Showing papers on "Heat exchanger published in 2008"

Heat exchanger/reactors (HEX reactors) : Concepts, technologies: State-of-the-art

Abstract: Process intensification is a chemical engineering field which has truly emerged in the past few years and is currently rapidly growing. It consists in looking for safer operating conditions, lower waste in terms of costs and energy and higher productivity; and a way to reach such objectives is to develop multifunctional devices such as heat exchanger/reactors for instance. This review is focused on the latter and makes a point on heat exchanger/reactors. After a brief presentation of requirements due to transposition from batch to continuous apparatuses, heat exchangers/reactors at industrial or pilot scales and their applications are described.

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

Abstract: The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.

Method and apparatus for an electrical vehicle

Abstract: One embodiment includes a vehicle that includes a battery to supply a flow of electrical energy, an electric motor arranged to propel the vehicle, a first control circuit coupled between the battery and the motor to control the flow of electrical energy to the motor; a first heat exchange loop thermally coupled with a heat exchanger and a heating element, the first heat exchange loop to circulate a first fluid to heat or cool a passenger cabin; a second heat exchange loop thermally coupled with the heat exchanger, the second heat exchange loop to circulate a second fluid to heat or cool the battery and a second control circuit to couple a charger to the battery and to perform charging operations on the battery using a voltage source powered from a line source.

Theoretical analysis of a vapour compression refrigeration system with R502, R404A and R507A

Abstract: This paper presents a detailed exergy analysis of an actual vapour compression refrigeration (VCR) cycle. A computational model has been developed for computing coefficient of performance (COP), exergy destruction, exergetic efficiency and efficiency defects for R502, R404A and R507A. The present investigation has been done for evaporator and condenser temperatures in the range of −50 °C to 0 °C and 40 °C to 55 °C, respectively. The results indicate that R507A is a better substitute to R502 than R404A. The efficiency defect in condenser is highest, and lowest in liquid vapour heat exchanger for the refrigerants considered.

Heat exchange enhancement

Abstract: A heat exchange structure includes elongated air ducts. Each air duct has a first opening and a second opening at two ends of the air duct to allow air to enter and exit the air duct, respectively. The heat exchange structure includes an exterior heat exchange surface and interior heat exchange surfaces, in which the exterior heat exchange surface is configured to receive thermal energy from heat generators that are mounted on the exterior heat exchange surface, and the exterior heat exchange surface dissipates a portion of the thermal energy received from the heat generators and transfers another portion of the thermal energy to the interior heat exchange surfaces. The interior heat exchange surfaces are in the elongated air ducts and configured to exchange thermal energy with air flowing in the air ducts, enhancing air flow in the air ducts by buoyancy of heated air.

Heat Exchanger Design

Abstract: eneral design considerations and design procedure are also illustrated in this paper and a flow diagram is provided as an aid of design procedure In design calculation, the MatLAB and AutoCAD software are used Fundamental heat transfer concepts and complex relationships involved in such exchanger are also presented in this paper The primary aim of this design is to obtain a high heat transfer rate without exceeding the allowable pressure drop This computer program is highly useful to design the shell&and&tu be type heat exchanger and to modify existing deign

Thermodynamic analysis of an R744-R717 cascade refrigeration system

Abstract: A thermodynamic analysis of carbon dioxide–ammonia (R744–R717) cascade refrigeration system is presented in this paper to optimize the design and operating parameters of the system. The design and operating parameters considered in this study include (1) condensing, subcooling, evaporating and superheating temperatures in the ammonia (R717) high-temperature circuit, (2) temperature difference in the cascade heat exchanger, and (3) evaporating, superheating, condensing and subcooling in the carbon dioxide (R744) low-temperature circuit. A multilinear regression analysis was employed in terms of subcooling, superheating, evaporating, condensing, and cascade heat exchanger temperature difference in order to develop mathematical expressions for maximum COP, an optimum evaporating temperature of R717 and an optimum mass flow ratio of R717 to that of R744 in the cascade system.

An advanced nonlinear switched heat exchanger model for vapor compression cycles using the moving-boundary method

Abstract: Simulation is commonly used to develop control and diagnostic algorithms. Because vapor compression cycles are essentially heat management devices, transient and steady-state heat exchanger performance must be predicted accurately. However, for hardware- and software-in-the-loop purposes, the simulation must run in real-time. To reconcile these competing needs, a new lumped parameter or moving-boundary heat exchanger model was created. Accuracy concerns are addressed by including finned surfaces, nonlinear air temperature distributions, and non-circular passages. In its current form, the model is applicable to single pass, cross-flow heat exchangers. The mathematical basis of the model is given and shown to be consistent with integral forms of the energy and continuity equations. Although known to be more computationally efficient than finite volume models, moving-boundary models become singular and fail under certain conditions. To address this shortcoming, particular attention was focused on algorithms for switching between different representations and rezoning wall temperatures. Robustness to changing flow regimes is demonstrated through simulation test cases, and model application to a chiller system is shown. As such, the model provides improved accuracy, robustness, and operating range while maintaining real-time capability.

Experimental study on a new internally cooled/heated dehumidifier/regenerator of liquid desiccant systems

Abstract: For providing good performance of dehumidifier and regenerator with certain dimensions, a new type of internally cooled/heated dehumidifier/regenerator based on the plate–fin heat exchanger (PFHE) was designed. To investigate the behavior of the new equipment, an experimental setup was established in an environment chamber with regulable temperature and humidity air. By the internally cooled dehumidification testing, effects of the cooling water temperature, the air flow rate and the desiccant temperature on the dehumidification performance and the cooling efficiency were presented. The behavior of internally cooled dehumidification process was compared with that of the adiabatic dehumidification process. The results suggested that the cooling efficiency decreased with the increasing of the cooling water temperature and desiccant with low temperature could bring more mass transfer coefficients. There is an optimal air flow rate to achieve the maximum absolute humidity decrease of the air. By the internally heated regeneration testing, effects of the air flow rate and the desiccant inlet temperature on the regeneration performance and air outlet parameters were discussed and also compared with those of the adiabatic regeneration process. It was concluded that the regeneration efficiency of internally heated regeneration was more than that of the adiabatic regeneration, and the internally heated regenerator could offer better thermal performance.

Electric vehicle thermal management system

Abstract: An efficient thermal management system (100) that utilizes a single heat exchanger (133) is provided. A refrigeration subsystem (103) cools the heat exchanger (133). A first coolant loop (139) in thermal communication with the heat exchanger (133) is used to cool the energy storage system (137). A second coolant loop (151) corresponding to the HVAC subsystem (107) is also in thermal communication with the heat exchanger (133). Preferably a third coolant loop (109) corresponding to the drive motor cooling subsystem (101) is coupleable to the HVAC coolant loop (151), thus providing an efficient means of providing heat to the HVAC subsystem (107).

Effects of baffle inclination angle on flow and heat transfer of a heat exchanger with helical baffles

Abstract: Numerical simulations were carried out to study the impacts of various baffle inclination angles on fluid flow and heat transfer of heat exchangers with helical baffles. The simulations were conducted for one period of seven baffle inclination angles by using periodic boundaries. Predicted flow patterns from simulation results indicate that continual helical baffles can reduce or even eliminate dead regions in the shell side of shell-and-tube heat exchangers. The average Nusselt number increases with the increase of the baffle inclination angle α when α α > 30°. The pressure drop varies drastically with baffle inclination angle and shell-side Reynolds number. The variation of the pressure drop is relatively large for small inclination angle. However, for α > 40°, the effect of α on pressure drop is very small. Compared to the segmental heat exchangers, the heat exchangers with continual helical baffles have higher heat transfer coefficients to the same pressure drop. Within the Reynolds number studied for the shell side, the optimal baffle inclination angle is about 45°, with which the integrated heat transfer and pressure drop performance is the best. The detailed knowledge on the heat transfer and flow distribution in this investigation provides the basis for further optimization of shell-and-tube heat exchangers.

Performance of a small-scale regenerative Rankine power cycle employing a scroll expander:

Abstract: A small scroll expander has been incorporated into a power cycle for performance evaluation. Using heat from a circulating hot oil supply, a working fluid (R123) was vapourized under pressure and fed to the inlet of the expander. Power generated was measured by a torque/rotation rate sensor as the power was delivered to a compressor. The exhausted working fluid was then sent through a regenerator to recover thermal energy, and then to an air-cooled condensation heat exchanger. To complete the cycle, the working fluid passed through a pump and was fed back to the boiler by way of the regenerator. The major components of the power cycle were monitored for performance, and from these values, overall cycle efficiency was determined. A model of the system was also developed in order to validate system state points and allow follow-on projections of cycle performance with better component efficiencies. Depending on the operating state points during testing, the power output from the cycle ranged from 18...