Horizontal Heat Research Articles

A numerical study on heating performance of horizontal and vertical earth-air heat exchangers with equal pipe lengths

In this study, heating performances of horizontal and vertical earth-air heat exchangers with equal pipe lengths were evaluated in ANSYS FLUENT 19.2 simulation program based on CFD for the winter period of Bitlis, Turkey. Thermal per?formance analyses regarding vertical and horizontal 3-D-modeled earth-air heat exchangers were evaluated in steady-state condition of the simulation program for different values of Re = 5?103, 104, 2?104, 4?104, 6?104, 8?104, and 105 numbers by using standard k-? turbulence model. Numerical results obtained from CFD based simulation program were compared with a numerical study in the literature, and it was determined that there was a consistency between the results. The pressure loss and fan power values of horizontal and vertical earth-air heat exchangers were also investigated in addition their thermal performances. A good agreement was found between the pressure loss values obtained from the theoretical and simulation calculations of both earth-air heat exchangers. Considering the temperature increases in both earth-air heat exchangers, the highest and lowest temperature increases were observed in vertical earth-air heat exchanger with 22.52 K and 10.67 K, respectively. The best thermal performance was observed in vertical earth-air heat exchanger for 5?103, 104, and 2?104 values of Reynolds number and in horizontal earth-air heat exchanger for 4?104, 6?104, 8?104, and 105 values of Reynolds number.

Investigations on the Selection of the Most Suitable Shell-to-Tube Diameter Ratio of a Horizontal Latent Heat Thermal Energy Storage

Investigations on the Selection of the Most Suitable Shell-to-Tube Diameter Ratio of a Horizontal Latent Heat Thermal Energy Storage

Study on Influence Factors of Horizontal Ground Heat Exchanger Performance Considering Climatic Conditions and Groundwater Flow

Study on Influence Factors of Horizontal Ground Heat Exchanger Performance Considering Climatic Conditions and Groundwater Flow

Numerical analysis of ground heat exchange by horizontal ground heat exchangers and a prediction of temperature effects on a subsurface ecosystem

Numerical analysis of ground heat exchange by horizontal ground heat exchangers and a prediction of temperature effects on a subsurface ecosystem

Cooling Performance of Ground Source Heat Pump Using Horizontal Arrangement Type Underground Heat Exchanger

Cooling Performance of Ground Source Heat Pump Using Horizontal Arrangement Type Underground Heat Exchanger

Experimental analysis of the heat transfer rate of phase change material inside a horizontal cylindrical latent heat energy storage system

Latent heat thermal energy storage system can help in the smooth operation of energy supply and demand. In the present work, experimental study was performed to analyze the heat transfer rate of phase change material inside an annulus. A copper pipe (centrally loaded) runs the length of a cylindrical container during both discharging and charging modes. The overall heat transfer rate is enhanced during phase change process by adding longitudinal fins with the copper pipe. These longitudinal fins were tilted at an angle of 120⁰. Paraffin wax is used as phase change material. The main objective of the experiment is to analyze the heat transfer rate during the solidification and liquefaction of PCM. Also, the effect of mass flow rate and inlet temperature of heat transfer fluid was analyzed. Conduction was found to be the primary heat transfer mechanism during the initial stages of charging. Once the PCM get liquefied inside the system, natural convection gets dominated. During the solidification of PCM conduction heat transfer get dominated. Also, it was observed that melting duration is strongly affected by the inlet temperature of HTF while the flow rate slightly affects the melting duration.

Experimental study on the thermal imbalance and soil temperature recovery performance of horizontal stainless-steel ground heat exchanger

Soil thermal imbalance has become a common problem for ground source heat pump (GSHP) system, leading to the fluctuation of ground temperature and decline of heat transfer efficiency. However, compared with vertical ground heat exchanger (GHE), there is a lack of research and evaluation on the soil thermal imbalance for horizontal GHE. Therefore, in this paper, to investigate the extent of soil thermal imbalance and its effects on performance of GSHP system, a sandbox experiment embedded with horizontal stainless-steel GHE was implemented. Various operation conditions were designed to explore effects of intermittent time, water content (rainfall) and buried depth of pipes on soil temperature distribution and restoration performance. The experimental data was validated by a numerical simulation. The results indicated that 5-day intermittent operation of GSHP leads to an increase of 6.41 ℃ in soil temperature. After 2-day natural recovery, soil temperature recovery rate can only reach 0.72. Increasing soil moisture content and intermittent control are effective solutions to mitigate thermal accumulation and improve thermal performance. The heat transfer performance of GHE with an intermittent ratio of 6:18 which GSHP system runs for 6 h and stops for 18 h during a day is 33% higher than that with the intermittent ratio of 14:10 and 10:14. The higher the water content, the lower the soil temperature fluctuation and the stronger the soil temperature recovery capacity. This can be attributed to the increase of soil thermal conductivity and capacity, while the decrease of thermal diffusivity.

A study on heating and cooling requirements for green buildings and refugee settlements

In this study, geothermal-based three different systems are examined comparatively and a decision-making method is used to find the best option to use in refugee settlements. Earth air heat exchanger (EAHE), vertical ground source heat pump (VGSHP), and horizontal ground source heat pump (HGSHP) are evaluated from the viewpoint of environmental impact, performance, economy, and health. This study is the first study related to the evaluation of EAHE and GSHP systems by using the analytical hierarchy process (AHP). It is concluded that EAHE is the best option for refugee settlements; also EAHE is a healthier option for the COVID-19 pandemic.

Thermal Performance Analysis of Horizontal Latent Heat Energy Storage with Irregular Snowflake Fins Based on Response Surface Methodology Optimization

Thermal Performance Analysis of Horizontal Latent Heat Energy Storage with Irregular Snowflake Fins Based on Response Surface Methodology Optimization

Effects of vertical and horizontal heating panel on heat loss from human legs

In China’s hot summer and cold winter zone, there are cold and humid in winter. If there is no heating measure, the human body will feel less comfortable in the cold environment. The traditional HVAC system consumes a lot of energy, and it is difficult to meet the thermal comfort needs of everyone. By creating a local thermal environment around the human body, the personalized heating system can significantly improve the thermal comfort level of the human body with lower energy consumption. In this paper, it is mainly analyzing the heating effect of the heating panel on the legs of the human body by theoretically analyzing the indoor temperature of 12 °C in the hot summer and cold winter zone. For the following two working conditions: the heating panel is placed vertically on the side of the human leg and the heating panel is placed horizontally under the feet. It is calculated that when the human body feels comfortable, the heat loss is about 45 W/m2∼50 W/m2. The conclusions are as follows: (1) When the heating panel is placed vertically on the side of the human leg, the thermal comfort needs are only met when the heating panel temperature is 70 °C and the distance between the heating panel and the leg is 5 cm or 10 cm. (2) When the heating panel is placed horizontally under the feet and the temperature of the heating panel is 70 °C, the local heat loss of the human body is less than 45W/m2, and the human body feels slightly warmer.

Back Analysis of a Horizontal Geothermal Plant Implemented in a Wine Production Process

The Salcheto winery has undertaken a process of reduction of its primary energy consumption and the implementation of green energy technologies. They adopted solar photovoltaic, wood biomass, and geothermal energy sources. A horizontal ground source heat exchanger (GSHE) plant is used to cool a part of the pressed grapes and control the wine production temperature. The goal of this work was to investigate some technical issues of the plant and to increase the efficiency of the whole system. The first step was the evaluation of the actual operating conditions of the GSHE plant, by performing a thermal response test. The results allowed us to find the thermal diffusivity of 3.5 × 10−7 m2/s, and the calculation with the IGSHPA standard indicated a cooling performance of about 6 kW. A survey during the harvest highlighted a peak power of 6 kW. Therefore, to improve the plant, some modifications were proposed and analyzed. In the new layout, the geothermal plant serves the condenser of the refrigeration unit, allowing cooling of the all production lines, instead of only one. The peak power was evaluated as 32 kW, and the GSHE can fulfil this, up to 18 kW. For higher power, the evaporative tower will supply the remainder, covering a maximum of 45%. Furthermore, the refrigeration unit may cover the cooling requirements of the entire residential and office building, without other plant improvements.

Thermal performance of building-integrated horizontal earth-air heat exchanger in a subtropical hot humid climate

The current energy crisis across the globe is a major obstacle to human growth and development. The majority of energy use is accounted for by buildings, which must be controlled and reduced using energy-efficient technologies. Several passive technologies have been shown to be effective in reducing building energy consumption. The earth-air heat exchanger (EAHE) is one such technology capable of saving energy in buildings without relying on habitual mechanical equipment. Though different types of EAHE models have been developed over the last few decades, building-integrated EAHE model development using real-time data is rarely seen for a subtropical climate. This paper thus evaluates the cooling performance of a building-integrated horizontal EAHE system in a warm and humid subtropical climate in Rockhampton, Australia. To measure the cooling performance, a building-integrated horizontal EAHE model is developed in Ansys Fluent. Impacts of relative humidity, air velocity, soil temperature, and air temperature on the building cooling performance have also been investigated. The building-integrated horizontal EAHE system reduced the temperature in a single room building by a maximum of 2.18 °C, saving 415.92 kWh energy (on average 59.91 kWh) during a 3-months summer. This equates to an energy cost savings of AU$190.31, with an average savings of AU$105.10. The energy saved by the present system will make a substantial contribution to building energy management.

Thermodynamic Evaluation of a Direct Expansion Ground-Sourced Heat Pump with Horizontal Ground Heat Exchangers Using Advanced Exergy Analysis

This paper deals with the advanced exergetic analysis of a horizontal direct-expansion ground sourced CO2 heat pump operating in a transcritical cycle. The cycle is thermodynamically modeled in Engineering Equation Solver (EES) considering the pressure drops in both high and low temperature heat exchangers, and the system is to provide a fixed heating load. Conventional exergy analysis orderly suggests a compressor, expansion valve, gas cooler and ground heat exchanger to be considered for system improvement, while tracing exergy destruction of all components in detail demonstrates true improvement potential of each and all components and the system as a whole and offers a different order. Advanced exergy analysis points out that the compressor is directly and indirectly responsible for 56% of the overall exergy destruction generated in the cycle, confirming the detrimental role of this component in the system. The second influential component is recognized to be a ground heat exchanger accounting for 20% exergy destruction of the compressor as well as submitting 89% avoidability in its own exergy destruction, and expansion valve proves to be the last option for system improvement according to this analysis.

An experimental study of flow boiling heat transfer of zeotropic mixture R32/R134a in a microchannel heat exchanger

This paper presents experimental data on heat transfer of a binary zeotropic mixture of refrigerants R32/R134a in a microchannel heat exchanger with a high specific surface within a range of parameters that is practically important for the development of cooling systems for microelectronics and space technology. The experiments were carried out in a horizontal heat exchanger with one-sided heating of a copper microchannel plate 20x40 mm, containing 21 rectangular microchannels with a cross-section of 335x930 μm, within the range of mass fluxes from 80 to 250 kg/m2s, and at an absolute pressure in the system ranged from 12 to 14 bar. A zeotropic mixture of refrigerants R32/R134a with a molar concentration of the initial mixture of 65%/35% was used as a working fluid. Experimental data were compared with model-based calculations that take into account the influence of changes in the concentrations of components in the liquid and gas phases.

Investigation of Thermal Conductivity and Convective Heat Transfer Coefficient of Water-based ZnO Nanofluids

Nanofluids are stable suspensions of nanoparticles in a conventional fluid. They have shown superior potential in heat transfer enhancement. In this research, ZnO/water nanofluids were prepared at various concentrations from 0.2 to 1.5vol%, and their thermal conductivity was measured. The results showed that the thermal conductivity of ZnO/water nanofluids depends on particle concentration and increases non-linearly with the volume fraction of nanoparticles. The effects of particles size and temperature on the thermal conductivity were also investigated at 1.5vol%. The results indicated that thermal conductivity enhanced with decreasing particles size and increasing with temperature. For nanofluids containing 10-15 nm and 45-50 nm particle sizes, the enhancements were 26.3 and 22.8% at 40oC, respectively. In this research, the convective heat transfer coefficient of ZnO/water nanofluids with the above particle sizes was also measured under laminar flow in a horizontal tube heat exchanger. It was observed that both nanofluids showed higher heat transfer coefficients compared to the base fluid at a constant concentration (1.5 vol%). For nanofluids with 10-15 nm and 45-50 nm particle sizes, the average heat transfer coefficient enhancement was 18.1 and 14.9% at Re=1115, respectively.

Utilization of Thermally Activated Building System with Horizontal Ground Heat Exchanger Considering the Weather Conditions

The thermally activated building system (TABS) can reduce the peak load by integrating with the ground heat exchangers. When integrated, the cost of groundwork and stability of the ground temperature would counteract because the weather conditions would influence the ground temperature in shallow depth. However, previous studies on TABS assumed constant ground temperatures such as average outdoor air temperature. In this study, ground temperatures in different depths are simulated for their detailed investigations, and simulated results of ground temperature were applied to building energy simulations for observing the load-handled ratio (LHR), representing the peak load reduction by TABS evaluated in various weather conditions. Simulation results of ground temperatures from 1 m to 39 m depths show that the temperature stabilized at 2 m to 11 m depths depending on the characteristics of the outdoor air temperature. LHR increased as the ground depth increased because the ground temperature at shallow depths increased during peak hours. Ground depths of 8 m were found ideal for maintaining consistent LHR for all weather conditions. Detailed observation of ground temperature and its effect on LHR in various weather conditions can help system engineers design and operate the TABS with the ground system.

An experimental work on the performance of a solar-assisted ground-coupled heat pump using a horizontal ground heat exchanger

Solar Assisted Ground Coupled Heat Pumps are thoroughly investigated today. Although the best method to extract heat from the earth is by using vertical ground heat exchangers, they are expensive. Horizontal ground heat exchangers are cheaper but the downside is that they are not so efficient. The main objective of this study is to find efficient, alternative methods to assist the horizontal ground heat exchanger in order to decrease the ground freezing period and increase its performances. For that, a Solar Assisted Ground Coupled Heat Pump system was established, using two solar assistance sub-systems (solar thermal panels and solar photovoltaic panels). A third heat source was considered, consisting in the residual heat lost from the building's heated basement. The results indicated that using auxiliary heat sources eliminated the ground freezing period. Although heat transfer into the Horizontal Ground Heat Exchanger increased the Seasonal Performance Factor by approximative 15% for the season peak, a high amount of heat was lost in the process. This study also addresses possible methods to reduce the heat loss. Overall, the results indicated better performance for the Horizontal Ground Heat Exchanger when transferring heat into it.

Experimental effect of inclination on the process of melting paraffin in a square cavity

Phase change material PCM is a promising strategy for reducing energy consumption in various applications. Among the large number of PCMs studied in the literature, paraffin are considered to be promising for latent heat thermal energy storage LHTES due to its appropriate thermal properties and their chemical stability. The interest of this work is to carry out an experimental procedure to visualize the phase change process of paraffin in a square cavity at different inclination angles. This article reveals how the melting rate could be affected by changing three orientations 90° (vertical heating), 0° (bottom horizontal heating) and 45° (inclined heating). The enclosure is heated on one side while the other walls are thermally insulated. The numerical photos, infrared thermal image and thermocouples-temperatures recorded during the melting processing are used to calculate the melting fractions and to estimate the intensity of heat transfer in different angles. The results show that the inclination angle has a great influence on the behavior of natural convection, affecting the front melting propagation and heat transfer rate. When the inclination angle decreases from 90° to 0° the convection currents in the cavity progressively evolve from a dominant single-cell movement to an unstable Rayleigh-Benard movement. The total melting time for the bottom and inclined heating cavities were, on average, 56% and 45% less than that of the vertical heating, respectively.

Experimental and numerical investigation of melting/solidification of nano-enhanced phase change materials in shell & tube thermal energy storage systems

In this work, the melting/solidification process of the nano-enhanced phase change materials (NePCM) was investigated experimentally and numerically using a horizontal shell & tube heat exchanger equipped with longitudinal fins. The NePCM was prepared by dispersing titanium dioxide nanoparticles (TiO2NPs) in stearic acid (SA). The effect of geometry parameters and nano particle content on melting/solidification rate of PCM were investigated. The results showed that using longitudinal fins could reduce the required time for melting and solidification by around 54% and 76%, compared to the system without fins, respectively. while the greatest effect of adding the TiO2-NPs was related to unfinned tube heat exchanger, which reduced the required time by 6% and 8% for melting and solidification, respectively. Furthermore, it was concluded that adding nanoparticles could offer its positive effect for enhancing the melting rate only while using unfinned tube heat exchanger.

Boundary layers in turbulent vertical convection at high Prandtl number

Many environmental flows arise due to natural convection at a vertical surface, from flows in buildings to dissolving ice faces at marine-terminating glaciers. We use three-dimensional direct numerical simulations of a vertical channel with differentially heated walls to investigate such convective, turbulent boundary layers. Through the implementation of a multiple-resolution technique, we are able to perform simulations at a wide range of Prandtl numbers ${Pr}$ . This allows us to distinguish the parameter dependences of the horizontal heat flux and the boundary layer widths in terms of the Rayleigh number $\mbox {{Ra}}$ and Prandtl number ${Pr}$ . For the considered parameter range $1\leq {Pr} \leq 100$ , $10^{6} \leq \mbox {{Ra}} \leq 10^{9}$ , we find the flow to be consistent with a ‘buoyancy-controlled’ regime where the heat flux is independent of the wall separation. For given ${Pr}$ , the heat flux is found to scale linearly with the friction velocity $V_\ast$ . Finally, we discuss the implications of our results for the parameterisation of heat and salt fluxes at vertical ice–ocean interfaces.