Cross-flow Plate Heat Exchanger Research Articles

Modelling an air handling unit, building and occupant variation regarding energy, moisture and frost protection based on measurements of an air handling unit and occupants’ moisture supply

Objectives of this paper are to propose a reasonable simulation model that can handle condensation and frost formation in heat exchangers dependent on moisture concentration and outdoor climate conditions, and to analyze risk of frost formation and discuss different frost protection strategies. Using psychometrics, American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) heat exchanger calculation, condensation and frost calculation methods, simulations models for heat recovery ventilation and energy recovery ventilation are developed. It is concluded that the risk of frost in heat exchangers is higher in northern Sweden than in southern Sweden and Denmark due to low outdoor air temperatures during the winter, however heat recovery systems in Copenhagen and Gothenburg still has a risk of frost formation even though these cities has relatively warm weather conditions. Out of several simulation models that are created during the study, the detailed model that takes condensation effect into consideration, is proven to be worthy to be used in further investigations, due to results that more accurately represent real word conditions. Risk of frost formation becomes significantly lower in every city when heat recovery ventilation is changed into energy recovery ventilation. Even though heat recovery ventilation is simulated only with the simplified model, it is safe to assume that it will still be effective in reality. Although bypass strategies were effective at eliminating the risk of frost in heat recovery units, they are not as efficient from an energy perspective. The more air is by-passed through the cross-flow plate heat exchanger, the fewer opportunities there are to recover energy from exhaust air, which leads to lower supply air temperatures and higher energy need for heating a living space.

Comparison of the Efficiency of Cross-Flow Plate Heat Exchangers Made of Varied Materials

This paper discusses a mathematical model for airflow through a cross-flow plate heat exchanger. The exhaust air is used to heat the supply air. Three kinds of plates are considered: made of aluminium, copper, and steel. The purpose of this research was to verify which material used to build the plate heat exchangers uses the exhaust air heat more efficiently. The method of the Trefftz function was used to determine approximate solutions to the analysed problem. The results obtained for 1.2 mm-thick plates and for external winter, summer, and spring–autumn temperatures are discussed. The results indicate that if the efficiency and price of the metals are considered, then steel is the best material for the plate heat exchanger. Thanks to the use of thin steel plates and the reduction in air exchange time to a few minutes, a cheap and efficient cross-flow heat exchanger can be obtained.

Analytical solution for heat transfer problem in a cross-flow plate heat exchanger

Cross-flow plate heat exchangers are used for plenty of applications in industrial and domestic sectors, and the analysis of heat transfer is a key for the evaluation of their performance. There are challenges for an analytical study because heat transfer in each channel is governed by a partial differential equation coupled with temperature fields in the adjacent channels representing a three-dimensional problem. The problem is even more complicated in the turbulent regime as the effective thermal diffusivity varies within the channel cross-section. In the present study, a separate set of governing equations and boundary conditions are considered for each part of the heat exchanger. Appropriate profiles for the flow velocity and thermal diffusivity are substituted into the governing equations of the channels. The resulting partial differential equations in the channels are solved using the separation of variables method. There remains an unknown boundary condition linked to the temperature field on the plate surface which is considered to be in the form of a two-variable series function whose coefficients are calculated by applying energy balance between the two sides of the plate. The obtained solution provides explicit expressions for the temperature fields in the plate and channels. A scaling analysis is conducted showing that the model is valid when Peclet numbers in both hot and cold channels are not small. The results are compared with empirical data and a numerical model, and the accuracy of the derived heat transfer coefficients is investigated. In harmony with the scaling analysis, a close agreement is observed in both laminar and turbulent flows for moderate and high Prandtl numbers and when Peclet number is greater than 1000 in the case of turbulent flow.

Study on mass transfer time relaxation parameter of indirect evaporative cooler considering primary air condensation

Air condensation phenomenon occurs when the indirect evaporative cooler (IEC) is applied in high temperature and humidity regions, where indoor exhaust air is used as secondary air to pre-cool the fresh air (primary air) in an air conditioning system. The mass transfer time relaxation parameter (β) in the phase change coefficient model (Lee model) is a key parameter in the coupled heat and mass transfer mechanism of IEC. As β is difficult to be obtained by theoretical calculation, the influence of β on the temperature and humidity parameters at the primary outlet of IEC heat exchanger is determined by experiments, and the piecewise fitting function of β on the inlet temperature of primary air is given. In view of the unsteady temperature evaporation condensation process of water in the primary channel and the heat and mass transfer process of the spraying liquid film in the secondary channel, β is applied to a computational fluid dynamics (CFD) model of a three-dimensional cross-flow plate IEC heat exchanger. The physical model of the improved three-dimensional cross-flow plate heat exchanger is verified and the error analysis is carried out. The results show that the accuracy of the model is greatly improved with a discrepancy of less than ±10% under different working conditions.

Performance enhancement of cabinet cooling system by utilizing cross-flow plate heat exchanger

Gas-gas plate heat exchanger is an important component to remove heat generated from electronic devices in the cabinet cooling system. The counter-flow plate heat exchanger is usually used due to its higher heat transfer performance than the cross-flow plate heat exchanger. However, in the cabinet cooling system, the overall dimensions for the heat exchanger is limited. Therefore, it is necessary to consider the overall dimensions of the system during heat exchanger design, but the traditional thermal design method of heat exchanger doesn’t consider the effect of system parameters. In this paper, a cross-flow plate heat exchanger is proposed to improve the cooling performance of cabinet cooling system, and is compared with the counter-flow plate heat exchanger. The ε-NTU method and effectiveness-thermal resistance method are applied to evaluate the performance. It is found that for large width of cabinet cooling system, the system with cross-flow plate heat exchanger has higher cooling performance and lower thermal resistance than the system with counter-flow plate heat exchanger. When the width is 700 mm, the cooling capacity of the two systems are 176.13 W/K and 138.95 W/K, respectively. The dimensionless thermal resistance can characterize the irreversibility of the heat transfer at constant mass flow rate.

A Three-Dimensional Thermo-hydrodynamic Simulation of Compact Cross-Flow Plate Heat Exchanger

This study is dedicated to the thermal analysis and thermo-hydrodynamic simulation of an air-to-air plate heat exchanger in order to solve its routine problem in industry. The compact type of cross-flow plate heat exchanger, in which corrugated plates pile up tightly and delicately brazed to each other, has been used in many situations and has many applications from food industries to petroleum and military. Routinely, after a certain lifespan, the brazed joints are detached and cause a mixture of hot and cold fluids as well as highly reduction of heat exchanger performance. This problem leads to increase the system maintenance significantly. Apart from the imposed cost and time for its maintenance, which is indeed a crucial problem? Finally, to have a better understanding, a threedimensional numerical investigation on thermo-hydrodynamic analysis of conjugate heat transfer was performed using computational fluid dynamics techniques. Forced convection heat transfer for fluid flow and conduction through solid material were considered as well. For simulation of steady state flow of Newtonian fluid, the governing equation was discredited by finite volume method and solved by the semi-implicit method for the pressure-linked equation. It was also found that both temperature and temperature gradient play an important role in this problem.

Experimental Investigation of Newtonian and Non-Newtonian Liquid Fow in Wavy and Straight Mini Channel cross Flow Plate Heat Exchanger

Experimental Investigation of Newtonian and Non-Newtonian Liquid Fow in Wavy and Straight Mini Channel cross Flow Plate Heat Exchanger

Analysis of the frost formation and freeze protection with bypass for cross-flow recuperators

A theoretical analysis of coupled heat and mass transfer inside the cross-flow plate heat exchanger used for energy recovery under frosting operating conditions was presented. Three selected frost control techniques were analysed on the base of original ε-NTU model. Frost-free operating conditions were determined for the cross-flow plate heat exchanger under different opening levels of bypass damper and face and bypass dampers. It was found that the implementation of the particular variant of heat exchanger performance and the values of critical outdoor temperatures for different operating conditions in which the onset of frosting occurs in the cross-flow flat plate heat exchanger depend upon the heat and mass transfer conditions realized in two decisive points on the return air channel surface known as the “cold corner” and “hot corner”. It was concluded, that the fully open bypass technique does not provide complete frost protection under sub-zero outdoor air temperature operating conditions.

Improving exergetic performance parameters of a rotating-tray air dryer via a simple heat exchanger

In this study, exergy analysis was applied for a rotating-tray dryer equipped with a cross-flow plate heat exchanger during drying of apple slices. Three drying air temperatures and tray rotation speeds in the range of 50–80 °C and 0–12 rpm, respectively, were employed. Two drying air velocities in the range of 1–2 m/s were adjusted for each drying temperature and rotation speed with and without application of the heat exchanger. The experiments were conducted to assess the effects of the experimental variables on the exergetic performance parameters of the dryer. Also, the effect of drying conditions on the quality of dried apple slices was assessed by determining rehydration ratio, apparent density, shrinkage, and surface color. In general, the exergetic performance parameters of the dryer depended profoundly on the drying air temperature and velocity. Interestingly, the exergetic efficiency of drying process was significantly improved from a minimum value of 23.0% to a maximum value of 96.1% by using the heat exchanger. Furthermore, the incorporation of heat exchanger did not negatively affect the quality of dried product. Therefore, the strategy presented herein could be a promising approach for waste energy recovery in drying without any unfavorable change in the quality of dried product.

Frost formation in the cross-flow plate heat exchanger for energy recovery

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0°C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters.

Comparative design study of a diesel exhaust gas heat exchanger for truck applications with conventional and state of the art heat transfer enhancements

The exhaust gas of heavy duty diesel engines can provide an important heat source that may be used in a number of ways to provide additional power and improve overall engine efficiency. The sizing of a heat exchanger that can manage the heat load and still be of reasonable size and weight without excessive pressure drop is of significant importance especially for truck applications. This is the subject of the present work. To approach the problem, a total of five different configurations are investigated and a comparison of conventional and state of the art heat transfer enhancement technologies is included. Two groups of configurations are examined: (a) a classical shell and tube heat exchanger using staggered cross-flow tube bundles with smooth circular tubes, finned tubes and tubes with dimpled surfaces and (b) a cross-flow plate heat exchanger, initially with finned surfaces on the exhaust gas side and then with 10 ppi and 40 ppi metal foam material substituting for the fins. Calculations were performed, using established heat exchanger design methodologies and recently published data from the literature to size the aforementioned configurations. The solutions provided reduce the overall heat exchanger size, with the plate and fin type consisting of plain fins presenting the minimum pressure drop (up to 98% reduction compared to the other configurations), and the 40 ppi metal foam being the most compact in terms of size and weight. Durability of the solutions is another issue which will be examined in a future investigation. However, coupling of the exhaust heat exchanger after a particulate trap appears to be the most promising solution to avoid clogging from soot accumulation.

Modelling and performance analysis of a cross-flow type plate heat exchanger for dehumidification/cooling

Modelling and performance analysis of a cross-flow type plate heat exchanger for dehumidification/cooling