The evaporator air filter is clean, the evaporator coil is clean, the blower wheel is clean, the belt is not slipping and no obstructions are in the ductwork. It has been decided that an airflow adjustment is required. The goal is to increase the cfm from cfm to cfm. Changing a pulley size or making an adjustment on the motor pulley if it is adjustable will accomplish this. The most economical and practical pulley to replace is the motor pulley. The motor pulley is less costly, it is the easy one to change, and as the smaller of the two pulleys, it probably has the greatest wear on it.
The smaller pulley will always wear the fastest as it is turning more revolutions per minute and it has a smaller circumference for the belt to spread the wear over. New RPM The two existing pulley sizes are now known, the rpms of both of the existing pulleys are known, and the existing cfm is known.
The new desired cfm for the system is also known. Now the missing information is; 1 What new blower rpm is required to obtain the new cfm? In this formula the 1 stands for what we have, and the 2 is for what we want. What we have is cfm with the blower speed of rpm. What we want is cfm, and are missing the new required rpm to go with the rpm. So, the unknown information is question one above, what new blower rpm is required to obtain the cfm?
Place the appropriate known values into the formula, crossmultiply and divide, and the answer are provided. Cross multiply times to get 3,, then divide that by to get The blower rpm required to move cfm on this system is rpm. As will be explained fully later, more cfm than necessary may seem like a benefit however, this is a costly mistake in terms of both comfort control and operating cost.
Correct airflow is always best, no more, no less. Now to answer the second question. What new motor pulley size is required to get the new blower rpm and cfm? This is found by using the first formula again. This time the unknown to be solved for is the new motor pulley dia which is DIA a. Notice that the motor rpm is not changed. The change will be in the motor pulley size.
Cross multiply 16 times to get 18, then divide by to get the new motor pulley size of The existing 8" pulley may not be able to be adjusted to that new diameter, and a new fixed pulley of exactly However, a fixed pulley close enough can be selected or a new adjustable pulley of the correct adjustment range can be selected. These pulley diameters are not outside diameter measurements, but are to be pitch diameter measurements. Those not familiar with pulley pitch diameter should read the section in this book on pulley nomenclature.
The third question now needs to be addressed. Since the blower will be moving more air, will this overload the motor, and if it does, what is the new horsepower required? Motor Horsepower Calculations As the blower rpm and cfm increase there is an increase in the amount of work which the motor is required to do. The amount of additional work in horsepower for even a small increase in rpm and cfm is impressive. Few technicians realize the large increase in load on a motor with even the smallest increases on adjustable pulleys.
To continue this example assume that the existing motor nameplate data was available from the start of the job and is as follows. Remember this is not the actual work the motor is doing, but is what the data plate states the motor is able to do. At this point it is not important to know what all this information is. Assume that when the technician measured the pulleys and obtained the motor information, that a motor running amperage measurement was taken.
This amperage is for the original conditions with a motor pulley of 8", a blower rpm of , and the cfm airflow rate. The running amperage under those conditions was found to be 16 amps. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.
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You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience. Bhope and Padole and Tomasz et al. An extensive work has been done on gasification but low capacity batch gasifiers have not received the adequate attention.
To this, should be added the fact that materials for blower construction need to demonstrate high heat resistance and ability to withstand sudden changes in both direction and temperatures. Inadequate and improper supply and control of air are other major causes of failures in a gasifiers. These failures are also due to lack of adequate as well as suitable blower which leads to the total collapse of the gasification process.
This research presents the design and development of a blower for use in the operation of a low capacity, batch type downdraft gasifier. While designing the blower, the most important impeller design parameters to be determined were grouped into three categories and used in the construction. The groups are: Geometrical Parameters Tip diameter, hub diameter and tip width , Operating conditions Inlet total pressure, inlet total temperature and fluid density , and Performance characteristics mass flow parameter, pressure ratio and specific speed.
Materials and methods 2. Some of these factors were the static pressure that the blower must overcome, the required average air flow volume, the shape and direction of the desired air flow, space limitations, audible noise allowances, available power, efficiency, air density, and cost.
Air flow and static pressure, along with available power considerations are generally the most critical for blower designs. These three address the fundamental questions on how much air is needed and what is it going to cost in system power to get it.
The blower provides the necessary airflow that is needed for the gasification of biomass. Blowers are usually available in AC or DC. The blower to be used should be capable enough to overcome the pressure exerted by the biomass and, subsequently, by the char.
A high pressure blower is usually ideal for down-draft type gasifier reactor, while low-pressure blower is used for cross-draft type reactor. Thus the amount of air needed for gasification needs to be calculated.
This is very important in determining the size of the blower needed for the reactor to be used in gasifying biomass. In this process it consumes about 1. For 3 complete combustion of wood about 4. On the other hand, rice husk was found to require 2. Too few blades are unable to fully impose their geometry on the flow, whereas too many of them restrict the flow passage and lead to higher losses. Most of the efforts to determine the optimum number of blades have resulted in only empirical relations given by Vibhakar as: [ ] 8 3.
For this work, 2. Volute pressure loss The Volute pressure loss was calculated from Eq. Thus , we recommend a 0. When this method is used, the impeller is divided into a number of assumed concentric rings, not necessarily equally spaced between inner and outer radii. The radius Rb of the arc is defining the blade shape between inner and outer radii. The blower casing was made of mild steel mm diameter by 2 piece, cut and drilled a hole of 17 mm and 70 mm diameters respectively.
A strip of 70 mm x mm mild steel was measured and cut to form the circumference of the casing. On the other circular plate, four holes of 7mm diameter was drilled at a square of 60 mm.
A 50 mm diameter round pipe mild steel was measured and cut to a length of mm while the other end was chamfered to 60o. An angle iron of 25 mm x 3 mm x 4 pieces was cut, drilled a hole of 80 mm diameter and welded to the circular sheet.
A circular sheet mild steel of 90mm diameter was cut, marked, divided into 8 equal parts and drilled a hole of 14 mm diameter at the center.
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