scholarly journals Effect of phase transitions on operation of air-to-air heat exchangers with drop irrigation

2021 ◽  
Vol 2119 (1) ◽  
pp. 012076
Author(s):  
M I Nizovtsev ◽  
V N Letushko
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Saline Solution ◽  
Experimental Studies ◽  
Maximum Temperature ◽  
Solution Flow Rate ◽  
Solution Flow ◽  
Winter Conditions ◽  
Temperature Efficiency ◽  
Positive Factor

Abstract The article presents the results of experimental studies of the thermal and humidity parameters of air flows of a regenerative air-to-air heat exchanger with drop irrigation and an intermediate heat carrier when operating in winter conditions with negative outside temperatures. The dependences of temperature and humidity efficiency of the heat exchanger on saline solution flow rate were determined, while the maximum temperature efficiency in the heating column was more than 70%. It is shown that under all investigated regimes in the heating column, moisture evaporated from the saline solution, and the air entering the room became more humid, which is a positive factor that increases the comfort of premises at negative outside temperatures.

Numerical Modeling and Experimental Studies of the Operational Parameters of the Earth-To-Air Heat Exchanger of the Geothermal Ventilation System

2021 ◽  
Vol 23 ◽  
pp. 42-64
Author(s):  
Boris Basok ◽  
Ihor Bozhko ◽  
Maryna Novitska ◽  
Aleksandr Nedbailo ◽  
Myroslav Tkachenko
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Ventilation System ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Operational Parameters ◽  
Cross Sectional ◽  
Distinctive Features ◽  
Sectional Shape ◽  
Experimental Bench

This article is devoted to the analysis of the heat engineering characteristics of the operation of an Earth-to-Air Heat Exchanger, EAHE, with a circular cross-sectional shape, which is a component of the geothermal ventilation system. The authors analyzed literature sources devoted to the research of heat exchangers of the soil-air type of various designs and for working conditions in various soils. Much attention is paid to the issues of modeling the operation of such heat exchangers and the distinctive features of each of these models. Also important are the results of experimental studies carried out on our own experimental bench and with the help of which the numerical model was validated. The results of these studies are the basis for the development of a method for determining the optimal diameter of an EAHE under operating conditions for soil in Kyiv, Ukraine.

Effects of Pressure and Channel Depth on Desorption in Microscale Fractal-Like Branching Heat Exchangers

2007 ◽  
Author(s):  
Mario Apreotesi ◽  
Greg Mouchka ◽  
Keith Davis ◽  
Alex Tulchinsky ◽  
Deborah Pence
Keyword(s):  
Heat Exchange ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Ammonia Solution ◽  
Solution Flow Rate ◽  
Channel Height ◽  
Channel Depth ◽  
Solution Flow ◽  
Flow Network ◽  
Oil Flow

Desorption in micro-scale plate heat exchangers having a branching flow network is investigated as a function of oil flow rate, solution flow rate, manifold pressure and channel depth. The solution is an aqueous-ammonia solution with an inlet concentration held fixed at 30%. Mass flow rate and ammonia mass fraction of the generated vapor stream are characterized as is the heat exchange effectiveness of the various heat exchange desorbers. The effects of operating or exit plenum pressure and channel height on desorption and heat transfer characteristics are considered. Microscale channels are employed for enhanced heat and mass transport. The branching nature of the flow network is employed for flow symmetry and low pressure drop penalties. An operational model is generated to correctly size and efficiently integrate the desorber into an absorption cycle.

Thermal Performance of Multipass Parallel and Counter-Cross-Flow Heat Exchangers

2006 ◽  
Vol 129 (3) ◽  
pp. 282-290 ◽  
Author(s):  
Luben Cabezas-Gómez ◽  
Hélio Aparecido Navarro ◽  
José Maria Saiz-Jabardo
Keyword(s):  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Cross Flow ◽  
Numerical Procedure ◽  
Complex Flow ◽  
Flow Heat ◽  
Small Elements ◽  
Effectiveness Data

A thorough study of the thermal performance of multipass parallel cross-flow and counter-cross-flow heat exchangers has been carried out by applying a new numerical procedure. According to this procedure, the heat exchanger is discretized into small elements following the tube-side fluid circuits. Each element is itself a one-pass mixed-unmixed cross-flow heat exchanger. Simulated results have been validated through comparisons to results from analytical solutions for one- to four-pass, parallel cross-flow and counter-cross-flow arrangements. Very accurate results have been obtained over wide ranges of NTU (number of transfer units) and C* (heat capacity rate ratio) values. New effectiveness data for the aforementioned configurations and a higher number of tube passes is presented along with data for a complex flow configuration proposed elsewhere. The proposed procedure constitutes a useful research tool both for theoretical and experimental studies of cross-flow heat exchangers thermal performance.

scholarly journals DEVELOPMENT OF HIGH EFFICIENT SHELL-AND-TUBE HEAT EXCHANGERS BASED ON PROFILED TUBES

2020 ◽  
Author(s):  
Djamalutdin Chalaev ◽  
◽  
Nina Silnyagina ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Hydraulic Resistance ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Corrugated Tube ◽  
The Heat Transfer Coefficient

The use of advanced heat transfer surfaces (corrugated tubes of various modifications) is an effective way to intensify the heat transfer and improve the hydraulic characteristics of tubular heat exchangers. The methods for evaluating the use of such surfaces as working elements in tubular heat exchangers have not been developed so far. The thermal and hydrodynamic processes occurring in the tubes with the developed surfaces were studied to evaluate the efficiency of heat exchange therein. Thin-walled corrugated flexible stainless steel tubes of various modifications were used in experimental studies. The researches were carried out on a laboratory stand, which was designed as a heat exchanger type "tube in tube" with a corrugated inner tube. The stand was equipped with sensors to measure the thermal hydraulic flow conditions. The comparative analysis of operation modes of the heat exchanger with a corrugated inner tube of various modifications and the heat exchanger with a smooth inner tube was performed according to the obtained data. Materials and methods. A convective component of the heat transfer coefficient of corrugated tube increased significantly at identical flow conditions comparing with a smooth tube. Increasing the heat transfer coefficient was in the range of 2.0 to 2.6, and increased with increasing Reynolds number. The increase in heat transfer of specified range outstripped the gain of hydraulic resistance caused by increase of the flow. Results and discussion. CFD model in the software ANSYS CFX 14.5 was adapted to estimate the effect of the tube geometry on the intensity of the heat transfer process. A two-dimensional axially symmetric computer model was used for the calculation. The model is based on Reynolds equation (Navier-Stokes equations for turbulent flow), the continuity equation and the energy equation supplemented by the conditions of uniqueness. SST-turbulence model was used for the solution of the equations. The problem was solved in the conjugate formulation, which allowed assessing the efficiency of heat exchange, depending on various parameters (coolant temperature, coolant velocity, pressure). The criteria dependences were obtained Nu = f (Re, Pr). Conclusions. The use a corrugated tube as a working element in tubular heat exchangers can improve the heat transfer coefficient of 2.0 - 2.6 times, with an increase in hydraulic resistance in the heat exchanger of 2 times (compared with the use of smooth tubes). The criteria dependences obtained on the basis of experimental studies and mathematical modeling allow developing a methodology for engineering calculations for the design of new efficient heat exchangers with corrugated tubes.

scholarly journals Numerical modelling of parameters of the operational parameters of an earth-to-air heat exchanger for geothermal ventilation

2020 ◽  
Vol 35 ◽  
pp. 41-48
Author(s):  
O. Nedbailo ◽  
I.. Bozhko ◽  
M. Tkachenko ◽  
S. Andreychuk
Keyword(s):  
Heat Exchanger ◽  
Numerical Model ◽  
Heat Exchangers ◽  
Ventilation System ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Operational Parameters ◽  
National Academy Of Sciences ◽  
Cross Sectional ◽  
Climate Conditions

The aim of this work is to develop a numerical model of the year-round operation of an earth-to-air heat exchanger (EAHE) with a circular cross-sectional shape with further its validation based on the obtained experimental data. We consider that these studies can form the basis for the development of methods for calculating and designing geothermal ventilation systems for climate conditions of Ukraine. The analysis of literature sources showed that now there are quite a lot of studies devoted to the issues of geothermal ventilation. The results of such heat exchanger modeling with various geometric data and which operate in their authentic soils under various hydraulic regimes and that are located at different depths are widely presented. However, these studies do not allow obtaining generalized patterns of heat transfer during the operation of the heat exchangers and the influence of the geometric parameters of the heat exchanger on the operation of the geothermal ventilation system as a whole. Much attention is paid to the issues of modelling the operation of such heat exchangers and the distinctive features of each of these models. Also important are the results of experimental studies carried out on our own experimental bench and with the help of which the numerical model was validated. To conduct experimental research on the operation of the geothermal ventilation system at the Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine an experimental stand was created. This stand is designed to study thermophysical processes during the operation of a geothermal ventilation system elements. The results of these studies are the basis for the development of a method for determining the optimal diameter of the earth-to-air heat exchanger under operating conditions for soil in Kyiv, Ukraine.

scholarly journals Calculation of the Efficiency of Regenerative Air Heat Exchanger with Intermediate Heat Carrier

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Mikhail Ivanovich Nizovtsev ◽  
V. Yu. Borodulin
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Heat Exchanger ◽  
Heat Carrier ◽  
Heat Transfer Process ◽  
Maximum Temperature ◽  
Operating Parameters ◽  
Air Flow Rate ◽  
Filling Height ◽  
Temperature Efficiency

The study deals with a new regenerative air heat exchanger with an intermediate heat carrier used in the systems of room ventilation. A physical and mathematical model of the heat transfer process is proposed. The influence of design and operating parameters on the temperature efficiency of the heat exchanger is analyzed. The possibility of a significant increase in its efficiency with a decrease in the packing diameter is shown. As a result of calculations, it was found that with a decrease in the filling height, the maximum temperature efficiency shifted towards a decrease in the air flow rate from its value determined from the equality of water equivalents of liquid and air.

scholarly journals Kaji efisiensi temperatur penukar panas dengan variasi aliran untuk aplikasi pengering

2018 ◽  
Vol 16 (2) ◽  
pp. 39
Author(s):  
Syukran Syukran
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Fluid Phase ◽  
Parallel Flow ◽  
Small Scale ◽  
Counter Flow ◽  
Flow Type ◽  
Temperature Efficiency

Abstrak Heat exchanger atau alat penukar panas adalah alat-alat yang digunakan untuk mengubah temperatur fluida atau mengubah fasa fluida dengan cara mempertukarkan panasnya dengan fluida lain. Pada sebuah penukar panas kemampuan mempertukarkan panas sangat ditentukan oleh tipe dan jenis aliran fluida yang melewati penukar panas. Secara garis besar penukar panas dibagi berdasarkan arah aliran fluidanya. Berdasarkan arah aliran fluida penukar panas  dibedakan menjadi 3 (tiga) jenis aliran, yaitu aliran searah (parallel flow), aliran berlawanan (counter flow) dan aliran silang (cross flow). Saat ini penukar panas banyak dipakai dalam  industri pengeringan produk-produk pertanian, perkebunan dan perikanan skala kecil dan menengah. Penggunaan penukar panas dalam bidang pengeringan saat ini sudah menjadi kebutuhan untuk mengatasi permasalahan produktifitas pengeringan. Umumnya penukar panas yang digunakan adalah tipe aliran berlawanan. Beberapa penelitian telah dilakukan untuk mengetahui efektifitas penukar panas tersebut yang umumnya berfokus pada jenis aliran berlawanan. Penelitian penelitian spesifik yang mengkaji perbandingan efisiensi penukar panas  untuk ketiga jenis aliran belum ditemukan. Penelitian ini dilakukan untuk mengetahui efisiensi temperatur penukar panas untuk jenis aliran jenis aliran melintang, sejajar, dan  berlawanan. Metode penelitian dilakukan fabrikasi 3 unit exchanger tipe gas-gas dengan dimensi 50 (P) x 10 (L) x 30 (T) dengan jumlah tube 17 susunan. Hasil  penelitian menunjukkan bahwa efisiensi temperatur untuk ketiga jenis penukar panas tersebut adalah 21,3% aliran melintang, 17,3% aliran berlawanan dan 15,9%  aliran sejajar. Hasil penelitian menyimpulkan bahwa efisiensi temperatur tertinggi diperoleh jenis penukar panas aliran melintang. Kata kunci : Penukar panas, aliran sejajar, aliran berlawanan, aliran silang, temperatur.  Abstrack Heat exchangers or heat exchangers are the means used to change the temperature of the fluid or to change the fluid phase by exchanging heat with other fluids. In a heat exchanger the heat exchange ability is greatly determined by the type and type of fluid flow passing through the heat exchanger. Broadly speaking the exchanger is divided based on the direction of fluid flow. Based on the direction of fluid flow exchanger is divided into 3 (three) types of flow, namely parallel flow, counter flow and cross flow. Currently, heat exchangers are widely used in the drying industry of small and medium-sized agricultural and small-scale plantation and fishery products. The use of exchangers in the field of drying is now a need to overcome the problems of drying productivity. Generally the exchanger used is the opposite flow type (counter flow). Several studies have been conducted to determine the effectiveness of these exchangers which generally focus on the opposite type of flow. Specific research studies that reviewed the efficiency of exchangers for the three types of flow have not been found. This research was conducted to find out the efficiency of heat exchanger temperature for flow type of cross flow, parallel flow and counter flow type. The research method was fabricated 3 units of gas-gas exchanger type with dimension 50 (P) x 10 (L) x 30 (T) with the number of tubes 17 staggered arrangement. The results show that the temperature efficiency for the three types of heat exchanger is 21.3% cross flow flow, 17.3% flow counter flow and 15.9% parallel flow flow. The results concluded that the highest temperature efficiency obtained by cross flow flow type exchanger. Keywords: Heat exchanger, parallel flow, counter flow, cross flow, temperature

Experimental Analysis to Optimize the Performance of Air Curtains and Heat Exchangers

2015 ◽  
pp. 590-640
Author(s):  
Samuel Mariano do Nascimento ◽  
Gustavo Galdi Heidinger ◽  
Pedro Dinis Gaspar ◽  
Pedro Dinho Silva
Keyword(s):  
Mathematical Model ◽  
Energy Consumption ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Environmental Conditions ◽  
Heat Exchangers ◽  
Heat Load ◽  
Experimental Studies ◽  
Air Curtain ◽  
Back Panel

This chapter reports an overview about experimental studies concerning the thermal performance of air curtains and heat exchangers installed in vertical open refrigerated display cases. The air curtain analysis shows the influence on the thermal performance by varying the width of the discharge air grille and the perforation density of the back panel by a mathematical model. The variation on the perforation density of the back panel and the width of discharge air grille alter significantly the thermal entrainment factor and the energy consumption of the equipment. Focusing the influence of environmental conditions on the performance of the heat exchanger, a second mathematical model was developed to evaluate the total heat load, its partial components and the condensate water mass. This analysis provides valuable information to the design of the air curtain and heat exchanger based on in-store environmental conditions and airflow efficiency.

scholarly journals Experimental Verification of an Analytical Mathematical Model of a Round or Oval Tube Two-Row Car Radiator

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3399
Author(s):  
Dawid Taler ◽  
Jan Taler ◽  
Marcin Trojan
Keyword(s):  
Mathematical Model ◽  
Heat Exchanger ◽  
Heat Flow ◽  
Heat Exchangers ◽  
Cfd Simulation ◽  
Experimental Studies ◽  
Hot Water ◽  
Heat Flow Rate ◽  
Cfd Modelling ◽  
Tube Heat Exchanger

The paper presents an analytical mathematical model of a car radiator, which takes into account various heat transfer coefficients (HTCs) on each row of pipes. The air-side HTCs in a specific row of pipes in the first and second passes were calculated using equations for the Nusselt number, which were determined by CFD simulation by the ANSYS program (Version 19.1, Ansys Inc., Canonsburg, PA, USA). The liquid flow in the pipes can be laminar, transition, or turbulent. When changing the flow form from laminar to transition and from transition to turbulent, the HTC continuity is maintained. Mathematical models of two radiators were developed, one of which was made of round tubes and the other of oval tubes. The model allows for the calculation of the thermal output of every row of pipes in both passes of the heat exchangers. Small relative differences between the total heat flow transferred in the heat exchanger from hot water to cool air exist for different and uniform HTCs. However, the heat flow rate in the first row is much higher than the heat flow in the second row if the air-side HTCs are different for each row compared to a situation where the HTC is constant throughout the heat exchanger. The thermal capacities of both radiators calculated using the developed mathematical model were compared with the results of experimental studies. The plate-fin and tube heat exchanger (PFTHE) modeling procedure developed in the article does not require the use of empirical correlations to calculate HTCs on both sides of the pipes. The suggested method of calculating plate-fin and tube heat exchangers, taking into account the different air-side HTCs estimated using CFD modelling, may significantly reduce the cost of experimental research for a new design of heat exchangers implemented in manufacturing.

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