos estacionarios se han usado para optimizar las diferentes arquitecturas de eyector y la operación global del sistema en ciertas condiciones de operación representativas, mientras que el análisis transitorio representa un enfoque más realista y tiene en cuenta la naturaleza impredecible e inestable de la climatología. El estudio se ha concluido con un análisis termoeconómico, el cual ha sido útil para discernir si los diseños altamente optimizados son competitivos al ser comparados con las soluciones de refrigeración que se encuentran actualmente consolidadas en el mercado. La principal conclusión del análisis en condiciones estáticas para la aplicación termosolar es que la transformación de potencia térmica a potencia de refrigeración puede alcanzar un rendimiento del 37.7%, mientras que el rendimiento global del sistema alcanza el 20.1% con diseños altamente optimizados de eyector para unas condiciones de evaporación y condensación de 13°C y 40°C, respectivamente. En condiciones dinámicas, la implementación de la geometría variable mejora en torno a un 40% el rendimiento del sistema de refrigeración, además de incrementar su operatividad. El tanque de almacenamiento térmico juega un papel relevante en este aspecto y, para una envergadura de colector parabólico de 7.1 m, un consumo nominal de 13.3 kW de potencia térmica del tanque ha resultado ser una solución de compromiso para mantener en equilibrio los principales indicadores de prestaciones. El análisis termoeconómico de la arquitectura más prometedora sugiere que el ahorro de coste operativo está lejos de poder compensar la elevada inversión inicial en equipamiento (16.905€ para una capacidad de refrigeración aproximada de 5.6 kW), destacando la dificultad del sistema para competir con las soluciones de refrigeración actualmente consolidadas en el mercado y resaltando la necesidad de considerar soluciones híbridas. La principal conclusión de la aplicación en motor de combustión es que la reducción de temperaturas en la línea de admisión por debajo de 4°C es factible, produciendo mejoras en el rendimiento volumétrico de en torno al 11%, no obstante, el sistema muestra vulnerabilidades al operar en puntos de motor diferentes al de diseño.[CA] Els sistemes de refrigeració per ejecció activats per calor d'origen renovable o fonts de calor residual tenen el potencial d'assolir estalvis energètics significatius al substituir o assistir als sistemes de refrigeració tradicionals. El seu camp d'aplicabilitat es ampli i el present treball s'ha centrat en un estudi detallat de dos aplicacions amb gran potencial seguint un enfocament computacional: (i) generació d'aire condicionat activat per energia solar tèrmica i (ii) refrigeració de l'admissió d'un motor de combustió reutilitzant l'energia tèrmica disponible en la línia d'escapament d'aquest. Les activitats d'investigació han estat dirigides a mitigar dos dels principals punts dèbils que caracteritzen als cicles de refrigeració per ejecció: la seua eficiència relativament baixa i la incapacitat mostrada per la configuració base del cicle d'ejecció per a operar de forma robusta en condicions d'operació allunyades de les de disseny. La primera qüestió ha sigut abordada principalment dissenyant geometries d'ejector altament optimitzades usant tècniques de mecànica de fluids computacional i optimitzant la integració de l'ejector en el conjunt del sistema de refrigeració. La segona qüestió s'ha abordat caracteritzant el comportament del sistema en condicions de disseny i fora de disseny. S'han proposat dos estratègies avançades per a fer front a la caiguda de prestacions que pateix el sistema quan opera en condicions fora de disseny, com són la utilització d'ejectors de geometria ajustable o la implementació de tancs de emmagatzemament tèrmic. La resposta del sistema s'ha analitzat en condicions fora de disseny amb dos aproximacions temporals complementàries. Els models estacionaris s'han usat per a optimitzar les diferents arquitectures d'ejector i l'operació global del sistema en certes condicions d'operació representatives, mentre que l'anàlisi transitori representa un enfocament més realista i té en compte la natura impredictible i inestable dels canvis en les condiciones climàtiques. L'estudi s'ha conclòs amb un anàlisi termoeconòmic, el qual ha sigut útil per a discernir si els dissenys altament optimitzats són competitius quan es comparen amb les solucions de refrigeració que es troben actualment consolidades al mercat. La principal conclusió de l'anàlisi en condicions estàtiques per a l'aplicació termosolar és que la transformació de potència tèrmica a potència de refrigeració pot arribar a un rendiment del 37.7%, mentre que el rendiment global del sistema arriba al 20.1 % amb dissenys altament optimitzats d'ejector per a unes condicions d'evaporació i condensació de 13°C i 40°C, respectivament. En condicions dinàmiques, la implementació de la geometria variable millora al voltant d'un 40% el rendiment del sistema de refrigeració, a més d'incrementar la seua capacitat de romandre en funcionament. El tanc d'emmagatzemament tèrmic juga un paper rellevant en aquest aspecte i, per a una llargària de col·lector parabòlic de 7.1 m, un consum nominal de 13.3 kW de potencia tèrmica del tanc ha resultat ser una solució de compromís per a mantenir en equilibri els principals indicadors de prestacions. L'anàlisi termoeconòmic de l'arquitectura més prometedora suggereix que l'estalvi de cost operatiu està lluny de poder compensar l'elevada inversió inicial en equipament (16.905€ per a una capacitat de refrigeració aproximada de 5.6 kW), posant de manifest la dificultat del sistema per a competir amb les solucions de refrigeració actualment consolidades al mercat i ressaltant la necessitat de considerar solucions híbrides. La principal conclusió de l'aplicació en motor de combustió és que la reducció de temperatures a la línia d'admissió per baix de 4°C és factible, produint millores en el rendiment volumètric de al voltant de l'11%, no obstant això, el sistema mostra vulnerabilitats a l'hora d'operar en punts de motor diferents al de disseny.[EN] Jet-ejector refrigeration systems powered by renewable heat or waste heat sources have the potential to achieve significant primary energy savings when substituting or aiding traditional refrigeration systems. Their field of applicability is vast and the present work has been focused on a detailed study of two applications with great potential following a computational approach: (i) air-conditioning generation powered by solar thermal energy and (ii) internal combustion engine intake air refrigeration powered by its exhaust line waste heat. The research efforts have been directed towards mitigating the negative effect of two of the main weak points of jet-ejector refrigeration systems: their relatively low efficiency and the incapacity of the baseline configuration to operate robustly away from the design conditions. The first issue has been addressed mainly by designing highly optimized jet-ejector geometries using computational fluid dynamics techniques and optimizing the jet-ejector integration in the overall system. The second one has been addressed by carrying out complete characterizations of the refrigeration system response in design and off-design conditions. Advanced strategies to face the refrigeration system performance decay away from design conditions have been proposed, like the utilization of adjustable jet-ejector architectures or the implementation of hot thermal storage tanks. The system response has been analyzed in off-design conditions with two complementary temporal schemes. The steady-state models have been used to optimize the jet-ejector architectures and the overall system operation for representative operating scenarios, while the transient analysis represents a more realistic approach and accounts for changes in climatic conditions, which have an unpredictable and unstable nature. The study has been concluded with a thermoeconomic analysis, which has been useful to discern if the highly optimized designs are competitive when compared to existing refrigeration solutions consolidated in the market. The main conclusions of the steady-state analysis for the solar application are that the transformation from thermal power to refrigeration power can achieve an efficiency of 37.7%, while the global efficiency achieves 20.1% when highly optimized jet-ejectors are used for an evaporating and condensing conditions of 13°C and 40°C, respectively. In dynamic conditions, the implantation of an adjustable jet-ejector brings improvements in refrigeration system efficiency of around 40%, besides improving its capacity to remain in operation. The thermal storage system plays a relevant role in this sense and, for a fixed parabolic trough collector span of 7.1 m, a nominal thermal power consumption of 13.3 kW represents a trade-off between the performance indicators subject to analysis. The thermoeconomic assessment of the most promising system architecture suggests that the operating cost savings are far from compensating for the capital expenditures (16,905€ for a refrigeration capacity of approximately 5.6 kW), evidencing the difficulties of the system to compete against refrigeration solutions currently consolidated in the market and outlining the interest in hybrid solutions. The main conclusion of the automotive application is that it is feasible to achieve in the engine intake line temperatures below 4°C, bringing improvements in volumetric engine efficiency of around 11%. Nevertheless, the system shows vulnerabilities when operating in engine operating points different from the design one.My most sincere acknowledgment to the whole CMT-Motores Térmicos team for giving me the opportunity of being part of it and the grant program Subvenciones para la contrataci ́on de personal investigador predoctoral for doctoral studies (reference ACIF/2018/124), awarded by Generalitat Valenciana, Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital and the European Union for funding this project.Ponce Mora, A. (2022). Feasibility Study of Jet-Ejector Refrigeration Systems as a Mechanism for Harnessing Low-Grade Thermal Energy from Different Sources [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18171

Ejector refrigeration: A comprehensive review

The increasing need for thermal comfort has led to a rapid increase in the use of cooling systems and, consequently, electricity demand for air-conditioning systems in buildings. Heat-driven ejector refrigeration systems appear to be a promising alternative to the traditional compressor-based refrigeration technologies for energy consumption reduction. This paper presents a comprehensive literature review on ejector refrigeration systems and working fluids. It deeply analyzes ejector technology and behavior, refrigerant properties and their influence over ejector performance and all of the ejector refrigeration technologies, with a focus on past, present and future trends. The review is structured in four parts. In the first part, ejector technology is described. In the second part, a detailed description of the refrigerant properties and their influence over ejector performance is presented. In the third part, a review focused on the main jet refrigeration cycles is proposed, and the ejector refrigeration systems are reported and categorized. Finally, an overview over all ejector technologies, the relationship among the working fluids and the ejector performance, with a focus on past, present and future trends, is presented. (C) 2015 Elsevier Ltd. All rights reserved

Recent Advances in Heat Pipes

Heat pipes are considered as an effective thermal solution, particularly in high heat flux applications and in situations where there is a combination of nonuniform heat loading, limited airflow over the heat-generating components, and space or weight constraints. This book is intended to explore some of the recent advances in heat pipes and their applications in thermal systems. The first chapter is an introductory chapter about the recent advances in heat pipes in general. The second chapter is about thermosyphon heat pipe technology; working principles, advantages, and disadvantages; application ranges; and using computational fluid dynamics in modeling thermosyphons. The third chapter is about recent research into loop heat pipes (LHPs). The last chapter presents a novel liquid-vapor separator-incorporated gravitational LHP

Screening of energy efficient technologies for industrial buildings' retrofit

This chapter discusses screening of energy efficient technologies for industrial buildings' retrofit

Estimation of Thermal and Hydraulic Characteristics of Compact Brazed Plate Heat Exchangers

This thesis work presents various performance estimation methods of compact brazed plate heat exchangers (BPHE) operating in single phase, condenser, evaporator, cascaded and transcritical applications. Such methods play a vital role in development of heat exchanger selection software and during geometry parameter estimation in the new product development process. The suitability of employing commercial computational fluid dynamics (CFD) codes for estimating single phase thermal and hydraulic performance is investigated. Parametric studies are conducted on geometries of single phase fluid sections to isolate and quantify the influence of individual geometric parameters. The influence of mesh characteristics, choice of boundary conditions and turbulent flow modeling on the accuracy of the thermal and hydraulic predictions is presented. Benefits of simulation of fluid flow in entire channels and characteristics of channel flow for different geometric patterns are also presented. A computationally light, general, robust and continuous rating calculation method is developed for implementation in BPHE selection software. The pressure-enthalpy based method provides a generic rating core for various types of applications and provides extensive post processing information of the heat transfer process. General single phase thermal and hydraulic empirical correlations are developed as functions of plate geometric parameters. For facilitating better integration of the developed calculation method with other refrigeration system simulation software, first or higher order continuity is maintained in the sub-routines used for calculating local heat transfer coefficients and refrigerant properties. A new finite grid interpolation method is developed for fast and accurate retrieval of refrigerant properties. The developed method is currently implemented in SSPG7 (BPHE selection software of SWEP International AB) for supporting transcritical CO2 calculations and cascaded heat exchanger calculations. Additionally, the methods developed for single phase and two phase test data evaluation based on meta-heuristic optimization routines is also presented. The application and results of using the developed rating models for various types of calculations is summarized. Other topics such as influence of variable fluid properties on BPHE rating calculations, influence of multi-pass flow arrangement on lumped BPHE rating calculations are briefly presented

Conjugate Heat Transfer Analysis in Cryogenic Microchannel Heat Exchanger

Printed circuit heat exchanger (PCHE) is a highly integrated plate type compact heat exchanger and most important as well as a most critical component in the cryogenic application. Compact heat exchangers are characterized by area density (? = AHT / V) i.e. heat transfer area per unit volume of the heat exchanger. The area density of compact heat exchanger is =700m2/m3 where the area density of printed circuit heat exchanger is = 25000m2/m3. Printed circuit heat exchangers are highly compact compared to conventional heat exchangers. The hydraulic diameter is less than 1mm. Printed Circuit Heat Exchanger manufacturing process is followed by chemical etching and chemical bonding. Microchannel for fluid flow are constructed by chemical etching of the metal plates according to different configuration then plates are stacked alternately and assembled by diffusion bonding. Due to its compact size, high efficiency, large heat transfer area PCHE (microchannel heat exchanger) are used in cryogenic refrigeration and liquefaction systems. A counter flow rectangular microchannel (40 mm × 1.6 mm × 1.2 mm) printed circuit heat exchanger is designed and simulated using commercial ANSYS FLUENT. The performance is investigated numerically with helium at cryogenic temperature. The performance is affected by axial conduction at low Reynolds number (Re = 100). Because of length and viscous nature, the fluid flow through the channel is laminar and thermally fully developed. The Nussle number (Nu), flux, dimensionless fluid temperature and wall temperature, effectiveness are determined for different Reynolds number Reynolds number (Re = 100) with varying material i.e. wall to fluid thermal conductivity ratio (ksf = 141.58 - 5061.5). Axial conduction (?) is calculated by using Kroeger’s equation. Effectiveness is calculated to investigate the thermal performance of the microchannel heat exchanger

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected