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How do you calculate overall heat transfer coefficient for a shell and tube heat exchanger?
When a cold object and a hot object are in direct contact (touching) heat will be transferred through thermal conduction.
Normally, heat transfer processes are categorized as thermal conduction, radiative transfer or convection.
Heat transfer through thermal conduction is the direct transfer of kinetic energy from one molecule to the nearby molecules. Because temperature is directly proportional to kinetic energy, interactions between neighboring particles exchange energy and that exchange energy gradually works it way from the higher temperature regions to the lower temperature regions. The process of the temperature becoming the same is called thermal equilibration.
Convective heat transfer occurs in fluids. If a gas, liquid, or other fluid, changes in fluid density change the buoyancy and will cause fluid to flow (a process called convection) and the heat contained in the warmer fluid is transferred to a new location by the physical movement of the fluid.
Radiative transfer occurs when a hot object radiates electromagnetic energy. While the sun is an obvious source of electromagnetic energy, it is also generated in smaller amounts by any object. The hotter objects radiate more electromagnetic energy and the cooler objects absorb it. This radiative transfer is important but not as noticeable usually as the other two. It does occur between objects whether they are in direct contact or not, but is usually so small as not to be important of the objects are touching.
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What is a dollar plate on a heat exchanger?
A dollar plate on a heat exchanger is a type of heat transfer surface that consists of a thin metal plate with a corrugated pattern on both sides. These plates are typically made of materials such as stainless steel or titanium and are used to increase the efficiency of heat transfer between two fluids. The corrugated pattern helps to enhance turbulence and promote heat exchange, making the overall process more effective and efficient.
What is the application of baffles in heat exchanger?
Baffles in heat exchangers serve to enhance heat transfer efficiency by directing the flow of fluids across the heat exchange surfaces. They create turbulence, which increases the fluid velocity and improves the mixing of the fluids, leading to more effective heat transfer. Additionally, baffles help support the tubes or plates within the exchanger, preventing vibration and ensuring structural integrity. Overall, they optimize thermal performance while minimizing pressure drop across the system.
Why counter current heat exchanger is more efficient?
Countercurrent heat exchangers are more efficient because they allow hot and cold fluids to flow in opposite directions, maximizing the temperature gradient throughout the length of the exchanger. This design enables a greater surface area for heat transfer and ensures that the cold fluid continuously encounters hotter fluid, maintaining a higher temperature difference. As a result, more heat is transferred compared to parallel flow designs, where the temperature difference diminishes along the flow path. Additionally, countercurrent flow reduces the risk of thermal shock and enhances overall system performance.
What is function of boiler circulating pump in boiler?
The boiler circulating pump is essential for maintaining the flow of water or steam within the boiler system. Its primary function is to circulate water from the boiler to the heat exchanger and back, ensuring efficient heat transfer and maintaining the desired temperature and pressure levels. This circulation helps prevent overheating and ensures uniform heating throughout the system, contributing to overall operational efficiency and safety.
What is meant by desuperheating vapor in hvac?
Desuperheating vapor in HVAC refers to the process of reducing the temperature of superheated refrigerant vapor before it enters the condenser. This is typically achieved by passing the vapor through a heat exchanger, where it loses heat to a cooling medium, such as water or air. Desuperheating helps improve the efficiency of the refrigeration cycle by ensuring that the refrigerant reaches the condenser at a lower temperature, thereby enhancing heat transfer and overall system performance.
What is the value of an overall heat transfer coefficient in an engine oil cooler?
I have a book (Introduction to heat transfer - Bergmann), there is an example of an oil cooler cooled by air (crossflow heat exchanger with both fluids unmixed). There is written: "... with an overall heat transfer coefficient of 53 W/(m²*K)."
What is the effect of overall heat transfer coefficient U to heat exchanger performance?
The equation for the duty of a heat exchanger is:Q=U*A*LMTDwhere:Q is the dutyA is the overall heat transfer areaLMTD is the log mean temperature difference.generally when desiging heat exchangers the desired duty is known, as are the desired inlet and outlet temperatures. Therefore we solve for A to find the overall heat transfer area.A= Q/(U*A*LMTD)If we hold Q and the LMTD constant, you can see that a larger overall heat transfer coefficient U, will result in a small exchanger area and, therefore; a smaller, less expensive piece of equipment.The the greater the U, the better the performance.
What is the ambient temperature formula used to calculate the overall heat transfer in a given environment?
The formula used to calculate overall heat transfer in a given environment is Q U A T, where Q is the heat transfer rate, U is the overall heat transfer coefficient, A is the surface area, and T is the temperature difference between the object and the environment.
What is Overall Heat transfer coefficient?
The overall heat transfer coefficient represents the rate at which heat is transferred between two mediums per unit area and per unit temperature difference. It combines the individual resistances to heat transfer in conduction, convection, and radiation into a single value. A higher overall heat transfer coefficient indicates a more efficient heat transfer process.
How does the resestance to heat transfer of the matrrial of the condenser pipe effect on the transfer coefficient?
The resistance to heat transfer of the material of the condenser pipe affects the overall heat transfer coefficient by increasing the overall thermal resistance. A higher resistance to heat transfer in the material of the condenser pipe will reduce the heat transfer coefficient, making heat transfer less effective. This can result in reduced efficiency in the condenser's operation.
How does dirty overall heat transfer coefficient affect water flow rate?
A decrease in the overall heat transfer coefficient due to fouling or dirt buildup can reduce the efficiency of heat transfer in a system. This can lead to a decrease in the water flow rate as the system needs to compensate for the reduced heat transfer efficiency. Increased resistance to heat transfer can result in higher energy consumption and reduced performance of the system.
Why heat transfer coefficient decrease with increase in fluid viscosity?
An increase in fluid viscosity can impede the movement of fluid molecules, reducing their ability to transfer energy through the fluid. This decreased fluid mobility results in a lower heat transfer coefficient, as there are fewer fluid molecules available to transport thermal energy across the surface. Additionally, higher viscosity fluids may form boundary layers that resist heat transfer across the fluid-solid interface, further reducing the overall heat transfer coefficient.
Does juice temperature increase with increasing convective heat transfer coefficient at any constant kettle surface temperature?
Yes, the juice temperature increases with an increasing convective heat transfer coefficient at any constant kettle surface temperature. The convective heat transfer coefficient represents the efficiency of heat transfer from the kettle to the juice. As the convective heat transfer coefficient rises, more heat is transferred from the kettle surface to the juice per unit of time. This increased efficiency results in a faster temperature rise in the juice. Therefore, a higher convective heat transfer coefficient enhances the overall heating process, leading to a greater temperature increase in the juice even when the kettle surface temperature remains constant.
What is a dollar plate on a heat exchanger?
A dollar plate on a heat exchanger is a type of heat transfer surface that consists of a thin metal plate with a corrugated pattern on both sides. These plates are typically made of materials such as stainless steel or titanium and are used to increase the efficiency of heat transfer between two fluids. The corrugated pattern helps to enhance turbulence and promote heat exchange, making the overall process more effective and efficient.
Why counter corrent flow is better than cocurrent flow for heat transfer?
Counter-current flow is more efficient for heat transfer because it maintains a higher temperature gradient along the entire length of the heat exchanger, allowing for a more continuous and effective transfer of heat. As the hot and cold fluids move in opposite directions, the temperature difference between them remains large resulting in a more efficient heat exchange process. In contrast, in co-current flow, the temperatures of the fluids tend to equalize more quickly along the length of the heat exchanger, reducing the overall effectiveness of heat transfer.
What is the application of baffles in heat exchanger?
Baffles in heat exchangers serve to enhance heat transfer efficiency by directing the flow of fluids across the heat exchange surfaces. They create turbulence, which increases the fluid velocity and improves the mixing of the fluids, leading to more effective heat transfer. Additionally, baffles help support the tubes or plates within the exchanger, preventing vibration and ensuring structural integrity. Overall, they optimize thermal performance while minimizing pressure drop across the system.
What are the advantages and disadvantages of spiral heat exchanger?
AdvantagesEfficient use of Temperature DifferenceThe fully countercurrent system(TYPE-1) is able to exchange heat even if temperature difference is extremely close. Most effective saving energy is possible.Low Fouling (Self Cleaning)The rotary current of spiral heat exchanger possesses the property of scraping off and spilling the dirty sedimentation(stagnation solid). Even though scales adhere to it, the cross-section of the adherent part becomes smaller, the flow-speed would be quickly and bring the function of self cleaning by single-pass flow.High Overall Heat Transfer CoefficientSpiral flow passage easily creates turbulent flow.Optimum flow speed can be gained by selecting the most suitable spiral channel. High Overall Heat Transfer Coefficient can be achieved.Easy MaintenanceThe heat transfer part is easily accessed and checked. It is possible to easily do by removing the cover of the both ends, for the inspection of the inside.The maintenance cost of Spiral Heat Exchanger is much lower than others.Space SavingSHE equipment volume is far compact comparing to Tubular Heat Exchanger. Plant space can be saved and plant initial cost can be saved.
